Properties of Imidazolium-Based Room Temperature Ionic Liquids that Effect CO2 Solubility and Selectivity for CO2/N2 and CO2/CH4 Gas Separations

摘要

Room temperature ionic liquids can be useful for several different applications because they are thermally stable, have an extremely small vapor pressure, and are liquid over a large temperature range. There has been a substantial increase in research that involves RTILs over the last 10 years. The bulk of the research involves using RTILs as an environmentally friendly reaction medium. There has also been an increasing amount of research in using RTILs for gas separations. Whether using RTILs as either a reaction medium or in gas separations, it is important to measure the physical properties of the ionic liquids (i.e. gas solubility, gas diffusion, viscosity, density, etc.) and to know what properties or chemical structures of the RTILs affect gas solubility and diffusion. This paper discusses a method for measuring gas diffusion coefficients in RTILs using a semi-infinite volume approach. The paper also discusses how regular solution theory can be used to model gas solubility and gas selectivity for gas pairs involving CO2. This model is used to find the best imidazolium-based RTIL for absorbing the largest amount of a gas per volume of RTIL for bulk fluid absorption. The model is also applied to membranes to show the feasibility of making RTIL based membranes for CO2/N2 and CO2/CH4 separations.