PROCESS FOR PRODUCING A PERCARBONATE

摘要

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 °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 °C of not more than 3νW/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.