GB2288990A - Catalyst for hydrogenation of oils - Google Patents

Abstract

A method of preparing a metal catalyst composition, comprises the steps of: i) mixing a composition of finely divided particulate catalytic metal in an oleophilic medium with a solvent which dissolves the oleophilic medium, thereby producing a dispersion of metal in a solution of said medium and solvent; ii) mixing particulate carrier material into the dispersion so that the metal impregnates the carrier material; and iii) separating the metal impregnated carrier material from said solution, the separated material constituting the metal catalyst composition. The exemplified metal is nickel having a particle size of 10 microns or less, and the carrier kieselguhr. A process is described for the hydrogenation of soya-bean oil.

Description

A METAL CATALYST COMPOSITION The present invention relates to a metal catalyst composition and a method of preparing same, the catalyst composition being intended particularly, but not exclusively, for use in the hydrogenation of oils (e.g. vegetable, animal and marine oils).

The edible vegetable oil industry depends to a very large degree on soft oils which are converted by hydrogenation to full or partially hydrogenated oils, and then further processed to make edible oils, margarine, cooking fats, and similar products. The hydrogenation of edible oils is conventionally carried out with the aid of a catalyst composition containing a catalytic metal. Typically the catalytic metal is nickel prepared by one of two methods; wet reduction of nickel formate or, in more recent years, dry reduction supported on a filter aid or kieselguhr.

It is well known that the most active and most selective hydrogenation catalyst is that produced by wet reduction of nickel formate in a soft refined oil such as refined soya bean oil. Such catalyst is also cheaper to produce than dry reduced catalyst. Wet reduced nickel catalyst has very small and fine particle size of almost colloidal dimensions, which gives rise to its high activity. However, the very small particle size renders the catalyst difficult to filter from the oil after hydrogenation. The small particles pass through filter cloth and through many filter papers. Thus, unless very thick filter paper is used, some particles pass through into the finished oil.

The use of thick filter papers slows the filtration process, but if small nickel particles are allowed to be passed into the finished oil, the oil has to be re-refined, which is an expensive process and slows the plant capacity of the edible oil refinery. Consequently, over recent years, the hydrogenation of edible oils has been carried out almost universally with dry reduced catalyst.

Dry reduced nickel is prepared by producing a substantially water insoluble nickel salt, such as hydroxide or carbonate, as a precipitate on a filter aid or kieselguhr. The precipitate is filtered off, dried, powdered and then roasted in a rotary furnace whilst passing hydrogen gas over the heated material. By this means, fine particles of nickel are produced in the furnace which are attached to the dry filter aid or kieselguhr particles. The product is easy to filter in a refinery and is therefore easier to use than wet reduced catalyst. However, dry reduced catalyst is not as active or selective as wet reduced catalyst and is more expensive to produce.

It is an object of the present invention to provide a metal catalyst composition which obviates or mitigates the disadvantages discussed above.

According to a first aspect of the present invention there is provided a method of preparing a metal catalyst composition, comprising the steps of: i) mixing a composition of finely divided particulate catalytic metal in an oleophilic medium with a solvent which dissolves the oleophilic medium, thereby producing a dispersion of the metal in a solution of said medium and solvent; ii) mixing particulate carrier material into the dispersion so that the metal impregnates the carrier material; and iii) separating the metal impregnated carrier material from said solution, the separated material constituting the metal catalyst composition.

The finally divided catalytic metal should have a relatively small grain size, e.g. of the order of 10 microns or less, whereas the carrier material is of larger particle size (e.g. in the range 10 to 80 microns).

As a result, the catalyst composition will have high activity and selectively characteristics (due to the small grain size of the catalyst metal) but good filtration characteristics provided by the carrier material (on which the metal is impregnated).

The composition of finely divided particulate catalytic metal in an oleophilic medium as required for step (i) of the process is preferably one produced by a wet reduction technique in which a metal salt which will decompose to the metal (e.g. the formate) is heated in an oleophilic medium. If the salt is one which yields hydrogen then the oleophilic medium, in which the reduction is effected, is preferably one which is at least partially hydrogenated by the hydrogen produced. In this case, the oleophilic medium in which the reduction is effected may be an unsaturated oil, e.g. a soft vegetable oil such as soya bean oil. For preference the unsaturated oil is one which, as a result of at least partial hydrogenation during the preparation of the catalytic metal, is a solid at room temperature. In this case, the composition of finally divided particulate catalytic metal and oleophilic medium as used for step (i) may conveniently be in the form of powder or flakes.

Examples of catalytic metals for use in the invention include cobalt, iron, palladium, platinum and (most preferably) nickel.

It is preferred that the catalytic metal/oleophilic medium composition used in step (i) is a conventional wet reduced nickel catalyst for which a typical grain size distribution is: Grain Size (microns) Vol.% < 10 99.9 10 to 20 0.03 20 to 40 0.03 40 to 80 0.03 > 80 0.01 The carrier material may, for instance, be diatomaceous earth, e.g. kieselguhr, or a filter aid.

The catalytic metal/oleophilic medium composition used in step (i) preferably contains 20% to 25% by weight of metal and is preferably mixed with the solvent in the ratio 1 part composition: 1-20 parts solvent. The solvent may, for example, be an aliphatic, cycloaliphatic or aromatic solvent. Examples of solvents include hydrocarbons (e.g.

hexane), ketones (e.g. acetone) and ethers (e.g. di-isopropyl ether).

Heating may be used to aid dissolution of the oleophilic medium. In this case, the dispersion is preferably cooled (e.g. to a temperature of 200 to 300 C) prior to addition of the carrier material.

The carrier material is preferably added to the dispersion in the ratio of 1-5 parts carrier material part metal. Examples of carrier material which may be used include, but are not limited to, diatomaceous earth, e.g. kieselguhr, or a filter aid.

In step (iii) the metal catalyst composition (comprising the finally divided metal impregnated on the carrier material) may be separated from the organic phase by any convenient means, e.g.

filtration or centrifugation. After separation, the metal catalyst composition may be dried, e.g. in a current of warm air or in a vacuum, to form a powder. It may well be found that some of the oleophilic medium remains associated with the metal catalyst. This can in fact be an advantage in that the retained oleophilic medium helps to give the catalyst composition non-pyrophoric properties. At least some of this residual oleophilic medium may be removed by solvent extraction (e.g. using hot acetone). However it is convenient to ensure that the final catalyst composition contains from about 30 to 40% by weight of oleophilic medium so as to assist in rendering the composition non-pyrophoric.

According to a second aspect of the present invention, there is provided a metal catalyst composition, comprising particulate catalytic metal impregnated onto a particulate carrier material, wherein a major portion of the metal has a grain size of 10 microns or less.

Preferably a major portion of the metal impregnated carrier comprises particles having a grain size greater than 10 microns, for instance in the range 10 to 100 microns.

For example, in a preferred composition in which the metal is nickel and the carrier material is filter aid, the nickel particles have the following grain size distribution: Grain Size (microns) Vol.% < 10 99.9 10 to 20 0.03 20 to 40 0.03 40 to 80 0.03 > 80 0.01 and the nickel impregnated filter aid has the following grain size distribution: Grain Size (microns) Vol.% < 10 10.6 10 to 20 15.7 20 to 40 20.2 40 to 80 33.8 > 80 19.7 A general outline of one method in accordance with the invention for producing a nickel catalyst composition will now be given by way of example only.

Firstly, wet reduced nickel catalyst is prepared by the conventional process of mixing nickel formate powder with a soft vegetable oil, such as soya bean oil, and heating the resultant slurry, preferably under vacuum and with agitation, to temperatures between 240-2700C. The nickel formate decomposes and liberates gases including hydrogen which, in the presence of the wet reduced nickel catalyst, hydrogenates the soya bean oil protective medium to hydrogenated soya bean oil. The resultant product, after cooling to 1200C for example, can be flaked or powdered since the soya bean oil has been hardened by this process.

The above process is entirely conventional and the finished product is a standard wet reduced nickel catalyst comprising 20-258 nickel.

In accordance with the present invention, the wet reduced nickel catalyst is then admixed with a solvent for soya bean oil or hydrogenated soya bean oil (such as the hydrocarbon hexane, or acetone, or di-isopropyl ether, or any one of the homologues of these) in a ratio of between 1 part wet reduced nickel catalyst to up to 20 parts of solvent. The mixture is agitated and heated in a vessel equipped with reflux condensers so that the hydrogenated soya bean oil protective medium is dissolved in the solvent, forming a dispersion of nickel particles in a solution of hydrogenated soya bean oil and solvent. The resultant slurry is cooled to about 20-450C, and filter aid or kieselguhr is added under agitation in a ratio of between 1 to 5 parts of filter aid or kieselguhr for every 1 part of nickel.

The resultant slurry is then filtered in a conventional filter, e.g.

a plate and frame filter, a rotary vacuum, or any other suitable conventional equipment, to produce a cake of nickel particles impregnated on to a filter aid or kieselguhr and a filtrate of hydrogenated soya bean oil in the solvent. The cake is then dried by means of a current of warm air, or by applying a vacuum, which results in a powdered nickel catalyst preparation comprising nickel particles adhered to large particles of filter aid or kieselguhr.

The filtrate, which comprises solution of hydrogenated soya bean oil in solvent, is then evaporated or distilled in conventional equipment to regenerate the solvent used. This leaves hydrogenated soya bean oil which can be sold as an article of commerce for use in either edible oil products or for oleo-chemicals.

As discussed above, the metal catalyst prepared in accordance with the present invention is suitable for use in the hydrogenation of soft vegetable oils and retains all the advantages of conventional wet reduced nickel catalysts, i.e. high selectivity and low cost, but has good filtration characteristics at least equal to those of a conventional dry reduced nickel catalyst.

A required starting material for the preparation method according to the present invention is a composition of particulate metal (in the above example the metal is nickel but examples of alternative metals are given above) in an oleophilic medium, but it will be appreciated that such a composition could be prepared by any suitable means and need not necessarily be prepared by the wet reduction process discussed above.

It will also be appreciated that the parameters of the method described above may be varied. For instance, the ratio of wet reduced catalyst to solvent and of filter aid or kieselguhr to nickel may be varied depending upon the requirements for the finished product.

The following non-limiting Example further illustrates the invention.

Example 50.95 gm of a conventional wet reduced nickel catalyst (obtained by the wet reduction of nickel formate by the process described above) containing 22.5% nickel (the remainder being hydrogenated soya bean oil) was agitated under reflux with one litre of acetone, maintained at boiling point, for two hours. This produced a suspension of nickel particles in a solution of hydrogenated soya bean oil and acetone.

The suspension was cooled to 450C and 11.54 gm of "Dicalite Speedplus" was added with continual stirring. "Dicalite Speedplus" is a commercially available kieselguhr (distributed by Redland Minerals Limited, Retford Road, Worksop, > ,ottinghamshire) which is quoted by the manufacturer as having the following particle size distribution: Particle Size (microns) Vol.% < 10 3 to 5 10 to 20 32 to 42 20 to 40 43 to 47 40 to 80 8 to 14 > 80 1 to 4 The temperature of the mixture was raised again to boiling point and the suspension of nickel particles and kieselguhr maintained for a further 30 minutes under reflux. The suspension was cooled to 450C and filtered through a Whatman No.l paper in an oven maintained at 400C. Once the filtration had substantially ceased, the resultant filter cake was washed twice successively with 100 ml of acetone at 450C to remove some of the oil which was found to be retained. The filter cake was dried in an oven at 400C yielding 35.8 gms of a friable powder which was screened through a 100 mesh British Standard sieve. Any oversizes were ground and re-sieved until all powder passed through the 100 mesh sieve.

The acetone was distilled off the filtrate to yield 26.5 gms of hydrogenated soya bean oil. At room temperature this oil was a hard, brittle, solid, with a slip point of 500C to 520 C, and therefore constituted a bi-product which could be utilised in the manufacture of edible oils such as pastry margarine or cooking fat. The acetone could be recycled for use in subsequent preparations of the nickel catalyst.

The particle size of the powdered nickel catalyst prepared as described above was measured and found to have the following distribution: Grain Size (microns) Vol.% < 10 10.6 10 to 20 15.7 20 to 40 20.2 40 to 80 33.8 > 80 19.7 As mentioned above, the nickel was obtained from a conventional wet reduced catalyst and thus has the grain size distribution given above for such a catalyst.

The difference in the particle size distribution shown by the final catalyst composition as compared with that of the "Dicalite Speedplus" is believed to be due to a combination of two factors; firstly a break down in the size of individual kieselguhr particles during the preparation process, and secondly the agglomeration of catalyst particles due to their retained oil content.

The powdered nickel catalyst was compared for activity (with respect to hydrogenation) and also selectivity with a conventional wet reduced nickel catalyst obtained from nickel formate.

In a one litre laboratory hydrogenator, 500 gms of refined and bleached soya bean oil were hydrogenated with a sufficient amount of nickel catalyst obtained as described above so that the total mixture contained 0.1% nickel. The hydrogenation was carried out for two hours at 1800C in a stream of hydrogen passing a rate of 100 litres per hour. The process was then repeated under identical conditions using the conventional wet produced nickel catalyst.

In both cases the soya bean oil was hydrogenated to a semisolid fat (suitable for manufacture of edible oils such as table margarine) with a slip point of 200C to 220 C.

The hydrogenated soya bean oil was separated from the nickel catalysts in both cases by filtration using a Whatman No.1 filter paper.

With the catalyst according to the present invention the soya bean oil filtered to a clear, bright oil, whereas with the conventional wet reduced nickel catalyst the filtered soya bean oil had a dark, greyish cast due to the fact that the conventional nickel catalyst did not filter adequately.

Claims (26)

1. A method of preparing a metal catalyst composition comprising the steps of: i) mixing a composition of finely divided particulate catalytic metal in an oleophilic medium with a solvent which dissolves the oleophilic medium, thereby producing a dispersion of metal in a solution of said medium and solvent; ii) mixing particulate carrier material into the dispersion so that the metal impregnates the carrier material; and iii) separating the metal impregnated carrier material from said solution, the separated material constituting the metal catalyst composition.

2. A method according to claim 1, wherein step (i) includes heating to aid the dissolution of the metal/medium composition in the solvent.

3. A method according to claim 2, wherein the dispersion is cooled prior to addition of the carrier material.

4. A method according to claim 3, wherein the dispersion is cooled to a temperature in the range of 200C to 45at.

5. A method according to any preceding claim, wherein the metal/medium composition is mixed with the solvent in the ratio 1 part composition:l-20 parts solvent.

6. A method according to any preceding claim, wherein the carrier material is added to the dispersion in the ratio of 1-5 parts carrier material:1 part metal.

7. A method according to any preceding claim, wherein the metal is selected from nickel, cobalt, iron, palladium, and platinum.

8. A method according to any preceding claim, wherein the metal/medium composition contains 20% to 25% by weight of metal.

9. A method according to any preceding claim, wherein a major portion of the metal has a grain size of 10 microns or less.

10. A method according to any preceding claim, wherein the oleophilic medium is a hydrogenated soft vegetable oil.

11. A method according to claim 10, wherein the oleophilic medium is soya bean oil.

12. A method according to any preceding claim, wherein the oleophilic medium is solid at room temperature.

13. A method according to any preceding claim, wherein the metal is nickel and the medium is an at least partially hydrogenated oil, and the nickel/oil composition is prepared by the reduction of nickel formate in an unsaturated form of the oil.

14. A method according to any preceding claim, wherein the carrier material has a grain size in the range 10 to 80 microns.

15. A method according to any preceding claim, wherein the carrier material is diatomaceous earth.

16. A method according to any one of claims 1 to 14, wherein the carrier material is filter aid.

17. A method according to any preceding claim, wherein the metal catalyst composition separated from said solution contains from 30% to 40% by weight of said oleophilic medium.

18. A metal catalyst composition, comprising particulate catalytic metal impregnated onto a particulate carrier material, wherein a major portion of the metal has a grain of 10 microns or less.

19. A metal catalyst composition according to claim 18, wherein a major portion of the metal impregnated carrier material comprises particles having a grain size in the range 10 to 100 microns.

19. A metal catalyst composition according to claim 18, wherein the metal is selected from nickel, cobalt, iron, palladium and platinum.

20. A metal catalyst composition according to claim 19, wherein the particulate metal is nickel.

21. A metal catalyst composition according to any one of claims 18 to 20, wherein the carrier material has a grain size in the range from 10 to 80 microns.

22. A metal catalyst composition according to any one of claims 18 to 21, wherein the composition contains from 30% to 40% by weight of an oleophilic medium.

23. A metal catalyst composition according to claim 22, wherein said oleophilic medium is an at least partially hydrogenated oil.

24. A metal catalyst composition according to claim 23, wherein said oil is an hydrogenated soft vegetable oil.

25. A method of preparing a metal catalyst composition, substantially as hereinbefore described with reference to example 1.

26. A metal catalyst composition, substantially as hereinbefore described with reference to example 1.