Xerogels, process for their preparation and their use

摘要

Xerogels are manufactured from a soln. of water glass brought to pH ≤ 3 with an acid ion exchange resin or a mineral acid. The silicic acid obtained is polycondensed to a SiO2 gel by the addn. of a base. If mineral acid was used in the 1st step, the gel is washed free of electrolyte with H2O. Water is removed from the gel by extractive distillation with an organic solvent that forms an azeotrope that separates into 2 phases on cooling. The water content is reduced to ≤ 5 wt.%. The resulting gel is dried at below the critical temp. and below the critical pressure of the organic solvent used for extractive distillation. äU