Carbon dioxide capture by aminoalkyl imidazolium-based ionic liquid: a computational investigation

Abstract

Efficient technologies/processes for CO₂ capture are greatly desired, and ionic liquids are recognized as promising materials for this purpose. However, the mechanisms for selectively capturing CO₂ by ionic liquids are unclear. In this study, the interactions between CO₂ and 1-n-amino-alkyl-3-methyl-imidazolium tetrafluoroborate, an amino imidazolium ionic liquid (AIIL), in its CO₂ capturing process, are elucidated with both quantum chemistry and molecular dynamics approaches on the molecular level. The effects of the straight aminoalkyl chain length in imidazolium-based cations on CO₂ capture are explored, and thereby the factors governing CO₂ capture for this ionic liquid family, e.g., ionic liquid structure, charge distribution, intermolecular interactions, thermodynamic properties and absorption kinetics, are analyzed. Molecular dynamics simulations are used to study the diffusion of the involved compounds and liquid structures of the CO₂–AIIL systems. The results show that the amino-alkyl chain length plays an important role in governing the absorption properties of AIILs, including the free energies of absorption, equilibrium constants, desorption temperature, absorption rate constants, diffusion coefficients, and organization of CO₂ around cations and anions. This study provides useful information about rational design of ionic liquids for efficient CO₂ capture.