Study On The Densities, Viscosities And Phase Equilibria Of Ionic Liquids/carbon Dioxide System

Plenty of volatile organic compounds were used in traditional chemical industry which makes them become the mian source of the pollution in the world today. As a green solvent, ionic liquid takes more and more attention of researchers for their negaligible saturate pressure and no volatile organic compounds released. The applications of combining the ionic liquids and another green solvent– supercritical carbon dioxide– have been under research now, and they are expected to make the chemical processes more friendly to the environment.While the application research of ionic liquids becomes more and more intensive, the ionic liquids property research becomes indispensible. In this research a falling body viscometer which can work at high pressures and high temperatures was designed. The viscosities of [bmim] [PF₆] + alcohol, and [bmim] [PF₆] + benzene binary systems at different temperatures and different pressures were measured. Combining the viscometer with a gas-liquid equilibrium equipment, the viscosities and densities of [bmim] [PF₆] + CO2 binary system at different temperatures and different pressures were measured. After analyzing the experiment results, the viscosity data were correlated at constant temperature, at constant pressure, and also at different temperatures and different pressures.Besides the experiment, the reported densities, viscosities and carbon dioxide solubility data for ionic liquids in the literatures were collected and analyzed. A group contribution method was introduced to estimate the densities of pure ionic liquids and their binary mixtures at different temperatures and different pressures. After some modification the method can even be used in the estimation of ionic liquids viscosities at different temperatures and different pressures. The average relative error (ARE) of the estimation for pure ionic liquids is 0.88 %, while the ARE for three pure ionic liquids which do not take participant in the correlation is 0.27 %. The estimation density ARE for binary ionic liquids mixtures is 1.22 %. The viscosity estimation ARE is bigger than that of density estimation, it can be 9.3 %.The collected carbon dioxide solubility data in ionic liquids were analyzed and correlated by activity coefficient method. In the correlation, the ionic liquid rich phase was calculated by NRTL model, while the carbon dioxide rich phase was calculated with RK equation of state. The NRTL model parameters for nine kinds of common ionic liquids with carbon dioxide were correlated, the nine kinds of ionic liquids are [bmim] [BF₄], [hmim] [BF₄], [omim] [BF₄], [bmim] [PF6], [hmim] [PF6], [emim] [NTf₂], [bmim] [NTf₂], [hmim] [NTf₂], and [bmpyr] [NTf₂].