(25c) High-Pressure Vapor-Liquid Equilibria of 1-Alkyl-1-Methylpyrrolidinium bis(trifluoromethylsulfonyl)imide Ionic Liquids and CO2
AIChE Annual Meeting
2019 AIChE Annual Meeting
Engineering Sciences and Fundamentals
High Pressure Phase Equilibria and Modeling
Sunday, November 10, 2019 - 4:04pm to 4:21pm
Room temperature ionic liquids (RTILs) are salts that have a melting point below 373.15 K and composed of an organic cation and an organic or inorganic anion. RTILs have tunable physical and chemical properties as well as extremely low vapor pressures (i.e. < 1.0 x 10-3 Pa). Carbon dioxide (CO2) is the most studied gas in ionic liquids, and pyrrolidinium-based ionic liquids have gained interest in recent years due to their high thermal stability and lower toxicity compared to pyridinium, phosphonium, imidazolium and ammonium ILs even though the viscosities are slightly higher than imidazolium ILs. In this study, vapor-liquid equilibrium for the binary systems of CO2 and 1-alkyl-1-methyl pyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquids ([CnC1pyr][NTf2] (n = 3,4,6)) were measured at 298.15, 318.15 and 338.15 K and at pressures up to 20 MPa using gravimetric (IGA and XEMIS microbalances) and volumetric (high-pressure view cell) methods. The solubility of CO2 in pyrrolidinium ionic liquids increases with decreasing temperature and increasing pressure for all three ionic liquids. The CO2 solubility also slightly increases with increase in alkyl chain length on the pyrrolidinium cation which may be due to entropic effects. The mixtures exhibit physical absorption with no indication of a chemical reaction between the components. The molar volume of the mixtures decreased with an increase in pressure; however,. the density displayed relatively little change due to the increased mass of the liquid phase with CO2 absorption. The Fickian diffusion of CO2 in pyrrolidinium based ionic liquids (~10-10 m2·s) was calculated at pressures up to 2 MPa and found to be slightly lower than the diffusivity of CO2 in an imidazolium based ionic liquid with the [NTf2] anion.