Phase Equilibrium And Thermodynamic Properties Of Alkali Metal Chloride+TMU/NMP+Water Ternary System

Electrolyte solutions are widely existed in industries,medicine,energy,environment and other fields.However,the hydration of anions and cations in solution,the electrostatic attraction between ions,and the interaction between ions and solvents result in the deviation of the electrolyte solutions from the ideal solution.Therefore,it is important to investigate the phase behavior and thermodynamic properties of the electrolyte solutions.In this paper,the ternary systems of MCl(M=Na,K,Rb,Cs)+TMU(tetramethylurea)/NMP(N-methylpyrrolidone)+ H2O were chosen to research the solution behavior of the electrolyte in mixed solutions.Part I:The phase behavior of the ternary systems of MCI(M=Na,K,Rb,Cs)+TMU/NMP+H2O at 288.2,298.2 and 308.2 K was discussed.For the solid-liquid equilibrium system,the solubility,density and refractive index of the saturated solution were determined.For the liquid-liquid equilibrium system,the tie line and binodal curves of the system were obtained.Then a complete phase diagram was completed.Four-parameter equations were used to fit the experimental data of the solid-liquid equilibrium system.Three-parameter equations were used to fit the data of binodal curves.Othmer-Tobias and Bancroft equations were used to correlate the data of tie lines.The experimental results show that higher concentration of TMU/NMP and lower temperature decreases the solubility of the electrolyte in the solutions.The density and refractive index of the system were affected both by the solubility and the temperature,determined by the temperature and the solubility of the electrolyte.The formation of the aqueous two phase system was determined by the concentration of the salts,the hydration ability of ions,and the polarity of the organic solvents.Part ?:Thermodynamic properties of the ternary system of MCl(M=Na,K,Rb,Cs)+TMU/NMP+H2O at 298.2 K was determined.The ion-selective electrode M-ISE(M=Na,K,Rb,Cs)and the Ag-AgCl electrode were used to compose the reversible cells without liquid junction:M-ISE|MCI(m),H2O|Ag-AgCl M-ISE|MCl(m),TMU/NMP(w),H20(1-w)|Ag-AgClThe electromotive force of MCI(M=Na,K,Rb,Cs)in TMU/NMP-H2O mixtures was obtained by potentiometric method at T=298.2 K.The Nernst equation together with Pitzer and the extended Debye-Hückel equations were applied to obtain the mean activity coefficient y±,osmotic coefficient ?,excess Gibbs free energies GE,the standard transfer Gibbs free energy ?Gt0 of the systems and the standard solubility product lnKsp,s0 of electrolyte in mixed solvents.Due to the addition of TMU or NMP,the activity coefficient of the electrolyte differed greatly for different electrolytes.The standard transfer Gibbs free energy of all the systems was positive,which indicated the non-spontaneous process of transfer from water to mixed solutions.