Continuous preparation of silica sols which contain large particles

US5964693A · kind A · utility

Assignee

• BAYER HEALTHCARE LLC · DE

Inventors

• Uwe Brekau · Cologne, DE
• Hans-Dieter Block · Cologne, DE
• Hans-Heinrich Moretto · Cologne, DE
• Peter C. Schmidt · Leverkusen, DE
• Peter Schober · Leverkusen, DE
• Werner Ludovici · Odenthal, DE

Key dates

• Filing date: May 26, 1993
• Grant date: Oct 12, 1999
• Expiry date: May 26, 2013

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01B33/1435
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

A process is provided for the preparation of aqueous silica sols having a particle size of 27 to 72 nm. by adding fresh acidic silica sol into the reactors of a multi stage cascade reactor wherein the reactors contain aqueous solution of colloidal silica sol of a pH of 8 or above. Each successive stage of the cascade reactor is supplied with overflow from the preceding stage. Alkaline compounds, such as alkaline sodium silicate solution, alkaline potassium silicate solution, sodium hydroxide solution or potassium hydroxide solution, are introduced into the first reactor or first reactors so that a pH value in the range of 8 to 12.5 is established in the reactors.