Research on CO₂ capture by imidazolium and alkali metal salt hybrid ionic liquids

LY Wang and LS Li and YL Xu and Y Li and Y Wang and TX Chu, JOURNAL OF MOLECULAR LIQUIDS, 379, 121646 (2023).

DOI: 10.1016/j.molliq.2023.121646

In this work, several alkali metal salts, shortened by MBF4 and CH3OOM(MAc, M = Li+, Na+, K+), were mixed with BmimBF4 or BmimAc separately to prepare kinds of hybrid absorbents (i.e., Bmim BF4-LiBF4, BmimBF4-NaBF4 and BmimBF4-KBF4 with the same anion of BF4(-), BmimAc-LiAc, BmimAc-NaAc and BmimAc-KAc with the same anion of acetate) to absorb CO2. The results show that the hybrid absorbents based on BmimBF4 has a relatively enhanced absorption effect on CO2, while the hybrid absorbent based on BmimAc has an inhibitory effect. When a low concentration of MBF4 was applied, LiBF4-BmimBF4 shows higher CO2 capacity than NaBF4-BmimBF4 and KBF4-BmimBF4 solutions. With the concentration of MBF4 increase, NaBF4-BmimBF4 and KBF4-Bmim BF4 become more favorable for CO2 absorption, which also appeared in the MAc-BmimAc systems. According to the MD simulation results, Na+ and K+ have stronger attraction forces with CO2, and Na+ is easier to make the BF4(-) anions to aggregate around it. According to the MD calculations, for the BmimBF4-MBF4 hydrid systems, Na+ has the weakest ability to aggregate and form M+ layer hindering the contact of CO2 and anion. Combining with its strongest ability to attract the BF4(-) anion, a largest space of BmimBF4 to accomodate more CO2 molecules is created. In comparison, for the physical-chemical absorbent BmimAc, the strong M+ aggregation and Ac(-) attraction by M+ are the main reasons for the decreased CO2 capacity, due to the reduced number of Ac(-) responsible for the chemically binding with CO2 during absorption. (C) 2023 Elsevier B.V. All rights reserved.

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