Air-Purge Regenerative Direct Air Capture Using an Externally Heated and Cooled Temperature-Swing Adsorber Packed with Solid Amine

Abstract

CO2 capture from air is crucial in achieving negative emissions. Based on conventional or newly developed high-enriching processes, we investigated the rough enrichment of CO2 from air via an externally heated or cooled adsorber (temperature-swing adsorption, TSA), along with air purge using double-pipe heat exchangers packed with low-volatility polyamine-loaded silica. A simple adsorption–desorption cycle was attempted in a TSA experiment, by varying the temperature from 20 °C to 60 °C using moist air, yielding an average CO2 concentration of product gas that was ~17 times higher than the feed air, but the CO2 recovery rate was poor. A double-step adsorption process was applied to increase CO2 adsorption and recovery simultaneously. In this process, substantial-CO2-concentration gas was used as the product gas, and the remaining gas was used as the reflux feed gas for adsorber. This method can provide a product gas with ~100 times higher CO2 concentration than raw gas, with a recovery ratio ~60% under the shortest adsorption/desorption time and the longest refluxing time of cycle operation. Therefore, the refluxing step significantly helped to enhance CO2 capture via adsorption from elevated-CO2-concentration recirculating gas. With this CO2 concentration, the product gas can serve as the CO2 supplement for the growing plant processes.