Tokuyama Process (High Temp, High Pressure)

8/10/2019 Tokuyama Process (High Temp, High Pressure)

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TECHNICAL PAPER

Isopropyl Alcohol by Direct Hydration of Propylene*

by Yasuharu Onoue**, Yukio Mizutani**, Sumio Akiyama**,usuke Izumi** and Hirofumi Ihara***

Summary: TokuyamaSoda has developed new processfor direct hydration of propylene oisopropanol n liquidphase. This processemploys highly active and selectivecatalyst systemwhich essentially comprisesan aqueous olutionof polytungsten ompoundswithin a selectivepHrange.

The irst commerciallant, havinga capacityof 30,000 metric ons of isopropanol er annum,has been successfullyn operation ince the beginningof June 1972 at TokuyamaSoda Co., Ltd.

he features of the processare simpleness, ow value or propyleneconsumption nd freedomfrom environmental ollutionproblems. These advantagesmake Tokuyama Process byfar moreeconomical han the conventional rocess or the manufactureof isopropanol.

1 Introduction

sopropanol is an important derivative of pro-

pylene in petrochemical industry. It is usedas solvent, dehydrating agent and disinfectant aswell as a base for the manufacture of acetoneand other compounds.

ince the first commercial production of iso-

propanol in 1920, most methods for hydratingpropylene to isopropanol have been based onthe use of concentrated sulfuric acid in a two-stage esterification-hydrolysis process. This pro-

cess, although resulting in substantial conversionof propylene, has the problems of severe cor-rosion and disposal or reconcentration of dilutespent acid.

any processes of direct hydration of propylenein one step in the presence of catalyst have beenstudied in order to avoid the disadvantages ofthe sulfuric acid process and to obtain the rapidconversion of propylene to isopropanol withthe lowest possible amount of by-products.

t is quite lately, however, that some economi-cal direct hydration processes for commercialisopropanol production have been developed.Now, with the rising market of isopropanol, theeconomic importance of isopropanol productionby direct hydration has been well recognized.

ecently Tokuyama Soda has developed anew economical process for direct hydration of

* Received December 9, 1972.* Research & Development, Tokuyama Soda Co.,td. (1-1, Mikage-cho, Tokuyama 745)

*** Development & Marketing, Tokuyama Soda Co.,td. (1-4-5, Nishi-Shinbashi, Minato-ku, Tokyo,

apan)

propylene to isopropanol in liquid phase. Thefirst commercial plant of this process, having acapacity of 30,000 metric tons of isopropanolper annum, has been successfully in operationsince the beginning of June 1972 at TokuyamaSoda Co., Ltd.

2 Hydration of Propylene

2.1 Reactionirect hydration of propylene is carried out

in the presence of catalyst according to the fol-lowing reversible equation:

C3H6+H2OCH3CH(OH)CH3 The reaction is exothermic, and the heat of

reaction calculated from available thermochemicaldata1) is about 12kcal/mol over a range of 400to 600K in vapour phase. The equilibrium constants by direct measure-ments2),3) for hydrating propylene are reportedas follows:

og10Kp=(1950/T)-6.06(vapour phase)og10Kc=(2045/T)-5.08(liquid phase)or the hydration with liquid and vapour

phases simultaneously present, the equilibriumcompositions of both phases can be estimated4)by thermochemical data, together with vapour-liquid equilibrium data.

lthough the formation of isopropanol is fa-vored by low temperatures and high pressures,optimum combination of reaction conditions isselected in consideration of both rate limitationand equilibrium limitation.

The major by-products in the direct hydrationof propylene are di-isopropyl ether, n-propanol

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Onoue, Mizutani, Akiyama, Izumi and Ihara: Isopropyl Alcohol by Direct Hydration of Propylene 51

and propylene oligomers.

2.2 Catalyst and Processn commercial realization of direct hydration,

it is important to develop active catalysts and

processes suitable for the effective application

of the catalyst systems.n recent years, various catalysts and pro-

cesses5)`9) for direct hydration of propylene havebeen proposed.

t seems necessary for a better understandingof Tokuyama Process to review some typicalhydration processes briefly.

he catalysts most widely proposed for thevapour-phase direct hydration of propylene aremineral acids such as phosphoric acid and he-teropoly acids on silica or diatomaceous earth,and solid acids of metal oxides.

he reaction is generally carried out by passingsteam and propylene in a molar ratio of 0.5`2.0:1 through the catalyst bed at a temperature from180 to 260 and under a pressure from 10 to65atm to maintain the reactants in gaseousstatc. The VEBA proccss10)`12) recently em-

ployed in commercial isopropanol productionis based on the use of a supported phosphoricacid catalyst in vapour phase.

he vapour-phase direct hydration, however,has the substantial disadvantage of low conver-sion of propylene per pass, for example 5`6%,

resulting in a high recycle rate. Consequently,the use of a propylene concentration of 99%or more is required for the feed. Moreover, thedisadvantages inherant to supported mineral acidcatalysts are decrease in hydration activity andthe incidence of corrosion13) on the metal sur-faces in contact with the product owing to mi-gration and depletion of the acid. In orderto avoid these difficulties, it is necessary to re-generate the catalyst and to neutralize the pro-duct.

The disadvantages of the low conversion and

concomitant recycle problems in vapour-phaseprocesses are overcome by the direct hydrationin the presence of liquid water, since the propylene conversion to isopropanol is markedly rai-sed by the increase in solubility of the productisopropanol in the excess liquid water.

he direct hydration with a solid catalystunder a high pressure at a high mole ratio ofwater to propylene can be preferably employedto obtain high per pass conversions of propylene.The reaction is generally carried out by passing

propylene and liquid water at a mole ratio ofwater to propylene between 10 and 15 overthe catalyst bed at a temperature from 230 to270 and a pressure from 200 to 300atm.For the hydration in the presence of liquid water,

tungsten oxide is widely used as an effectivecomponent of catalyst14).okuyama Soda has also proposed an active

catalyst15) 17) which comprises zirconium state. This catalyst is suitable for both vapour-

phase and liquid-phase processes. The examples

Fig. 1 Effect of Temperature on Propylene Con- ersion to Isopropanol in Vapour-Phase

ydration

Fig. 2 Effect of Pressure on Propylene Conversiono Isopropanol in Liquid-Phase Hydration

Volume 15, No. 1, May 1973


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of the results of propylene hydration with thezirconium tungstate catalyst in vapour phase andliquid phase are shown in Fig. 1 and Fig. 2,respectively, in comparison with the data ofliquid-phase hydration over tungsten oxide ca-talyst by Zabor et al.18)

he use of insoluble solid catalysts eliminatesthe difficulties of the remarkable migration anddepletion of acid which take place in the hydrationwith supported acid catalysts. However, underthe severe hydrothermal conditions in the liquid-

phase hydration under high pressure, gradualdepletion or crystallization of the effective com-

ponents of catalyst is inevitable, and consequentlyboth the decrease in hydration rate and someoperating troubles will occur. Recently, Deut-sche Texaco has developed a trickle process19)in vapour and liquid phases applying cationexchange resins as catalysts under milder con-ditions of 130 150@ and 60 100 atm. Oneof the main problems in this process is probablythe hydrolysis of sulfonic acid groups of theresin catalyst which causes the irreversible lossof catalytic activity.

n order to overcome the difficulties in thefixed bed processes with solid catalysts, the liquidphase hydration with the solid catalyst dispersedin water can be employed20)`22).n this process,

propylene is treated with water at an elevatedtemperature and pressure in the presence of anaqueous suspension of fine particles of the ca-talyst. Although high space-time yields basedon catalyst are obtainable by the suspension pro-cess, some operational difficulties of separationand circulation of the suspended particles cannot be avoided.

okuyama Soda fully examined the disadvan-tages and difficulties in the typical processes de-scribed above through its own extensive experi-ments, and attained to a conclusion that theliquid-phase direct hydration with an aqueoussolution of catalyst would be most profitablefor the production of isopropanol. Some ca-talyst systems in a state of aqueous solution havebeen ofTered in recent patents23) 25)

However, these systems have the disadvantagesof low selectivity for hydration in the case ofaqueous solution of copper halide catalyst andlow stabilities of catalyst components, such asaluminium sulfate, ferric sulfate, chromium sul-fate and molybdic acid which are hydrolyzed toinsoluble hydroxides at high temperature and

Onoue, Mizutani, Akiyama, Izumi and Ihara:

Table 1 Effect of Anion on Rate of Propyleneydration

pressure in aqueous solution.okuyama Soda studied systematically the ca-

talytic activities and stabilities of aqueous solutionsof various acid compounds in the direct hydrationof olefins, and finally developed an excellentcatalyst system of a stable aqueous solution underhigh temperature and pressure. It was foundfrom the study that the rate of hydration wasmarkedly increased by the presence of somekinds of polyatomic anions as shown in Table 1.

he activation energy of the propylene hy-dration with the catalyst solution of polyatomicanions is about 24kcal/mol which is 6kcal/molhigher than that in the case of the catalyst so-lution of sulfate anions.

According to the known mechanfolefin hydration in very dilute aqueous acid,the hydration rate is proportional to the acidconcentration, and the counter anions have noeffect on the rate. Since the medium effect onthe activity coefficient of each component invery dilute acid solution is considerably small,the effect of the polyatomic anion on both thehydration rate and the activation energy is pro-bably interpreted by assuming an intermediateof an activated complex containing the anion.

3 Tokuyama Direct Hydration Process

3.1 Catalyst Systemhe catalyst system employed in Tokuyama

Process30)`34) essentially comprises a dilute aqsolution of definite kinds of polytungsten com-

pounds within a selective pH range. This ca-talyst system is highly active and remarkablyselective for hydrating propylene to isopropanol.This system is also very stable because the ca-talyst components are strongly resistant to hy-

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Isopropyl Alcohol by Direct Hydration of Propylene 53

drolysis. Such high stability of the catalyst sys-tem is well maintained at all times in operationby the careful control of poisons which causethe decomposition of the catalyst. The catalystlife is, therefore, very long in continuous operation.

Tokuyama Process gives, moreover, higher perpass conversions of propylene owing to intimatecontact between dissolved propylene and thecatalyst solution in the liquid phase than in thecase where solid catalyst systems are employed.

ig. 3 shows an example of the experimentalresults of propylene hydration with the Tokuyamacatalyst system by a continuous flow reactor.3.2 Kinetics of Hydration

n the hydration of propylene with the To-kuyama catalyst system, the reaction takes placebetween dissolved propylene and water in an

aqueous solution. The hydration rate is con-troled by the reaction step, provided equilibriumis at all times maintained in the distributionof propylene between vapour and liquid phases.

Data obtained with Tokuyama catalystystem at 200kg/cm2.G.

Fig. 3 Effect of Temperature on Propylene Con- ersion to Isopropanol in Liquid-Phase

ydration

Because of large excess of water, the rate is givenby the following equation via a pseudo-first orderkinetic treatment:

=kl(Cp-Ci/kl)=kg(Pp-Pi/Pwe.kg)where

ki, kg: rates of conversion of propylene tosopropanol in solution at unit con-

entration of propylene in solution,nd at unit pressure of propylene inapour phase, respectively.

i, Kg: equilibrium constants in liquid andapour phases, respectively.

p, Ci: concentrations of propylene and iso-

ropanol in solution, respectively.p, Pi: partial pressures of propylene and

sopropanol in vapour phase, res-

ectively.

we: equilibrium partial pressure of watern vapour phase.

his basic rate equation can be suitably ap-

plied to calculate conversion or space-time yieldin process design and economic evaluation.3.3 Process Description

he flow scheme of Tokuyama Process isshown in Fig. 4.

iquid propylene is preheated and fed to areactor under pressure. The catalyst solutionrecovered from the azeotrope column is pre-heated by heat exchange with the reactor effluent

and fed to the reactor operating at 240`270and 150`250atm. The reaction takes placein the liquid phase between dissolved propyleneand water. The aqueous solution containingisopropanol and catalyst is withdrawn from thereactor and cooled by heat exchange and thenflashed under reduced pressure in a gas separatorwhere the unconverted propylene dissolved inthe solution is separated and recycled. The

Fig. 4 Flow Diagram of Tokuyama Prricrs,



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Onoue, Mizutani, Akiyama, Izumi and Ihara:

liquid is sent to the azeotropic column, fromwhere azeotropic mixture of isopropanol and wateris drawn off and sent to further distillation stepsfor purification and dehydration. The aqueoussolution containing catalyst from the bottom ofthe azeotrope column joins with fresh water andis recycled to the reactor. The azeotrope al-cohol is freed of the light impurities in the firstrectifying column and then dehydrated in twofurther columns with benzene as the dehydrat-ing agent. To obtain a high grade isopropanol(99.99% purity), another additional distillationstep is necessary.

nder the optimum reaction conditions, therange of propylene conversion per pass is about60`70% and selectivity to isopropanol basedon the converted propylene is as much as 98`99%. The major by-product is di-isopropylether.

In Tokuyama Process, both the spent gasfrom the reactor and all the by-products drawnoff at the purification section are completelyutilized as fuel for heating in the system.3.4 Features of Process

okuyama Process has a number of advantagesbased on its own catalyst system and processdesign. The features of the process confirmedin commercial operation are as follows:(1) The catalyst system comprises a homogene-

ous dilute aqueous solution which maintains highactivity and excellent selectivity for hydratingpropylene to isopropanol.(2) The catalyst solution is so highly stabiliz-ed that it is circulated repeatedly in the reactionsystem without any additional treatments. Ca-talyst life is, therefore, very long.(3) Since the reaction is carried out in aqueoussolution under high pressure, the formation ofisopropanol is markadly favoured by equilibriumeffect.(4) The amount of unconverted propylene to

be recycled is small owing to high conversionrate of propylene, and consequently this processdoes not require highly concentrated propylenefeed. Commercial propylene of about 95% con-centration is normally used.(5) The amount of by-products is remarkablysmall because the reaction takes place in anaqueous solution of highly selective catalyst. Or-ganic acids and aldehydes are hardly detectablein the reaction product. A high grade iso-propanol is easily obtained at the purification

section.

(6) Since the reaction is carried out in aqueoussolution, the heat loss incidental to evaporationand condensation of water can be avoided.(7) Because of absence of corrosion in the sys-tem, easy operation and maintenance of equip-ments are possible.(8) The process is simple. It is also a com-pletely closed system free from waste substances,and consequently the process can clear all theenvironmental protective regulations.3.5 Quality of Product

rypical data of the product isopropanol ob-tained in Tokuyama Process are given in Table 2.3.6 Economics

he economics of Tokuyama Process are shownin Table 3. They include the entire processingof propylene to 99.99% isopropanol.3.7 Other Applications

okuyama Process is also applicable to theeconomical production of ethanol and butanols.

4 Conclusionesides the low value for propylene consump-

tion, simpleness of process and freedom fromenviromental pollution problems by nature ofthe process itself make Tokuyama Process by farmore economical than the conventional processfor the manufacture of isopropanol.

n the recent trend of the process for isopro-

Table 2 Typical Properties of Product

Table 3 Economics of Tokuyama SodaDirect Liquid-Phase Hydration Process

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Isopropyl Alcohol by Direct Hydration of Propylene 55

panol production toward direct hydration, To-kuyama Soda will greatly contribute to the

proceeding of this trend through experience inits own commercial plant.

References

1) Stull, D. R. et al., The Chemical Thermodynamicsf Organic Compounds , (1967) John Wiley &ons, Inc., New York.

2) Stanley, H. M. et al., J. Soc. Chem. Ind., (London),3, 205 (1934).

3) Majewski, F. M. et al., Ind. Eng. Chem., 30, 2031938).

4) Cope, C. S., J. Chem. Eng. Data, 11, 383 (1966).5) Berkman, S. et al., Catalysis , (1940), Reinhold

ub. Corp., New York.6) Tapp, W. J., Ind. Eng. Chem., 40, 1619 (1948); 42,

698 (1950); 44, 2020 (1952).7) Hammer, W. F., ibid., 46, 1841 (1954); 48, 1621

1956); 50, 1365 (1958); 52, 962 (1960).8) Winfield, M. E., Catalysis , Vol. 7, (1960) Rein-

old Pub. Corp., New York.9) Ogino, Y., J. Japan Petrol. Inst., 5, 487 (1962).10) HydrocarbonProcessing, 46, (11), 195 (1967).11) Hibernia Chemie, Japan, 43-26846 (1968).12) Europ. Chem. News, July 24, 32 (1970); March 10,

2 (1972).

13) Hibernia Chemie, Brit. 1, 106,424 (1968).14) Kline, C. H. et al., Ind. Eng. Chem., 57, (9), 53

1965).15) Tokuyama Soda, Japan 43-6603 (1968).16) Tokuyama Soda, U. S. 3,450, 777 (1969).17) Tokuyama Soda, Brit. 1,192,692 (1970).18) Zabor, R. C. et al., Actes Congr. Intern. Catalyse, 2e,

aris, 1960, 2, 2601 (1961).19) Europ. Chem. News, Nov. 19, 36 (1971).20) Imperial Chemical Industries Ltd., Brit., 727, 665

1955).21) Montecatini, Brit. 883,039 (1961).22) Montecatini, Japan 38-12903 (1963).23) Pullman Incorporated, U. S. 3, 328,469 (1967).24) Japan, Bureau of Industrial Technics, Japan 42-

411 (1967).25) Japan, Bureau of Industrial Technics, Japan 43-

7206 (1968).26) Lucas, H. J. et al. J. Am. Chem. Soc., 56, 460 (1934).27) Taft, R. W., Jr. et al., ibid., 73, 3792 (1951).28) Taft, R. W., Jr. et al., ibid., 74, 5372 (1952).29) Nakaya, H. et al., Bull. Chem. Soc. Japan, 44, 1175

1971).

30) Tokuyama Soda, Brit. 1,281, 120 (1972).31) Tokuyama Soda, Ger. 2, 022,568 (1973).32) Tokuyama Soda, Japan Open, 47-31908 (1972).33) Tokuyama Soda, Japan Open, 47-31909 (1972).34) Tokuyama Soda, Japan Open, 47-31910 (1972).


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Tokuyama Process (High Temp, High Pressure)