(391c) Microwave Regeneration of Ionic Liquid Sorbents for Direct Air Capture: Finite Element Modelling and Experimental Demonstration

As the world strives toward carbon neutrality to stave off an impending global climate disaster, decreasing reliance on fossil fuels is an essential step to reaching emission mitigation targets. Significant research efforts are being made toward electrifying industrial processes, reducing dependence on combustion for heating and energy supply. Direct air capture (DAC) of CO₂ is no exception. It is a key area in which electrification will drastically improve carbon capture efficiency of existing technologies. Reactive absorption of CO₂ is essential to reach the required selectivities for effective DAC, which has a feed of only 0.04% CO₂. This reaction is exergonic, and thus energy is required to reverse it and regenerate the sorbent for cycling. Supplying this energy via microwaves is a promising method for regeneration as many DAC materials react with CO₂ to form charged functionalities, which respond more intensely to microwave irradiation. In this study, we present the successful microwave-assisted regeneration of a CO₂-reactive ionic liquid (IL), 1-ethyl-3-methylimidazolium 2-cyanopyrrolide, which has been shown to have excellent CO₂ capacities (~1 mol CO₂/kg sorbent) at DAC relevant conditions. We further incorporated this IL into a metal organic framework (MOF), specifically zinc imidazolate framework 8 (ZIF-8), to form a powdery composite sorbent, which is assessed via breakthrough analysis for both absorption and desorption and under humid conditions. To model the microwave regeneration of these sorbents and assess energy utilization, the Maxwell equations were coupled with the Navier-Stokes transport equations and solved via finite element modeling. We find that the distribution of the electromagnetic energy is highly dependent on sample geometry and the dielectric properties of the sample. These results provide key insight into the relevant parameters for improving energy efficiency in microwave-based separations, and will inform the geometries and measurement techniques for future studies.