GB805960A - Improvements in or relating to the preparation of diarylmethanes by a catalytic process, and catalysts for use therein - Google Patents

Abstract

A catalyst consists of a silica gel support on which is deposited from 0.001 to 3 millimoles of a strong mineral acid or 0.04 to 0.25 millimoles of alumina per gram of support for use in the preparation of diarylmethanes by condensation of an alkyl-substituted aromatic hydrocarbon having at least one unsubstituted nuclear carbon atom with formaldehyde (see Group IV (b)). Specified acids for use in the catalyst are sulphuric, phosphoric, phosphotungstic and silicotungstic acids. Sulphuric acid is preferred and may be used in a concentration between 0.01 and 1.5 millimoles per gram of support. The support preferably has both a relatively high surface area and porosity; if the surface area is between 100 and 500 square metres per gram the average pore diameter should be 50-100 <\>R, and if between 500 and 800 square metres per gram, 20-50 <\>R. Preferred catalysts have deposited on the silica not more than one-half the amount equivalent to a monomolecular layer of a polybasic mineral acid substantially nonvolatile at the reaction conditions. The sulphuric acid-onsilica gel catalysts may be prepared by spraying the silica with a 1 to 10 per cent by weight aqueous solution of sulphuric acid and if necessary the treated gel dried at 150 DEG C. to reduce the water content to below 30 per cent by weight. Other acidic catalysts are prepared similarly. The alumina-on-silica gel catalysts may be prepared by treating the silica with an aqueous solution of aluminium nitrate followed by calcining at 400-700 DEG C. for 2-48 hours. Silica-alumina catalysts prepared by other methods must be similarly calcined before use. In use the catalysts may become contaminated by carbonaceous deposits. They may be regenerated by a conventional oxidative regeneration by burning the catalyst in an oxygencontaining gas; part or all of the mineral acid may be lost and should be replaced as described above. Specification 766,498, [Group IV (b)], is referred to.ALSO:Diarylmethanes are prepared by condensing an alkyl-substituted aromatic hydrocarbon having at least one unsubstituted nuclear carbon atom with formaldehyde in the presence of a catalyst comprising a silica gel support on which is deposited from 0.001 to 3 millimols. of a strong mineral acid or 0.04 to 0.25 millimols. of alumina per gram of support (see Group III). The hydrocarbon used is preferably monocyclic containing not more than 6 carbon atoms in any one alkyl group and no more than 15 carbon atoms in the molecule. Methylbenzenes having 1 to 5 methyl groups are preferred but ethylbenzene-toluenes and -xylenes, diethylbenzenes, cumene and isopropyl-toluenes and -xylenes may be used. A mixed feed can be employed. The formaldehyde can be added anhydrous or in aqueous solution and as a liquid or vapour stream. It may also be added as paraformaldehyde or other substance liberating formaldehyde under reaction conditions. 37 per cent aqueous formalin is particularly suitable. The process is preferably carried out in the liquid phase at a sufficiently high temperature to permit prompt removal of water added to or formed in the reaction zone as a vapour stream also containing some hydrocarbon. The vapour is condensed and hydrocarbon is returned to the reaction zone, any formaldehyde appears in the aqueous condensate and may be recovered and returned to the reaction. Batch or continuous operation may be used. Temperatures of 100-200 DEG C. are preferred, and the temperature is preferably near but preferably below the boiling-point of the hydrocarbon, or initial boiling-point in the case of a mixed feed, for hydrocarbons boiling up to 185 DEG C. it is preferably within 20 DEG C. of the boiling-point. Pressures of 1-10 atmospheres may be used, atmospheric being preferred. The reaction takes place very quickly, and is generally complete within 2 to 5 seconds of the addition of monomeric formaldehyde. The rate of addition of formaldehyde is controlled so that the amount of formaldehyde present is such that it can be completely converted within 1 minute. The molar ratio of hydrocarbon feed to formaldehyde monomer is preferably very high, e.g. between 30 and 2000:1. In batch operation, the ultimate ratio of hydrocarbon feed to formaldehyde is in excess of the stoichiometric molar ratio of 2:1 and may be between 3:1 and 20:1. In continuous operation the steady state mixture preferably contains by weight, not more than 60 per cent, e.g. 5-20 per cent of condensation products and 40-95 per cent of hydrocarbon feed. The amount of catalyst is between 1 and 30 weight per cent based on the liquid content of the reaction mixture, which is preferably an agitated slurry of catalyst in the liquid. Specification 766,498 is referred to.