GB263199A - An improved process for the production of active silica gels with fine capillary pores - Google Patents

Abstract

263,199. I. G. Farbenindustrie Akt.- Ges. Dec. 19, 1925, [Convention date]. Right to Patent relinquished. Silica.-Silica gel having fine 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 2 and 6.5. 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 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 a neutral, weakly alkaline, or slightly acid reaction, and containing at least 50 and preferably 120 or more grams, silica per litre, and salts produced in the reaction are preferably removed by washing. If the jelly is strongly acid, the washing may he effected first with alkaline water, then with distilled water, and then with water having the same or a lower hydrogen-ion concentration than the jelly possesses. The drying temperature may be high or low but is preferably over 120‹ C. and may be conducted in stages, the first stage being below 400‹ C., for instance 75-200‹ C. The drying may be effected in air or in vacuo, or in contact with hot combustion gases in tunnel or rotary ovens. The jelly may be more or less completely purified, with or without pressure, before or after drying or pre-drying, after which a further purification may be effected, preferably after a treatment with water vapour. The drying may be preceded by moulding the completely or partially purified jelly or precipitate, preferably while containing about 90 per cent of water. In an example, the jelly is produced from sodium silicate, sulphuric acid, and ice, the sol being coagulated by heating and stirring. The jelly is broken up and washed to remove nearly all the salts, until it gives a yellow or bluish-green coloration with bromo-cresol green, or a yellow coloration with cresol red. Preferably the washing-water, containing hydrochloric acid, gives a bluish-green coloration with bromo-cresol green, when its pH is about 3. The jelly is dried in hot air at 150-200‹ C., followed if necessary by a higher temperature. Specifications 255,863 and 255,864 are referred to. The Specification as open to inspection under Sect. 91 (3) (a) gives the limits of pH as 1 to 6.5. This subject-matter does not appear in the Specification as accepted.