CA1229096A

CA1229096A - Process for hydrogenolysis of carboxylic acid esters

Info

Publication number: CA1229096A
Application number: CA000401903A
Authority: CA
Inventors: Michael W. Bradley; Norman Harris; Keith Turner
Original assignee: Davy Mckee Oil and Chemicals Ltd
Current assignee: Johnson Matthey Davy Technologies Ltd
Priority date: 1981-04-29
Filing date: 1982-04-28
Publication date: 1987-11-10
Also published as: JPS58500993A; BR8207962A; WO1982003854A1; MX156577A; JPH0457655B2; SE8303027L; IT1190783B; NL8220121A; NZ200442A; NL191438C; GB2116552B; SE452154B; AU560590B2; GB2116552A; AU8336582A; FI831848L; FI831848A0; GB8306413D0; SE8303027D0; NO824396L

Abstract

ABSTRACT OF THE DISCLOSURE
Catalytic hydrogenolysis of carboxylic acid esters to produce alcohols is conducted in the vapor phase using hydrogen gas and a catalyst comprising a reduced mixture of copper oxide and zinc oxide, at temperatures at from about 75°C to about 300°C and pressures from about 0.1 kg/cm2 to about 100 kg/cm2 absolute. The ester may be essentially any of a vaporisable ester. The process is preferably carried out in a continuous manner, using a solid pelletized catalyst.

Description

~229~

PROCESS FOR HYDROGENOLYSIS_OF CARBOXYLIC ACID~ESTERS
J

This invention relates to the hydrogenolysis of carboxylic acid esters.
Hydroaenolysis of carboxylic acid esters has been described on numerous occasions in the literature. Typically in such a reaction the -CO-O- linkage of the ester group is cleaved so that the acid moiety of the ester group i5 reduced to an alcohol whilst the alcohol moiety is released as free alcohol acco~ding to the following equation:
RlCR2 ~ 2H2 = RlCH2OH ~ HOR2 (I) where Rl and R2 are each alkyl radicals, for example.
According to page 129 et seq of the book "Catalytic Hydrogenation in Organic Synthesis" by M. Freifelder, published by John Wiley and Sons Inc (1978), the catalyst of choice for t~is reaction is said to be barium promoted cop~er chromite. Typical reaction condit.ions include use of temperatures in the region of 250C and pressures in the range of 225-250 atmospheres (about 22.81 MPa to about 25.35 MPa). Although a good yield of alcohol is often obtained using this technique for hy~3rogenolysis of an ester, the temperature necessary or conversion of the ester to alcohol is also conducive to side reactions. For example, the resulting alcohol may undergo further hydrogenolysis to hydrocarbon or may react with s~arting material to produce a higher molecular weig~-t ester that is more difficult to hydroye~olyse.
Besides these side reactions copper chromite catalysts have other disadvantages for commercial scale operation. In particular, the use of copper chromite catalysts is environmentally hazardous and necessitates the adoption of special and costly handling techniques on account of the toxicity of chromium. Moreover it is difficult to produce successive batches of copper chromite w.ith reproduci~le catalyst ac~ivity.
J

United States Patent Specification No. 2079414 describes a process for catalytic hydrogenation of esters using catalys-ts such as fused copper oxide, either wholly or partially r~duced, which may be promoted with oxide promoters such as manganese oxide, zinc oxide, magnesium oxide or chromium oxide. Particularly recommended catalysts are those comprising copper oxide promoted by chromium oxide, e.g.
copper chromite. According to page 3, right-hand column line 57 et seq.: "In operating in the vapour phase it is preferred to use temperatures within the range of 300C to 400C". It is also stated that: "The best conversions to alcohols are obtained at the highest pressures obtainable in the available equipment and at the lowest temperatures consistent with obtaining a practical rate of reaction" (page 4, right hand column, line 2 et seq.~. The Examples describe batch reactions and in all cases the pressure is 2500 psia or higher (17250 kPa or higher), whilst in all cases the temperature is 250C or higher; in most cases i-t exceeds 300~C. A limitation to the process is that methyl esters cannot be used because methanol, which would be a hydrogenation product from a methyl ester, is subject to gaseous decomposition (see page 5, right hand column, line 58 et ~). Similar considerat:ions would appear to prevent the application of the process to esters of formic acid since the formic acid moiety would also be likely to yield methanol.
Further teaching of the use of chromites as catalysts for hydrogenation of esters will be found in United States Paten~ Specification ~o. 2109844.
Example 4 of Vnited States Patent Specification No.
3197418 discloses the preparation of a copper-~inc catalyst which can be used in the liquid phase hydrogenation of oils and fats at pressures in excess of 120 kg/cm2 (11776 kPa) and at a temperature of 3~0~C.
Vnited States Patent 5pecification No. 2241417 teaches the produc~ion of higher aliphatic alcohols by liquid ~3L2~9~3~6 phase hydrogenation of glycerides in the presence of copper-containing catalysts at temperature of 200C to 400C
and at pressures of 60 to 500 atmospheres (5884 to 49033 kPa).
Hydrogenolysis of esters to saturated hydrocarbons using catalysts having as essential ingredients an indium or rhodium component and a halogen component is described in United States Paten-t Specification No. 4067900.
Catalytic hydrogenolysis of formate esters present in oxo reaction products using Ni catalysts is described in East German Patent Specification No. 92440 (see Chem. Abs., 124069j, Vol 78 (1973), page 439). O-ther references to hydrogenation of formates include a paper by E. Lederle, Anales Real Soc. Espan. Fis. y Quim. (Madrid) 57B, pages 473-S (1961). Also West German Patent Specification No.
902375 describes the production of methanol by hydrogenation of alkyl formates at pressures of 20 to 50 atmospheres (1961 to 4903 kPa) using copper chromite catalysts; there is a passing suggestion to incorporate zinc oxide in the catalyst.
Catalytic cleavage of formic acid esters is described in British Patent Specification No. 1277077.
According to this proposal a hydrogenation catalyst containing copper and nickel is used but the formyl radical is reported to he dehydrogenated in the course of the reaction and appears as carbon monoxid Production of ethylene glycol by hydrogenolysis is suggested by some references including United States Patent Specification No. 4113662 which teaches hydrogenation of esters to alcohols at temperatures of 150VC to 450C and pressures of 500-10,000 psig (3450-69000 kPa) using catalysts comprising cobalt, zinc and copper. Examples IV, V and VIII
describe comparative experiments using polyglycolide and ~ethyl glycolate with Cu-Zn oxides as catalyst at 250~C and at pressures of at least 2800 psig tl9421 kPa~, i.e.
conditions under which the ester (polyglycolide or methyl ~Z~909~;

glycolate) is in the liquid phase. United States Patent Specification ~o. 2305104 describes hydrogenation of alkyl glycolates using catalysts containing Zn, Cr, and Cu to produce ethylene glycol. Vapour phase hydrogenation oE
oxalate esters at temperatures of 150~C to 300C for the production of ethylene glycol has been described in United States Patent Specification No. 4112245; this process uses a copper chromite or copper zinc chromite catalyst and re~uires that the oxalate ester has a sulphur content of less than 0.4 ppm.
It would be desirable to provide a process for effectirlg hydrogenolysis of esters with negligible formation of by-products or of "heavies" which can be effected under mild conditions.
It would further be desirable to provide a process for effecting hydrogenolysis of methyl esters of aliphatic C2+ monocarboxylic acids without significant decomposition of product methanol in the course of the reaction.
It would also be desirable to provide a hydrogenolysis process which utilises a simple catalyst that can be prepared with reproducible catalyst activity.
The present invention accordin~ly seeks to provide an improved process for effectinc3 hydrogenolysis of alkyl esters of aliphatic C2+ monocarboxylic acid esters which can be effected under mild conditions.
It also seeks to provide a process for the production of ethanol by eEfecting hydrogenolysis of alkyl acetates in high yield and at high conversions under mild conditions.
According to the present invention there is provided a continuous process for the production of an optionally substituted C2+ alkyl alcohol which comprises:
vaporising an alkyl ester of a C2+
aliphatic monocarboxylic acid in a stream of a hydrogen-5 2;~9~

containing gas to form vaporous mixture containing the ester in vapour form and hydrogen, the partial pressure of the ester in the vaporous mixture being at least about 0.05 kg/cm2 (about 4.9 kPa);
supplying the vaporous mixture to a catalytic reaction zone containing a charge of a eatalyst consisting essentially of a reduced mixture of copper oxide and zine oxide;
contacting the vaporous mixture with the eatalyst at a temperature of from 150C to 240C and at a pressure in the range of from 5 kg/em2 absolute (491 kPa) up to 50 kg/em2 absolute (4906 kPa); and reeovering from the catalytic reaction zone a reaction product comprising at least one optionally substituted C2+ alkyl alcohol.
The ester may be essentially any vaporisable alkyl ester of a C2+ aliphatic monocarboxylic acid.
Amongst esters that may be mentioned are those of the general ~ormula:
R COOR' in whieh R represents a substituted or unsubstituted monovalent hydrocarbon radical and R' represents an alkyl radical. Preferably the ester of formula RCOOR' has a boiling point at atmospheric pressure of not more than about 300C. Examples of possible substituents on the radical R inelude oxygen atoms as well as hydroxy and alkoxy groups. Preferably R and R' eaeh contain from 1 to 12 earbon atoms. Typically R is seleeted from alkyl, alkenyl, alkoxyalkyl, and hydroxyalkyl radieals.
Sueh esters may be derived from the following aeids:
aeetie aeid;
propionie acid;
n- and iso-butyric acids;
n- and iso-valeric aeids;

.: ;

- 6 - 1229~96 caproic acid;
caprylic acid;
capric acid;

2-ethylhexanoic acid;
glycolic acid;
pyruvic acid;
acrylic acid;
methacrylic acid;
alpha- or beta-crotonic acid;
methoxyacetic acid;
lactic acid;
and the like.
Preferably the acid contains from 2 to 12 carbon atoms.
The ester is further derived from an alkyl alcohol. Suitable alkyl alcohols may be selected from:
methanol;
ethanol;
n- or lso-propanol;
n-, iso-, sec- or t-butanol;
pentan-l- or -2-ol;
2-methyl-butan-2-, -3- or -4- ol;
hexanols;
heptanols;
octanols (e.g. 2-ethyl-hexanol~;
cetyl alcohol;
lauryl alcohol;
I and the like.
Preferably the alkyl alcohol contains not more than 12 carbon atoms.
As examples of specific esters there may be mentioned:
alkyl acetates te.g. methyl, ethyl, n- and so-propyl, and n-, iso-, sec-and t-butyl acetates);
alkyl propionates (e.g. n-propyl propionate);

,,~ r~;.
~,', `` ~

.

~2~ 6 alkyl n-butyrates (e.g. n-butyl n -butyrate);
alkyl iso~butyrates (e.g. iso-butyl lso-butyrate);
alkyl n-valerates te.g. n-amyl valerate);
alkyl iso-valerates (e.g. methyl lso_ valerate);
alkyl caproates (e.g. ethyl caproate);
alkyl caprylates (e.g. methyl caprylate);
alkyl caprates (e.g. ethyl caprate);
alkyl 2-ethylhexanoates (e.g. 2-ethylhexyl 2-ethylhexanoate);
alkyl alkoxyacetates (e.g. methyl methoxyacetate); alkyl glycolates (e.g. methyl and ethyl glycolates);
alkyl lactates (e.g. ethyl lactate);
alkyl pyruvates (e.g. ethyl pyruvate);
and the like.
In the process of the invention the vaporous mixture to be contacted with the catalyst contains, in addition to the ester, hydrogen either alone or in admixture with other gases tdesirably gases inert to the ester and the catalyst). The gaseous mixtures containing hydrogen include inert gases such as nitrogen, or carbon monoxide.
The term "hydrogen-containing gas" as us~d herein includes both substantially pure hydrogen gas as well as gaseous mixtures containing hydrogen.
~ The hydrogenolysis process o the present ; 30 invention is conducted at a temperature of between 150~C
and 240C~ Typically the temperature is between l~O~C and 240C. The total pressure is between 5 kg/cm2 a~solute (491 kPa) and 50 kg/cm2 absolute (4906 kP~, and even more preferably between 5 kg~cm2 absolute t491 kPa~ and 25 kg/cm~ absolute (2453 kPa).

The catalyst is a mixed metal oxide catalyst that consists essentially of a reduced mixture of copper oxide and zinc oxide. By the term "consists essentially of" we mean that the catalyst includes as essential ingredients in the mixture before reduction copper oxide and zinc oxide, but may also include amounts of other metal oxides that do not materially alter the basic characteristics of the catalyst as well as inert fillers or supports, such as carhon.
The catalyst may be der~ved from a mixture which contains only copper oxide and zinc oxide. Alternatively it may include one or more other materials, such as an inert support or other material that is effectively catalytically inactive in the ester hydrogenolysis 15 reactionO
The mixture of CuO and Zn0, before reduction, preferably contains from about S to about 95 percent by weight, typically from about 10 to about 70 percent by weight, of CuO
and from about 95 to about 5 percent by weight, typically from about 90 to about 30 percent by weight, of ZnO. Hence the mixture may contain, for example, from about 20 to about 40 percent by weigllt of CuO and from about 60 to about 80 percent by weight of ZnO. A preferred mixture, for example, comprises from about 30 to about 36 percent by weiqht of CuO and from about 62 to about 68 percent by weight of ZnO. Other particularly preferred mixtures comprise from about 65 to about 85 percent by weight of CuO and from about 35 to about 15 percent by weiqht of ZnO, for example mixtures comprising from about 68 to about 75 percent by weight of CuO and from about 32 to about 25 percent by weight of ZnO. As already mentioned, the hydrogenolysis catalyst may contain minor amounts of other materials such as carbon, sodium, titanium, r~irconium, manqanese, silica, diatomaceous earth, kieselquhr, and aluminium oxide. Such other materials do not usually comprise more than about 20 percent by weiqht calcula~ed (except in the case of carbon) as oxide. In the case of sodium it is best not to ~2~
g exceed about 0.5 percent by weight, calculated as oxide.
Hence other preferred catalysts include mixtures comprising from about 40 to about 50 weight peroent each of CuO and ZnO and from 0 to about 20 weight percent of alumlna. The catalyst is, however, preferably essentially free from other metals, particularly from metals of Group VIII of the Periodic Table, such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt, as well as from Group VI8 metals, such as Cr, Mo, and W, from the metals Tc, Ag, Re, Au and Cd, and also fro~ elements of atomic number 80 and above, e.g. Hg and Pb. By the term "essentially free" we mean that the catalyst contains not more than about 0.1 wt~ (i.e. not more than about 1000 ppm~, and preferably not more than about 250 ppm, of the element in question. The catalyst lS may be prepared by any of the methods known in the art of forming a composite of copper oxide and ~inc oxide. The catalyst may be prepared by fixing the separate oxides, by coprecipitation of the oxalates, nitrates, carbonates, or acetates, followed by calcination. The coprecipitation method is preferred. Generally, the mixture of CuO and ZnO is reduced by hydrogen or carbon monoxide at a temperature in the range of between about 160C anclabout 250C
for several hours, preferably for 8 to 29 hours, prior to contact with the vaporous mixture containing ester and hydrogen. If the catalyst is charged in a pre-reduced form the period required for reduction can be reduced accordingly.
The mixture of CuO and ~nO is reduced prior to its use as catalyst in the hydrogenolysis step. ~ydrogen or CO, or mixtures thereof, are generally mixed with a diluent gas such as steam, nitrogen, or combustion gas, to maintain the catalyst bed temperature and to carry away the heat of reduction.
Reduction of the mixture of CuG and'~nO is complete when no more hydro~en or carbon monoxide is being f`

_ 1 0 reacted as shown by analysis of the inlet and outlet gas.
Whe~ using hydrogen complete reduction of the mixture occurs when the total amount of water produced ~n the reduction i~ equal to the stoichiometric value of water which should be produced when a given amount of copper oxide is reduced to copper. This value is about 0.079 kg of water per kg of catalyst for a mixture containing 35 weight percent of CuO.
An inert carrier material may be included in the hydrogenolysis catalyst composition. The catalyst is generally formed into pellets, tablets, or any other suitable shape prior to use, by conventional techniques.
It is advantageous that the mixture oE CuO and ZnO
have an internal surface area of from about 25 to about 50 sq.~.
per gram. The internal surface area may be determined by the well-known BET method.
The process of the present invention is carried out in a continuous manner. In the preferred method of continuous operation, an ester, or a mixture of esters, a hydrogen containing gas, and optionally, a carrier gas such as nitrogen, may be brought together and, under the desired pressure contacted in the vaporous state with the catalyst. The reaction zone advantageously is an elongated tubular reactor wherein the catalyst is ~5 positioned.
In the hydrogenolysis process of the invention the primary reaction observed is that of equation ~I) above. Hence a monocarboxylic ester yields a mixture of alcohols, one derived fxom the carboxylic acid moiety and one derived from ~he alcohol moiety. Some esters, for example ethyl acetate, may produce a single alcohol as the alcohol derived from the carboxylic acid moiety in this case is the same as that derived from the alkyl moiety.
The alcohol product or products from the hydrogenolysis reaction may be separated from the hydrogen by . ~

9~6 condensation and the excess hydrogen can be compressed and recycled to the reaction zone. The crude alcohol product may be used in this form or it can be further purified in a conventional manner such as by fractional distillation.
s If desired, any unconverted portion of the ester or ester mixture may be separated from the reaction product and recycled to the reaction zone and, preferably, admixed with fresh feed gases priox to entering the reaction zone.
In operating the process of the invention the partial pr,essure of the ester may vary within wide limits, e.~. from about 0.05 kg/cm '(4.9 kPa) or less up to about 10 kq/~2 (981 kPa) or more. Care must however be taken to ensure that at all times the temperature of the vaporous mixture in contact with the catalyst is above the dew point of the ester and of any other condensible component present under the prevailing pressure conditions.
The vaporous mix.ture preferably contains at least an amount of hydrogen corresponding to the stoichiometric quantity of hydrogen required for hydrogenolysis. Usually an excess of hydrogen over the .~
.~ , .

-12- ~2~9~
stoichiometric quantity will be present. In this case the excess hydrogen remaining after product recovery can be recycled to the catalytic reaction zone. As will be apparent from equation (I) above, 2 moles of hydrogen are required for hydrogenolysis of each carboxylic acid ester group present in the ester molecule. If the ester contains non-aromatic unsaturation (i.e. carbon-carbon double or triple bonds) such unsaturated linkages may also undergo hydrogenation under the hydrogenolysis conditions employed. Hence the stoichiometric quantity of hydrogen required for reduction of 1 mole of an unsaturated mono-ester may correspond to 3, 4 or more moles of hydrogen.
The hydrogen:ester molar ratio within the vaporous mixture may vary within wide limits, e.g. from about 2:1 to about 100:1 or more. This ratio will depend, at least to some extent, on the volatility of the ester used. Typically the hydrogen:ester molar ratio is at least about 25:1.
Although the process of the invention is generally applicable to alkyl esters of aliphatic C2+ monocarboxylic acids, best results will usually be obtained with esters boiling at temperatures of not more than about 300C at atmospheric pressure. Whilst it is possibl~ to utilise esters having still higher boiling points, the use of higher boiling point materials limits the partial pressure of the ester that can be used in the vaporous mixture and hence limits the rate of hydrogenol~sis~ If extremely high boiling esters are used then rates of reaction will be correspondingly reduced.
Certain alkyl esters of aliphatic C2~
monocarboxylic acids may undergo ~hermal decomposition at temperatures approaching 300C and possibly at temperatures b~low their boiling point at atmospheric B

pressure. When using such esters the temperature during hydroqenolysis should not be so high that significant thermal decomposition of the ester ~ccurs. ?
In general it is preferred to use alkyl esters of C2+ aliphatic monocarboxylic acids containing from 3 to 20 car~on atoms.
According to a further aspect of the present invention there is pro~ided a continuous process for the production of ethanol in which a vaporous mixture containing (1) an alkyl ester of acetic acid and (2) hydrogen, in which vaporous mixture the partial pressure of the ester is at least about 0~05 kg/cm2 (about 4.9 kPa), is continuously fed into contact with a catalyst consisting essentially of a reduced mixture of copper oxide and zinc oxide at a temperature in the range of from 150C up to 240C and at a pressure in the ranqe of from 5 kg/cm2 absolute (491 kPa) up to 50 kg/cm2 absolute (4906 kPa), and resulting ethanol is recovered.
2Q In the hydrogenolysis of acetic acid esters to produce ethanol the temperature preferably ranges from 180C to 240C and the pressure from 5 kg/cm2 absolute (491 kPaJ to 35 kg/cm2 absolute (3435 kPa).
In all cases recovery of the hydrogenolysis products can be effected in conventional manner, e.q. by condensation followed, if desired, by fractional distillation under normal, reduced or ele~ated pressure.
The invention is further illustxated in the follvwinq Examples.

~ ~ ~2~9~

Example 1 n-butyl butyrate was pumped at a rate of 3.8 ml/hr to an electrically heated gas/liquid mixing device to which hydrogen was also supplied at a controlled rate and pressure. The resulting vaporous mixture was passed through a lagged, electrically heated line t~ a pre-heating coil prior to passage through a tubular reactor packed with 146 ml of a powdered catalyst. Both the tubular reactor and the pre-heating coil were immersed in a molten salt bath which was heated to 174C. The vaporous mixture exiting the reactor was passed through a water cooled condenser and the resulting condensate was collected in a water-cooled knock out pot. The exit gas pressure was controlled to 10.55 kg/cm2 absolute (1035 kPa). The non-condensed gases were then passed through a let-down valve, the gas flow xate being monitored downstream from this valve in a wet gas meter. A gas flow rate of 46.4 litres/hr (measured at atmospheric pressure) was maintained throughout the experiment. The ester partial pressure in this experiment was 0.12 kg/cm2 (12 kPa) and the hydrogen:ester molar ratio was 84.3:1. The liquid hourly space velocity was 0.025 hr~l.
The liquid condensate was analysed by gas chromatography using a 2 metre stainless steel column t6 mm outside diameter) packed with polyethylene glycol (nominal molecular weight 20,000) on Chromosorb PAW, a helium gas flow rate of 30 ml/minute and a flame ionisation detectorO (The word "Chromosorb~' is a Registered Trade Mark). Th~ instrument was fitted with a chart recorder having a peak integrator and was calibrated using a mixture of n-butanol and n-butyl butyrate of known composition. The condensate was shown to contain a mixture of 99.62 wt ~ butanol and 0.28 wt % n-butyl butyrate, corresponding to a 99.7% conversion -15- ~29096 with essentially 100% selectivity.
The catalyst used in this Example was charged to the reactor as a co-precipitated mixture of CuO and ZnO containing 33+3% Cuo and 65+3% ZnO having a particle size in the range of 1.2 mm to 2.4 mm and an internal surface area of about 45 sq. m. per gram. This was pre-reduced in the reactor using a 5 vol % H2 in N2 gas mixture at 200C for 17 hours followed by pure hydrogen at 200C for 8 hours, the gas flow rate in each case being about 20 Iitres/hr (measured at atm~spheric pressure using the wet gas meter) and the gas pressure being 10.55 kg/cm2 absolute (1035 kPa). After this pre-reduction stage the catalyst was at all times maintained in a hydrogen-containing atmosphere.
Example 2 The procedure of Example 1 was repeated using ethyl acetate in place of n-butyl butyrate at a feed rate of 7.4 mls/hr and a hydrogen flow rate of 41.9 litres/hr (measured at atmospheric pressure by means of the wet gas meter). In this experiment the liquid hourly space velocity was 0.05 hr~l, the salt bath temperature was 185C and the exit gas pressure was 10.55 kg/cm2 absolute (1035 kPa). The hydrogen:ester molar ratio was 23.3:1 and the ester partial pressure 25 was 0.43 kg/cm2 (42 kPa). The liquid condensate was shown to contain a minor amount of ethyl acetate, a major amount of ethanol and a trace of n-butanol. The observed conversion to ethanol was 97.1~ and the selectivity to ethanol was about 95~.
Exam~e 3 When the procedure of Example 2 was repeated at a salt bath temperature of 203C, with a gas flow rate of 160.4 litres/hr and a liquid feed flow rate (of ethyl acetate) of 34~8 ml/hr (i.e. a liguid hourly space ~ t ~2~9~g6 velocity of 0.24 hr-l), both ethyl acetate and ethanol were identified in the liquid condensate but essentially no n-butanol was formed. The hydrogen:ester molar ratio was 19.0:1 and the ester partial pressure was 0.53 kg/cm2 (52 kPa). The conversion of ester was 82~6% and the selectivity to ethanol was approximately 1 00% .
Example 4 The procedure of Example 1 was repeated using methyl acetate in place of n-butyl butyrate at a feed rate of 75 mls/hr (i.e. a liquid hourly space velocity of 0.51 hr~l) and a hydrogen flow rate of 115.2 litres/hr (measured at atmospheric pressure). In this experiment the salt bath temperature was 194C and the 15 exit gas pressure was 9.49 kg/cm2 absolute (935 kPa).
The hydrogen:ester molar ratio was 5.06:1 and the ester partial pressure was 1.57 kg/cm2 (154 kPa). The liquid condensate was shown to contain 55.7 wt~ methyl I acetate, 10.02 wt% ethyl acetate, 15.24 wt% ethanol, and ¦ 20 18095 wt~ methanol. The observed conversion to ethanol ~ was 52.4 mol%.
¦ Example 5 ! The procedure ~f Example 4 was repeated at a ' salt bath temperature of ~17C with an exit gas pressure ] 25 of 8.86 kg/cm2 absolute (868 kPa), with a gas flow rate of ~25 litres/hr, and with a liquid feed flow rate (of methyl acetate) of 75 ml/hr. In this Example the partial pressure of methyl acetate was 0,81 kg/cm2 (79 kPa), whilst the hydrogen:ester molar ratio was 9.9:1.
The liquid hourly space velocity was 0.51 hr~l. The liquid condensate was shown to contain l9r31 wt% methyl acetate, 11.19 wt~ ethyl acetate, 35.64 wt~ ethanol, and 31.96 wt~ methanoi. The observed conversion to ethanol was 72.40 mol%~
Example 6 ~.

The procedure of Example 1 was repeated using ~ec-butyl acetate in place of n-butyl butyrate at a feed rate of 118 mls/hr (i.e. a liquid hourly space velocity of 0.81 hr~l) and a hydrogen flow rate of 193.9 litres/hr (measured at atmospheric pressure). In this experiment the salt bath temperature was 203C and the exit gas pressure was 10.55 kg/cm2 absolute tlO35 kPa). This corresponded to an ester partial pressure of 1.37 kg/cm2 1134 kPa) and a hydrogen:ester ~olar ratio of 6.7:1. The liquid condensate was shown to contain 6.0 wt% ethyl acetate, 20.6 wt% ethanol, 40.1 wt%
sec-butyl acetate, and 33.3 wt~ sec-butanol. The observed conversion to ethanol was 59.9 mol~ and the selectivity to ethanol and sec-butanol was essentially 100~.
Example 7 t-butyl acetate was pumped at a rate of 18.3 ml/hr to an electrically heated gas/liquid ~ixing device to which hydrogen was also supplied at a controlled rate and pressure via an electrically heated line. The resulting vap~rous mixture was passed through a lagged, electrically heated line to a pre-heating coil prior to passage through a tubular stainless steel reactor packed with 15 ml of a crushed catalyst. Both the tubular reactor and the pre-heating coil were immersed in a molten salt bath. The temperature of the salt bath was adjusted until the temperature of the vaporous mixture, as detected by a thermoc~uple positioned immediately upstream from the catalyst bed, was 2Ql~C. The vaporous mixture exiting the reactor was passed through a water cooled condenser and then through a second refriger~ted condenser through which coolant at -15~C was passed.
The resulting condensate was collected in a refrigerated knock out pot also ~ept at -15C. The exit gas pressure was controlled t~ 26.7 ky/cm~ absolute ~2622 kPa).

~,, !36 The non~condensed yases were then passed through a let-down valve, the gas flow rate being monitored downstream from this valve in a wet gas meter. A gas flow rate of 156.6 litres/hr (measured at atmospheric pressure) was maintained throughout the experiment. The liquid hourly space velocity of the t-butyl acetate was 1.22 hr~l, the H2:ester molar ratio was 47.0:1, and the ester partial pressure was 0.55 kg/cm2 ~54 kPa).
The liquid condensate was analysed by gas chromatography using a 2 metre stainless steel column (6mm outside diameter) packed with polyethylene glycol (nominal molecular weight 20,000) on Chromosorb PAW, a helium gas flow rate of 30 ml/minute and a thermal conductivity detector. The instrument was fitted with a chart recorder having a peak integrator and was ; calibrated using a mixture of ethanol, t-butanol, ethyl acetate, t-butyl acetate and water of known composition.
¦ ¦ Gas chromatographic analysis showed the condensate to contain:-19.87 wt% ethanol

3.18 wt~ t-butanol 0.74 wt~ ethyl acetate, 65.58 wt~ t-butyl acetate 6.51 wt~ water This corresponds to a 56.5% conversion of t-butyl acetate. Although the selectivity to ethanol and t-butanol appears to ~e high, accurate assessment of selectivity was difficult because some of the t-butanol underwent dehydration to iso-butene which was detected as a product but not collected.
The catalyst used in this Example was charged to the reactor as a co-precipitated mixture o~ CuO and Zno containing 33+3% CuO and 65+3~ 2nO having a .. . ..

~L~29~6 particle size in the range of 1.2 mm to 2.4 mm and an internal surface area of about 45 sq.m. per gram. This was pre-reduced in the reactor using a 5 vol % H2 in N2 gas mixture at 200~C for 16 hours followed by pure hydrogen at 200C for 16 hours, the gas flow rate in each case being about 20 litres/hr (measured at atmospheric pressure) and the gas pressure being 15.5 kg/cm2 absolute (1518 kPa). After this pre-reduction stage the catalyst was at all times maintained in a hydrogen-containing atmosphere.
Example 8 The procedure of Example 7 was repeated using ethyl lactate at a feed rate of 15.9 ml/hr. The reactor pressure was 16.4 kg/cm2 absolute (1608 kPa) and the inlet temperature was 234C. The gas flow rate was 156.6 litres/hr (measured at atmospheric pressure). The liquid hourly space velocity was 1.06 hr~l. In this Example the H2:ester molar ratio was 47.0:1 and the , ~ ester partial pressure was 0.34 kg/cm2 (33.4 kPa).
I 20 Gas chromatographic analysis showed the , condensate to contain:-i 12.62 wt% ethanol 0.25 wt% n-propanol ~i 14.41 wt~ 1,2-propanediol i 25 64.49 wt% ethyl lactate.
~i This corresponds to a 34.7~ conversion of ethyl lactate with a selectivity of 97.7% to 1,2-propanedi~l and 2.3% to n-propanol.
Example 9 The procedure of Example 7 was repeated using methyl methoxyacetate at a feed rate of 17~3 ml~hr. The reactor pressure was 29 kg/cm2 absolute (2850 kPa) and the inlet temperature was 217C. The gas flow rate was 157.2 litres/hr (measured at atmospheric pressure). The liquid hourly space velocity was 1.15 hr~l~ the ~ .

1229~)~6 H2:ester molar ratio was 37,5:1. and the ester partial pressure was 0,75 kg/cm2 (73.6 kPa).
Gas chromatographic analysis showed the condensate to contain--22.23 wt~ methanol 0.62 wt~ ethanol 46.55 wt% 2-methoxyethanol 23.23 wt% methyl methoxyacetate

4.53 wt~ methoxyethyl methoxyacetate.
This corresponds to a 77.6~ conversion of methyl methoxyacetate with a selectivity of 2.0% to ethanol, 93.2~ to methoxyethanol and 4.6~ to methoxy~thyl methoxyacetate.
Example 10 The procedure of Example 7 was repeated using a mixture comprising 75 mol % methyl glycolate and 25 mol% methanol at a feed rate of 10.0 ml/hr. The reactor pressure was 28.1 kg/cm2 absolute (2760 kPa) and the inlet temperature was 210C. The gas flow rate was 0 155.4 litres/hr (measured at atmospheric pressure). The liquid hourly space velocity was 0.67 hr~l, the H2:ester molar ratio was 39:1, and the es~er partial pressure was 0.7 kg~cm2 ~68.6 kPa).
Gas chromatographîc analysis showed the condensate to contain a mixture of methanol, methyl glycolate, and ethylene glycol.
Calculations indicated a 13~7% conversion of methyl glycolate with a selectivity ~f approximately ~8.0% to ethylene glycol.
Exam~le 11 U~ing a procedure similar to that of Example 7 but with a catalyst voIume ~ 50 ml, the hydrogenolysis of ethyl acetate was investigated using a crushed catalyst 35 comprising a reduced mixture of 71.5~ CuO and 18,5~ 2nOr ~L229~9ç;

with a liquid feed rate of 21.7 ml/hr, corresponding to a liquid hourly space velocity of 0.43 hr~l and a 5 mol~ ethyl acetate in hydrogen feed mixture (i.e. a 19:1 hydrogen:ester molar ratio). The conversion observed at 11.6 kg/cm2 absolute (1138 kPa) and 150C was 65.1%
with essentially quantitative formation of ethanol. The partial pressure of the ester in this run was 0.55 kg/cm2 (54 kPa). Under the same pressure and flow conditions at 200C the observed conversion was 90.6~, also with essentially quantitative producti~n of ethanol.
Example 12 When Example 11 was repeated using as catalyst a reduced mixture of 44.3~ CuO, 46.3% ZnO and 9.4%
A12o3, the conversion at 150C was 48.9%. The partial pressure of the ethyl acetate in this run was 0.55 kg/cm2 (54 kPa), whilst the hydrogen:ester molar ratio was 19:1. The observed conversion at 200C was 84.2~. In each case essentially quantitative formation of ethanol was observed.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A continuous process for the production of an optionally substituted C2+ alkyl alcohol which comprises:
vaporising an alkyl ester of a C2+ aliphatic monocarboxylic acid in a stream of a hydrogen-containing gas to form a vaporous mixture containing the ester in vapour form and hydrogen, the partial pressure of the ester in the vaporous mixture being at least about 0.05 kg/cm2 (about 4.9 kPa);
supplying the vaporous mixture to a catalytic reaction zone containing a charge of a catalyst consisting essentially of a reduced mixture of copper oxide and zinc oxide;
contacting the vaporous mixture with the catalyst at a temperature of from about 150°C to about 240°C and at a pressure in the range of from about 5 kg/cm2 absolute (about 491 kPa) up to about 50 kg/cm2 absolute (about 4906 kPa); and recovering from the catalytic reaction zone a reaction product comprising at least one optionally substituted C2+ alkyl alcohol.

2. A process according to claim 1, in which the pressure is in the range of from about 5 kg/cm2 absolute (about 491 kPa) to about 25 kg/cm2 absolute (about 2453 kPa).

3. A process according to claim 2, in which the temperature is in the range of from about 180°C to about 240°C.

4. A process according to claim 1, in which the catalyst consists essentially of a reduced mixture of copper oxide and zinc oxide derived from a mixture consisting essentially of, before reduction, from about 10 to about 70 percent by weight CuO and about 90 to about 30 percent by weight ZnO.

5. A process according to claim 4, in which the mixture consists essentially of from about 20 to about 40 percent by weight CuO and from about 60 to about 80 percent by weight ZnO.

6. A process according to any one of claims 1 to 3, in which the catalyst consists essentially of a reduced mixture of copper oxide and zinc oxide derived from a mixture consisting essentially of, before reduction, from about 65 to about 85 percent by weight CuO and about 15 to about 35 percent by weight ZnO.

7. A process according to any one of claims 1 to 3, in which the catalyst consists essentially of a reduced mixture derived from a mixture consisting essentially of, before reduction, from about 40 to about 50 weight percent of CuO, from about 40 to about 50 weight percent of ZnO, and from 0 to about 20 weight percent of alumina.

8. A process according to any one of claims 1 to 3, in which the ester is selected from those of the general formula RCOOR', in which each of R and R' comprises an alkyl radical containing from 1 to 12 carbon atoms.

9. A process according to claim 1, in which the ester is an alkyl acetate and the reaction product comprises ethanol.

10. A process according to claim 9, in which the ester is methyl acetate and the reaction product comprises a mixture of methanol and ethanol.

11. A process according to claim 9, in which the ester is ethyl acetate and the alkyl alcohol in the reaction product consists essentially of ethanol.

12. A process according to claim 1, in which the ester is an alkyl butyrate and the reaction product comprises n-butanol.

13. A process according to claim 12, in which the ester is n-butyl butyrate and the alkyl alcohol in the reaction product consists essentially of n-butanol.

14. A process according to claim 1, in which the partial pressure of the ester is in the range of from about 0.05 kg/cm2 (about 4.9 kPa) to about 10 kg/cm2 (about 981 kPa).

15. A process according to claim 1, in which the ester is supplied at a rate corresponding to a liquid hourly space velocity of from 0.24 hr-1 to 1.22 hr-1.

16. A continuous process for the production of ethanol in which a vaporous mixture containing (1) an alkyl ester of acetic acid and (2) hydrogen, in which vaporous mixture the partial pressure of the ester is at least about 0.05 kg/cm2 (about 4.9 kPa), is continuously fed into contact with a catalyst consisting essentially of a reduced mixture of copper oxide and zinc oxide at a temperature in the range of from about 150°C up to about 240°C and at a pressure in the range of from about 5 kg/cm2 absolute (about 491 kPa) up to about 50 kg/cm2 absolute (about 4906 kPa), and resulting ethanol is recovered.

17. A process according to claim 15, in which the pressure is in the range of from about 5 kg/cm2 absolute (about 491 kPa) to about 35 kg/cm2 absolute (about 3435 kPa).

18. A process according to claim 16, in which the temperature is in the range of from about 180°C to about 240°C.

19. A process according to claim 16, in which the ester is methyl acetate or ethyl acetate.

20. A process according to claim 16, in which the catalyst consists essentially of a reduced mixture of copper oxide and zinc oxide derived from a mixture consisting essentially of, before reduction, from about 10 to about 70 percent by weight CuO and about 90 to about 30 percent by weight ZnO.

21. A process according to claim 20, in which the mixture consists essentially of from about 20 to about 40 percent by weight CuO and from about 60 to about 80 percent by weight ZnO.

22. A process according to any one of claims 16, 18 and 19, in which the catalyst consists essentially of a reduced mixture of copper oxide and zinc oxide derived from a mixture consisting essentially of, before reduction, from about 65 to about 85 percent by weight CuO and about 15 to about 35 percent ZnO.

23. A process according to any one of claims 16, 18 and 19, in which the catalyst consists essentially of, before reduction, from about 40 to about 50 weight percent of CuO, from about 40 to about 50 weight percent of ZnO, and from 0 to about 20 weight percent of alumina.

24. A process according to claim 16, in which the ester is supplied at a rate corresponding to a liquid hourly space velocity of from 0.24 hr-1 to 1.22 hr-1.