Study On Phase Equilibrium Of Solid Solute In Supercritical System

Phase equilibrium of supercritical fluid system is a key factor in development of supercritical fluid technology. This work makes systematic and theoretical experimental study on the phase equilibrium of solid and supercritical fluid system based on molecular kinetic theory, quantum-chemical calculation and statistical mechanics. The main content of the thesis are as follows:An experimental instrument based on the dynamic method is set up and modified to determine the experimental solubility data of solid in supuercritical system. The reliability of the instrument is verified. Electronic balance weighing, ultraviolet spectrometer and gas chromatography are used to measure the concentration of solid solute. Solubilities of solid solute including benzene sulfonamide, ammonium benzoate, bisphenol A, bisphenol S, dimethyl terephthalate in pure supercritical CO2(SCCO2) are investigated in this work; ternary system including benzene sulfonamide with cosolvent, ammonium benzoate with cosolvent, mixture solute of ammonium benzoate and benzamide in SCCO2are also studied. The experimental temperature is ranging from308to328K over a pressure range of11.0to21.0MPa. Ethanol, acetone ethylene glycol and ethyl acetate are chosen as cosolvent with mole fraction from0.01to0.04. The solubility data obtained in this work are first determined and have not been reported in literature. The determinations make a great contribution to the supercritical phase equilibrium data bases, which provide supporting for the application of supercritical fluid technology.An assumption is proposed based on the theory of molecular motion to investigate the effect of temperature and pressure on the solubility of solutes in supercritical CO2. The difference in solubility between different solute and different cosolvent, the effect of cosolvent molar fraction and mixture solute on solubility are investigated by analysis of molecular structure, and interactions between solute and solvent moleculars.Correlation of9empirical models based on density or pressure, including Chrastll, A-L, K-J, Tang, S-S, Bartle, M-T, Yu and Gordillo are made to experimental data and the parameters of each empirical models are obtained. The average absolute relative deviation (AARD) is used to evaluate9semi-empirical models. The self-consistency of the experimental data is satisfactorily determined by M-T model. The dissolving thermodynamic property of solid solute was calculated by Chrastll, K-J and Bartle models. Experimental solublities in ternary system are correlated by Gonzalez, T-G, Sovova and modified Sovova models. The parameters for each model are obtained and the value of AARD are calculated.The molecular interaction between solute molecule and solvent molecule is calculated by density function theory (DFT) method. GaussianO3procedure is adopted to process the calculation of the interactions between solute and CO2, solute and cosolvent, and solute mixture. The effects of solute structure and cosolvent on solubility are further analyzed by calculation result. According to the mechanism of solid dissolving in SCCO2, a solubility model is proposed through molecular interaction and physicochemical properties of solute and solvent. Data samples including18aromatic compounds are set up as the selection method of solid solute in this work. The parameters in the model are obtained by correlation and regression of available solubility data of18different compounds in SCCO2. Accroding to the same selection criteria of data samples, another10soild solutes are chosen for the prediction calculation by the new model. The calculation solubilities show good aggrement with those in literature under high pressure (P>13.0MPa). The average AARD for10solutes is17.70%, which indicates the new model is of good performance in solubility prediction, broader applicability and high-accuracy.For the purpose of solubility prediction without experimental data, this work makes exploration to build a model based on statistical association fluid theory (SAFT) to predict solubility of solid solute in SCCO2. The energy expressions for the solute in solid phase and supercritical phase are established according to references respectively. The solubility predictions for10solid solutes in SCCO2are investigated by SAFT model. The solubility predictions show fairly good accuracy, the average AARD%for10solutes is1.42%. SAFT model could provide innovative research idea and method for theoretical prediction of solublity of solute in SCCO2.This research is financially supported by the National Natural Science Foundation of China (No.21176012), the Natural Science Foundation of Jiangsu Province (No. BK2012595).