Liquid Phase Catalyst

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HYDROFORMYLATIONWITH

SUPPORTED LIQUID PHASE RHODIUM CATALYSTS

L A Gerritsen

Delft University Press





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PROEFSCHRIFT

TER VERKRIJGING VAN DE GRAAD VAN DOCTOR

IN DE TECHNISCHE WETENSCHAPPEN AAN DE

TECHNISCHE HOGESCHOOL DELFT, OP GEZAG VAN

DE RECTOR MAG NIFICUS PROF. DR. IR. F. J. KIEVITS,

VOOR EEN COMMISSIE AANGEWEZEN DOOR HET

COLLEGE VAN DEKANEN TE VERDEDIGEN OP

WOENSDAG 12 DECEMBER 1979 TE 16.00 UUR

DOOR

LEENDERT ARIE GERRITSEN

scheikundig ingenieur

geboren te H. I Ambacht

A o o b

Delft University Press /19 79



Dit proefsch ri f t is goe dgek eurd do or de prom otor

PROF. DR. J. J. F. SCHO LTEN



Aan JokeAan mijn ouders



DANKBETUIGING

Aan allen die hebben bijgedragen aan de totstandkoming van dit proefschrift

betuig ik mijn oprechte dank.

In het bijzonder gaat mijn dank uit naar:

- de afstudeerders Ir. W. Klut, Ir. J.M. Herman, Ir. M.H. Vreugdenhil en

A. van Meerkerk, die door hun enthousiasme, inzet en originaliteit belangrij

ke bijdragen aan het onderzoek leverden.

- collega Ir. N.A. de Munck voor de nuttige en plezierige samenwerking.

- Dr.ir. G. Hakvoort en Ir. Th.W. de Loos, van het Laboratorium voor Anorgani

sche en Fysische Chemie THD, voor hun hulp bij de DSC en Cailletet metingen,

Ir. P. Bode, van het Interuniversitair Reactor Instituut THD, voor de neutron

activeringsanalyse metingen, Ir. E. Izeboud, van het Laboratorium voor Organi

sche Chemie THD, en Ir. E.B.M. Doesburg, van het Laboratorium voor Anorgani

sche en Fysische Chemie, voor de assistentie bij respectievelijk de aldolcon-

densatie en silaniserings experimenten, Ir. D. Schalkoord, van de Tussenafde-

ling Metaalkunde THD, en de Heren A.M. Kiel en S.M.G. Nadorp, van het Cen

traal Laboratorium DSM te Geleen, voor de SEM en RMA opnamen, en de Heren

J. Teunisse en N. van Westen, van het Laboratorium voor Chemische Technologie

THD, voor de vele textuurmetingen.

- de Heer P.H. Hermans, vertaler Engels te Geleen, voor de zorgvuldige correc

tie van de tekst.

- Me j. M.J.A. Wijnen, Mevr. J.P.H, de Groot-Mervel, en de heren W.J. Jongeleen

en J.H. Kamps voor de nauwkeurige bewerking van het manuscript.

- de medewerkers van de servicegroepen en diensten van het Laboratorium voor

Chemische Technologie voor de diverse werkzaamheden die zij ten behoeve van

dit onderzoek hebben verricht.

Het overleg met verschillende medewerkers van het Centraal Laboratorium

van DSM te Geleen heb ik steeds zeer gewaardeerd.

Tenslotte dank ik de Heer L. Boshuizen voor diens dagelijkse steun.

VI



CONTENTS

SUMMARY 1

1 . INTRODUCTION 5

1.1 History of hydroformylation 5

1.1.1 Cobalt catalysis 5

1.1.2 Rhodium catalysis 7

1.2 Heterogenizing of homogeneous catalysts 9

1.3 Supported Liquid Phase Catalysis 10

1.4 Objective and scope of the thesis 13

References 16

2. GENERAL DESCRIPTION OF THE SYSTEM, CATALYST PREPARATION AND

CHARACTERIZATION 19

Summary 19

1. Introduction 20

2. Experimental 21

2.1 Materials 21

2.2 Catalyst preparation 21

2.3 Catalyst characterization 22

2.4 Catalytic performance ' 23

2.5 Infrared spectroscopy 25

2.6 Activity tests for the unwanted consecutive reaction:

aldol condensation of aldehydes 25

2.7 Neutron activation analysis 25

3. Results 26

3.1 SLPC versus physically adsorbed catalysts 26

3.2 Comparison with Rony's SLP catalyst 27

3.3 Infrared spectroscopy 27

3.4 Aldol condensation 29

3.5 PPh,-distribution in the support 30

3.5.1 Nitrogen capillary condensation and mercury

porosiraetry 30

3.5.2 X-ray microanalysis 32

3.5.3 Electron I'licroscopy 33

4. Discussion - 33

Acknowledgements 38

VII



List of symbols

References

3. THE LOCATION OF THE CATALYTIC SITES

Summary

1. Introduction

2. Experimental

3. Results

3.1 DSC measurements

3.2 Activity measurements

3.2.1 Influence of the PPh, phase change on activity

3.2.2 Activity of a fully-loaded SLPC in ethylene

hydroformy1ation

3.2.3 Activity of a non-supported solid catalyst solution

3.3 Surface tensions

3.4 Investigation into the possibility of diffusional retardat

of the reaction rate

3.4.1 Determination of the diffusion coefficients and

solubilities of the reactants in PPh,

3.4.2 Calculations

4. Discussion

Acknowledgements

List of symbols

References

4. INFLUENCE OF THE TYPE OF SUPPORT, THE DEGREE OF PORE FILLING, AND

ORGANIC ADDITIVES ON THE CATALYTIC PERFORMANCE

Summary

1. Introduction

2. Experimental

2.1 General

2.2 Modification of silica 00 0-3E

2.3 Determination of adsorption isotherms of RhHCOfPPh,), on

the supports

3. Results

3.1 Adsorption isotherms of RhHCO(PPh,;),

3.2 Influence of the type of support

3.3 Influence of the degree of liquid loading

3.4 Shortening of the time of activation

VIII



3.4.1 Addition of aldol condensation products 67

3.4.2 Addition of polyethylene glycol 67

3.4.3 Modification with tri(ethoxy)phenylsilane 69

3.4.4 Influence of catalyst pretreatment on the results 693.5 Surface tensions 69

4. Discussion 69

Acknowledgements 72

List of symbols 72

References 73

5. THE APPLICATION OF VARIOUS TERTIARY PHOSPHINES AS SOLVENT LIGANDS 75

Summary 75

1. Introduction 76

2. Experimental 76

3. Results 77

3.1 TGA-measurements 77

3.2 Influence of the various phosphines on the catalytic

performance 78

4. Discussion 81

Acknowledgements 83

Symbols 83

References 84

6. THE KINETICS OF PROPYLENE HYDROFORMYLATION 85

Symmary 85

1. Introduction • 86

2. Experimental 86

3. Results 86

3.1 Diffusional retardation 86

3.2 Relation between degree of conversion and rate of reaction 88

3.3 Influence of the rhodium complex concentration on the kinetics 88

3.4 Temperature dependency 90

3.5 Influence of the partial pressure of hydrogen, carbon monoxide

and propylene 91

4. Discussion . 93

Acknowledgements 95

List of symbols 95

References 96

IX



7. OPTIMUM CONDITIONS FOR PROPYLENE HYDROFORMYLATION WITH SLP RHODIUM

CATALYSTS. COMPARISON BETWEEN A FUTURE SLPC PROCESS AND THE LOW

PRESSURE 0X0 PROCESS 97

1. Introduction 972. Optimum conditions for propylene hydroform/lation with SLP

rhodium catalysts 98

2.1 The support , 98

2.2 Degree of liquid loading 99

2.3 Rhodium concentration 99

2.4 Choice of the solvent ligand 100

2.5 Degree of conversion 101

2.6 Reaction conditions and feed composition 101

3. Comparison of the SLPC process and the LPO process , 102

References 105

SAMENVATTING 107

X



Summary

In 1965 Wilkinson demonstrated that hydridocarbonyltris(triphenylphosphine)

rhodium(I), RhHCO(PPh,)_, is a superior homogeneous catalyst for the hydro-

formylation of olefins to aldehydes, also called the OXO-reaction:

— R - CH„ - C H T - C (normal)

^- '^ ^ H

R - CH = CH2 + H2 + CO :r 0

R - CH - C"^ Ciso )

' "^H

CH3

This homogeneous catalyst is active already under very mild conditions and

possesses a high selectivity towards the formation of normal aldehydes. However,

the very high price of the rhodium calls for recovery of the catalyst from the

products. By heterogenizing the homogeneous catalyst, this cumbersome and

expensive operation can be avoided.

This thesis deals with the preparation and characterization of a new,

heterogeneous rhodium catalyst for the hydroformylation of ethylene or

propylene, and with its performance in long-term experiments (up to 80 0 hrs)

under technologically realistic conditions (total pressure: 1.2-1.57 MPa;

temperature: 40-199°C).

The catalyst solution, composed of RhHCO(PPh ) , dissolved in a low-volatile

solvent, has been heterogenized by impregnating it into a porous inorganic or

organic support material, in which the catalyst solution is captivated by

strong capillary forces. This means that the prinaiple of Supported LiquidPhase Catalysis has been applied.

Furthermore, one of the ligands of the rhodium complex, triphenylphosphine,

has been chosen as a solvent. Not only is this an excellent solvent, which is

low-volatile and wets the supports, but it also offers the advantage of

strongly suppressing the dissociation of triphenylphosphine from the rhodium

complex. In this way a heterogeneous catalyst has been obtained, which produces

n-butyraldehyde with great selectivity and after a test period of 800 hrs still

does not show any loss of activity (Chapter 2 ) .

Nitrogen capillary condensation measurements on fresh and used catalysts

demonstrate that at incomplete pore filling the smallest pores are entirely

1



filled up with catalyst solution, whereas the walls of the larger pores are

merely covered with a thin layer of physisorbed catalyst solution. X-ray micro

analysis reveals that the catalyst solution is homogeneously distributed over

the cross-section of a catalyst particle (Chapter 2 ) .

The transition from solid to liquid triphenylphosphine, and vice versa, du

ring the hydroformylation proves to have no influence on the activity and the

apparent activation energy. From this it follows that we are dealing with

heterogeneous catalysis, in which only the rhodium complexes at the phase

boundary between gas and liquid PPh,, or between gas and solid PPh,, are

involved in the hydroformylation reaction . The inactivity of the rhodium

complexes in the PPh,-solution itself is due to the strong coordination of the

rhodium complexes with the surrounding PPh,-solvent and to the low solubility

of carbon monoxide in PPh,, and no t to strong diffusional retardation of the

reaction rate in the liquid phase. At the gas-PPh, phase boundary, however, the

coordination of the rhodium complexes with free triphenylphosphine is only half

of that outside the phase boundary. Owing to this, and to the much higher CO-

concentration in the gas phase, the equilibria between the various rhodium

complexes shift towards CO-containing complexes exhibiting catalytic activity

for hydroformylation (Chapter 3 ) .

The adsorption of the rhodium complex from the triphenylphosphine solution

on various supports has been investigated. Particularly on silica-alumina and,

to a lesser degree, on silica, the rhodium complex proves to be preferentially

adsorbed with respect to PPh,. On macroreticular polystyrene-2 0% divinylbenzene,

XAD-2, only slight adsorption is observed. This means that the activity of our

catalyst is not only determined by the area of the gas-PPh, phase boundary, but

also by the degree of adsorption of rhodium complex on the walls of the pores;

the larger the gas-PPh, phase boundary and the weaker the adsorption, the

higher the activity for hydroformylation. On this ground, the low activity of

Y-alumina and silica-alumina supported catalysts can be explained by the very

strong adsorption of the rhodium complex on the Lewis-acid sites in the surface

of these supports. The high activity with XAD-2 and, to a lesser degree, with

silicas is attributed to the much smaller adsorption of the rhodium complex

(Chapter 4 ) .

On six supports the degree of liquid loading has been varied. It appears

that on supports which strongly adsorb the rhodium complex, the activity per

gram of rhodium goes through a maximum at a certain degree of liquid loading.

With XAD-2, however, the activity per gram of rhodium decreases continuously

2



with increasing liquid loading. These phenomena, too, can be explained by the

change in the extensiveness of adsorption of the rhodium complex with the

degree of loading and also by the change of the area of the gas-PPh, phase

boundary as a function of the degree of loading (Chapter 4 ) .

Catalysts supported on silica and silica-alumina have a long activation

time (120 hr s) . This is attributed to the gradual accumulation of a small

quantity of high-boiling aldol products, formed by aldol condensation of the

produced aldehydes, in the pores of the support. These aldol products adsorb

via hydrogen bridging on the surface silanol groups, as a result of which the

adsorption of rhodium complexes is suppressed and the silica surface is trans

formed from hydrophilic into organophilic. Thus, more and more rhodiumcomplexes become available at the gas-PPh, phase boundary, while, in addition,

the catalyst solution continues to spread further over the support. This

results in a slow increase in activity (Chapter 4 ) .

The presence of a small quantity of aldol products in a used catalyst

solution could indeed be demonstrated by means of IR-spectroscopy (Chapter 2 ) .

The activation time can be shortened to a few hours and the activity and

selectivity be increased by previous addition of aldol products or polyethylene

glycol to the catalyst solution, or by chemical modification of the silica

surface with tri(ethoxy)phenylsilane (Chapter 4 ) .

Although, as appears from the foregoing, the accumulation of a small

quantity of aldol products in the catalyst is allowable and sometimes even

desirable, the aldol condensation should yet be suppressed as much as possible.

A separate study has shown that this can be achieved by choosing sodium-poor

silicas or XAD-2 as support material; PPh, proved to be inactive and

RhHCO(PPh,), only slightly active for aldol condensation (Chapter 2 ) .

Owing to its unduly high volatility, P Ph, cannot be used as a solvent

ligand at temperatures above 10 0°C. Therefore, a large number of other, low-

volatile phosphines has been tested in the hydroformylation of propylene at 80 -

199°C. At temperatures up to 140 °C tri(p-tolyl)phosphine, tri(2 -cyanoethyl)-

phosphine and S(+)-(2 -phenylbutyl)diphenylphosphine appeared to be the most

suited. Above 150°C, however, all catalysts tested so far proved to deactivate,

probably owing to metallation of the coordinated phosphine ligands by the

rhodium metal (Chapter 5 ) .

The kinetics of the heterogeneous-catalytic hydroformylation of propylene

with RhHCO(PPh,), dissolved in PPh, have been investigated. The results can be

described by a rate equation of the following form:



. , rr,uil r il-03 r ,0.09 , ,0.23-0.08 , --oinn/DT-,r' =k-[ Rh] •[P(-=] ' [ PH ] ' fPcO^ '^'^P (-7910 0/RT)

This reaction rate equation differs remarkably from the equation valid for the

homogeneous-catalytic hydroformylation in the presence of a second solvent, for

instance toluene, besides PPh,, where the reaction is first order in hydrogen.

This difference in the kinetics raises the presumption that when use is made of

a large excess of PPh, in the absence of a second solvent, as in our case, the

addition of propylene to the complex is rate-determining (when a slight excess

of PPh, is used in the presence of a second solvent, the oxidative addition of

hydrogen is rate-determining).

The broken order in CO, and the influence of the CO-pressure on the

selectivity towards n-butyraldehyde, can be accounted for by a shift of the

location of the equilibria between the various rhodium complexes in the

catalyst solution (Chapter 6 ) .

The thesis concludes with some general remarks on the choice of the

technical-economic optimum catalyst and reaction conditions, and with a

comparison between a heterogeneous SLPC-process and the new low-pressure hydro

formylation process of Union Carbide, in which Wilkinson's catalyst is applied

homogeneously in a gassparged reactor (Chapter 7 ) .

4



C H A P T E R 1

INTRODUCTION

1.1 History of hydroformylation

1.1.1 Cobalt catalysts

The catalytic conversion of an olefin with carbon monoxide and hydrogen

into an aldehyde:

CH- — CH — CHO normal isomer

CH — CH, iso isomer

CHO

known as the 0X0 or hydroformylation reaction, is one of the oldest and most

widely used applications of homogeneous catalysis in the organic-chemical in

dustry.

The reaction was discovered by Roeien [1] in 1938 during an investigation

into the origin of oxygenated compounds in the products of the Fischer-Tropsch

synthesis carried out with a catalyst containing 30 w % of cobalt, 2 w % of

thorium oxide, 2 w % of magnesium oxide and 66 w % of Kieselguhr, and it be

came soon recognized that only the cobalt component is capable of catalyzing

the hydroformylation reaction. Since under the usual conditions of the

Fischer-Tropsch synthesis part of the cobalt dissolves in the organic reaction

medium, it was obvious to conclude that the catalyst is in effect a soluble

cobalt carbonyl complex [2]. The reaction mechanism, proceeding under the in

fluence of such catalytic complexes, was first described by Heck and Breslow

[3] and reviewed by Orchin and Rupilius [ 4 ] . Under reaction conditions the

active cobalt carbonyl HCo(CO) . is formed.

Since then industry has increasingly used Co (CO) , dissolved in the or-

Z o

ganic reaction medium, as catalyst precursor for hydroformylation purposes.

Cobalt complexes were employed for the first time in the 10 kgs/year Ruhr-

chemie plant at Holten, Germany, in 1942 for the manufacture of C.. - C _ al

cohols from higher olefins [5]. Owing to hostilities at the end of World War II

this plant has never been completed. The first commercial hydroformylation

process was then realized by Enjay Chemical Company, USA, making use of the

5

R - CH = CH + CO + H

R -



technology of Ruhrchemie.

From that time a large number of companies have developed their own process

technologies, the most important processes being those licensed by BASF [6,7],

Ruhrchemie [ 8 ] , Kuhlmann [ 9 ] , ICI [5] and Mitsubishi [ 10 ] . All of these are

based on the use of Co_(CO)„ as a catalyst, and they differ only in the cobalt

recovery step, in which the cobalt catalyst is removed from the aldehydes

formed and subseq uently recycled to the hydroformylation reactor. The various

cobalt recovery schemes are given by Lemke [ 9 ] , who states that this step is

the most expensive and cumbersome one;a very large number of patents deal with

this subject.

Typical reaction conditions in cobalt catalyzed hydroformylation are

temperatures of 110 to 180°C, H /CO ratios ranging from 1:1 to 1:3 mol/mol,

and total pressures of 2 0 to 35 MPa. These very high total pressures are ne

cessary to prevent decomposition of the active complex HCo(CO) into cobalt

metal, which forms strongly adhesive deposits on the reactor walls and on all

other parts of equipment. Under those severe reaction conditions the mainte

nance and investment costs are high, and the yields of useful products are low:

about 2 mole % of the olefin is hydrogenated to paraffin and the liquid pro

ducts consist to 7 8-8 2 w % of aldehyde, 10 -12 w % of alcoliol, 2 w % of formiate

and 6-8 w % of high-boiling products, like aldols, ketones and acetales [ 6 ] .

Normal-to-branched aldehyde ratios generally come between 3:1 and 4:1 mol/mol.

At Shell Oil Laboratories an interesting catalyst modification was dis

covered by Slaugh and Mullineaux in 1966 [11,12]. By adding to the reaction

medium a tertiary phosphine, arsine or phosphite, such as tri-n-butylphosphine,

these workers succeeded in stabilizing the cobalt catalyst. Under hydroformyla

tion conditions the catalytically active CoH(CO,)PBu complex is formed ac

cordingly to the following reaction equation:

Co-(CO) o + H- + 2 P Bu, t2 CoH(CO),PBu, + 2 CO

Other equilibria playing a role in the reaction mechanism have been mentioned

by Whyman [13] and by Van Boven [ 1 4 ] . The stabilization of the modified cobalt

catalyst is due to the fact that a phosphine molecule has less ir-acceptor

capability than carbon monoxide. Hence, the electron Tr-back-donation from co

balt to carbon monoxide is enhanced, resulting in a strengthening of the

metal-carbon monoxide bond.

Technological advantages of introducing the modified cobalt catalyst are a

decrease of the total pressure to 5-10 MPa, an increase of the normal-to-

branched aldehyde ratio to about 7:1 mol/mol (unmodified cobalt catalysts 3:1

6



to 4 : 1 ) , and a relatively easy separation of the cobalt catalyst from the pro

ducts, by simple distillation, which enables the catalyst to be recycled to the

hydroformylation reactor dissolved in high-boiling byproducts. About 1 0 w % of

this catalyst solution is fed to a catalyst recovery section to prevent accu

mulation of high-boiling byproducts.

Disadvantages of the Shell catalyst are a much lower activity -the activity

for 1-pentene hydroformylation with the modified catalyst, for example, de

creases by a factor of one hundred at 1 10 -15 0°C [ 1 2 ] - and a much higher hydro-

genation activity. Not only are all aldehydes hydrogenated to alcohols, but

also 1 0 mole % of olefin is hydrogenated [ 1 5 ] . Therefore, the modified cobalt

catalyst is unsuited when aldehydes are to be obtained as end products. Cur

rently, only Shell uses the modified catalyst to produce higher linear alcohols

from a-olefins at total pressures of 5-10 MPa and temperatures of 170-180°C

[16].

1.1.2 Rhodium catalysts

The cobalt catalyst may be replaced by other group VIII metals. Iridium,

for instance, gives much lower yields, together with significant hydrogenation

[17], and ruthenium is only slightly active [ 1 8 ] . Promising results as regards

activity and selectivity were obtained with relatively cheap platinum complexes

modified with tertiary phosphines and tin(II) chloride [ 1 9 ] . • .

Howe ver, so far the best results have been achieved with rhodium. The use

of rhodium was first described by Schiller [20] and Veryard [ 2 1 ] . Because of

2 4

the much higher activity of rhodium carbonyl (10 -10 times that of cobalt car

bonyl at 130 °C and 2 9.4 MPa total pressure), very mild reaction conditions are

now applicable. High-pressure equipment is no longer req uired, byproduct formation is low, only aldehydes are produced, and olefin hydrogenation does not

occur. However, unmodified rhodium carbonyls are very active double-bond iso-

merization catalysts, and therefore they have never been commercialized.

Modifying these rhodium carbonyls with tertiary phosphines, Wilkinson [22],

in 19 6 5 , and Slaugh and Mullineaux [ 2 3] , in 1 96 6, succeeded in developing a

hydroformylation catalyst that does not give rise to isomerization. Since that

time this catalyst system has been thoroughly investigated and extensively

described in literature; an excellent review is due to Pino [ 2 4 ] . The hydro

formylation mechanism and the effect of various reaction conditions on the

catalytic performance has been described by Wilkinson [ 2 5 ] . With triphenylphos

phine (PPh.) as one of the ligands the components active under hydroformylation

conditions are RhH(CO) PPh and RhH(CO)^(PPh ) , both of which are character-

7



ized by a very high activity, selectivity and stability. Wilkinson [25] showed

the catalyst to be active already at room temperature and atmospheric pressure.

Notwithstanding its decreasing effect on activity, a high P/Rh ratio is essen

tial for obtaining a high selectivity to normal aldehyde. At 9 0-1 25 °C and 0 .7 -

1.5 MPa total pressure, the normal-to-iso butyraldehyde ratio for propylene

hydroformylation in molten PPh, (P/Rh = 601 mol/mol) reaches a value of about

13, and the loss of olefin by hydrogenation is only 0.3-0.4 mole %; no alcohols

are detected. The remarkable stability of the rhodium complex wa s demonstrated

by Craddock [ 2 6 ] ; this worker found that the rhodium complex did not precipi-

tateduring recirculation nor lost activity after vacuum distillation at 180°C.

In 1975, after ten years of research and development. Union Carbide, New

York, USA, was the first to employ the new catalyst system commercially in two

large plants for the production of n-butyraldehyde, starting from propylene,

and for the production of propionaldehyde on the basis of ethylene [27,28].

This process is called the Low P ressure 0 X 0 (LPO) process. It operates at 8 0 -

120°C and 1.3-2.7 MPa total pressure, so under much milder conditions than the

classical cobalt-based 0X0 process. The normal-to-iso butyraldehyde ratio comes

in the attractive range from 8:1 to 1 6:1 , depending on the reaction conditions,

and the byproduct formation is low. The rhodium complex, RhHCO( PPh ) , along

with an excess of free triphenylphosphine (P/Rh = about 10 7 mol/mol), is dis

solved in a mixture of butyraldehyde and high-boiling byproducts from aldehyde

trimerization. The gaseous reactants are bubbled through this stirred liquid

catalyst solution and the produced aldehydes are continuously stripped from

the liquid and, together with the non-converted reactants, removed via the top

of the reactor.

At present, all three catalyst systems described above are still operation

al, and in use at 35 companies all over the world, having a total production

9

capacity of 3.5 x 10 kgs/year, 80 w % being butyraldehydes obtained from pro

pylene hydroformylation [ 1 5 ] . By aldolization and hydrogenation part of the n-

butyraldehyde is converted into 2-ethylhexanol, which, upon esterification with

phthalic acid, yields di(2-ethylhexyl)phthalate, called DOP, a very important

plasticizer in PVC production [ 2 9 ] . Since the normal butyraldehyde is suitable

for aldolization only, the normal-to-iso butyraldehyde ratio should be as high

as possible. Still another part of the n-butyraldehyde is hydrogenated to n-

butanol, which makes an excellent solvent.

The importance of using rhodium in carbon monoxide reactions is illustrated

by the Monsanto process for the very selective carbonylation of methanol to

acetic acid under the very mild reaction conditions of 1 80°C and 3-4 MPa total

pressure [ 30 ] . The first commercial plant, with a capacity of 1 50 x 10 kg s/

8



year, went on stream in 19 70 [31 ]. A new process, still under development at

Union Carbide, USA, is the production of ethylene glycol directly from hydrogen

and carbon monoxide in the presence of certain rhodium carbonyl clusters [ 3 2 ] .

1.2 Heterogenizing of homogeneous catalysts

Apart from their use for hydroformylation purposes, organometallic complex

es have in the past twenty years become adopted for many other interesting ap

plications in homogeneous catalysis. In the USA over twenty industrial process

es employ homogeneous catalysts [33 ]. There is an increasing trend to use high

ly selective, but at the same time also very expensive and rare homogeneous or

ganometallic catalysts and/or ligands for the small-scale production of

valuable organic compounds. The annual world output of rhodium, used for in

stance in hydroformylation, is only three to four thousand kgs; the rhodium

price is now about $ 3 0,0 00 /kg. Cobalt, on the other hand, used in the convent

ional 0X0 process, costs only $ 20/kg. Because of this high rhodium price,

nearly complete recovery of rhodium from the produced aldehydes is a prere

quisite. According to Cornils [15] the rhodium content of the produced alde

hydes should be kept below 0.3 ppm. When this condition is fulfilled, the cost

of the spent rhodium will equal the cost of the cobalt spent in the 0X0 pro

cess. For a homogeneous rhodium based catalyst to be commercially successful, a

very expensive and cumbersome rhodium recovery step is therefore needed; the

same holds for other precious homogeneous catalysts and for the very expensive

and sophisticated ligands that are sometimes used. Furthermore, the metal and/

or ligands contaminate the products, and homogeneous catalysts may cause severe

corrosion of the equipment, as, for example, in Wacker-type processes [34].

The recovery, contamination and corrosion problems may be circumvented by

heterogenizing the homogeneous catalysts, that is to say by transferring the

catalyst into a phase other than either the reactants or products. Hence, a

continuous separation between the catalyst and the products is affected already

in the reactor.

Heterogenizing of homogeneous catalysts can be realized by any of the fol

lowing methods:

a) dispersion of a catalyst solution in the pores of a support (Supported

Liquid Phase Catalyst) [ 5 5 ] ;

b) physical adsorption of the organometallic complex on a support [35,36,37,38];

c) chemically anchoring of the organometallic complex to an organic [39,40,41,

42] or inorganic [43,44,45,46] support;

d) application of organometallic complexes with ligands insoluble in the

9



reactant or product phase [47,48,49];

e) immobilisation of the organometallic complex on resins or zeolites by ion

exchange [50,51];

f) application of a gassparged reactor [ 5 2 ] ;

g) application of a catalytic liquid membrane reactor [53];

h) application of a membrane-type reactor [5 4] .

Methods a_, b, e , f and Ii are not suitable for continuous liquid phase re

actions because the catalyst is rapidly dissolved in the liquid reactants and/

or products.

For a detailed discussion of the above mentioned methods of heterogenizing

homogeneous catalysts and their applications to several review articles may be

referred [56-62]. In this thesis only method a_ is dealt with, the so-called

SLPC method, which was used in the present study for the reasons set forth in

Section 1.4, Objective and Scope of the Thesis.

1 .3 S u p p o r t e d L i q u i d P h a s e C a t a l y s i s

A supported liquid phase catalyst is a catalyst system in which a catalyti

cally active liquid is dispersed in the pores of an inert porous support,

where it is strongly captivated by capillary forces. The catalytically active

liquid may be a molten salt, a liquid metal, an acid or a solution of an or

ganometallic complex in a high-boiling solvent. In order to avoid drying-up of

the solution in the pores by evaporation, the volatility of the solvent should

be low.

The history of supported liquid phase catalysis dates back as far as 19 36 ,

when research workers of Universal Oil Company, Los Angelos, USA, applied

phosphoric acid, capillary-condensed in the pores of Kieselguhr, as a catalyst

for dimerizing lower olefins to high octane gasoline [ 6 2 ] . Today, this

catalyst is still used for the production of styrene and cumene by alkylation

of benzene with ethylene and propylene, respectively.

The SLPC principle is applied on a large scale in the field of fused salt

catalysis. The Deacon reaction,

2 HCl + y 0^ ? CI2 + H2O

and the oxidative chlorination of hydrocarbons, e.g. ethylene,

C^H^ + 2 HCl + i 0^ t CH CICH CI + H O

10



employ a catalyst that consists of a mixture of copper chloride, one or more

alkali metal chlorides and one or more rare earth metal chlorides deposited on

a porous support. The alkali metal lowers the melting point to the extent that

the mixture will be partly or completely molten under reaction conditions. Now

adays industrial interest is focussed primarily on the one-step synthesis of

vinyl chloride from ethylene.

Another very important example of fused salt catalysis is the oxidation of

sulphur dioxide for synthesizing annually hundred of billions of kgs sulphuric

acid. Reaction conditions are 420-610°C and atmospheric pressure. The catalyst

is composed of 6 w % V-O, promoted with K^SO., on Kieselguhr. A survey of many

other fused salt catalyzed reactions is given by Kenney [63].

The first publication about the use of a supported liquid phase catalyst

in the field of organometallic complex catalysis is due to Bond in 196 6 [ 6 4 ] ,

who isomerized 1-pentene with a solution of rhodium trichloride in ethylene

glycol deposited on Kieselguhr.

In 1969 Rony [65] reported on the hydroformylation of propylene with

RhCOCl(PPh ) , dissolved in benzyl butyl phthalate and brought into the pores of

silica gel. As demonstrated in the respective patent [66] this catalyst system

is also suited for hydrogenation and isomerization of lower olefins. The same

research-group oxidized ethylene to acetaldehyde with PdCl^/CuCl_ dissolved in

ethylene glycol on Kieselguhr, and carbonylated methanol to acetic acid with

RhCl .3 H O in pentaerythrityl tetravalerate on silica gel [ 6 7 ] .

Theoretically, diffusional retardation of the rate of reaction, if occur

ring in a SLPC, will be greatest in the liquid phase because liquid phase dif-

4 5fusion is 10 to 10 slower than gas phase diffusion. So, in moderately fast

reactions, such as those catalyzed by organometallic complexes, the activity

of an SLPC will mainly depend on the liquid layer thickness. Diffusional re

tardation is less severe in thin liquid layers, meaning that the activity of

an SLPC will be highest if the liquid is distributed as a thin liquid layer on

the inner surface of the porous support. This goes to show that the liquid

distribution is a most important factor in supported liquid phase catalysis.

Theoretically, the distribution of the liquid varies with the contact

angle of the liquid on the support, the texture of the catalyst (pore size

distribution and interconnectivity of the pores) and with the liquid loading,

i.e. the degree of pore filling with liquid, which can be varied from 0 to

100%. So, in the case of a given support and a given liquid, the liquid dis

tribution, and hence the activity, will only be influenced by the liquid

loading. Theoretical models describing this influence, are given by Rony [ 6 8 ] ,

Abed [69] an dV iU ad se n [70] .

11



Abed's model does not require knowledge of the liquid distribution, as this

is accounted for by a so-called dusty gas constant, an empirical parameter

which depends solely on the type of support and the liq uid loading. The re

actants diffuse via both the gas phase and the liquid phase into the interior

of the catalyst particle and the effective diffusion coefficient is calculated

with the aid of the above-mentioned dusty gas constant. However, the model is

based on the rather unrealistic assumption that the reaction in the liquid

phase is not diffusionally retarded. This can only be true at very low liquid

loading.

Rony, on the other hand, assumes diffusional retardation to occur in both

the liquid and the gas phase regions in an ideal cylindrical pore. The liquid

layer thickness (6) is calculated as a function of the liquid loading ( 6 ), by

means of the following equation:

e = 6(1 - e"^* + e'"*)

where a and n are empirical parameters.

The most realistic model is that suggested by Villadsen [ 7 0 ] , who, describ

ing the liquid distribution on the basis of the theory of capillary condensa

tion in porous supports, assumes that at intermediate degrees of liquid loading

the smallest pores are totally filled up with liquid, whereas the larger ones

merely carry a thin layer of physically adsorbed liquid on the inner surface.

The liquid distribution is determined by measuring the pore size distribution

of a bare and a loaded support. Both liquid and gas phase diffusion are in

cluded in Villadsen's calculations.

Recently, Villadsen showed that the situation may be more complicated than

initially proposed by him, because above a certain degree of liquid loading the

liquid agglomerates, resulting in the formation of large liquid-filled regions,

called liquid clusters, the dimensions of which are many times larger than the

average pore diameter [ 7 1 ] . The size of the liquid clusters depends on the

liquid loading and, in an irregular way, on the pore diameter. Up to now no the

ory has come forward for predicting the clustering mechanism and the size of the

clusters to any degree of accuracy. As to this latter point, it is surprisingly

that the models of Abed and Rony, as well as that of Villadsen, all fit in so

well with their experimental data. This may be attributed to the large number

of empirical parameters incorporated in their models.

12



1.4 OBJECTIVE AND SCOPE OF THE THESIS

The objective of the present study is to develop a technologically applic

able heterogeneous active, selective and stable catalyst for the gas phase

hydroformylation of lower olefins and substituted olefins, such as ethylene,

propylene, butenes, allylalcohol, allylacetate and vinylacetate. The need

to search for such a new catalyst system sprang from the consideration that the

catalyst systems known in literature do not seem suitable for the reasons, set

forth below.

Hydroformylation in the liquid phase

From literature it appears that up to now heterogeneous hydroformylation

has mostly been studied in batchwise-operated stirred tank reactors or auto

claves in the liquid phase, using rhodium complex catalysts chemically anchored

to organic or inorganic supports. A drawback of such a system is the possible

dissolution of the rhodium complex from the support into the liquid reactants

and/or products and the consequent inadmissible loss of rhodium and deactiva

tion of the catalyst. Lang [ 7 2 ] , for instance, mentioned an elution of 0.5 - 10

ppm of rhodium from macroreticular polystyrene, functionalized with dibutyl-

phosphine or dimethylamine, into the products, whereas for economic application

the amount of rhodium lost in the products, should be less than 0.3 ppm [ 1 5 ] .

Oxygen in the feedstock was shown to promote rhodium elution [43] and the

rhodium was redistributed along the catalyst bed. On the whole not much is

known about the stability of chemically anchored catalysts, because most

research workers test their catalysts batchwise in stirred autoclaves. Under

reaction conditions the rhodium complex may desorb from the support into the

liquid phase and readsorb after cooling down of the reaction mixture at the end

of an experiment [ 7 3 ] . Furthermore, in most studies the normal-to-branched al

dehyde ratio appears to be low. It is evident therefore that hydroformylation

should preferably not be carried out in the liquid phase.

Hydroformylation in the gas phase

Workers at Monsanto, St. Louis, USA, heterogenized a RhClCO(PPh,)^ catalyst

for gas-phase hydroformylation of propylene in three different ways:

1) by strong physical adsorption of the rhodium complex on an inorganic

support [ 35 ] .

13



2) by application of a supported liquid phase catalyst [ 6 5 ] .

3) by application of a gassparged reactor [ 5 2 ] .

Although an excess of free triphenylphosphine was used, the normal-to-iso

butyraldehyde ratio was surprisingly low (2:1 mol/mol), in each of the three

cases.

A much higher normal-to-iso butyraldehyde ratio of about 13:1 mol/mol was

obtained by Wilkinson, when bubbling a mixture of gaseous propylene, carbon

monoxide and hydrogen through a stirred solution of RhHCO(PPh,), in molten PPh,

[22, 7 4 ] . In 19 75 , industrial hydroformylation of ethylene and propylene, with

the aid of the Wilkinson catalyst dissolved in low volatile aldehyde trimeriza

tion products and a large excess of free triphenylphosphine, was realized for

the first time by Union Carbide, New Y ork, USA,in a gassparged reactor.

Although the process seems very attractive, the presence of a catalyst recovery

section in the process raises a presumption of either loss or deactivation of

catalyst.Bryant [75 ] mentions a maximum daily activity loss of 0.75 % calculated

on the initial activity; this would mean complete deactivation of the catalyst

after 3 20 0 hrs streamtime. The technological merits of this process over our

SLPC-process will be discussed in more detail in Chapter 7 of this thesis.

Another study on gas-phase hydroformylation of lower olefins is due to Arai

[4 6 ], who reports on the kinetics of the hydroformylation of ethylene, propyl

ene and butenes, making use of [RhCl(CO)-]_ chemically anchored to a poly

styrene-coated silica gel. Besides considerable hydrogenation of the olefins,

deactivation of the catalysts was observed after a streamtime of two hours.

Finally, in the Laboratory of the Department of Chemical Technology, Delft

University of Technology, Spek [37 , 76 ] and Tjan [3 8, 77 ] studied the gas-phase

hydroformylation of ethylene and propylene in the presence of Rh(TT-allyl)CO-

(PPh,)- physically adsorbed as a monomolecular layer on an inorganic support.

They found such a catalyst to deactivate slowly at high pressure and

tenperature owing to:

1) slow surface migration of the rhodium complex into the smallest pores,

where it is less accessible to the reactants;

2) dissociation of triphenylphosphine from the rhodium complex, followed by

dimerization of the rhodium complex to inactive rhodium compounds.

The normal-to-iso butyraldehyde ratio was low (2:1 mol/mol).Combination of the above-mentioned findings led us to the conclusions that:

1) excess triphenylphosphine is needed to avoid complex dimerization and

achieve a high normal-to-branched aldehyde ratio;

2) transport of the rhodium complex must be avoided by chemical bonding of the

14



rhodium complex to the support*;

3) hydroformylation should be preferably performed in the gas phase to prevent

leaching out of the rhodium complex.

In view of considerations 1 , 2_ and 3 , we decided to perform the hetero

geneous gas phase hydroformylation of ethylene and propylene with rhodiumhydri-

docarbonyltris(triphenylphosphine), RhHCO(PPh-),, dissolved in one of its own

ligands, PPh,, or other tertiary phosphines. This catalyst solution is hetero

genized by strong capillary condensation in the pores of an inorganic or

organic support. So, the principle of supported liquid phase catalysis is

applied, one of the ligands being the solvent. Compared with the practice of

using a gassparged reactor [2 2, 7 3 ] , this method of heterogenizing offers the

following advantages: a very large gas-PPh, phase boundary; absolutely no

rhodium loss; easier process operation; no corrosion problem.

The catalyst performance has been tested under realistic technological

conditions of 1.2 - 1.57 MPa total pressure and 40 - 199°C in a continuous iso

thermal plug flow tubular reactor over periods of up to 80 0 hours.

*Chemically anchoring of the rhodium complex to a support is studied separately

by De Munck [7 8] and will not be further discussed in this thesis.

15



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C H A P T E R 2

HYDROFORMYLATION WITH SUPPORTED LIQUID PHASE RHODIUM CATALYSTS

Part I. General Description of the System, Catalyst Preparation and

Characterization *)

by

L.A. Gerritsen, A. van Meerkerk, M.H. Vreugdenhil and J.J.F. Scholten,

Department of Chemical Technology,

Delft University of Technology,

Julianalaan 136,

26 28 BL Delft, The Netherlands

Summary

Hydridocarbonyltris(triphenylphosphine)rhodium(I) dissolved in triphenyl

phosphine and capillary condensed in the pores of a support material, is

applied in the heterogeneous hydroformylation of propylene at 90°C and 1.57

MPa total pressure. The activity and selectivity of this new catalyst are high

compared with those of known analogues. No sign of deactivation is observed

over a period of more than 800 hrs. - -

A small weight increase of the used catalyst, occasionally observed, can

be attributed to some accumulation of low-volatile aldol condensation products

in the pores. The aldol condensation reaction can be suppressed by using

macroreticular polystyrene-divinylbenzene, XAD-2, or sodium-poor silica as

support material.

New bands in the I.R. spectrum of rhodium complexes are detected at 19 4 7 ,

1993, 200 2 and 20 7 0 cm" , which cannot be assigned to known rhodium complexes.

Nitrogen capillary condensation proves the catalyst solution at 5 6 % pore

filling to be mainly located in the smallest pores of the support. X-Ray

Microanalysis reveals a rather uniform distribution of the catalyst solution

across a catalyst particle.

*) Paper submitted for publication in Journal of Molecular Catalysis.

19



1 I n t r o d u c t i o n

In 1965 Wilkinson [1] showed RhHCO(PPh ) , to be a superior homogeneous

hydroformylation catalyst. Since then, research at heterogenization of this

very precious catalyst has received high priority [2 -10 ] . Attention has been

focussed in particular on the chemical anchoring of the rhodium complexes on

organic and on inorganic supports. Possible drawbacks attaching the use of such

immobilized catalyst systems in liquid phase operation are the slow leaching-

out of the rhodium complex [1 1,12 ,13] and the generally low selectivity towards

the straight aldehydes, which are industrially more important than the branched

aldehydes [14-18].

In the case of gas-phase hydroformylation an attractive alternative for

chemically anchored catalysts is presented by a Supported Liquid Phase

Catalyst, SLPC, in which the rhodium complex is dissolved in a non-volatile

solvent and immobilized in the pores of a support by strong negative

capillary forces. One advantage of such an SLPC system might be the preserva

tion of the original liquid environment of the rhodium complex, because this

protects it from chemical modification by interaction with the surface of the

support, a phenomenon sometimes observed in chemically and physically immobilized systems. A large gas-liquid contact area may be mentioned as a further

advantage.

Although SLP catalysts have already been applied in a number of industri

ally important reactions since 1936 [18,19], Rony [ 2 0 ] , in 196 9, was the first

to try them out in the heterogeneous hydroformylation of propylene, with

RhClCO(PPh,) dissolved in benzyl butyl phthalate on silica gel as a support.

However, notwithstanding the large excess of dissolved free PPh, (P/Rh = 56

mol/mol) used by him, the normal-to-iso butyraldehyde ratio appeared to be

disappointingly low (n/iso = 2 ) . Rony does not give any details about the

stability of the catalyst; in a subsequent paper [2 1] he merely states: "the

catalyst had a tendency to activate and deactivate with time".

In the present study it will be demonstrated by means of a few examples

that dissolution of RhHCO(PPh ) , in PPh yields an excellent SLPC system for

hydroformylation of propylene under mild reaction conditions. For more examples

describing the performance of these catalysts reference may be had to the

relevant patents [22,23]. Furthermore, the texture, structure and analysis of

our SLP catalysts will be discussed.

20



2. Experimental

2.1 Materials

RhHCO(PPh ) was prepared by the method of Ahmad [24 ]. Triphenylphosphine

(Fluka, Switzerland, 99.5%) was used as received. Benzene (Merck, Germany,

99.7%) and toluene (Merck, Germany, 99%) were dried over molecular sieve 3A

(Union Carbide, USA). Nitrogen (Air Products, USA, 99.98%) was freed of

oxygen and water over BASF catalyst R3-11 and molecular sieve 3A, respectively.

Propionaldehyde (Merck, Germany, 99.0%) was distilled before use. Hydrogen

(99.99%), propylene (99.5%), ethylene (99.9%) and carbon monoxide (99.5%) were

all obtained from Air Products, USA. Silica 00 0-3E, silica-alumina LA-30, y-

alumina 005-0.75 E (all from Akzo Chemie, Amersfoort, The Netherlands), Kiesel

guhr MP-99 (Eagle Pitcher, USA) , silica Dll-11 (BASF, Arnhem, The Netherlands),

silica S (DSM, Geleen, The Netherlands) and Amberlite XAD-2 (Serva, Germany)

were crushed if necessary, and sieved to the desired size fraction of 0.42-0.50

mm.

2.2 Catalyst preparation

Except for XAD-2 and silica S, the supports were dried in vacuo (0.1 kPa),

first at 150°C for 3 hrs and then at 500°C for 16 hrs. Only silica S and

XAD-2 were dried in air at 120°C for 16 hrs. The dried supports were placed in

the catalyst preparation apparatus shown in Fig. 1.

Calculated amounts of RhHCO(PPh ) and PPh, were dissolved in benzene or

toluene at 70°C under flowing nitrogen. The total volume of the catalyst solu

tion was taken exactly equal to the total pore volume of the support. Thecatalyst solution was added dropwise to the stirred support, which was likewise

held at 70°C. Next, the benzene was slowly evaporated under flowing nitrogen

at room temperature for 3 hrs and then at 90°C for 16 hrs, during which period

the PPh, could redistribute in the pore system. By varying the PPh,/benzene

volume ratio in the catalyst solution, several degrees of liquid loading, i.e.

degrees of pore filling with catalyst solution, could be realized after

evaporation of the benzene. The dry and free-flowing catalyst particles were

stored at -20°C. The catalyst preparation is fully reproducible, as it turnedout that two batches of catalyst showed the same catalytic performance.

21



- coohng

N2

-oil (70°C)

N, (70°C)

y ~ oil(70°C)

Figure 1 Catalyst preparation apparatus.

A = reflux cooler, B = catalyst solution holder,

C = support holder, D = magnetic stirrer.

2.3 Catalyst charac terization

The SLPC is completely characterized by the following parameters:

: the type of support

6 : the degree of liquid loading, defined as the degree of the pore volume

filled up with catalyst solution at 90°C3

[Rh] : the rhodium complex concentration in PPh, at 90 °C (mol/m )

P/Rh : the molar phosphine-to-rhodium ratio (mol/mol)

The texture of the support and of the catalyst was determined by nitrogen

capillary condensation [25] at -196°C on a Carlo Erba 18 00 "Sorptomatic", or

by mercury porosimetry [26] on a Micromeritics 9 05-1 apparatus. The repro

ducibility was better than 3% in both cases.

The distribution of the PPh across cleaved catalyst particles embedded in

Woods metal, was determined by X-ray microanalysis, RMA, on a Jeol JXA-50A

22



a p p a r a t u s w i t h a l a t e r a l r e s o l u t i o n o f a b o u t 1 ym .

Pho tograp hs on coupes o f ba re and loaded s up po r t s o f abo u t 50 nm th i c kn es s

were t aken by t r a ns m iss io n e l ec t ro n mic rosc opy , TEM, on a P h i l i p s EM-300

a p p a r a t u s w i t h a maximum m a g n i f i c a t i o n o f 1 7 5 , 0 0 0 . C l e av e d p a r t i c l e s w e r e

pho tog raphe d by sca nn in g e l e c t ro n mic rosc opy , SEM, on a JSM-U3 ap pa ra tu s wi th

a l a t e r a l r e s o l u t i o n o f 1 ym .

2 . 4 Catalytic performance

T he c a t a l y t i c pe r f o rm a n c e w as s t u d i e d i n a s t a n d a r d c o n t i n u o u s - f l o w e q u i p

men t su i t e d f o r t o t a l p re ss u r e s up t o 2 MPa and t em pe ra tu r es up t o 300°C (F ig .

Figure 2 Continuous-flow app aratu s [2 7] .

A = pu r i f ic at ion , PI = Flow Ind ica tor , LI =

Level In dic ato r, PC = Press ure C on tro l le r , PI =

Pressu re I nd ica tor , PIA = Press ure Ind ica tor and

Alarm, PIC = Pressure Ind ica tor and C on tro l le r ,

TCA = Tem perature C on tro lle r and Alarm, TCI =

Temperature Con trol le r and In dic ato r, TR =

Tem perature Rec order, TRC = Tem perature Recorder

and C on tro l le r , API = D iffe re nt ia l Pressure

Indicator. I tems 1-10 are mentioned in the text .

23



Hydrogen, carbon monoxide and, either, ethylene or helium were stripped of

oxygen, water and carbon dioxide by leading them over BASF catalyst R3-11,

molecular sieve 3A and sodium hydroxide on asbestos ("Ascarit"). Liquid pro

pylene was metered from reservoirs ( i) and ( 2 ) , evaporated and mixed with the

other reactants in evaporator ( 3 ) . Next, the gas mixture was passed through

heated tubes to a 0.200 m long fixed-bed reactor (s ) (inner diameter O.OIO m)

placed in an air-fluidized-bed oven M J permitting isothermal operation to

within 0.5°C. The operating conditions were so chosen as to assure ideal plug

flow and exclude pore or film diffusional retardation of the chemical

reaction rate in the gas phase. After release of the total pressure to 0.1 MPa,

the product mixture was periodically sampled via sampling valve ( 6 ) , analyzed

gaschromatographically on a Porapack-PS column (?) (Waters Ass. Inc., USA) at

120°C, with helium being used as the carrier gas, and detected catharometrical-

ly. The peak areas were recorded ( s ) , and integrated on a digital integrator

( 9 ) (Infotronics 3 0 9 ). Following measurement of the flow in soap film meter

(10) , the product mixture was vented to the atmosphere.

Aldehydes being the only products observed, the conversion of olefin [£,)

was calculated as follows:

A BP P

e + Ap p o

where A and A are the integrated peak areas for aldehyde and olefin,

respectively, and B is an internal normalization factor correcting for the

difference in thermal conductivity between aldehyde and olefin,

The selectivity (S) is calculated as the ratio of the peak areas for

normal- and iso-butyraldehyde:

A

^ = - A ÎSO

The thermal conductivities of normal- and iso-butyraldehyde are equal.

The reactor was operated differentially, so that the initial reaction rate

(r) could be expressed as:

W F T

24



i.e. in cm olefin at 0.101 MPa and 25°C (the atmospheric conditions under

which the flow was measured in the soap film meter), per gram of rhodium metal

in the reactor and per second.

After the start of an experiment the reactor temperature was stepwise

raised to its final value in a period of two hrs.

2.5 Infrared spectroscopy

Reflection I.R. spectroscopy of catalyst particles results in poorly re

solved spectra, whereas transmission I.R. is not applicable owing to the large

size of our catalyst particles. Therefore, we extracted the catalyst solution

from the fresh or used catalyst particles (0.6 g) with 2 g of carbon tetra

chloride, and recordered the spectrum of the CCl.-extract on a Beckman-4210

spectrophotometer,

2.6 Activity tests for the unwanted consecutive reaction: aldol condensation

of aldehydes

To check which of the catalyst components is responsible for the highly3

undesired aldol condensation, freshly distilled propionaldehyde (4 cm ) , used

as a model compound, and support (0.4 g) were brought under nitrogen into

each of a series of about five glass sample tubes capable of withstanding

pressures up to one MPa. After sealing, the sample tubes were placed in a

thermostatic bath at 90 °C. After various lengths of time, the sample tubes were

successively broken and the contents were analyzed gaschromatographically at

95°C on a SP-22 50 -on-Chromosorb G. HP. column, and detected by means of flame

ionization.The reaction mixture proved to consist of nonconverted propionaldehyde,

2-methyl-2-pentenal, 3-hydroxy-2-methylpentanal and a small amount of higher

boiling products (trimers and tetramers).

2.7 Nevtron activation analysis

The sodium content of the supports was determined by neutron activation

analyses, using the single comparator method, with zinc as the referencematerial [2 8] .

25



3 Results

3.1 SLPC versus physically adsorbed catalysts

The activity and stability for propylene hydroformylation of a typical SLPC3

(Kieselguhr MP-99 support, 6 = 0.44 , [Rh] = 5.51 mol/m , P/Rh = 74 4 mol/mol) as

functions of the streamtime (t.) are shown in Fig. 3. The activity and stabili

ty of a typical physically adsorbed catalyst (Rh(Tr-allyl)CO(PPh ) on y-alumina

00 0-3 P, according to Tjan [29]), are included for comparison.

10

/•cm3ci>

- p°lgRh.sj

1 1 1 1

2 0 0 4 0 0 6 0 0^ t(j (hrs)

8 0 0

Figure 3 Activity and stability for propylene hydroformyla

tion of a typical SLPC(x) and a physically adsorb

ed catalyst (o).

P = 1.57 MPa; Cj/H^/CO = 1/1/1; t = 90°C; W/F =

. 0.987 X 10 '^ g Rh.s/cra C^.

It is seen here that after 15 0 hrs streamtime the SLPC is six times more

active than the physically adsorbed catalyst. The SLPC shows no sign of de

activation after 8 00 hrs, whereas the physically adsorbed catalyst deactivates

to 1 0 % of its initial activity in the first 15 0 hrs. Moreover, the selectivity

of the SLPC is not only time-independent, but also nuch higher (S = 9) than

that of the physically adsorbed catalyst (S = 2 ) . Both catalysts produce more

than 9 9 .5 % aldehydes.

26



3.2 Com parison with Rony's SLP catalyst

To compare the performance of the new catalyst with Rony's SLPC, two

catalysts were prepared and tested under the same reaction conditions. The one

according to Rony [ 21] was made with RhHCO(PPh ) and an excess of PPh (P/Rh=

56 mol/mol) dissolved in di(2-ethylhexyl)phthalate (DOP), the other one, dis

cussed in the present study, with RhHCO(PPh ) dissolved in PPh (P/Rh = 74 4

mol/mol).

3 0

2 0

10

n

^9 0

1

r '

/ • c m ^ C s N

( ^ g R h s )

1 1 1 1

200— tj (hrs)

300 400

Figure 4 Activity and stability for propylene hydroformyla

tion of two SLPC's, both prepared with an excess

of PPh-. X : PPh as solvent; o : DOP as solvent.

P = 1.57 MPa; c /IU/CO = 1/1/1; t = 90°C; W/F =.57 MPa; C /H /CO = 1/1/1; t

-3 3 =

0.987 x 10 g Rh.s/cm C Catalyst: silica 000-3E,

S = 0.56, [Rh] = 5.5 mol/m^.

The activity of the catalyst made with DOP is four times that of the PPh

system, which fits in with our findings after addition of polyethylene glycol

to the catalyst solution, described in part III of this series [ 3 0 ] , The

selectivity, however, which is a very important parameter in hydroformylation,

is much better for our PPh, system (7.8 against only 3.1 for the DOP catalyst).

3.3 Infrared spectroscopy

Typical I.R. spectra of the CCl.-extract of a fresh and used SLPC are

shown in Fig. 5. The same results were arrived at by using CH.Cl^ as an

extraction agent.

27





of H- and CO to be a reversible reaction.

A q uite different, but very interesting observation is the following: after

an SLP-catalyst has been used in long-term hydroformylation experiments at high

conversion levels, additional strong bands are noted at 17 25 and 168 5 cm and

a weak band at 164 0 cm , together with weak bands in the region 270 0-3 00 0 cm .

Upon comparison with the bands in the I.R. spectra of pure compounds, and also

with literature data [ 3 1 ] , we assigned these to a small amount of butyraldehyde

(1725 cm ) and low-volatile dehydrated aldol condensation products such as

2-ethyl-2-hexenal (16 85 , 16 40 cm" ) , condensed in the catalysts during use at

high conversion levels. Bands due to non-dehydrated 2-ethyl-2-hydroxyhexanal

have never been observed.

3.4 Aldol condensation

In general, used catalysts show a small increase in weight of 0-6 w %,

depending on catalyst and reaction conditions. For example, used in the hydro

formylation of ethylene at 90°C and 1.2 MPa total pressure, a silica 000-3E SLP

catalyst (6 = 0.31) shows an increase in weight of 4.93 % after 144 hrs , whereas

a silica S catalyst (6 = 0.79) does not change in weight at all over a period

of 14 1 hrs. In both cases the conversion of ethylene was about 1 3 %. As evidenc

ed by I.R. spectroscopy, this small weight increase is to be attributed to the

accumulation of low-volatile aldol condensation products in the pores of the

catalyst. The aldol condensation products are due to aldol condensation of the

propionaldehyde or butyraldehyde formed. Qualitatively, we established that the

higher the weight increase, the stronger the absorption band at 1.685 cm

In general, we did not observe any detrimental effects of these aldol con

densation products. On the contrary, previous addition of 10 w % of a mixture

of aldol condensation products to the catalyst solution on silica 000-3E even

proved to decrease the activation time in hydroformylation from 20 0 hrs to

less than 10 hrs, whereas both the activity and selectivity slightly increased.

This point will be dealt with in part III of this series [ 3 0 ] . A practical

difficulty caused by accumulation of aldol products might be that in the long

run the catalyst solution gets completely driven out of the pores. Therefore,

measures have to be taken to suppress the formation of these aldol products as

much as possible.

To assess the individual activities of the support, P Ph, and rhodium

complex for the unwanted aldol condensation, we examined in how far the con

version of propionaldehyde at 9 0°C is promoted by each of these agents.

29



Table 1 Conversion (%) of propionaldehyde to aldol condensation products at

90°C, as a function of time

Na-content^ x 1 0^ i \ ^ 5^^ £^0 ^40

(w %) (%) (%) (%) (%) (%)

supports

Y-alumina 005-0.75 E

silica-alumina LA-30

silica 000-3E

silica Dll-11silica S

Kieselguhr MP-99

XAD-2 (extracted)

PPh

PPhJ + RhHC0(PPh2)j

blank run

800

698

4900

< 100036

1410

-

-

-

_

9,8

3.8

3.6

3.20.3

0.3

1.0

-

0.3

-

a : Na-content as determined by neutron activation analysis.

b : conversion of propionaldehyde after 2 , 5, 1 0 , 20 and 40 hrs reaction time.

The results (Table 1) show that by far the greatest activity was measured

for the supports, the most active one being y-alumina 00 5-0 .75 E, As to silica,

we noted that the activity decreases with the sodium content, as was also

observed by Beranek [ 3 2 ] . Silica S did not show any activity; the same is true

for PPh . The rhodium complex was only slightly active in the first twenty hrs,

which proves that it gradually lost its activity for aldol condensation. The

low activity of the macroreticular polystyrene-20% divinylbenzene XAD-2 must be

attributed to a slight contamination with sodium even after 25 hrs of extrac

tion with refluxing water, met hanol, ethyl ether and pentane. The low activity

2of Kieselguhr MP-99 is explained by its low surface area of only 18 m /g,

3.5 PPh^-distribution in the supportÓ

3.5.1 Nitrogen capillary condensation and mercury porosimetry

The pore size distribution before and after loading of the support with

catalyst solution was studied by nitrogen capillary condensation (Fig. 6) and

16.1

6.6

7.4

4.00.5

0.7

1.7

-

0.8

0.3

25.5

10.9

13.3

6.01.0

1.3

2.9

0.3

2.1

0.6

40.0

18.5

23.9

11.21.5

2.4

4.5

0.6

3.8

1.1

53.0

29.6

39.8

18.52.1

5.3

6.4

1.0

3.8

2.2

30



mercury porosimetry (Fig. 7 ) . In order to account for the weight increase of

the support due to loading, use has been made of a conversion factor, W /

Wsupport

, which converts the measured cumulative pore volume of the catalyst,

expressed in cm per gram of catalyst, into the cumulative pore volume per gram

of support. In this way, a direct comparison between the loaded and unloaded

support can be made.

1 0

0.5-

101 2— • Tp (nm)

Figure 6 Pore size distribution of an unloaded (x) and a

PPh, loaded (o) silica 000-3E support, as determin

ed by nitrogen capillary condensation at -196°C;

theor0.56.

1 0

0 5 -s.

Figure 7 As Figure 6, but determined by mercury porosimetry.

31



Fig. 6 shows that most of the PPh, is present in the smallest pores of the

support. The transitional pores are only partially filled up. Mercury porosi

metry reveals a striking different distribution; all of the PPh_ prove s to be

collected in the smallest pores (Fig. 7 ) . Qualitatively the same results were

obtained for all other support materials investigated in the catalytic perfor

mance tests [3 0] .

The PPh -distribution in a fresh and a used catalyst are qualitatively

identical. Sometimes a used catalyst shows a small decrease in total cumulative

pore volume (say, 5 % ) , owing to accumulation of low-volatile products in the

pores.

3.5.2 X-ray microanalysis

The PPh distribution across a catalyst particle with a diameter of 0.42-

0.50 mm was measured by RMA (Fig. 8 ) .

101

— Particle coordinate (i im)

Figure 8 PPh, distribution across a catalyst pellet. A =

Si-signal, B = P-signal, both on silica 000-3E

with 5 = 0.56; C = P-signal on XAD-2 with 6 =

0.65.

The phosphorus-linescans prove that the catalyst is not a so-called mantle-

catalyst, i.e. there is no PPh enrichment at the outer surface of the

particles. In silica 0 00 -3E a decrease of the silicium-signal is generally

accompanied by an increase of the phosphorus-signal. This shows the porosity to

be non-uniform, the more porous regions being filled up with PPh . The dimensi

ons of these PPh,-enriched regions are as large as 16 ym. XAD-2 (linescan C)

shows a somewhat more uniform distribution, which must be attributed to the

32

/



relatively regular framework of microspheres in this material.

3.5.3 Electron microscopy

Examination of coupes of catalyst material by TEM, and of cleaved catalystparticles by SEM gave no additional information on the PPh distribution; at

enlargements up to 1 75,000 ,PPh, could not be distinguished from the support,

nor could differences be observed between the images of a bare and loaded

support.

4 . Discussion

I. R. measurements

It is seen from Table 2 that the I.R. absorption bands of the CCl.-extract

of a used SLP catalyst do not coincide with the bands in the I.R. spectra

characteristic of the intermediates in Wilkinson's associative mechanism [33]

nor with anyone band attributable to dimeric rhodium complexes.

Table 2 I.R. spectra of several rhodium complexes

position of

complex I.R. bands (cm )

RhHC0(PPh2), 1920, 2000, 2040

W \\i{CQ}^{??\\^)^ 1 9 4 2, 1980, 2050

Rh(COC,H^)CO(PPh ) 1643, 1650, 1943, 1990

[Rh CO(PPh )2]2 1740 , 1980

[m\{,CO)^{?Ph^)^]^ 1770, 1800, 1992, 2017

RhH(CO), PPh 1980

RhHCO(PPh ) on PS/20% DVB 195 2, 2000

this study 1947, 1993, 2002, 2070

One should, however, bear in mind that the catalytically active amount of

rhodium complex may only be a small fraction of the total amount of rhodium

complexes present, which implies that the associative mechanism cannot be

literature

34,

36

34

34

37,

39,

35

38

40

33



excluded on the strength of our I.R. measurements alone. It is furthermore

important to note that Wilkinson [3 4,35 ,36] detected his intermediates at 25°C

and atmospheric pressure in benzene solutions, whereas we examined our catalyst

extracts after hydroformylation at 90°C and 1.2 MPa total pressure with

RhHCO(PPh,), dissolved in PPh (P/Rh = 74 4 mol/mol).

The only results bearing some resemblance to ours are those published by

Pittman [3 9,40 ] for RhHCO(PPh ) chemically anchored to polystyrene - 1%

divinylbenzene, functionalized with PPh.-groups. Apart from the very weak

_1 ^

bands we found at 199 3 and 20 70 cm , which may have escaped Pittman's atten

tion owing to less resolution in the polystyrene-system, his and our results

are fairly identical. Although he does not give an interpretation of his I.R.results, we think it most probable that at the high P/Rh ratio and the high

temperature and pressure used by Pittman and by us, PPh -rich rhodium complexes

are formed, the spectra of which have so far not been disclosed in the

literature (rhodium complexes with three or four PPh ligands).

Catalytic performance

In Table 3 the activities and selectivities of several known heterogeneous

catalysts for hydroformylation of propylene are compared with those of our SLP

catalyst. Where necessary for comparison, the activities and selectivities of

the latter have been calculated for the reaction conditions applied in the

literature study referred to. The calculations are based on the kinetics of

ou r SLPC system [ 4 1 ] . As to catalyst systems D and E in Table 3 , we point out

that here the calculated activity and selectivity of our SLPC system may be

less meaningful because the extrapolation had to be made to reaction conditions

beyond the region of the kinetic measurements.

Table 3 shows our SLPC system to be about six times more active than the

systems A, C and D. The SLPC we prepared according to Rony's method, using DOP

as a solvent (system B ) , is four times more active than our SLPC system made

with P Ph, as a solvent. The same is true for the SLPC described by Rony (E) ,

which is about two times more active than our SLPC system. This higher activity

of SLPC systems with solvents other than PPh was also found by us after

gradual dilution of the PPh, solvent with polyethylene glycol, as will be

further elucidated in part III of this series [3 0].A very important conclusion,

however, is that our SLPC system has an appreciably higher selectivity than

any other heterogenized catalyst system. Furthermore, our SLPC appeared to be

perfectly stable over a period of at least 8 00 hrs (Fig. 3 ) .

The excellent performance of our SLPC must be ascribed to the use of molten

34



Table 3 Comparison between the performance of the SLP catalyst and other

heterogenized catalysts for hydroformylation of propylene.

,'7

s y s t e m

-

A

SLPC

B

SLPC

C

SLPC

D

SLPC

E

SLPC

P / R h

/ m o l \

I m o l

2

7 4 4

5 6

7 4 4

6 0 1

7 4 4

1

7 4 4

5 6

744

P

(MPa)

1 . 5 7

1 . 5 7

1 . 5 7

1 . 5 7

1 . 5 8

1 . 5 8

6 . 8 7

6 . 8 7

3 . 4 8

3 . 4 8

t

(°C)

90

90

90

90

125

125

125

125

136

136

r/ m ol C^ \

I mol R h .s /

0 . 0 0 4

0 . 0 2 5

0 . 1 0 5

0 . 0 2 5

0 . 1 0 8

0 . 5 8 7

0 . 0 7 7

0 . 4 7 6

0 . 6 6 5

0 . 3 1 6

S

/ Ao l

l^molj

2 . 0

9 . 3

3 . 1

7 . 5

15 .0

23 .0

1.1

4 . 4

2 . 0

8 . 3

s t a b ^

-

.

+

+

+

7

+

?

+

?

+

a: A = Rh(TT-allyl)CO(PPh ) physically adsorbed on y-alumina 0 00 -3P (see

Section 3.1 of this paper).

B = SLPC system according to Rony (see Section 3.2 of this paper).

C = gassparged reactor filled with RhHCO(PPh ) dissolved in PPh [ 4 2 ] .

D = rhodium complex chemically anchored to Cabosil, which is functionalized

with (C2HÔ)2Si(CH2)2P(C^H5)2 [ 4 3 ] .

E = SLPC described by Rony; RhClCO(PPh ) dissolved in butyl benzyl

phthalate with an excess of PPh and immobilized on silicagel [ 2 0 ] .

SLPC = our SLPC system; RhHCO(PPh ) dissolved in PPh and immobilized on a

support.

b: stability: + = stable; - = deactivation; ? = unknown.

PPh, as a solvent. The function of this large excess of PPh is fourfold:

a) Immo bilization of the catalyst on the support

We found that molten PPh, is spontaneously adsorbed by all support

materials applied in our study, which means that the contact angle of PP h, on

35



the support materials is smaller than 90°. Judged by the naked eye, the

contact angle of PPh on quartz and of PPh on sapphire at 90°C and under

nitrogen is about 3 0°. This indicates that PPh is a suitable solvent wetting

the support and strongly immobilized by capillary forces; calculations with

the Washburn relation [44], P = -2 a. „ cos 9/r , yield capillary pressures as

Lb p _high as -6.5 MPa (r = 10 nm, a,- (90°C) = 37.5 x 10" N/m [45], 6 = 30°).

p Lub) Solvent

PPh is an excellent solvent for RhHCO(PPh_)_; its low vapour pressure of

only 2.63 Pa at 90°C [45] prevents contamination of the produced aldehydes

with PPh_ and drying-up of the catalyst solution, provided the catalyst is

used below 100°C.

c) Improvement of the selectivity

Because of the very large excess of free PPh,, rhodium complexes with at

least two or three PPh, ligands will be present, which account for the observed

high selectivity [33].

d) Stabilization of the rhodium complex

According to Wilkinson [34], the dimerization of RhHCO(PPh,) to inactive

dimers (eq. 2 and 3 ) only takes place after dissociation of one PPh,-group

from RhHCO(PPh2)2 (eq. 1 ) .

RhHC0(PPh3)2 ; RhHC0(PPhj)2 + PPh^ ' (1)

2 RhHC0(PPh2)2 t [RhCO(PPh2)2]2 + H^ (2)

[RhCO(PPh3)2]2 - 2C0 ; [Rh(CO)2(PPh3)2]2 (3)

As the equilibrium (1) is shifted far to the left by the large excess of free

PPh , the dimerization, eqs. 2 and 3, is suppressed, so that the activity

for hydroformylation is high. Furthermore, decomposition of RhHCO(PPh ) to

complexes still more deficient in PPh is prevented [ 7 ] . The absence of I.R.

bands of dimers in the spectrum of a used catalyst (Fig. 5) supports this view.

Although the hydroformylation activity will generally decrease with in

creasing P/Rh ratio [46,47], the activity of the SLPC is still remarkably high.

This should be ascribed to the very large gas-PPh phase boundary created by

dispersing the PPh, in the porous support (see also part II of this series

[27]).

36



Aldol condensation

The disadvantage of accumulation of aldol condensation products in the

pores of the support is circumvented by selecting support materials that are

inactive for aldol condensation, such as sodium-poor silica S or Amberlite

XAD-2, RhHCO(PPh,), itself is only slightly active for aldol condensation,

whereas PPh was found to be completely inactive, as is also reported in

literature [48].

PPh -distribution in the support

Nitrogen capillary condensation shows the catalyst solution at 56% liquid

loading to be preferentially capillary-condensed in the smallest pores (micro

pores and part of the transitional pores), which is in agreement with theory

(Fig. 6 ) . Besides, PPh is physically adsorbed as a thin liquid layer on the

walls of all pores in which no capillary condensation takes place (Fig. 6 ) .

Hence, inasmuch the porosity of the support is constant throughout the catalyst

particle, a uniform PPh distribution is realized. Villadsen [ 1 9 ] , in his

theoretical treatment of SLPC systems, rightly remarks that owing to the inter

connectivity between the por es, the capillary-condensed liquid tends to

cluster, thereby reducing the surface energy of the meniscii. In X-ray micro

analysis of an SO_-oxidation catalyst composed of V.O_/K.S-0_ on Kieselguhr,

he observed liquid clusters as large as 50-100 ym. Our RMA results of a PPh,

catalyst solution on silica (Fig. 8) indeed revealed local P-enrichment in

areas of at most 16 ym. However, the Si-signal also varies, so that the P-

enrichment in some areas may have to be ascribed to a local increase in porosity.

The uniform P-signal in XAD-2 (Fig. 8) suggests that clustering does not occur

in this macroreticular resin. However, the lateral resolution of RMA being only

one ym, clusters smaller than one ym might yet occur in XAD-2. Further attempts

at visualizing PPh,-clusters by TEM or SEM have failed.

Mercury reveals a type of PPh distribution q uite different from that dis

closed by nitrogen capillary condensation (compare Fig. 6 and 7 ) , Most likely

the very high mercury pressure applied (333 MPa) drives the PPh out of the

transitional pores into the smallest pores of the support. This would be the

thormodynaraically most favoured situation in the presence of mercury.

37



Acknowledgements

We thank Mr. N. van Westen and Mr. J. Teunisse for carrying out the

nitrogen capillary condensation and mercury porosimetry measurements, Ir. E.

Izeboud for his assistance in the aldol condensation experiments, Mr. A.M. Kiel

and Mr. S.M.G. Nadorp (Central Laboratory, DSM, Geleen) for the SEM and TEM

measurements, Ir. D. Schalkoord for the RMA measurements, and Ir. P. Bode for

the neutron activation analysis measurements.

The investigations were supported (in part) by the Netherlands Foundation

for Chemical Research (SON) with financial aid from the Netherlands

Organization for the Advancement of Pure Research (ZWO).

List of symbols

A

F

P

P/Rh[Rh]

^90

rP

S

t

t ,

cat

PPh,

support

iP

peak area

flow of olefin at 0.1 MPa and 25°C

total pressure

molar phosphine to rhodium ratiorhodium complex concentration in PPh, at 90 °C

reaction rate at 90°C

pore radius

selectivity = n/iso ratio

reaction temperature

streamtime

cumulative pore volume

weight of rhodium metal in the reactor

total weight of a batch of catalyst afte r evaporation

of benzene

total weight of P Ph, used in catalyst preparation

total weight of support used in catalyst preparation

internal normalization factor

liquid loading at 90°C

contact angleconversion

surface tension

a.u.3 ,

cm / s

MPa

mol/molmol/m

cm'^/g Rh.s

nm

mol/mol

•c

hrs

cm /g

degrees

N/m

38



R e f e r e n c e s

1. J.A. Osborn, G. Wilkinson, J.F. Young, Chem. Comm. (1965), 17.

2. A. Hershman, K.K. Robinson, J.H. Craddock, J.F. Roth, Ind. Eng. Chem.,Prod. Res. Dev. 8 , (1969), 372.

3. E. Bayer, V. Schurig, Angew. Chem., Int. Ed. T4 , (1975), 493.

4. W.O. Haag, D.D. Whitehurst, Meeting Cat. Soc. Houston, Texas, (1971).

5. J.P. Pinnavaia, P.K. Welty, J. Am. Chem. Soc. 9]_, (1975), 3819.

6. E. Montovani, N. Palladino, A. Zanobi, J. Mol. Catal. 3 , (1977/78), 28.

7. Th.G. Spek, J.J.F. Scholten, J. Mol. Catal. 3, (1977/78), 81.

8. P.W.H.L. Tjan, J.J.F. Scholten, Proa. Sixth Int. Cong r. Cat., The Chem.

Soc., London,(1977), 488.

9. Y. Dror, J. Manassen, J. Mol. Catal. 2_, (1977), 219.

10. A.F. Borowski, D.J. Cole-Hamilton, G. Wilkinson, Nouv. J. Chim. 2 , (1978),

137.

11. W.H. Lang, A.T. Jurewicz, W.O. Haag, D.D. Whitehurst, L.D. Rollmann, J.

Organometal. Chem. 134, (1977), 85.

12. R.F. Batchelder, B.C. Gates, F.P.J. Kuijpers, Proa. Sixth Int. Congr. Cat.,

The Chem. S oc , London, (1977), 499.

13. M. Bartholin, C H . Graillat, A. Guyot, G. Goudurier, J. Bandiera,

C. Naccache, J. Mol. Catal. 3_, (1977/78), 17.

14. K.G. Allum, R.D. Hancock, I.V. Howell, R.C Pitkethly, P.J. Robinson, J.

Catal. 43, (1976), 322.

15. A.A. Oswald, L.L. Murrell, Prepr. Div. Petr. Chem.,Am. Chem. Soc, 19 (1),

(1974), 162.

16. CU. Pittman, R.M. Hanes, Ann. N.Y. Acad. Sai. 239, (1974), 162.

17. W.O. Haag, D.D. Whitehurst (Mobil Oil Corp.), US Patent 4098727 (1978).

18. C.N. Kenney, Catal. Rev. - Sai. Eng. U_, (1975), 197.

19. J. Villadsen, H. Livbjerg, Catal. Rev. - Sai. Eng. l]_, (1978), 203.

20. P.R. Rony, J. Catal. £, (1969), 142.

21. P.R. Rony, J.F. Roth^ J. Mol. Catal. 1_, (1975/76), 13.

22. L.A. Gerritsen, J.J.F. Scholten (ZWO), Neth. Patent Appl. 7700554 (1977),

7712648 (1977) and 7902964 (1979).

23. L.A. Gerritsen, J.J.F. Scholten (Stamicarbon B.V.), German Patent Appl.

2802276 (1978).

24. N. Ahmad, S.D. Robinson, M.F. Uttley, J. C hem. Soc, Dalton Trans. (1972),

843.

25. J.CP. Broekhoff, Ph.D. thesis, Delft, The Netherlands, 1969.

26. L.A. de Wit, J.J.F. Scholten, J. Catal. 36, (1975), 36.

39



27. L.A. Gerritsen, J.M. Herman, W. Klut, J.J.F. Scholten, part II of this

series, to be submitted for publication in J. Mol. Catal.

28. P.J.M. Korthoven, M. de Bruin, J. Radioanal. Chem. 35^, (1977), 127.

29. P.W.H.L. Tjan, Ph.D. thesis. Delft, The Netherlands, 19 76 .

30. L.A. Gerritsen, J.M. Herman, J.J.F. Scholten, part III of this series, to

be submitted for publication in J. Mol. Catal.

31. N. Nakanishi, P.H. Solomon, Infrared Absorption Spectroscopy, 2th ed.,

Holden Day, 19 77 .

32. L. Beranek, M. Kraus, Comprehensive Chemical Kinetics, C H . Bamford and

C.F.H. Tipper (eds.), Elsevier, Amsterdam, 1 97 8, 33 7.

33. D. Evans, J.A. Osborn, G. Wilkinson, J. Chem. Soc. (A), (1968), 3133.

34. D. Evans, G. Yagupsky, G. Wilkinson, J. Chem. Soc. (A), (1968), 2660.

35. L. Vaska, J. Am. Chem. Soc. 88^, (1966), 4100.

36. G. Yagupsky, C.K. Brown, G. Wilkinson, J. Chem. Soc. (A), (1970), 13 9 2 .

37. D.E. Morris, H.B. Tinker, Chemtech. 2 , (1972), 554.

38. R.L. Pruett, J.A. Smith, J. Org. Chem. 3 4 , (1969), 327.

39. C U . Pittman, L.R. Smith, J. Am. Chem. Soc. 91_, (1975), 1749.

40. C U . Pittman, L.R. Smith, R.M. Hanes, J. Am. Chem . Soc. 9 7 , (1975), 1742.

41. L.A. Gerritsen, W. Klut, M.H. Vreugdenhil, J.J.F. Scholten, part V of this

series, to be submitted for publication in J. Mol. Catal.

42. G. Wilkinson (Johnson, Matthey & Co., Ltd.), French Patent 2072146 (1970).

43. A.A. Oswald, L.L. Murrell (Exxon), Neth. Patent 7308749 (1973).

44. E.W. Washburn, E.W. Bunting, J. Am. Ceram. Soa. 5_, (1 9 2 2), 48.

4 5. M.V. Forward, S.T. Bowden, W.J. Jones, J. Chem. Soc. (1949), S 121.

46. K.L. Olivier, F.B. Booth, Hydroa. Proa. 4 , (1970), 112.

47. J. Hjortkjaer, J. Mol. Catal. 5_, (1979), 377.

4 8. A.L. Stautzenberger, J.L. Paul (Celanese Corp.), US Patent 4009003 (1977).

40



C H A P T E R 3


Part II. The Location of the Catalytic Sites *)

by

L.A. Gerritsen, J.M. Herman, W. Klut and J.J.F. Scholten,



Julianalaan 136,


Summary

Hydridocarbonyltris(triphenylphosphine)rhodium(I), dissolved in triphenyl

phosphine and capillary-condensed into the pores of a support,is applied in

the catalytic heterogeneous hydroformylation of ethylene and propylene.

Catalysts with triphenylphosphine in the liquid and in the solid state, do

not show any difference in apparent activation energy and catalytic activity.

From this it follows that we are dealing with a case of heterogeneous catalysis,

i.e. that only the rhodium complexes at the gas-triphenylphosphine phase

boundary are involved in the reaction.

The inactivity of the rhodium complexes outside the phase boundary is most

likely due to high coordination of these complexes with free triphenylphosphine

molecules, and to the very low solubility of carbon monoxide in triphenyl

phosphine, and not to an extreme liquid-phase diffusional retardation of the

rate of reaction.


41




In part I of this series [1] and in the relative patents [2,3], the

preparation, characterization and performance of a supported liquid phase

rhodium catalyst have been discussed. This catalyst may be applied in the

hydroformylation of ethylene, propylene and other alkenes, under the very mild

reaction conditions of 90°C and 1.57 MPa total pressure, and it has the

additional advantage of being highly selective towards the formation of normal

butyraldehyde.

It is known from lite ratu re [4,5,6,7] t hat whe n the Wilkinson catalyst is

used in homogeneous hydroformylation, in the presence of an organic solvent, an

increase of the P/Rh ratio (by addition of PPh,) causes a strong decrease in

catalytic activity. Our supported liquid phase rhodium catalyst, on the other

hand (which does not contain an organic solvent), shows a remarkable high

activity at high P/Rh ratio owing to the large surface area of the gas-liquid

phase boundary.

The present paper deals with the question if in our experiments diffusional

retardation of the rate of reaction plays a role. The localization of the

centres of catalytic activity will also be discussed. . '

2 E x p e r i m e n t a l

The preparation and characterization of the catalyst, as well as the

apparatus and the chemicals used, have been dealt with in part I of this

series [1 ] .

A non-supported rhodium catalyst, dissolved in solid triphenylphosphine,was prepared by mixing 2 5.0 g of PPh^ with 0.12 2 g of RhHC0 (PPh,)2, and melting

this mixture with continuous stirring for 0.75 hrs under flowing nitrogen at

90°C. The mixture was solidified by cooling to room temperature and crushed

into small particles. Physical adsorption of methane at -196 °C showed the BET2

surface area to be 0.31 m /g. From this a mean particle diameter of 20 ym was

calculated.

The melting points of PPh, and of the supported and non-supported catalyst

solutions were determined with a du Pont differential scanning calorimeter

(type 910) connected to a du Pont thermal analyzer, type 990.

The solubilities and diffusion coefficients of the reactants in PPh, were

determined by means of a Cailletet apparatus described by Lemkowitz [ 8 ] .

Surface tensions were measured with a Cenco-du Noiiy tensiometer from

42



Central Scientific Company, Chicago, USA.

3. Results

3.1. DSC measurements

The results are presented in Table 1.

Table 1; Melting points of PPh, and of PPh, with dissolved rhodium catalyst, as

determined by DSC

Melting point (°C)

a. PPhj (99.5%)* 79.3

b. 0.49 w% RhllCOCPPhj), dissolved in PPh^ 77.5

a. as b. , but capillary-condensed into Kieselguhr MP-99

(20 < r < 10 00 nm); 6 = 0.44; fresh catalyst 75.6

d. as c., after use in hydroformylation for 70 hrs 74 .7

e as b., but capillary-condensed into y-alumina 005-0.75 E

(4 < r < 50 n m ) ; 6 = 0.44; fresh catalyst 53.0

ƒ. as b. , but capillary-condensed into silica 000-3E

(2 < r < 50 n m ) ; 6 = 0.56; fresh catalyst see text

V

*) Melting point at an ethylene pressure of 0.4 MPa: 80°C (determined in the

Cailletet apparatus [10]).

The melting point of PPh, nearly agrees with the literature value of 80°C

[11,12]. Dissolution of 0.5 w% rhodium complex in PPh,, appeared to lower the

melting point by 1.8°C. Capillary condensation in Kieselguhr MP-99 further

lowered the melting point by 1.9°C. This effect is relatively small owing to

the macroporous nature of Kieselguhr.

Upon capillary condensation of the catalyst solution in the microporous y-

alumina 005-0.75 E, a much greater lowering of the melting point (24.5°C) was

observed, whereas calculation of the melting peak area showed only 6.2 w% of

the PP h, to be in the solid state.

With silica 000-3E being used as a support, no melting at all was observed

43



in the temperature range from -140 °C to 1 0 0 °C Obviously, the strong van der

Waals interaction between PPh, and the walls of the pores keep the triphenyl

phosphine in the liquid state, and this effect is the more pronounced according

as the pore radii are smaller.

Because of the low solubility of the reactants CO, H, and alkenes, in PPh ,

(see hereafter) no extra lowering of the melting point is to be expected during

hydroformylation (see footnote Table 1 ) .

3.2 Activity measurem ents '

3.2.1 Influence of the PPh., phase change on activityFor determining if the activity is influenced by a solid-to-liquid or

inverse transformation of the PPh, phase, we selected the Kieselguhr supported

catalyst, because with this support only a small decrease in melting point had

been observed. Furthermore, upon transition of the melting point, all of the

PPh, had been found to be either in the solid or in the liquid state.

Hydroformylation of propylene was chosen as the test reaction. Upon

attainment of a constant activity at 9 0° C, the reaction temperature was lowered

to 50.5°C and then stepwise increased to 106.8°C. The results are presented in

Fig. 1.

\

2 0

- 2 0

ln(r) \

V- 6 2 8 3 0 3 2

— > y x l C (K - ' )

F ig u r e 1 Ar r h e n iu s p lo t f o r t h e h y d r o f o r m y la t i o n o f p r o p y le n e .

P = 1.57 MPa; c /H,/C0 = l/l/l;t = 50.5 to 106.8°C;-3 3 =

W/F = 0.981 X 10 g Rh.s/cm C Catalyst: Kieselguhr

MP-99, 6 = 0.44, [Rh] = 10.14 mol/m^, P/Rh = 40 6 raol/

mol, particle diameter: 0.42 - 0.50 mm.

44



The results clearly demonstrate the absence of any jump in activity around

the melting point of the catalyst solution in the pores of the support. More

over, the apparent activation energy, 79.1 kJ/ mol, remains constant throughout

the range of temperatures investigated. A similar observation was made during

hydroformylation of ethylene, where the apparent activation energy remains at

61.1 kJ/mol throughout the temperature range from 66.8°C to 96.9°C.

This might suggest that the kinetics are not influenced by a liquid-to-

solid or inverse phase change of triphenylphosphine. Such a conclusion, however,

is somewhat premature, because in carrying out the measurements in the DSC and

Cailletet apparatus, we noted that, depending on the rate of cooling,

crystallization of PPh , may be retarded by as much as 20 -40 °C.

We therefore did another experiment with a new Kieselguhr SLP catalyst

having an analogous composition as the foregoing one. Measurement of the rate

of propylene hydroformylation was now started at 60°C, and continued whilst the

temperature was stepwise increased to 10 7.5 °C. The DSC measurements have proved

beyond any doubt that at the starting temperature (60°C) all PPh , was in the

solid state. The results are given in Fig. 2.

6

4

2

n

- - r=^^C5>(« H g R h . s )

BBmf

7 8 , 5 ^

66 y *

, 1 ' m e l t

11

g i

1

' ^ - « - x - x - » -

1

20 40—'td (hrs)

60

Figure 2 Influence of melting and freezing of PPh- in a rhodium

SLP catalyst on the rate of propylene hydroformylation.

P = 1.57 MPa; c /H-/CO = 1/1/1; t = 60 to 107.5°C.

-3 3 =

W/F = 3.040 x 10 g Rh.s/cm' C Catalyst: Kieselguhr

MP-99, 6 = 0.44, [Rh] = 7.51 mol/m^, P/Rh = 547 mol/

mol, particle diameter: 0.42 - 0.50 mm.

The numbers in the graph refer to the temperatures at

which the rates were observed.

45



Fig. 2 shows a plot of the activities at a standard temperature of 90 °C.

These activities were calculated from the observed rates by means of the

Arrhenius equation, with the apparent activation energy being taken equal to

79.1 kJ/ mol; this value had been found in the experiment plotted in Fig. 1, andalso in that performed with the non-supported catalyst referred to in Section

3.2.3.

Fig. 2 shows that when the temperature is raised from 60 to 9 1°C, the

activity goes up by a factor of only 1 .7. We ascribe this to redistribution of

the PPh, over the support during the melting stage, in the course of which the

surface area of the gas-PPh, phase boundary increases to a small extent. That

this small increase in activity is not due to the phase transition is evident

from the reverse step (see Fig. 2 ) ; upon cooling from 10 7.5°C to 60°C the ,

activity remains practically eq ual. Moreover, it is higher now than at the

initial temperature of 6 0 °C, which supports the supposition of an original

redistribut ion.

Hydroformylation of ethylene with a similar catalyst yielded an analogous

result: a temperature rise from 45 to 90 °C (about 15°C above the melting point

of the catalyst solution in the pores) increased the catalytic activity by a

factor of no more than 2.5.

3.8.2 Activity of a fully-loade d SLPC in ethylene hydroformylation

For calculating the degree of liquid diffusional retardation and comparing

the activities of a supported and a non-supported catalyst solution, knowledge

of the activity of an SLPC with a precisely known surface area of the gas-PPh,

phase boundary is needed. We therefore measured the catalytic activity of a

fully-loaded SLPC for hydroformylation of ethylene at 90 °C; in such a catalyst

the surface area consists of the PPh, catalyst solution only. The results are

presented in Fig. 3.3 =

After an induction period of 70 hrs, the activity settles at 146 cm C-/

g Rh.s. Methane adsorption at -1 96 °C yields a total surface area of 4.16 m^/2

g cat, from which a BET surface area of the gas-PPh, phase boundary of 8.68 m /

g PPh, is calculated. The activity per unit surface area of PPh, at 9 0°C,6 — 7

r" , is then found to be 0.36 x 10 " raol C~/m PPh s.

3.2.3 Activity of a non- suppo rted solid catalyst solution

The activity of a non-supported solid catalyst solution for hydroformyla

tion of ethylene and propylene was measured in the temperature range from 5 3°C

to 70°C, i.e. well below the melting point of the catalyst solution (7 7.5°C;

Table 1 ) . For the results see Table 2.

46



160

120

8 0

4 0

OO 2 4 6 8 1

— t d ( hr s)

F i g u r e 3 C a t a l y t i c p e rf o rm a n c e of a f u l l y - l o a d e d SLPC for

h y d r o f o r m y l a t i o n of e t h y l e n e .

P = 1.2 MPa; C^/H2/C0 = 1 / 1 / 1 ; t = .90 °C; W/F =

0 . 5 7 6 x 10 ^ g R h .s /c m ' C C a t a l y s t ; s i l i c a 0 0 0 - 3 E ,

6 = 1.0 0, [Rh] = 5.50 mol/m^, P/Rh = 743 m ol /mo l ,

p a r t i e l e d i a m e t e r : 0 . 4 2 - 0.50 mm.

T a b l e 2: A c t i v i t y of t h e - n o n - s u p p o r t e d c a t a l y s t

olefin

ethylene

propylene

r

/ \cm

\ g R h . s ;

23. 0«

0.69^

1

a

^90

cm \\% R h . s ;

102.7

4.79

^90 °

/ mol \

V S-v7.40

0.35

â

/ kJ \

r°V

62.0 (59-70°C)

78.7 (53-65°C)

a: P = 1.2 M Pa; C 2 / H 2 / C O = 1 / 1 / 1 ; t = 6 5 ° C ; W /F = 2 . 2 6 x 10 - g R h . s / c m ' c .

b: P = 1 . 57 M P a ; c / H 2 / C 0 = 1 / 1 / 1 ; t = 6 5 ° C ; W /F = 4 . 9 7 8 x l O ^ g R h . s / c m ' ^ c

a: activity at 90°C, calculated from the activities with the Arrhenius equation.

d: activity at 90°C per unit surface area of PPh,.

The apparent activation energies are equal to those found for the supported

catalyst solution (see Section 3.2.1). However, calculated per unit surface

area of catalyst solution, r , the activity of the non-supported catalyst

solution is 20.6 times higher than that found for the fully-loaded silica-

47

http://grh.s/

http://grh.s/



supported catalyst (7.40 x 1 0 " mol/m PPh,.s and 0.36 x 10 mol / m PPh s,

respectively). The lower activity of the supported catalyst is due to with

drawal of rhodium complexes from the PPh, solution via adsorption to the pore

walls. The adsorption isotherms for RhHCO(PPh,), on three support materials

are presented in Fig. 4; a more detailed description of the adsorption

phenomenon is given in part III of this series [ 1 3 ] .

.„c /nnol'- 0 ds X l 0 6 ( ^^

0 20 -

0-15 -

0 - 1 0 -

0 05

^ 'SFigure 4 Adsorption isotherms for RhHC0(PPh.) at 90°C on

various supports. Surface concentration C , , as a

function of the equilibrium concentration of

RhHCO(PPh,), in PPh,, C ,.3- 3 3 sol

* = XAD - 2; 0 = silica 000-3E; x = silica-alumina

LA-30.

With the aid of the adsorption isotherm for silica 00 0-3 E, the real rhodium

concentration in the silica-supported catalyst solution is calculated to be a

factor of 5.6 lower than the value derived from the amount of rhodi um used. The

catalytic activity being first order in rhodium complex concentration, the

difference in activity between the non-supported and the fully loaded silica

catalyst now reduces to a factor of 20 .6/ 5.6 = 3 . 7 . In our view this final

difference can be accounted for by the fact that in the supported catalyst a

very thin layer of liquid is in contact with the support surface; owing to the

support surface, the total amount of complexes withdrawn by adsorption is

larger than found from the isotherm measurement, in which an excess of PPh,

48



solution was in contact with the support material.

3.3 Surface tensions

The surface tension of PPh, was determined at 90°C under a flowing 1:1

mixture of hydrogen and carbon monoxide. The experiment was repeated with PPh_3 " ^

in which 24.7 mol/m RhHCO(PPh,), was dissolved. Both experiments yielded a

surface tension of 42 .7 x 10 ^ N/m.

3.4 Investigation into the possibility of diffusional retardation of thereaction rate

3.4.1 Determ ination of the diffusion coefficients and solubilities of the

reat^tants in PPh,

Diffusion coefficients and solubilities of the reactants (H2, CO, C-H, and

C,H^) in PPh, not being available from literature, we measured these q uantities

in the Cailletet apparatus. The results are presented in Table 3; a more

detailed account will be published elsewhere [ 1 0 ].

Table 3: Solubilities and diffusion coefficients of hydrogen, carbon monoxide,

ethylene and propylene in PPh, at 90°C

Dissolved gas D X 10exp

2^

I m

D , X 10calc

9 aSolubility

mol

m3 PPh. .MPa

hydrogen

carbon monoxide

ethylene

propylene

0.98

1.00

1.09

0.95

0.78

0.64

14.3

23.0

242.4

731.7

a: diffusion coefficient at 90°C, calculated from the Wilke-Chang correlation

[14].

The agreement between the experimental and calculated diffusion

coefficients is satisfactory. The solubility of hydrogen in PPh, is one-third

of that in similar organic solvents, e.g. benzene [15] .

49



3.4.2 Calculations

The rate of hydroformylation of ethylene being 20 to 60 times that of

propylene, we may restrict our calculation of the diffusional retardation of

the rate of reaction to the case of ethylene.In the diffusional transport of the reactants from the gas mixture outside

the catalyst particles to the rhodium complexes in the supported catalyst

solution, three stages may be distinguished:

a) film diffusion

b) pore diffusion

c) diffusion into the catalyst solution.

Diffusion of products goes through the same stages, but in the reverse

sequence.

4 5The diffusion coefficient in the gas phase being 10 to 10 times that in

the liquid phase, diffusional retardation of the rate of reaction (if any) will

mainly take place in the catalyst solution. Calculations by Chu's method [ 1 6 ] ,

prove the non-occurrence of diffusional retardation in the film around the

catalyst particle. Diffusional retardation inside the non-liquid-filled part of

the pores must be excluded because measurements have shown that the activity of

a silica 00 0-3 E SLPC (r = 5.7 nm, 6 = 0.56) used in hydroformylation ofethylene at 90°C and 1.2 MPa total pressure, is independent of the catalyst

particle diameter between 0.46 and 3.30 nm.

The non-diffusional retarded kinetics of the hydroformylation of ethylene

being unknown, it is im.possible to determine the degree of diffusional

retardation in the catalyst solution by anyone of the methods generally

recommended in literature [ 1 7 ] . We therefore conducted the calculation along

the following lines:

a) The hydroformylation reaction is assumed to take place in the bulk of the

PPh, only. For the time being, we therefore ignore the particular position

of the highly active rhodium complexes at the gas-PPh, phase boundary.

b) The situation at the gas-PPh, phase boundary in the hydroformylation of

ethylene at 90°C and 1.2 MPa total pressure, is schematically outlined in

3

Fig. 5. The gas phase concentration of each reactant is 134 mol/m . The con

centrations of IL, CO and C^H. in the catalyst solution at the gas-PPh,

phase boundary are 5.72 , 9.20 and 96 .96 mol/m PPh,, respectively (see Table

3 ) . Fig. 5 shows that the thickness of the reaction zone, 6 , is equal to

the penetration depth of the least soluble reactant, i.e. hydrogen. The

greater the penetration depth,the smaller the diffusional retardation of the

50



c he m ic al r e a c t i o n r a t e .

140H2,C0.C2

120

100

Gos 80phase

6 0

4 0

2 0

0

- | & )

- PPh3

6r

-

-

CO

c^

^^ 1 ^2

Fi gu re 5 Co nc en tra tio ns of 11^, CO and CÛ. at and around th e

gas-PPh-

pressure

gas-PPh- phase boundary at 90°C and 0.4 MPa partial

c ) I n t h e s t a t i o n a r y s t a t e , t h e am ount o f h y d ro g e n ( t h e l e a s t s o l u b l e r e a c t a n t ;

s e e b a b o v e ) , r e a c t i n g p e r u n i t s u r f a c e a r e a a nd p e r u n i t t i m e i n t h e b u l k

o f t h e c a t a l y s t s o l u t i o n , r , i s e q u a l t o t h e a mo un t o f h y d ro g e n

t r a n s f e r r e d p e r u n i t s u r f a c e a r e a an d p e r u n i t t im e i n t o t h e c a t a l y s t

s o l u t i o n b y l i q u i d p h a s e d i f f u s i o n a t t h e g a s - P P h , p h a s e b o u n d a r y , w h e r e

90

dC,

d x 0( 1 )

By substituting for r" 0.36 x 10 mol C ^ m PPh^.s (Section 3.2.3), and

for D 1.09 X 10 "^ m2/s (Table 3 ) , we find:

'7

dCH,

dx330 mol/m

d) Assuming dC|j /dx for every x-value to be eq ual to dC|) /dx | x = 0 (dashed line

in Fig. 5 ) , we can calculate a minimum penetration depth, 6 In realitv

51



the absolute value of dC,, /dx will decrease with increasing x an d, there-"2

fore, the real penetration depth, 6 , will be larger than the calculated

value for 6m m

dC

"2

dx^ ^ . (2)

0 6 .m m

3,With Cji |x = 0 being the solubility of hydrogen (5.7 2 mol/m ) , this yields:

6 . =1 7 .3 mm.min

Co m p ar iso n o f t h i s l a s t v a l u e w i t h t h e m ean p a r t i c l e d i a m e t e r o f t h e

c a t a l y s t s u se d b y u s ( 0 . 4 6 mm) r e v e a l s t h a t t h e min im um p e n e t r a t i o n d e p th

i s many t i m e s l a r g e r t h a n t h e m ean l e n g t h o f t h e l i q u i d - f i l l e d p a r t o f t h e

p o r e s . H e n ce , u n d e r h y d r o f o r m y l a t i o n c o n d i t i o n s , t h e w ho le c a t a l y s t s o l u t i o n

i s s a t u r a t e d w i th d i s s o l v e d r e a c t a n t s , an d t h e h y d r o f o r m y l a t io n o f e t h y l e n e

i s n o t d i f f u s i o n a l l y r e t a r d e d . T h i s o f c o u r s e a l s o h o l d s f or t h e h y d r o

f o r m y l a t i o n o f p r o p y l e n e .

e) We now r e j e c t ass um pt io n a and suppose t h a t th e rhodiu m complexes a t the

g a s - P P h , p h a se b o u n d a r y a r e c o n s i d e r a b l y m ore a c t i v e t h a n t h e r h od i umc o m p l ex e s in t h e b u l k o f t h e P P h , . I t i s e v i d e n t t h a t i n t h i s c a s e t h e

a m o u n t o f h y d r o g e n r e a c t i n g p e r u n i t su r f a c e a r e a a n d u n i t t i m e i n t h e b u l k

o f t h e P P h , - a n d , h e n c e , t h e a m o u n t o f h y d r o g e n t r a n s f e r r e d i n t o t h e

c a t a l y s t s o l u t i o n p e r u n i t s u r f a c e a r e a a nd u n i t t i m e - w i l l b e s m a l l e r

than the measured total r e a c t i o n r a t e . T h e n , r i n e q u a t i o n 1 h a s t o b e

re p l ac ed by a much sm al l e r number , so th a t dCu /d x |x = 0 w i l l a l s o become

sm al le r . I t t hen fo l low s f rom eq ua t io n 2 th a t 6 . i s l a rg e r th an 17 .3 mm,

t h e v a l u e c a l c u l a t e d u n d e r d . T h e r e f o r e , i f t h e rh o d i u m c o m p le x e s a t t h eg a s- PP h ., p h a s e b o u n d a ry s h o u l d c o n t r i b u t e c o n s i d e r a b l y t o t h e t o t a l r e a c t i o n

r a t e , t h e m inim um p e n e t r a t i o n d e p t h of t h e r e a c t a n t s w ould e v en b e g r e a t e r ,

m ea nin g t h a t d i f f u s i o n a l r e t a r d a t i o n i n t h e l i q u i d c a t a l y s t s o l u t i o n do es

n o t t a k e p l a c e .

f ) C a l c u l a t i n g t h e d i f f u s i o n a l r e t a r d a t i o n o f t h e r a t e o f h y d r o fo r m y l a ti o n o v e r

a n o n - s u p p o r t e d solid c a t a ly s t so lu t io n may be done in the same way , bu t

t h i s i s h i n d e r e d by t h e s c a r c i t y o f d a t a on d i f f u s i o n o f g a s e s t h r o u g h

o r g a n i c s o l i d s . As r e g a r d s t h e s e l f - d i f f u s i o n o f b e n z o i c a c i d t h r o u g h

c r y s t a l l i n e b e n z o i c a c i d , M cGhie [ 18 ] m e n t i o n s a d i f f u s i o n c o e f f i c i e n t o f

-19 2 96 .8 X 10 m / s a t 90°C, which va lue i s a fa c to r o f 10 lower tha n thed i f f u s i o n c o e f f i c i e n t s i n o r g a n i c l i q u i d s ( c om p ar e T a b l e 3 ) . T h e r e f o r e , t h e

52



diffusion coefficient of hydrogen in solid PPh, will, for the time being,

-1 8 2be taken equal to 10 m / s.

The solubility of hydrogen in solid PP h, must also be estimated. Wc found

that the solubility of ethylene in solid PPh, is about half that in liquid

PPh,; therefore the solubility of hydrogen will be taken equal to half the

value stated in Table 3.

In the case of ethylene hydroformylation on the non-supported catalyst

(activity: 7.40 x 10 mol C /m PPh . s ) , we then calculate a minimum

-3hydrogen penetration depth of 1.7 x 10 nm. From this it follows that, as

expected, the reaction takes place at the gas-solid PPh, phase boundary

only, and is highly diffusionally retarded in the solid state.

4 . Discussion

The preceding considerations seem to be at variance with one another. In

the liquid phase diffusional retardation is absent so that all rhodium

complexes must be active, whereas in the solid state strong diffusional

retardation does occur, indicating that here the reaction is restricted to the

gas-PPh, phase boundary. This would imply the occurrence of an activity jump

around the melting point, but no such jump has been observed (see Figs. 1 and

2 ) . Furthermore, contrary to expectation, the specific activity of the non

supported solid catalyst is practically equal to that of the supported liquid

phase catalyst. It is obvious to conclude therefore that exclusively the

rhodium complexes at the gas-PPh, phase boundary are catalytically active,

both in the solid and in the liquid state, which would mean that the reaction

is essentially heterogeneous.

An explanation of this might be souglit in a strong surface enrichment of

PPh, with dissolved rhodium complexes, caused by a difference in surface

tension between RhHCO(PPh,), and PPh,. However, there being no evidence of

such a difference, this explanation has to be rejected. Obviously the surface

tensions must be nearly equal because of the close resemblance between the

outer spheres of the two molecules.

As we see it, the inactivity of the dissolved complexes is to be explained

as follows. In our experiments the P/Rh ratio in the PPh, solution was 500 to

75 0 mol/ mol. It is likely that under such conditions Wilkinson's associative

mechanism [19] is operative, so that we are dealing with the following

equilibria:

53





2r" reaction rate per unit surface area of catalyst solution mol/m .s

2

5 , surface area of the gas-PPh, phase boundary m /g PPh,

X distance from the gas-PPh, phase boundary m

6 . minimum penetration depth mm m ' '^6 real penetration depth m

The other symbols used in this paper are defined in part I of this series.

References

1. L.A. Gerritsen, A. van Meerkerk, M.H. Vreugdenhil, J.J.F. Scholten,

part I of this series, submitted for publication in J. Mol. Catal.


7712648 (1977) and 7902964 (1979).


2802276 (1978).

4. K.L. Olivier, F.B. Booth, Hydroc Proa. 4_, (1970), 112.

5. A.R. Sanger, L.R. Schallig, J. Mol. Catal. 3 , (1977/78), 101.

6. A.R. Sanger, J. Mol. Catal. 3_, (1977/78), 221.

7. J. Hjortkjaer, J. Mol. Catal. 5_, (1979), 377.

8. S.M. Lemkowitz, J. Goedegebuur, P.J. van den Berg, J. Appl. Chem . Eiotechnol.

2A , (1971), 229.

9. L.A. Gerritsen, G. Hakvoort, to be published.

10. J.M. Herman, L.A. Gerritsen, Th.W. de Loos, to be submitted to J. Chem .

Eng. Data.

11. M.V. Forward, S.T. Bowden, W.J. Jones, J. Chem . Soo. (1949), S 121.

12. P. Walden, R. Swinne, Z. Physikal. Chem . 79, (1912), 700.

13. L.A. Gerritsen, J.M. Herman, J.J.F. Scholten, part III of this series, to

be submitted for publication in J. M ol. Catal.

14. C R . Wilke, P. Chang, A.I.Ch.E.J. }^, (1955), 264.

15. Landolt-Bornstein, Bd. 4, 6. Auf1., Springer Verlag, Berlin, (1976), 111.

16. C.J. Chu, J. Kalil, W.A. Wetteroth, Chem . Eng. Progr. 49_, (1953), 141.

17. G. Astarita, Mass Transfer with C hemical Reaction, Elsevier, Amsterdam,

1967.

18. A.R. McGhie, J.N. Sherwood, J. Chem . Soc, Farad. Trans. 1 , (1972), 553.

19. D. Evans, J.A. Osborn, G. Wilkinson, J. Chem . Soc (A), (1968), 3133.

20. C.K. Brown, G. Wilkinson, J. Chem . Soc. (A), (1970), 2753.

55



C H A P T E R 4


Part III. Influence of the Type of Support, the Degree of Pore Filling, and

Organic Additives on the Catalytic Performance *)

by

L.A. Gerritsen, J.M. Herman and J.J.F. Scholten,



Julianalaan 136,


Summary

Hydridocarbonyltris(triphenylphosphine)rhodium(I), dissolved in triphenyl

phosphine and captivated in the pores of a support by strong capillary forces,

is applied in the heterogeneous hydroformylation of ethylene and propylene. The

activity of this supported liquid phase rhodium catalyst is highly dependent

on the type of support and the degree of pore filling, owing not only to a

variation in surface area of the gas-PPh, phase boundary, but also to a

variation in the degree of adsorption of the rhodium complexes onto the support

surface.

The long activation time of the catalyst on certain silicas and silica-

alumina is due to a slow increase of the complex concentration in the PPh.,

caused by slow desorption of the rhodium complexes from the support surface,

and by additional spreading of the catalyst solution over the support. Both

phenomena are induced by a small quantity of aldol condensation products

slowly formed by consecutive reactions of the produced aldehydes.

The activation time of the catalyst is appreciably shortened and the

activity and selectivity increased, by previous addition of aldol condensation

products or polyethylene glycol to the catalyst solution, or by modification

of the silica surface with tri (etI)oxy)phenylsilane.


57




In part I of this series [1 ] and in the relative patents [2,3], an outline

has been given of the preparation and characterization of a supported liquid

phase rhodium catalyst, along with evidence of its excellent performance in the

heterogeneous hydroformylation of ethylene and propylene under the very mild

reaction conditions of 90°C and 1.57 MPa total pressure.

In part II of this series [4] we demonstrated that the hydroformylation is

a heterogeneous reaction, catalyzed by the rhodium complexes at the gas-PPh,

phase boundary only; the rhodium complexes in the bulk of the PPh, are inactive

owing to the low solubility of carbon monoxide in PPh, and to the high degree

of coordination with PPh,.

This paper deals with the influence of the type of support, of the degree

of pore filling and of organic additives on the catalytic performance.

2 E x p e r i m e n t a l

2.1 General

The preparation and characterization of the catalyst, the high-pressure

continuous-flow apparatus for testing the catalytic performance, the support

materials and all chemicals used have been discussed in part I. As stated

there, we pretreated the supports in vacuo at 50 0°C for 16 hrs, with the

exception of silica S and macroreticular polystyrene-20 % divinylbenzene XAD-2,

which were predried at 120°C. The apparatus for measuring the surface tensions

is referred to in part II. The polyethylene glycols, PEG-200 and PEG-1 00 0

(>98%) were obtained from Merck, the nonylphenolpolyethylene glycol NNP-1 0

{>99%) from Servo (Delden, The Netherlands). An aldol condensation product

mixture was prepared as described in part I of this series with the aid of a

Y-alumina 00 5-0.7 5 E catalyst; it consisted mainly of 2 -methyl-2-pentenal, 3-

hydroxy-2-methylpentanal and a small amount of higher-boiling products such as

trimers and tetramers.

2.2 Mod ification of silica 000-ZE

The modification of the silica 000-3E surface with tri(ethoxy)phenylsilane

was carried out by Mitchell's procedure [ 5 ] . After modification, the silica

contained 2.06 w% of carbon, while the pore volume appeared to have decreased

58



3 3 2

from 0.85 cm /g to 0.76 cm /g and the BET surface area from 203 m /g to 1882

m /g. The volume averaged mean pore radius had remained at 5.7 nm.

2.3 Determination of adsorption isotherms of RhHCO PPh„)„ on the supports

Varying amounts of RhHCO(PPh2)3 (0.02 08 -0.15 00 g ) , about 8.00 g of PPh^ and

3.00 g of support material (particle diameter: 0.35-0.42 mm) were brought into

the adsorption apparatus shown in Fig. 1. The supports had been pre-dried in

vacuo at 15 0°C for three hrs, and then at 50 0°C for sixteen hrs. The macro

reticular polystyrene-2 0% divinylbenzene, type XAD-2, had been pre-dried at

120 °C at atmospheric pressure for sixteen hrs.

-L.-B=

oil 7 0 ' C

H2 /C0 (90°C)

Figure 1 Adsorption apparatus.A: filter; B: PPh^ + RhHCO(PPh ) + support; C:

heating jacket.

After an equilibration period of two hrs, in which a hydrogen/carbon

monoxide mixture (1:1) was continuously bubbled through the PPh, solution, we

separated the light-yellow PPh, solution from the loaded support by filtration

and determined its rhodium content by neutron activation analysis, using 'the

single comparator' method, with zinc as reference material [ 6 ] . The amount of

rhodium adsorbed on the support was calculated from the difference in rhodium

content of the filtrate, before and after adsorption of the rhodium complex on

the support.

59



3. Results

3.1 Adsorption isotherms of RhHC O(PPh.,),

Adsorption isotherms of RhHCO(PPh,) in molten PPh at 90 °C on three

different supports are plotted in Fig. 2.

0 2 0

0-15

0-10 •

o 0 5

Figure 2 Adsorption isotherms of RhHCO(PPh-). in molten PPh..

at 90°C on three supports.

* = XAD - 2 ; 0 = s il ic a 000-3E; x = s ili ca -a lu m in a

LA-30; a = sil ica -al um in a LA-30, not d rie d in vacuo;

b = adsorption on si l ica -alu m ina LA-30 from di( 2- eth yl -

hexyllphthalate (l)OP) as a solvent.

N o t w i t h s t a n d i n g t h e l a r g e e x c e s s o f f r e e P P h , ( i n i t i a l P/R h r a t i o : 1 3 51 -1 89

m o l / m o l ) , a n d t h e p h y s i c a l s i m i l a r i t y o f t h e o u t e r sp h e r e s o f RhH CO (PPh,)_ a nd

PPh^ , i t i s e v id en t from F ig . 2 th a t the rhodium complexes show a gre a t e r

t e n d e n c y t o a d so r b on s i l i c a 0 00 -3 E t h a n P P h , ; a s i m i l a r p r e f e r e n c e f o r

a d s o r p t i o n i s o b s e r v e d on s i l i c a - a l u m i n a LA -3 0. P r e f e r e n t i a l a d s o r p t i o n o f t h e

c om p le x on t h e o r g a n o p h i l i c XAD-2 r e s i n , h o w e ve r , i s r e l a t i v e l y s m a l l . F u r t h e r

m o r e , t h e d e g r e e o f a d so r p t i o n on s i l i c a - a l u m i n a LA -30 i s n o t i n f l u e n c e d by

p r e - d r y i n g in vacuo (se e po in t a in F ig . 2 ) , or by u si ng DOP as a so lv en t (b ) .

We emph as ize t h a t th e a ds or p t io n i so the rm s have been m easured wi th an amount

o f PP h , h i g h l y i n e x c e s s o f t h e am ou nt o f su p p o r t , w h e r e a s i n p r a c t i c e t h e

p o r e s of t h e SLPC a r e o n ly p a r t i a l l y f i l l e d w i t h c a t a l y s t s o l u t i o n , and t h e

60



volume of solution in the pores is small compared with the support volume. This

means that, particularly in microporous supports, all rhodium complexes are

very near to, or even in direct contact with, the support surface. Consequently,

the adsorption of the rhodium complexes in an SLPC is more extensive than

depicted in Fig. 2.

Examples of strong adsorption of rhodium complexes, though not in PPh,, are

known from the literature. For the adsorption of Rh(Tr-allyl)CO(PPh,)^ dissolved

in a mixture of toluene and pentane on yalumi na, Spek [7] observed an enthalpy

of adsorption of -117 kJ/mol. Hartig [8] recovered RhHCO(PPh,), from a solution

in toluene, or in aldol condensation products, by strong reversible adsorption

on synthetic magnesium silicate, whereas on a number of aluminas he even

observed irreversible and destructive adsorption.

3.2 Influence of the type of suppo rt

A large number of commercially available materials were tested for their

suitability as catalyst supports in the hydroformylation of ethylene. The

degree of liqiiid loading, i.e. the degree of pore filling with catalyst

solution, in these tests was 5 0 %. The texture of the supports, before and after

loading with catalyst solution, is given in Table 1. Also included in Table 1

is the surface area of the gas-PPh, phase boundary per unit volume of catalyst

solution, Sppj , calculated from the BET catalyst surface area, S_ , by

multiplying S^^ by a factor W^^^/Wpp,^ .

The catalytic performance of catalysts on various supports in the hydro-

formylation of ethylene is presented in Figs. 3 and 4.

Figures 3 and 4 show that X AD-2 is the preferred support material, both

with respect to activity and to time of activation, i.e. the time needed to

reach the final stable activity level. The silica-supported catalysts have a

medium activity, while the activities of catalysts on the aluminas and the

activated carbon are low. The very long activation times of catalysts on

certain silicas and on silica-alumina LA-3 0 are noteworthy. A simple

correlation between Sp». (Table 1) and the activities is not observed.

3.3 Influence of the degree of liquid loading

With silica 00 0-3 E, y-alumina 00 5-0 .75 E, Kieselguhr MP-99 and XAD-2 being

used as supports, the degree of liquid loading was varied between 0.038 and

1.00 . With silica S and silica-alumina LA-30 only some orienting experiments

were performed.

61



Table 1 Texture of the various supports, before and after loading with catalyst solution

Support

XAD-2'^

silica S

silica 00 0-3E'^

Kieselguhr MP-99

silica-alumina LA-30

silica Dll-11

silicagel

Y-alumina 005-0.75E'^

Y-alumina 000-3P'''

activated carbon

Vcum

/ 3\cm

\ g /

0.69

1.05

0.85

1.03

0.59

0.87

0.86

0.74

0.72

0.37

Before

BET

/ 2\m

\g /

300

101

203

18

156

120

431

170

240

1024

/dV \

r J

\ p/max

(nm)

9.0

17.0

5.7

248.0

5.4

1800.0

15.1

3.6

8.5

4.5

2.7

\h'^

0.65

0.79

0.55

0.43

0.50

0.54

0.55

0.43

0.60

0.48

6^m

---

0.80

0.52

0.44

0.43

0.39

---

0.38

0.53

0.50

After

Vcum

/ 3 \cm 1

\g caty

0.10

0.27

0.40

0.26

0.36

---

0.34

0.35

0.36

BET

\g cat/

—

13

39

9

28

37

---

74

66

439

/ \/dV \

(nm)

20.0

12.0

340.0

6.3

794.0

15.9

---

9.5

5.0

2.7

^PPhj

/ 2 \1 •\g PP^/

28

118

28

117

117

---

392

210 •

2705

a: measured by nitrogen capillary condensation at -196°C in the region 2 < r < 50 nm.

b: measured by mercury porosimetry in the region 2 < r < 7000 nm.

a: degree of liquid loading at 90°C calculated from the amount of catalyst solution impregnated in the support

d: degree of liquid .loading measured by nitrogen capillary condensation or mercury porosimetry.



450

300

150

O

O 5 0 1 0 0 1 5 0 2 0 0

— t(j (hrs)

Figure 3. Influence of the type of support on the activity and the activation

behaviour of an SLPC in the hydroformylation of ethylene.

P = 1.2 MP a; C2/H2/CO = 1 /1/1; t = 90 °C; W/F = 0.570 x 1 0" ^ g Rh.s/cm^ c".

Support: • = XAD-2; • = silica 0 00 -3E, 0 = Kieselguhr MP-9 9; * = silica-alumina

LA-30; + = Y-alumina 00 5-0.7 5 E; V = y-alumina 00 0-3 P, x = activated carbon.

For all supports: 6 = ca. 0.50, [Rh] = 5.50 mol/ m , P/Rh = 743 mol/mol.

2 4 0

180

120

6 0

0

0 5 0 1 0 0 1 5 0 2 0 0

— td (hrs)

Figure 4. Influence of the type of silica on the activity and activation be

haviour of an SLPC for the hydroformylation of ethylene.

The same reaction conditions as Fig. 3.

Support: V = silica S; 0 = Kieselguhr MP-99 ; • = silica 00 0-3 E; * = silica-

alumina LA-30; X = silica Dll-1 1; A = silicagel. For all supports: 6 = ca. 0.50 ,

[Rh] = 5.50 mol/ m^, P/Rh = 74 3 mol/raol.

63



The influence of the degree of liquid loading on the distribution of the

catalyst solution in the support was measured by nitrogen capillary condensa

tion at -196°C. Results obtained with some typical silica 000-3E SLPC's are

given in Fig. 5.

0-8

0 6

0 2

0

1 ^-- (-f^)

- - ' - ' - ^

101 2 5— - Tp (nm)

10-;

Figure 5 Pore size distribution of a silica 000-3E SLPC at

various degrees of liquid loading. The cumulative

pore volume V is plotted as a function of the pore' cum ' '

radius.

X = bare support: 0 : 6 = 0.038; A : &

0.56; . ; 6 = 0.65; V : 6 = 0.88.

0.17;

It is clearly seen from this Figure that the catalyst solution in silica

00 0-3E is distributed as predicted by the theory of capillary condensation [ 9 ] :

at low liquid loadings the walls of the pores are covered with a thin layer of

physically adsorbed PPh,, whereas at higher liquid loadings the thickness of

this layer increases, and the smaller pores get completely filled up with

capillary-condensed PPh,. As capillary condensation is always attended with

adsorption in larger pores, Sppj^ (calculated from S_p„; see Section 3.2) re-

presents the sum of the meniscus area and the PPh,-covered internal surface.

Results for silica 000-3E catalysts with various degrees of liquid loading are

given in Table 2.

64



Table 2 Surface area of the gas-PPh, phase boundary, S-p, , on silica 000 -3E

at various degrees of liquid loading

6

0

0.038

0.075

0.17

0.32

^BET

• ' \[, catj

203

188

177

142

81

SpPh3

/ J \mV hi

5869

2773

1116

363

6

0.55

0.65

0.83

0.96

1.00

^BET/ 2 \

m

[s cat;

39

26

10

8

4

S/

V

PPh.,2^

m

PPhj

118

71

21

17

10

The results in Table 2 reflect the strong decrease in surface area of the

gas-PPh, phase boundary with increasing liquid loading. The still relatively

large surface area of a fully loaded silica 0 00 -3E catalyst (6 = 1.00 ; the

surface area was measured by methane adsorption at -1 96 °C) suggests that the3

pore volume of the support is somewhat higher than the value of 0.85 cm /g

mentioned in Table 2.

The influence of the degree of liquid loading on the activation behaviour

and on the final activity level of silica 000-3E catalysts in the hydroformy

lation of ethylene is shown in Fig. 6. In experiments with the other supports

the time of activation was practically independent of the degree of liquid

loading.

It is evident that the activation on a silica 000-3E support comprises two

stages: a very fast activation during the first four hrs, up to a level which

is higher according as the degree of liquid loading increases, and a slower

activation up to a final stable level. The activation times are longest at

medium degrees of liquid loading. The influence of the degree of liquid loading

on the final activity level reached on various supports is presented in Fig. 7.

It is clear from Fig. 7 that the influence of the degree of liquid loading

on the final activity level highly depends on the type of support: the activity

on silica 00 0 -3E, silica S, silica-alumina LA-30 and y-alumina 00 5-0 .75 E

decreases with the degree of liquid loading, whereas XAD-2 shows the opposite

trend. The activity of Kieselguhr-supported catalysts is not influenced by the

degree of liquid loading.

65



200

150

100

100- ^ td hrs)

150 200

Figure 6. Activation behaviour and final activity level of silica 000-3E

supported catalysts during hydroformylation of ethylene as functions of the

degree of liquid loading.

P = 1.2 MPa; C^/ I IT /CO = 1/1/1; t = 90°C; W/F = 0.570 x lO ' g Rh.s/cm C^.

Ca ta ly st : s i l i c a 00 0- 3E ;« :6 = 1.00; 0:5 = 0. 75; x:6 = 0.56 ; +:6 = 0.3 2; A:6

0 . 1 7 ; . :6 = 0.075; V:6 = 0. 03 8; [Rh] = 5.50 mol/m^; P/Rh = 743 mol/mol .

500

400

300 -

Figure 7. Final activity level of SLPC's

for hydroformylation of ethylene versus

degree of liquid loading, for six differ

ent support materials.

P = 1.2 MPa; C^/Hj/CO = 1/1/1; t = 90°C;

W/F = 0.570 X 10-2 g Rh.s/cm ' C^.

Catalyst: + = XAD-2; A = silica 000-3E;

* = silica S; X = silica-alumina LA-30;

D= Kieselguhr MP-99; 0 = y-alumina 005-

0.75 E; 5 = variable; [Rh] = 5.50 raol/m ;

P/Rh = 743 mol/mol.

66



3.4 Shortening of the time of activation

3.4.1 Addition of aldol condensation products

A d d i t i o n of 10 vo l % of an a l d o l c o n d e n s a t i o n p r o d u c t m i x t u r e p r e p a r e d by

a l d o l c o n d e n s a t i o n of p r o p i o n a l d e h y d e to th e c a t a l y s t s o l u t i o n , and s u b s e q u e n t

i m p r e g n a t i o n on s i l i c a 0 0 0 - 3 E , y i e l d e d an SLPC wi th 6 = 0 . 56, [Rh] = 5. 53 mol/

3 3

m an d P/Rh = 668 m o l / m . The c a t a l y s t was t e s t e d in th e h y d r o f o r m y l a t i o n of

p r o p y l e n e .

100 150

— t(j (hrs)

F i g u r e 8 C a t a l y t i c p e rf o rm a n c e of some s i l i c a 000-3E SLP

c a t a l y s t s in the h y d r o f o r m y l a t i o n of p r o p y l e n e .

X = s i l i c a 0 00 -3 E; • = 10 vol % of a ld o l c o n d e n s a t i o n

] i roduc ts added ; * = 10 vol % of p o l y e t h y l e n e g l y c o l ,

PEG-200, added; 0 = s i l i c a 0 0 0- 3E m o d i f i e d w i th t r i -

( e t h o x y ) p h e n y l s i l a n c .P = 1.57 MPa; C^/Hj/CO = 1 / 1 / 1 ; t = 90°C; W/F =

0 .978 x lO -' g Rh.s/cm c

C a t a l y s t p r o p e r t i e s : see t e x t .

I t i s e v i d e n t t h a t t h i s a d d i t i o n of a l d o l c o n d e n s a t i o n p r o d u c t s s h o r t e n s

t h e t i m e of a c t i v a t i o n f ro m 200 h r s to 5 h r s and, f u r t h e r m o r e , ha s a s l i g h t

i m p r o v i n g e f f e c t on b o t h s e l e c t i v i t y and f i n a l a c t i v i t y .

3.4.2 Addition of polyethylene glycol

We also stu died the ef fe ct of var ious amounts of polyethylene glycol (mean

molecular weight: 200; type PEG-200) on the ca ta ly t i c performance. A typ ical

67



result with a silica 0 00 -3E SLPC to which 10 vol % of PEG-20 0 had been added,

achieved in propylene hydroformylation, is given in Fig. 8. For a comparative

survey of all results see Table 3.

Table 3 Propylene hydroformylation with silica 00 0-3 E SLP catalysts

containing various amounts of PEG-200

PEG-200

(vol %)

0

2

10

20

30

50

65

85*

93=

P/Rh

/ \1 mol \

753

750

699

613

536

383

248

114

49

200

10

10

10

5

4

8

4

4

5.8

5.4

9.0

8.4

8.8

9.9

12.4

16.2

12.0

7.8

8.3

8.6

8.8

8.6

7.8

7.3

5.6

4.0

a: P = 1.57 MPa; C /Hj/CO = 1 /1/ 1; t = 90° C; W/F = 0.984 x 1 0 "^ g Rh.s/cm"^ C

3 =b: The activity goes up to a maximum of 24 .8 cm C /g Rh.s within 4 hrs and

3 =then decreases vvithin 40 hrs to a stable level of 16.2 cm C /g Rh.s.

3 =a: The activity goes up to a maximum of 34 cm C /g Rh.s within 4 hrs and then

3 =decreases within 5 0 hrs to a stable level of 12.0 cm C /g Rh.s.

Table 3 and Fig. 8 show that addition of polyethylene glycol not only

shortens the activation time, but also increases the selectivity and the final

activity. The selectivity is maximum at 2 0 vol % of PEG-2 00 . Catalysts

containing more than 6 5 vol % of PEG-20 0 deactivate and have a low selectivity.

Similar results were obtained upon addition of 1 0 vol % of PEG-2 0 0 to

catalyst solutions on silicagel and on silica Dll-11 . As to catalysts on

silica-alumina LA-30, Kieselguhr MP-99 and y-alumina 005-0.75 E, no effect of

PEG-200 was observed.

Addition of 1 0 vol % of polyethylene glycol with a mean molecular weight of

1000, type PEG-1 0 0 0, to the catalyst solution on silica 000 -3E reduces the

activation time during hydroformylation of propylene from 2 00 hrs to 10 hrs.

The activity and selectivity, however, increase only slightly; at 9 0°C and3 =

1.57 MPa total pressure, the activity is 6.0 cm C,/g Rh.s and the selectivity

activation activity selectivity

time • 3 =\ /



8. The same results were obtained upon addition of 10 vol % of nonylphenolpoly

ethylene glycol, NNP-10, which is quite similar in nature to PEG-1000.

3.4.3 Modification with tri(ethoxy)phenylsilane

The inner surface of a silica 000-3E support was changed from hydrophilic

into organophilic by reaction of the surface silanol groups with tri(ethoxy)-

phenylsilane, prior to loading the support with catalyst solution (6 = 0.63;

[Rh] =5 .5 1 mol/m ; P/Rh = 753 mol/mol). Fig. 8 shows that this reduces the

activation time in the hydroformylation of propylene from 200 hrs to 10 hrs,

3 = 3 =

whereas the activity is enhanced from 5.8 cm C /g Rh.s to 7.1 cm C /g Rh.s,

and the selectivity from 7.8 to 8.8.

3.4.4 Influence of catalyst pretreatment on the results

A fresh silica 000-3E SLP catalyst (6 = 0.56; [Rh] = 5.50 mol/m^; P/Rh =

743 mol/mol) was pretreated under flowing hydrogen/carbon monoxide (1:1) at

90°C and 0.98 MPa total pressure. After 122 hrs ethylene was added and the

total pressure was raised to 1.2 MPa (C_/H^/CO = 1/1/1). The activation

behaviour and the final stable activity level proved not to be influenced by

this pretreatment. (The catalytic performance of the non-pretreated catalyst is

shown in Fig. 4.)

3.5 Surface tensions • • . •'

3The surface tension of a PPh, solution of RhHCO(PPh ) , (6.5 mol/m PPh,)

was measured under flowing nitrogen at 9 1°C both before and after addition of-3

4.2 w% of PEG-200. In both cases a surface tension of 43.9 x 10 N/m was

observed. The same value was found upon addition of NNP-10.

4 . Discussion

Activity

Hydroformylation with ou r supported liquid phase rhodium catalysts being

heterogeneous in nature (see part I I), one would expect, at the first instance

at least, a linear correlation to exist between catalytic activity and surface

area of the gas-PPh, phase boundary. However, such a correlation is not found

(compare the Sppj^ -values in Table 1 and 2 with the activities in Figs. 3 and 4

and in Fig. 7, respectively), and we attribute this to the varying

adsorbability of rhodium complexes on the surface of the various supports

69



(Fig. 2 ) . It is obvious that any adsorption of rhodium complexes will lower the

rhodium concentration in the catalyst solution and at the gas-PPh, phase

boundary, thereby causing a decrease in activity because only the rhodium

complexes at the gas-PPh- phase boundary are involved in the hydroformylation

reaction. This means that the activity is determined not only by the surface

area of the gas-PPh, phase boundary, but also by the degree of adsorption of

the rhodium complexes on the various supports.

The higher catalytic activity on the non-polar organophilic XAD-2 than on

silica-alumina (Fig. 3 ) , is therefore explained by the lower degree of

adsorption of rhodium complexes on XAD-2 than on silica-alumina (Fig. 2 ) ; this

high degree of adsorption on silica-alumina LA-30 is most probably due to the

polarity of the surface OH-groups and also to the presence of strong Lewis acid

sites. The same explanation holds for the low activity on y-aluminas (Fig. 3 ) ,

which are likewise known to possess strong Lewis acidity after high-temperature

pretreatment [10,11]. It is interesting to note in this context that Rony [12,

1 3 ] , when hydroformylating propylene with another type of SLP catalyst, like

wise observed a lower activity on an alumina than on a silica support.

These Lewis acid sites are, obviously, not the only sites capable of

adsorbing RhHCO(PPh,),, because the silica 000-3E surface, with its weak

Brönsted acidity only [14,15], still exhibits a relatively strong power of

adsorption (Fig. 2 ) , which may be attributed to a weak interaction between the

iT-electrons of the phenyl groups in RhHCO(PPh,), and the silanol groups [16,17].

The low activity on activated carbon (Fig. 3) is to be attributed to the

microporosity of the carbon used, that is to say to the unfavourably low ratio

between the volume of catalyst solution and the complex adsorbing contact area

between catalyst solution and support, and hence to the very high degree of

adsorption of rhodium complexes.

Influence of the degree of liquid loading

At low degrees of liquid loading, catalysts on silica 0 0 0-3E, silica S, y-

alumina 00 5-0 .75 E and silica-alumina LA-30 exhibit a low activity, notwith

standing the very large gas-PPh, phase boundary. This is attributed to the fact

that at low loading the catalyst solution is contained in the smaller pores

(Fig. 5 ) , meaning that the surface area of the swpport-PPh, phase boundary per

unit volume of catalyst solution is large. This, as well as the intensified van

der Waals interaction between the rhodium complexes and the pore walls at a

short distance of the surface, causes extensive adsorption of rhodium complexes

and hence a low activity.

At higher liquid loading, the surface area of the support-PP'h, phase

70



boundary per unit volume of catalyst solution decreases, with the result that

the activity increases. To this it must be added that owing to the much larger

distance between the rhodium complexes and the pore walls in larger pores the

van der Waals interaction strongly decreases, resulting in a higher equilibrium

concentration of the complexes in the PPh, solution. At the same time, however,

the surface area of the gas-PPh, phase boundary decreases (Table 2 ) , which has

an opposed and lowering effect on the activity. At a certain degree of liquid

loading this activity-decreasing effect becomes predominating, which implies

that the activity will go through a maximum somewhere (Fig. 7 ) .

The high activity of XAD-2 at low liquid loading (Fig. 7) is in accordance

with the weakness and small extent of adsorption of rhodium complexes (Fig. 2 ) .

Owing to the heterogeneous nature of the hydroformylation reaction, as well

as to the occurrence of adsorption of rhodium complexes, our results are not

directly comparable with those published on other SLPC systems [12,13,18,19];

nor are the theoretical models for SLP catalysts [2 0,2 1,2 2,2 3] applicable to

our catalysts.

Activation behaviour

Since SLPC's on most supports do not show signs of activation (Figs. 3 ,4 ),

the activation observed on silica and silica-alumina LA-30 supported catalysts

cannot be due to something like a slow chemical transformation of inactive

rhodium complexes into active ones.

Further, the identity in catalytic performance of a pretreated and a non-

pretreated silica 000-3E catalyst (Section 3.4.4) indicates that the activation

observed on the latter cannot be ascribed to a kinetically controlled re

distribution of the catalyst solution in the support. This proves that the

cause of the activation is to be sought in the hydroformylation conditions

themselves.

Since usually a small amount of aldol condensation products is formed under

hydroformylation conditions (see part I ) , it is logical to conclude that the

activation is related to the formation of these aldol condensation products.

This view is supported by the shortening of the activation time upon addition

of aldol condensation products beforehand (Fig. 8 ) .

However, these products do not induce activation on all supports. E.g. y-

alumina 005-0.75 E itself is very active for the catalytic formation of aldol

products (see part I ) , whereas the SLP catalyst on this support is very rapidlyactivated to a stable level, which is not further influenced by the aldol

products (Fig. 3 ) . We therefore must exclude the possibility that the

activation proceeds via a mechanism in which the aldol products either decrease

71



the surface tension of the gas-PPh, phase boundary, or affect the equilibria

between the various rhodium complexes in the catalyst solution. On the contrary,

we think that the aldol products, e.g. 3-hydroxy-2-methylpentanal, strongly

adsorb via hydrogen bridging on the surface silanol-groups, thereby suppressing

the adsorption of the rhodium complexes. Thus more and more rhodium complexes

become available at the gas-PPh, phase boundary, and this results in a slowly

increasing activity. As a further conseq uence, the hydrophilic silica surface

is gradually transformed into an organophilic surface; this decreases the

surface tension of the support-PP\i phase boundary and thus causes additional

spreading of the catalyst solution over the support.

The fact that silica 000 -3E catalysts, upon addition of PEG-20 0 - which is

known to render silicas organophilic by reaction with surface silanol groups

[24,25] - also show a short activation time, supports the correctness of the

above view. Additional strong evidence is provided by the short activation time

observed with a tri(ethoxy)phenylsilane-modified silica 000-3E SLPC.

The dehydroxylated hydrophobic silica S does not show an activation time

because of its inactivity for aldol condensation (sodium-poor silica; see part

I ) ; its high activity is explained by the low adsorbability of the rhodium

complexes in the absence of silanol groups.

Kieselguhr MP-99 has a very short activation time because of its relatively

low activity for aldol condensation (see part I) and the only slight adsorption

of rhodium complexes, which are both due to the very small surface area of

Kieselguhr.

A ck no v/ 1 e d g e m e n t s


for Chemical Research (SON) with financial aid from the Netherlands Organization

for the Advancement of Pure Research (ZWO).

L i s t of s y m b o l s

2amount of rhodium metal adsorbed on a support mol/ m

3concentration of rhodium complex in PPh, after adsorption mol/ m

2BET surface area m /g

2surface area of the gas-PPh- phase boundary m /g PPh,

ads

sol

^BET

SpPh,

72



volume averaged mean pore radius nm

max

W total weight of the SLP catalyst after impregnation g

of the support with catalyst solution

W , total weight of PPh, used in catalyst preparation g

The other symbols used in this paper are indicated in parts I and II of this

series.

References

1. L.A. Gerritsen, A. van Meerkerk,M.H. Vreugdenhil, J.J.F. Scholten, part 1,

submitted for publication in J. Mol. Catal.

2. L.A. Gerritsen, J.J.F. Scholten (ZWO), Neth. Patent Appl. 77005 54 (1977),

7712648 (1977) and 7902964 (1979).

3. L.A. Gerritsen, J.J.F. Scholten (Stamicarbon B . V . ) , German Patent Appl.

2802276 (1978).

4. L.A. Gerritsen, J.M. Herman, W. Klut, J.J.F. Scholten, part II, submittedfor publication in J. Mol. Catal.

5. T.O. Mitchell, Ph.D. thesis. North Western Univ., USA, 1971.

6. P.J.M. Korthoven, M. de Bruin, J. Radioanal. Chem. 35_, (1977), 127.

7. Th.G. Spek, J.J.F. Scholten, J. Mol. Catal. }_, (1977/78), 81.

8. U. Hartig, Ph.D. thesis, Aachen, Germany, 197 2.

9. J.C.P. Broekhoff, Ph.D. thesis. Delft, The Netherlands, 1969.

10. J.B. Peri, J. Catal. 4T, (1976), 227.

11. J.B. Peri, J. Phys. Chem. 69, (1965), 220.

12. P.R. Rony, J. Catal. 14_, (1969), 142.

13. P.R. Rony (Monsanto Company), Brit. Patent 118 5453 (1970).

14. C C Arraistead, A.J. Tyler, F.H. Hambleton, S.A. Mitchell, J.A. Hockey, J.

Phys. Chem. T^, (1969), 3947.

15. T. Masuda, H. Taniguchi, K. Tsutsumi, H. Takahashi, Bull. Chem. Soc Japan

S}_, (1978), 1965.

16. J.A. Cusumano, M.J.D. Low, J. Phys. Chem. 74_, (1970), 792.

17. J.A. Cusumano, M.J.D. Low, J. Phys. Chem. 7£, (1970), 1950.

18. H. Livbjerg, K.F. Jensen, J. Villadsen, J. Catal. AS_, (1976), 216,

19. H. Komiyama, H. Inoue, J. Chem. Eng. Japan 8 , (1975), 310.

20. P.R. Rony, Chem. Eng. Sci. Z3, (1968), 1021.

21. R. Abed, R.G. Rinker, J. Catal. 31_, (1973), 119.

73





C H A P T E R 5


Part IV. The Application of various tertiary Phosphines as Solvent Ligands *)

by

L.A. Gerritsen, W. Klut, M.H. Vreugdenhil and J.J.F. Scholten,



Julianalaan 136,


Summary

The heterogeneous catalytic hydroformylation of propylene is carried out at

90 -19 9° C and 1.57 MPa total pressure, over a supported liquid phase rhodium

catalyst. Besides triphenylphosphine, various other tertiary phosphines may be

used as solvent ligands. It turned out that tri(p-tolyl)phosphine, tri(2-cyano-

ethyl)phosphine and S(+)-(2-phenylbutyl)diphenylphosphine are very attractive

solvent ligands, as they provide the catalysts with excellent stability and

selectivity, and satisfactory activity. The volatility of these ligands being

relatively low, the supported liquid phase rhodium catalysts can be applied at

temperatures up to ca. 14 0° C, without severe loss of phosphine by evaporation.

Above 150°C deactivation of the catalysts is observed; this is thought tobe due to metallation of the coordinated ligands by the rhodium metal.


75



1 . I n t r o d u c t i o n

Previous parts of this series [1,2,3] and the relative patents [4,5] dealt

with the application of hydridocarbonyltris(triphenylphosphine)rhodium(I),

dissolved in triphenylphosphine and capillary-condensed into the pores of a

support, in the heterogeneous hydroformylation of ethylene and propylene at

90°C and 1.2 to 1.57 MPa total pressure. We have seen that under these very

mild reaction conditions, the catalyst combines a high selectivity towards the

formation of n-butyraldehyde with an excellent stability.

For a number of reasons it would be desirable to use reaction temperatures

above 90 °C. For example, it is uneconomic to dissipate the high exothermic

heat of reaction (-138 kJ/mol) at a low temperature level. Further, at 90 °C and

1.57 MPa total pressure (C~/H-/CO = 1/1/1) the propylene conversion should not

exceed 21.4%, in order to prevent capillary condensation of butyraldehyde into

the pores of the catalyst [ 6 ] ; in the hydroformylation of, for instance,

butenes or allylalcohol, the conversion should even be lower for the same

reason.

With triphenylphosphine being used as a solvent ligand, temperatures above

90 °C have the drawback that too much PPh, will evaporate out of the catalyst

per unit time [ 7 ] , causing the catalyst to dry up, while at the same time the

produced aldehydes become contaminated with phosphine.

In order to circumvent these difficulties we decided to prepare SLP

catalysts with several new low-volatile tertiary phosphines as solvent ligands,

and test these in the temperature range from 90 to 199°C.

2 . Experimental

The preparation and characterization of the catalysts, as well as the high-

pressure continuous-flow apparatus, are described in part I of this series.

The solvent ligands were obtained from Strem Chemicals Inc., USA; tri(bi-

phenyl)phosphine was prepared by Worrall's procedure [ 8 ] .

The volatility of some phosphines was determined by Thermogravimetric

Analysis (TGA). This was done by weighing 0.01 g of a Kieselguhr MP-99 SLP

catalyst (6 = 0.44) containing the particular phosphine as a solvent ligand

into a 15 yl sample pan, heating the sample at 1 30 °C under 0.1 MPa of flowing

dry nitrogen, and measuring the decrease in weight as a function of time in a

Perkin Elmer thermobalance, type TSG-1. The reproducibility of the measure

ments was better than 10%.

76



The melting points of the phosphines were determined under flowing nitrogen

in a du Pont Instruments 91 0 differential scanning calorimeter, coupled to a du

Pont 990 thermal analyzer.

3 . Results

3.1 TGA-measurements

The vapour p re ss ur e o f most pho sph ines be in g unknown, th e r a t e s o f

e v a p o r a t i o n w e re d e t e r m i n e d b y TGA. T he r e s u l t s a r e p r e se n t e d i n F i g . 1 .

— - t i m e ( h r s )

0 10 20 30 400

0 8

1 6

2 4

Figure 1 Weight decre ase (AG) as a fun ction of time at 130°C. Ca ta ly st :

Kieselgu hr MP-99; 6 = 0.4 4; [Rh] = 28.6 mol/m ; so lve nt lig an d: x =

t r iphenylphosphine; 0 = t r ibenzylpho sphine , • = t r i (p- tolyl )ph osph ine;

A = t r i (2-cyanoethy l)phosph ine; * = S(+)-(2-ph enylbutyl )diphenyl-

phosphine.

F i g . 1 sh ow s t h a t am ong t h e f i v e s o l v e n t l i g a n d s i n v e s t i g a t e d , t r i p h e n y l

p h o s p h i n e h a s t h e h i g h e s t r a t e o f e v a p o r a t i o n , f o ll o w e d b y t r i b e n z y l p h o s p h i n e ,

w h er ea s t h i s r a t e i s v e r y low f o r S ( + ) - ( 2 - p h e n y l b u t y l ) d i p h e n y l p h o s p h i n e , t r i -

( p - t o l y l ) p h o s p h i n e a nd t r i ( 2 - c y a n o e t h y l ) p h o s p h i n e . At a h i g h s p a ce v e l o c i t y o f

t h e c a r r i e r g a s , t h e r a t e s o f e v a p o r a t i o n a r e p r o p o r t i o n a l t o k , ' S - p . - e x p

( -AH/RT) , where AH i s th e en tha lpy of co nd en sa t io n . U nf or tu na te l y , th e AHv a l u e s o f t h e co mp ou nd s i n q u e s t i o n a r e n o t g iv e n in t h e l i t e r a t u r e ; t h e r e f o r e

we o n l y w i sh t o p o i n t o u t t h a t o u r r e s u l t i s i n a g r e em e n t w i t h t h e f a c t t h a t

t h e v a p ou r p r e s s u r e o f S ( + ) - ( 2 - p h c n y l b u t y l ) d i p h e n y l p h o s p h i n e a t 174°C i s o n l y

26 .7 Pa (prod uc t in fo rm at io n from S t rem Chem ica l s I n c . ) , whereas th e vapour

77



pressure of triphenylphosphine at 17 4°C amounts to 2 22 .4 Pa [ 7 ] .

The gradual decrease of the rate of evaporation with time (Fig. 1) is due

to the decrease in surface area, S„p , of the evaporating phosphine with time,

and also to the lowering of the vapour pressure of the phosphine, because,

according to Kelvin's Law, the vapour pressure will decrease as more and more

smaller pores in the Kieselguhr support become involved in the process of

evaporation.

3.2 Influence of the various phosphines on the catalytic performance

Unless otherwise stated, the catalysts consist of RhHCO(PPh,), dissolved in

the particular tertiary phosphine (concentration: 28.6 mol/m ) and capillary-

condensed into the pores of Kieselguhr MP-99 (6 = 0.44). The catalysts were

tested for hydroformylation of propylene at the temperatures mentioned in the

text and at 1.57 MPa total pressure (C"/H2/C0 = 1/1/1).

Catalytic performance at 90 C

The results at 90 °C are presented in Fig. 2. The selectivities given in the

graph are time-independent. The melting points of the pure pliosphines are given

in parentheses behind the various ligands in the legend. As mentioned in part

II of this series with respect to triphenylphosphine, the melting point of the

catalyst solution in Kieselguhr MP-99 is about 4 °C lower than that of the

free phosphine. This is confirmed by the result with tri(p-tolyl)phosphine,

the melting point of the catalyst solution in Kieselguhr being 14 2.8 °C, where

as that of the free phosphine is 147.4°C.

The strong influence of the type of solvent ligand on activity and

selectivity first of all proves that the exchange between the excess of solvent

ligand and the PPh, ligand originally bound to the rhodium complex is a very

rapid reaction, which shifts the equilibrium completely towards rhodium

complexes coordinated with the new ligand.

It further follows from Fig. 2 that at 90 °C triphenylphosphine is the

preferred solvent ligand, the catalyst having a high activity and selectivity.

A catalyst with tri(a-naphthyl)phosphine also shows a high activity but de-

activ:ites slowly, while the selectivity is only 1.9. Catalysts with triphenyl

phosphine oxide and with triphenylarsine have a high initial activity, but de

activate rapidly and their selectivity is low. Triphenylamine and triphenyl-

bismuth are not included in Fig. 2 , because the catalysts became inactive with

in a few hours. The activity and selectivity of catalysts with tri(p-tolyl)-

phosphine and S(+)-(2-phenylbutyl)diphenylphosphine are satisfactory.

78





Catalytic performance at 90-199 C

Catalysts containing the low-volatile phosphines were tested at

temperatures above 9 0 ° C The results are described below.

Tri(p-tolyl)phosphine, 1^^^^ - 147.4°C

After 70 hrs streamtime at 90°C, the temperature was stepwise raised to

139 °C over a period of 40 hrs. No deactivation was observed. At higher

temperatures the selectivity increases and reaches a maximum of 7.1 at 130 °C.

The apparent activation energy is constant throughout the range from 90 to

139°C, and amounts to 78.7 kJ/mol.

At 156.5°C the catalyst remains stable for 16 hrs, after which it de

activates to 40% of its initial activity within 22 hrs.

Tri(a-naphthyI)phosphine, T ^ = 287.5 C

At temperatures above 90°C the catalyst deactivates continuously, while the

selectivity decreases from 1.9 at 90°C to 1.45 at 1 6 9 ° C At 199°C the activity

completely vanishes within one hour.

TriibiphenyDphosphine, T = 174.7°C

At temperatures above 90°C, the catalyst deactivates: at 119.5°C the

activity decreases 25% in 23 hrs (S = 4 .1 ); after 6 hrs at 166 .8°C the decrease

in activity is 18% (S = 2 . 9 ). At 184.8°C the catalyst loses 56% of its activity

in 19 hrs, while the selectivity decreases to 2.4.

S(+)-(2-phenylbutyl)diphenylphosphine (liquid at room temperature)

Between 85 and 112°C the catalyst is stable for more than 340 hrs . When

the partial pressure of carbon monoxide is lowered from 0.52 MPa to 0.049 MPa,

the selectivity at 90 °C goes up from 3.4 to 7.8, and the activity from 4.7 to

7.4 cm' c /g Rh.s.

Tri(2-oyanoethyl)phosphine, T .. - 97.b C

In view of its very low activity of only 0.05 cm C /g Rh.s found at 90°C,

the stability of the catalyst was tested at 130°C. At this temperature no de

activation was observed for more than 70 hrs. At 130°C the catalyst shows an

activity of 0.68 cm C,/g Rh.s, and an attractive selectivity of 8.6. At 139°C

and at 150°C the catalyst deactivates. The apparent activation energy in the

temperature range from 85 to 130°C is constant and amounts to 83.6 kj/mol. The

selectivity does not vary with temperature.

Bis (1, 2-diphenylphosphino)ethane, T .. - 136 CTUG Lu 7 _

At 153°C the catalyst has a very low but constant activity of 0.22 cm C,/

80



g Rh.s, and a selectivity of only 1.5.

Tri(p-methoxyphenyl)phosphine, T JJ. - 125.8 C

At 140°C activation takes as long as 1 90 hrs in which period the activity3 =

gradually increases to at most 36 cm C /g Rh.s. Hereafter, the activity begins

3 =to decrease, reaching a level of 30 cm C /g Rh.s after 26 0 hrs streamtime. The

selectivity is 5.5.

Tribenzylphosphine, T ^,= 155 C

At 117°C the catalyst activates slowly to a stable level of 3.6 cm C /

g Rh.s in 170 hrs; the selectivity is 1.9. At 14 0°C the catalyst is stable for

more than 22 hrs. Between 90 and 14 0°C the apparent activation energy is only

37.5 kj/mol. The selectivity is invariably 1.9.

Tri(o-methoxyphenyl)phosphine, T ., - 190 C

Between 90 and 139°C the catalyst deactivates continuously. At 119°C, for

instance, the activity decreases from 0.4 to 0.3 cm C~/g Rh.s in 70 hrs. The

selectivity diminishes from 4 to 2 in the same period.

4, Discussion

A heterogeneous hydroformylation catalyst to be used in industrial practice

should possess a high activity and selectivity, while a stable activity at 90 °C,

and by preference at higher temperatures, is a prerequisite. At the reaction

temperature the solvent ligand should have a low volatility. Among the limited

number of phosphines tested in this study, we therefore recommend the following

phosphines as suitable solvent ligands in supported liquid phase rhodium

catalysts for the hydroformylation of propylene:

- tri(p-tolyl)phosphine: stable catalytic performance up to 139°C; high3 =

activity (78.0 cm C /g Rh.s)* and selectivity (6.9)*.

- S( + )-(2-phenyll)Utyl)diphenylphosphine: stable catalytic performance up to

112°C; high activity (7.4 cm C"/g Rh.s) and selectivity (7.8) at 90°C and

low carbon monoxide partial pressure (0.049 MPa ).

- tri(2-cyanoethyl)phosphine: stable catalytic performance up to 130°C; low3 =

activity (0.68 cm C /g Rh.s)* and high selectivity (8.6)*.

'^)Activity and selectivity at 1.57 MPa total pressure and at the temperature

indicated in the text.

81



- tribenzylphosphine: stable catalytic performance at 1 40 °C; high activity3 -

(7.0 cm C /g Rh.s)* and low selectivity (1.9)*. Owing to the high volatility

(Fig. 1) not applicable at high temperature.

- tri(p-methoxyphenyl)phosphine: stability at 140°C still uncertain; high

activity (36 cm C"/g Rh.s)* and selectivity (5.5)*.

- triphenylphosphine: stable catalytic performance up to at least 106.8°C; high

3 =activity (16.2 cm C /g Rh.s)* and selectivity (11.5)* (see part V of this

series). Owing to the high volatility not applicable at high temperature

(Fig. 1 ) . , -

It must be emphasized, however, that the above-mentioned phosphines have

only been tested at on e olefin-carbon monoxide-hydrogen ratio, while

particularly the carbon monoxide partial pressure may have a definite influence

on both activity and selectivity. Therefore, to select the optimum solvent

ligand, the above-mentioned phosphines should be further investigated under

other reaction conditions.

Not suitable as solvent ligands at 90°C are triphenylarsine, triphenyl

amine, triphenylbismuth and triphenylphosphine oxide. These compounds yield

deactivating catalysts, most probably owing to their weak coordination to the

rhodium complexes [9 ] .

The low activity of bis(l,2-diphenylphosphino)ethane is due to its strong

chelating coordination to the rhodium complex [10,11], which hinders

coordination of the reactants. The same may hold for tri(2 -cyanoethyl)-

phosphine.

Although not experimentally verified, the deactivation of the catalysts at

high temperatures is probably due to metallation of the coordinated ligands by

the rhodium metal, a phenomenon extensively described in the literature for

many tertiary phosphines [12-16]. The rate of metallation and, hence, the rate

of deactivation of the catalyst, depends on the type of phosphine and on the

reaction conditions such as temperature and hydrogen pressure. Tri(o-methoxy-

phenyl)phosphine and tri(a-naphthyl)phosphine, for instance, are readily

metallated (see Fig. 3) and, therefore, cause already deactivation at 9 0°C. If

use is made of ligands forming strained four-membered rings (Fig. 3 ) , e.g. tri-

(p-tolyl)phosphine, deactivation does not set in until above 140°C. It should

be noted that this deactivation of rhodium catalysts in the hydroformylation

of propylene above 15 0°C, has also been observed by Wilkinson [17] and Olivier

[18].

*) Activity and selectivity at 1.57 MPa total pressure and at the temperature

indicated in the text.

82



Rh H

P

OCH3 "CH3

Figure 3 Metallation of tri(a-naphthyl)phosphine (a) and tri(p-tolyl)phosphine

( b ) .

Furthermore, no simple correlation has been observed between the activity

or selectivity for propylene hydroformylation and the steric or electronic

parameters of the various phosphines [ 9 ] , probably because the properties of

the ligands can only be described by a combination of steric and electronic

parameters. Moreover, Clark [19] demonstrates that the situation is even more

complex, because the steric demand of a phosphine molecule stronly depends on

the type of organometallic complex onto which it is coordinated. The cone angle

of tripher.yli)hosphine, for instance, varies from 95 to 15 3 degrees.

A c k n o w l e d g e m e n t s

We thank DSM, Geleen, the Netherlands, for loan of tri(biphenyl)pnospliine

and S(+)-(2-phenylbutyl)diphenylphosphine.


for Chemical Research (SON) with financial aid from the Netherlands Organiza

tion of the Advancement of Pure Research (ZWO).

S y m b o l s

The symbols used in this paper are explained in parts I, II and III of this

series.

83



References

1. L.A. Gerritsen, A. van Meerkerk, M.H. Vreugdenhil, J.J.F. Scholten, part I

of this series, submitted for publication in J. Mol. Catal.


series, submitted for publication in J. Mol. Catal.

3. L.A. Gerritsen, J.M. Herman, J.J.F. Scholten, part III of this series,



7712648 (1977) and 7902964 (1979).


2802276 (1978).

6. P.W.H.L. Tjan, Ph.D. thesis. Delft, The Netherlands, 1976.

7. M.V, Forward, S.T. Bowden, W.J. Jones, J. Chem. Soc, (1949), S 121.

8. D.E. Worrall, J. Am. Chem . Soo. 52_, (1930), 2933.

9. C A . Tolman, Chem. Rev. T]__, (1977), 314.

10. A.R. Sanger, J. Mol. Catal. 3 , (1977/78), 221.

11. A.R. Sanger, J. Chem. Soc, Chem. Comm ., (1975), 895.

12. W. Keim, J. Organometal. Chem. 1£, (1968), 179.

13. W. Keim, J. Organometal. Chem. 19 , (1969), 161.

14. J.M. Duff, B.L. Shaw, J. Chem. Soc. Dalton, (1972), 2219.

15. G.W. Parshall, W.H. Knoth, R.A. Schunn, J. Am. C hem. Soc 91^, (1969), 4990.

16. C E . Jones, B.L. Shaw, B.L. Turtle, J. Chem. Soc Dalton, (1974), 992.

17. C.K. Brown, G. Wilkinson, J. Am. Chem. Soc. (A), (1970), 2753.

18. K.L. Olivier, F.B. Booth, Am. Chem. Soc, Petr. Div. Prepr. 14_ (3), (1969),

A7.

19. H.C Clark, Isr. J. Chem. 15_, (1976/77), 210.

84



C H A P T E R 6

HYDROFORMYLATION WITH SUPPORTED LIQUID PHASE RHODIUfI CATALYSTS

Part V. The Kinetics of Propylene Hydroformylation *)

by

L.A. Gerritsen, W. Klut, M.H. Vreugdenhil and J.J.F. Scholten,



Julianalaan 136,


Summary

We studied the kinetics of the heterogeneous hydroformylation of propylene,

using hydridocarbonyltris(triphenylphosphine)rhodium(I), dissolved in tri

phenylphosphine and capillary condensed into the pores of a support, as a

catalyst.

The results can be described by the power rate eq uation:

r =k^.[Rh].p«^.pJ^.p^Q.exp (- E^/R T),

where E , the apparent activation energy, is equal to 7 9.1 kJ/ mol, and the

reaction orders a, b and a are 1.03, 0.09 and 0.23 respectively. The reactionorder in carbon monoxide, a, is pressure dependent, and at carbon monoxide

pressures above 0.15 MPa equal to 0.08. [Rh] is the rhodium complex concentra

tion in PPh,.

The selectivity towards n-butyraldehyde is not influenced by the hydrogen

and propylene pressures, but varies strongly with the partial pressure of

carbon monoxide. When this partial pressure is lowered from 0.52 to 0.05 MPa,

the selectivity increases from 10 to 3 0. Similarly, an increase in temperature

from 70 to 106.8°C raises the selectivity from 6.7 to 11.5.

With Kieselguhr and polystyrene-2 0% divinylbenzene (XAD-2) being used as

catalyst supports, the rate of reaction is first order in rhodium complex


85



concentration in the solvent ligand PPh,.

The kinetics differ significantly from those found in homogeneous hydro

formylation in, for instance, toluene.

1. Introduction

In the preceding parts of this series [1 ,2,3,4 ] and in the relative patents

[5,6] the preparation and characterization of supported liquid phase rhodium

catalysts have been described, together with their performance in the hetero

geneous hydroformylation of ethylene and propylene at 90-199°C and 1.2-1.57 MPa

total pressure. We also discussed the influence of such parameters as the type

of support, the degree of liquid loading, the type of tertiary phosphine and

the introduction of certain organic additives into the catalyst solution.

The present paper deals with the kinetics of the hydroformylation of

propylene by means of SLP rhodium catalysts. Attention will be paid in

particular to the question in how far the kinetics differ from those found in

homogeneous catalysis with rhodium complex dissolved in, for instance, benzene

or toluene; in SLP catalysis using P Ph, as a catalyst solvent we are dealing

with heterogeneous hydroformylation (see part II of this series).

2 . Experimental

The preparation and characterization of the catalysts, as well as the

continuous-flow apparatus for measuring the catalytic performance, have been

described in part I of this series. For the chemicals and supports used see

part I and part III, respectively.

3. Results

3.1. Diffusional retardation

To find out if, and to what degree, the reaction rate is retarded by porediffusion, the activity and selectivity for propylene hydroformylation were

determined for two silica 000-3E catalysts with different mean particle

diameters: 0.46 mm (the usual size) and 3.22 mm. The mean pore radius, r , of

2 "

silica 00 0-3 E is 5.7 nm, and the BET surface area 203 m /g (see part III).

86



After being loaded with the catalyst solution (6 = 0.56), the BET surface area2

of both catalysts is 39 m /g cat.

6

4

2

00 100 200 300 400

^tjj (hrs)

Figure 1 Activity and selectivity in propylene hydroformyla

tion as a function of time, for two catalyst

particle diameters.

P = 1.57 MPa; Cj/H^/CO = 1/1/1; t = 90°C; W/F =

0.987 X 10 ' g Rh.s/cm^ c3

Catalyst: silica 000-3E; 6 = 0.56; [Rh] = 5.5 mol/m ;

P/Rh = 744 mol/mol.

The r e s ul t s (Fig. 1) show th at th e ca ta l yt ic a c t i vi t y is not influenced by

the pa r t i c l e diamete r, proving th at in th ese mesoporous s i l i c a 000-3E supported

ca ta ly sts t he chemical re ac ti on ra te i s not slowed down by pore di ffus io na l

effects.

Also when the catalyst is supported on Kieselguhr MP-99 (<5 = 0.44, [Rh] =3

5.7 mol/m ) , the activity and selectivity in propylene hydroformylation are

independent of the particle diameter between 0.46 and 2.61 mm; this is in

conformity with the macroporous texture of Kieselguhr (r = 248 nm, S„„_ = 18-J p Bhl

m /g; see part III).

Furthermore, calculations by Chu's method [ 7 ] , demonstrate the non

occurrence of diffusional retardation in the film around the catalyst particle.

SLP hydroformylation being heterogeneous in nature (see part II),

diffusional retardation in the liquid catalyst solution need not be considered.

87





Table 1 Influence of the rhodium complex concentration on the activity and

selectivity for propylene hydroformylation

[Rh]* P/Rh rgg S

(mol \ / mol \ / cm-5 C

m / y mol / \ g Rh.s

5.7 719 6.12 8.9

10.1 406 5.26 9.8

28.2 148 5.96 9.0

84.7 51 6.27 9.5

100 .0 4 4 5.95 9.5

a: reaction conditions: P = 1.57 MPa; c /H2/C0 = 1/1/1; t = 90°C; W/F = 0.981x

10"^ g Rh.s/cm^ c"

b\ concentrations based on the weight of rhodium complex used in the catalyst

preparation; these are not equal to the actual concentrations because of

adsorptive withdrawal of rhodium complexes onto the pore walls (see part

III).

As is seen in Table 1, the activity per g of rhodium is independent of the

rhodium complex concentration, which means that the activity per unit volume

of catalyst solution is first order in rhodium complex concentration; further

more, the selectivity also proves to be independent of the rhodium complex

concentration.

With macroreticular polystyrene-20% divinylbenzene, XAD-2, being used as a

support, the activity and selectivity are neither influenced by changes in3

rhodium complex concentration between 5.5 and 50.1 mol/m .

When the rhodium complex concentration of a silica 000-3E supported

catalyst is increased over the same range, no simple first-order relation is3

found to exist; at 50.1 mol/ m the activity per g of rhodium is twice higher

than expected. This is because the adsorptive interaction between the rhodium

complex and the surface of the silica support exceeds the interaction on the

two supports mentioned above, as is illustrated by the different shape of the

adsorption isotherm of the rhodium complex (see part III, Fig. 2 ) . Whereas in

the tests with Kieselguhr MP-99 and XAD-2 we operated in the linear range of

the isotherms, the measurements on the silica 00 0-3 E supported catalysts we

carried out also outside this range. Therefore, in the latter case, a

correction has to be made for the lower extent of adsorption of rhodium

complexes at the higher rhodium concentration.

89



The observed orders in rhodium complex concentration on XAD-2 and

Kieselguhr MP-99 point to a linear relationship between the concentration in

the bulk of the PPh, and at the phase boundary gas-PPh,.

3.4 Temperature dependency

The apparent activation energy was determined from an Arrhenius plot (Fig.

3 ) . The melting point of the catalyst solution in Kieselguhr MP-99 was found to

be 74 .7°C (see part II) , which points to a phase transition of the catalyst

solution within the temperature range investigated (50.5 to 106.8°C).

4

2

0

-2

2 6 2 8 3 0

^ J-x 10^ (K-'')

Figure 3 Arrhenius pl ot for propylene hydrofo rmylation.

P = 1.57 MPa; Cj/Hj/CO = 1/ 1 /1 ; t = 50 .5 - 106.8°C;

W/F = 0.98 1 X 10-3 g Rh.s/cm' C^.

C ata ly st: Kieselguhr MP-99; 6 = 0.44 ; [Rh] = 1 0 .1

mol/m^; P/Rh = 406 mol/mol.

F i g . 3 shows tha t the apparent ac t i va t i o n e n e r g y i s c o n s t a n t ( 7 9 . 1 k J / m o l )

be tween 50 .5 and 106 .8°C. The a b se n c e o f an a c t i v i t y j um p a r o u nd t h e m e l t i n g

p o i n t o f t h e c a t a l y s t s o l u t i o n i s t o b e a s c r i b e d t o the he terogeneous n a t u r e o f

t h e h y d r o f o r m y l a ti o n r e a c t i o n ( s e e a l s o p a r t I I ) .

T he t e m p e r a t u r e s t r o n g l y i n f l u e n c e s t h e s e l e c t i v i t y ( F i g . 4 ) . I t i s se en

t ha t b el ow 70 °C t h e s e l e c t i v i t y i s t e m p e r a t u r e i n d e p e n d e n t , w h e r e a s a b ov e 70°C

i t s t r o n g l y i n c r e a s e s .

90

l n ( r )

\

I i m e l t

\' I



12

10

8

6

'320 340 360 38 0-* T (K)

Figure 4 Selectivity as a function of temperature.

Reaction conditions and catalyst as in Fig. 3.

3.5 Influence of the partial pressures of hydrogen, carbon monoxide and

propylene.

The reaction rate and the selectivity were determined as functions of the

partial pressure of each reactant. By admixing the appropriate amount of helium,3the total flow rate was kept at 2.25 cm /s and the total pressure at 1.57 MPa.

In this way, one of the partial pressures could be varied, while the other two

were held constant at 0.52 MPa. Similarly, the partial pressures of hydrogen

and carbon monoxide were varied from 0.05 to 0.52 MPa , and that of propylene

from 0.20 to 0.52 MPa. The results are presented in Fig. 5.

By means of the least squares method, the results were fitted into a power

rate equation of the form:

, a b a

^ = ^ • P C I P H ^ P C O

The reaction orders are compiled in Table 2.

We also made a purely phenomenological distinction between the reaction

rates for n- and isobutyraldehyde formation in the following way:

S

n = ^TT • ^

and1

T = • T

ISO S + 1

The reaction orders for r and r. are also presented in Table 2.

n IS O '^

91

- s rrioC\

\mo\J /

r/

http://mo/J

http://mo/J

http://mo/J



2 0

1-5

1 0

-~ In (P |)

F ig u r e 5 R e a c t i o n r a t e f o r p r o p y le n e h y d r o f o r m y la t i o n a s a

f u n c t i o n of t h e p a r t i a l p r e s s u r e s o f t h e r e a c t a n t s .

X = ca rbon m onoxide ; o = hydrogen , • = p ro py le ne .

P = 1.57 MPa; t = 90 °C .

C a t a l y s t : Kie se lgu hr MP-99 ; 6 = 0 .4 4 ; [Rh] = 5 .5

mol/m ; P/Rh = 744 m ol/m ol.

T a b l e 2 R e a c t i o n o r d e r s f o r p r o p y l e n e h y d r o f o r m y l a t i o n a t 9 0 °C

p ^ Q ( <0 .1 5 M P a ) p^Q (>0 .15 MPa)

r

^ n

r .

1 .0 3

1 .04

0 . 9 9

0 . 0 9

0 . 0 9

0 . 0 6

0 . 2 3

0 . 2 2

0 . 6 6

0.08

0 .03

0 .66

The reaction order in propylene is about one, that in hydrogen close to

zero. The reaction order in carbon monoxide is a function of the carbon

monoxide partial pressure, and changes from 0.23 at low carbon monoxide

pressure to 0.08 at high CO pressure.

The influence of the various partial pressures on the selectivity is given

in Fig. 6.

It is seen that the selectivity strongly increases at low carbon monoxide

partial pressures. The hydrogen and propylene partial pressures hardly

influence the selectivity.

92



o 0-15 0-30 0-45

-^ P| (MPa)

Figure 6 Selectivity as a function of the partial pressures

of the reactants at 90°C.

X = carbon monoxide; o = hydrogen; • = propylene.

Catalyst and reaction conditions as in Fig. 5.

It was further found that at a hydrogen partial pressure of 0.21 MPa in

stead of the usually employed 0.52 MPa, the reaction orders in carbon monoxide

were equal to those given in Table 2. This furnishes additional proof that the

kinetics are not influenced by the hydrogen partial pressure.3

With XAD-2 being used as a support (6 = 0.65 ; [Rh] = 5 . 5 mol/m and P/Rh =

744 mol/mol) the reaction orders appeared to be equal to those indicated for a

Kieselguhr supported catalyst in Table 2.

4. Discussion

Diffusional retardation being absent (see section 3 .1 ), we can directly

proceed with a discussion of the kinetics.

The most interesting observation is the broken order in carbon monoxide

pressure (c = 0.2 3), which tends to the much lower value of 0.08 at CO partial

pressures above 0.15 MPa. Moreover, the selectivity towards normal butyralde

hyde strongly increases with decreasing CO pressure, which is of great

significance, both from a practical and from a theoretical point of view. As we

see it, these facts are to be explained as follows.

In a catalyst solution several different rhodium complexes are in

equilibrium [8 ] :

93



CO CO

RhH(PPh3)^ J RhHC0(PPh3)j t RhHCO(PPh2)2:^ RhH(CO)2(PPh5)2 ^ RhH(CO)2PPh2

PPhj PPhj - PPhj

(A) (B) CC) (D) (E)

Wilkinson [9,10,11], in studying the homogeneous hydroformylation with

RhHCO(PPh,), dissolved in benzene or toluene, proved that the complexes C, D

and E are catalytically active. For reasons to be advanced later in this

discussion, complex B may in the presence of a large excess of PPh, and in the

absence of other solvents, as used by us, also contribute considerably to the

total activity.

IVhen PPh- is used as a solvent, triphenylphosphine strongly competes with

carbon monoxide for coordination with rhodium(I). The lower the CO partial

pressure, the higher the degree of PPh,-coordination, and, in line with what is

known about the role of the PPh,-coordination in homogeneous hydroformylation

[9,12], the higher the selectivity towards normal butyraldehyde and the slower

the rate of reaction.

From spectroscopic studies [10 ] we know that in homogeneous hydroformyla

tion addition of CO to the alkyl complex, Rh(C,Hy)C0(PPh,)2, and subsequent

insertion of the CO, is a very fast reaction, and that the order in carbon

monoxide is zero or even negative [9,12,13]. In our heterogeneous case the same

will be true, but the zero-order dependency is obscured by the positive

influence the increase in CO partial pressure has on the formation of lower

PPh,-coordinated complexes and, hence, on the rate of reaction. Of course, at

higher CO partial pressures, this effect levels off, which is in line with our

observation above a CO partial pressure of 0.15 MPa.

The rate of reaction is about zero order in hydrogen, contrary to what is

found in homogeneous hydroformylation, where the oxidative hydrogen addition to

the acyl complex (Rh(COC,H-,)CO(PPh,) , with x = 1 or 2) is generally considered

to be rate-determining, the reaction being first order in hydrogen. Hence, in

the case of the PPh,-rich complexes dissolved in an excess of PPh, (P/Rh = 744

mol/ mol) with which we are dealing in this study, hydrogen addition has to be

rejected as the rate-determining step.

The rate of reaction was found to be first order in propylene; therefore,

TT-addition of propylene to the PPh,-rich complexes is most probably rate-

determining. Obviously, for steric and electronic reasons, addition of

propylene proceeds slowly in systems with a high PPh, coordination.

It is interesting to note that Cavalieri d'Oro et al [ 1 4 ] , in studying

homogeneous hydroformylation with a relatively large excess of PPh , in toluene

94



(P/Rh = 150 mol/mol), also arrived at a rate of reaction that is zero-order in

hydrogen pressure, whereas the orders in propylene and carbon monoxide were

0.55 and -0.09 respectively.

Furthermore,within the range of pressures investigated the propylene and

hydrogen pressures hardly influence the position of the equilibria between the

various complexes, and therefore have no effect on the selectivity. This also

accounts for the constancy of the reaction order in carbon monoxide upon a

variation in hydrogen pressure.

In view of the remarkable difference with the kinetics of homogeneous

hydroformylation (where especially complexes D and E, and possibly C, are known

to be active) we presume that in the presence of a large excess of PPh, and in

the absence of other solvents, we are dealing with kinetics related with

catalysis by higher PPh,-coordinated complexes: complex C, but in particular

complex D, might play a dominant catalytic role under these conditions. However,

definite clarity on this point can only be obtained through combination of more

extensive kinetic measurements (especially covering a larger range of carbon

monoxide pressures) with in situ spectroscopic studies of the complex

structures.

Acknowledgements


for Chemical Research (SON) with financial aid from the Netherlands Organiza

tion for the Advancement of Pure Research (ZWO).

List of symbols

a, b, a reaction order

E apparent activation energy kJ/mol2 3F flow of olefin at 0.1 MPa and 25°C cm /s

P total pressure MPa

P/Rh molar phosphine to rhodium ratio mol/mol

p partial pressure MPa

[Rh] rhodium complex concentration in PPh at 90 °C mol/m

R gas constant J/mol.K

I3 _r reaction rate cm C /g Rh.s

r mean pore radius nm

P

95



3 = 3r' reaction rate cm C /m PPh-.s

5 selectivity = n/iso —

T absolute temperature K

t temperature °C

t, streamtime hrs

d

W weight of rhodium metal in the reactor g

6 degree of liquid loading at 90 °C —

References

1. L.A. Gerritsen, A. van Meerkerk, M.H. Vreugdenhil, J.J.F. Scholten, part I

of this series, submitted for publication in J. Mol. Catal.



3. L.A. Gerritsen, J.M. Herman, J.J.F. Scholten, part III of this series,


4. L.A. Gerritsen, W. Klut, M.H. Vreugdenhil, J.J.F. Scholten, part IV of this



771 264 8 (1977) and 7902 964 (1979).

6. L.A. Gerritsen, J.J.F. Scholten (Stamicarbon B . V . ) , German Patent Appl.

2802276 (1978).

7. C.J. Chu, J. Kalil, W.A. Wetteroth, Chem. Eng. Progr. A9_, (1953), 141 .

8. D. Evans, C Yagupsky, G. Wilkinson, J. C hem. Soc (A), (1968), 2660.

9. C.K. Brown, G. Wilkinson, J. C hem. Soc (A), (1970), 2753.

10. C Yagupsky, C.K. Brown, G. Wilkinson, J. Chem. Soa. (A), (1970), 139 2.

11. D. Evans, J.A. Osborn, G. Wilkinson, J. Ch em. Soc (A), (1968), 3133.

12. J. Hjortkjaer, J. Mol. Catal. S_, (1979), 377.

13. K.L. Olivier, B.L. Booth, Am. Chem. Soc, Petr. Div. Prepr. j£(3), (1969),

A7.

14. P. Cavalieri d'Oro et al. Proa. Symp. Homog. Catal., Veszprem, (1978), 76.

96



C H A P T E R 7

Optimum Conditions for Propylene Hydroformylation with SLP Rhodium Catalysts.

Comparison between a Future SLPC Process and the Low Pressure Oxo Process.

1. Introduction

The foregoing Chapters extensively dealt with the various catalytic and

process parameters in SLPC hydroformylation. In the present Chapter we shall go

into the question as to which parameters are to be preferred from a technical-

economic point of view, for a future SLPC hydroformylation process.

While the research work described in this thesis was in progress. Union

Carbide Corp., USA, disclosed more detailed information about another new

hydroformylation process for the catalytic production of aldehydes. In this so-

called Low Pressure Oxo Process (LPO process) [1] Wilkinson's hydroformylation

catalyst is applied homogeneously in a gassparged reactor instead of hetero-

geneously in a fixed bed as in our case. The merits of this process will be

compared with those of the heterogeneous SLPC process.

97



2 . Optimum conditions for propylene hydroformylation with SLP rhodium catalysts

2.1 The Support

In Chapter 4 it has been explained why supports ensuring a large surface

area of the gas-PPh, phase boundary and a low degree of adsorptive withdrawal

of rhodium complexes are to be preferred. Some examples are silica 00 0-3 E, de

hydroxylated silica (silica S) and the macroreticular polystyrene-2 0% divinyl

benzene XAD-2.

When the commercially available silica 000-3E is used as support material,

the catalyst can be further improved by silanizing the silica surface with tri-

(ethoxy)phenylsilane, or by adding aldol condensation products or polyethylene

glycol to the catalyst solution beforehand. This treatment reduces the

activation time of the catalyst to a few hours and, moreover, enhances the

activity per g of rhodium and the selectivity towards n-butyraldehyde.

XAD-2, although satisfying the above-mentioned requirements, attaches

several drawbacks: a lower thermal conductivity and a greater brittleness than

silica 000-3E, as well as a possible collapse of its texture around 150°C.

Silica S is a very attractive alternative, but not yet available

commercially.

Accumulation of high-boiling aldol condensation products in the pores of

the support should be avoided because this may give rise to catalyst caking

and rinsing-out of the catalyst solution. As stated in Chapter II, the various

supports generally show a far higher activity for aldol condensation than

either the rhodium complex or the PPh,. By using a sodium-poor support without

strong acidic sites, as e.g. sodium-poor silica S and XAD-2, the aldol

condensation activity can be largely suppressed.

Having chosen an optimum support on the basis of the above considerations,

one might try to adapt the texture of the support as best as possible to the

technical-economic requirements.

Macroporous supports with a small surface area offer the advantage of a

low degree of adsorptive complex withdrawal from the solvent ligand while,

moreover, the unwanted capillary condensation of the products (the aldehydes)

will take place only at a relatively high aldehyde partial pressure in this

class of supports (Kelvin's la w) . On the other hand, they have the disadvantage

of creating a small surface area of the gas-phosphine phase boundary per unit

volume of catalyst solution, while the decrease in PPh, vapour pressure (by

98



which drying-up of the catalyst and phosphine poisoning of the aldehydes is

suppressed) is much smaller than in the application of microporous supports.

Probably, the best choice will be a texture with characteristics in between

these two extremes. Therefore we prefer mesoporous supports with pore r;idii in

the range from 5 to 20 nm.

Of course, physical charaateristios, like hardness and resistance against

attrition, electrostatic charge build-up and heat conductivity, are important

as well. Kieselguhr is probably too soft a material, whereas XAn-2 has limited

heat conductivity and stability. In view of the foregoing, sodium-poor hydro

phobic a-alumina - a very hard material - certainly also deserves consideratioa

2.2 Degree of liquid loading

In Chapter 4 of this thesis we argued that when silica is used as a support,

degrees of liquid loading in the intermediate range from 0.3 to 0.75 warrant

the highest activity pe r gram of rhodium; it will be obvious that this is

important for the rhodium economy of the process. However, realization of a

minimum reactor volume calls for maximum activity pe r unit of catalyst volume;

the degree of liquid loading should then be taken as high as possible (see Fig.

1 ) . A technical-economic optimalization has still to be made; for the time

being we advise 5-values of around 0.7.

Finally, we have to bear in mind that at high degrees of loading the

capillary forces by which the catalyst solution is fixed in the pores are

relatively weak, so that for technical reasons too high 6-values should be

avoided.

2.3 Rhodium concentration

Using silica 000-3E as a support we found that when the rhodium concentra

tion in PPh, is increased from 5.5 to 50.1 mol/m , the catalytic activity for

• 3 =

propylene hydroformylation goes up from 4.1 to 8.9 cm C /g Rh.s (Chapter 6 ) ,

meaning that the reactor volume can be reduced by a factor of (50.5/5.5) x

(8.9/4.1) = 19.8. Tests with Kieselguhr MP-99 have shown that the rhodium

3concentration can oven be increased as high as 100 mol/m .

The best choice for technical applications has not yet been made; this

calls for further study. Of course, too high a rhodium concentration might

cause an unacceptably high heat generation per unit of reactor volume, while

too low a P/Rh ratio involves the hazard of destabilization of the catalyst.

99





2.5 Degree of conversion

In order to arrive at a minimum recycle, the conversion per pass should be

as high as possible. The degree of conversion, however, has to be kept just

below the value at which capillary condensation of the aldehydes sets in. This

maximum allowable degree of conversion depends on the reaction temperature, the

partial pressure of olefin, the texture of the catalyst and, of course, on the

volatility of the aldehydes. For instance, in propylene hydroformylation at

90°C and 1.57 MPa total pressure (C~/H2/C0 = 1/ 1 / 1), and using a catalyst with

a mean pore radius of 10 nm, the maximum degree of conversion is calculated to

be 21.4%, while in ethylene hydroformylation the upper limit is 45.7%. In

practice, we recommend to adjust the degree of conversion at 8 0 % of the

calculated maximum value.

2.6 Reaction conditions and feed composition

As explained in Section 2.4 above, the reaction temperature should be as

high as possible: with tri(p-tolyl)phosphine as solvent ligand a temperature of

up to 1 40°C is applicable, while with triphenylphosphine the temperature should

not exceed 100°C.

The reaction rate equation for propylene hydroformylation reads:

I , rnl,1 r ll-03 r ,0.09 r lO.23 -0.0 8 , ^nmn/n-rl

r' =k-[Rh]-[p^^] ' [ P H ] ' [Pco^ '^^P ^~ 79100/RT),

and the selectivity strongly increases on lowering the carbon monoxide partial

pressure (Chapter 6 ) . Hence, in order to achieve a high activity and

selectivity, the propylene pressure should be as high as possible, whereas the

carbon monoxide and hydrogen pressures should be low. A disadvantage of such

conditions is the accessory low maximum allowable degree of conversion.

The feed has to be purified from oxygen (which oxidizes the PPh ) over a

Cu-on-alumina catalyst. Highly unsaturated compounds, such as acetylene,

propyne and butadiene, may strongly coordinate with rhodium and have to be

removed by selective hydrogenation over a Pd-Cr-on-alumina catalyst [ 1 ] .

Sulphur compounds, such as hydrogen sulphide and carbonyl sulphide should also

be removed [2] .' The choice between technical grade (about 7 % propane) and

polymer grade (<0.5% propane) depends on technical-economic considerations.

101



3 . C o m p a r i s o n of t h e S L P C p r o c e s s and t h e L P O p r o c e s s

Since 19 7 1, Union Carbide Corp., Johnson Matthey § Co. Ltd. and Davy

Powergas Ltd., have been developing a new Low Pressure Oxo process (LPO), using

RhHCO(PPh-), as a catalyst. In 1975 the process was commercially applied for

the first time.

The details of the LPO process were published in 197 7 [ 2 ] ; the flow diagram

is shown in Fie. 2.

Purge gas

r^r^

Aldehydes

Figure 2 Flow diagram of the LPO-process.

Propylene and synthesis gas are purified (A) and combined with recycle gas. The

combined gas stream is fed through a gas distributor into the stainless steel,

cylindrical hydroformylation reactor (B) , which is filled with a catalyst

solution composed of RhHCO(PPh,), and free triphenylphosphine dissolved in a

mixture of butyraldehydes and high-boiling aldol condensation products from

aldehyde trimerization. The composition of the catalyst solution is as follows

[ 3 ] : Rh-metal 27 .5 x 10'-^ w%, PPh^ 7.5 w%, butyraldehydes 35 w%, trimers 50 w%

and other high-boiling products 7.5 w%. These figures show that the rhodium3

concentration is only 2.3 mol/m , the P/Rh ratio 1 07 mol/mol and the total

weight of rhodium present in the reactor 9.82 kg. The total volume of catalyst

3 3

solution is 42 m ; the reactor volume is 86 m (diameter 3.90 m and height

7.20 m ) . The temperature in the reactor is 95°C and the total pressure is 1.5

M P a . The liquid contents are kept constant by so adjusting the flow rate of the

recycle gas stream that the amount of aldehydes removed just balances the

amount of aldehydes produced. If, nevertheless, high-boiling products

accumulate in the reactor, part of the catalyst solution is withdrawn from the

reactor into the catalyst system (G) , where the rhodium complex is recovered

and recycled to the reactor. If the rhodium complex has lost its activity, the

102



catalyst solution is withdrawn, concentrated and recovered.

The gaseous effluent is passed through a liquid separator (C) that minimizes

rhodium losses, and from there through a condenser (D) to a product surge tank

(E). The overhead gas stream is passed through a liquid separator (F) and is

recycled to the hydroformylation reactor. Part of the recycle stream is purged

to control the level of inerts in the process (propane, methane and carbon

dioxide). The liquid effluent from the product surge tank goes into a

distillation train where propylene, propane, isobutyraldehyde, n-butyraldehyde

and high-boiling products are separated.

The compositions of various streams are given in Table 1.

Table 1 Compositions of various streams in the LPO process

Compound

hydrogen

carbon monoxide

propylene

propane

methane

n-butyraldehyde

isobutyraldehyde

carbon dioxide

aldol products

*

(mol %)

90.0

10.0

^2(mol %)

54.0

45.5

0.5

0.01

S3

(mol %)

48.3

9.9

20.5

14.3

3.7

1.8

0.3

1.2

h(mol %)

50.9

4.7

14.9

14.6

3.9

8.8

1.0

1.2

^5

(mol %)

54.7

6.1

14.9

15.8

4.3

2.5

0.4

1.3

^6(mol %)

0.01

0.06

4.82

4.40

0.08

82.59

7.14

0.39

0.52

') S^: 21 00 kg/hr; S2: 3900 kg/ hr; S^: 264 00 kg/hr; S^: 264 00 kg/hr; S-: 204 00

kg/hr; S,: not given.

The production of butyraldehydes, calculated from streams 3 and 4 , amounts

to 559 0 kg/hr of n-butyraldehyde and 550 kg/hr of isobutyraldehyde (total

production 49 12 0 x 10 kg/year). Consequently, the selectivity is 10.2 and the

activity 0.248 mol C,/mol Rh.s. The degrees of conversion of the reactants are

as follows: propylene: 33.4%, hydrogen: 3.5% and carbon monoxide: 56 .5%.

In order to compare these activity and selectivity values with those in the

SLPC process, we now calculate the reaction rate and the selectivity of the

SLPC process for the conditions of the LPO process (p„= = 0.266 MPa, p =

103



0.744 MPa, P„„ = 0.110 MPa, T = 368 K ) , using the kinetic data given in Chapter

6. Starting from an activity of 8 cm" C"/g Rh.s and a selectivity of 8.5 for a

silica SLPC at 90°C and 1.57 MPa total pressure (Chapter 6 ) , we found the

corresponding values under LPO conditions to equal 0.021 mol C,/mol Rh.s and

24.5, respectively.

The selectivity in the SLPC process appears to be appreciably higher, which3

is a most important feature: at a production rate of 49 12 0 x 10 kg/year of

butyraldehydes and a price difference of $ 0.21/kg between n- and isobutyr

aldehyde, the 5 w% higher selectivity towards n-butyraldehyde means a

$ 51 5,7 60 / year higher product yield from the SLPC process.

In the SLPC process the activity per mol rhodium is a factor of twelve

lower than in the LPO process. Nevertheless, the reactor in the SLPC process

can be designed to a smaller scale by using a much higher rhodium concentration3

than in the LPO process: at a rhodium concentration of 10 0 mol/m PPh,, and 70 %

liquid loading on silica 00 0 -3 E, the rhodium weight per unit reactor volume is

3 3

2.821 kg Rh/m as against 0.114 kg Rh/m in the LPO process. This means that

the reactor volume can be taken a factor of (2.821/0.114)/12 = 2.1 smaller than

in the LPO process. True, the initial rhodium investment costs are a factor of

twelve higher than in the LPO process, but against this, one should place that

the activity of the SLPC can be appreciably enhanced by choosing other reaction

conditions.

Besides the activity and selectivity, the stability of the catalyst is of

course a very important feature. The presence of a catalyst recovery section in

the LPO process suggests deactivation of the catalyst. In this context we point

out that Bryant [4] mentions a daily activity loss of at most 0.75 % calculated

on the initial activity; this corresponds to complete deactivation of the

catalyst after 3200 hrs streamtime. The SLPC, on the contrary, shows no sign of

deactivation in a period of at least 8 00 h rs , which means a further advantage

of the SLPC system.

Other advantages of the SLPC system are: no entrainment of catalyst

solution, as in the LPO process, by the gas stream leaving the reactor, and the

use of a fixed bed reactor, which is very simple to operate.

Finally, it should be noted that the hazard of phosphine getting gradually

lost by evaporation is equally great in the two processes. Although at

temperatures around 9 5°C these losses are relatively small, pre-saturation of

the feed gas stream with phosphine should be considered. Of course, application

of higher-boiling phosphines, such as tri(p-tolyl)phosphine, tri(2 -cyanoethyl)-

phosphine and S(+)-(2-phenylbutyl)diphenylphosphine would be even more re-

commendable.

104



References

1. L.A. Maddox (Celanese Corp.), German Patent Appl. 2638798 (1977).

2. R. Fowler, H. Connor, R.A. Baehl, Chem. Eng., (1977), 110.

3. E.A.V. Brewester, R.L. Pruett (Union Carbide Corp.), German Patent Appl.

2715685 (1977).

4. D.R. Bryant, E. Billig (Union Carbide Corp.), German Patent Appl. 28 02 92 3

(1978).

105



Samenvatting

In 196 5 toonde Wilkinson aan, dat hydridocarbonyltris(trifenylfosfine)-

rhodium(I), RhHCO(PPh.,),, een uitstekende homogene katalysator is voor de hy-

droformylering van olefinen tot aldehyden, ook wel de OX O-reactie genoemd:

R - CH = CH., H^ + CO

/ O

R - CH- - CH , — C (normaal)

2 2 ^ ^

(iso )

Deze homogene katalysator is reeds onder zeer milde reactieomstandigheden ac

tief en bezit een hoge selectiviteit voor de vorming van normaal-aldehyden. De

zeer hoge jirijs van het rhodium vraagt echter om terugwinning van de katalysa

tor uit de produkten. Door de homogene katalysator te heterogeniseren, kan deze

moeilijke en kostbare bewerking worden vermeden.

Dit proefschrift behandelt de bereiding en de karakterisering van een

nieuwe heterogene rhodiumkatalysator voor de hydroformyloring van etheen of

propeen, alsmede zijn gedrag tijdens lange-duurexperimenten (tot 80 0 uur) onder

technologisch realistische omstandigheden (totaaldruk: 1.2-1.57 MPa; tempera

tuur: 40-199°C).

De katalysatoroplossing, bestaande uit RhHCO(PPh-), opgelost in een wéinig-

vluchtig oplosmiddel, is geheterogeniseerd door deze te impregneren in een po

reus anorganisch of organisch dragermateriaal, waarin de katalysatoroplossing

wordt vastgehouden door sterke capillaire krachten. Dit betekent dat het prin

cipe van Supported Liquid Phase Catalysis is toegepast.

Verder is één van de liganden van het rhodiumcomplex, trifenylfosfine, ge

kozen als oplosmiddel. Niet alleen is dit een uitstekend oplosmiddel dat wéinig-

vluchtig is en de dragers bevochtigt, maar het biedt ook het voordeel dat dis

sociatie van trifenylfosfine van het rhodiumcomplex sterk wordt tegengegaan.

Hierdoor is een lieterogene katalysator verkregen, die zeer selectief n-butyral

dehyde vormt en na een beproevingsperiode van 80 0 uur nog geen enkele verminde

ring van activiteit voor hydroformyloring vertoont (Hoofdstuk 2 ) .

Uit metingen van de capillaire condensatie van stikstof a.in verse en ge

bruikte katalysatoren blijkt, dat bij niet-volledige porievulling de kleinste

poriën geheel met katalysatoroplossing zijn gevuld, terwijl de wanden van de

107



grotere poriën slechts bedekt zijn met een dunne laag gefysisorbeerde katalysa

toroplossing. Röntgen-microanalyse toont aan, dat de katalysatoroplossing homo

geen over de doorsnede van een katalysatordeeltje is verdeeld (Hoofdstuk 2 ) .

De overgang van vast naar vloeibaar trifenylfosfine, en vice versa, tijdens

de hydroformyloring blijkt geen invloed te hebben op de activiteit en de

schijnbare activeringsenergie. Hieruit volgt, dat wij te maken hebben met hete

rogene katalyse, waarbij alleen de rhodiumcomplexen aan het grensvlak tussen

gas en vloeibaar PPh,, of tussen gas en vast PPh,, bij de hydroformyleringsreac-

tie betrokken zijn. De inactiviteit van de rhodiumcomplexen in de PPh,-oplos-

sing zelf is toe te schrijven aan de sterke coördinatie van de rhodiumcomplexen

met het omringende PPh,-oplosmiddel en aan de lage oplosbaarheid van kool

monoxide in PPh,, en niet aan sterke diffusieremming van de reactiesnelheid in

de vloeistoffase. Aan het fasegrensvlak gas-PPh, echter is de coördinatiegraad

van de rhodiumcomplexen met vrij trifenylfosfine slechts half zo groot als bui

ten het fasegrensvlak. Hierdoor, en mede als gevolg van de veel hogere CO-con

centratie in de gasfase, verschuiven de evenwichten tussen de verschillende

rhodiumcomplexen naar CO-bevattende complexen die katalytische activiteit voor

hydroformylering bezitten (Hoofdstuk 3 ) .

De adsorptie van het rhodiumcomplex vanuit de trifenylfosfineoplossing op

diverse dragers is onderzocht. Vooral op silica-alumina en, in mindere mate, op

silica, blijkt het rhodiumcomplex preferent ten opzichte van PPh, te worden ge

adsorbeerd. Op macroreticulair polystyreen-20% divinylbenzeen, XAD-2, vindt

slechts geringe adsorptie plaats. Dit betekent dat de activiteit van onze kata

lysator niet alleen wordt bepaald door de grootte van het fasegrensvlak gas-

PPh-, maar ook door de mate van adsorptie van het rhodiumcomplex op de wanden

van de poriën; hoe groter het fasegrensvlak gas-PPh, en hoe zwakker de adsorp

tie, des te hoger de activiteit voor hydroformylering. Op grond hiervan kan de

lage activiteit van katalysatoren met y-^lumina en silica-alumina als drager

worden verklaard door de sterke adsorptie van het rhodiumcomplex op de Lewis-

zure centra in het oppervlak van deze dragers. De hoge activiteit met X AD-2 en,

in mindere mate, met silica' s, wordt toegeschreven aan de veel geringere ad

sorptie van het rhodiumcomplex (Hoofdstuk 4 ) .

Op een zestal dragers is de vloeistofbeladingsgraad gevarieerd. Het blijkt

dat met dragers die het rhodiumcomplex sterk adsorberen, de activiteit per gram

rhodium bij een bepaalde vloeistofbeladingsgraad door een maximum gaat. Met

XAD-2 echter neemt de activiteit per gram rhodium bij toenemende vloeistofbela-

lingsgraad continu af. Ook deze verschijnselen kunnen worden verklaard uit de

108



verandering van de uitgebreidheid van de adsorptie van het rhodiumcomplex met

de beladingsgraad en tevens uit de verandering van het oppervlak van het fase

grensvlak gas-PPh, als functie van de beladingsgraad (Hoofdstuk 4 ) .

Katalysatoren met silica en silica-alumina als drager hebben een lange ac

tiveringstijd (120 uur) . Dit wordt toegeschreven aan de geleidelijke opbouw van

een geringe hoeveelheid hoogkokende aldolprodukten, gevormd door aldolcondensa-

tie van de geproduceerde aldehyden, in de poriën van de drager. Deze aldol

produkten adsorberen via waterstofbrugvorming op de silanolgroepen aan het op

pervlak, waardoor de adsorptie van rhodiumcomplexen wordt onderdrukt en het si-

licaoppervlak van hydrofiel in organofiel overgaat. Aldus komen er steeds meer

rhodiumcomplexen aan het fasegrensvlak gas-PPh, beschikbaar, terwijl tevens dekatalysatoroplossing zich verder over de drager verspreidt. Dit resulteert in

een langzame toename van de activiteit (Hoofdstuk 4 ) .

De aanwezigheid van een geringe hoeveelheid aldolprodukten in een gebruikte

katalysatoroplossing kan met behulp van IR-spectroscopie inderdaad worden aan

getoond (Hoofdstuk 2 ) .

Een verkorting van de activeringstijd tot een paar uur en een verhoging van

de activiteit en selectiviteit, bereikt men door reeds vooraf aldolprodukten of

polyethyleenglycol aan de katalysatoroplossing toe te voegen, of door het sili-

caoppervlak chemisch te modificeren met tri(ethoxy)fenylsilaan (Hoofdstuk 4 ) .

Hoewel, zoals uit het voorgaande blijkt, de opbouw van een geringe hoeveel

heid aldolprodukt in de katalysator toelaatbaar en soms zelfs wenselijk is,

moet de aldolcondensatie toch zoveel mogelijk worden onderdrukt. Een afzonder

lijk onderzoek heeft aangetoond dat dit mogelijk is door natrium-arme silica's

of XAD-2 als drager te kiezen; PPh, en RhHCO(PPh,), bleken inactief respectie

velijk slechts matig actief te zijn voor aldolcondensatie (Hoofdstuk 2 ) .

Vanwege zijn te hoge vluchtigheid is PPh, niet bruikbaar als oplosmiddel-

ligand bij temperaturen boven 100°C. Daarom is een groot aantal andere minder-

vluchtige fosfines getoetst op hun bruikbaarheid als oplosmiddelligand in de

hydroformylering van propeen bij 80-199°C. Bij temperaturen tot 140°C blijken

tri(p-tolyl)fosfine, tri(2-cyanoethyl)fosfine en S(+)-(2-fenylbutyl)difenyl-

fosfine het meest geschikt te zijn. Boven 150°C deactiveren echter alle tot nu

toe beproefde katalysatoren, hetgeen waarschijnlijk is toe te schrijven aan me-

tallering van de gecoördineerde fosfineliganden door het rhodiummetaal (Hoofd

stuk 5) .

De kinetiek van Je heterogeen-katalytische hydroformylering van propeen met

RhHCO(PPh,), opgelost in PPh , is onderzocht. De resultaten kunnen beschreven

109





STELLINGEN

1. Het gedrag van geimmobiliseerde metaalcomplex katalysatoren dient bij voor

keur te worden bestudeerd onder dynamische condities. Bij batchgewijze expe

rimenten, bijvoorbeeld in autoclaven, bestaat het gevaar dat afspoeling van

metaalcomplexen uit de katalysator optreedt, en de invloed hiervan op de re-

. sultaten wordt onderschat.

• A.J. Moffat, J. Catal. 18^, (1970), 193.

2. De nog slechts beperkte kennis van de verdeling van vloeistoffen in poreuze

dragers vormt één van de belangrijkste hindernissen bij de beschrijving van

het gedrag van "supported liquid phase catalysts".

J. Villadsen, H. Livbjerg, Catal. Rev.-Sci. Eng. 17_ (2), (1978), 203.

•j . Het is merkwaardig dat de auteurs van Chem istry of Catalytic Processes wel

aandacht besteden aan het (niet geheel onverwachte) lineaire verband tussen

de initiële adsorptiewarmte van zuurstof op metalen en de vormingswarmte van

het corresponderende hoogste oxide van die metalen, maar niet aan het veel

belangrijker feit dat de initiële adsorptiewarmten hoger zijn dan de vor-

mingswarmten.

B.C. Gates, J.R. Katzer, G.C.A. Schuit in "(7/zemistrj/ of Catalytic Processes ,

McGraw-Hill, New-York, 19 79 , biz. 20 2.

Documents

Liquid Phase Catalyst