Study On Gas-liquid Phase Equilibrium Of Vacuum Distillation Of Selenium-based Binary Alloy

Selenium(Se)-based alloys have good semiconductor properties and are widely used in the manufacturing of photovoltaic cells,rectifiers and other electron devices.With the development of electronic industry,the demand for high-purity selenium is increasing,and the reserves and production of selenium are very limited,so it is of great significance to purify low-grade selenium and recycle wasted Se-based alloys.Vacuum distillation technology has the characteristics of short flow,no pollution and high raw material recovery.It can be widely used in the purification of low-grade selenium and the recycling of wasted Se-based alloys.In this paper,the thermodynamic properties and vapor-liquid equilibrium of Se-based binary alloy in vacuum distillation are systematically studied,which provides theoretical guidance for the selection of vacuum distillation parameters in the process of purification and recovery.According to the existence of liquid-liquid equilibrium in most Se-based binary systems,Se-Te,Se-Bi,Se-Pb and Se-Sb are predicted by Wilson equation,NRTL(Non-random two liquid)equation and R-K(Redlich-Kister)polynomial.The reason of the special shape of the activity curve of components in Se-based binary system was analyzed.The reliability of the calculated activities was verified by calculating other thermodynamic properties from the calculated activities.The results show that Se-Te belongs to weak deviation system,Wilson equation,NRTL equation and R-K polynomial can accurately calculate the activities of components in this system.For Se-Bi,Se-Pb,Se-Sb,Se-Sn and Se-Tl binary systems with strong deviations,when the experimental activities are sufficient,the R-K polynomial can calculate the activities of components in systems more precisely.When the experimental activities cover a short concentration range(20～45%),the prediction effect of NRTL equation is better.According to the theory of vapor-liquid equilibrium,the vapor-liquid equilibrium(VLE)phase diagrams of Se-based binary alloy of full concentration were drawn.The vacuum distillation separation experiments of Se-Te,Se-Bi,Se-Pb and Se-Sn binary alloys were carried out,and the reasons for the large deviation between the experimental and calculated VLE data of the systems containing stable compounds were analyzed.By comparing the experimental results of vacuum distillation with the theoretical calculations of VLE phase diagram,the experimental values of the VLE phase diagram of Se-Te binary system are in good agreement with the calculated data,while some experimental values of the VLE phase diagram of Se-X(X=Bi,Pb,Sn)binary system are quite different from the calculated data.The effect of compounds on vapor-liquid phase equilibrium in Se-based binary systems was discussed.