Rational Design and Screening of Ionic Liquid Absorbents for Simultaneous and Stepwise Separations of SO₂ and CO₂ from Flue Gas

Abstract

In this work, a rational ionic liquid (IL) design and screening strategy, including vapor−liquid equilibrium-based absorption−selectivity−desorption index, simultaneous and stepwise separations, thermodynamic and physical property constraints, and process simulation, is established to remove SO 2 and CO 2 from flue gas. Based on the UNIFAC method, the vapor−liquid equilibrium composition of flue gas is considered to calculate the absorptivity, selectivity, and desorptivity of two separation processes. Through benchmark solvents, melting points, and viscosity constraints, five optimal ILs are obtained. Finally, optimal ILs with reported ILs 1-ethyl-3-methylimidazolium tetracyanoborate [EMIM][TCB] and 1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF 4 ] are introduced to Aspen Plus. In light of solvent requirements and energy consumption analysis, 1-(2hydroxyethyl)-imidazolium bis(trifluoromethylsulfonyl)amide [C 2 OHIM][Tf 2 N] and 1-ethylpyridinium dicyanamide [C 2 PY]-[DCA] are selected as the best IL absorbents, the processes of which save 55.71 and 31.25% solvent and 70.73 and 24.52% energy compared to [EMIM][TCB] and [EMIM][BF 4 ], respectively. Furthermore, stepwise separation saves at least 50% energy compared to simultaneous separation.

Combined Superbase Ionic Liquid Approach to Separate CO2 from Flue Gas

“…Furthermore, stepwise processes for the capture and separation of SO 2 and CO 2 have been reported to save ∼50% of the energy compared to simultaneous separation processes. 38 …”

“…Optimization of the dual-IL system in terms of the ratio of [P 66614 ]­[Tetz] to [P 66614 ]­[Benzim] and the flow rate/residence time of the gases in the ILs could feasibly increase the SO 2 uptake and, therefore, the CO 2 uptake and lifetime of [P 66614 ]­[Benzim], improving the overall efficiency of the process for longer-term operation. Furthermore, stepwise processes for the capture and separation of SO 2 and CO 2 have been reported to save ∼50% of the energy compared to simultaneous separation processes …”

“…Furthermore, stepwise processes for the capture and separation of SO 2 and CO 2 have been reported to save ∼50% of the energy compared to simultaneous separation processes. 38 In addition, such a dual-IL system, with stepwise separation of SO 2 and CO 2 from flue gas, could provide pure gas streams (albeit diluted in an inert gas) during desorption and regeneration of the IL. The pure SO 2 gas streams could be utilized as feedstocks for processes such as conversion to elemental sulfur and/or used in sulfuric acid production, 39 and the CO 2 stream could be used in the production of chemicals and fuels such as urea, a major agricultural fertilizer, or methane (dry reforming or hydrogenation), as well as in the food and beverage industries.…”

Cation functional group effect on SO2 absorption in amino acid ionic liquids

“…ILs based on imidazolium ( Li et al, 2021a ; Doblinger et al, 2021 ), guanidinium ( Wang et al, 2007 ; Geng et al, 2022 ), and pyridinium ( Zeng et al, 2014 ; Yan et al, 2019 ) can physically dissolve the gas. In addition to experimental efforts ( Huang et al, 2014 ; Cui et al, 2020 ; Wang et al, 2021a ; Cui et al, 2021b ; Geng et al, 2021 ; Liu et al, 2022b ; Hou et al, 2022 ) and theoretical and computational studies ( Wang et al, 2007 ; Wang et al, 2022a ; Mohammadi et al, 2022 ) to investigate the solubility of gases in ILs, ab initio and first principle investigations have also been conducted to inspect the structure and mechanism of the complex of IL and SO 2 gas ( Gu et al, 2013 ; Herrera et al, 2017 ; Cui et al, 2020 ; Wang et al, 2020 ; Li et al, 2021a ; Li et al, 2021b ; Yin et al, 2021 ; Zhu et al, 2021 ; Liu et al, 2022b ). For example, Wang et al (2007) simulated the solubility of CO 2 and SO 2 in guanidium-based IL and Zhang et al (2020) investigated the stability effect of ILs during the CO 2 absorption process in the presence of SO 2 .…”

Virtual Issue: A Multiscale View on Molecular and Process Design

“…3 Likewise, Lei et al 4 focused on IL design for aromatic mixture separations. Garciadiego et al discussed the separation of hydrofluorocarbon mixtures, 5 while Wang et al 6 considered the separation of CO 2 and SO 2 from gaseous mixtures. Meanwhile, Zhang et al tackled the design of deep eutectic solvents 7 for CO 2 absorption.…”