Process for purifying phosphorous acid

US4834960A · kind A · utility

Assignee

• Hoechst GmbH · DE

Inventors

• Jurgen Grosse · Hürth, DE
• Gunther Schimmel · Lechenich, DE
• Bernhard Hofmann · Peißenberg, DE

Key dates

• Filing date: Apr 18, 1988
• Grant date: May 30, 1989
• Expiry date: Apr 18, 2008

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01B25/163
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

The purification of phosphorous acid which is formed in halogenations of hydrocarbon derivatives using phosphorus trihalides is carried out in the context of preparing phosphorous acid in a reaction zone by reacting a mixture of phosphorus trichloride and water which has been finely divided by means of steam at temperatures between 150.degree. and 200.degree. C. in the gas phase. In this process, the liquid reaction product drains into a concentrating evaporation zone which has a downstream first separation zone. Inert gas is introduced to the lower part of the first separation zone. A melt is withdrawn from the first separation zone into a crystallizing zone. The waste gases from the reaction zone are treated with a washing liquid in a second separation zone before being passed into the atmosphere. The washing liquid used is an aqueous solution of never-purified phosphorous acid, which can have been prepurified by hydrolysis and stripping.