Food-pharmaceutical quality phosphoric acid preparation - by treating urea phosphate with nitric acid, then with nitrous acid, passing air and reducing nitrate with saccharide(s) or formic acid

摘要

Process for preparing "human food" quality phosphoric acid starting from "purified" technical quality phosphoric acid, obtd. by treatment of urea phosphate with nitric acid and which contains urea nitrates, comprises the following successive stages effected in continuous or batch mode: -a) Treatment of the starting phosphoric acid, which contains 30-50%P205, 2-7%nitrate ions and 0.5-3% of urea, with nitrous acid formed in situ and a molar ratio of nitrous acid/urea of 2-4/1 until all the urea has been converted to nitrogen, carbon dioxide and water b) entraining the gaseous nitrogen-containing cpds. forming from the reaction with urea, and other gas product of a current of air through the phosphoric acid, until the emerging gas is colourless c) treating the phosphoric acid, in which the nitrate content has risen to 3-8% due to the stage a) treatment, with a reducing agent chosen from di- or monosaccharides and formic acid d) concentrating the phosphoric acid to a 55-62% P205 content and treating it with 30% hydrogen peroxide or another substance producing uncontaminated nascent oxygen, until the acid is decolourised. This final prod. comprisises 75-85% of H3PO4 containing 0-20ppm nitrate ions, free of urea and at most 2ppm of arsenic, less than 10ppm fluorine and less than 5ppm of heavy metals (expressed as lead). Food quality phosphoric acid used to prepare soft drinks and refreshments and as a requesting agent in foods. It may be used to prepare othophosphates and polyphosphates used as buffering agents and preservatives in the food and pharmaceutical industry and may also be used in fermentation broths used to produce synthetic proteins etc. 'Food quality' phosphoric acid is obtd. from wet process phosphoric acid at reasonable cost avoiding costly purifs. or use of high cost thermic process phosphoric acid.