GB596591A - Improvements in or relating to inorganic oxide particles of spherical shape and their manufacture - Google Patents

Abstract

<PICT:0596591/III/1> Inorganic oxide particles of spherical shape are produced by passing a sol of at least one difficulty reducible oxide capable of forming a hydrogel in droplet form through a fluid suspending medium and regulating the pH of the sol and the suspension time of the droplets so that they set while still suspended to a firm hydrogel having a spherical shape, and subsequently ageing the particles for at least six hours before drying them. The sols employed may be of silica, alumina, titanium oxide, zirconia, thoria or ceria, or of mixed oxides, e.g., silica-alumina. The suspending medium may be liquid, the droplets moving upwardly or downwardly therein or constituting an emulsion with the liquid, or gaseous, and in this case, the sol may be sprayed into a rising air stream. Suitable suspending liquids are kerosene and the oil known under Registered Trade Mark "Nujol." For emulsions, kerosene, or carbon tetrachloride diluted with a hydrocarbon, with an emulsification agent such as resin or pitch may be employed. The pH varies from 6 to 10 for silica sols produced by the acidification of water glasses, from 4.3 to 7 for silica sol formed by the hydrolysis of say ethyl orthosilicate, and from 4.5 to 7 for alumina sols produced by the addition of aluminium amalgam to water, or by precipitation of alumina from aluminium salts, washing, and redissolving in say acetic or formic acid. Ageing may be for 6-24 hours, either in air or in water, or in a solution of pH 2 to 7, or 7 to 8, or in the organic suspending liquid. Drying of the particles is generally below 350 DEG C., infra-red radiation being advantageously employed. The particles are suitably calcined at 350-900 DEG C. Catalysts suitable for cracking, reforming and dehydrogenation of hydrocarbons may contain other active compounds introduced into the sol prior to the formation of the spherical particles, or by impregnating the wet or dry spheres. Thus, a compound of chromium, vanadium or molybdenum, e.g., ammonium molybdate, may be added to an alumina sol; or dried spheres of silica may be impregnated with an aluminium salt solution, and then heated. Other catalysts mentioned are alumina-chromia or alumina-molybdena containing a small amount of magnesia, and silica-alumina containing zirconia, thoria or boron oxide. A suitable apparatus comprises vessels 1, 5 for, for example, sodium silicate and hydrochloric acid, a mixing vessel 4 and a chamber 11 containing kerosene &c. through which the droplets fall. The spherical particles are swept away by a current of oil from pump 13 to separator 16, the oil being recirculated. Specification 576,058 is referred to.