Gas separation by ionic liquids: A theoretical study. (2nd November 2018)

• Record Type: Journal Article
• Authors: Zhao, Yongsheng; Pan, Mingguang; Kang, Xuejing; Tu, Wenhui; Gao, Hongshuai; Zhang, Xiangping
• Is Part Of: Chemical engineering science. Volume 189(2018)
• Page Start: 43
• Page End: 55
• Publication Date: 2018-11-02
• Subjects: Ionic liquids -- Gas separation -- CO2 capture -- Mechanism -- Hydrogen bond; Chemical engineering -- Periodicals; Génie chimique -- Périodiques; Chemical engineering; Periodicals; Electronic journals; 660
• DOI: 10.1016/j.ces.2018.05.044
• Languages: English
• ISSNs: 0009-2509

Abstract

Highlights: ILs applied to gas separation (CO2 /CH4, C2 H2 /C2 H4, and NH3 /CH4 ) were investigated. Interaction mechanism between ILs and gases was studied by quantum chemistry. Hydrogen bonds play a crucial role in gas separation. ILs are promising to be used as absorbents for gas separation (e.g. CO2 separation). Abstract: Ionic liquids (ILs) have great potential for separating gases as well as avoiding solvent loss and environmental pollution. An in-depth understanding of the interaction mechanism between ILs and gases is extremely important for exploring and developing high-performing ILs for gas separation. Quantum chemistry is a powerful approach for gaining insight into separation mechanisms. Herein, with the aid of this method, the interaction mechanisms of three representative ILs, i.e., diethylmethylsulfonium tricyanomethane ([S221 ][CCN3 ]), triethylsulfonium acetate ([S222 ][Ace]), and 1-2(-hydroxyethyl)-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([OHemim][NTf2 ]), with CO2 /CH4, C2 H2 /C2 H4, and NH3 /CH4 mixtures are studied. The results show that hydrogen bonds (H-bonds), which are mainly electrostatic dominant (and sometimes even covalent dominant when the H-bond is sufficiently strong), play a crucial role in gas separation. Furthermore, there is a linear relationship between the distance of the H-bonds and both electron density ( ρ BCP ) and Laplacian values (∇ 2 ρ BCP ). Symmetry adapted perturbation theory revealed that electrostatic energies are the main contributors to the total attractive energies between ILs and gases ([OHemim][NTf2 ]-NH3, [S221 ][CCN3 ]-CO2, and [S222 ][Ace]-C2 H2 ). Therefore, based on the above results, we can design the ILs with specific functional groups, which are easy to form H-bonds with the gases to be separated.