GB380796A - Improvements in or relating to the manufacture of silica gel and like adsorbent oxide gels - Google Patents

Abstract

The production of low-density heat-resistant gels of the type obtained by washing and drying a hydrogel is characterized in that the hydrogel prior to drying and preferably after washing is impregnated with a water-soluble salt such as sodium or potassium sulphate or chloride, or preferably an alkaline earth salt such as calcium chloride, or with a wholly volatilizable salt such as ammonium chloride, sulphate or nitrate, which salt is removed either by washing the dried gel, or by volatilization during the drying operation. Gels of silica, and of oxides of metals such as tungsten, tin, aluminium, titanium or germanium, and mixtures thereof are specified. In examples, sodium silicate solution is added to hydrochloric acid, the jelly is washed with water at 105-175 DEG F., soaked in say 15 per cent solution of calcium chloride, partially dried by passing air at 75-120 DEG C. thereover, and finally dried at 300 DEG -400 DEG C. The gel is caused to adsorb water vapour until it is 30 per cent or more saturated, and finally leached with water preferably at about 180 DEG F. The product is dried by passing air at 600 DEG F. thereover. If a granular gel is not required, the adsorption of water vapour may be omitted. The apparent density of the final product varies inversely with the quantity of salt employed, and with the temperature of the initial washing water. When say ammonium chloride is used, the washed hydrogel is soaked in a 20 per cent solution of the salt, and dried at a temperature increasing to 500-600 DEG F., completely volatilizing the salt. The gels may be employed as catalyst carriers, or for refining lubricating oils. The effect on the density of activation at various temperatures is indicated.