GB728279A - Method for the manufacture of a silica-metal oxide composite - Google Patents

Abstract

A silica-metal oxide composite is prepared by commingling a silica sol with a gellable hydrous metal oxide sol and with an acidic solution of metal salt, contacting the resultant mixture with a basic medium to form a firm hydrogel, and drying the gel. The metal present in the oxide sol and the salt solution may be aluminium, magnesium, zirconium, beryllium, vanadium, thorium, or tantalum. The mixture preferably has an SiO2 content of 4-10 per cent. and a pH of 2-5; the amount of metal salt may be equivalent to 0.5-15 per cent. by weight of the final dried composite. For the preparation of silica-alumina composites, water glass is added to a mixture of sulphuric, hydrochloric, nitric, or acetic acid and a solution of aluminium sulphate, nitrate, or acetate; alumina sol is added to the resultant mixture. Spheroidal particles are formed by dispersing the mixture into an atmosphere containing ammonia, methylamine, or ethylamine; the particles are collected in aqueous liquid having a temperature of 30 DEG -105 DEG C. and a pH of 7-10, washed with ammonium sulphate solution, dried at 40 DEG -315 DEG C., and calcined at 425 DEG -760 DEG C. Alternatively the mixture may be dispersed into a hot immiscible liquid. The bulk density and the average pore diameter of the final composite may be varied by altering the proportion of metal oxide sol to metal salt solution; thus silica-alumina composites having an alumina content of 2.5-75 per cent. may be made with bulk densities of 0.4-0.8 gms./cc., and similar composites having an alumina content of 5-35 per cent may have an average pore diameter of 40-90 . The products are useful as catalysts in cracking, hydroforming, or desulphurization of hydrocarbons, alkylation of aromatic or isoparaffinic hydrocarbons, polymerization of unsaturated hydrocarbons, the reaction of xylene with benzene to produce toluene, and the dehydration of alcohols to form hydrocarbons. Examples describe the preparation of silica-alumina catalysts according to the invention, and also by impregnation and cagellation methods, with comparative figures for activity, &c.