Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-08-10
2004-01-06
Nguyen, Cam N. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
C502S327000, C502S335000, C502S355000, C502S415000, C502S439000
Reexamination Certificate
active
06673743
ABSTRACT:
This invention relates to catalysts and in particular to catalysts suitable for use for hydrogenation, especially the hydrogenation of oils and fats.
Oils and fats are often either partially or fully hydrogenated in a batch slurry process by suspending a particulate nickel catalyst in the oil or fat and feeding hydrogen thereto while heating the mixture, typically to a temperature in the range 80 to 250° C., possibly under pressure, e.g. at a pressure of up to 30 bar abs. For partial hydrogenation, the pressure is usually under 10 bar abs., for example 2 to 4 bar abs. For oil or fat hydrogenation, the catalyst should have a high activity so that the desired degree of hydrogenation can be achieved in a short time and/or a small amount of nickel can be employed. The catalyst should also exhibit a good selectivity in the case of partial hydrogenation so that over-hydrogenation of the oils and fats is minimised. Furthermore it is desirable that the residual catalyst can be readily filtered from the hydrogenated oil or fat and that the catalyst show good refuse properties.
Catalysts often employed for this process are nickel on a support of e.g. alumina and are characterised by, inter alia, a high nickel surface area per gram of nickel. Typical catalysts having a high nickel content are described in EP 0 168 091, wherein the catalyst is made by precipitation of a nickel compound and then a soluble aluminium compound is added to the slurry of the precipitated nickel compound while the precipitate is maturing, i.e. ageing. After reduction of the resultant catalyst precursor, the reduced catalyst typically has a nickel surface area of the order of 90 to 150 m
2
per g of total nickel. The catalysts have a nickel/aluminium atomic ratio in the range 2 to 10. Reduced catalysts having a nickel/aluminium atomic ratio above 2, in which at least 70% by weight of the total nickel has been reduced to elemental nickel, have a total nickel content of more than about 66% by weight.
Nickel/alumina hydrogenation catalysts, having a total nickel content of 5 to 40% by weight, but also having a high nickel surface area, made by a different route are described in U.S. Pat. No. 4,490,480. In the process of this latter reference, a nickel ammine complex, particularly a nickel ammine carbonate, is heated in the presence a transition alumina: this results in the precipitation of a nickel compound, such as nickel hydroxide or basic nickel carbonate, intimately associated with the alumina. In this latter process, an alumina powder may be slurried with a solution of the nickel complex, or shaped units, such as spheres or cylindrical extrudates, typically having a minimum dimension above about 1.5 mm, formed from the alumina are impregnated with a solution of the nickel complex. While catalysts having a nickel surface area over 130 m
2
per g total nickel, and indeed in some cases above 200 m
2
per g total nickel, are described, such high surface area products are all made by the aforesaid impregnation route using shaped alumina units: the catalysts made by slurrying alumina powder with the nickel complex have nickel surface areas significantly below 130 m
2
per g total nickel. While catalysts made using the preformed, shaped alumina units are of utility in fixed bed hydrogenation processes, they are unsuitable for the aforesaid batch slurry hydrogenation process as their size renders them liable to settling out from the slurry, and also, when used for partial hydrogenation, they tend to give over hydrogenation of the fats and oils. The aforementioned U.S. Pat. No. 4,490,480 indicates that catalysts suitable for batch slurry hydrogenation may be made by grinding high nickel surface area catalysts made by the aforesaid impregnation route using shaped alumina units. However the production of such catalysts by such a technique involves additional processing steps of forming the alumina into the shaped units and the subsequent comminution step.
Catalysts made directly from an alumina powder of 60-70 &mgr;m size containing 18-28% by weight of nickel and having a nickel surface area of up to 123 m
2
per g of nickel are also described in the aforesaid U.S. Pat. No. 4,490,480. However we have found that such materials had a relatively poor activity for the hydrogenation of oils.
We have now found that nickel/alumina catalysts having a high activity and/or good selectivity may be made by the aforesaid process employing a slurry of the alumina powder if an alumina powder having a small particle size is employed. Surprisingly, despite the use of a small particle size alumina, the catalysts are readily filtered from the hydrogenated fat or oil.
It has been proposed in GB 926 235 to make hydrogenation catalysts by this route using kieselguhr as the support. However, we have found that catalysts made using small particle size kieselguhr, as opposed to transition alumina, do not exhibit high nickel surface areas.
Accordingly we provide a method of making a nickel/alumina catalyst containing 5 to 75% by weight of total nickel comprising slurrying a transition alumina powder having a surface-weighted mean diameter D[3,2] in the range 1 &mgr;m to 20 &mgr;m with an aqueous solution of a nickel ammine complex, heating the slurry to cause the nickel amine complex to decompose with the deposition of an insoluble nickel compound, filtering the solid residue from the aqueous medium, drying and, optionally after calcining the solid residue, reducing the solid residue.
By the term total nickel, we mean the amount of nickel whether present in elemental or combined form. Generally however at least 70% by weight of the total nickel in the reduced catalyst will be in the elemental state.
The term surface-weighted mean diameter D[3,2], otherwise termed the Sauter mean diameter, is defined by M. Alderliesten in the paper “A Nomenclature for Mean Particle Diameters”; Anal. Proc., vol 21, May 1984, pages 167-172, and is calculated from the particle size analysis which may conveniently be effected by laser diffraction for example using a Malvern Mastersizer.
The transition alumina may be of the gamma-alumina group, for example a eta-alumina or chi-alumina. These materials may be formed by calcination of aluminium hydroxides at 400-750° C. and generally have a BET surface area in the range 150-400 m
2
/g. Alternatively, the transition alumina may be of the delta-alumina group which includes the high temperature forms such as delta- and theta-aluminas which may be formed by heating a gamma group alumina to a temperature above about 800° C. The delta-group aluminas generally have a BET surface area in the range 50-150 m
2
/g. The transition aluminas contain less than 0.5 mol of water per mole of Al
2
O
3
, the actual amount of water depending on the temperature to which they have been heated. The alumina should be porous, preferably having a pore volume of at least 0.2 ml/g, particularly in the range 0.3 to 1 ml/g.
It is preferred that the small particle size alumina has a relatively large average pore diameter as the use of such aluminas appears to give catalysts of particularly good selectivity. Preferred aluminas have an average pore diameter of at least 12 nm, particularly in the range 15 to 30 nm. [By the term average pore diameter we mean 4 times the pore volume as measured from the desorption branch of the nitrogen physisorption isotherm at 0.98 relative pressure divided by the BET surface area]. During the production of the catalyst, nickel compounds are deposited in the pores of the alumina, and so the average pore diameter of the catalyst will be less than that of the alumina employed, and decreases as the proportion of nickel increases. It is preferred that the reduced catalysts have an average pore diameter of at least 10 nm, preferably above 15 nm and particularly in the range 15 to 25 nm.
On the other hand, irrespective of the nickel content of the catalyst, the particle size of the catalyst is essentially the same as the particle size of the transition alumina, and so the catalysts generally have a
Johnson Matthey PLC
Nguyen Cam N.
Pillsbury & Winthrop LLP
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