GB2050372A - Process for the alkoxylation of alcohols - Google Patents

Abstract

A process for the production of alkylene glycol mono alkyl ethers by the alkoxylation of alcohols in the presence of a molybdenum or tungsten heteropoly acid catalyst. The process is particularly useful in the alkoxylation of alcohols to give high ratios of mono- to di-alkoxylated products.

Description

SPECIFICATION Process for the alkoxylation of alcohols This invention relates to a process for the production of alkylene glycol ethers by the alkoxylation of alcohols and more particularly to the use of the heteropoly acids of molybdenum and tungsten as catalysts in the alkoxylation of alcohols.

In the commercial production of alkylene glycol ethers by the alkoxylation of the lower alcohols, the product distribution, or ratio of mono-, di-, tri- and higher alkoxylates, is of considerable importance. The mono-alkoxylates are, in the main the most important commercial products but their production is always accompanied by the production of some of the di-, tri- and higher alkoxylates.

From studies using the ethoxylation of ethanol as a model it appears that as a general rule the slower the reaction the higher the proportion of the mono-ethoxylate in the final product. For example, the ethoxylation of ethanol at 160"C using an ethanol to ethylene oxide mole ratio of 6:1 and no catalyst gives a product in which the mole ratio of mono- to di-ethoxylate is of the order of 18. However, while this ratio represents a good mono- to di-ethoxylate product distribution the uncatalysed reaction is unacceptably slow having a half-life of the order of 100 minutes. On the other hand when ethanol is ethoxylated under the same conditions using potassium hydroxide as catalyst the reaction proceeds at an acceptable rate with a half-life of the order of 8 minutes but the ratio of mono- to di-ethoxylate is much less favourable being of the order of 6.

It follows, that an alkoxylation process which combined the features of a relatively fast reaction rate and a product with a relatively high mono- to di-alkoxylate ratio would have considerable merit. It has now been found that the oxo acids of certain transition elements may be used as catalysts to give an alkoxylation process which combines the abovementioned desired features.

Accordingly, the invention provides a process for the production of alkylene glycol mono-alkyl ethers which process comprises the reaction of a C2 to C4 alkylene oxide with a C1 to C5 alcohol in the presence of a soluble catalyst comprising a heteropoly acid of molybdenum or tungsten.

Throughout the specification and claims the term "heteropoly acid of molybdenum or tungsten" refers to those compounds which comprise linked MoO6 and/or WO6 octahedra surrounding one or two central (hetero) atoms. The heteropoly acids of tungsten and molybdenum are discussed in the the standard texts "Advanced Inorganic Chemistry. A Comprehensive Text", A F Cotton and G Wilkinson, Second Revised and augmented Edition, Interscience New York 1966, pp 938-946, "Comprehensive Inorganic Chemistry", Editors J. C. Bailar, H. J. Emelius, R. Nyholm and A. F. Trotman-Dickenson, First Edition, Pergamon Press 1973, Volume 3 pp 739-741 and pp 767-768 and more comprehensively in Volume 4 pp 656-672 of the latter reference.

Considered in terms of the ratio of the number of central hetero atoms to the number of peripheral metal atoms the heteropoly acids of molybdenum and tungsten fall into four main groups, the 1:6, 1:9, 1:12 and 2.18 groups, and three minor groups, the 1:10,1:11 and 2:17 groups. The four main groups may be represented by the following formulae in which n represents the valency of the hetero atom, X represents the hetero atom and M represents a molybdenum or tungsten atom

1:6 series 1:9 series 1:12 series 2:18 series.

The hetero atom X may be chosen from a wide range of elements including the cations of phosphorous, silicon, boron, copper, zinc, iron, aluminium, germanium, vanadium, chromium, gallium, tellurium, manganese, beryllium, cerium, iodine, cobalt, tin, arsenic, antimony, bismuth, selenium, titanium, nickel and cerium. Preferred cations include those of phosphorus and silicon.

While M is usually chosen from either molybdenum or tungsten certain of the heteropoly acids of molybdenum and tungsten contain both molybdenum and tungsten and in others one or more but not all of the molybedenum or tungsten atoms may be replaced by one or more other metal atoms such as, for example, vanadium, manganese, iron cobalt, nickel, copper, zinc, and titanium.

Preferred heteropoly acids for use in the process of the invention include phosphomolybdic acid (H3PMo,2040 xH20) The heteropoly acids of molybdenum and tungsten may conveniently be prepared by the acidification of molybdate and tungstate solutions containing other oxo anions. For example, phosphopoly acids of molybdenum or tungsten may be prepared by the dissolution of molybdenum or tungsten oxides in phosphoric acid. In the process of the invention the heteropoly acids of molybdenum and tungsten may be used as catalysts in the form of purified compounds or in crude form, for example, without isolation from the reaction mixture in which they were prepared.

The amount of the heteropoly acid of molybdenum or tungsten used as catalyst in the process of the invention will depend to a large extent on the nature of the catalyst used and the alcohol and alkylene oxide which are being reacted. However, in general a catalyst level in the range of from 10 to 5,000 ppm, based on the weight of the alcohol reactant, is suitable provided that the catalyst is soluble in the alcohol reactant at the level of use. A range of from 100 to 1000 ppm is preferred.

Suitable alcohols for use in the process of the inventon include the primary and secondary C1 to C6 alcohols such as methanol, ethanol, propanol, isopropanol, butanol, 1-methylpropanol and 2methylpropanol. Suitable alkylene oxides include ethylene oxide, propylene oxide and butylene oxide.

The temperature at which the process of the invention is carried out will depend on a number of factors including the heating and cooling facilities available on the reaction vessel and the pressure at which the reaction vessel may be operated. However, in general, a temperature in the range of from 50 to 250"C is satisfactory and a temperature in the range from 80 to 200"C is preferred.

The process of the invention may be used to particular advantage in the production of ethylene glycol mono-alkyl ethers by the ethoxylation of ethanol, iso-propanol and n-butanol.

The invention is now illustrated, but not limited, by the following Examples.

Examples lto4 In order to demonstrate the effectiveness of the process of the invention ethanol was ethoxylated in an autoclave at a temperature of 1 60 C according to the following general procedure.

Ethanol containing the dissolved catalyst was charged into an evacuated autoclave. The autoclave and contents were heated with stirring to a temperature of 1 600C. Ethylene oxide (EO) was then introduced into the autoclave and the contents were heated with stirring until the reaction was complete.

The progress of the reaction was monitored by sampling the reaction mixture at regular intervals. The samples were quenched and analysed by vapour phase chromatography over 10% Carbowax 20M/ Chromosorb W using added butanol as an internal standard (Chromosorb is a Registered Trade Mark). The data from the analyses were used to calculate the reaction half-life (t1/2) and the mole ratio of the products ethylene glycol mono ethyl ether (EGE) and diethylene glycol mono ethyl ether (DEGE).

The results are recorded in Table 1 in which Examples 1 and 2 are comparative Examples not of the invention and PMA refers to the catalyst phosphomolybdic acid (H3PMoa2040.24H2O).

TABLE 1 Ex- Catalyst ample Mole Ratio Level t1/2 Mole Ratio No EtOH:EO Catalyst (w/w (min) EGE:DEGE w.r.t. EtOH) 1 6:1 None - 104 18.5:1 2 6:1 KOH 100 ppm 8.5 6.5:1 3 6:1 PMA 1750 ppm < < 5 10.1:1 4 6:1 PMA 525 ppm 5 10.8:1

Claims (12)

1. A process for the production of an alkylene glycol mono-alkyl ether which process comprises reacting C2 to C4 alkylene oxide with a C1 to C6 alcohol in the presence of a soluble catalyst comprising a heteropoly acid of molybdenum or tungsten as hereinbefore defined.

2. A process according to claim 1 wherein in said heteropoly acid catalyst the hetero atom is chosen from phosphorus and silicon.

3. A process according to claim 1 or claim 2 wherein said catalyst is a heteropoly acid of molybdenum and the heteroatom is phosphorus.

4. A process according to any one of claims 1 to 3 inclusive wherein said catalyst is phosphomolybdic acid.

5. A process according to any one of claims 1 to 4 inclusive wherein said catalyst is used at a level in the range of from 10 to 5,000 parts per million based on the weight of the alcohol.

6. A process according to any one of claims 1 to 5 inclusive wherein said catalyst is used at a level in the range of from 100 to 1,000 parts per million based on the weight of the alcohol.

7. A process according to any one of claims 1 to 6 inclusive wherein said alcohol is chosen from methanol, ethanol, 1 -propanol, isopropanol, 1 -butanol, 1 -methylpropanol and 2-methylpropanol.

8. A process according to any one of claims 1 to 7 inclusive wherein said alcohol is chosen from ethanol, 2-propanol and 1-butanol.

9. A process according to any one of claims 1 to 7 inclusive wherein said alkylene oxide is ethylene oxide and said alcohol is ethanol.

10. A process according to any one of claims 1 to 9 inclusive wherein the reaction is carried out at a temperature in the range of from 50 to 2500C.

11. A process substantially as hereinbefore described with reference to Example 3 or Example 4.

12. An alkylene glycol mono-alkyl ether prepared according to the process of any one of claims 1 to 11 inclusive.