Study On Salt Selection And Saline Extraction In Separation Process

The salt selection, salt effects on Liquid-Liquid Equilibria (LLE) and salt extraction of 2-methylpyrazine-water mixtures were studied by theoretical analysis and experiment.Salt selection is the key problem for separation process adding salt. The Gibbs free energy of transfer of salt in six ternary organic solvent-H2O-salt mixtures where salting-out phenomenon occurs at 25℃ was calculated with the solvation model and scaled particle theory. The results are compared with salt effect on Vapor-Liquid Equilibria (VLE) or LLE. In most cases, salt effect on VLE or LLE is increasing with the increasement of the Gibbs free energy of transfer of salt in systems containing water. The results show that salt effect can be explained by the theory of the Gibbs free energy of transfer. Therefore, the Gibbs free energy of transfer can be used as a guide in salt selection in separation process adding salt.LLE containing salts is a part of salt extraction. By applying turbidity analysis, the equilibrium solubility of five ternary systems of organic solvent-water-salt are determined at 25℃, and the solubility diagrams are drawn and empirical equations of solubility are regressed. The phase split ability of various organic solvent-water-salt systems was studied. There are many factors affecting the phase separation, such as the type and concentration of solvent and salts. According to the variation of organic solvent phase volumes after separation, three types of LLE containing salt have been observed: typeⅠ(Vinitial7 the phase split is easy; when pH<7 the phase split is difficult. LLE data for the ternary systems of organic solvent-water-salt were measured at 20 and 25℃. The experimental data of the ternary systems were correlated with the electrolyte NRTL model. The interaction parameters for the electrolyte NRTL model were estimated with the Simplex method. The calculated results are basically consistent to the experimental data.Salt extraction for separation of 2-methylpyrazine-water mixture was developed. Optimum conditions of salt extraction were investigated: w(NaOH)=60%, temperature 30-40℃,and the extracting ratio m(NaOH aqueous solution)/m(2- methylpyrazine-water mixture)=0.5/1. Under such conditions, the concentration of 2- methylpyrazine in extract phase could reach 96.11%, and dehydration ratio of 2-methylpyrazine-water azeotropic mixture was 95.5%. In addition, the stability of NaOH aqueous solution was investigated.