Wacker-Chemie Gmbh

Peter Scherm

Gunter Kratel

Ernst Muhlhofer

A process for continuously rendering finely divided, pyrogenic silica hydrophobic at low temperatures in the presence of a hydrophobicizing aid such as aliphatic alcohols having from 1 to 3 carbon atoms. The process of rendering silica hydrophobic is conducted at temperatures of from 60.degree. to 350.degree. C., and more preferably from 80.degree. to 150.degree. C., over a period of from 2 to 5 hours, and more preferably from 3 to 4 hours. The hydrophobicizing agents are known organohalosilanes and the preferred hydrophobicizing aid is methanol. The hydrophobicizing aid is used in amounts of from 2% to 15% by weight, and more preferably in amounts of from 2% to 10% by weight, based on the weight of silica used.

Hydrophobicization of pyrogenic silica

The invention relates to a process for continuously hydrophobicizing pyrogenic, finely divided silica, in which the waste gases are fed back to a mixing chamber upstream of the SiO.sub.2 reaction flame.

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Emmerting, Germany

Peter Scherm