| Supercritical fluids (SCFs) have many superior properties like those of liquids and gases, and have the characteristics of green and environmental solvents. Supercritical Fluid Extraction (SFE) is a new and green promising separation technology, which has a great application foreground in many industrial and newly high-tech fields. But, pure SCF has limitations as its lack of dissolution and selective capacity, which affect a great deal of the applications and industrial productions of the SCF technology. It has been found that the addition of a small amount of organic solvents, which are called cosolvents, to a SCF can dramatically affect its solvent power. The addition of cosolvents to a SCF is considered as one of the key factor for the industrial application of SFE. So, it is quite necessary to strengthen the experimental and theoretical study on the phase equilibrium of solute in SFE with cosolvent, and it is no doubt it has important theoretical meaning and practical value for accelerating the industrial application of SFE.There are mainly following four aspects of the study on the phaseequilibrium of solute in SCF with cosolvent in my thesis:(1) The experimental equipment was perfected for measuring the solid phase equilibrium in SCF with cosolvent using the flow type method. Moreover, the reliability of the experimental set-up was further verified in our work.(2) In our work, the experimental research is more comprehensive for the study on the solubility of solid solute in SCF with and without cosolvent at temperatures 308.15, 318.15 and 328.15 K, and pressures from 8.0 to 23.0 MPa, respectively. Supercritical carbon dioxide was used as the SCF, and the solid solutes included nonpolar solute, anthracene, and polar solute, such as benzoic acid, propyl /7-hydroxybenzoate and methyl /7-hydroxybenzoate. The pure and mixed cosolvents were studied at the mole concentration of 1.0-4.0 mol%. The pure cosolvents included ethanol, ethyl acetate, ethylene glycol, 1-propanol, acetone, butanone, hexane and cylcohexane, and the mixed cosolvents were solvents equally mixed (mole ratio 1:1) by two organic solvent, such as ethanol and ethyl acetate, 1 -propanol and cylcohexane, acetone and hexane.(3) The effects of temperature, pressure, the property and the concentration of cosolvent were studied on the basis of experimental research. The mechanism and effect of the cosolvent on the solubility were profoundly analyzed, and the principle for selecting cosolvent was advised. The measured solubilities in supercritical CO2 without and with cosolventswere correlated using the model in the literatures, such as the Chrastil equation, the modified Chrastil equation, the chemical associated model and the S-T model. The calculated results indicated good agreement with the experimental data.(4) Three thermodynamic phase equilibrium models were developed using the thermodynamics theory and the chemical theory on the basis of our experimental and literature data. ( I ) Molecular Connectivity Index Method (MCI). According to the chemical theory, the molecule was the cadre of the compound, and the compound properties were decided by the molecule characteristics, the combination method and so on. So, the quantified relations between the structure and property of the compound could be found by studying those connections of molecule structural information and the property of the compound. In our work, a new topological index (kzE) has been developed on the basis of modifying the valence of vertex (At) for hetero-atoms used in molecular connectivity index, and then, by studying the quantified relations between the structure and the solubility in SC-CO2 of the series compound of benzoic acid with different functional group, the relating equation was obtained. The results indicated the structural information, such as the type, the position and the length of the substituting group could influence the solute solubility, which would be well correlated by the topological index (kxE)- Further more, the polar and nonpolar solute solubilities in other SCFs, including SC-C2H6,SC-CHF3? SC-CCIF3, were studied using the MCI method. In conclusion, the new topological index is easily be calculated, conveniently used, and has explicit physical meanings and favorable structural selection and property relativity. The calculated results had good agreement with the experimental data. ( II ) Using the PR equation of state and the PR mixing rule, the thermodynamic phase equilibrium model (MPR-2) was developed based on the thermodynamics theory. According to the characteristics of the system between solid solute and SCF, the calculating method of the volume parameter of mixed compounds (bm) and the energy parameter of the SCF (asc/.) were modified. When the MPR-2 model was used in ternary supercritical system, which included solid solute, SCF and cosolvent, it was necessary to consider the SCF and the cosolvent as a psuedo-component, and to calculate the equation parameters a|Y and 6|f of thepsuedo-component using the VDW-1 mixing rule. Therefore, the ternary supercritical system could be simplified to a binary one. At last, using a great amount of solubility data in our work and literatures to validate the reliability of the MPR-2 model, all the results showed that this model has a better precision. (Ill) According to the thermodynamics theory, a new expanded liquid model (ELM) for solid solubilities in supercritical fluids with and without cosolvents was proposed on the assumption that the supercritical fluid was known as an expanded liquid. The ELM model was used to calculate some experimental and literature data, and the results...
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