Shell catalyst, a process for its production and its use

Details Shell catalyst, a process for its production and its use Shell catalyst, a process for its production and its use

1994-09-26

1998-07-21

Lewis, Michael

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Inorganic carbon containing

502182, B01J 2118

Patent

active

057835144

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a shell catalyst containing 0.3 to 5% by weight and, more particularly, 0.5 to 2% by weight of palladium on an active carbon support, based on the dried catalyst, obtainable by impregnation of the support with an aqueous palladium salt solution, precipitation of palladium and reduction (activation).


BACKGROUND OF THE INVENTION

The hardening of unsaturated fats, oils and fatty acids on an industrial scale by hydrogenation is carried out with nickel catalysts in the form of fine powders in intensively stirred autoclaves under hydrogen pressures of up to 20 bar and at temperatures of up to 250.degree. C. Particular problems arise above all in the hydrogenation of fatty acids. On the one hand, nickel soaps are formed at the temperatures mentioned and can only be removed from the product by distillation. In addition, the activity and life of the catalyst are reduced through the dissolving out of nickel from the catalyst. On the other hand, separation of the catalyst from the product is complicated and leads to increased losses of product.
These disadvantages can be avoided by using palladium catalysts. Palladium is acid-resistant. Accordingly, no soaps requiring separation are formed. The life of such a catalyst is thus so long that economically justifiable continuous hydrogenation in a fixed catalyst bed is possible. Accordingly, there is no longer any need for the complicated separation of the catalyst from the product.
In addition, palladium catalysts are eminently suitable for the hydrogenation of edible fats because the hydrogenated product contains no residual nickel at all.


RELATED ART

A catalyst of the type mentioned at the beginning is known from CA-B-1,157,844. As described in detail in this document with references from the patent literature, the production of a supported noble-metal catalyst generally consists of the three steps of impregnation, precipitation and reduction. For example, this document cites GB-B-799,871 in which a support material is impregnated with PdCl.sub.2 solution and is precipitated with NaHCO.sub.3 as Pd(OH).sub.2.
Similar processes are described in U.S. Pat. No. 2,749,359, U.S. Pat. No. 3,736,266 and DE 28 50 510.
According to CA-B-1,157,844, the activity of the palladium catalyst is increased by first charging a catalyst support of extruded active carbon with water or an organic liquid before it is impregnated with the palladium salt solution. In this way, the noble metal is only applied to the support in an outer shell. After an impregnation time of 1 hour, the pH value is adjusted to around 4.0 by addition of sodium hydroxide solution so that palladium precipitates as hydroxide. The production of the catalyst is completed by filtration, washing, drying and reduction.
The problem addressed by the present invention was to provide a catalyst of the type mentioned at the beginning which would combine considerably higher activity with a longer life. In addition, the invention set out to provide a simpler and more economical process for the production of such a catalyst.


BRIEF SUMMARY OF THE INVENTION

According to the invention, the solution to this problem is characterized in that active carbon showing an alkaline reaction, more particularly with a pH value of at least 8, is impregnated with the palladium salt solution and the supernatant liquid is separated off after it has reached a pH value of at least 1, more particularly at least 3 and preferably at least 4.
It has surprisingly been found that particularly active catalysts with a very long life are obtained if the basicity present in the carbon is sufficient to increase the pH value of the noble metal salt solution after impregnation to a minimum level which is sufficient for precipitation. In this case, all the palladium contained in the solution is precipitated in a peripheral zone of the support. The supernatant solution is palladium-free, so that there is no need to add an alkali, for example sodium hydroxide, to complete the precipitation process. A shell-typ

REFERENCES:
patent: 2749359 (1956-06-01), Calkins et al.
patent: 3138560 (1964-06-01), Keith et al.
patent: 3736266 (1973-05-01), Schrage

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