Equilibrium Characteristics of KH₂PO₄ Production by Liquid, Liquid Extraction with a Trialkyl Amine-Based Solvent Mixture: A Case Study

Abstract

This study evaluates the equilibrium characteristics of H3PO4 and KCl for the production of KH2PO4 by liquid, liquid extraction with organic solvent mixtures (trialkyl amine N235, isoamyl alcohol, and sulfonated kerosene). The extraction equilibrium for aqueous H3PO4 or for the reaction of H3PO4 with KCl was obtained. For the former case, the partition coefficient for extracting a standard H3PO4 solution first decreased rapidly and then slowly increased with the increase in H3PO4 content. In addition, the reaction enthalpy also showed a turning point. For the latter case, aqueous H3PO4 reacted with KCl and the organic phase separated the Cl– ions from PO4 3– to produce KH2PO4. The acid content presented a significant effect on the correlation between the separation performance and the molar ratio of H3PO4 to KCl. This was due to the fact that N235 dominated the partition process at low acid concentrations while the isoamyl alcohol dominated the extraction at high acid concentrations with the transition occurring at the equimolar concentration of H3PO4 in the organic phase and N235. The results also show that, at low acid concentrations, the solvent mixture provided a high extraction capacity, due to which the separation performance depended on the ratio of raw materials more than the selectivity of the solvent.