CA1264727A

CA1264727A - Alcohols production by hydrogenation of carboxylic acids

Info

Publication number: CA1264727A
Application number: CA000506453A
Authority: CA
Inventors: Melanie Kitson; Peter Sefton Williams
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1985-04-13
Filing date: 1986-04-11
Publication date: 1990-01-23
Anticipated expiration: 2007-01-23
Also published as: CN86102452A; NZ215765A; CN1006788B; DE3689050T2; DE3689050D1; NZ215766A; EP0198682B1; AU592980B2; AU592981B2; US4777303A; AU5601286A; DE3677809D1; US5061671A; JPS61275234A; EP0198681B1; JPS61275237A; US4990655A; US4826795A; JPH0825931B2; CA1262719A

Abstract

Case 5930(2) ABSTRACT OF THE DISCLOSURE

ALCOHOLS PRODUCTION BY HYDROGENATION OF CARBOXYLIC ACIDS

Ethanol is produced from acetic acid or propanol is produced from propionic acid by contacting either acetic acid or propionic acid in the vapour phase with hydrogen at elevated temperature and a pressure in the range from 1 to 150 bar in the presence of a catalyst comprising as essential components (i) a noble metal of Group VIII of the Periodic Table of the Elements, and (ii) rhenium, optionally on a support, for example a high surface area graphitised carbon.

Description

Case 5930(2) ~X5~i47~7 ALCOHOLS PRODUCTION BY HYDROGENATION OF CARBOXYLIC ACIDS

The present invention relates ln general to the hydrogenation of carboxylic acid~. In particular the present invention relates to a process for the hydrogenation of acetic and propionic acids in the presence of a catalyst comprising a noble metal of Group VIII of the Periodic Table of the Elements and rhenium to produce respectively ethanol and propanol.
The hydrogenation of carboxylic acids to produce the corresponding alcohol using supported Group VIII noble metal catalysts is known from, for example, USP-A-4524225; USP-A~4104478;
GB-A-1534232; GB-A-1551741 and EP-A-147219. Of the aforesaid patent~, all e~cept GB-A-1534232 relate to the hydrogenation of C4 and higher carboxylic acids snd, in common with GB-A-1534232, to operation in the liquld phase. Moreover, EP-A-147219 represents an intervening publication in the sense thst it was published after the priority date claimed for thç subJect applica~ion on an application claiming an earlier priority date than the sub~ect application.
G~-A-1534232 relates to the production of alcohol~ by the catalytlc hydrogenatlon of carboxylic acids, including acetic acid and propionic acid, at elevatet temperature and pressure in the presence of water andlor solvents using as catalyst pallatium/rhenium on a support, the palladium to rhenium weight ratio of the catalyst being in the range from 0.01 to 5:1. The process is operated at pressures in the range from 50 to 1000 atmospheres. The only processes exenplified are the hydrogenation of C4 and hlgher dibaslc acids at very high pressures We have found that operatlon of a Group VIII noble metal catalyst in the llquid phase suffers from the disadvantage that leaching of both rhenium and Group VIII noble metal from the catalyst can occur. Not only leaching of the catalytic metals but also undesirable leaching of oxide-containing supports ~an occur.
We have now suprisingly found that operation in the vapour phase provides high and comparatively long-lived catalytic activity and selectivity at lower pressure~ than those previou~ly employed.
Furthermore, op~ration in the vapour phase substantially overcomes the leaching problem associated with liquid phase operation.
Accordingly, the present invention provides a process for the production of either ethanol fro~ acetic acid or propanol from propionic acid which proces~ comprlses contacting either acetic acid or propionic acid in the vapour phase ~ith hydrogen at elevated temperature and a pressure in the ranBe from 1 to 150 bar in ~he presence of a catalyst comprising as essential components (i) a noble metal of GrOUP VIII of the Periodic Table of the Elements, and (ii) rhenium.
In addition to the alcohol, the process of the invention generally produces the corresponding e3ter as a by-product, for - example the hydrogenation of acetic acid generally also producesethyl acetate and the hydrogenation of propionic acid generally also produces propyl propionate. The proportion of the ester in the product ~ay be increased, if desired, by for example operating at low conversions, for exa~ple at less than 50% conver~ion per pass, or by introducing an acidic function into the catalyst to promote 'in situ' esterlfication. Alternatively, the proportion of alcohol may be increased, for example by co-feeding water or by operatlng at very high conversions per pass.
Both acetic and propionic acids are commercially available in large tonnages and may be used in the process of the presen~
invention in their commercially available forms without further purification, Alternatively, they may be further purified if desired.
Hydrogen, too, is commercially available on a large scale and 47~7 may be used with or wlthout further purificatfon.
The catalyst comprises a first component which is a noble metal of Group VIII and a second component which i8 rhenium. For the avoidance of doubt, the noble metal~ of Group VIII are the metals osmium, palladium, platinum, rhodium, ruthenium and iridium. Of the aforesaid metals of Group VIII, palladium and ruthenium are preferred.
Preferably the catalyst further includes a support. Suitable supports include high surface area graphi~ised carbons, graphites, silicas, alumina~ and silica/aluminas, of which high surface area graphitised carbons and silicas are preferred. Preferred silica supports are those having a high surface area, typically greater than 50 m2/g.
Particularly preferred supports are the high surface area graphitised carbons described in GB-A-2136704 (BP Case No. 5536).
The carbon is preferably in particulate form e.8. as pellets. The size of the carbon particles will depend on the pressure drop acceptable in any given reactor (which gives a minimum pellet size~
and reactant diffusion constrsnt within the pellet (which gives a maximum pellet size). The preferred minimum pellet size iq 0.5 ~m and the preferred maximum is 10 mm, e.g. not more than 5 ~m.
The carbons are preferably porous carbons. Nith the preferred particle sizes the carbon will need to be porous to meet the preferred 3urface area charateri~tics.
Carbons may be characterised by their BET, basal plane, and edge surface areas. The BET surface area is the surface area determined by nitrogen adsorption using the method of Brunauer Emmett and Teller J. Am. Chem. Soc. 60,309 (1938). The basal plane surface area is the surface area determined from the heat of adsorption on the carbon of n-dotriacontane from n-heptane by the method described in Proc, Roy. Soc. A314 pages 473 - 498, with particular reference to page 489. The edge 3urface area is the surface area determined from the heat of adsorption on the carbon of n-butanol from n-heptane a~ disclosed in the Proc. Roy. Soc. article mentioned above with particular reference to page 495.

~47~7 The preferred carbons for use in the present invention have a BET ~urface area of at least 100 m~/g, more preferably at least 200 m2/g, most preferable at least 300 m2/g. The BET surface area is preferably not greater than 1000 m2/g, re preferably not greater than 750 ~2/g.
The ratio of BET to basal plane surface area i5 preferabIy not greater than 4:1~ more preferably not greater than 2.5:1. It ls particularly preferred to use carbons with ratios of BET to basal plane surface area of not greater than 1.5:1.
It is preferred to use carbons with ratios of basal plane surface area to edge surface area of at least 10:1, preferably at least 100:1. It is not believed tha~ there is an upper limit on the ratio, although in practice it will not usually exceed 2C0:1.
The preferred carbon support may be prepared by heat treating a carbon-containing starting material. The starting material may be an oleophillic graphlte e~g. prepared as disclo~ed in GB 1,168,785 or may be a carbon black.
However, oleophillic graphites contain carbon in the form of very fine particles in flake form and are therefore not very suLtable materials for use a3 cataly~t supports. We prefer to avoid their use. Similar con$ideratlons apply to carbon blacks which also have a very fine particle size.
The preferred materials are activated carbons derived from vegetable materials e.g. coconut charcoal, or from peat or coal or from carbonizable polymers. The materials sub~ected to the heat treatment preferably have particle sizes not less than these indicated above as being preferred for the carbon support.
The preferred starting materials have the following characteristics: BET surface area of at least 100, more preferably at least 500 m2/g.
The preferred heat treatment procedure for preparing carbon supports having the defined characteristlcs, comprise successively (1) heating the carbon in an inert atmosphere at a temperature of from 900~ to 3300C, (2) oxldizing the carbon at a temperature between 300C and 1200C, (3) heating in an inert atmosphere at a 47;~7 temperature of between 900C and 3000C.
The oxidation step is preferably carried out at temperatures between 300 and 600C when oxygen (e.g. as air) i9 u~ed as the oxidi 3 ing agent.
The duration of the heating in inert gas i8 not critical. The time needed to heat the carbon to the required maximum temperature is sufficient to produce the required changes in the carbon.
The oxidation ~tep must clearly not be carried out under conditions such that the carbon combusts completely. It is preferably carried out using a gaseous oxidizing agent fed at a controlled rate to avoid over oxidation. Exa~ples of gaseou~
oxidising agents are steam, carbon dioxide, and gases containing molecular oxygen e.g. air. The o~idation is preferably carried out to give a carbon weight 1088 of at least 10% wt based on welght of carbon sub~ected to the oxidation step, more preferably at least 15%
wt.
The weight loss is preferably not greater than 40% wt of the carbon sub~ectecl to the o~idation step, more preferably not greater than 25% wt of the carbon.
The rate of supply of oxidi~ing agent is preferably such that the de~ired we~ght 1088 take~ place over at least 2 hours, more preferably at least 4 hours.
Where an inert atmosphere is required it may be supplied by nitrogen or an inert gas.
Suitably the catalyst comprise~ from 0.1 to 10% by weight Group VIII noble metal preferably from 0.5 to 5% by weight Group VIII noble metal and from 0.1 to 20% by weight rhenium, preferably from 1 to lOX by weight rhenium, the remainder of the catalyst comprising the support.
The catalyst may be further modified by the incorporation of a metal or metals of Group IA, Group IIA or Group IVA, preferably by a metal of Group IA of the Periodic Table of the ElementR. A suitable metal is potas~ium. The amount of the motifying metal(s) may suitably be in the range from 0.1 to 20% by weight based on the total weight of the cataly~t. The addition of a modifying metal to 1~i47~7 - 6 - 22935-~70 the catalyst can have the advantageous effect that carbon-carbon bond hydrogenolysis can be suppressed to a greater or lesser extent during the hydrogenation, thereby improving the selectivity of the process to desired products.
The catalyst may be prepared by a variety of methods.
One method of preparing the catalyst comprises impregnating the support with an aqueous solu-tion of soluble compounds of rhenium and the Group VIII noble metal which compounds are thermally decomposable/reducible to the metal and/or metal oxide.
Impregnation may be by way of co-impregnation or sequen-tial impregnation, preferably by sequential impregnation. Sequen-tial impregnation is preferably effected in the order Group VIII
noble metal followed by rhenium.
A preferred method of producing a catalyst for use in the process of the present invention comprises the steps of:
(A) impregnating a support with a solution o~ a soluble Group VIII noble metal compound thermally decomposable/
reducible to Group VIII noble metal and subsequently removing the solvent therefrom, (B) heating the Group VIII noble metal on the support either (i) in the presence of an inert gas at an elevated tem-perature in the range from 150 to 350C, or (ii) in the presence of an oxygen-containing gas at a temperature in the range from 100 to 300~C, provided that when the support is a high surface area graphitised carbon the upper temperature limit is 200QC, and (C) impregnating the Group VIII noble metal impregnated 7~7 support with a solution of a soluble rhenium compound th~rmally decomposable/reducible to rhenium metal and/or oxide and thereafter removing the solvent therefrom.
The Group VIII noble metal on the support is heated in the presence of either an inert gas, for example nitrogen, or an oxygen-containing gas, for example air~ Heating in the presence of an inert gas may suitably be accomplished at an elevated tem-perature in the range from 150 to 350C. Heating in the presence of an oxygen-containing gas may suitably be accomplished at an elevated temperature in the range from 100 to 300C, provided that when a high surface area graphitised carbon is used as support the upper temperature limit is 200C.
In this embodiment of the in~ention it is not necessary that a solvent in which the Group VIII metal is substantially in-soluble be used in step (C) of the process. Thus any suitable solvent may be usec~ in steps (A) and (C) of the process. Suitable solvents include independently water and alkanols, for example ethanol.
An advantage of the heating step (steplB)) is that the noble metal of Group VIII is rendered less prone to leaching in step (C) of the process.
Preferably, a further step is interposed either between step (A) and step (B) wherein the Group VIII noble metal impreg-nated support is dried, suitably by heating at a temperature in the range from 50 to 150C. It will be appreciated by those skilled in the art that this step may be incorporated into step .-~

i47;~7 7a - 22~35-870 (B)l if desired.
Suitable Group VIII noble metals which are decomposable/
reducible to the metal include salts of the metals, for example carboxylates, nitrates and compounds in which the Group VIII noble metal is present in the anion moiety, for example ammonium i47~7 tetrachloropalladate and ammonium tetranltropalladate. Suitable rhenium compounds which are decomposable/reducible to rhenium metal and/or oxide include dirhenlum decacarbonyl, ammonlum perrhenate and rhenium hepto~ide.
The metal of Group IA, Group IIA or Group IVA of the Periodic Table of the elements may be added to the catalyst composition at any point during its preparation. Thus, the supported palladium/rhenium catalyst may be impregnated with a solution of a soluble compound of the metal. Alternatively, a soluble cpound of the metal may be added to the co-impregnation solution or either of the sequential impregnation solutions.
A preferred catalyst comprises palladium and rhenium supported on a high surface area graphitised carbon of the type described in the aforesaid G~-A-2136704. Contrary to the teaching of the aforesaid EP-A-0147219 (cf Comparison C) regarding unacceptable selectivity 1088es and unde~irable productivity lo~ses in the hydrogenation of maleic acid when the average palladium crystallite size is 100 Angstrom~ or less, we have found that in the hydrogenation of scetic or propionic acids the catalyst selectivity and productivity is substantially independent of average palladium crystallite size in the rangs from 30 to 150 AngstrQms. ~e may therefore use catalysts in which the average palladium crystallite ~ize is in the range from 30 to 99.9 Angstroms.
Before use in the proce~s of the invention the catalyst is preferably activated by contact at elevated te~perature with either hydrogen or a hydrogen/inert gas, for example nitrogen, mixture for a period of from l to 20 hours. The elevated temperature msy suitably be in the range from 200 to 350C. Alternatively, the catalyst may be activated by heating to the reaction temperature in the presence of the reactants.
Nhilst the precise nature of the catalyst on the support can not ~e determined with any degree of confidence, it is believed that the Group VIII noble metal component is in the form of the elemental metal and the rhenium component is in the form of the elemental metal and/or an oxide thereof.

i4~7 The process of the in~ention may suitably be operated at an elevated temperature ln the range from 100 to 350C, preferably from 150 to 300C. The pressure may suitably be less than 50 bar.
The process may be operated batchwise or contlnuously, preferably continuously. The cataly~t may be employed ln the form of a fixed bed, a moving bed or a fluidi~ed bed. The Gas Hourly Space Velocity for continuous operation may ~uitably be in the range from 50 to 50,000 h-l, preferably from 2000 to 30,000 h-1.
The process of the invention will now be further illustrated by reference to the following Examples.
CATALYST PREPARATION
Catalysts were prepared according to the procedures outlined below. In the procedures, HSAG carbon denotes high surface area graphieised carbon, prepared and characterised as follow3:-The carbon used as ~upport was prepared from a commercially available activated carbon ~old by Degussa under the designation BK
IV. The activated carbon was heat treated as follow~. The carbon was heated from room temperature in a stream of argon to 1700C over a period of about one hour. When the temperature reached 1700C the carbon was allowed to cool in the stream of argon to 25C. Thecarbon was then heated in air in a ~uffle furnace at approxima~ely 520C for a time known from experience to give a weight loss of 20 ~wt. The carbon was then heated in argon to between 1800C and 1850C in argon. The carbon was allowed to cool to room temperature in an argon atmosphere. The resulting graphite-containing carbon was then ground to 16-30 ~esh bSS.
The resulting carbon had the following properties:
B~T surface area 710 m2/g basal plane surface area 389 m2/g edge 3urface area 2.3 m2/g BET/basal surface area ratio 1.83 basal plane/edge surface area ratio 169 Example 1 In the following procedures nominal loading is defined as weight of metal (not salt) added to the ~uppor~ expressed as a 47;~7 percentsge of the weight of support.
A. An aqueou~ ~olution containing dissolved palladlum nitrate and rhenium heptoxide (Re207) was added to ~SAG carbon. The water was removed on a rotary evaporator, and the resulting impregnated carbon was then dried at 100C in a vacuum oven overnight. The amounts of the various components were chosen to give four cataly~ts with nominal losdings as follows: Al-2.5~ Pd, 5% Re; A2-2.5~ Pd, 2%
Re; A3-2.5% Pd, 10% Re; A4-5% Pd, Re excluded from the preparation.
B. The procedure used in the pr~paration of catalyst A wa~
followed, except that an appropriate amount of ammonium perrhenate was u~ed lnstead of Re207, and the amounts of components were chosen to give four catalysts with nominal loadings as follows:
Bl-5% Re, 2.5X Pd; B2-SX Re, 10% Pd; B3-5~ Re, 0.5% Pd;
B4-5% Re, Pd excluded.
C. An aqueous solution of palladium nitrate was added to HSAG
carbon, the ~olvent was removed on a rotary evaporator, and the resulting impregnated carbon catalyst dried overnight at 100C ~n a vacuum oven. The ca~alyst wa~ then cooled and transferred to a glass tube r and was then heaeed in a ~tream of hydrogen from ca 30 to-280C over a period of ~ix hours. After ten hours at 280C, the catalyst ~as cooled under hydrogen, and then purged for several hours with nitrogen.
The palladium on carbon was then mixed with an aqueous solution of Re207, the solvent again removed on a rotary evaporator, and the catalyst dried overnight at 100C in a vacuum oven. The amounts of palladium nitrate and rhenium heptoxide were chosen to give nominal loadings of 2.5% Pd and 5% Re in the final catalyst.
D. The procedure used in the preparation of catalyst C was repeated, except that prior to impregnation of rhenium, the palladium impregnated carbon catalyst was treated in nitrogen at 300C instead of hydrogen at 280C.
E. The procedure used in the preparation of catalyst C was repeated, except that the hydrogen treatment step prior to lmpregnation of rhenium was replaced by an air treatment step aa follows. The palladium lmpregnated carbon was heated from 20 to 180C in flowing air over six hour~, and held at 180C for four hours, before coolin in air to 30C.
F. Thi~ catalyst wa~ prepared according to procedure C except that after drying, the palladium on carbon catalyst was not heated in hydrogen, and the solvent used for the impregnation of rhenium was ethanol instead of water.
_. Procedure C wa5 used, except that i~mediately before the rhenium impregnation stage, the reduced palladium on carbon catalyst 10 was treated in flowing nitrogen by heating from 30C to ca 650-700C
over three hours, holding at 650 - 700C for a Eurther sixteen hours, and then cooling to 30C. The effect of thi~ additional step was to increase the palladium crystallite size ~a~ measured by XRD) from 30 A~gstrom (cataly~t from procedure C) to 150 ~ngstrom (catalyst from thls procedure).
H. Caealysts containing ruthenium, rhenium and potassium were prepared as follows. HSAG carbon wa3 mixed with a solution containing ruthenium trichloride and ammonium perrhenate, rhe ~olvent was removed on a rotary evaporator, and the resulting catalysts dried ca 100C overnight in a vacuum oven. The catalyst was then heated in flo~ing hydrogen from ca 30 to 300C over two hours, held at 300C for one hour, then cooled under hydrogen and purged with nitrogen. The reduced catalysts were then impregnated with potassium from an aqueous solution of potassium acetate. The amounts of the various ingredients were adJusted to give four catalysts with nominal loadings as follow~:
H1-5% Re, 5% Ru, (K excluded); H2-5% Re, 5% Ru, 10% R;
H3-5% Ru, 5% K (Re excluded); H4-5% Ru (Re and K excluded).
I. A catalyst containing ruthenlum and rhenium was prepared according to procedure C, except that ruthenium nitrosyl nitrate replaced palladium nitrate, the ruthenium on carbon catalyst was dried at 120C not 100C, and was then heated in hydrogen to 300C
at 4C/minute, and held at 300C for one hour. The amounts of the ingredients were chosen to give nominal loadings of 1% Nthenium and 10% rhenium.

7~7 J. A ruthenium/rhenium catalyst was prepared a~ in procedure I~
except that rhenium was impregnated first.
K. Procedure A was used except that HSAG carbon was replaced by Davison 57 silica, ammonium tetrachloropalladate was uQed instead of palladium nitrata, and only one cataly~t containing nominally 2.5X
Pd and 5% Re was prepared.
L. Procedure C was used for the preparation of a catalyst contalning platinum and rhenium. Tetrammine platinou~ hydroxide replaced palladium nitrate, and the nominal loadings were 1~ Pt and 5% Re.
CATALYST TESTING
For experiments at pressures in ehe range 1 - 11 barg, 2.5 mls of catalyst was loaded into a corrosion resistant stainless steel tube of internal diameter 6 - 7 mm, and the reactor tube assembly placed in a tubular furnace. The catalyst was then activated by heating at atmospheric pressure in a stream of hydrogen to either 280 or 300C over a two hour period, and then holding at the final temperature for one hour. After activation, the catalyst was cooled in hydrogen to the desired reaction temperature. A mixture of carboxylic acid vapour and hydrogen was then passed over the catalyst, and pre~sure was ad~usted to the required value by means of a back-pressure regulator. The vapour/hydrogen mixture was formed in a vapourising zone, to which acetic acid liquid and hydrogen gas were separately metered. The product vapours andgases leaving the reactor were sampled on-line and analysed by gas-liquid chromatography (glc).
For experiments conducted at 11-50 barg, a simllar procedure and apparatus was used, except that the tube had internal diameter 10 mm, up to 10 mls of catalyst wa~ employed, and product~ were passed to a condenser, and gas and liquid products were analysed separately, again by glc.
In both procedures, temperature was measured by means of a thermocouple inserted into the catalyst bed.
The product mixtures typically contained the appropriate alcohol and ester ~the latter formed by esterification of alcohol ~4727 with unreac~ed acid), together with traces of the appropriate dialkyl ether, and aldehyde, and by-product methane, ethaue and ~with propionic acid only) propane. In general, with carhon and silica supported cataly~t~, the maln product i~ alcohol, especially at high conversionY.
For the purposes of the Examples, convers~ons and ~electivities have been calculated as respectively, the proportion of carboxylic acid hydrogenated, and the proportlon of the hydrogenated carboxylic acid which i8 not converted into alkane by-product. Thus, selectlvity denote3 the ability of the catalyst to carry out hydrogenation without alkanation. In all examples (unless stated otherwise) only trace amounts (~2%) of dialkyl ether and aldehyde are formed.
DEFINITIONS
WHSV = Weight Hourly Space Velocity - kg liquid feed per kg catalyst per hour.
LHSV - Liquid Hourly Space Velocity 3 litres liquld feed per litre of catalyst per hour.
Productivity - kg acid converted per kg catalyst per hour.
Examples 2 - 7 Acetic acid was hydrogenated over the catalysts prepared in procedure A Example 1, and procedure C Example 1. The WHSY was ca 1.1 (LHSV 3 0.353, the ratio hydrogen to acetic acid was ca ll:l molar, and the pressure was 10.3 barg. In each case the catalyst was activated at 300C, except for the catalyst of Example 7 (C), which was activated at 280C. The results are collected in Table 1. Steady catalyst activity was observed in all cases. No deactivation was observed over run perlods of up to 24 hours.

~xample C~talyst Y/~CCo~ver~lon s,~ y

2 Al 222 27.2 91

3 Al 202 15.0 90

4 A2 202 6.3 93.6 A3 201 38.2 95.9 6 A4 200 0.6 30.4 7 C 217 52.1 93 L I L
The results show the benefit of sequential impregnation of Pd and Re (Example 7), and the poor performance of catalyst A4 (Example 6), which contains only palladium, and i5 not a catalyst according to the invention.
Examples 8 - 13 -The same procedure as in Examples 2 - 7 was followed, but using the catalysts prepared according to procedure B Example 1. All catalysts were actlvated at 300C. Re~ults are presented in Table Exa~ple C~talyst TJCConversion Selectivity 8 Bl 180 15.4 97.0 9 Bl 210 37.5 95.1 Bl 239 69.0 89.0 11 B2 210 45.0 95.0 12 B3 210 18.5 96.9 13 B4 210 13.7 97.6 _ 1 1.. 1 I I
The Catalyst of Example 13 is not according to the present invention, and is included for the purpo~es of comparison.
Examples 14 - 17 The catalyst prepared by procedures C, D, E and F of Example 1 werP compared in the hydrogenation of acetic acid. The procedure of Examples 2 - 7 was followed, except that the WHSV was ca 4 (LHSV - 1.34~, and the ratio hydrogen to acetic acid was 9:1 molar.
The catalysts were activated at 280C before use, and the reaction temperature wa~ 228 -230C. Results are collected in Table 3.

7;~7 _ E~ample Catalyst Productivity Selectivity (kg/kg cat/h) (C) 14 C ~.292.2 D 1.392.1 16 E 1.187.0 ¦17 F 0.9594.5 lo I I L
The results show that within experimental error, ca~alysts of similar high activity may be generated using a range of ~equential impregnation techniques.
Examples 18 The procedure of Examples 14 - 17 was repeated using the catalyst prepared according to procedure G Example 1. The productivity was ound to be 1.0 kg/kg cat/h, with 92.7%
selectivity. Within experimental error, these results are similar to those obtained in Example 14, even though the catalyat of this Example has Pd crystallites (as determined by XRD) of average ~ize 150 Angstrom, whereas that of Example 14 has an average Pd cry~tallite size of only 30 Angstrom. The results show that no significant losses of activity and selectivity result when catalysts containing small Pd crystallites of ~100 Angstrom are employed in 25 contrast to the teaching of EP-A-147219 (Comparison C).
Example 19 The catalyst prepared by procedure C was tested in acetic acid hydrogenation at 50 b~rg and 227C. The WHSV was 15, and the ratio hydrogen:acetic acid was 9:l ~olar. The catalyst was activated at 30 280~C.
The acetic acid conversion was 40%, with 96% selectivity.
This corre~ponds to a productivity of 6 kg/kgcat¦h acetic acit converted. Under ~imilar conditions but with ~SV - 3.6, conversion was 74Z with 96~ selectivity.
Examples 20 - 24 The catalysts prepared by procedure H were tested in the hydrogenation of acetic acid. The catalysts were activated at 1~i47~7 300C. The WHSV was ca 1.1 (LHSV = 0.35), and the ratio hydrogen to acetic acld was 11:1 m~lar. Results are collected in Table 4.

Example Catalyst P/btrg T/~C Conversion Selectlvlty 22 H2 10 194 54 58.5 23 H3 10 203 35.2 8.7 24 H4 5 201 22.3 5.9 L 1 .. I 1.......... I
The results show the beneficial effect of potassium in improving selectivity, and that catalysts H3 and H4 which are not according to the present invention, show very poor performance.
Examples 25 - 28 Catalysts prepared by procedures I and J of Example 1 were examined in the hydrogenation of propionic ac~d. The procedure of Examples 2 - 7 was repeated, except that only 2 mls of catalyst was employed, LHSV - 1, the ratio of propionic acid to hydrogen was 1:10 molar, the pressure was 9 barg, and the catalyst were activated at 280C. Results are collected in Table 5. In each case, the concentration of aldehyde in the product was greater than the trace amounts encountered in other Exa~ples. Independent selectivities to aldehyde are therefore reported.

Example Catalyst T/C Conversion Selectivity Selectivity (%) (%)(% aldehyde) I 202 22.5 97 4 26 I 223 32.0 94 3 27 J 201 12.5 97 5 28 J 222 23.0 96 5 The results show that sequential impregnation of Ru then Re yields better catalysts than sequential impregnation of Re then Ru.

: :..-. .. . ..

47~7 Examples 29 and 30 The catalysts prepared by procedure K Example 1 were tested in the hydrogenation of acetic acid. The procedure of ~xamples 2 - 7 was adopted, except that the catslyst of Example 30 was activated at 450C, and that of 29 at 300Cr Re~ults are collected in Table 6.

¦ Example ¦ Catalyst ¦ T/C ¦ Conversion ¦ Selectivity ¦
. . _ 29 K 209 12.2 91.7 R 210 10~5 95.3 Example 31 The catalyst prepared by procedure L was employed for the hydrogenation of acetic ac$d, according to the procedure of Examples 14 - 17. The conversion was 11.0% (productivity 0.5 kg/kg cat/h converted) with 93.8% selectivity.
Example 32 The catalyst prepared according to procedure Bl was used for the liquid phase hydrogenation of acetic acid. 1.01 g of the powdered cataly~t was charged to a 100 ml stainless steel autoclave, along with 50.2 g of acetic acid. The autoclave was flushed and then pressurised with hydrogen to 100 barg, and heated with stirring to 200aC, at which temperature it was held for 6.0 hours. After cooling, the liquid phase product was removed and filtered, and analysed both for organic products and rhenium and palladium metals. The final pre~sure after cooling ~as 50 barg.
The product was found to contain 27.9X wt ethyl acetate and 2% wt ethanol (corresponding to a productivity of 1.5 kg/kg cat~h converted by hydrogenation). In addition, 16~ of the rhenium and 0.06~ of the palladium originally on the catalyst was found to have leached into solution.
This example demonstrates that considerable leaching of rhenium can occur in the liquid phase hydrogenation of acetic acid. This is in contra~t to reactions carried out in the gas phase, where no i47~7 detectable loss of rheniu~ occur~.
Thi~ is not an example according to the present invention because it was carried out ln the liquld pha~e. It is included only for the purpose of co~parison.

Claims

Case 5930(2) The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1 A process for the production of either ethanol from acetic acid or propanol from propionic acid which process comprises contacting either acetic acid or propionic acid in the vapour phase with hydrogen at elevated temperature and a pressure in the range from 1 to 150 bar in the presence of a catalyst comprising as essential components (i) a noble metal of Group VIII of the Periodic Table of the Elements, and (ii) rhenium.

2 A process according to claim 1 wherein the noble metal of Group VIII is palladium.

3 A process according to claim 1 wherein the noble metal of Group VIII is ruthenium.

4 A process according to claim 1 wherein the catalyst is supported.

5 A process according to claim 4 wherein the support is a high surface area graphitised carbon.

6 A process according to claim 4 wherein the support is a silica.

7 A process according to claim 1 wherein the catalyst is modified by incorporation of a metal of Group IA of the Periodic Table of the Elements.

8 A process according to claim 7 wherein the modifying metal is potassium.

9. A process for the production of a catalyst for use in the process of claim 1 which process comprises the steps of:
(A) impregnating a support with a solution of a soluble Group VIII noble metal compound thermally decomposable/
reducible to the Group VIII metal and subsequently removing the solvent therefrom, (B) heating the Group VIII noble metal on the support either (i) in the presence of an inert gas at an elevated tempera-ture in the range from 150 to 350°C, or (ii) in the presence of an oxygen-containing gas at a temperature in the range from 100 to 300°C, provided that when the support is a high surface area graphitised carbon the upper temperature limit is 200°C, and (C) impregnating the Group VIII noble metal impreg-nated support with a solution of a soluble rhenium compound thermally decomposable/reducible to rhenium metal and thereafter removing the solvent therefrom.

10. A process according to claim 1 wherein the catalyst is activated before use by contact at elevated temperature with either hydrogen or a hydrogen/inert gas mixture at a temperature in the range from 200 to 350°C for a period of from 1 to 20 hours.

11. A process according to claim 1 wherein the catalyst is activated by heating to the reaction temperature in the presence of reactants.

12. A catalyst for use in the process of claim 1 comprising palladium and rhenium supported on a high surface area graphitised carbon wherein the average palladium crystallite size is in the range from 30 to 99.9 Angstroms.

13. A modification of the process of claim 1 wherein the corresponding ester is co-produced and the proportion of co-produced ester is increased either by operating at low conversions per pass or by introducing an acidic component into the catalyst.