Combined Experimental and Theoretical Study of the Competitive Absorption of CO2 and NO2 by a Superbase Ionic Liquid

Reviewing and screening ionic liquids and deep eutectic solvents for effective CO2 capture

CO₂ capture is essential for both mitigating CO₂ emissions and purifying/conditioning gases for fuel and chemical production. To further improve the process performance with low environmental impacts, different strategies have been proposed, where developing liquid green absorbent for capturing CO₂ is one of the effective options. Ionic liquids (IL)/deep eutectic solvents (DES) have recently emerged as green absorbents with unique properties, especially DESs also benefit from facile synthesis, low toxicity, and high biodegradability. To promote their development, this work summarized the recent research progress on ILs/DESs developed for CO₂ capture from the aspects of those physical- and chemical-based, and COSMO-RS was combined to predict the properties that are unavailable from published articles in order to evaluate their performance based on the key properties for different IL/DES-based technologies. Finally, top 10 ILs/DESs were listed based on the corresponding criteria. The shared information will provide insight into screening and further developing IL/DES-based technologies for CO₂ capture.

Combined Superbase Ionic Liquid Approach to Separate CO2 from Flue Gas

Superbase ionic liquids (ILs) with a trihexyltetradecylphosphonium cation and a benzimidazolide ([P₆₆₆₁₄][Benzim]) or tetrazolide ([P₆₆₆₁₄][Tetz]) anion were investigated in a dual-IL system allowing the selective capture and separation of CO₂ and SO₂, respectively, under realistic gas concentrations. The results show that [P₆₆₆₁₄][Tetz] is capable of efficiently capturing SO₂ in preference to CO₂ and thus, in a stepwise separation process, protects [P₆₆₆₁₄][Benzim] from the negative effects of the highly acidic contaminant. This results in [P₆₆₆₁₄][Benzim] maintaining >53% of its original CO₂ uptake capacity after 30 absorption/desorption cycles in comparison to the 89% decrease observed after 11 cycles when [P₆₆₆₁₄][Tetz] was not present. Characterization of the ILs post exposure revealed that small amounts of SO₂ were irreversibly absorbed to the [Benzim]^- anion responsible for the decrease in CO₂ capacity. While optimization of this dual-IL system is required, this feasibility study demonstrates that [P₆₆₆₁₄][Tetz] is a suitable sorbent for reversibly capturing SO₂ and significantly extending the lifetime of [P₆₆₆₁₄][Benzim] for CO₂ uptake.