Development of a novel, through-flow microwave-based regenerator for sorbent-based direct air capture

In this work an all-electric regenerator is developed for the desorption of CO2 from air-capture sorbents using microwaves. An electromagnetic model was made for a continuous flow radial desorber and its dimensions were optimised for maximal microwave utilisation. Based on the optimal dimensions an actual prototype, capable of desorbing CO2 from a commercial supported amine sorbent in fixed- or moving-bed configuration was built to demonstrate the concept and to study performance characteristics. TSA experiments using nitrogen as purge gas to produce enriched air (1 to 2 vol.% CO2) were done. Productivities of up to 1.5 kg CO2/kgsorb./d were demonstrated, with a total energy duty of 25 MJ/kg CO2. Compared to traditional TVSA desorption, the energy duty is similar while the productivity is significantly higher. The process can be further improved by creating an even more homogeneous electric field (preventing hot spots in the regenerator) and by enabling desorption under vacuum conditions to produce pure CO2. Overall, microwave desorption is demonstrated as an effective way to circumvent heat transfer limitations present during more traditional thermal desorption processes using polymeric sorbents.