An enhancement of CO2 capture in a type-III porous liquid by 2-Methylimidazole zinc salt (ZIF-8)

Abstract

Porous liquids (PLs) with porosity and fluidity have shown great potential in gas separation. In this work, a type-III PLs were synthesized by mixing 2-Methylimidazole zinc salt (ZIF-8) nanoparticles as the main units and 1-Ethyl-3-methylimidazolium Bis(trifluoro-methanesulfonyl)-imide ([EMlm][NTf2]) as the solvent. Molecular dynamics simulation evidenced the permanent, vacant, rigid pores of PLs. The prepared PLs were characterized, and their CO2 uptake performances were obtained using a CO2 static absorption system. ZIF-8 could significantly increase the CO2 absorption capacity of the porous liquid, and when the mass fraction of ZIF-8 inside PLs was 10 wt%, the CO2 absorption capacity increased by 143 %. Then, the CO2 absorption characteristics of porous liquids were studied in different conditions, including temperature, pressure, and concentration of the ZIF-8. The CO2 adsorption heat calculated by the Clausius–Clapeyron relation is −6.5 kJ/mol. The absorption rate of PLs was studied using the damping film theory. The CO2 uptake capacity of the PLs decreased with temperature but increased with pressure and CO2 concentration. Subsequently, the absorption-adsorption model was established to predict the CO2 uptake capacity of PLs. The theoretical values agree with the experimental values, indicating that the developed absorption-adsorption model can predict the CO2 uptake properties of PLs. Finally, analysis of the CO2 cyclic performance of the PLs showed the PLs could be regenerated under negative pressure, and the CO2 uptake capacity remained stable after five cycles, indicating the [EMIm][NTf2]/ZIF-8 PLs could be applied in CO2 capture.