Low temperature water vapor pressure swing for the regeneration of adsorbents for CO2 enrichment in greenhouses via direct air capture

Abstract

CO2 enrichment in greenhouses can be achieved by extracting CO2 from the outside air. For this purpose, adsorbents based on Na2CO3 or K2CO3 are promising for trapping and releasing atmospheric CO2. Even though the CO2 capture by these adsorbents has been studied before, there is not much information about their regeneration at low temperatures and using air as flushing gas. In this work an experimental design study has been performed to understand the effect of temperature, water vapor pressure and air flow rate on CO2 desorption. The results show that K-based adsorbents are a more attractive option given their higher CO2 capture capacity and lower energy consumption compared to the Na-based ones. The estimated amount of K-based adsorbent with a capture capacity of 0.1 mmol CO2/gads and regenerated at 50 °C with 90 mbar H2O would occupy only 2% of the total volume contained in a closed greenhouse, fulfilling its daily CO2 demand.