Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Silicon containing or process of making
Reexamination Certificate
2002-07-26
2003-03-18
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Silicon containing or process of making
C502S162000, C502S167000, C518S715000, C568S389000, C568S398800, C568S399000, C568S881000, C568S885000, C568S950000, C585S250000, C585S260000, C585S270000, C585S274000, C585S277000
Reexamination Certificate
active
06534436
ABSTRACT:
This invention relates to catalysts comprising cobalt supported on a solid silica support and in particular to a method for manufacturing such catalysts.
Catalysts comprising cobalt on a support such as silica or alumina are known in the art for hydrogenation reactions, e.g. for the hydrogenation of chemicals such as aldehydes and nitrites, fats and oils and for the preparation of hydrocarbons from synthesis gas via the Fischer-Tropsch reaction.
WO-A-96/04072 discloses a cobalt on transition alumina catalyst containing between 3 and 40% by weight of cobalt and having a cobalt surface area greater than 30 m
2
/g cobalt.
EP-A-0013275 discloses coprecipitated cobalt-silica hydrogenation catalysts prepared by adding an alkaline precipitating agent to a heated mixture containing cobalt cations, silicate anions and solid porous carrier particles under agitation thereby to precipitate the cobalt and silicate ions onto the solid support particles.
EP-A-0029675 discloses coprecipitated nickel hydrogenation catalysts prepared by adding an alkaline precipitating agent to a heated mixture containing cobalt cations, aluminium anions and solid porous particles under to precipitate the nickel and aluminium ions onto the solid support particles.
In certain reactions it may be beneficial to use cobalt deposited on a silica support rather than cobalt on alumina because the acid sites present on alumina may promote undesirable reactions, e.g. it may reduce the selectivity to primary amines in the hydrogenation of nitrites. Furthermore silica supported catalyst may be preferred for use in acid reaction media where gamma alumina supports may show a tendency to dissolve to some extent.
In comparison with other catalytic metals such as copper and nickel used for hydrogenation reactions, cobalt is a relatively expensive and so, to obtain the optimum activity, it is desirable that as much as possible of the cobalt present is in an active form accessible to the reactants. It is therefore desirable to maximise the surface area of the cobalt in the supported catalysts.
Accordingly we now provide a process for manufacturing a catalyst which comprises a cobalt species on a solid silica support, comprising mixing together particles of a solid silica support and an aqueous solution of cobalt ammine carbonate, and heating to an elevated temperature sufficient to effect decomposition of the cobalt ammine carbonate and precipitation of a basic cobalt carbonate onto said support.
In one embodiment of the invention we provide a method of making a catalyst comprising a cobalt species on a silica support, comprising the steps of mixing a silica particulate material with an aqueous solution of a soluble cobalt compound, heating the mixture of p articulate material and cobalt compound to effect precipitation of a basic cobalt carbonate species on the silica, filtering the solid residue from the aqueous medium, and drying.
In a further embodiment of the invention we also provide a process for the production of a catalyst comprising saturating silica support particles with an aqueous solution of cobalt ammine carbonate, and removing the excess of the solution, before heating the resulting product to a temperature sufficient to effect decomposition of the cobalt ammine carbonate.
The solid residue comprising the catalyst may be calcined and, optionally, reduced.
The term “cobalt species” is used broadly to include both elemental cobalt and cobalt in combined form, e.g. as compounds such as cobalt oxides and cobalt hydroxycarbonates. The catalyst in its reduced form is useful for catalysing hydrogenation reactions. The catalyst may, however, be provided as a precursor wherein the cobalt is present as one or more compounds, such as oxides or hydroxy carbonates, reducible to elemental cobalt. In this form, the material may be a catalyst precursor and may be treated to reduce the cobalt compounds to metallic cobalt or the material may itself be a catalyst and used as supplied, e.g. for oxidation reactions. The cobalt surface area figures used herein apply to the material after reduction, but the invention is not limited to the provision of reduced catalyst.
By the term total cobalt, we mean the amount of cobalt whether present in elemental or combined form. Generally however at least 70% by weight of the total cobalt in the reduced catalyst will be in the elemental state.
The catalysts of the invention preferably have a cobalt to silicon atomic ratios in the range 0.01 to 50, particularly 0.03 to 25 and especially 0.05 to 10.
The particulate silica may be formed from natural sources, e.g. as kieselguhr, or may be a synthetic, e.g. precipitated silica. The particulate silica may be in the form of a powder or a shaped granular material, e.g. as extruded or tabletted silica pieces. Suitable powdered silicas typically have particles of surface weighted mean diameter D[3,2] in the range 3 to 100 &mgr;m and a BET surface area in the range 10 to 500 m
2
/g. Granular silicas may have a variety of shapes and particle sizes, depending upon the mould or die used in their manufacture. For example the particles may have a cross-sectional shape which is circular, lobed or other shape and a length from about 1 to >10 mm. The surface area is generally in the range 10-500 m
2
/g, preferably 100-400 m
2
g
−1
. The pore volume is generally between about 0.1 and 4 ml/g, preferably 0.2-2 ml/g and the mean pore diameter is preferably in the range from <2 to about 30 nm.
The cobalt compound is most preferably a cobalt ammine complex which is formed in situ in aqueous solution by dissolving basic cobalt carbonate in a solution of ammonium carbonate in aqueous ammonium hydroxide, to give a product of the desired cobalt content. The cobalt ammine carbonate solution may be made by dissolving basic cobalt carbonate in an aqueous solution of ammonium carbonate containing additional ammonium hydroxide. The relative amounts should be such that the pH of the solution is in the range 7.5 to 12, preferably 9 to 12. The solution preferably contains 0.1 to 2.5 moles of the cobalt complex per liter. As the concentration of cobalt increases, then generally the proportion of carbonate ions relative to hydroxide ions in the basic cobalt carbonate feed should be increased. The cobalt ammine complex compound is then heated, e.g. to a temperature in the range 60 to 110° C., to cause the cobalt ammine complex to decompose with the evolution of ammonia and carbon dioxide and to deposit a basic cobalt carbonate on the surface, and in the pores, of the silica. This step is conveniently carried out when slurrying silica powders with the cobalt compound so that the slurry is then maintained at the elevated temperature for a period, hereinafter the ageing period.
The amount of cobalt in the catalyst may be varied by varying the relative amount of cobalt and support present in the reaction mixture and by controlling the concentration of the solution of cobalt compound.
During the ageing step at least part of the silica dissolves and reacts with the cobalt complex to form a high surface area “cobalt silicate”. Although cobalt silicates of various compositions may be formed, generally about one cobalt atom reacts to form “cobalt silicate” for each molecule of silica dissolved. The solid material comprising basic cobalt carbonate, “cobalt silicate” and any unreacted silica is then filtered from the aqueous medium, washed and dried.
Alternatively the cobalt compound is absorbed into the pore structure of the silica particle by impregnating the particle with the solution of cobalt compound. The impregnation may be repeated to increase the amount of cobalt compound absorbed by the silica particle, preferably with drying between each impregnation. The particles may then conveniently be separated from the remaining solution and the ageing process may be carried out by heating them e.g. to a temperature above 100° C. for the ageing period of at least 60 minutes, preferably at least 100 minutes to decompose the cobalt compound held within the particles to depos
Bailey Stephen
Gray Gavin
Lok Cornelis M
Bell Mark L.
Hailey Patricia L.
Imperial Chemical Industries PLC
Pillsbury & Winthrop LLP
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