Studies On The Phase Behavior Of Binary Mixtures Including Supercritical Fluid

Supercritical fluids possess special physico-chemical properties that are different to gas and liquid.In the recent years,the theoretical studies and the applications of supercritical fluids technology are prevalent.The phase-equilibrium engineering problem has always played a fundamental and crucial role in supercritical fluids studies and provided significant direction to the applications of supercritical fluids technology.In this work,the phase-equilibrium experimental measurement and theoretical calculation for the systems involving supercritical fluid have been investigated.The gas-liquid critical properties of propylene(ethylene) + hydrogen systems were measured in the olefin-rich region with visual observation.The critical temperature of both systems decreased slightly with the increasing concentration of hydrogen,whereas the critical pressure increased dramatically with the increase in the concentration of hydrogen.The PR equation of state coupled with van der Waals one-fluid mixing rule was used to correlate the experimental data and four combining rules including van der Waals-1,van der Waals-2,Panagiotopoulos-Reid and Berthelot's-Lorentz combining rule were discussed.The correlation results of critical temperature showed that all combining rules were accurate and similar to each other. The prediction results of critical pressure obtained by van der Waals-1 and Berthelot's-Lorentz combining rules were less accurate than the rest of two combining rules.Furthermore,the group contribution equation of state Predictive Soave-Redlich-Kwong(PSRK) was used to predict the critical points and the results agreed well with the experimental data.PR equation of state coupled with the van der Waals one-fluid mixing rule was used to calculate and predict the critical temperature and critical pressure of various classical binary mixtures including nonpolar,polar and associating systems, respectively.Four combining rules including van der Waals-1,van der Waals-2, Panagiotopoulos-Reid and Berthelot's-Lorentz combining rule were investigated systematically and compared with each other.The calculation results of critical temperature demonstrated that all combining rules provide satisfactory performance. As indicated by the prediction results of critical pressure,the similar deviations were obtained using van der Waals-1 and Panagiotopoulos-Reid combining rules.On the other hand,the van der Waals-2 and Berthelot's-Lorentz combining rules gave similar accuracy.The prediction of critical pressure for associating systems were less satisfactory when compared with nonpolar and polar systems and more suitable equations of state and mixing rules were expected.The modified HVOS mixing rule(M-HVOS) was proposed and the predicted results for high pressure vapor-liquid phase equilibrium of various systems indicated that the M-HVOS had improved performance for asymmetric systems and was better than HVOS and MHV1 mixing rules.A new excess free energy mixing rule that employs a low-pressure reference state was proposed.This new low-pressure mixing rule(LPMR),coupled with the original UNIFAC method and the SRK equation of state,led to an improved group contribution equation of state(LPMR-SRK).The LPMR-SRK was used to predict the high pressure vapor-liquid phase equilibrium of various systems and the results were compared with that of the PSRK,M-PSRK, VTPR and LCVM models.It was found that satisfactory simulation was obtained by LPMR-SRK model for vapor-liquid phase equilibrium of systems whose components can involve various degrees of nonideality and asymmetry.The solubilities of propylene in semicrystalline linear isotatic polypropylene at 75 and 95℃were measured by the pressure decay method.The experimental results showed the solubility of gas increased with increasing pressure and decreased with increasing temperature.At 95℃,the isothermal solubility curve reached an inflection point when the pressure was increased to about 50 bar and then increasing of solubility slowed down significantly when the pressure was above 50 bar.The experimental data were correlated with the SL equation of state and the fitting result was satisfactory.The solubilities of subcritical and supercritical fluids in various polymers were modeled by the CK-SAFT,PC-SAFT,SL and SWP equations of state.The comparisons between the four models indicated that PC-SAFT and SL EoS provide most satisfactory results for the amorphous polymer systems.With regard to semicrystalline polymer systems,the PC-SAFT showed a poorer performance compared with SL and SWP EoS.In most cases,the performance of the CK-SAFT was least satisfactory.