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    HYDROFORMYLATIONWITHSUPPORTED LIQUID PHASE RHODIUM CATALYSTS

    L A Gerritsen

    Delft University Press

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    HYDROFORMYLATIONWITHSUPPORTED LIQUID PHASE RHODIUM CATALYSTS

    oo ou o(f . ^o 1

    IPniMihiiiNiiuhii nliiiii

    o a-^ o

    BIBLIOTHEEK TU DelftP 1606 4042

    455056

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    Het onderzoek werd uitgevoerd met financ ile steun van de NederlandseOrg anisat ievo orZu iverW etens cha ppe l i jkO nde rzoek , a ls onderdeel van hetprogram ma van de Stich t ing Sc heiku ndig O nderzoek in Nederland.

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    HYDROFORMYLATIONWITHSUPPORTED LIQUID PHASE RHODIUM CATALYSTS

    PROEFSCHRIFT

    TER VERKRIJGING VAN DE GRAAD VAN DOCTORIN DE TECHNISCHE WETENSCHAPPEN AAN DETECHNISCHE HOGESCHOOL DELFT, OP GEZAG VANDE RECTOR MAG NIFICUS PROF. DR. IR. F. J. KIEVITS,VOOR EEN COMMISSIE AANGEWEZEN DOOR HETCOLLEGE VAN DEKANEN TE VERDEDIGEN OPWOENSDAG 12 DECEMBER 1979 TE 16.00 UUR

    DOORLEENDERT ARIE GERRITSEN

    scheikundig ingenieurgeboren teH.I Ambacht

    A o o b

    Delft University Press /19 79

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    Dit proefsch ri f t is goe dgek eurd do or de prom otorPROF. DR.J. J.F. SCHO LTEN

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    AanJokeAan mijn ouders

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    DANKBETUIGING

    Aan allen die hebben bijgedragen aan de totstandkoming van dit proefschriftbetuig 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 belangrijke 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 neutronactiveringsanalyse metingen, Ir. E. Izeboud, van het Laboratorium voor Organische Chemie THD, en Ir. E.B.M. Doesburg, van het Laboratorium voor Anorganische 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 enS.M.G.Nadorp, van het Centraal Laboratorium DSM te Geleen, voor de SEM en RMA opnamen, en de HerenJ. Teunisse en N. van Westen, van het Laboratorium voor Chemische TechnologieTHD,voor de vele textuurmetingen.

    - de Heer P.H. Hermans, vertaler Engels te Geleen, voor de zorgvuldige correctie van de tekst.

    - Me j. M.J.A. Wijnen, Mevr. J.P.H, de Groot-Mervel, en de heren W.J. Jongeleenen J.H. Kamps voor de nauwkeurige bewerking van het manuscript.

    - de medewerkers van de servicegroepen en diensten van het Laboratorium voorChemische Technologie voor de diverse werkzaamheden die zij ten behoeve vandit onderzoek hebben verricht.

    Het overleg met verschillende medewerkers van het Centraal Laboratoriumvan DSM te Geleen heb ik steeds zeer gewaardeerd.

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

    VI

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    CONTENTS

    SUMMARY 11.INTRODUCTION 5

    1.1 History of hydroformylation 51.1.1 Cobalt catalysis 51.1.2 Rhodium catalysis 7

    1.2 Heterogenizing of homogeneous catalysts 91.3 Supported Liquid Phase Catalysis 101.4 Objective and scope of the thesis 13References 16

    2.GENERAL DESCRIPTION OF THE SYSTEM, CATALYST PREPARATION ANDCHARACTERIZATION 19Summary 191. Introduction 202.Experimental 21

    2.1 Materials 212.2 Catalyst preparation 212.3 Catalyst characterization 222.4 Catalytic performance ' 232.5 Infrared spectroscopy 252.6 Activity tests for the unwanted consecutive reaction:

    aldol condensation of aldehydes 252.7 Neutron activation analysis 25

    3. Results 263.1 SLPC versus physically adsorbed catalysts 263.2 Comparison with Rony's SLP catalyst 273.3 Infrared spectroscopy 273.4 Aldol condensation 293.5 PPh,-distribution in the support 30

    3.5.1 Nitrogen capillary condensation and mercuryporosiraetry 30

    3.5.2 X-ray microanalysis 323.5.3 Electron I'licroscopy 33

    4. Discussion - 33Acknowledgements 38

    VII

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    List of symbolsReferences

    3. THE LOCATION OF THE CATALYTIC SITESSummary1. Introduction2. Experimental3. Results

    3.1 DSC measurements3.2 Activity measurements

    3.2.1 Influence of the PPh, phase change on activity3.2.2 Activity of a fully-loaded SLPC in ethylene

    hydroformy1ation3.2.3 Activity of a non-supported solid catalyst solution

    3.3 Surface tensions3.4 Investigation into the possibility of diffusional retardat

    of the reaction rate3.4.1 Determination of the diffusion coefficients and

    solubilities of the reactants in PPh,3.4.2 Calculations

    4. DiscussionAcknowledgementsList of symbolsReferences

    4. INFLUENCE OF THE TYPE OF SUPPORT, THE DEGREE OF PORE FILLING,ANDORGANIC ADDITIVES ON THE CATALYTIC PERFORMANCESummary1. Introduction2.Experimental

    2.1 General2.2 Modification of silica 00 0-3E2.3 Determination of adsorption isotherms of RhHCOfPPh,),on

    the supports3. Results

    3.1 Adsorption isotherms of RhHCO(PPh,;),3.2 Influence of the type of support3.3 Influence of the degree of liquid loading3.4 Shortening of the time of activation

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    3.4.1 Addition of aldol condensation products 673.4.2 Addition of polyethylene glycol 673.4.3 Modification with tri(ethoxy)phenylsilane 693.4.4 Influence of catalyst pretreatment on the results 693.5 Surface tensions 69

    4.Discussion 69Acknowledgements 72List of symbols 72References 73

    5. THE APPLICATION OF VARIOUS TERTIARY PHOSPHINES AS SOLVENT LIGANDS 75Summary 751. Introduction 762.Experimental 763. Results 77

    3.1 TGA-measurements 773.2 Influence of the various phosphines on the catalytic

    performance 784.Discussion 81Acknowledgements 83Symbols 83References 84

    6. THE KINETICS OF PROPYLENE HYDROFORMYLATION 85Symmary 851. Introduction 862.Experimental 863. Results 86

    3.1 Diffusional retardation 863.2 Relation between degree of conversion and rate of reaction 883.3 Influence of the rhodium complex concentration on the kinetics 883.4 Temperature dependency 903.5 Influence of the partial pressure of hydrogen, carbon monoxide

    and propylene 914.Discussion . 93Acknowledgements 95List of symbols 95References 96

    IX

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    7.OPTIMUM CONDITIONS FOR PROPYLENE HYDROFORMYLATION WITH SLP RHODIUMCATALYSTS. COMPARISON BETWEEN A FUTURE SLPC PROCESS AND THE LOWPRESSURE 0X0 PROCESS 971. Introduction 972.Optimum conditions for propylene hydroform/lation with SLP

    rhodium catalysts 982.1 The support , 982.2 Degree of liquid loading 992.3 Rhodium concentration 992.4 Choice of the solvent ligand 1002.5 Degree of conversion 1012.6 Reaction conditions and feed composition 101

    3. Comparison of the SLPC process and the LPO process , 102References 105

    SAMENVATTING 107

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    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 0R - CH - C"^ Ciso )

    ' "^HCH3

    This homogeneous catalyst is active already under very mild conditions andpossesses a high selectivity towards the formation of normal aldehydes. However,the very high price of the rhodium calls for recovery of the catalyst from theproducts.By heterogenizing the homogeneous catalyst, this cumbersome andexpensive operation can be avoided.

    This thesis deals with the preparation and characterization of a new,heterogeneous rhodium catalyst for the hydroformylation of ethylene orpropylene, and with its performance in long-term experiments (up to 80 0 hrs)under technologically realistic conditions (total pressure:1.2-1.57MPa;temperature:40-199C).

    The catalyst solution, composed of RhHCO(PPh ) , dissolved in a low-volatilesolvent,has been heterogenized by impregnating it into a porous inorganic ororganic support material, in which the catalyst solution is captivated bystrong 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 islow-volatile and wets the supports, but it also offers the advantage ofstrongly suppressing the dissociation of triphenylphosphine from the rhodiumcomplex. In this way a heterogeneous catalyst has been obtained, which producesn-butyraldehyde with great selectivity and after a test period of 800 hrs stilldoes not show any loss of activity (Chapter 2 ) .

    Nitrogen capillary condensation measurements on fresh and used catalystsdemonstrate that at incomplete pore filling the smallest pores are entirely

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    filled up with catalyst solution, whereas the walls of the larger pores aremerely covered with a thin layer of physisorbed catalyst solution. X-ray microanalysis reveals that the catalyst solution is homogeneously distributed overthe cross-section of a catalyst particle (Chapter 2 ) .

    The transition from solid to liquid triphenylphosphine, and vice versa, during the hydroformylation proves to have no influence on the activity and theapparent activation energy. From this it follows that we are dealing withheterogeneous catalysis, in which only the rhodium complexes at the phaseboundary between gas and liquid PPh,, or between gas and solid PPh,, areinvolved in the hydroformylation reaction.The inactivity of the rhodiumcomplexes in the PPh,-solution itself is due to the strong coordination of therhodium complexes with the surrounding PPh,-solvent and to the low solubilityof carbon monoxide in PPh,, and no t to strong diffusional retardation of thereaction rate in the liquid phase. At the gas-PPh, phase boundary, however, thecoordination of the rhodium complexes with free triphenylphosphine is only halfof that outside the phase boundary. Owing tothis,and to the much higher CO-concentration in the gas phase, the equilibria between the various rhodiumcomplexes shift towards CO-containing complexes exhibiting catalytic activityfor hydroformylation (Chapter 3 ) .

    The adsorption of the rhodium complex from the triphenylphosphine solutionon various supports has been investigated. Particularly on silica-alumina and,to a lesser degree, on silica, the rhodium complex proves to be preferentiallyadsorbed with respect to PPh,. On macroreticular polystyrene-2 0% divinylbenzene,XAD-2,only slight adsorption is observed. This means that the activity of ourcatalyst is not only determined by the area of the gas-PPh, phase boundary, butalso 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, thehigher the activity for hydroformylation. On this ground, the low activity ofY-alumina and silica-alumina supported catalysts can be explained by the verystrong adsorption of the rhodium complex on the Lewis-acid sites in the surfaceof these supports. The high activity with XAD-2 and, to a lesser degree, withsilicas 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 appearsthat on supports which strongly adsorb the rhodium complex, the activity pergram of rhodium goes through a maximum at a certain degree of liquid loading.With XAD-2,however, the activity per gram of rhodium decreases continuously2

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    with increasing liquid loading. These phenomena, too, can be explained by thechange in the extensiveness of adsorption of the rhodium complex with thedegree of loading and also by the change of the area of the gas-PPh, phaseboundary as a function of the degree of loading (Chapter 4 ) .

    Catalysts supported on silica and silica-alumina have a long activationtime (120 hr s) . This is attributed to the gradual accumulation of a smallquantity of high-boiling aldol products, formed by aldol condensation of theproduced aldehydes, in the pores of the support. These aldol products adsorbvia hydrogen bridging on the surface silanol groups, as a result of which theadsorption of rhodium complexes is suppressed and the silica surface is transformed 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. Thisresults in a slow increase in activity (Chapter 4 ) .

    The presence of a small quantity of aldol products in a used catalystsolution could indeed be demonstrated by means of IR-spectroscopy (Chapter 2 ) .

    The activation time can be shortened to a few hours and the activity andselectivity be increased by previous addition of aldol products or polyethyleneglycol to the catalyst solution, or by chemical modification of the silicasurface with tri(ethoxy)phenylsilane (Chapter 4 ) .

    Although, as appears from the foregoing, the accumulation of a smallquantity of aldol products in the catalyst is allowable and sometimes evendesirable, the aldol condensation should yet be suppressed as much as possible.A separate study has shown that this can be achieved by choosing sodium-poorsilicas or XAD-2 as support material; PPh, proved to be inactive andRhHCO(PPh,),only slightly active for aldol condensation (Chapter 2 ) .

    Owing to its unduly high volatility, P Ph, cannot be used as a solventligand at temperatures above 10 0C. Therefore, a large number of other, low-volatile phosphines has been tested in the hydroformylation of propylene at 80 -199C.At temperatures up to 140 C tri(p-tolyl)phosphine, tri(2 -cyanoethyl)-phosphine and S(+)-(2 -phenylbutyl)diphenylphosphine appeared to be the mostsuited. Above 150C, however, all catalysts tested so far proved to deactivate,probably owing to metallation of the coordinated phosphine ligands by therhodium metal (Chapter 5 ) .

    The kinetics of the heterogeneous-catalytic hydroformylation of propylenewithRhHCO(PPh,),dissolved in PPh, have been investigated. The results can bedescribed by a rate equation of the following form:

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    . ,rr,uilr 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 thehomogeneous-catalytic hydroformylation in the presence of a second solvent, forinstance toluene, besides PPh,, where the reaction is first order in hydrogen.This difference in the kinetics raises the presumption that when use is made ofa large excess of PPh, in the absence of a second solvent, as in our case, theaddition of propylene to the complex is rate-determining (when a slight excessof PPh, is used in the presence of a second solvent, the oxidative addition ofhydrogen is rate-determining).

    The broken order in CO, and the influence of the CO-pressure on theselectivity towards n-butyraldehyde, can be accounted for by a shift of thelocation of the equilibria between the various rhodium complexes in thecatalyst solution (Chapter 6 ) .

    The thesis concludes with some general remarks on the choice of thetechnical-economic optimum catalyst and reaction conditions, and with acomparison between a heterogeneous SLPC-process and the new low-pressure hydroformylation process of Union Carbide, in which Wilkinson's catalyst is appliedhomogeneously in a gassparged reactor (Chapter 7 ) .

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    C H A P T E R 1

    INTRODUCTION

    1.1 Historyofhydroformylation

    1.1.1 Cobalt catalysts

    The catalytic conversionof anolefin with carbon monoxideandhydrogenintoanaldehyde:

    CH- CH CHO normal isomer

    CHCH, iso isomer

    CHO

    knownas the 0X0 orhydroformylation reaction,is one of theoldestandmostwidely used applicationsofhomogeneous catalysisin theorganic-chemicalindustry.

    The reactionwasdiscoveredbyRoeien[1] in 1938duringan investigationintotheoriginofoxygenated compoundsin theproductsof theFischer-Tropschsynthesis carriedoutwithacatalyst containing30 w % ofcobalt,2 w % ofthorium oxide,2 w % ofmagnesium oxideand 66 w % ofKieselguhr,and it became soon recognized that onlythecobalt componentiscapableofcatalyzingthe hydroformylation reaction. Since undertheusual conditionsof theFischer-Tropsch synthesis partof thecobalt dissolvesin theorganic reactionmedium,it wasobvioustoconclude thatthecatalystis ineffectasolublecobalt carbonyl complex [2].Thereaction mechanism, proceeding underthe influenceofsuch catalytic complexes,wasfirst describedbyHeckandBreslow[3] andreviewedbyOrchinandRupilius [ 4 ] . Under reaction conditionstheactive cobalt carbonyl HCo(CO).isformed.

    Since then industryhasincreasingly usedCo (CO) ,dissolvedin the or-Z o

    ganic reaction medium,ascatalyst precursorforhydroformylation purposes.Cobalt complexes were employedfor thefirst timein the 10 kgs/year Ruhr-chemie plantatHolten, Germany,in 1942 for themanufactureof C.. - C _ alcohols from higher olefins[5].Owingtohostilitiesat the end ofWorldWar IIthis planthasnever been completed.Thefirst commercial hydroformylationprocesswasthen realizedbyEnjay Chemical Company,USA,makinguse of the

    5

    R- CH = CH + CO + HR-

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    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 arebased on the use of Co_(CO) as a catalyst, and they differ only in the cobaltrecovery step, in which the cobalt catalyst is removed from the aldehydesformed and subseq uently recycled to the hydroformylation reactor. The variouscobalt recovery schemes are given by Lemke [ 9 ] , who states that this step isthe most expensive and cumbersome one;a very large number of patents deal withthis subject.

    Typical reaction conditions in cobalt catalyzed hydroformylation aretemperatures of 110 to 180C, 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 necessary to prevent decomposition of the active complex HCo(CO) into cobaltmetal,which forms strongly adhesive deposits on the reactor walls and on allother parts of equipment. Under those severe reaction conditions the maintenance 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 products consist to 7 8-8 2 w % of aldehyde, 10 -12 w % of alcoliol, 2 w % of formiateand 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 wasdiscovered by Slaugh and Mullineaux in 1966 [11,12].By adding to the reactionmedium a tertiary phosphine, arsine or phosphite, such as tri-n-butylphosphine,these workers succeeded in stabilizing the cobalt catalyst. Under hydroformylation conditions the catalytically active CoH(CO,)PBu complex is formed accordingly 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 mentionedby Whyman [13] and by Van Boven [ 1 4 ] . The stabilization of the modified cobaltcatalyst is due to the fact that a phosphine molecule has less ir-acceptorcapability than carbon monoxide. Hence, the electron Tr-back-donation from cobalt to carbon monoxide is enhanced, resulting in a strengthening of themetal-carbon monoxide bond.

    Technological advantages of introducing the modified cobalt catalyst are adecrease 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 3:16

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    to 4 : 1 ) , and a relatively easy separation of the cobalt catalyst from theproducts,by simple distillation, which enables the catalyst to be recycled to thehydroformylation reactor dissolved in high-boiling byproducts. About 1 0 w % ofthis catalyst solution is fed to a catalyst recovery section to prevent accumulation of high-boiling byproducts.

    Disadvantages of the Shell catalyst are a much lower activity -the activityfor 1-pentene hydroformylation with the modified catalyst, for example, decreases by a factor of one hundred at 1 10 -15 0C [ 1 2 ] - and a much higher hydro-genation activity. Not only are all aldehydes hydrogenated to alcohols, butalso 1 0 mole % of olefin is hydrogenated [ 1 5 ] . Therefore, the modified cobaltcatalyst is unsuited when aldehydes are to be obtained as end products. Currently, only Shell uses the modified catalyst to produce higher linear alcoholsfrom a-olefins at total pressures of 5-10 MPa and temperatures of 170-180C[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 regardsactivity and selectivity were obtained with relatively cheap platinum complexesmodified with tertiary phosphines and tin(II) chloride [ 1 9 ] . .

    Howe ver, so far the best results have been achieved with rhodium. The useof rhodium was first described by Schiller [20] and Veryard [ 2 1 ] . Because of

    2 4the much higher activity of rhodium carbonyl (10 -10 times that of cobalt carbonyl at 130 C and 2 9.4 MPa totalpressure),very mild reaction conditions arenow applicable. High-pressure equipment is no longer req uired, byproduct formation is low, only aldehydes are produced, and olefin hydrogenation does notoccur. 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 ahydroformylation catalyst that does not give rise to isomerization. Since thattime this catalyst system has been thoroughly investigated and extensivelydescribed in literature; an excellent review is due to Pino [ 2 4 ] . The hydroformylation mechanism and the effect of various reaction conditions on thecatalytic performance has been described by Wilkinson [ 2 5 ] . With triphenylphosphine (PPh.) as one of the ligands the components active under hydroformylationconditions are RhH(CO) PPh and RhH(CO)^(PPh ) , both of which are character-

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    ized by a very high activity, selectivity and stability. Wilkinson [25] showedthe catalyst to be active already at room temperature and atmospheric pressure.Notwithstanding its decreasing effect on activity, a high P/Rh ratio is essential 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 propylenehydroformylation in molten PPh, (P/Rh = 601 mol/mol) reaches a value of about13,and the loss of olefin by hydrogenation is only0.3-0.4mole %; no alcoholsare detected. The remarkable stability of the rhodium complex wa s demonstratedby Craddock [ 2 6 ] ; this worker found that the rhodium complex did not precipi-tateduring recirculation nor lost activity after vacuum distillation at 180C.

    In 1975, after ten years of research and development. Union Carbide, NewYork, USA, was the first to employ the new catalyst system commercially in twolarge 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 -120C and1.3-2.7MPa total pressure, so under much milder conditions than theclassical cobalt-based 0X0 process. The normal-to-iso butyraldehyde ratio comesin 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 ) , alongwith an excess of free triphenylphosphine (P/Rh = about 10 7mol/mol),isdissolved in a mixture of butyraldehyde and high-boiling byproducts from aldehydetrimerization. The gaseous reactants are bubbled through this stirred liquidcatalyst solution and the produced aldehydes are continuously stripped fromthe liquid and, together with the non-converted reactants, removed via the topof the reactor.

    At present, all three catalyst systems described above are still operational,and in use at 35 companies all over the world, having a total production

    9capacity of 3.5 x 10 kgs/year, 80 w % being butyraldehydes obtained frompropylene hydroformylation [ 1 5 ] . By aldolization and hydrogenation part of the n-butyraldehyde is converted into 2-ethylhexanol, which, upon esterification withphthalic acid, yields di(2-ethylhexyl)phthalate, called DOP, a very importantplasticizer in PVC production [ 2 9 ] . Since the normal butyraldehyde is suitablefor aldolization only, the normal-to-iso butyraldehyde ratio should be as highas 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 illustratedby the Monsanto process for the very selective carbonylation of methanol toacetic acid under the very mild reaction conditions of 1 80C and 3-4 MPa totalpressure [ 30 ] . The first commercial plant, with a capacity of 1 50 x 10 kg s/8

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    year,went on stream in 19 70 [31 ]. A new process, still under development atUnion Carbide, USA, is the production of ethylene glycol directly from hydrogenand carbon monoxide in the presence of certain rhodium carbonyl clusters [ 3 2 ] .

    1.2 Heterogenizingofhomogeneous catalysts

    Apart from their use for hydroformylation purposes, organometallic complexes have in the past twenty years become adopted for many other interesting applications in homogeneous catalysis. In the USA over twenty industrial processes employ homogeneous catalysts [33 ]. There is an increasing trend to use highly selective, but at the same time also very expensive and rare homogeneous organometallic catalysts and/or ligands for the small-scale production ofvaluable organic compounds. The annual world output of rhodium, used for instance in hydroformylation, is only three to four thousand kgs; the rhodiumprice is now about $ 3 0,0 00 /kg. Cobalt, on the other hand, used in the conventional 0X0 process, costs only $ 20/kg. Because of this high rhodium price,nearly complete recovery of rhodium from the produced aldehydes is a prerequisite.According to Cornils [15] the rhodium content of the produced aldehydes should be kept below 0.3 ppm. When this condition is fulfilled, the costof the spent rhodium will equal the cost of the cobalt spent in the 0X0process.For a homogeneous rhodium based catalyst to be commercially successful, avery expensive and cumbersome rhodium recovery step is therefore needed; thesame holds for other precious homogeneous catalysts and for the very expensiveand sophisticated ligands that are sometimes used. Furthermore, the metal and/or ligands contaminate the products, and homogeneous catalysts may cause severecorrosion of the equipment, as, for example, in Wacker-type processes [34].

    The recovery, contamination and corrosion problems may be circumvented byheterogenizing the homogeneous catalysts, that is to say by transferring thecatalyst into a phase other than either the reactants or products. Hence, acontinuous separation between the catalyst and the products is affected alreadyin the reactor.

    Heterogenizing of homogeneous catalysts can be realized by any of thefollowing 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

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    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 reactions because the catalyst is rapidly dissolved in the liquid reactants and/or products.

    For a detailed discussion of the above mentioned methods of heterogenizinghomogeneous catalysts and their applications to several review articles may bereferred [56-62].In this thesis only method a_is dealt with, the so-calledSLPC method, which was used in the present study for the reasons set forth inSection 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 catalytically active liquid is dispersed in the pores of an inert porous support,where it is strongly captivated by capillary forces. The catalytically activeliquid may be a molten salt, a liquid metal, an acid or a solution of an organometallic complex in a high-boiling solvent. In order to avoid drying-up ofthe solution in the pores by evaporation, the volatility of the solvent shouldbe 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, appliedphosphoric acid, capillary-condensed in the pores of Kieselguhr, as a catalystfor dimerizing lower olefins to high octane gasoline [ 6 2 ] . Today, thiscatalyst is still used for the production of styrene and cumene by alkylationof benzene with ethylene and propylene, respectively.

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

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    employ a catalyst that consists of a mixture of copper chloride, one or morealkali metal chlorides and one or more rare earth metal chlorides deposited ona porous support. The alkali metal lowers the melting point to the extent thatthe mixture will be partly or completely molten under reaction conditions. Nowadays industrial interest is focussed primarily on the one-step synthesis ofvinyl chloride from ethylene.

    Another very important example of fused salt catalysis is the oxidation ofsulphur dioxide for synthesizing annually hundred of billions of kgs sulphuricacid. Reaction conditions are 420-610C and atmospheric pressure. The catalystis composed of 6 w % V-O, promoted with K^SO., on Kieselguhr. A survey of manyother fused salt catalyzed reactions is given by Kenney [63].

    The first publication about the use of a supported liquid phase catalystin 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 ethyleneglycol deposited on Kieselguhr.

    In 1969 Rony [65] reported on the hydroformylation of propylene withRhCOCl(PPh ) , dissolved in benzyl butyl phthalate and brought into the pores ofsilica gel. As demonstrated in the respective patent [66] this catalyst systemis also suited for hydrogenation and isomerization of lower olefins. The sameresearch-group oxidized ethylene to acetaldehyde with PdCl^/CuCl_ dissolved inethylene glycol on Kieselguhr, and carbonylated methanol to acetic acid withRhCl .3 H O in pentaerythrityl tetravalerate on silica gel [ 6 7 ] .

    Theoretically, diffusional retardation of the rate of reaction, if occurring 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 fastreactions,such as those catalyzed by organometallic complexes, the activityof an SLPC will mainly depend on the liquid layer thickness. Diffusional retardation is less severe in thin liquid layers, meaning that the activity ofan SLPC will be highest if the liquid is distributed as a thin liquid layer onthe inner surface of the porous support. This goes to show that the liquiddistribution is a most important factor in supported liquid phase catalysis.

    Theoretically, the distribution of the liquid varies with the contactangle of the liquid on the support, the texture of the catalyst (pore sizedistribution 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 to100%.So, in the case of a given support and a given liquid, the liquid distribution, and hence the activity, will only be influenced by the liquidloading. Theoretical models describing this influence, are given by Rony [ 6 8 ] ,Abed [69] an dV iU ad se n [70] .

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    Abed's model does not require knowledge of the liquid distribution, as thisis accounted for by a so-called dusty gas constant, an empirical parameterwhich depends solely on the type of support and the liq uid loading. The reactants diffuse via both the gas phase and the liquid phase into the interiorof the catalyst particle and the effective diffusion coefficient is calculatedwith the aid of the above-mentioned dusty gas constant. However, the model isbased on the rather unrealistic assumption that the reaction in the liquidphase is not diffusionally retarded. This can only be true at very low liquidloading.

    Rony, on the other hand, assumes diffusional retardation to occur in boththe liquid and the gas phase regions in an ideal cylindrical pore. The liquidlayer thickness (6) is calculated as a function of the liquid loading ( 6 ), bymeans 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 condensation in porous supports, assumes that at intermediate degrees of liquid loadingthe smallest pores are totally filled up with liquid, whereas the larger onesmerely carry a thin layer of physically adsorbed liquid on the inner surface.The liquid distribution is determined by measuring the pore size distributionof a bare and a loaded support. Both liquid and gas phase diffusion are included in Villadsen's calculations.

    Recently, Villadsen showed that the situation may be more complicated thaninitially proposed by him, because above a certain degree of liquid loading theliquid agglomerates, resulting in the formation of large liquid-filled regions,called liquid clusters, the dimensions of which are many times larger than theaverage pore diameter [ 7 1 ] . The size of the liquid clusters depends on theliquid loading and, in an irregular way, on the pore diameter. Up to now notheory has come forward for predicting the clustering mechanism and the size of theclusters to any degree of accuracy. As to this latter point, it is surprisinglythat the models of Abed and Rony, as well as that of Villadsen, all fit in sowell with their experimental data. This may be attributed to the large numberof empirical parameters incorporated in their models.

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    1.4 OBJECTIVE AND SCOPE OF THE THESIS

    The objective of the present study is to develop a technologically applicable heterogeneous active, selective and stable catalyst for the gas phasehydroformylation of lower olefins and substituted olefins, such as ethylene,propylene, butenes, allylalcohol, allylacetate and vinylacetate. The needto search for such a new catalyst system sprang from the consideration that thecatalyst systems known in literature do not seem suitable for the reasons, setforth below.

    Hydroformylation in the liquid phase

    From literature it appears that up to now heterogeneous hydroformylationhas mostly been studied in batchwise-operated stirred tank reactors or autoclaves in the liquid phase, using rhodium complex catalysts chemically anchoredto organic or inorganic supports. A drawback of such a system is the possibledissolution of the rhodium complex from the support into the liquid reactantsand/or products and the consequent inadmissible loss of rhodium and deactivation of the catalyst. Lang [ 7 2 ] , for instance, mentioned an elution of 0.5 - 10ppm of rhodium from macroreticular polystyrene, functionalized with dibutyl-phosphine or dimethylamine, into the products, whereas for economic applicationthe 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 therhodium was redistributed along the catalyst bed. On the whole not much isknown about the stability of chemically anchored catalysts, because mostresearch workers test their catalysts batchwise in stirred autoclaves. Underreaction conditions the rhodium complex may desorb from the support into theliquid phase and readsorb after cooling down of the reaction mixture at the endof an experiment [ 7 3 ] . Furthermore, in most studies the normal-to-branched aldehyde ratio appears to be low. It is evident therefore that hydroformylationshould preferably not be carried out in the liquid phase.

    Hydroformylation in the gas phase

    Workers at Monsanto, St. Louis, USA, heterogenized aRhClCO(PPh,)^ catalystfor gas-phase hydroformylation of propylene in three different ways:

    1) by strong physical adsorption of the rhodium complex on an inorganicsupport [ 35 ] .

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    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-isobutyraldehyde ratio was surprisingly low (2:1 mol/mol),in each of the threecases.

    A much higher normal-to-iso butyraldehyde ratio of about 13:1 mol/mol wasobtained by Wilkinson, when bubbling a mixture of gaseous propylene, carbonmonoxide and hydrogen through a stirred solution ofRhHCO(PPh,),in molten PPh,[22,7 4 ] . In 19 75 , industrial hydroformylation of ethylene and propylene, withthe aid of the Wilkinson catalyst dissolved in low volatile aldehyde trimerization products and a large excess of free triphenylphosphine, was realized forthe first time by Union Carbide, New Y ork, USA,in a gassparged reactor.Although the process seems very attractive, the presence of a catalyst recoverysection in the process raises a presumption of either loss or deactivation ofcatalyst.Bryant [75 ] mentions a maximum daily activity loss of 0.75 % calculatedon the initial activity; this would mean complete deactivation of the catalystafter 3 20 0 hrs streamtime. The technological merits of this process over ourSLPC-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, propylene and butenes, making use of [RhCl(CO)-]_ chemically anchored to a polystyrene-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, DelftUniversity of Technology, Spek [37 , 76 ] and Tjan [3 8, 77 ] studied the gas-phasehydroformylation 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 andtenperature 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 (2:1mol/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 the14

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    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 heterogeneous gas phase hydroformylation of ethylene and propylene with rhodiumhydri-

    docarbonyltris(triphenylphosphine),RhHCO(PPh-),,dissolved in one of its ownligands, PPh,,or other tertiary phosphines. This catalyst solution is heterogenized by strong capillary condensation in the pores of an inorganic ororganic support. So, the principle of supported liquid phase catalysis isapplied, one of the ligands being the solvent. Compared with the practice ofusing a gassparged reactor [2 2, 7 3 ] , this method of heterogenizing offers thefollowing advantages: a very large gas-PPh, phase boundary; absolutely norhodium loss;easier process operation; no corrosion problem.

    The catalyst performance has been tested under realistic technologicalconditions of 1.2 - 1.57 MPa total pressure and 40 - 199C in a continuous isothermal plug flow tubular reactor over periods of up to 80 0 hours.

    *Chemically anchoring of the rhodium complex to a support is studied separatelyby De Munck [7 8] and will not be further discussed in this thesis.

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    vol.2, p. 43, eds. I. Wender and P. Pino, John Wiley, New York, N.Y.,(1977).

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    Catal., The Chem. So c, London,(1977),p. 499.40.R.H. Grubbs, L.C. Kroll, E.M. Sweet, J. Maarom ol. Sci. Chem.A7 (5),(1973)

    1047.41.C U . Pittman, L.R. Smith, R.M. Hanes, J. Am. Chem. Soc. 97_,(1975),1742.42.R.H. Grubbs, Chemteoh. 1_, (1977),512.43.K.G. Allum, R.D. Hancock, I.V. Howell,R.C.Pitkethly, P.J. Robinson, J.

    Catal. 43,(1976),322.44.L.J. Boucher, A.A. Oswald, L.L. Murrell, Pepr. Div. Petr. Chem., Am . Chem.

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    (1978),137.49.Y. Dror, J. Manassen, J. Mo l. C atal. 2_,(1977),219.50.W.O. Haag, D.D. Whitehurst, Meeting Cat. Soc. Houston, Texas,(1971).51.J.P. Pinnavaia, P.K. Welty, J. Am. Chem . Soc. 97,(1975),3819.52.A. Hershman, K.K. Robinson, J.H. Craddock, J.F. Roth, Ind. Eng. Chem.,

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    60.CU . Pittman, Chemteoh. l^, (1971),416.61.D.D. Whitehurst, Prepr. V'th Canad. Symp. C atal. , Calgary, 1977, p. 182.62. G. Egloff, Ind. Eng. C hem.28,(1968),1461.63. C.N. Kenney, Catal. Rev. - Sai. Eng. U_, (1975),197.64. G.J.K. Acres, G.C. Bond, B.J. Cooper, J.A. Dawson, J. Catal. 6_,(1966),

    139.65.P.R. Rony, J. Catal. 14_,(1969),142.66.P.R. Rony, J.F. Roth (MonsantoCompany),Belg. Patent 711042 (1968). .67.P.R. Rony, J.F. Roth, J. Mol. Catal. J_,(1975/76),13.68.P.R. Rony^, Chem. E ng. Sai. 23,(1968),1021.69.R. Abed, R.G. Rinker, J. Catal. 31_,(1973),119.70.H. Livbjerg, B. Sorensen, J. Villadsen, Chem. React. Eng. II, Adv. C hem.

    Ser. 133^,(1974),242.71.H. Livbjerg, K.F. Jensen, J. Villadsen, J. Catal. 45_,(1976),216.72.W.H. Lang, A.T. Jurewicz, W.O. Haag, D.D. Whitehurst, L.D. Rollmann, J.

    Organometal. Chem. 154,(1977),85.73.J. Moffat, J. Catal. j_8(1970),193.74.G. Wilkinson (Johnson, Matthey & Co.Ltd.),German Patent 2064471 (1971).75.D.R. Bryant, E. Billig (UnionCarbide),German Patent 2802923 (1978).76.Th.G. Spek, J.J.F. Scholten, J. Mol. Catal. ,(1977/78),81.77.P.H.W.L. Tjan, J.J.F. Scholten, Proa. Sixth Int. Congr. Catal., The Chem.

    Soc,London,(1977),p. 488.78.N.A. De Munck, Ph.D. thesis. Delft, The Netherlands, to appear,(1980).

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    C H A P T E R 2

    HYDROFORMYLATION WITH SUPPORTED LIQUID PHASE RHODIUM CATALYSTS

    PartI.General Descriptionofthe System, Catalyst PreparationandCharacterization *)

    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 triphenylphosphine and capillary condensed in the pores of a support material, isapplied in the heterogeneous hydroformylation of propylene at 90C and 1.57MPa total pressure. The activity and selectivity of this new catalyst are highcompared with those of known analogues. No sign of deactivation is observedover a period of more than 800 hrs. --

    A small weight increase of the used catalyst, occasionally observed, canbe attributed to some accumulation of low-volatile aldol condensation productsin the pores. The aldol condensation reaction can be suppressed by usingmacroreticular polystyrene-divinylbenzene, XAD-2,or sodium-poor silica assupport 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 % porefilling to be mainly located in the smallest pores of the support. X-RayMicroanalysis reveals a rather uniform distribution of the catalyst solutionacross a catalyst particle.

    *) Paper submitted for publication in Journal of Molecular Catalysis.19

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

    In 1965 Wilkinson [1] showed RhHCO(PPh ) , to be a superior homogeneoushydroformylation catalyst. Since then, research at heterogenization of thisvery precious catalyst has received high priority [2 -10 ].Attention has beenfocussed in particular on the chemical anchoring of the rhodium complexes onorganic and on inorganic supports. Possible drawbacks attaching the use of suchimmobilized catalyst systems in liquid phase operation are the slow leaching-out of the rhodium complex [1 1,12 ,13] and the generally low selectivity towardsthe straight aldehydes, which are industrially more important than the branchedaldehydes [14-18].

    In the case of gas-phase hydroformylation an attractive alternative forchemically anchored catalysts is presented by a Supported Liquid PhaseCatalyst, SLPC, in which the rhodium complex is dissolved in a non-volatilesolvent and immobilized in the pores of a support by strong negativecapillary forces. One advantage of such an SLPC system might be the preservation of the original liquid environment of the rhodium complex, because thisprotects it from chemical modification by interaction with the surface of thesupport,a phenomenon sometimes observed in chemically and physically immobilized systems. A large gas-liquid contact area may be mentioned as a furtheradvantage.

    Although SLP catalysts have already been applied in a number of industrially important reactions since 1936 [18,19], Rony [ 2 0 ] , in 196 9, was the firstto try them out in the heterogeneous hydroformylation of propylene, withRhClCO(PPh,) dissolved in benzyl butyl phthalate on silica gel as a support.However, notwithstanding the large excess of dissolved free PPh, (P/Rh = 56mol/mol) used by him, the normal-to-iso butyraldehyde ratio appeared to bedisappointingly low (n/iso = 2 ) . Rony does not give any details about thestability of the catalyst; in a subsequent paper [2 1] he merely states: "thecatalyst had a tendency to activate and deactivate with time".

    In the present study it will be demonstrated by means of a few examplesthat dissolution of RhHCO(PPh ) , in PPh yields an excellent SLPC system forhydroformylation of propylene under mild reaction conditions. For more examplesdescribing the performance of these catalysts reference may be had to therelevant patents [22,23]. Furthermore, the texture, structure and analysis ofour SLP catalysts will be discussed.

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    2. Experimental2.1 Materials

    RhHCO(PPh) waspreparedby themethodofAhmad [24 ]. Triphenylphosphine(Fluka,Switzerland, 99.5%)wasusedasreceived. Benzene (Merck, Germany,99.7%)andtoluene (Merck, Germany,99%)were dried over molecular sieve3A(Union Carbide, USA). Nitrogen (AirProducts,USA,99.98%)wasfreedofoxygenandwater over BASF catalystR3-11 andmolecular sieve3A,respectively.Propionaldehyde (Merck, Germany, 99.0%)wasdistilled before use. Hydrogen(99.99%),propylene (99.5%), ethylene (99.9%)andcarbon monoxide (99.5%) wereall obtained fromAirProducts,USA.Silica 00 0-3E, silica-aluminaLA-30,y-alumina 005-0.75E(allfrom Akzo Chemie, Amersfoort,TheNetherlands),Kieselguhr MP-99 (Eagle Pitcher, USA) , silica Dll-11 (BASF, Arnhem,TheNetherlands),silicaS(DSM,Geleen,TheNetherlands)andAmberlite XAD-2 (Serva, Germany)were crushedifnecessary,andsievedtothedesired size fractionof 0.42-0.50mm.

    2.2 Catalyst preparation

    ExceptforXAD-2andsilicaS, thesupports were dried in vacuo (0.1 kPa),firstat150Cfor3hrs andthenat500Cfor 16 hrs. Only silicaSandXAD-2 were driedin air at120Cfor 16 hrs.Thedried supports were placedinthe catalyst preparation apparatus showninFig.1.

    Calculated amountsofRhHCO(PPh) andPPh, were dissolvedinbenzeneortolueneat70C under flowing nitrogen.Thetotal volumeofthecatalyst solutionwastaken exactly equaltothetotal pore volumeof thesupport.Thecatalyst solutionwasadded dropwisetothestirred support, whichwaslikewiseheldat70C. Next,the benzenewasslowly evaporated under flowing nitrogenat room temperaturefor3hrs andthenat90Cfor 16 hrs, during which periodthe PPh, could redistributein thepore system.ByvaryingthePPh,/benzenevolume ratioin thecatalyst solution, several degreesofliquid loading, i.e.degreesofpore filling with catalyst solution, couldberealized afterevaporationof thebenzene.The dry andfree-flowing catalyst particles werestoredat-20C.Thecatalyst preparationisfully reproducible,asitturnedout thattwobatchesofcatalyst showedthesame catalytic performance.

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    -coohng

    N2

    -oil(70C)N, (70C)

    y ~ oil(70C)

    Figure 1 Catalyst preparation apparatus.A=reflux cooler,B =catalyst solution holder,C=support holder,D =magnetic stirrer.

    2.3 Catalyst charac terizationThe SLPCiscompletely characterizedby thefollowing parameters:

    : thetypeofsupport6 : thedegreeofliquid loading, defined as thedegreeof thepore volume

    filledupwith catalyst solutionat90C 3[Rh] : therhodium complex concentration inPPh,at90 C (mol/m)P/Rh : themolar phosphine-to-rhodium ratio (mol/mol)

    The textureof thesupportand of thecatalystwasdetermined bynitrogencapillary condensation [25]at-196Con aCarlo Erba 18 00 "Sorptomatic",orby mercury porosimetry [26]on aMicromeritics 9 05-1 apparatus.Thereproducibilitywasbetter than3% inbothcases.

    The distributionof the PPh across cleaved catalyst particles embeddedinWoods metal,wasdeterminedbyX-ray microanalysis, RMA,on aJeol JXA-50A22

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    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-300a 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 epho 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 tha 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 300C (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 andAlarm, 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 Recorderand C on tro l le r , API = D iffe re nt ia l PressureIndicator. I tems 1-10 are mentioned in the text .

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    Hydrogen, carbon monoxide and, either, ethylene or helium were stripped ofoxygen,water and carbon dioxide by leading them over BASF catalyst R3-11,molecular sieve 3A and sodium hydroxide on asbestos ("Ascarit"). Liquidpropylene was metered from reservoirs ( i) and ( 2 ) , evaporated and mixed with theother reactants in evaporator ( 3 ) . Next, the gas mixture was passed throughheated tubes to a0.200m long fixed-bed reactor (s ) (inner diameter O.OIO m)placed in an air-fluidized-bed oven M J permitting isothermal operation towithin 0.5C. The operating conditions were so chosen as to assure ideal plugflow and exclude pore or film diffusional retardation of the chemicalreaction 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 ) , analyzedgaschromatographically on a Porapack-PS column (?) (Waters Ass. Inc., USA) at120C,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 Pe + 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 thedifference in thermal conductivity between aldehyde and olefin,

    The selectivity (S) is calculated as the ratio of the peak areas fornormal- and iso-butyraldehyde:

    A^ = - A ^

    ISO

    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:

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    i.e. incmolefin at 0.101 MPa and 25C (the atmospheric conditions underwhich the flow was measured in the soap filmmeter),per gram of rhodium metalin the reactor and per second.

    After the start of an experiment the reactor temperature was stepwiseraised to its final valuein aperiod of two hrs.

    2.5 Infrared spectroscopy

    Reflection I.R. spectroscopy of catalyst particles results in poorly resolved spectra, whereas transmission I.R. is not applicable owing to the largesize of our catalyst particles. Therefore,weextracted the catalyst solutionfrom the fresh or used catalyst particles (0.6 g) with2 gof carbon tetrachloride, and recordered the spectrum of the CCl.-extracton aBeckman-4210spectrophotometer,

    2.6 Activity tests for the unwanted consecutive reaction: aldol condensationof aldehydes

    To check which of the catalyst components is responsible for the highly3undesired aldol condensation, freshly distilled propionaldehyde (4cm) , usedasamodel compound, and support (0.4 g) were brought under nitrogen intoeach ofaseries of about five glass sample tubes capable of withstandingpressuresup toone MPa. After sealing, the sample tubes were placed inathermostatic bathat90 C. After various lengths of time, the sample tubes weresuccessively broken and the contents were analyzed gaschromatographicallyat95C onaSP-22 50 -on-Chromosorb G. HP. column, and detected by meansofflameionization.The reaction mixture proved to consist of nonconverted propionaldehyde,2-methyl-2-pentenal, 3-hydroxy-2-methylpentanal andasmall amount of higherboiling products (trimers andtetramers).

    2.7 Nevtron activation analysis

    The sodium content of the supports was determinedbyneutron activationanalyses,using the single comparator method, with zincasthe referencematerial [2 8] .

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    3 Results

    3.1 SLPC versus physically adsorbed catalystsThe 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 stability of a typical physically adsorbed catalyst (Rh(Tr-allyl)CO(PPh ) on y-alumina00 0-3 P, according to Tjan [29]),are included for comparison.

    10/cm3ci>- plgRh.sj

    1 1 1 12 0 0 4 0 0 6 0 0^ t(j(hrs) 8 0 0

    Figure 3 Activity and stability for propylene hydroformylation of a typical SLPC(x) and a physically adsorbed catalyst (o).P = 1.57 MPa; Cj/H^/CO = 1/1/1; t = 90C; W/F =

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

    It is seen here that after 15 0 hrs streamtime the SLPC is six times moreactive than the physically adsorbed catalyst. The SLPC shows no sign of deactivation after 8 00 hrs, whereas the physically adsorbed catalyst deactivatesto 1 0 % of its initial activity in the first 15 0 hrs. Moreover, the selectivityof the SLPC is not only time-independent, but also nuch higher (S = 9) thanthat of the physically adsorbed catalyst (S = 2 ) . Both catalysts produce morethan 9 9 .5 % aldehydes.

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    3.2 Com parison with Rony's SLP catalyst

    To compare the performance of the new catalyst with Rony's SLPC, twocatalysts were prepared and tested under the same reaction conditions. The oneaccording 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,discussed in the present study, with RhHCO(PPh ) dissolved in PPh (P/Rh = 74 4mol/mol).

    3 0

    2 0

    10

    n

    ^9 01

    r '

    / c m ^ C s N( ^ g R h s )

    1 1 1 1200 tj (hrs) 300 400

    Figure 4 Activity and stability for propylene hydroformylation of two SLPC's, both prepared with an excessof PPh-. X : PPh as solvent; o : DOP as solvent.P = 1.57 MPa;c /IU/CO= 1/1/1; t =90C; W/F =.57 MPa; C /H /CO = 1/1/1; t

    -3 3 =0.987x 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 PPhsystem, which fits in with our findings after addition of polyethylene glycolto the catalyst solution, described in part III of this series [ 3 0 ] , Theselectivity, however, which is a very important parameter in hydroformylation,is much better for our PPh, system (7.8 against only 3.1 for the DOPcatalyst).

    3.3 Infrared spectroscopyTypical 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 usingCH.Cl^as anextraction agent.

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    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 highconversion levels, additional strong bands are noted at 17 25 and 168 5 cm anda 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 alsowith literature data [ 3 1 ] , we assigned these to a small amount of butyraldehyde(1725 cm ) and low-volatile dehydrated aldol condensation products such as2-ethyl-2-hexenal (16 85 , 16 40 cm" ) , condensed in the catalysts during use athigh conversion levels. Bands due to non-dehydrated 2-ethyl-2-hydroxyhexanalhave 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 hydroformylation of ethylene at 90C and 1.2 MPa total pressure, a silica 000-3E SLPcatalyst (6 = 0.31) shows an increase in weight of 4.93 % after 144 hrs , whereasa silica S catalyst (6 = 0.79) does not change in weight at all over a periodof 14 1 hrs. In both cases the conversion of ethylene was about 1 3 %. As evidenced by I.R. spectroscopy, this small weight increase is to be attributed to theaccumulation of low-volatile aldol condensation products in the pores of thecatalyst. The aldol condensation products are due to aldol condensation of thepropionaldehyde or butyraldehyde formed. Qualitatively, we established that thehigher the weight increase, the stronger the absorption band at 1.685 cm

    In general, we did not observe any detrimental effects of these aldol condensation products. On the contrary, previous addition of 10 w % of a mixtureof aldol condensation products to the catalyst solution on silica 000-3E evenproved to decrease the activation time in hydroformylation from 20 0 hrs toless 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 practicaldifficulty caused by accumulation of aldol products might be that in the longrun the catalyst solution gets completely driven out of the pores. Therefore,measures have to be taken to suppress the formation of these aldol products asmuch as possible.

    To assess the individual activities of the support, P Ph, and rhodiumcomplex for the unwanted aldol condensation, we examined in how far the conversion of propionaldehyde at 9 0C is promoted by each of these agents.

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    Table 1 Conversion (%) of propionaldehyde to aldol condensation productsat90C,as a function of time

    Na-content^ x 1 0^ i \ ^ 5^^ ^0 ^40(w %) (%) (%) (%) (%) (%)

    supportsY-alumina 005-0.75 Esilica-alumina LA-30silica 000-3Esilica Dll-11silica SKieselguhr MP-99XAD-2 (extracted)PPhPPhJ + RhHC0(PPh2)jblank run

    800698

    4900< 100036

    1410---_

    9,83.83.63.20.30.31.0-

    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 measuredfor 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 alsoobserved by Beranek [ 3 2 ] . Silica S did not show any activity; the same is truefor PPh . The rhodium complex was only slightly active in the first twenty hrs,which proves that it gradually lost its activity for aldol condensation. Thelow activity of the macroreticular polystyrene-20% divinylbenzene XAD-2 must beattributed to a slight contamination with sodium even after 25 hrs of extraction 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 support3.5.1 Nitrogen capillary condensation and mercury porosimetry

    The pore size distribution before and after loading of the supportwithcatalyst solution was studied bynitrogen capillary condensation (Fig. 6) and

    16.16.67.44.00.50.71.7-

    0.80.3

    25.510.913.36.01.01.32.90.32.10.6

    40.018.523.911.21.52.44.50.63.81.1

    53.029.639.818.52.15.36.41.03.82.2

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    mercury porosimetry (Fig. 7 ) . In order to account for the weight increase ofthe support due to loading, use has been made of a conversion factor, W /W support , which converts the measured cumulative pore volume of the catalyst,expressed in cm per gram of catalyst, into the cumulative pore volume per gramof support. In this way, a direct comparison between the loaded and unloadedsupport can be made.

    1 0

    0.5-

    101 2 Tp (nm)

    Figure 6 Pore size distribution of an unloaded (x) and aPPh, loaded (o) silica 000-3E support, as determined by nitrogen capillary condensation at -196C;theor 0.56.

    1 0

    0 5 -s.

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

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    Fig. 6 shows that most of the PPh, is present in the smallest pores of thesupport. The transitional pores are only partially filled up. Mercury porosimetry reveals a striking different distribution; all of the PPh_ prove s to becollected in the smallest pores (Fig. 7 ) . Qualitatively the same results wereobtained for all other support materials investigated in the catalytic performance tests [3 0] .

    The PPh -distribution in a fresh and a used catalyst are qualitativelyidentical. Sometimes a used catalyst shows a small decrease in total cumulativepore volume (say, 5 % ) , owing to accumulation of low-volatile products in thepores.

    3.5.2 X-ray microanalysisThe 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 000-3Ewith 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 theparticles. In silica 0 00 -3E a decrease of the silicium-signal is generallyaccompanied by an increase of the phosphorus-signal. This shows the porosity tobe non-uniform, the more porous regions being filled up with PPh . The dimensions 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 the32 /

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    relatively regular frameworkofmicrospheresinthis material.

    3.5.3 Electron microscopyExaminationofcoupesofcatalyst materialbyTEM,and ofcleaved catalystparticlesby SEMgavenoadditional informationon the PPh distribution;at

    enlargementsup to1 75,000 ,PPh, couldnot bedistinguished fromthesupport,nor could differencesbeobserved betweentheimagesof abareandloadedsupport.

    4 . Discussion

    I. R. measurements

    Itisseen from Table2thatthe I.R.absorption bandsof theCCl.-extractofausedSLPcatalystdo notcoincide withthebandsin the I.R.spectracharacteristicof theintermediatesinWilkinson's associative mechanism[33]nor with anyone band attributabletodimeric rhodium complexes.

    Table2 I.R.spectraofseveral rhodium complexes

    positionofcomplex I.R.bands (cm )RhHC0(PPh2), 1920,2000,2040W \\i{CQ}^{??\\^)^ 1 9 4 2, 1980, 2050Rh(COC,H^)CO(PPh ) 1643,1650, 1943,1990[Rh CO(PPh)2]2 1740 , 1980[m\{,CO)^{?Ph^)^]^ 1770, 1800, 1992,2017RhH(CO),PPh 1980RhHCO(PPh) onPS/20%DVB 195 2, 2000this study 1947, 1993,2002,2070

    One should, however, bearinmind thatthecatalytically active amountofrhodium complexmayonlybe asmall fractionof thetotal amountofrhodiumcomplexes present, which implies thattheassociative mechanism cannotbe

    literature34,

    36343437,39,

    35

    3840

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    excluded on the strength of our I.R. measurements alone. It is furthermoreimportant to note that Wilkinson [3 4,35 ,36] detected his intermediates at 25Cand atmospheric pressure in benzene solutions, whereas we examined our catalystextracts after hydroformylation at 90C and 1.2 MPa total pressure withRhHCO(PPh,),dissolved in PPh (P/Rh = 74 4 mol/mol).

    The only results bearing some resemblance to ours are those published byPittman [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 attention owing to less resolution in the polystyrene-system, his and our resultsare 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 hightemperature and pressure used by Pittman and by us, PPh -rich rhodium complexesare formed, the spectra of which have so far not been disclosed in theliterature (rhodium complexes with three or four PPh ligands).

    Catalytic performance

    In Table 3 the activities and selectivities of several known heterogeneouscatalysts for hydroformylation of propylene are compared with those of our SLPcatalyst. Where necessary for comparison, the activities and selectivities ofthe latter have been calculated for the reaction conditions applied in theliterature study referred to. The calculations are based on the kinetics ofou rSLPC system [ 4 1 ] . As to catalyst systems D and E in Table 3 , we point outthat here the calculated activity and selectivity of our SLPC system may beless meaningful because the extrapolation had to be made to reaction conditionsbeyond the region of the kinetic measurements.

    Table 3 shows our SLPC system to be about six times more active than thesystems A, C and D. The SLPC we prepared according to Rony's method, using DOPas a solvent (system B ) , is four times more active than our SLPC system madewith 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 activityof SLPC systems with solvents other than PPh was also found by us aftergradual dilution of the PPh, solvent with polyethylene glycol, as will befurther elucidated in part III of this series [3 0].A very important conclusion,however, is that our SLPC system has an appreciably higher selectivity thanany other heterogenized catalyst system. Furthermore, our SLPC appeared to beperfectly 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 molten34

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    Table 3 Comparison between the performance of the SLP catalyst and otherheterogenized catalysts for hydroformylation of propylene.

    ,'7s y s t e m-

    ASLPC

    BSLPC

    CSLPC

    DSLPC

    ESLPC

    P / R h/ m o l \I m o l

    27 4 4

    5 67 4 4

    6 0 17 4 4

    17 4 4

    5 6744

    P(MPa)

    1 . 5 71 . 5 7

    1 . 5 71 . 5 7

    1 . 5 81 . 5 8

    6 . 8 76 . 8 7

    3 . 4 83 . 4 8

    t(C)

    9090

    9090

    125125

    125125

    136136

    r/ m ol C^ \I mol R h .s /

    0 . 0 0 40 . 0 2 5

    0 . 1 0 50 . 0 2 5

    0 . 1 0 80 . 5 8 7

    0 . 0 7 70 . 4 7 6

    0 . 6 6 50 . 3 1 6

    S/ Ao ll^molj2 . 09 . 3

    3 . 17 . 5

    15 .023 .0

    1.14 . 4

    2 . 08 . 3

    s t a b ^-

    .+

    ++

    7+

    ?+

    ?+

    a: A = Rh(TT-allyl)CO(PPh ) physically adsorbed on y-alumina 0 00 -3P (seeSection 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 (C2H^O)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 supportmaterials applied in our study, which means that the contact angle of PP h, on

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    the support materialsissmaller than 90. Judgedbythe naked eye,thecontact angleofPPh onquartz and of PPh onsapphireat90C and undernitrogenis about 3 0. This indicates that PPh isasuitable solvent wettingthe support and strongly immobilizedbycapillary forces; calculations withthe Washburn relation [44],P =-2a. cos9/r ,yield capillary pressuresas

    Lb p _high as -6.5 MPa(r =10 nm, a,- (90C)=37.5x10" N/m[45],6 = 30).p Lub) SolventPPh isanexcellent solvent forRhHCO(PPh_)_;its low vapour pressureof

    only 2.63Paat 90C [45] prevents contamination of the produced aldehydeswith PPh_ and drying-up of the catalyst solution, provided the catalystisused below 100C.c) Improvement of the selectivity

    Becauseofthe very large excessoffree PPh,, rhodium complexes withatleast twoorthree PPh, ligands willbepresent, which account for the observedhigh selectivity [33].d) Stabilization of the rhodium complex

    AccordingtoWilkinson [34], the dimerizationofRhHCO(PPh,) toinactivedimers (eq.2and 3 ) only takes place after dissociationofone PPh,-groupfrom 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)isshifted far to the leftbythe large excess of freePPh,the dimerization, eqs.2and 3, issuppressed,sothat the activityfor hydroformylation is high. Furthermore, decompositionofRhHCO(PPh) tocomplexes still more deficientinPPh is prevented [ 7 ] . The absenceofI.R.bands of dimersinthe spectrum ofaused catalyst (Fig.5)supports this view.

    Although the hydroformylation activity will generally decrease with increasing P/Rh ratio [46,47],the activity of the SLPCisstill remarkably high.This shouldbeascribedtothe very large gas-PPh phase boundary created bydispersing the PPh,inthe porous support (see also partIIof this series[27]).36

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    Aldol condensation

    The disadvantage of accumulation of aldol condensation products in thepores of the support is circumvented by selecting support materials that areinactive for aldol condensation, such as sodium-poor silica S or AmberliteXAD-2,RhHCO(PPh,),itself is only slightly active for aldol condensation,whereas PPh was found to be completely inactive, as is also reported inliterature [48].

    PPh -distribution in the support

    Nitrogen capillary condensation shows the catalyst solution at 56% liquidloading to be preferentially capillary-condensed in the smallest pores (micropores 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 thewalls of all pores in which no capillary condensation takes place (Fig. 6 ) .Hence,inasmuch the porosity of the support is constant throughout the catalystparticle, a uniform PPh distribution is realized. Villadsen [ 1 9 ] , in histheoretical treatment of SLPC systems, rightly remarks that owing to the interconnectivity between the por es, the capillary-condensed liquid tends tocluster, thereby reducing the surface energy of the meniscii. In X-ray microanalysis 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 inareas 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 occurin this macroreticular resin. However, the lateral resolution of RMA being onlyone ym, clusters smaller than one ym might yet occur inXAD-2.Further attemptsat visualizing PPh,-clusters by TEM or SEM have failed.

    Mercury reveals a type of PPh distribution q uite different from that disclosed by nitrogen capillary condensation (compare Fig. 6 and 7 ) , Most likelythe very high mercury pressure applied (333 MPa) drives the PPh out of thetransitional pores into the smallest pores of the support. This would be thethormodynaraically most favoured situation in the presence of mercury.

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    Acknowledgements

    We thank Mr. N. van Westen and Mr. J. Teunisse for carrying out thenitrogen capillary condensation and mercury porosimetry measurements, Ir. E.Izeboud for his assistance in the aldol condensation experiments, Mr. A.M. Kieland Mr.S.M.G.Nadorp (Central Laboratory, DSM, Geleen) for the SEM and TEMmeasurements, Ir. D. Schalkoord for the RMA measurements, and Ir. P. Bode forthe neutron activation analysis measurements.

    The investigations were supported (in part) by the Netherlands Foundationfor Chemical Research (SON) with financial aid from the NetherlandsOrganization for the Advancement of Pure Research (ZWO).

    Listofsymbols

    AFPP/Rh[Rh]^90rPStt ,

    cat

    PPh,support

    iP

    peak areaflow of olefin at 0.1 MPa and 25Ctotal pressuremolar phosphine to rhodium ratiorhodium complex concentration in PPh, at 90 Creaction rate at 90Cpore radiusselectivity = n/iso ratioreaction temperaturestreamtimecumulative pore volumeweight of rhodium metal in the reactortotal weight of a batch ofcatalyst afte r evaporationof benzenetotal weight of P Ph, used in catalyst preparationtotal weight of support used in catalyst preparation

    internal normalization factorliquid loading at 90Ccontact angleconversionsurface tension

    a.u.3 ,cm / sMPamol/molmol/mcm'^/g Rh.snmmol/molchrscm /g

    degreesN/m

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    C H A P T E R 3

    HYDROFORMYLATION WITH SUPPORTED LIQUID PHASE RHODIUM CATALYSTS

    Part II. The Locationofthe Catalytic Sites*)

    by

    L.A. Gerritsen, J.M. Herman, W. Klut 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 triphenylphosphine and capillary-condensed into the pores of a support,is applied inthe catalytic heterogeneous hydroformylation of ethylene and propylene.

    Catalysts with triphenylphosphine in the liquid and in the solid state, donot 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 phaseboundary are involved in the reaction.

    The inactivity of the rhodium complexes outside the phase boundary is mostlikely due to high coordination of these complexes with free triphenylphosphinemolecules,and to the very low solubility of carbon monoxide in triphenylphosphine, and not to an extreme liquid-phase diffusional retardation of therate of reaction.

    *) Paper submitted for publication in Journal of Molecular Catalysis.41

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

    In part I of this series [1] and in the relative patents [2,3],thepreparation, characterization and performance of a supported liquid phaserhodium catalyst have been discussed. This catalyst may be applied in thehydroformylation of ethylene, propylene and other alkenes, under the very mildreaction conditions of 90C and 1.57 MPa total pressure, and it has theadditional advantage of being highly selective towards the formation of normalbutyraldehyde.

    It is known from lite ratu re [4,5,6,7] t hat whe n the Wilkinson catalyst isused in homogeneous hydroformylation, in the presence of an organic solvent, anincrease of the P/Rh ratio (by addition of PPh,) causes a strong decrease incatalytic activity. Our supported liquid phase rhodium catalyst, on the otherhand (which does not contain an organic solvent),shows a remarkable highactivity at high P/Rh ratio owing to the large surface area of the gas-liquidphase boundary.

    The present paper deals with the question if in our experiments diffusionalretardation of the rate of reaction plays a role. The localization of thecentres of catalytic activity will also be discussed.