Molecular Simulation and Experimental Study on Low-Viscosity Ionic Liquids for High-Efficient Capturing of CO2

Abstract

In recent decades, ionic liquids (ILs) have been developed as an ideal and reversible decarbonization solvent. However, some pitfalls, such as the low CO2 capacity and high viscosity of ILs, limit their further scale up and industrial application. Therefore, in this work, three novel functional ILs [N8881][NIA], [N8881][For], and [N8881][Ac] were synthesized after using a molecular design method to capture CO2 at 303.15–333.15 K and pressures up to 1000 kPa. The experimental results illustrate that [N8881][NIA] presents the smallest viscosity and the highest CO2 solubility. The capacity order is [N8881][NIA] > [N8881][For] > [N8881][Ac] under the same experimental conditions. The CO2 recyclability experiments using [N8881][NIA] show the stability of CO2 solubility after 5 cycles. The quantum chemistry simulations at the level of DFT/B3LYP with 6-311++G(d,p) basis sets were used to study the CO2 absorption mechanism in the studied ILs from the molecular viewpoint. Simulation results illustrated that the higher interaction energy between CO2 and ILs means more CO2 absorbed in these ILs, which agreed well with the experimental results. The atoms in molecules theory and the function of the reduced density gradient were also used to calculate the interactions in these IL–CO2 systems. Results show that the majority of these interactions present an electrostatic character.