Enhancement of CO2/N2 selectivity by hydroxyl or nitrile functionalized ionic liquid immobilized on mesoporous silica
Mojtaba Mirzaei, Fatemeh Bahrami, Ali Sharifi, Mohamma Reza Jalali
Abstract
• Two task-specific imidazolium-based ionic liquids (TSILs) were synthesized. • TSILs contained a butyronitrile or a hydroxypropyl chain on cation ring. • TSILs were immobilized on the mesoporous amorphous silica and MCM-41 via impregnation. • Adsorption capacities (CO 2 ) and selectivities (CO 2 /N 2 ) of adsorbents were evaluated. • Nitrate is cheaper and more readily available compared to other anions. Two task-specific imidazolium-based ionic liquids (ILs) with different cation alkyl chain and the same nitrate anion [NO 3 ] were synthesized and immobilized on mesoporous silica using a wet impregnation-vaporization method to give supported ionic liquids (SILs). The sorbents were characterized using NMR, BET, TGA, and XRD techniques. The CO 2 adsorption capacity alongwith CO 2 /N 2 selectivity of the adsorbents were evaluated by the pass of dry CO 2 or N 2 under atmospheric pressure. The effect of temperature, flow rate, humidity and IL's percentage in adsorption process was studied. Among sorbents, [CNC 3 mim][NO 3 ] and (MCM-41)-[CNC 3 mim][NO 3 ](20) with 3.06 wt.%, and 2.21 wt.%, respectively exhibited the highest adsorption capacities. Interestingly, a higher content of IL in SILs(x) resulted in lower CO 2 adsorption capacity but increased CO 2 /N 2 selectivity. The CO 2 -rich sorbents were efficiently recycled within 40 min under 2 kPa at 70 °C. Recycle tests demonstrated SILs(x) samples are stable and can be used as new option in CO 2 capture processes. Comparative CO 2 absorption of [NO 3 ]-based ILs under the same conditions.