Extraction of sulphuric acid by methyl diphenyl phosphate and tributyl phosphate

Abstract

The extraction equilibria in the sulphuric acid–methyl diphenyl phosphate–water and sulphuric acid–tributyl phosphate–water systems were investigated. The activities of methyl diphenyi phosphate and tributyl phosphate were calculated in the range of aqueous 0–10M-H₂SO₄, with the aid of the Gibbs–Duhem relationship. The experimental data found are consistent with the formation of the [H(H₂O)₃(MePh₂PO₄)₄⁺][HSO₄^–] complex with the equilibrium constant K= 2 × 10^–3(mol/kg MePh₂PO₄)^–1. At higher acid concentrations complete miscibility of MePh₂PO₄and H₂SO₄ is observed. At low concentrations of H₂SO₄, the acid is extracted by tributyl phosphate in the form of H₂SO₄(H₂O)₆(Bu₃PO₄)₃ with K= 20 (mol/kg Bu₃Po₄)^–3. Some summarizing remarks on the extraction of HNO₃, HCl, and H₂SO₄ by MePh₂PO₄ and Bu₃PO₄ are also given.