GB1427310A - Process for producing naoh,3,5 h2o crystlas - Google Patents

Abstract

1427310 Purifying caustic soda AJINOMOTO CO Inc 24 May 1974 [29 May 1973 14 Dec 1973] 23475/74 Heading C1A The invention claimed is crystals of composition NaOH.3¢H 2 O of cubic form, at least 0À5 mm.<SP>3</SP> in size and containing not more than 0À15% by weight of NaCl. Also claimed is a process for the production of these crystals which comprises contacting a 33-45% by weight homogeneous NaOH solution, at a temperature below 10‹ C., which is supersaturated with NaOH with NaOH. 3.5H 2 O crystals or with a 33-45% by weight NaOH solution containing NaOH.3.5H 2 O crystals as seed material without applied cooling and allowing the mixture obtained to warm up either of its own accord or with applied heat to a temperature at or approaching that at which the aqueous phase is saturated with respect to NaOH.3.5H 2 O and separating off the NaOH. 3.5H 2 O crystals which have separated. The homogeneous 33-45% NaOH solution can be obtained by (1) cooling a homogeneous 45-55% impure aqueous NaOH solution to less than 35‹ C., removing NaCl crystals and diluting with water; or (2) cooling a 33-45% NaOH solution to 10-0‹ C., with or without addition of NaCl crystals as seed material and separating the precipitated NaCl crystals; or (3) diluting a 45-55% homogeneous NaOH solution with water and cooling; or (4) making homogeneous a mother liquor from which NaOH. 3À5H 2 O crystals have been removed, and cooling it to render it supersaturated with respect to NaOH.3À5H 2 O. Method (2) is preferred.