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- Designing silica xerogels containing RTIL for CO2 capture and CO2/CH4 separation: Influence of ILs anion, cation and cation side alkyl chain length and ramificationPublication . Dos Santos, Leonardo; Bernard, Franciele L.; Polesso, Barbara B.; Pinto, Ingrid S.; Frankenberg, Claudio C.; Corvo, Marta C.; Almeida, Pedro L.; Cabrita, Eurico J; Einloft, SandraCO2 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 Tukey's test (5%).
- Enhancement of CO2/N2 selectivity and CO2 uptake by tuning concentration and chemical structure of imidazolium-based ILs immobilized in mesoporous silicaPublication . Duczinski, Rafael; Polesso, Barbara B.; Bernard, Franciele L.; Ferrari, Henrique Z.; Almeida, Pedro L.; Corvo, Marta C.; Cabrita, Eurico J; Menezes, Sónia; Einloft, SandraImidazolium-based ionic liquids (ILs) with different cation alkyl chain ([i-C5mim] or [C4mim]) and inorganic anions ([Cl−], [Tf2N−], [PF6−] and [DCA−]) were synthesized and immobilized in commercial mesoporous silica. The synthesized supported ILs (SILs) were characterized using NMR, FTIR, TGA, BET, SEM and TEM. CO2 sorption capacity, reusability and CO2/N2 selectivity were assessed by the pressure-decay technique. The effects of IL concentration, cation and anion chemical structure in CO2 sorption capacity and CO2/N2 separation performance wereevaluated. Tests evidencedthatthe presenceofbranching on thecation alkylsidechainincreases CO2/N2 selectivity. The immobilization of the IL [i-C5TPIm][Cl] on mesoporous silica in different concentrations (50, 20, 10 and 5 %) revealed that lower IL concentration results in higher CO2 sorption capacity. Immobilization of ILs containing fluorinated anions at low concentrations in the mesoporous silica support may promote the improvement of the CO2/N2 selectivity without interfering on CO2 sorption capacity of the original support. CO2 sorption capacity value shown by sample SIL-5 % - [i-C5TPIm][Tf2N] (79.50 ± 0.70mg CO2 g-1) was close to the value obtained for the pristine mesoporous silica (81.70 ± 2.20mg CO2g-1) and the selectivity (4.30 ± 0.70) was more than twice of the one obtained for the support alone (2.32 ± 0.4). Recycle tests demonstrated that the ILs immobilized in mesoporous silica samples are stable, providing a new option to be used in CO2 capture processes.