Supercritical Co <sub> 2 </ Sub> Alcohols Binary Phase Equilibrium Of Systems Research

Vapor-liquid phase equilibrium data of isobutanol, tertbutanol and 2-butanol in carbon dioxide from 323.2K to 353.2K in the range from high pressure to subcritical area were measured by constant-volume visual high pressure cell; Vapor-liquid phase equilibrium data of 1-pentanol,2-pentanol, isopentanol and tertpentanol in carbon dioxide from 313.1K to 343.5K at high pressure to subcritical area were measured by variable-volume visual high pressure cell. The effects of pressure, temperature on equilibrium compositions were discussed. At the constant pressure, the solubility of CO2 in liquid phase or in vapor phase decreased with the increasing temperature; At the constant temperature, the solubility of CO2 in liquid phase increased with the increasing pressure, and the solubility of CO2 in vapor phase had a maximum with pressure.Critical pressure and critical compositions of seven binary system at experimental temperature were found based on the properties that compositions of vapor phase and liquid phase were equal at critical point. Critical pressures for the binary system were higher than critical pressure of each composition in the system. With the increasement of critical temperature, critical pressure increased and critical molar fraction of carbon dioxide decreased.The phase equilibrium models for every binary system were estalished using Peng-Robinson equation of state coupled with Van der Waals-1, Van der Waals-2, Panagiotopoulous-Reid and Stryjek-Vera mixing rules, and model parameters were calculated by the least square method. Meanwhile, the relative deviations were analyzed. The following conclusions were drawn:Peng-Robinson equation of state model together with Van der Waals-2 mixing rule(PR2) could be applied to describe the phase behavior for binary system containing CO2 and alcohol in the range from high pressure to sub-critical area. The expressions of the binary interaction parameters from PR2 model vs temperature were obtained by fitting the binary interaction parameters vs temperature, and all expressons were cube polynomials.Based on the parameters from PR2, the densities and molar volumes of vapor and liquid phase were determined and the variation laws of molar volume and density vs pressures and temperatures were discussed. P-x-y, Vm-P-x, P-ρphase diagrams for seven binary system were drawn.Also in the work partial molar volumes of CO2 and alcohol in vapor and liquid phase at vapor-liquid equilibria for the seven binary system were determined from generalized relation equation of partial molar properties on basis of the binary action parameters obtained by PR2. The variation regulations of partial molar volume of each component in vapor phase and liquid phase with pressures and temperatures were summarized. The effects of adddition of each component on vapor phase and liquid phase volume were discussed, and the causes that the phenomena formed were analyzed by intermolecular interaction force.Krichevsky-Ilinskaya equation was used to correlate dependence of solubility of CO2 in seven liquid alcohol on pressure. Three important parameters:Henry's constant(H1,2P2s), Margulea constant A, and partial molar volume of CO2 at infinite dilution(V1∞) were calculated by multiple linear regression based on Krichevsky-Ilinskaya equation. The different reasons of the solubility of CO2 in isomer alcohol were explained with intermolecular interaction theory, and also were interpreted by association action between CO2 and alcohol molecule according to alcohol molecular structures and properties. A new solubility equation applied to describe the solubility of alcohol in high pressure CO2 was provided on basis of Chraistil equation and the new equation was:C=ρk·exp(a/T)+b+c·ρm. The new equation had higher accuracy than traditional Chraistil equation.