| Computer Simulation of the Anion Effect in Gas Absortpion of Ionic Liquids Hubert Stassen1; 1INSTITUTO DE QUíMICA - UNIVERSIDADE FEDERAL DO RIO GRANDE DO SUL, Porto Alegre, Brazil; PAPER: 257/Molten/Regular (Oral) SCHEDULED: 11:45/Sat. 26 Oct. 2019/Ambrosia A (77/RF) ABSTRACT: Ionic liquids are currently investigated as promising materials for the absorption, storage, and separation of gases, such as CO2 [1], and H<sub>2</sub>S [2] among others. Ionic liquids based on the imidazolium cation are intensively studied for these purposes [3]. The possibility of combining distinct cations with different anions permits an easy design of ionic liquids. In an attempt to extract the structure-gas absorption relationship, we performed molecular dynamics computer simulations [4] on ionic liquids containing the 1-butyl-3-methylimidazolium cation and several anions (acetate, prolinate, BF<sub>4</sub><sup>-</sup>, Br<sup>-</sup>) interacting under typical experimental conditions (298 K, 10 bar gas pressure) with different gases (CO<sub>2</sub>, N<sub>2</sub>, methane, H<sub>2</sub> S). Two series of simulations have been carried out to characterize the physical absorption of the gases: i) ionic liquids containing 0.25 molar fractions of the gases, and ii) pure ionic liquids interacting with the gas phase. The first series of simulations revealed that the structure of the ionic liquids is essentially maintained when the gas is dissolved. N<sub>2</sub> and methane are only found in the apolar domains of the ionic liquids presenting a tendency of separating phases, whereas CO<sub>2</sub> and H<sub>2</sub>S also enter the polar domains of the ionic liquid producing stable solutions. The second series of simulations demonstrated that the ionic liquids only weakly absorb N<sub>2</sub> and methane, but are able to capture large amounts of CO<sub>2</sub> and, especially, H<sub>2</sub>S from the gas phase. In this process of physical absorption of the gases, the small BF<sub>4</sub><sup>-</sup> anion, offering several coordination sides for the gas molecules, performs best. References: [1] S. Zeng, X. Zhang, L. Bai, X. Zhang, H. Wang, J. Wang, D. Bao, M. Li, X. Liu, S. Zhang, Chem. Rev. 117 (2017), 9625-9673. [2] M.S. Shah, M. Tsapatsis, J.I. Siepmann, Chem. Rev. 117 (2017), 9755-9803. [3] N.M. Simon, M. Zanatta, J. Neumann, A.L. Girard, G. Marin, H. Stassen, J. Dupont, Chem. Phys. Chem 19 (2018), 2879-2884. [4] J. de Andrade, E.S. Böes, H. Stassen, J. Phys. Chem. B 106 (2002), 3546-3548 and 13344-13351. |
