GB2031883A - Catalytic hydrogenation of oxalic esters - Google Patents

Abstract

Oxalic esters are hydrogenated at an elevated temperature not exceeding about 250 DEG C., suitably at about 40 - 250 DEG C., with gaseous hydrogen in the presence of a Ru or Ni catalyst. At the lower end of the temperature range the hydrogenation is selective to the glycolic ester whilst at the upper end it is selective to ethylene glycol. In the intermediate range, at about 130 - 150 DEG C., both products may appear, the precise transition temperature range depending also on other parameters such as the nature of the catalyst and the hydrogen pressure. The hydrogenation may be carried out with the oxalic ester in the gas or in the liquid phase.

Description

SPECIFICATION Process of catalytic hydrogenation This invention relates to a process for hydrogenating oxalic esters.

More particularly, the present invention relates to a catalytic process for hydrogenating oxalic esters, by which it is possible selectively to obtain both the semi-hydrogenated products, glycolic esters, and the fully hydrogenated product, ethylene glycol.

The products obtained (glycolic acid and esters and ethylene glycol) are important compounds having known and wide industrial application of considerable interest. The glycolic acid is of course, readily obtained from the glycolic ester by hydrolysis.

In fact, glycolic acid and the esters thereof are employed as agents in the dyeing and tanning of hides, and in the fields of textile dyeing, welding, adhesive products, and detersives, etc.

On the other hand, ethylene glycol is a well-known large-scale industrial product, the applications of which range from coolants (for motors, etc.) and hydraulic fluids (for brakes) etc. to the manufacture of polyester fibres in the textilefield,of solvents for cellulose esters,resins,etc,and of laquers,paints,resins,adhesives etc.

Several methods are known for preparing glycolic acid or glycolic esters and for preparing ethylene glycol; for example glycolic acid from formaldehyde and CO in an acid medium; glycol from ethylene oxide, etc.

Processes for preparing ethylene glycol by catalytic hydrogenation of oxalic esters have also been described.

The vapour phase hydrogenation of oxalic esters or glycolic acids and esters to ethylene glycol in the presence of catalysts based on chromates and chromites of copper and of zinc, on copper and aluminium, on copper oxides and on oxides of other metals, Raney nickel, etc. at high temperatures (of the order of 300"C) and under hydrogen pressure is known. The processes are conducted under rather severe operating conditions as regards temperature and pressure. In consequence, the interest offered by these processes is limited, having also regard for their low yields, which adversely affect profitability.

As far as we are aware, processes for hydrogenating oxalic esters in the liquid phase, which can be adjusted so as to lead selectively to the preparation of glycolic esters or of ethylene glycol, have not been described so far.

It is an object of the present invention to provide a simple and economic process for hydrogenating oxalic esters, leading to the production of ethylene glycol and of glycolic esters, optionally in a predominating and selective manner.

It is another object of this invention to provide a process for preparing ethylene glycol by hydrogenation of oxalic esters, free from the drawbacks attributed to the prior art processes.

According to the invention the hydrogenation is conducted with gaseous hydrogen in the presence of at least one catalyst selected from ruthenium and nickel at an elevated temperature not exceeding about 250"C.

Suitably the temperature used is at least about 40"C.

It is possible, by suitably selecting the operative conditions, selectively to obtain the products of the partial hydrogenation of the oxalic esters, namely the corresponding glycolic esters, for which only one of the esterifying groups of the oxalate is hydrogenated, as well as the product of the total hydrogenation, namely ethylene glycol.

The general reactions involved are schematically the following: + 2H2 catalyst (1) ROOC-COOR + 2H2 catalyst ROOCCH2OH + ROH (2) ROOC-COOR + 4H2 catalyst HOCH CH OH + 2ROH wherein R is preferably either an alkyl group having up to 8 carbon atoms, or an alkoxyl containing up to 6 carbon atoms, it being understood that the R's may be the same or different.

Oxalic esters in which R is in general an inert group, i.e. one which does not interfere with the desired hydrogenating reaction, are compatible with the process of the present invention. Consequently, oxalic esters in which group R, beside having the above-mentioned meanings, is also an aralkyl, are interalia also suitable.

The esters can be substituted, in their turn, by alkoxyls, amino-, cyano-, carboxyl-groups, etc., such as are inert in the reaction conditions.

As by-product of reactions (1) and (2) alcohol ROH is obtained, which can be separated and recycled in a conventional carbonylation process, in an integrated cycle, for the production of oxalic esters.

Methyl, ethyl, butyl, and di-(2-methoxy-ethyl)-oxalates have, amongst others, proved to be efficacious.

The process according to the present invention offers a wide range of operative possibilities; in fact it can be advantageously conducted in the liquid or gas phase by suitably selecting temperatures, operating pressures and catalyst.

The process of the invention, when it is practised in the liquid phase, is conducted at temperatures in the range of from 40"C to 250"C approximately and at a hydrogen pressure higher than approximately 10 atm., preferably at temperatures ranging from 60"C to 200"C and at a pressure of some 40 to 150 atm. In particular, the reaction is directed towards the mono-hydrogenation products, glycolic esters, if the temperature is maintained between about 40"C and 1 50 C, at the same above-said pressures, with a tendency for the hydrogenation to proceed further at the upper end of this temperature range.

On the contrary, the hydrogenation is conducted increasingly up to ethylene glycol, if the temperature is maintained at values exceeding about 1300C in the same range of pressure.

The reaction in the liquid phase can be conducted in the absence of solvents, or in the presence of suitable solvents, including mono- or poly-functional alcohols having up to 10 carbon atoms and the ethers and poly-ethers, acyclic, acrylic or cyclic.

Among the alcohols, the following have proved to be efficient: primary, secondary and tertiary aliphatic and cycloaliphatic alcohols having up to 10 carbon atoms, such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, cyclohexyl alcohol, sec.-butyl alcohol, tert.-butyl alcohol etc; the alcohols of formula R'O [(CH2)nOlmH in which R' is an alkyl having up to 10 carbon atoms and m and n are integers from 1 to 10, such as cellosolve; and polyhydroxylated alcohols such as ethylene glycol, 1,2-propandiol, 1,3-propandiol, butylene glycols, glycerine, etc.

Among the ethers, those which have proved to be efficient include those of formula R"-O-R"', in which R" and R"' are alkyls or cycloalkyls having up to 10 carbon atoms, such as diethylether, dipropylether, ethylbutylether, etc.; the polyethers of formula R"[O(CH2)n]mOR"', wherein R" and R"', m and n have the meaning already specified, such as dimethylethers of mono-, di- and tri-ethylene glycols. etc.; and among the cyclic ethers, tetrahydrofurane; and among the cyclic polyethers, dioxane and the crown -ethers.

When solvents are employed, the reaction can be conducted in concentration conditions varying according to the choice made by the man skilled in the art; at any rate the concentration is not critical for the course of the reaction.

Analogously, the reaction times may vary over a wide range depending on the other parameters employed, on the efficiency of stirring, etc. For indicative purposes we may say that times of the order of 30 minutes are generally sufficient.

At the conclusion of the reaction, the reaction products can be easily separated according to conventional methods, for example by distillation with fractionation under reduced pressure, etc.

Alternatively, as indicated above, the reaction according to this invention may be conducted in the gas phase. In this case the process is suitably conducted at temperatures ranging from about 80"C to 200"C and under at least atmospheric pressure. The contact times between the oxalic ester and catalyst may vary widely, suitably from 0.1 to 10 seconds; values of the order of from 0.5 to 1 second are usually effective.

Through a proper choice - which can be easily made by a technician skilled in the art of the parameters in the ranges indicated hereinbefore, it is possible selectively to direct the reaction towards the formation of glycolic esters or of ethylene glycol, as desired.

The separation of the products obtained, whether from liquid or gas phase operation, can be carried out using conventional techniques. Optionally hydrogen, alcohol etc. can be recycled.

As regards the catalyst, it is composed - as mentioned hereinabove - of at least one component selected from ruthenium and nickel or Raney nickel. They can be used either as metals or in the form of salts or other derivatives, such as the chlorides, nitrates, carbonates, hydroxides, oxides or salts of organic acids such as the acetate, acetylacetonate, etc. Furthermore, they can be used either as such or supported on inert carriers, such as carbon, silica, kieselguhr, alumina, etc., suitably according to conventional techniques, for example by impregnation, precipitation, etc. Prior to use, the catalyst is activated in a hydrogen stream etc., again suitably in accordance with known techniques.

For example, efficient supported catalysts of Ni and Ru are prepared by impregnating the carrier with an aqueous solution of a salt of Ni and/or Ru (suitably the chloride or nitrate). Successively, one or more impregnations are carried out until the desired concentration of active component has been deposited. The catalyst is then dried, e.g. in an oven at about 1 200C and activated in a hydrogen stream for 2 hours suitably at about 3000 - 5000C.

Similarly, Raney-Ni catalyst can be prepared according to conventional methods, see, for example, H.Adkins - Reaction of Hydrogen - Univ. of Winsconsin, Ed. 1937, page 20.

The catalyst - depending on the technique employed, i.e. liquid phase or gase phase - is utilized in suspension, in a fixed bed, in a fluid bed, etc, and in general according to conventional techniques.

The weight ratio of the active part of the catalyst to the oxalic ester is not critical. Nevertheless it may be mentioned that molar ratios between active catalyst and oxalic ester in the range of from 1 1000 to 1 10 are effective. The expression "active catalyst" used herein will be understood to mean the Ru or Ni catalyst not including the support, if any.

Hydrogen can be fed as such or in admixture with inert gases (nitrogen etc.) in the range of the above-indicated partial pressures.

The process of the invention is particularly advantageous because of the high selectivity which can be achieved. Another advantage consists in the reaction conditions, which are milder in comparison with those of the most pertinent known technique, and are convenient for industrial scale operation.

The process will be now further described in the following examples, which are given for illustrative purposes, and are followed by a run, not in accordance with the invention, for comparison purposes.

Example I Into a vertical 1-liter autoclave, made of steel and equipped with a stirrer having Teflon (Registered Trade Mark) blades and with a Teflon sheath for a thermocouple, a glass beaker was introduced, which was rendered integral with the walls of the autoclave by an asbestos coating.

Into the resulting container the following materials were introduced: - butyl oxalate 15 g (74 m. moles) - 2-methoxyethanol (Cellosolve (Registered Trade Mark)) 80 cc - catalyst composed of 5% Ru supported on carbon, activated at 400"C for 2 hours 1g The container was pressurized with H2 to 140 atm, heated to 180"C and stirred at such temperature for 3 hours. After cooling, the residual pressure was released, and the solution, filtered from the catalyst, was 'distilled under reduced pressure. The fraction passing at 80 - 85"C/15 mm Hg contained 4 g (64 m. moles) of ethylene glycol.

Example 2 Into the autoclave of Example 1 and following the same procedure the following materials were introduced: - ethyl oxalate 15 g (102 m. moles) - ethylene glycol monoethylether (ethylcellosolve) 80 cc - Ru (5%) catalyst on silica 2g The autoclave was pressurized with 160 atm. of H2 and stirred for 3 hours at 1800C. Proceeding as described in Example 1 there was obtained a fraction which distilled between 60"C and 85"C/15 mm Hg, found to consist in a mixture composed of: - ethylene glycol 2 g (32 m. moles) - ethyl glycolate 4 g (38 m. moles) Example 3 Into the autoclave of Example 1 and following the same procedure, the following materials were introduced:: - di-(2-methoxy-ethyl)-oxalate 20 9(97 m. moles) - 2-methoxy-ethanol 150 cc - Ru/C catalyst (activated as in Example 1) 2g The autoclave was pressurized to 160 atm. with H2 and heated to 1700C, keeping the whole stirred for 1 hour at this temperature. By operating according to Example 1,6,05 g (97 m. moles) of ethylene glycol were obtained.

Example 4 Into the autoclave of Example 1 and following the same procedure, the following materials were introduced: - di-(2-methoxy-ethyl)-oxalate 20 g (97 m moles) - 2-methoxy-ethanol 150 cc - Ru/C catalyst activated as in Example 1 29 The autoclave was pressurized with 120 atm. of H2 and heated to 1 200C, keeping the whole stirred for 2 hours.Proceeding as in Example 1, the following was obtained: - ethylene glycol traces - 2-methoxy-ethyl glycolate 8.8 g (66 m. moles) - unaltered oxalate 4.5 g (22 m. moles) Example 5 Into the autoclave of Example 1 and following the same procedure, the following materials were introduced: - di-(2-methoxy-ethyl)-oxalate 20 g (97 m. moles) - ethylene glycol mono-methylether 150 cc - Ru/c catalyst activated as in Example 1 29 The autoclave was pressurized with H2 to 120 atm. and heated to 170"C, keeping the whole stirred for 1 hour.Following the procedure of Example 1, the following was obtained: - ethylene glycol 4.2 g (67 m. moles) - 2-methoxy-ethyl-glycolate 3.4 g (25 m. moles) The catalyst from this test was separated by filtration and utilized for a test identical with the preceding one as regards both procedure and amounts of reagents. The following products were obtained: - ethylene glycol 4 g (64 m. moles) - 2-methoxyethyl glycolate 3.6 g (27 m. moles) The filtered catalyst was recycled further 4 times in as many tests, in which the reagents amounts and the experimental conditions were the same as those indicated hereinabove.

Each of these tests provided amounts of ethylene glycol ranging from 60% and 70% of the calculated value, and amounts of glycolate comprises between 40% and 30% of the calculated value. Thus, no appreciable deterioration of the catalyst occurred in these tests.

Example 6 Into the autoclave of Example 1 and following the same procedure, the following materials were introduced: - butyl oxalate 20 g (99 m. moles) -Ru/Ccatalyst activated as in Example 1 lg The autoclave was pressurized with H2 to 50 atm. and heated to 130 C, keeping the whole stirred for 2 hours at such temperature.After working up as in Example 1, the following were obtained: - butyl glycolate 9.2 g (70 m.moles) - unaltered butyl oxalate 7 g (35 m. moles) - ethylene glycol traces Example 7 Into the autoclave of Example 1 and following the same procedure, the following materials were introduced: butyl oxalate (15 9 (74 m. moles) - catalyst consisting of 5% Ru on C and activated as in Example 1 2g - dimethoxyethane 30 cc The autoclave was pressurized with H2to 40 atm. and heated to 130"C, keeping the whole stirred at such temperature for 5 hours.After working up as in Example 1, the following were obtained: - butyl glycolate 8 g (60 m moles) - unaltered butyl oxalate 2 g (10 m. moles) - ethylene glycol traces Example 8 Into the autoclave of Example 1 and following the same procedure, the following materials were introduced: - ethyl oxalate 10 g (68 m. moles) - Ru (5%) on C, activated as in Example 1 2g - tetrahydrofurane 30 cc The autoclave was pressurized with H2 to 40 atm. and the whole was stirred at 130"C for 8 hours. After working up as in Example 1, a fraction distilling at 60"C - 700C/1 5 mm Hg was obtained, consisting of 7 g (67 m. moles) of ethyl glycolate.

Example 9 Into a glass phial the following materials were introduced: - di-(2-methoxy-ethyl)-oxalate lOg (48 m. moles) - cellosolve 30 cc - catalyst composed of Ni supported on xp- kieselguhr (50% of Ni) activated with H2 at 400"C for 2 hours 5g The phial was introduced into a rocking autoclave, which was then pressurized to 160 atm. with H2 and heated to 180"C; rocking was carried out for 10 hours.

After cooling the product was worked up as in Example 1 to give: - 2.1 g (34 m. moles) of ethylene glycol 3 g (14 m moles) of unaltered oxalate.

Example 10 Into the apparatus of example 9, the following materials were introduced: - di-(2-methoxy-ethyl)oxalate 10 g (48 m. moles) - tetrahydrofurane 30 cc - Raney-Ni 5g (This catalyst was prepared according to H. Adkins - Reactions of Hydrogen - University of Winsconsin, ed.

1937 - page 20) The autoclave was pressurized with H2 to 200 atm. and heated to60 C; rocking was conducted for 6 hours.

After working up as in Example 1, the following were obtained: - 2-methoxyethyl-glycolate 3.4 g (25 m. moles) - unaltered oxalate 4 g (20 m.moles) - ethylene glycol nil Example 11 3 g of a catalyst consisting of Ru (5%) deposited on alumina, previously activated by treatment with a H2 flow at 300"C for 2 hours, were introduced into a glass reactor for catalysis in the gaseous phase, equipped with a fritted baffle. The reactor was then introduced into a muffle maintained at 160"C.

A hydrogen stream (5 1/h) was bubbled through a vessel containing ethyl oxalate maintained at 95"C. The H2 stream, saturated with oxalate, was passed over the catalyst, with a residence time of 0.8 seconds.

At the outlet of the reactor there was a trap maintained at 0 C.

90 minutes after the beginning of the test, the liquid deposited in the trap (1 g) was collected and analyzed by gas chromatography. It was found to be composed of ethyl oxalate (0.7 g), ethyl glycolate (0.2 g) and ethyl alcohol (0.1 9).

Comparative run Into the apparatus of example 9, the following materials were introduced: - di-(2-methoxy-ethyl)-oxalate 10 g (48 m. moles) - celiosolve 30 cc - conventional catalyst consisting of Cu chromite (prepared according to H. Adkins Reaction of Hydrogen - Univ. of Winsconsin, ed. 1937, page 12) 5g The autoclave was pressurized with 160 atm. of H2 and heated to 180"C, with stirring maintained for 10 hours.

After working up as in Example 1, the following were obtained: - ethylene glycol 1.07 g (17 m. moles) - glycolate 1.3 g (9 m. moles) - unaltered oxalate traces The gases discharged from the autoclave contained, among other materials, also methane and CO2.

Claims (21)

1. A process for catalytically hydrogenating oxalic esters, in which an oxalic ester of the formula ROOC-COOR wherein the R's, which may be the same or different, are alkyls having up to 8 carbon atoms, alkoxyls having up to 6 carbon atoms, or aralkyls, optionally substituted by groups inert under the reaction conditions, is hydrogenated by gaseous hydrogen in the presence of at least one catalyst selected from ruthenium, nickel and nickel-Raney, at an elevated temperature not exceeding about 250"C.

2. A process according to claim 1 wherein the hydrogenation is conducted at about 40" - 250"C.

3. A process according to claim 1 or 2 in which the oxalic ester is the methyl, ethyl, butyl or di-2-methoxyethyl ester.

4. A process according to claim 1, 2 or 3 in which the catalyst comprises metallic ruthenium and/or metallic nickel or a compound thereof selected from the chlorides, nitrates, carbonates, oxides, hydroxides and salts of organic acids.

5. A process according to any of the preceding claims, in which the molar ratio between the active catalyst and the oxalic ester is from 1 : 1000 to 1:10.

6. A process according to any of the preceding claims, in which the catalyst is employed on an inert carrier selected from carbon, silica, kieselguhr and alumina.

7. A process according to any of the preceding claims, in which the catalyst is first activated in a hydrogen stream at a temperature ranging from about 300 to about 5000C.

8. A process according to any of the preceding claims, in which the catalyst is employed in suspension.

9. A process according to any of the preceding claims 1 - 7, in which the catalyst is employed either in the fixed bed or in the fluid bed technique.

10. A process according to any of the preceding claims, conducted in the liquid phase at a hydrogen pressure of at least 10 atm.

11. A process according to claim 10, in which the temperature used is from about 60 to 200"C and the hydrogen pressure from about 40 to 150 atm.

12. A process according to claims 10 to 11, in which glycolic esters are selectively and prevailingly obtained by operating at temperatures in the approximate range of 40 to 1 500C.

13. A process according to claims 10 and 11, in which ethylene glycol is selectively and prevailingly obtained whilst operating at a temperature higher than approximately 1300C.

14. A process according to any of the preceding claims, conducted in the presence of a solvent selected from mono- and poly-functional aliphatic and cycloaliphatic alcohols having up to 10 carbon atoms, and linear and cyclic ethers and polyethers.

15. A process according to claim 14, in which the solvent used is an alcohol selected from methyl, ethyl, propyl, butyl, cyclohexyl, sec. butyl, tert. butyl alcohols, alcohols of formula R'O[(CH2)n-O]mH, in which R' is an alkyl having up to 10 carbon atoms and m and n are integers from 1 to 10, and polyfunctional alcohols.

16. A process according to claim 15 in which the solvent used is ethylene glycol, 1 .2-propandiol, 1.3-propandiol, butylene glycol or glycerol.

17. A process according to claim 14, in which the solvent used in an ether selected from those of the formula R"-O-R"', in which R" and R"' are selected from alkyls, cycloalkyls having up to 10 carbon atoms, or a polyether of the formula R" [O-(CH2)n]mOR"', wherein R", R"' have the above meaning and m and n are integers from 1 to 10.

18. A process according to claim 17 wherein the solvent used in diethyl ether, dipropyl ether, ethyl-butyl ether, tetrahydrofurane, dioxane or a crown-ether.

19. A process according to any of claims 1 - 9, carried out in the gas phase at a temperature ranging from 80" to 2000C approximately and under at least atmospheric hydrogen pressure and for a contact time of at least 0.1 second.

20. A process for catalytically hydrogenating oxalic esters, as described in any of the foregoing examples.

21. Glycolic esters and ethylene glycol, when obtained by a process set forth in any of the foregoing claims.