The manufacture of monosodium phosphate from wet process acid by amine extraction

Price, Roger Nelson Davey

The manufacture of monosodium phosphate from wet process acid by amine extraction

Master Thesis

1974

Publisher

University of Cape Town

Department

Department of Chemical Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

Monosodium phosphate (NaH₂PO₄) may be prepared from a mixture of phosphoric acid and sodium chloride on the principle that an amine in organic solution can extract the elements of hydrochloric acid (HCl). This is possible because amines are more selective for hydrochloric than for phosphoric acid. If wet process phosphoric acid is used, the impurities must be separated in some way from the final product. The work described here involves a study of the distribution of phosphoric acid itself, and the impurities trivalent iron and sulphate, between aqueous solutions and kerosene solut ions of the commercial amine Amberlite LA-1. In a countercurrent extraction process, approximately twenty theoretical stages would be needed to reduce the iron concentration to the food grade level. Sulphate is held in the organic phase. Monosodium phosphate can be recovered by stripping the organic phase with a sodium chloride solution. An attempt was made to explain the extraction of phosphoric and sulphuric acids from a mixture. It was found that amine extraction followed a pattern similar to that of gas adsorption, and a modified BET equation gave a fair but not highly accurate fit of the distribution data.

Keywords

Chemical Engineering

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