Liquid-liquid extraction of oxalic acid from aqueous solutions with tributyl phosphate and a mixed solvent at 303.15 K

The phase diagram of the water + oxalic acid + tributyl phosphate ternary system was obtained at 303.15 K. Experiments were also conducted on the equilibrium distribution of oxalic acid between aqueous solutions and tributyl phosphate (TBP) + hexane (H) mixed solvent (with a 60/40 TBP/H percent volume ratio). Analysis of the results shows that the presence of a diluent (H) generally increases the selectivity when compared with pure TBP. This fact improves the extraction of oxalic acid from its aqueous solutions, but similar average distribution coefficients are obtained when the mixed solvent is used instead of pure TBP. A multistage cross-flow extraction process was performed in order to verify the accuracy of the basic equilibrium data and to obtain the number of stages required to extract oxalic acid from its aqueous solutions. This number was also graphically determined by using a distribution diagram in Bancroft's coordinates and analytically calculated by assuming virtual immiscibility between the feed and the extraction solvents.