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

Abstract

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 aw in the aqueous phase, whereas in the latter, as with the binary TBP–H2O system, water decreases with decreasing aw.