(368bi) The Effect of Ionic Liquids Molar Volume on CO2/N2 and CO2/CH4 Pure and Mixed Gas Solubility Selectivity for Industrial Applications

Ionic liquids (IL) are alternative candidates for CO₂ capture due to their negligible vapor pressure, and ability to tune the cations and anions based on the application needs. This class of solvents have been evaluated extensively to capture CO₂ from post-combustion and natural gas. However, solubility data of the less soluble gas N₂ and CH₄ are very scarce which makes it difficult to select the right ionic liquid that would yield the best CO₂/N₂ and CO₂/CH₄ solubility selectivity for these industrial applications. Through COSMO-RS and available literature data, multiple combinations of ionic liquids have been screened and narrowed to top eight candidates based on solubility selectivity. Due to the very low solubility and scarcity of N₂ and CH₄ data in ionic liquids, we measure high pressure gravimetric solubility up to 140 bar of these gases to reduce uncertainty and obtain more accurate solubility selectivity respectively. From our results, we show that small molar volume ionic liquids with low viscosity yield a higher solubility selectivity due to its ability to absorb less N₂ and CH₄ from the absence of free volume in the IL structures. In addition to obtaining the pure gas solubility selectivity, we also look at mixed gas solubility selectivity. Traditionally, pure gas solubilities are used to estimate the selectivity of mixed gas; however, due to entropy effects of gases absorbing into the liquid phase, the real selectivity is often lower. We develop a mixed gas sorption system to investigate the phase behavior of ionic liquids with CO₂/CH₄ and CO₂/N₂ mixtures. In particular, we seek to gain a fundamental understanding on the effect of CO₂ dissolution, a highly soluble gas, on the solubility of a less soluble gas (CH₄ or N₂). The real selectivity of CO₂/CH₄ and CO₂/N₂ mixtures at various gas compositions in ionic liquids at low partial pressures up to 30 bar, at 35 ËšC are studied. The mixed gas solubilities in the IL are obtained by analyzing the number of moles of desorbed gas from the IL in a 5 cm³ sample chamber that expands into a 500 cm³ ballast volume, with the compositions attained through gas chromatography. The real selectivity will be compared to the ideal selectivity of these gases previously measured gravimetrically and the subsequent Henry’s law constants derived from these isotherms.