CO2 capture from ambient air using hydrated Na2CO3 supported on activated carbon honeycombs with application to CO2 enrichment in greenhouses

CO2 capture from ambient air is an interesting option for CO2 enrichment in greenhouses. In this study, adsorbents comprised of hydrated Na2CO3 supported over activated carbon honeycombs were prepared, characterized and tested for CO2 capture from air. The adsorption of H2O and the formation of the hydrates were studied by means of FT-IR spectroscopy. The inlet CO2 concentration showed to have a major influence on the conversion yield into NaHCO3, and the results fitted well to the Toth model. A statistical model of the CO2 capture capacity was obtained to get insight into the key parameters of the adsorption process. The air temperature and its moisture content showed to have the largest impact on the CO2 capture, while the flow rate had a minor influence. The chemical reaction path during the CO2 adsorption showed to be determined by the relative humidity conditions inside the reactor. Addition of more salt on the carrier showed to improve the CO2 capture capacity, but this is limited by the strength of the honeycomb carrier. Finally, a preliminary desorption test via a mild temperature and moisture swing was run to assess the feasibility of the process for application in greenhouses. The results showed that the required volume of adsorbent would be roughly 1/1000 of the total volume of a closed greenhouse assuming a target CO2 level of 1200 ppm.