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Microwave regeneration and thermal and oxidative stability of imidazolium cyanopyrrolide ionic liquid for direct air capture ...

by Michelle K Kidder, Yensil Park
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Understanding the oxidative and thermal degradation of CO2 sorbents is essential for assessing long-term sorbent stability in direct air capture (DAC). The potential degradation pathway of imidazolium cyanopyrrolide, an ionic liquid (IL) functionalized for superior CO2 capacity and selectivity, was evaluated under accelerated degradation conditions to understand the secondary reactions that can occur during repetitive absorption-desorption thermal-swing cycles. The combined analysis from various spectroscopy, chromatography, and thermal gravimetric measurements indicated that radicalic and SN2 mechanisms in degradation are encouraged by the nucleophilicity of the anion. Thickening of the liquid and gas evolution are accompanied by 50% reduction in CO2 capacity after a 7-day exposure to O2 under 80 °C. In order to prevent long exposure to conventional thermal heating, we demonstrate microwave (MW) regeneration of the CO2-reactive IL where dielectric heating at 80 and 100 °C rapidly desorbs CO2 and regenerates the IL without any measurable degradation.