GB968742A - Improvements in or relating to sodium perborate trihydrate - Google Patents

Abstract

Sodium perborate trihydrate, NaBO3.3H2O or NaBO2.H2O2.2H2O of coarse grain, e.g. 0.5-2 mm., is made by crystallizing a highly concentrated aqueous sodium perborate solution having an atomic or molecular ratio of Na : B : active oxygen : H2O of approximately 1 : 1 : 1 : max. 7 in the presence of at least 10% by weight of solid sodium perborate trihydrate based on the weight of the final product, at a temperature of 15 DEG to 85 DEG C. The crystalline product may be dried. The highly concentrated solution of perborate may be obtained by the reaction of boric acid, borax or sodium metaborate with hydrogen peroxide or sodium peroxide with/without the use of caustic soda and the addition of water; alternatively the perborate solution may be made by melting dry or moist sodium perborate tetrahydrate and maintaining the melt at 70 DEG C. for a few minutes with or without the addition of hydrogen peroxide. The dustless granulate may be used directly in the preparation of bleaching or self-acting washing agents and is formed mechanically e.g. with the aid of a roll from a highly concentrated solution or plastic mass before or during its crystallization. The trihydrate used for seeding may be that obtained by the process. Stabilizers may be added to mixture to be crystallized, e.g. sodium stannate, sodium silicate, magnesium silicate, magnesium chloride and potassium pyrophosphate. Specifications 737,304 and 802,434 are referred to.