Preparation of sodium carbonate peroxide and its dry granular products

Abstract

Sodium percarbonate is traditionally made in a crystallisation process from aqueous hydrogen peroxide and sodium carbonate with recycle of mother liquor in the presence of a substantial concentration of a salting-out agent, conventionally sodium chloride. The invention provides a process intended to be conducted without addition of chloride salting-out agent in which the dissolution step (1) is controlled to restrict the sodium carbonate concentration to below 95 %; preferably 60 to 90 % of its saturated concentration at a temperature preferably controlled to at most 35 DEG C and the mole ratio of hydrogen peroxide: sodium carbonate in the reaction vessel is controlled to between 0.7 to 1.2:1, and preferably about 1:1. In some embodiments at least a fraction of the mother liquor introduced into the dissolution tank (1) is obtained by extraction from the reaction vessel (6) and in other embodiments a fraction of the sodium percarbonate (2) is introduced in solution in the mother liquor (4) and a fraction is introduced in particulate form (8) directly into the reaction vessel (6). Large particle sodium percarbonate is provided which has a 7 day aged heat emission at 40 DEG C of not more than 3 mu W / g measured in a microcalorimeter over 16 hours that is lower than the heat emission from conventionally produced sodium percarbonate employing a chloride salting-out agent.

Description

technical field [0001] The present invention relates to a process for the preparation of persalts, and more particularly to the preparation of sodium percarbonate and sodium percarbonate so prepared. It also relates to sodium percarbonate itself and compositions comprising sodium percarbonate. Background technique [0002] Sodium percarbonate term as used herein, is that the molecular formula is Na 2 CO 3 1.5H 2 o 2 Sodium carbonate peroxyhydrate is the name commonly used in the industry, and is often called PCS. Despite its wide range of uses due to its oxidizing and disinfectant properties, PCS is currently most widely used as a bleaching agent in detergent compositions, especially concentrated and super concentrated compositions that have been advocated by the detergent industry since the 1980s agent, or as a bleaching agent in dishwashing compositions or as a bleach additive, or as a bleaching agent in hard surface cleaning compositions. [0003] Sodium percarbonat...

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Problems solved by technology

[0008] Although theoretically wet processing can be operated without a salting-out agent, the absence of a salting-out agent results in lower conversion of reagents to PCS, and lower recovery of PCS from solution, so that the returned mother liquor contains higher concentrations of supernatants. Hydrogen peroxide, thus increasing the possibility of premature crystallization on return, and the degree of loss of hydrogen peroxide during return

[0009] Perhaps the most acute problem faced by persalt manufacturers wishing to wet process PCS is the fact that wet processing often employs salting-out agents to operate the process effectively, yet the resulting product may have undesired the nature of

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