GB2250287A

GB2250287A - Alcohol production by the hydrogenation of fatty acid esters

Info

Publication number: GB2250287A
Application number: GB9124969A
Authority: GB
Inventors: Eduard Karel Poels; Dirk Ryk Evert Polman; Johannes Josephus Vreeswijk
Original assignee: Uniqema BV
Current assignee: Uniqema BV
Priority date: 1990-11-27
Filing date: 1991-11-25
Publication date: 1992-06-03
Also published as: GB9124969D0; FR2669628A1; GB9025708D0; KR920009743A; CA2055960A1

Abstract

In a process for the hydrogenation of fatty esters to alcohols, using a copper containing catalyst, the activity of the catalyst is maintained by treatment with water vapour, such as by including 1.0% to 1.8% by weight water in the ester feed.

Description

FATTY ESTER HYDROGENATION This invention relates to a process of fatty ester hydrogenation, in particular to catalytic hydrogenation using a copper containing catalyst.

From GB 2116552 (Davy Mckee) it is known that fatty esters, especially the methyl esters of fatty acids, can be hydrogenated by passing the ester together with hydrogen over a reduced CuO/ZnO catalyst, with the formation of the corresponding fatty alcohol and methanol.

We have found that as the catalyst is continuously used in this reaction its activity is reduced, that is the yield of the reaction falls with time.

We have now discovered that if the catalyst with such reduced activity is exposed to water vapour at least some of its activity is returned, so that it may then be used further without significant loss of yield.

Thus, according to the invention, there is provided a process for the preparation of a fatty alcohol in which a fatty ester is passed together with hydrogen over a copper containing catalyst characterised in that the catalyst is treated with water vapour to assist in the maintenance of the activity thereof.

The catalyst is treated with water vapour before, or simultaneously with, being contacted with the fatty ester and hydrogen.

According to a first embodiment of the invention, the hydrogenation process is carried out stepwise. In a first step fatty ester and hydrogen are passed over the catalyst to generate the corresponding fatty alcohol. In a second step water vapour is passed over the catalyst thereby to regenerate its activity. In a third step further fatty ester and hydrogen are passed over the catalyst to generate further fatty alcohol. This embodiment of the invention is conveniently carried out by retaining the catalyst in the reactor, turning off the supply of fatty ester to the reactor and replacing it with a supply of water vapour and then turning off the supply of water vapour and reinstating the supply of ester to the reactor.

The supply of hydrogen gas to the reactor may suitably be maintained during the supply of water vapour.

This embodiment of the invention has the advantage that the water vapour after passing over the catalyst may be separately collected and will not therefore significantly adulterate the fatty alcohol product.

In a second embodiment of the invention, the feed to the catalyst comprises a mixture of fatty ester and water together with hydrogen. The level of water to be added to the fatty ester feed may be from 0.1% to 2% by weight such as from 1.0% to 1.8%, such as about 1%. Alternatively, the water vapour may be fed continuously into the hydrogen gas supply.

This embodiment enables the hydrogenation reaction to be carried out continuously. Sufficient water vapour may be passed over the catalyst in this way to substantially stabilise its activity. In this embodiment however, water becomes entrained in the fatty alcohol product and may therefore need to be subsequently removed, for example by distillation.

While not wishing to be bound by any theory, the applicants believe that during the hydrogenation reaction the electronic state-of the copper in the catalyst progressively changes causing a loss in activity and that the treatment with water vapour causes a partial oxidation of Cm(0) to Cu(I), thereby regenerating the activity. It is not thought that the moisture content of the catalyst plays an important role, since the treatment with water vapour has not been found to lead to any significant uptake of water by the catalyst.

The invention is particularly suited to the hydrogenation of the esters of fatty acids, by which we mean any vaporisable ester of an aliphatic carboxylic acid, especially those derived from natural oils and fats particularly the esters of C12 to C18 fatty acids with C1-C5 alcohols, especially with methanol.

The hydrogenation reaction preferably is carried out of a temperature of 2000 to 2300C and at a pressure of 3 to 5 Mpa. The molar ratio of the ester to hydrogen is dependent on the chain length distribution of the ester feed and can be calculated by the ratio of the vapour pressure of that mix at the reaction pressure to the total pressure. Hydrogen gas per se is used, although the use of mixtures thereof with other gaseous components is also possible.

The catalyst is a copper-containing catalyst, especially a copper-zinc catalyst. Such catalysts are known in the art, for example in GB 2116552 (Davy McKee) referred to above, GB 1436773 (Du Pont), US 3923694 (ICI) and US 4283581 (chevron). A typical catalyst consists of a reduced mixture of copper oxide and zinc oxide which may also include amounts of other metal oxides as well as fillers or supports such as carbon. The CuO/ZnO mixture before reduction preferably contains 5-95%, such as 10-70% by weight CuO and 95-5%, such as 90-30t by weight ZnO.

Any other materials present do not usually comprise more than 20% by weight of the catalysts.

The catalyst may be prepared by methods known in the art, for example by co-precipitation, calcination and reduction using hydrogen or carbon monoxide at 160 -250 C for 8 to 24 hours.

We are aware of European patent specification EP-A-350762 (Henkel) which describes the gas phase dehydrogenation of aliphatic 1,2-diols containing 5 to 60 weight percent of water to form 1,2-ketone-alcohols in the presence of a copper containing catalyst. In this process, the water is said to increase selectivity and suppress dimerisation without suppressing activity. The high heat capacity of the steam retards cooling.

The present invention on the other hand concerns the activity ofthe catalyst used in a different reaction, ie.

the hydrogenation of esters to alcohols, and is in no way suggested by the disclosure of EP-A-350762.

EXAMPLE 1 In this example the catalyst was an activated copper/zinc catalyst with a Cu/Zn weight ratio of 0.55.

The catalyst was mounted in a hydrogenation reactor. A mixture of C12 to C methyl esters (flow rate 7 Kg/hr) and hydrogen (750 Nm /hr) were fed to the reactor at a temperature of 205or and 4 MPa. The crude fatty alcohol was separated from the output of the reactor, its quantity of non-converted methyl esters being used to calculate the efficiency of the hydrogenation reaction. The hydrogen was recycled to the input of the reactor.

In a first experiment the initial conversion of the reaction was 97.2%. After a period of 50 hours, the efficiency had fallen to 97%. From this point onwards water was included in the feed at level 1.2% by weight based on the methyl ester feed rate. The conversion of the reaction then increased to 97.7% at which level it remained, so long as water was maintained in the feed.

In a second experiment the initial conversion of the reaction was 97.6%. After a period of 50 hours, the conversion had fallen to 96.9%. From this point 1.8% by weight water was included in the feed. The conversion then stabilised at 97%. After a period of 90 hours the water level in the feed was reduced to 1% by weight.

Conversion was maintained at 97%. After a further period of 50 hours, the water supply to the feed was switched off, whereupon a significant fall in efficiency occurred, being below 96% after a further 60 hours.

These examples demonstrate the benefit of including water in the ester/hydrogen feed in maintaining the activity of the catalyst.

Claims

1. A process for the preparation of a fatty alcohol in which a fatty ester is passed together with hydrogen over a copper containing catalyst characterised in that the catalyst is treated with water vapour to assist in the maintenance of the activity thereof.

2. A process according to Claim 1, wherein a mixture of fatty ester and water is passed, together with hydrogen over the catalyst.

3. A process according to Claim 2 in which water entrained in the fatty alcohol product is subsequently removed therefrom.

4. A process according to Claim 1 carried out step wise in which in a first step fatty ester and hydrogen are passed over the catalyst, in a second step water vapour is passed over the catalyst and in a third step further fatty ester and hydrogen are passed over the catalyst.

5. A process according to Claim 1, wherein the catalyst is a copper-zinc catalyst.

6. A process according to Claim 5, wherein the catalyst is a reduced Cu0/ZuO catalyst.

7. A process according to Claim 1, wherein the fatty ester is the methyl ester of a fatty acid.

8. A process according to Claims 2 and 7 wherein the water entrained in the fatty alcohol product is separated therefrom together with the methanol which is also formed in the reaction.