Method for preparing hydrophobic fumed silica

A method is disclosed for the preparation of hydrophobic fumed silicas which are useful as reinforcing fillers in rubber compositions. The method comprises a first step wherein an aqueous suspension of fumed silica is contacted with an organosilicon compound and in the presence of a catalytic amount of an acid to effect hydrophobing of said silica. In a preferred method, the first step is conducted in the presence of a water miscible organic solvent which facilitates hydrophobing of said silica with said organosilicon compound. The fumed silica used herein preferably has a BET surface area greater than 50 m2/g. In a second step of this method, the aqueous suspension of hydrophobic fumed silica is contacted with a water-immiscible organic solvent at a solvent to silica weight ratio greater than 0.1:1 to effect separation of a hydrophobic fumed silica from the aqueous phase. In a preferred process, the recovered hydrophobic fumed silica has a surface area within a range of 100 m2/g to 750 m2/g.