Dielectric Heating of Ionic Liquids: A Successful Strategy to Enhance Regeneration Kinetics in Direct Air Capture

Abstract

Climate change mitigation strategies have driven research on energy-efficient sorbents for direct air capture (DAC). Ionic liquids (ILs) offer a flexible design and the possibility of integration with dielectric heating, presenting an opportunity to enhance cyclic CO2 recovery and significantly reduce the cost and energy consumption in DAC processes. Building upon an experimentally validated strategy to synthesize a range of quaternary ammonium salts with amino acid anions and a quat molecule counterion, a sustainable IL, [N4444][Tau+Lys], was designed to be coupled with microwave irradiation. This integrated approach led to a substantial enhancement in regeneration performance compared with conventional thermal heating, increasing the maximum CO2 desorption rate and total recovered CO2 by up to ∼496% and ∼66%, respectively. A comparative analysis of energy consumption further demonstrated an ∼62% reduction in total input energy when using microwave heating (0.26 kWh versus 0.69 kWh). The mechanism through which microwave radiation assists in overcoming energy barriers, thereby enhancing the carbamate decomposition reaction rate, has been investigated. It is recognized that the low ionization energy of amino sulfonic acid (taurine) combined with the high proton affinity of lysine in [N4444][Tau+Lys] not only reduces the viscosity of IL and influences the formation of polar dianion intermediates but also facilitates the crossing of the proton transfer energy barrier and coupling persistent transition states with microwave irradiation in each energy cycle.