Purification of caustic soda

US6113657A · kind A · utility

Assignee

• BASF SE

Inventors

• Dieter Schlafer · Ludwigshafen, DE
• Michael Mauss · Oldenburg, DE
• Matthias Rauls · Ludwigshafen, DE
• Dieter Baumann · Greven, DE

Key dates

• Filing date: Mar 13, 1998
• Grant date: Sep 5, 2000
• Expiry date: Mar 13, 2018

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C01D1/30
• WIPO field: Materials, metallurgy
• WIPO sector: Chemistry

Abstract

In a process for preparing crystalline NaOH.3.5H.sub.2 O, NaOH.3.5H.sub.2 O is allowed to crystallize from an aqueous sodium hydroxide solution which contains sodium chloride and is saturated in respect of NaOH.3.5H.sub.2 O and the crystals formed are separated from the solution using a mechanical solid/liquid separation apparatus, wherein the solid/liquid separation is carried out under conditions under which the crystalline NaOH.3.5H.sub.2 O is freed sufficiently of residual solution adhering to the surface for the sodium chloride content of the crystalline NaOH.3.5H.sub.2 O obtained to be less than 100 mg per kg. The crystalline NaOH.3.5H.sub.2 O is subjected to an additional purification step, which may include the at least superficial melting or the at least superficial dissolution of the crystals, in combination with a solid/liquid separation step. The additional purification step. The additional purification step comprises washing the crystalline NaOH.3.5H.sub.2 O separated off.