Separation Of Azeotropic Mixture By Salt Effect

In this paper,salt effects on Liquid-Liquid Equilibrium (LLE) and Vapor-Liquid Equilibrium(VLE)were presented and analyzed. Salt selection and recent progress of salt effect and their separation application in chemical engineering were reviewed in detail. The LLE of tetrahydrofuran -water-salt system and the VLE of acetonitrile-water- ethylene glycol-CaCl2 system were measured and correlated.The apparatus and analysis methods for measuring LLE of THF - water-salt systems were set up, and solubility curves for KF,KCl,NaCl,NaNO₂,CaCl₂ dissolved in THF-water system were measured at 101.3kPa , 25℃. The data were correlated by Lorentzian equation, and the correlation results agreed well with the experimental results. The experiments of muti-stage salt extraction for separation of THF-water were carried out. According to the experimental results, the effective separation agents for such a process are KF and CaCl₂. High Purity THF can be obtained by salt extraction based on salt effects.. The VLE of acetonitrile - water-ethylene glycol-CaCl2 system at 101.3kPa with various solvent ratio and different salt concentration were measured by VLE experiments. The data were correlated by NRTL activity coefficient equation, and correlation results agreed well with the experimental results. The experimental data and correlation results show that the mixed solvent of ethylene glycol-CaCl2 could greatly increase the relative volatility of acetonitrile to water.Batch saline extractive distillation experiments for separation of acetonitrile-water were carried out, using glycol-CaCl₂ solution contained 10% CaCl₂ as mixed solvent, with solvent ratio 1:1. High purity acetonitrile was obtained experimentally by such a process. Comparing to the batch extractive distillation using ethylene glycol as solvent to separate acetonitrile-water mixture,the solvent used in the batch saline extractive distillation process can be greatly reduced.