PROCESS FOR MAKING HYDROPHOBIC SILICA WITH REDUCED SURFACE AREA UNDER NEUTRAL CONDITIONS

摘要

The present invention is hydrophobic silica gels having a reduced surface ar ea and a method for their preparation under natural conditions. The method comprises two steps, where in the first step the pH o f a mixture comprising a silica hydrosol and colloidal silica is adjusted with a base to within a range of pH 3 to pH 6 to facilitate formation of a silica hydrogel having incorporated therein colloidal silica. In the second step the silica hydrogel is contacted with an organosilicon compound in the presence of a catalytic amount of a strong acid to effect hydrophobing of the silica hydrogel to form a hydrophobic silica gel having a surface area within a range of about 100 m2/g to 450 m2/g in the dry state. In a preferred process the hydrophobic silica gel is contacted with a sufficient quantity of a water-immiscible organic solvent to convert the hydrophobic silica hydrogel into a hydrophobi c silica organogel. A water soluble compound of cerium or iron may be added during conduct of the second step to improve heat stabilit y of the hydrophobic silica gel.