GB263198A - An improved process for the production of wide-porous active silica - Google Patents

Abstract

263,198. I. G. Farbenindustrie Akt.-- Co. Dec. 19, 1925, [Convention date]. Right to Patent relinquished. Silica.-A silica gel having wide pores is obtained by treating a silica jelly before or during- drying and in any case before contraction is complete, with an electrolyte such as to impart to it a hydrogen-ion concentration pH between 7 and 10. The jelly may be prepared in any suitable way, preferably by way of a neutral or nearly neutral or slightly acid sol, and the electrolyte may be added in the form of a suitably adjusted washing-water. The materials mentioned as initial materials for the production of the gel are soluble or insoluble silicates, zeolites, slags, silicon tetrachloride, or silicon fluoride, and the decomposing agents may be acids, or solutions of metallic salts, in which case the gels may contain metallic oxides or hydroxides. It is preferred to obtain the jelly from a sol of neutral, faintly alkaline, or faintly acid reaction and containing at least 50 and preferably over 120 grams. silica per litre, and salts produced in the reaction are preferably removed by washing. The method of drying is comparatively unimportant and it may be effected comparatively rapidly in a current of air or in vacuo at ordinary or raised temperature or in a current of hot combustion gases. The jelly may be more or less completely purified, with or without pressure, before or after drying or pre-drying or between individual stages of drying, whereupon a further purification may follow, preferably after treatment with water vapour. In the examples, the jelly is produced from sodium silicate, sulphuric acid and ice, the sol being coagulated by heating and stirring. Coagulation may also be effected by heating the sol poured on to sheet metal or into moulds in a furnace, and the jelly may be moulded by stamping. The jelly may be washed until nearly all the salts are removed and the jelly gives a red-violet colour with cresol red, a washing-water giving a redviolet colour with cresol red being preferably used, the pH value being between 8 and 9, and the drying may be effected in a current of air at 150-200‹ C. followed if desired by a higher temperature. Specification 255,863 is referred to. The Specification as open to inspection under Sect. 91 (3) (a) gives the limits of pH as 7 to 13, and contains an example in which the silica jelly is dried at 20-120‹ C. or 150-200‹ C., washed with water and then with 0.006N caustic soda, and dried at 200-600‹ C. This subjectmatter does not appear in the Specification as accepted.