Extraction of hydrochloric acid and sulphuric acid by solutions of tributyl phosphate in carbon tetrachloride, benzene, and chloroform

The extraction of HCl into solutions of tributyl phosphate (TBP) in CCl₄, C₆H₆ (20-100% v/v TBP), and chloroform (80-100% v/v TBP) and of H₂SO₄ into tributyl phosphate-carbon tetrachloride mixtures (80-100% v/v TBP) has been studied. It was compared with the systems involving nitric acid. Good agreement was found between data published for undiluted tributyl phosphate and the results of our experiments. A distinct diluent effect was noted in the systems with HCl for C₆H₆ and CCl₄ where, with nitric acid, no effect was observed. The activities of tributyl phosphate were calculated over the range aqueous 0-9N hydrochloric acid by use of the Gibbs-Duhem relationship. The equilibrium constants for the interconversion of TBP,H₂O into TBP,HCl,4H₂O and into TBP, HNO₃,H₂O were estimated to be 0·064 and 6·1 moles/l., respectively. In both cases, the standard reaction entropy is the dominating term in the standard change of free energy ΔG°. There is a distinct difference between water partition in systems containing HCl and H₂SO₄, and the HNO₃-H₂O-TBP system. In the former, the water content of the organic phase increases with decreasing water activity a_w in the aqueous phase, whereas in the latter, as with the binary TBP-H₂O system, water decreases with decreasing a_w.