Systematic investigation of nitrile based ionic liquids for CO2 capture: A combination of molecular simulation and ab initio calculation

Abstract

Molecular simulation and ab initio calculation are performed to investigate CO2 capture in four nitrile (-CN) based ionic liquids (ILs), namely 1-n-butyl-3-methylimidazolium thiocyanate [BMIM][SCN], 1-n-butyl-3- methylimidazolium dicyanamide [BMIM][N(CN)2], 1-n-butyl-3- methylimidazolium tricyanomethane [BMIM][C(CN)3], and 1-n-butyl-3-methylimidazolium tetracyanoborate [BMIM][B(CN)4]. In neat ILs, the simulated densities match well with experimental data, and the cation-anion interaction becomes weaker with increasing number of -CN. In CO2/IL systems, CO2 molecules are preferentially located at the CO2/IL interface, which is consistent with the observed minimum in the potential of mean force. The solubility and diffusivity of CO2 in the four ILs increase as [BMIM][SCN] < [BMIM][N(CN) 2] < [BMIM][C(CN)3] < [BMIM][B(CN)4], thus increasing number of -CN is beneficial for CO2 capture. CO 2 solubility is identified to be governed by the binding energy of cation-anion, rather than the binding energy of CO2-anion. The computational study provides quantitative microscopic insight into the role of -CN in CO2 sorption and diffusion, and it suggests that [BMIM][B(CN)4] might be an interesting candidate for CO2 capture. © 2014 American Chemical Society.