GB2086894A

GB2086894A - Production of alkylene glycols

Info

Publication number: GB2086894A
Application number: GB8132248A
Authority: GB
Original assignee: Imperial Chemical Industries Ltd
Current assignee: Imperial Chemical Industries Ltd
Priority date: 1980-11-10
Filing date: 1981-10-26
Publication date: 1982-05-19
Also published as: GB2086894B

Abstract

A process for the production of an alkylene glycol, for example ethylene or propylene glycol, comprises contacting the corresponding alkylene carbonate with water in the presence of a sulphite salt. The alkylene carbonate may be produced in situ from an epoxide and carbon dioxide.

Description

SPECIFICATION Production of alkylene glycols This invention relates to the production of alkylene glycols.

Alkylene glycols, especially ethylene glycol are conventionally produced by reacting the corresponding expoxide with excess water in the absence of a catalyst. The process produces the monomeric glycol together with polyglycols, the proportion of polyglycols increasing with concentration of the product. If a high yield of monoglycol is required therefore, the reaction is carried out in the presence of a substantial excess of water. The excess water is removed by distillation if a concentrated glycol is required. The distillation of water from glycol is expensive and requires a considerable amount of energy.

It has been proposed to carry out the process in the presence of carbon dioxide and a quaternary ammonium halide (UK 1 177,877 2,011,400-2) and also in the presence of carbon dioxide and a tertiary amine (UK Patent 1,538,122). These processes enable substantially stoichiometric quantities of water to be employed. However when a quaternary ammonium halide is used there is a danger of corrosion of the apparatus employed and a tertiary amine undergoes side reactions.

Alkylene glycols may also be produced by the hydrolysis of alkylene carbonates. Alkylene carbonates may themselves be produced from alkylene oxides by reacting them with carbon dioxide in the presence of a suitable catalyst. There is a tendency when alkylene carbonates are hydrolysed in the presence of certain catalysts for example potassium carbonate, to produce undesired by-products for example glycollic acid.

This invention comprises a process for the production of an alkylene glycol, for example ethylene or propylene glycol which comprises contacting the corresponding alkylene carbonate with water in the presence of a sulphite salt, for example an alkali metal, alkaline earth metal, quaternary ammonium or quaternary phosphonium sulphite.

The process may be carried out at a temperature in the range 20 to 2000C and preferably 50 to 1 500C. It preferably is carried out at a partial pressure of carbon dioxide of at most 30 bars and if desired the partial pressure of carbon dioxide may be reduced by operating the process at low pressures and/or passing a stream of inert gas over or through the reaction mixture to remove carbon dioxide formed in the process. The process is preferably carried out at a pressure of at most 30 bars absolute and more preferably 1 to 5 bars absolute.

The process is suitably carried out in the presence of at least 0.5 moles per litre of the sulphite and suitably the solution may be saturated with the sulphite.

If desired an excess of water may be presented but it is preferred in order to minimise the cost of distilling water from the glycol product, that this should be at most a 10 fold excess and it is preferred that it should be at most a molar excess.

If desired, the alkylene carbonate may be produced from an epoxide and carbon dioxide in situ.

According to a preferred form of the invention an alkylene glycol, for example ethylene or propylene glycol is produced by reacting the corresponding epoxide with water to produce the corresponding glycol in the presence of carbon dioxide and a sulphite salt for example an alkali metal, alkaline earth metal, quaternary ammonium or quaternary phosphonium sulphite.

This process has a high selectivity for producing a monoglycol and causes little difficulty as regards corrosion of apparatus. It is particularly suitable for the production of ethylene glycol from ethylene oxide.

The preferred process may be carried out at a temperature in the range 20 to 2000C preferably 70 to 1 600C and more preferably 90 to 1 500C. The partial pressure of carbon dioxide is suitably 1 to 200 atmospheres and is preferably 5 to 30 atmospheres.

If desired an excess of water may be used but for the reasons given above it is preferred that there should be no more than a 10 fold excess of water. Preferably any excess of water is at most a molar excess. The catalyst concentration in this form of the invention is as described above.

The catalyst is suitably lithium, sodium, potassium, rubidium or cesium sulphite. A quaternary ammonium or phosphonium sulphite preferably comprises 4 hydrocarbon groups (with may be alkyl, aryl, aralkyl and/or alkaryl groups). Suitably the quaternary ammonium or phosphonium sulphite has 4 to 50 and preferably 4 to 10 carbon atoms. If desired the quaternary ammonium or phosphonium group may form part of an ion exchange resin.

If desired the glycol produced may be distilled from the catalyst. The catalyst may be re-used in the process and in this case it is preferred to provide a solvent for the catalyst in the process which boils at a higher temperature than the glycol product and which is substantially inert, for example a polyglycol ether or other high boiling ether.

EXAMPLE 1 Ethylene oxide gas was bubbled through water (68g) at 50C until 369 had dissolved. The resulting solution was transferred to an autoclave which was pressurised to 200 psig with helium, sealed and the solution was then stirred and heated to 1000C. Samples of liquid were removed from the autoclave after the times shown and analysed by GLC for MEG, DEG and TEG.

It was found that the selectivity to monoethylene glycol whilst initially high, fell rapidly with glycol accumulation as shown in Table 1.

TABLE 1

Selectivity (%) l Time MEG (hours) (wt o/o) MEG DEG TEG 0.1 3.53 I 97.4 2.6 0 1.0 18.19 77.7 20.1 2.2 4.7 26.13 73.5 22.3 4.2 6.0 1 30.38 70.3 23.6 6.1 7.2 33.0 67.7 26.2 6.1 EXAMPLE 2 Ethylene oxide gas was bubbled through a solution of sodium sulphite in water (0.33 mol/l,73.3g) until 39.2 g has dissolved. The resulting solution was transferred to an autoclave which had been purged with carbon dioxide.

The autoclave was sealed and pressurised with carbon dioxide to 200 psig. The solution was then stirred and heated to 1000C. Samples of liquid were removed from the autoclave at the stated intervals and analysed by GLC for MEG, DEG and TEG.

It was found in this case that the selectivity to MEG was consistently higher than in comparative example 1 at the same MEG concentrations. This is illustrated by the results in Table 2.

TABLE 2

Selectivity ( /0) Time MEG (hours) (wt %) MEG DEG TEG 0 2.09 94.3 5.7 0 40 26.19 84.1 15.0 0.82 100 30.41 81.3 17.2 1.40 160 1 33.18 79.4 79A 18.4 2.15 EXAMPLE 3 Ethylene oxide gas was bubbled through distilled water (19.29) until 44.929 had dissolved. This solution was added to an autoclave containing 40cm3 of a solution of sodium sulphite in water (approximately 2.0 molAlitre previously purged with carbon dioxide). The autoclave was then sealed and pressurised to 300 psig with carbon dioxide. The solution was stirred and heated to 1000C. Samples of liquid were removed from the autoclave at the stated intervals and analysed by GLC for MEG, DEG and TEG.

It was found that with the higher concentration of sodium sulphite used in this example the selectivity to MEG was higher than in Examples 1 or 2 (when compared at the same MEG concentrations). This is illustrated by the results in Table 3.

TABLE 3

Selectivity ( /O) Time MEG (hours) (wt o/O) MEG i DEG TEG 70 8.55 96.6 3.4 0 123 16.30 94.3 5.7 0 238 18.50 93.5 6.5 0 333 20.86 92.6 7.4 0 EXAMPLE 4 A solution of methyltriphenylphosphonium sulphite (15.85g, 0.025 moles) in water (90g, 5.0 moles) was charged with a 1 litre titanium autoclave at ambient temperature. Ethylene oxide (1 10g, 2.5 moles) was admitted from a cylinder and the reactor pressured with carbon dioxide to 1 50 psig at ambient temperature.The reactor was heated with stirring to 1 300C. Additional carbon dioxide was added to maintain the pressure at 300 psig during the run. Samples were taken during the run and analysed by GLC for MEG, DEG and TEG. The results are tabulated in Table 4.

TABLE 4

Selectivity (%) Time MEG (hours) I (wt o/o) MEG DEG TEG 60 24.15 65.7 34.3 N.D.

120 49.3 61.0 39.0 N.D.

180 49.3 60.9 37.5 1.6 N.D. means not detected MEG means monoethylene glycol DEG means diethylene glycol TEG means triethylene glycol psig means pounds per square inch gauge GLC means gas /liquid chromatography Selectivity is based on ethylene oxide converted

Claims

1. A process for the production of an alkylene glycol which comprises contacting the corresponding alkylene carbonate with water in the presence of a sulphite salt.

2. A process as claimed in claim 1 which is carried out at a temperature in the range of 50 to 1500C.

3. A process as claimed in claim 1 or 2 which is carried out at a pressure of 1 to 5 bars absolute.

4. A process in which an alkylene glycol is produced by reacting the corresponding epoxide with water to produce the corresponding glycol in the presence of carbon dioxide and a sulphite salt.

5. A process as claimed in claim 4 which is carried out at a temperature in the range of 90 to 1 500C and at a partial pressure of carbon dioxide of 5 to 3Q atmospheres.

6. A process as claimed in any preceding claim in which the sulphite salt is an alkali metal, quaternary ammonium or quaternary phosponium salt

7. A process as claimed in any preceding claim in which at most a molar excess of water is present.

8. A process as claimed in any preceding claim in which ethylene glycol is produced.

9. A process as claimed in any preceding claim in which the glycol produced is distilled from the catalyst and the catalyst is re-used in the process.

10. A process as claimed in claim 9 in which a solvent for the catalyst which boils at a higher temperature than the glycol product and which is substantially inert is present.

11. A process as claimed in any preceding claim whenever carried out substantially as described with reference to Example 2,3 or4.

12. Alkylene glycols whenever produced by a process as claimed in any preceding claim.