(253e) Molar Volume Dependence of N2 Solubility in Ionic Liquids

Ionic liquids (ILs) have received increasing attention in recent years for their potential use in many different processes, particularly carbon capture. Many gas streams from which one might want to remove CO₂ also contain nitrogen. ILs that could be used for these separations include a diverse range of possible cation/anion combinations. It is therefore necessary to know the solubility of nitrogen in a broad range of ionic liquids. Unfortunately, there is a fair amount of disagreement amount the relatively limited N₂ solubility data available in the literature, most likely due to the challenges in measuring low solubility gases. Here we present nitrogen solubility data in a set of ionic liquids composed primarily of imidazolium cations with BF₄ and Tf₂N anions, as well as several phosphonium and ammonium cations with Tf₂N anions. The different ion combinations have molar volumes ranging from 150 cm³/mol to 650 cm³/mol. We have used a gravimetric microbalance produced by Rubotherm GmbH for solubility measurements at 60°C and pressures up to 150 bar. The resulting isotherms can be used to determine Henry's law constants for nitrogen in each IL. We will present results showing that the primary effect on the solubility of nitrogen in ILs is the molar volume of the liquid, with some differences between imidazolium and ammonium cations. Because of the low solubility of nitrogen in ILs and the time intensive nature of solubility experiments, the molar volume can be used as a quick estimate of the Henry's law constant for nitrogen in ionic liquids.