A method of producing silica gels of high water stability for use as drying agents

摘要

Silica gel is prepared by mixing an acid solution and an alkali metal silicate solution containing 27.5-31% by volume, based on the dried gel, of pulverulent additives of 1-5 m diameter to form a hydrosol, coagulating the hydrosol to a hydro-gel and immediately cooling the gel, then ageing in an aqueous solution for 1.5-7 hours below the gel-forming temperature, effecting base exchange for removal of trapped alkali metal ions, washing and calcining at 300-450 DEG C. The coagulation may be effected by dispersing the hydrosol in a H2O-immiscible liquid, e.g. mineral oil, and leaving until gel formation occurs. The pulverulent additive may be silica gel powder or SiO2/Al2O3 gel powder. The silicate solution may be mixed with an acid solution of an Al salt to form a gel containing up to 3% Al2O3. The gel particles may be aged at 4 DEG C. and the base exchange may be effected by washing with dilute Al2(SO4)3 solution or dilute H2SO4.