Gas Separation Properties of Ionic Liquids and Porous Liquids

With a constant rise in carbon emissions, developing effective gas separation techniques for carbon capture is critical for combating climate change. Type III porous liquids represent a promising new class of porous material that combines the free volume of porous solids and the nonvolatile properties of ionic liquids. The resulting permanent porosity can be used to adjust the gas separation properties of an ionic liquid, including the 𝐶𝑂₂/𝑁₂ selectivity and CO₂ and N₂ permeabilities. In this project, the zeolites Hydrogen-Zeolite Socony Mobil-5 (H-ZSM-5) and Sodium-Zeolite Socony Mobil-5 (Na-ZSM-5) were suspended in the ionic liquids, Trihexyltetradecylphosphonium bromide ([P66614][Br]) and 8,8′-(3,6-dioxaoctane-1,8-diyl)bis(1,8- diazabicyclo[5.4.0]undec-7-en-8-ium)bis(trifluoromethanesulfonyl)imide ([DBU-PEG][NTf₂]) respectively. The membranes of the ionic liquids and their porous liquids at varying concentrations were tested and analyzed for their 𝐶𝑂₂/𝑁₂ selectivity and their CO₂ and N₂ permeabilities. The goal of this work is to understand the gas transport in porous liquids, explore how the addition of zeolites impacts gas separation of an ionic liquid, and assess how varying the concentration of free volume in the porous liquids influences gas separation performance. The results show that incorporating H-ZSM-5 with [P66614][Br] enhances the 𝐶𝑂₂/𝑁₂ selectivity as well as the CO₂ and N₂ permeabilities as the zeolite concentration increases. The addition of Na-ZSM-5 in [DBU-PEG][NTf₂] improved the 𝐶𝑂₂/𝑁₂ selectivity but led to a decrease in CO₂ and N₂ permeabilities. These results demonstrate that the addition of zeolites into ionic liquids can be used to adjust gas separation properties for carbon capture.