GB2083026A - Production of alkylene glycols - Google Patents

Abstract

An epoxide is reacted with water to produce a glycol in the presence of carbon dioxide and a tertiary phosphine.

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 epoxide 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 Patents 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 bb 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.

According to the present invention an epoxide for example ethylene or propylene oxide is reacted with water to produce the corresponding glycol in the presence of carbon dioxide and a tertiary phosphine.

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

The process may be carried out at a temperature in the range 20 to 2000C preferably 70 to 1600C and more preferably 90 to 1 SOC C. The partial pressure of carbon dioxide is suitably 1 to 200 atmospheres and is preferably 5 to 30 atmospheres. Suitably the total pressure is in the range 1 5 to 300 atmospheres and preferably 6 to 50 atmospheres. Preferably no permanent gases are present.

The tertiary phosphine should be free from substituents such as OH groups which would react with the alkylene oxide. It may be a tri-hydrocarbyl phosphine. The hydrocarbyl groups may be alkyl.

aryl, aralkyl or alkaryl and different hydrocarbyl groups may be present in the same molecule for example the phosphine may be a trialkyl, triaryl or alkyl, aryl tertiary phosphine. Suitably the phosphine has 3 to 50 carbon atoms. If desired the phosphine may be of the resin type which for example may comprise a styrene polymer or copolymer which comprises tertiary phosphine groups as substituents.

It least is preferred to use a phosphine having at least 1 2 carbon atoms or one which is substituted with atleast on are group especially a phenyl group, because these phosphines tend to form a separate liquid phase from the glycol and thus are readily recoverable from the crude product as a separate layer which may be re-used in the process. In order to assist the phase separation and to facilitate recycle an inert solvent for example benzene, xylene or petroleum ether may be present. Such a solvent has no adverse effect on the reaction and may enable normally solid phosphines to be handled more readily.

Phosphines of the resin type are readily separable from the product by filtration. Phosphines other than the above are preferably sufficiently volatile to be readily separable by distillation.

It is preferred that the reaction medium should, if the phosphine is soluble in it, comprise 0.1 to 2 moles per litre of phosphine.

COMPARATIVE EXAMPLE Ethylene oxide gas was bubbled through water (68 g) at 50C until 36 g 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 (%) Time MEG (hours) (wt %) MEG DEG TEG 0.1 3.53 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 30.38 70.3 23.6 6.1 7.2 33.00 67.7 26.2 6.1 EXAMPLE 1 Ethylene oxide gas was bubbled through distilled water (20.2 g) at 50C until 51.7 g had dissolved.

The resulting solution was transferred to an autoclave which contained triphenylphosphine (5 g) dissolved in benzene (10.55, 12 ml) and which had been purged with carbon dioxide. Carbon dioxide was introduced until the pressure reached 300 psig and the autoclave was sealed. The solution was then stirred and heated to 1300 C. Samples of liquid were removed from the autoclave after the times shown. The samples separated into layers and the aqueous glycol layer was analysed by GLC for MEG, DEG and TEG.

It was found that the selectivity to MEG was considerably higher than in the comparative example at equivalent MEG concentrations. This is illustrated in Table 2.

TABLE 2

7 Selectivity (%) Time MEG (hours) (wit %) MEG DEG TEG 0.01 0.08 100.0 0 0 0;07 3.53 98.9 1.1 0 0.30 ~ 18.19 94.5 5.5 0 0.42 26.t3 92.0 8.0 0 0.50 30.38 90.8 9.2 0 0.55 33.00 90.0 10.0 0 0;;84 51.40 - 84.5 15.5 0 1.05 63.60 80.9 17.8 1.3 1.10 64.10 80.7 17.9 1.4 2.07 78.51 75.7 22.3 2.0 EXAMPLE 2 Ethylene oxide was bubbled into water (20.9 g) until 51.5 g had dissolved. The solution was then transferred to a 300 ml autoclave, containing 10 g of catalyst (triphenylphosphine) dissolved in 25 ml benzene which had been previously purged with CO2. The autoclave was then pressurised with CO2 to 300 psig, sealed and stirred. The temperature was raised to 1300 C. Samples of liquid were removed from the autoclave after the times shown. The liquid separated into a catalyst/solvent layer and an aqueous glycol layer.The aqueous glycol layer was analysed by GLC for MEG, DEG, and TEG.

It was found that the selectivity to MEG was higher than in both the comparative example and example 1 at equivalent MEG concentrations. Results are shown in Table 3.

Selectivity % based Time MEG (hours) (wt %) MEG DEG TEG 0.01 0.8 100.0 0 0 0.05 3.53 99.4 0.6 0 0.28 18.t9 96.3 3.7 0 0.40 26.t3 94.6 5.4 0 0.48 30.38 93.9 6.1 0 0.50 33.00 93.3 6.7 0 0.75 51.40 89.5 10.5 0 0.90 - 58.00 - 88.2 11.3 0.5 1.00 63.60 87.0 12.5 0.5 1.05 64.t0 86.9 12.6 0.5 2.00 71.38 85.5 13.8 0.7 4.85 83.05 83.t 16.0 0.9 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 (11)

1. A process of producing a glycol which comprises reacting an epoxide with water in the presence of carbon dioxide and a tertiary phosphine.

2. A process as claimed in Claim 1 which is carried out at a temperature in the range 70 to 1 600C.

3. A process as claimed in Claim 1 or 2 in which the partial pressure of carbon dioxide is 5 to 30 atmospheres.

4. A process as claimed in any preceding claim in which the phosphine is a trihydrocarbyl phosphine having 3 to 50 carbon atoms.

5. A process as claimed in any preceding claim in which the phosphine has at least 12 carbon atoms or at least 1 aryl group and in which the phosphine is recovered from the glycol as a separate liquid phase and is re-used in the process.

6. A process as claimed in Claim 5 in which an inert solvent is present to assist phase separation.

7. A process as claimed in any preceding claim in which the reaction medium comprises a phosphine which is soluble in it and comprises 0.1 to 2 moles per litre of phosphine.

8. A process as claimed in any preceding claim whenever carried out at a total pressure of 6 to 50 atmospheres.

9. A process as claimed in any preceding claim in which the epoxide is ethylene oxide and the glycol is ethylene glycol.

10. A process as claimed in Claim 1 whenever carried out substantiaily as described in any of the examples.

11. Glycols whenever produced by a process as claimed in any preceding claim.