Solvay Interox (societe Anonyme)

Other

Solvay Interox Gmbh

Solvay Interox Sa

Romano Pardini

Soraya Parvaneh

Alun P James

Graham R Horne

Richard Roesler

Stefano Bigini

Pier-Luigi Deli

Manfred Mathes

Lido Signorini

Robert Owen

Uwe Droste

Corrado Baccani

Sodium percarbonate is traditionally made in a crystallization 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 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 35C. 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 is obtained by extraction from the reaction vessel and in other embodiments a fraction of the sodium percarbonate is introduced in solution in the mother liquor and a fraction is introduced in particulate form directly into the reaction vessel. Large particle sodium percarbonate is provided which has a 7 day aged heat emission at 40C. of not more than 3 &mgr;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.

Sodium percarbonate and process for producing sodium percarbonate

Sodium percarbonate exhibits a tendency to decompose in built compositions and particularly detergent compositions built with zeolites. The tendency can be ameliorated by selecting sodium percarbonate which intrinsically has a mean particle size of from 500 to 1000 microns and not more than 20% by weight of below 350 microns and has a moisture pick-up when measured in a test at 80% relative humidity and 32&deg; C. after 24 hours of not greater than 30 g/1000 g sample. A suitable sodium percarbonate can be made most conveniently by crystallisation from a bulk saturated solution of sodium percarbonate in a crystalliser/classifier that does not employ a conventional chloride salting-out agent.

Compositions containing sodium percarbonate

The present invention relates to an apparatus for the continuous manufacture of solid particles of alkali metal persalts by reaction of an aqueous hydrogen peroxide solution with an aqueous solution of an alkali metal salt and crystallization of the persalt. The persalt is formed in a crystallizer classifier, which is made up of stirred region and a growth region for the persalt crystals a non-stirred clarifying region for the solution and a classification region for the particles obtained by elutriation in a liquid stream withdrawn in the clarifying region.

Process for the manufacture of persalt particles

Sodium percarbonate is traditionally made in a crystallization 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 (,) 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 (,) is obtained by extraction from the reaction vessel (,) and in other embodiments a fraction of the sodium percarbonate (,) is introduced in solution in the mother liquor (,) and a fraction is introduced in particulate form (,) directly into the reaction vessel (,). Large particle sodium percarbonate is provided which has a 7 day aged heat emission at 40&deg; C. of not more than 3 &mgr;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.

Process for producing sodium percarbonate

Continuous process for the manufacture of solid particles of alkali metal persalts by reaction of an aqueous hydrogen peroxide solution with an aqueous solution of an alkali metal salt and crystallization of the persalt formed in a crystallizer-classifier comprising a stirred formation and growth region for the persalt crystals, a nonstirred clarifying region for the solution and a classification region for the particles obtained by elutriation in a liquid stream withdrawn in the clarifying region. Plant for manufacturing the said particles.

Continuous process for the manufacture of solid alkali metal persalt particles coated by crystallization of a supersaturated aqueous solution of persalts and covering of the persalt particles in a post-crystallization vessel into which at least one coating agent is introduced and in which crystallization of the coating agent around the persalt particles is carried out under controlled temperature and stirring conditions.

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I-Rosignano-Solvay, Italy

Romano Pardini