Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Silicon containing or process of making
Reexamination Certificate
2000-06-21
2004-04-06
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Silicon containing or process of making
C502S159000, C502S240000, C502S244000, C502S344000, C502S345000, C568S360000, C568S361000, C568S376000
Reexamination Certificate
active
06716789
ABSTRACT:
The present invention relates to a process for preparing oxidic catalysts comprising copper in an oxidation state >0 by treatment of a solid oxidic support material with an aqueous copper salt solution and subsequent calcination. The present invention also relates to the catalysts obtainable by this process and to their use for dehydrogenating secondary alcohols to the ketones, especially for dehydrogenating cyclohexanol to cyclohexanone.
The catalytic dehydrogenation of secondary alcohols is widely used in industry for producing ketones, for example for the production of cyclohexanone from cyclohexanol (see for example K. Weissermel, H.-J. Arpe, Industrielle Organische Chemie, 4th edition Verlag Chemie, Weinheim, 1994, p. 274). These processes are known in numerous variations (excepting the embodiment of the present invention) and therefore need only be explained in principle. The processes typically involve passing the alkanol, or an alkanol/ketone mixture, over a copper catalyst at elevated temperature, generally above 200° C. Here it is important to note that the catalytic dehydrogenation of alcohols to ketones is reversible and that the position of the equilibrium will shift toward the starting materials with decreasing temperature. Furthermore, equilibration is slow at a low temperature, making it generally impossible to achieve all but low conversions. If, in contrast, the process is carried out at elevated temperature, for example at above 400° C., lower selectivities to the product of value are obtained, since side reactions, for example dehydration of the alcohols or dimerization of the product ketones, will take place at these temperatures to an appreciable extent in some instances.
Alkanols are frequently dehydrogenated at below 400° C. using catalysts comprising copper as an active component on a solid, usually oxidic support. The copper content of such catalysts can be up to 50% by weight, based on the total weight of the catalyst. Typical support materials of oxidic type are ceramic oxides such as silicon dioxide, e.g., silica, silicates, alumosilicates, aluminum oxide, zirconium dioxide and titanium dioxide, also zeolites and pumice. As well as copper as active component, prior art catalysts frequently comprise a small amount of alkali metals as promoters.
GB-A-1081491 discloses Cu/Al
2
O
3
, SU-A 465 217 discloses Cu/Li/SiO
2
and SU-A 522853 discloses Cu/K/Al
2
O
3
for the nonoxidative dehydrogenation of cyclohexanol. The copper catalysts in question are usually prepared by applying the active copper component either to a prefabricated support, by precipitation of a copper salt or by impregnation with a suitable copper salt solution, or by coprecipitating the components making up the catalyst.
Chang et al. (Appl. Catal. A 103 (1994), 233-42) describe copper catalysts for the dehydrogenation of cyclohexanol to cyclohexanone which are obtainable by reductive precipitation of copper on &agr;-Al
2
O
3
as support. Reductive precipitation has the disadvantage that, in general, the support first has to be seeded with a noble metal such as platinum, rhodium, iridium, gold or palladium in order that uniform deposition of copper on the support may be achieved. This creates additional costs. In addition, the catalysts described by Chang et al. are difficult-to-tablet powders having limited processibility into shaped articles such as tablets. These catalysts are therefore not suitable for industrial use.
Chung et al. (Appl. Catal. A 115 (1994), 29-44) further describe copper catalysts which are obtainable by alkali precipitation of copper from an aqueous copper salt solution onto a silicon dioxide support. True, the catalysts obtainable by the process described therein have comparatively high selectivity, but their activity is too low for the desired applications.
In addition, prior art catalysts lose activity with increasing time on stream. Consequently, in a prolonged run, the operating temperature of the reactor has to be continually raised, entailing a loss of selectivity. Moreover, raising the temperature speeds up the deactivation of the catalyst.
It is an object of the present invention to provide a catalyst for the nonoxidative dehydrogenation of secondary alcohols to the corresponding ketones which combines high activity with high selectivity. In addition, the catalyst shall not lose its activity in prolonged operation. Moreover, the catalyst shall be economical to obtain and have advantageous mechanical properties.
We have found that this object is achieved by catalysts which are obtainable by treating a solid oxidic support material with aqueous copper salt solutions comprising at least one organic water soluble polymer which binds copper ions coordinatively and subsequent calcination.
The present invention accordingly provides a process for preparing an oxidic catalyst comprising copper in an oxidation state>0, which comprises treating a solid oxidic support material with an aqueous solution comprising at least one copper salt and at least one organic water soluble polymer which binds copper ions coordinatively in a concentration of from 0.1 to 100 g/l and then calcining. The present invention further provides the catalysts obtainable by this process.
According to the invention, suitable water soluble polymers which bind copper ions coordinatively either have carboxylate groups or have amino groups and/or carboxamide groups. Polymers containing carboxylate groups are customarily homo- or copolymers of ethylenically unsaturated carboxylic acids, for example homo- and copolymers of acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid. In general, suitable polymers containing carboxylate groups contain not less than 50 mol %, based on the total number of constitutive monomers, of the aforementioned ethylenically unsaturated carboxylic acids.
Suitable comonomers are in particular monomers having a high solubility in water (i.e., >60 g/l at 25° C.), for example the amides of the aforementioned ethylenically unsaturated carboxylic acids, N-vinyllactams and the hydroxyalkyl esters of the aforementioned ethylenically unsaturated carboxylic acids. Preferred polymers containing carboxylate groups are acrylic acid homopolymers and copolymers.
Typical polymers containing amide groups are the homo- and copolymers of amides of monoethylenically unsaturated carboxylic acids, for example polymers of acrylamide and/or of methacrylamide. In general, such polymers containing at least 50 mol % of units derived from monomers contain amide groups in polymerized form. Suitable comonomers are the aforementioned ethylenically unsaturated carboxylic acids or N-vinyllactams. A further class of polymers containing amide groups contain not less than 50 mol % of units derived from N-vinyllactams such as N-vinylpyrrolidone, N-vinylcaprolactam and N-vinylpiperidone. Suitable comonomers for N-vinyllactams are the aforementioned ethylenically unsaturated carboxylic acids, their amides, their hydroxyalkyl esters, vinyl acetate, vinyl propionate and vinyl-substituted nitrogenous heterocycles such as vinylpyridines and vinylimidazole.
Amino-containing polymers include not only homo- and copolymers of amino-containing monomers but also such polymers as are obtainable by polymer-analogous conversion of functional groups into amino functions. Examples of the first monomers are homo- and copolymers of aminoalkyl acrylates and methacrylates such as N,N-dimethylaminoethyl acrylate and N,N-dimethylaminoethyl methacrylate, of vinylpyridines and of vinylimidazoles. Suitable comonomers for the amino-containing monomers are, for example, the amides of ethylenically unsaturated carboxylic acids, N-vinyllactams and vinyl-substituted nitrogenous heterocycles. Polymers whose amino groups are obtainable by polymer-analogous reaction of functional groups on the polymer include the hydrolysis products of polymers based on N-vinylamides, for example the hydrolysis products of homo- and copolymers of N-vinylacetamide, and also the hydrogenation products of polymers
Gehrken Henning-Peter
Heineke Daniel
Hesse Michael
Meissner Ruprecht
BASF - Aktiengesellschaft
Keil & Weinkauf
Wood Elizabeth D.
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