EP0223814A1

EP0223814A1 - PROCESS FOR THE PRODUCTION OF $i(GAMMA)-BUTYROLACTONE

Info

Publication number: EP0223814A1
Application number: EP86903503A
Authority: EP
Inventors: Keith 12 The Avenue Fairfield TURNER; Mohammad 19 Maidstone Drive Marton SHARIF; Colin 7 Mount Leven Road RATHMELL; John Wilson John Clapham House Firby KIPPAX; Anthony Benjamin 37 Weston Crescent CARTER; John 2 Cleveland View Kirk Merrington SCARLETT; Arthur James 30 Mereshead Sands Acklam REASON; Norman 22 Grantham Road HARRIS
Original assignee: Davy Mckee London Ltd
Current assignee: Johnson Matthey Davy Technologies Ltd
Priority date: 1985-06-04
Filing date: 1986-06-04
Publication date: 1987-06-03
Also published as: JPS63500099A; KR870700615A; JPH0753723B2; BR8606710A; ES8707516A1; GB8514001D0; ES556313A0; WO1986007358A1

Abstract

Du gamma-butyrolactone est produit par hydrogénolyse en phase vapeur d'un ester d'alkyle d'un acide bicarboxylique C4, par exemple du maléate de diéthyle, sur un catalyseur réduit d'oxydes mélangés de Cu-Cr ou Cu-Zn. Deux zones adiabatiques d'hydrogénolyse sont utilisées. Le mélange sortant de la première de ces zones est chauffé (de 5o par exemple) et le mélange chauffé résultant est acheminé vers la seconde zone dans laquelle il se rééquilibre à une température supérieure afin d'augmenter la production de butane-1,4-diol aux dépens du butane-1,4-diol. Des températures comprises entre 190o et 260oC, des pressions comprises entre 3 et 30 bars, et un rapport molaire H2:ester compris entre 50:1 et 1000:1 sont des conditions typiques de réaction.Gamma-butyrolactone is produced by vapor phase hydrogenolysis of an alkyl ester of a C4 bicarboxylic acid, for example diethyl maleate, on a reduced catalyst of mixed Cu-Cr or Cu-Zn oxides. Two adiabatic hydrogenolysis zones are used. The mixture leaving the first of these zones is heated (by 5o for example) and the resulting heated mixture is conveyed to the second zone in which it rebalances at a higher temperature in order to increase the production of 1,4-butane diol at the expense of butane-1,4-diol. Temperatures between 190o and 260oC, pressures between 3 and 30 bar, and a H2: ester molar ratio between 50: 1 and 1000: 1 are typical reaction conditions.

Description

PROCESS FOR THE PRODUCTION OF GAMMA-BUTYROLACTONE This invention relates to a process for the production of gamma-butyrolactone, more particularly to a process for the production of gamma-butyrolactone by hydrogenolysis of a dialkyl ester, usually a di-(Cn to C^ alkyl) ester, of a C^ dicarboxylic acid, such as maleic acid, fumaric acid or succinic acid.

Gamma-butyrolactone is used as a solvent for various reactions, as a solvent for high polymers, and as a chemical and synthetic intermediate for production of a nylon polymer.

It is often produced from butane-l,4-diol which is itself made by reacting acetylene and formaldehyde by the Reppe reaction to give but-2-yne-l,4-diol which is then hydrogenated to form butane-l,4-diol.

Alternatively it has been proposed in EP-B-0018162 to react allyl alcohol, which can be produced from propylene, with iso-butylene to form allyl t;-butyl ether. This compound is then hydroformylated using, for example a rhodium complex hydroformylation catalyst to give 4-t- butoxybutyraldehyde, which is then oxidised and cleaved with the aid of an acid catalyst followed by dehydration and cyclization to give gamma-butyrolactone.

There have also been a number of proposals to produce butane-l,4-diol from maleic anhydride. According to these proposals maleic anhydride, which is produced by oxidation of butane or benzene, is esterified to give a diester of maleic acid which is then hydrogenated in one or more stages to give butane-l,4-diol. Alternatively it is proposed that, maleic acid or anhydride should be directly hydrogenated. In some of these proposals butyrolactone is an intermediate product.

US-A-4001282 describes a process for production of butyrolactone by passing vaporised maleic acid, maleic anhydride, or a mixture thereof together with water and hydrogen over a metallic catalyst capable of hydrogenolysing a carboxylic group to a hydroxymethyl group. Typical catalysts include copper-zinc catalysts (such as Girdler G-66 ARS and G-66-BRS) and copper chro ite catalysts (such as Girdler G-13). Besides butyrolactone the reported products include succinic acid anhydride, propionic acid, butyric acid, propanol and n- butanol.

US-A-4048196 teaches production of butane-1,4- diol and/or tetrahydrofuran by multi-stage catalytic hydrogenation of maleic anhydride or succinic anhydride. In a first liquid phase hydrogenation step maleic anhydride or succinic anhydride is hydrogenated over a nickel catalyst to give butyrolactone. This is then hydrogenated in the liquid phase over a copper/zinc oxide or hydroxide catalyst to give butane-l,4-diol and tetrahydrofuran.

In US-A-4083809, US-A-4105674 and GB-A-1534136 there is described a process for producing butyrolactone using a Cu-Pd catalyst for vapour phase hydrogenation of maleic acid, succinic acid, their anhydrides, and mixtures of two or more thereof.

US-A-2079414 describes use of copper chromite as a catalyst for effecting hydrogenation of esters. It is recommended that, in operating in the vapour phase, temperatures within the range of 300°C to 400°C should be used. Diethyl succinate is mentioned.

US-A-2040944 recommends use of temperatures of 230°C to 400°C for hydrogenation of esters of non-aromatic polybasic acids with a monohydric aliphatic alcohol containing at least four carbon atoms. It recommends . copper chromite as catalyst and teaches that the catalyst can be prepared by ignition of a copper ammonium chromate precipitate and used without further treatment or after reduction by hydrogen at a temperature of 500°C or higher. It goes on to mention that either the liquid phase or vapour phase can be used, depending largely upon the ester to be hydrogenated. Pressures of 100 to 250 bar are recommended, as well as use of about 5 to 20 moles of hydrogen per mole of ester. Example 1 describes a liquid phase batch reaction in which crude butyl succinate is hydrogenated at 3000 p.s.i.g. (207 bar) at 255°C using a copper chromite catalyst.

A discussion of the use of copper chromite as a catalyst for hydrogenation of esters'is to be found in "Organic Reactions", Vol. 8, published in 1954 by J. Wiley and Sons, Inc. Chapter 1 of this reference book is by Homer Adkins and is entitled "Catalytic Hydrogenation of Esters to Alcohols". Table II on page 15 lists two experiments in which diethyl succinate is reacted at 5000 p.s.i. (345 bar) and 150°C for 4 hours and at 3300 p.s.i. (227.5 bar) and 250°C for 6.5 hours respectively. This reference suggests that the "copper chromite" catalyst is more correctly described as an approximately equimolecular combination of cupric oxide and cupric chromite, i.e. CuO, CuCr₂0₄.

Production of copper chromite catalysts for use in hydrogenation of esters is described in FR-A-1276722. This recommends use of ester hydrogenation conditions including use of temperatures between 100°C and 350°C, preferably between 200°C and 300°C, and hydrogen pressures preferably between "50 hpz" and "500 hpz" (by which is presumably meant between 50 bar and 500 bar).

Production of butane-l,4-diol and tetrahydrofuran by a process in which a dialkyl maleate is subjected to hydrogenolysis in the liquid phase in the presence of a copper chromite catalyst is described in GB-A-1454440 and GB-A-1464263. A similar liquid phase process using nickel-based catalysts is described in GB-A-1587198. Hydrogenation of a di-(C, to C- alkyl) succinate at 100 to 300 atmospheres and 200°C to 260°C over a copper chromite catalyst to produce butane-l,4-diol is described in DE-A-2719867.

US-A-4172961 describes in Example 1 experiments in which a mixture of dibutyl butoxysuccinate, dibutyl maleate and dibutyl fumarate is hydrogenated using a copper chromite catalyst at 2000 psig to 4000 psig (141.65 bar to 282.26 bar) and at a temperature of 250°C to yield butane-1,4-diol. A two stage hydrogenation procedure in which a dialkyl maleate is hydrogenated first to the corresponding dialkyl succinate in a first hydrogenation zone and then the resulting dialkyl succinate is hydrogenated to yield butane-l,4-diol in a second hydrogenation zone is described in US-A-4032458. Copper chromite is suggested as 1_he catalyst for use in both hydrogenation zones; use of temperatures of about 100°C to about 200°C and hydrogen pressures of about 2000 psig to about 3500 psig (about^' 141.65 bar to about 247.11 bar) in the first hydrogenation is recommended, whilst use of temperatures of about 225°C to about 300°C and pressures of about 3000 psig to about 4000 psig (about 241.95 bar to 282.26 bar) in the second hydrogenation zone is said to provide the necessary severity of operating conditions required to convert substantially all of the dialkyl esters to a product comprising butane-l,4-diol and monohydric alkanol.

Butyrolactone is produced, according to GB-A- 1168220, by vapour phase hydrogenation of maleic anhydride, succinic acid, an ester of maleic acid, an ester of succinic acid, or an ester of fumaric acid in the presence of a copper-zinc catalyst to which may be added small amounts of one or more promoters other than chromium. This specification mentions that the preparation of butyrolactone by hydrogenation of the chosen starting materials was already known and states (see page 1, lines 23 to 25):

"It is also possible to carry out the hydrogenation in the vapour phase when the preferred catalyst is copper- chromite."

GB-A-1168220 continues (see page 1, lines 29 to 39):

"Furthermore hitherto known hydrogenation processes in the vapour phase suffer from the disadvantage of having to be carried out at a relatively high temperature, for example, about 300°C, and moreover in order to obtain a good conversion rate, the reaction material should be fed to the catalyst at low speed. It is also difficult to reactivate the copper-chromite catalyst, when the activity has been lowered by use for a period of time." It is an object of the present invention to provide a novel improved process for the production of gamma-butyrolactone using as a starting material a precursor that can be produced from maleic anhydride and hence ultimately from butane or benzene as feedstock. According to the present invention there is provided a process for the production of gamma- butyrolactone which comprises: providing first and second hydrogenolysis zones, each containing a charge of a heterogeneous ester hydrogenolysis catalyst; supplying to the first hydrogenolysis zone at an elevated pressure and at an elevated first feed temperature in excess of the threshold temperature for the hydrogenolysis reaction a vaporous feed stream comprising a dialkyl ester of a C^ dicarboxylic acid in vapour form and excess hydrogen; allowing the ester to undergo hydrogenolysis in the first hydrogenolysis zone under substantially adiabatic reaction conditions thereby to form a vaporous first reaction mixture that is substantially free from the starting ester and contains, in addition to unreacted hydrogen, gamma-butyrolactone and butane-l,4-diol in a first molar ratio; heating the vaporous first reaction mixture; supplying a second vaporous feed stream comprising resulting heated vaporous first reaction mixture to the second hydrogenolysis zone at a second feed temperature in excess of the threshold temperature for the hydrogenolysis reaction; allowing the second vaporous feed stream to react further and to equilibriate under substantially adiabatic reaction conditions in the second hydrogenolysis zone; and recovering from the second hydrogenolysis zone a vaporous second reaction mixture containing, in addition to unreacted hydrogen, gamma-butyrolactone and butane-1,4- diol in a second molar ratio that is greater than the first molar ratio.

Preferably the hydrogenolysis catalyst comprises copper chromite. It is especially preferred to use a reduced copper chromite catalyst which contains, before reduction, from about 25 to about 45% by weight of copper and from about 20 to about 35% by weight of chromium.

Preferably the ester is a di-(C-, to C» alkyl) ester of a but-2-en-l,4-dioic acid or of succinic acid.

In operating the process of the invention with a copper chromite catalyst it is preferred to operate at a temperature of at least about 170°C. Hence the first feed temperature preferably lies in the range of from about 170°C to about 260°C, and even more preferably in the range of from about 190°C to about 230°C. The two hydrogenolysis zones are each operated substantially adiabatically. The first reaction mixture thus exits the first hydrogenolysis zone at a temperature above the first inlet temperature. The second inlet temperature at which the cooled vaporous first reaction mixture is supplied as second vaporous feed mixture to the second hydrogenolysis zone is preferably at least about 5°C higher than the temperature at which the vaporous first reaction mixture exits the first hydrogenolysis zone. Typically the second inlet temperature is at least about 10°C higher, e.g. about 15°C higher, than the exit temperature from the first hydrogenolysis zone. In most cases the second inlet temperature will not usually be more than about 25°C higher than the exit temperature from the first hydrogenolysis zone. The operating pressure is preferably at least about 3 bar but not more than about 30 bar, and is most preferably in the range of from about 15 bar to about 25 bar. Usually it is at least about 20 bar.

The two hydrogenolysis zones may each comprise a separate reactor which is operated under substantially adiabatic conditions. Alternatively the two hydrogenolysis zones may comprise separate beds of catalyst in the same reactor vessel.

The dialkyl ester of a C^ dicarboxylic acid used in the process of the invention is preferably derived from an alkyl alcohol containing from 1 to 4 carbon atoms. Examples of such esters include diethyl maleate, diethyl fumarate, diethyl succinate, and mixtures of two or more thereof. Other suitable esters include., the dimethyl, di-rt-propyl, di- i-propyl, di-n-butyl, di-^-butyl, and di-sec-butyl esters of maleic, fumaric and succinic acids, as well as mixtures thereof. Preferably the ester is selected from diethyl maleate, diethyl fumarate, diethyl succinate, and mixtures of two or more thereof. Besides using an undiluted ester as feedstock it is also possible to use a solution of the ester in a suitable inert solvent, e.g. methanol, ethanol, or n- or iso- propanol.

It is desirable to pretreat the ester feedstock, e.g. by distillation, so as to remove substantially all of any sulphurous or halogenated impurities present in the feedstock. It is also preferred to remove substantially all water therefrom.

The ester or ester solution feed can be admixed with recycled ester recovered in the product recovery section, of the plant. If a di-(C, to C_* alkyl) maleate or fumarate is used as starting material, then the product stream from the second hydrogenolysis zone may include a minor amount of the corresponding dialkyl succinate; this can be recycled from the product recovery section of the plant for admixture with the di-(C^ to C^ alkyl) maleate or fumarate or solution thereof used as fresh feed supplied to the first hydrogenolysis zone. Usually a ready market can be found for the co-product butane-1,4- diol. The plant operator can adjust the output from the plant to meet market requirements for butane-l,4-diol and gamma-butyrolactone either by adjusting the operating temperatures of the hydrogenolysis zones or by recycling a part of the gamma-butyrolactone product or a part of the byproduct butane-l,4-diol from the product recovery section for admixture with the ester or ester solution feed.

The process requires that the starting ester and any other condensible component present be in the vapour phase in the first and second hydrogenolysis zones. This means that the composition of the vaporous mixture must be controlled so that, under the selected operating conditions, the temperature of the mixture in contact with the catalyst is always above the dew point of the ester and of any other condensible component present. The and of any other condensible component present. The temperature of the mixture in contact with the catalyst is at all times preferably at least about 5°C, more preferably at least about 10°C, and even more preferably at least about 15°C, higher than the dew point of the mixture. This can normally be achieved by selecting an appropriate gas:ester ratio in the vaporous mixture. A convenient method of forming a vaporous mixture for use in the process of the invention is to spray the liquid ester or ester solution into a stream of hot hydrogen-containing gas so as to form a saturated or partially saturated vaporous mixture. Alternatively such a vaporous mixture can be obtained by bubbling a hot hydrogen-containing gas through a body of the liquid ester or ester solution. If a saturated vapour mixture is formed it should then be heated further or

..^'ii-lαted with more gas so as to produce a partially saturated vaporous mixture prior to contact with the catalyst.

Reduction of a maleate or fumarate ester to gam a- butyrolactone involves reaction of 3 moles of H₂ with each mol of ester, according to the following equation:

R-0-CO-CH=CH-CO-0-R + 3H₂ = 2R0H + (I) where R is an alkyl radical containing from 1 to 4 carbon atoms.

However, when a succinate ester .is hydrogenolysed, only 2 moles of H₂ are consumed:

CH₀ - CH I - i -^■

R-0-CO-CH₂-CH₂-CO-0-R + 2H₂ = 2R0H + CH₂ C=0 (II ) ^ 0 where R is as defined above.

The vaporous mixture will normally contain excess hydrogen. It may additionally contain a minor amount of carbon oxides. The vaporous mixture may further include vaporised inert solvent (if used) and one or more inert hydrogen supply in a major or minor amount. It may also include vaporous material recycled from the product recovery section. Preferably the hydrogen supply is substantially free from sulphur compounds, from halogens such as Cl₂, and from halogen-containing compounds such as HC1.

In the vaporous mixture the H₂:ester molar ratio is typically at least about 50:1 up to about 1000:1 or more. Preferably it is at least about 150:1 up to about 500:1. The presence of the excess hydrogen and of any inert gases that may be present helps to moderate the temperature rise in the first hydrogenolysis zone. In practice the reduction of a maleate ester, such as diethyl maleate, is more complex than is suggested by equation (I) above and results in production of variable amounts of by-products, including tetrahydrofuran, butane-l,4-diol and i-butanol. Although the reaction mechanism has not been fully elucidated yet, the currently available evidence is consistent with the following sequence:-

- 11 -

CH - C0₂Et CH₂ - C0₂Et

C

CH₃CH₂CH₂CH₂OH The preferred catalyst used in the first and/or second hydrogenolysis zone is a reduced copper chromite catalyst. This should be prepared by careful reduction of copper chromite prior to use. Preferably the catalyst is reduced at a temperature of not more than about 200°C, for an extended period using a mixture of H₂ and an inert gas, such as nitrogen, methane or argon. A typical gas used for reduction of the catalyst is an H₂ in N₂ mixture containing, for example, from about 1% up to about 15% by volume of H₂. Usually the catalyst is reduced for at least about 24 hours prior to use. Best results are obtained when reduction is effected for several days at a temperature of from about 120°C to about 180°C prior to use in the process of the invention. It will usually be unnecessary to exceed about 10 days reduction pre-treatment. If the catalyst is reduced at a temperature in excess of about 200°C, the activity is noticeably inferior to the activity obtained by reduction at lower temperatures. If the catalyst is supplied in pre- reduced form then the period of reduction can be shorter. In the later stages of pre-treatment higher H₂ concentrations can be used; thus H₂ can replace the H₂/N₂ mixture towards the end of the reduction pre-treatment. It is best to use an elevated pressure during this pre- treatment period; for example, pressures of from 1 up to about 50 bar or higher can be used. After the reduction treatment the catalyst should be maintained under an inert gas, a hydrogen/inert gas mixture or hydrogen until use. The formula of copper chromite may be written as CuCr₂0^. However, it is known that copper chromite is non- stoichiometric and some authors have, for example, described a copper chromite catalyst as copper chromium oxide of the formula CuO.CuCr₂0^. Thus the catalyst may contain- an excess of copper oxide. It may further or alternatively contain a minor amount of at least one stabilizer, such as barium or manganese. The catalyst contains, before reduction, from about 25 to about 45% by weight of copper and from about 20 to about 35% by weight of chromium. The most preferred catalysts are those containing from about 32 to about 38% by weight of copper and from about 22 to about 30% by weight of chromium. Such catalysts preferably contain no more than about 15% by weight of a stabilizer or stabilizers, if present. It may be supported on a suitable inert carrier. Desirably the catalyst is in finely divided form having an internal surface area, as measured by the well-known BET method, of at least about 30 sq. m. per gram and preferably at least about 60 sq. m. per gram. Preferably it is formed into cylindrical pellets or into other conventional catalyst shapes, such as rings, saddles, or the like. Other catalysts that may be used in the first and/or second hydrogenolysis zone of the process of the invention include a reduced copper oxide/zinc oxide catalyst of the type disclosed in WO-A-82/03854.

The ester is preferably supplied to the first hydrogenolysis zone at a rate corresponding to a liquid hourly space velocity in the range of from about 0.1 to about 0.6 hr or higher, for example up to about 1.5 hr or even up to about 3.0 hr^" . By the term "liquid hourly space velocity" we mean the number of unit volumes of the liquid ester supplied to the vaporization zone per unit volume of catalyst per hour. This normally corresponds to a gaseous hourly space velocity in the range of from about 2500 hr^"1 up to about 16000 hr^-1, for example up to about 85000 hr^-1, most preferably in the range of from about 8000 to about 30000 hr^"1. By the term "gaseous hourly space velocity" we mean the number of unit volumes of vaporous mixture measured at 1 bar and 0°C passed over a unit volume of catalyst per hour.

Usually the feed temperature to the second hydrogenolysis zone is at least about 190°C. If desired further gas and/or ester can be admixed with the product stream from the first hydrogenolysis zone prior to admission to the second hydrogenolysis zone in order to adjust the temperature or the H₂:ester molar ratio. It is also contemplated that one or more materials recovered from the product recovery section of the plant (e.g. dialkyl succinate, unreacted dialkyl maleate or fumarate, gamma- butyrolactone and/or butane-l,4-diol)can be admixed with the product stream from the first hydrogenolysis zone prior to admission to the second hydrogenolysis zone, instead of or in addition to recycling such material to the inlet end of the first hydrogenolysis zone.

The reduction of a di-(C^ to C₄ alkyl) maleate to the corresponding di-(C^ to C₄ alkyl) succinate according to equation (III) above is an exothermic reaction. As the yield of by-product tetrahydrofuran is found to be dependent upon the maximum temperature to which the reaction mixture is exposed in the hydrogenolysis zones and upon the residence time at elevated temperatures, it is preferred to use a di-(Cπ to C , alkyl) succinate as the ester supplied to the first hydrogenolysis zone or as a major component thereof, rather than the corresponding di-(Cτ to C₄ alkyl) maleate or fumarate, since this results in production of a correspondingly smaller temperature rise in the first hydrogenolysis zone and hence in production of a smaller proportion of by-product tetrahydrofuran. Hence, in a particularly preferred process according to the invention a di-fC^ to C₄ alkyl) maleate or fumarate, such as diethyl maleate or fumarate, is hydrogenated to the corresponding di-(C^ to C alkyl) succinate, such as diethyl succinate, in a hydrogenation zone upstream from the first hydrogenolysis zone using a catalyst which either has little or no ester hydrogenolysis activity or which is maintained under conditions such that ester hydrogenolysis and formation of butane-l,4-diol are minimised. Prior to entry to the first hydrogenolysis zone, the di-^-^ to C₄ alkyl) succinate- containing reaction mixture from the upstream hydrogenation zone is cooled, if necessary, prior to entry to the first hydrogenolysis zone in order to remove the heat of hydrogenation of the C:C bond of the maleate or fumarate ester prior to entry to the first hydrogenolysis zone. In this way the temperature rise in the first hydrogenolysis zone is kept as small as possible and the production of by¬ product tetrahydrofuran is thereby minimised. As examples of catalysts that can be used in the upstream hydrogenation zone when using a di-(C^ to C alkyl) maleate or fumarate, there can be mentioned, for example, copper oxide/zinc oxide catalysts of the type disclosed in WO-A-82/03854, supported nickel, palladium, ruthenium, and cobalt hydrogenation catalysts, zinc oxide, copper chromite catalysts, and copper chromite catalysts which have been deliberately deactivated to reduce their ester hydrogenolysis characteristics. When using copper chromite catalysts, which may or may not have been deactivated, it is expedient to supply the di-(C-, to C alkyl) maleate or fumarate to the upstream hydrogenation zone at a relatively high rate, for example at a rate corresponding to a liquid hourly space velocity of at least about 1.0 hr^-1, preferably from about 3.0 hr^"1 to about 6.0 hr^"1. For convenience and ease of construction and operation of the plant it is preferred to operate any upstream hydrogenation zone for conversion of dialkyl maleate and/or fumarate to dialkyl succinate at substantially the same pressure as is used in the first and second hydrogenolysis zones. Hence typical operating pressures in the upstream hydrogenation zone range from about 3 bar to about 30 bar and preferably lie in the range of from about 15 bar to about 25 bar. Vapour phase hydrogenation conditions are usually selected in the upstream hydrogenation zone. The inlet temperature to the upstream hydrogenation is preferably kept as low as is practicable consistent with use of vapour phase conditions and is typically in the range of from about 160°C to about 180°C. The volume of catalyst in the upstream hydrogenation zone is selected to provide the desired high rate of ester throughput.

The reaction mixture exiting the upstream hydrogenation zone is supplied as feed mixture to the first hydrogenolysis zone. Prior to introduction to the first hydrogenolysis zone the reaction mixture exiting the upstream hydrogenation zone is cooled somewhat so as to enable as low an inlet temperature as possible to be used in the first hydrogenolysis zone and thereby limit the maximum temperature achieved therein. Further hydrogen and/or fresh feed ester and/or one or more materials recycled from the product recovery zone may be admixed with the reaction mixture from the upstream hydrogenation zone prior to its introduction into the first hydrogenolysis zone. The product mixture exiting the second hydrogenolysis zone contains, in addition to unreacted hydrogen and possibly other gases, a mixture of condensible materials including gamma-butyrolactone and alkyl alcohol (e.g. a C^ to C alkyl alcohol) derived from the alkyl moiety of the dialkyl ester starting material. The condensible materials may further include butane-l,4-diol, dialkyl succinate and possibly also a small amount of unreacted ester and minor amounts of byproducts, including n-butanol and tetrahydrofuran. These condensible materials are preferably condensed from, the product mixture and separated in any suitable fashion, e.g. by distillation in one or more stages under normal, elevated or reduced pressure. In designing a suitable product recovery system, it should be borne in mind that some of the components present in the product mixture are capable of forming azeotropic mixtures with one or more other components of the product mixture. The liquid gamma-butyrolactone product and any butane-l,4-diol formed can be passed forward for purification whilst any minor byproducts can be used as fuel for the process. The alkyl alcohol can be recycled for reaction with further maleic or succinic anhydride or with further maleic acid, fumaric acid or succinic acid to form fresh dialkyl C₄ dicarboxylic acid ester for use in the process of the invention. Any unreacted starting ester (e.g. dialkyl maleate) and/or intermediate ester (e.g. dialkyl succinate) can be recycled for admixture with the ester or ester solution feed. If desired some of the gamma- butyrolactone, and/or butane-l,4-diol byproduct, can be recycled for admixture with the product stream from the first hydrogenolysis zone. The unreacted hydrogen-containing gases from the product recovery step can be recycled. Purge lines can be used to control the level of inerts and/or byproducts in the circulating gas stream and in any^"liquid recycle line. In order that the invention may be clearly understood and readily carried into effect a preferred form of plant designed to operate a process in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawing which is a flow diagram of a plant for effecting hydrogenolysis of diethyl maleate.

It will be appreciated by those skilled in the art that, as the drawing is diagrammatic, many further items of equipment, such as temperature and pressure sensors, valves, control equipment, and the like, will be required in a commercial plant. The provision of such ancillary items of equipment forms no part of the present invention and will be in accordance with conventional chemical engineering practice. Moreover the provisions for heat exchange within the illustrated plant are merely one way of achieving the desired temperature levels and any other equivalent system of heat exchange can be used instead.

Referring to the drawing, diethyl maleate is fed in line 1 and admixed with a liquid recycle stream in line 2 containing diethyl succinate, and possibly also gamma- butyrolactone a,nd/or butane-l,4-dipl. The combined liquid stream is fed by pump 3 to feed heater 4 in which it is heated to 245°C by steam supplied in line 5. The resulting hot liquid stream is passed to a spray nozzle 6 in feed saturator 7, in which the resulting spray encounters an ascending stream of hot hydrogen-containing gas supplied in line 8 at 25 bar. Liquid is withdrawn from the bottom of feed saturator 7 in line 9 and is pumped by a feed saturator pump 10 to circulation heater 11 before being sprayed back into feed saturator 7 through nozzle 12. Reference numeral 13 indicates a spray eliminator pad in the top of feed saturator 7. The ester vapour laden stream exits feed saturator 7 in line 14 and passes to a steam heater 15 in which its temperature is raised to 190°C. The H₂:ester molar ratio is approximately 200:1. This mixture is then passed under substantially adiabatic reaction conditions through a first bed 16 of copper chromite catalyst containing 25% by weight of copper and 35% by weight of chromium and having a surface area of 85 m /g. The vaporous reaction mixture exits first bed 16 at an exit temperature of 205°C. Analysis of this first reaction mixture indicates the absence of diethyl maleate and shows that, besides hydrogen and inert gases (e.g. CO, . C0₂, methane, propane, N₂, Ar and any other inert gases which may be present in the hydrogen supply to the plant), also significant amounts of diethyl succinate, ethanol, tetrahydrofuran, n-butanol, gamma-butyrolactone, and butane-l,4-diol. In passage through first bed 16 under the substantially adiabatic reaction conditions employed in the process, diethyl maleate is converted smoothly and substantially quantitatively to diethyl succinate, which is then converted to products including ethanol, tetrahydrofuran, ji-butanol, gamma- butyrolactone, and butane-l,4-diol, and some minor byproducts. The size of the catalyst charge in first bed 16 is preferably selected in relation to the rate of supply of vaporous diethyl maleate thereto so that reaction can proceed substantially to equilibrium in bed 16. The rate of supply of vaporous diethyl maleate to bed 16 corresponds to a liquid hourly space velocity of about 0.45 hr^"1.

The vaporous first reaction mixture exits first bed 16 at 205°C and is passed by way of line 17 to heat exchanger 18, in which it is heated to 215°C, and is then passed to a second bed 19 of the same copper chromite catalyst. In passage through bed 19 further hydrogenation reactions take place and the reaction mixture re- equilibriates to yield a second reaction mixture containing a higher gamma-butyrolactone:butane-l,4-diol molar ratio than that of the first reaction mixture. The volume of catalyst in the second bed 19 is approximately twice that in the first bed 16; hence the rate at which vaporous diethyl maleate is supplied to bed 16 corresponds to a liquid hourly space velocity, taken over both beds 16 and 19, of about 0.15 hr^"1.

The second reaction mixture passes in line 20 to a heat exchanger 21 and then to a product cooler 22, in which it is cooled by means of cooling water supplied in line 23, to product catchpot 24. The liquid condensate is recovered in line 25, whilst the gases exit in line 26. The liquid condensate is passed through a pressure let-down valve 27 to a pressure let-down catchpot 28 and thence to a product recovery section 29 in which the product butane-l,4-diol is separated from gamma-butyrolactone, from tetrahydrofuran, from ethanol, from r-butanol, from diethyl succinate, and from any other minor components present in the condensate. Separation of the condensate in product recovery section 29 can be achieved, for example, by distillation in several stages, including a "light ends" distillation stage to remove tetrahydrofuran, ethanol, n-butanol and other low boiling byproducts, and then distillation of the resulting bottoms product to yield an overhead product comprising an azeotrope of gamma-butyrolactone and diethyl succinate and a bottom product comprising butane-l,4-diol. The gamma- butyrolactone/diethyl succinate azeotrope can be separated by distillation using a water-flooded distillation tower. Tetrahydrofuran is recovered in line 30, gamma-butyrolactone in line 31, and butane-l,4-diol in line 32. Diethyl succinate, and possibly also some butane-l,4-diol and/or gamma-butyrolactone, is recycled in line 2.

Fresh hydrogen is supplied to the plant in line 33 and is fed by way of compressor 34 and cooler 35 for admixture with the recycled gas in line 26. The combined gas stream is compressed by recycle compressor 36 and fed to line 8.

A gas purge stream is taken in line 37 after passage through pressure let-down valve 38 and is combined with the vent gas in line 39 from catch pot 28; the combined stream in line 40 passes to gas purge condenser 41 which is fed with refrigerant in line 42 from refrigeration unit 43. The purge gas exits in line 44 whilst any condensate is recovered in line 45 and fed to product recovery section 29. A purge can be taken from the bottom of feed saturator 7 in line 46 as necessary.

It will readily be appreciated by those skilled in the art that the illustrated plant can, with relatively little modification, be opera.ted using another dialkyl ester of a C₄ dicarboxylic acid as feedstock, such as diethyl succinate or a mixture of diethyl maleate and diethyl succinate, in place of diethyl maleate. Some changes to the design of the product recovery section 29 may, however, be required. Such diethyl succinate or a mixture thereof with diethyl maleate may, for example, be produced from diethyl maleate by hydrogenation in an upstream hydrogenation zone (not shown), the product of which is fed to the illustrated plant in line 1.

In an alternative modification of the plant of the drawing diethyl maleate supplied in line 1 is hydrogenated in the vapour phase to diethyl succinate in a hydrogenation zone (not shown) in line 14 upstream from the first hydrogenolysis zone. Such upstream hydrogenation zone contains, for example, a relatively small charge of copper chromite catalyst and the rate of passage of ester therethrough preferably corresponds to a liquid hourly space velocity of at least about 3.0 hr^"1. Prior to entry to first hydrogenolysis zone 16 the resulting hydrogenated ester containing reaction mixture, which now contains a minor amount only each of diethyl maleate and butane-1,4- diol and a major amount of diethyl succinate, is cooled to remove the heat of hydrogenation of the C:C bond of the unsaturated ester starting material.

Claims

CLAIMS:

1. A process for the production of gamma- butyrolactone by hydrogenolysis of a dialkyl ester of a C₄ dicarboxylic acid characterised in that it comprises: providing first and second hydrogenolysis zones, each containing a charge of a heterogeneous ester hydrogenolysis catalyst; supplying to the first hydrogenolysis zone at an elevated pressure and at an elevated first feed temperature in excess of the threshold temperature for the hydrogenolysis reaction a vaporous feed stream comprising a dialkyl ester of a C dicarboxylic acid in vapour form and excess hydrogen;- allowing the ester to undergo hydrogenolysis in the first hydrogenolysis zone under substantially adiabatic reaction conditions thereby to form a vaporous first reaction mixture that is substantially free from the starting ester and contains, in addition to unreacted hydrogen, gamma-butyrolactone and butane-l,4-diol in a first molar ratio; heating the vaporous first reaction mixture; supplying a second vaporous feed stream comprising resulting heated vaporous first reaction mixture to the second hydrogenolysis zone at a second feed temperature in excess of the threshold temperature for the hydrogenolysis reaction; allowing the second vaporous feed stream to react further and to equilibriate under substantially adiabatic reaction conditions in the second hydrogenolysis zone; and recovering from the second hydrogenolysis zone a vaporous second reaction mixture containing, in addition to unreacted hydrogen, gamma-butyrolactone and butane-l,4-diol in a second molar ratio that is greater than the first molar ratio.

2. A process according to claim 1, characterised in that the heterogenous hydrogenolysis catalyst comprises copper chromite.

3. A process according to claim 2, characterised in that the copper chromite catalyst contains, before reduction, from about 25 to about 45% by weight of copper and from about 20 to about 35% by weight of chromium.

4. A process according to any one of claims 1 to 3, characterised in that the first feed temperature ranges from about 170°C to about 260°C.

5. A process according to claim 4, characterised in that the first feed temperature is from about 190°C to about 230°C.

6. A process according to any one of claims 1 to 5, characterised in that the second feed temperature is at least about 5°C higher than the temperature at which the vaporous first reaction mixture exits the first hydrogenolysis zone.

7. A process according to any one of claims 1 to 6, characterised in that the second feed temperature is at least about 190°C.

8. A process according to any one of claims 1 to 7, characterised in that the hydrogen:ester molar ratio in the first vaporous feed stream is in the range of from about 50:1 to about 1000:1.

9. A process according to any one of claims 1 to 8, characterised in that the first feed temperature is at least about 5°C above the dew point of the first vaporous feed stream.

10. A process according to any one of claims 1 to 9, characterised in that the second feed temperature is at least about 10°C above the dew point of the second vaporous feed stream.

11. A process according to any one of claims 1 to

10, characterised in that the pressure lies in the range of from about 3 bar to about 30 bar.

12. A process according to any one of claims 1 to

11, characterised in that the ester is fed to the first hydrogenolysis zone at a rate corresponding to a liquid hourly space velocity of from about 0.1 hr^"1 to about 0.6 hr^"1.

13. A process according to any one of claims 1 to 12, characterised in that the ester is a di-(C, to C₄ alkyl) ester of a C₄ dicarboxylic acid.

14. A process according to claim 13, characterised in that the ester is selected from diethyl maleate, dialkyl fumarate and mixtures thereof.

15. A process according to claim 13, characterised in that the ester is selected from diethyl succinate, and mixtures thereof with one or both of diethyl maleate and diethyl fumarate.

16. Gamma-butyrolactone, whenever produced by a process according to any one of the preceding claims.