Process for the production of chromium trioxide
AssigneeBritish Chrome & Chemicals Limited
InventorsDanvers A. Swales, Michael A. Marshall
Life of this patent
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Abstract
Chromium trioxide contaminated with sulphate is purified by washing with an aqueous purifying wash liquor, generally water or aqueous chromic acid, while at a temperature above 50.degree. C. and centrifuging the washed product. Washing is generally conducted on the centrifuge. The chromium trioxide is preferably made by reacting sodium dichromate with from 2.4 to 2.8 mols sulphuric acid. The process can be operated to produce a novel product consisting of crystalline, non-fused, chromium trioxide that is substantially pure. The novel product can be in the form of pellets.
Claims10
A process in which a purified product containing more than 95% chromium trioxide and less than 3% total sulphate, expressed as sodium bisulphate, is obtained from a crude crystalline product made by reacting concentrated aqueous sodium dichromate with sulphuric acid and separating the resultant crystalline crude product from the reaction liquor, the process comprising washing the crude crystalline product with a purifying wash liquor selected from the group consisting of water and an aqueous solution of chromic acid and in which part at least of the washing is conducted by spraying the wash liquor onto the crude product while the product and the liquor are at a temperature above 50.degree. C. and below the fusion temperature while centrifuging and wherein centrifuging is continued until the water content is less than 3%.
Dependencies are inferred from the claim text.