Study On The Equilibrium Of Multi-Component System Containing Solid And Supercritical Carbon Dioxide

Supercritical carbon dioxide (SC-CO2) is an attractive alternative for traditional solvents in green chemistry. However, commercial exploitation of supercritical CO2 technology has been relatively limited due to the lack of fundamental data on supercritical CO2 solute systems and the weak modeling of phase equilibrium. The purpose of this research was to investigate the equilibrium of multi-component system containing solid in supercritical carbon dioxide. The main work is as follows.New equipment for supercritical fluid phase equilibrium determination was developed, which passed a hydrostatic test. It is more stable and reliable than the existing one. The results of experiment for single and mixed solute systems were determined using UV and HPLC, respectively. Reliable HPLC analysis methods were developed. p-Toluenesulfonamide (p-TSA), sulfanilamide (SNA), benzenesulfonam-ide, sulfanilic acid and benzamide were chosen as model typical organic solutes and their solubilities in supercritical CO2 or in cosolvent immersed supercritical CO2 were first investigated in binary, ternary and quaternary systems over a range of temperatures (308 K-328 K) and pressures (8.0～21.0 MPa). The mixed solute systems includes:p-TSA+SNA (molar ratio 1:1), benzenesulfonamide+benzamide (molar ratio 1:1), p-TSA+SNA (molar ratio 1:1)+cosolvents. The investigated cosolvents included methanol, ethanol, glycol, ethyl acetate and acetone. The total number of data points is 272, which largely contribute to the supercritical phase equilibrium data bases and is fundamental to model building in the work.The effect of temperature, pressure, molecular structure, molecular interactions, cosolvent concentration on the solubility of solutes in supercritical CO2 was investigated. The work focused on the influence of molecular structure on the single solute solubility, the molecular interactions between cosolvent and solute, and that between different solutes.The existing models, especially the density-based models were analyzed using the experimental data. Chrastil, K-J and M-T models showed good results among them, with relatively better correlation precision. But they also had some problems such as unstable calculation. The work analyzed the molecular interactions between solvent and solute, and then modified Chrastil model by introducing an empirical expression aTv+b for the mixing entropy to the equilibrium constant of the hypothetical complexation reaction. The new model M1 received good correlation results. The other two modified models (M2 and M3) for K-J and M-T were gotten by the same way. The new models received good correlation results with better precisions (as least 3%-6%) in the model checking which used 1603 data points for 71 compounds including the experimental ones. The modifications were successful.Two density-based models used for cosolvent systems (Chrastil-G and M-T-S) were modified, and got M4 and M5 in turn. The new models received good correlation results with better precisions in the model checking which used 219 data points for 7 compounds. The new models received good correlation results with better precisions about 2%.All the modified density-based models were weak in solubility prediction. Based on the cross-sectional study on the theory of chemical bond and topology theory, a novel valence was defined and then some revised molecular connectivity indices (RMCIs) were established. By inserting RMCIs into the new density-based model M1, some new models were consequently exploited. The special information of aromatic, series was collected by using the RMCIs model to calculate the solubility of 30 aromatic compounds. The solubility prediction for the other 5 similar structure compounds received good results using the correlated equation.The work discussed the relations between macro-properties and microscopic structure properties, providing new methods to explore the better supercritical fluid phase equilibrium models.The work was supported by the National Natural Science Foundation of China (No.20776006), and the Scientific Research Innovation Fund of BUCT.