Impurities effect on CO2 capture from flue gas by energy-efficient diazole-functionalized ionic liquid solvents

As one of the main greenhouse gases, carbon dioxide (CO2) excessive emission has brought a series of climate change and environmental concerns, especially vast majority of CO2 emission from coal-fired flue gas due to characteristics of energy structure in China, so CO2 capture from flue gas is crucial to achieve carbon neutrality and mitigate these problems. Functionalized ionic liquid (IL) hybrid solvents have been regarded as potential absorbents for CO2 capture, but they still face great challenge how to simultaneously realize high CO2 mass uptake, low energy consumption and great tolerance under flue gas situation. In this study, the diazole-functionalized IL (DZIL) 1-ethyl-3-methylimidazolium triazole ([Emim][Triz]) was synthesized and blended with N-methylimidazole (N-MI) to form novel DZIL binary anhydrous solvents for CO2 capture from flue gas. The results indicated that the DZIL solvent ([Emim][Triz]/N-MI) with mass ratio of 90 wt%/10 wt% can not only absorb 0.112 g CO2/g absorbent under a feed of 15 % CO2 in N2 at 40 °C and 1 bar, but also shows lower regeneration energy consumption of 1.49 GJ/t CO2, which is 65 % less than that of 30 wt% MEA solution (4.28 GJ/t CO2). Meanwhile, the results of impurities effect demonstrated that the presence of H2O can improve CO2 capacity and keep good recyclability of DZIL solvents, CO2 absorption and recyclability performance have almost no change in the presence of O2, but a decrease less than 10 % in the presence of SO2 occurs due to strong interaction between SO2 and DZIL. The mechanism analysis revealed that both cation [Emim]+ and anion [Triz]− of the DZIL can react with CO2 to form Emim-CO2 and [Triz-CO2]−, respectively, and the former plays a dominant role in CO2 absorption. The presence of H2O attenuates the formation of Emim-CO2 but promotes CO2 absorption capacity by introducing a new pathway of [Triz]− reacting with H2O and CO2 to form [HCO3]−. This study provides a feasible thought for CO2 capture from flue gas with functionalized IL as energy-efficient absorbents to solve environmental problems. © 2024 Elsevier B.V.