CO2 enrichment in ambient air by temperature swing adsorption and its applications for stimulating plant growth in greenhouses

Adsorption on proper adsorbents is one of the commonly used technologies to capture carbon dioxide. Zeolites, such as 13X, exhibit good adsorption capacity and selectivity towards CO₂. Compared with CO₂ capture from large point sources with high concentration of CO₂, direct capture from the ambient air plays a better role in the reduction of greenhouse gases. On the other hand, greenhouse crops can be benefited from CO₂ enrichment, typically around 1000 ppm. By applying temperature swing adsorption to ambient air, CO₂ concentration can be enriched from 400 ppm to about 1000 ppm, which can then be directly used for greenhouse CO₂ enrichment. The proposed method not only helps the capture of CO₂ from air but also provides an enriched CO₂ stream to greenhouses. In this study, the performance of zeolite 13X was evaluated in a fixed bed reactor for enriching ambient CO₂ concentration from 400 ppm to 1000 ppm by temperature swing adsorption under different operating conditions such as ambient temperature and moisture content. Results showed that 13X performed well for both CO₂ adsorption and desorption, and an enrichment factor of 3 can be reached, demonstrating the feasibility of the proposed TSA method. A lower adsorption temperature and a higher desorption temperature would result in a higher enriched CO₂ concentration. Finally, economic analyses have been carried out to compare the unit cost of proposed method for capturing one tonne CO₂ with the cost of other air capture technologies and the cost of CO₂ supply in current greenhouse operations. The unit cost of CO₂ enrichment by temperature swing adsorption seems to be quite competitive if the adsorption and desorption capacity of the currently tested adsorbent could be increased by six times to the level as reported in the literature.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat