Combined Superbase Ionic Liquid Approach to Separate CO(2) from Flue Gas

[Image: see text] Superbase ionic liquids (ILs) with a trihexyltetradecylphosphonium cation and a benzimidazolide ([P(66614)][Benzim]) or tetrazolide ([P(66614)][Tetz]) anion were investigated in a dual-IL system allowing the selective capture and separation of CO(2) and SO(2), respectively, under realistic gas concentrations. The results show that [P(66614)][Tetz] is capable of efficiently capturing SO(2) in preference to CO(2) and thus, in a stepwise separation process, protects [P(66614)][Benzim] from the negative effects of the highly acidic contaminant. This results in [P(66614)][Benzim] maintaining >53% of its original CO(2) uptake capacity after 30 absorption/desorption cycles in comparison to the 89% decrease observed after 11 cycles when [P(66614)][Tetz] was not present. Characterization of the ILs post exposure revealed that small amounts of SO(2) were irreversibly absorbed to the [Benzim](−) anion responsible for the decrease in CO(2) capacity. While optimization of this dual-IL system is required, this feasibility study demonstrates that [P(66614)][Tetz] is a suitable sorbent for reversibly capturing SO(2) and significantly extending the lifetime of [P(66614)][Benzim] for CO(2) uptake.