| 摘要 |
PROBLEM TO BE SOLVED: To produce a highly pure phosphoric acid having a low content of impurity metals by hydrating purified phosphorus oxychloride by adding pure water thereto, and concentrating the obtained hydrated product. SOLUTION: Phosphorus oxychloride is purified by distillation to provide a phosphorus oxychloride having <=10 ppb impurity metal content. The obtained phosphorus oxychloride is fed to a reactor vessel made of a fluororesin, and heated to 10-110 deg.C. Pure water is added to the heated phosphorus oxychloride in the mixing ratio regulated so that the concentration of the reactant may be 5-74 wt.%, and the obtained mixture is hydrated at a temp. of 10-110 deg.C for 30-180 min to provide the hydrated product. The hydrated product is concentrated under a reduced pressure of 5-50 mmHg at a temp. of 60-110 deg.C to remove hydrogen chloride generated by the hydration together with the water to provide the objective phosphoric acid having <=10 ppb content of the impurity metals. Preferably, the reactor vessel made of the fluororesin can be the one in which at least a surface contacting with the aqueous solution of the phosphorus oxychloride to be hydrated is made of the fluororesin.
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