Hydrogenation process

Details Hydrogenation process Hydrogenation process

1992-10-21

1994-06-28

Dees, Jose' G.

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568885, 554143, C07C 2704

Patent

active

053248716

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a process for the hydrogenation of native fats, oils and fat derivatives, such as fatty acids and fatty acid esters, to fatty alcohols in a fixed-bed reactor, more particularly in co-current, hydrogen being recirculated in a stoichiometric excess, more particularly in an excess of 10 to 100 fold, and the fat, oil or fat derivative passing through the reactor only


RELATED ART

In a known process of this type, for example for the hydrogenation of fatty acid methyl ester, the actual hydrogenation reaction takes place in one or more fixed-bed reactors arranged in tandem at temperatures in the range from 200.degree. to 250.degree. C. and under a hydrogen pressure of 200 to 300 bar. To this end, the fatty acid methyl ester is pumped under pressure into the plant where it is mixed with compressed hydrogen, heated with the compressed hydrogen to the reaction temperature and introduced into the reactor from above.
After passing through the reactors, the reaction mixture is cooled and separated in a separator into the liquid phase and the gas phase. The liquid phase is expanded and delivered to the methanol separation unit while the gas phase, which consists mainly of hydrogen, is recirculated via a compressor. In the methanol separation unit, which is in the form of an evaporator, the fatty alcohol is freed from the methanol and may then be used for its intended purpose without further purification.
However, the catalytic hydrogenation of fats, oils and fat derivatives to fatty alcohols in a fixed-bed reactor (trickle-bed method), particularly under adiabatic conditions, requires a large excess of hydrogen of 10 to 100 times the stoichiometric quantity to ensure that a large part of the heat of reaction is dissipated through the large excess of gas. This is because excessive temperatures in the catalyst bed lead increasingly to secondary products and shorten the life of the catalyst.
In industrial plants, the hydrogen is recirculated for economic reasons. To this end, the hydrogen has to be cooled to around 50.degree. C. after passing through the reactor at 230.degree. C., compressed by the recycle gas compressor and reheated to the reaction temperature in a peak heater. The economy of a hydrogenation process such as this in regard to capital investment and operating costs is thus largely determined by the specific recycle gas demand (Nm.sup.3 H.sub.2 /t reaction product).
Accordingly, the problem addressed by the present invention was to minimize the specific hydrogen demand by process measures without significant losses having to be accepted in regard to the specific reactor load, product selectivity and catalyst life.


SUMMARY OF THE INVENTION

According to the invention, the solution to this problem for a process of the type mentioned at the beginning is characterized in that the hydrogen is passed successively through, at least, two fixed-bed reactors without the gas issuing from the reactors and entering the following reactors being cooled and in that the fat, oil or fat derivative are simultaneously introduced into the reactors.
The process according to the invention may be carried out irrespective of the particular type of reactor used, for example a shaft reactor or tube bundle reactor, and irrespective of its method of operation, for example adiabatic or isothermal. In hydrogenation plants comprising n reactors, the specific recycle gas volume is reduced to 1
. The accumulation of volatile components in the gas phase leads to only a slight loss of performance of the order of 5 to 10% for the second reactor and the following reactors. Neither the selectivity nor the useful life of the catalyst is significantly affected.
In another embodiment, the process is carried out using two reactors.
In another advantageous embodiment of the process according to the invention, the liquid reaction products are removed from the gas issuing from the preceding reactors before the gas enters the following reactor. It is of particular advantage in this regard if the liqu

REFERENCES:
patent: 4804790 (1989-02-01), Schuett
patent: 4942266 (1990-07-01), Fleckenstein et al.
patent: 5043485 (1991-08-01), Fleckenstein et al.
patent: 5124491 (1992-06-01), Fleckenstein et al.

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