Method of modifying the surface properties of finely divided metal oxides

Abstract

Abstract A process for producing hydrophobic finely divided fume silica which comprises the following steps in the specified sequence: A. FORMING, IN A FIRST REACTION ZONE, PARTICLES OF A FUME SILICA HAVING A SIZE OF LESS THAN APPROXIMATELY 150 MILLIMICRONS BY THERMAL DECOMPOSITION AND HYDROLYSIS IN THE VAPOR PHASE OF A VOLATILE SILICON HALIDE, THE SAID FUME SILICA PARTICLES HAVING AN ACIDITY CORRESPONDING TO A PH of approximately 2.0, and including a hydrogen halide and water adsorbed on their surfaces, B. PASSING THE THUS-PRODUCED FUME SILICA PARTICLES OUT OF THE SAID FIRST REACTION ZONE AND SUBJECTING THEM TO A DEACIDIFICATION AND DEHYDRATION PRETREATMENT TO REDUCE THEIR ACIDITY TO A VALUE CORRESPONDING TO A PH of approximately 4.0 by removing substantially all of the adsorbed hydrogen halide and water therefrom, C. PASSING THE THUS-PRETREATED PARTICLES OF FUME SILICA TOGETHER WITH WATER VAPOR INTO A SECOND REACTION ZONE INTO CONTACT WITH A STREAM OF HOT GASES CONTAINING SUBSTANTIAL PROPORTIONS OF AN ORGANOHALOSILANE WHILE THE SECOND REACTION ZONE IS MAINTAINED AT A TEMPERATURE BETWEEN APPROXIMATELY 400* AND APPROXIMATELY 800* C and the particles therein are maintained in a fluidized state and maintained therein for a period sufficient to convert them to hydrophobic fume silica particles, THE FOREGOING STEP, (C) OF THE PROCESS BEING PERFORMED IN THE ABDENCE OF MOLECULAR OXYGEN, AND D. SEPARATING AND RECOVERING THE HYDROPHOBIC FUME SILICA PARTICLES THUS PRODUCED FROM THE HOT GASES AND HYDROGEN HALIDE FORMED FROM THE ORGANOHALOSILANE WHILE STILL CONTINUING TO EXCLUDE MOLECULAR OXYGEN FROM CONTACT WITH THE PARTICLES UNTIL THE PARTICLES HAVE COOLED TO A TEMPERATURE BELOW 400* C.

Inventors

• 👤 Dieter Schutte
• 👤 Jean Diether
• 👤 Helmut Brunner

Bibliographic Details