Designing silica xerogels containing RTIL for CO2 capture and CO2/CH4 separation: Influence of ILs anion, cation and cation side alkyl chain length and ramification

CO₂ separation from natural gas is considered to be a crucial strategy to mitigate global warming problems, meet product specification, pipeline specs and other application specific requirements. Silica xerogels (SX) are considered to be potential materials for CO₂ capture due to their high specific surface area. Thus, a series of silica xerogels functionalized with imidazolium, phosphonium, ammonium and pyridinium-based room-temperature ionic liquids (RTILs) were synthesized. The synthesized silica xerogels were characterized by NMR, helium pycnometry, DTA-TG, BET, SEM and TEM. CO₂ sorption, reusability and CO₂/CH₄ selectivity were assessed by the pressure-decay technique. Silica xerogels containing IL demonstrated advantages compared to RTILs used as separation solvents in CO₂ capture processes including higher CO₂ sorption capacity and faster sorption/desorption. Using fluorinated anion for functionalization of silica xerogels leads to a higher affinity for CO₂ over CH₄. The best performance was obtained by SX- [bmim] [TF₂N] (223.4 mg CO₂/g mg/g at 298.15 K and 20 bar). Moreover, SX- [bmim] [TF₂N] showed higher CO₂ sorption capacity as compared to other reported sorbents. CO₂ sorption and CO₂/CH₄ selectivity results were submitted to an analysis of variance and the means compared using Tukeyu0027s test (5%).