Thermodynamic study on two adsorption working cycles for direct air capture

Direct capture of CO2 from air, i.e. DAC, is considered as a potential solution to address anthropogenic climate change in the near future. This work provides a comparative assessment of DAC by using five adsorbents, i.e. SIFSIX-3-Ni, NbOFFIVE-1-Ni, N2H4/Mg-MOF-74, TRI/PE-MCM-41 and DETA/PPN-6, based on equilibrium working capacity and exergy efficiency analysis. Vacuum-pressure swing adsorption (VPSA) and temperature vacuum swing adsorption (TVSA) cycles are compared by adjusting working parameters. Adsorption temperature/pressure, desorption temperature/pressure and CO(2 )concentration are analyzed. For working capacity, SIFSIX-3-Ni can achieve 1.08 mmol.g(-1 )at 6 mbar adsorption and 1 mbar desorption partial pressure in VPSA cycle. N2H4/Mg-MOF-74 performs the most outstanding working capacity in TVSA cycle. The results show that raising pressure of air is an unsatisfactory choice to increase working capacity due to the large amount of energy demand of compression process. Thus, TVSA is a promising process applied in DAC. When desorption pressure is 4 mbar and adsorption temperature is 25 ?C, the maximum exergy efficiency among these adsorbents is 50.9% of DETA/PPN-6. Amine-modified adsorbents have an excellent performance above two metal-organic frameworks (MOFs) in most situations. These findings can provide helpful guides when choosing appropriate adsorbents and cycles for DAC.

Automated summary

This study provides a comparative assessment of direct air capture (DAC) using five different adsorbents. It analyzes the working capacity and exergy efficiency of DAC cycles using vacuum-pressure swing adsorption (VPSA) and temperature vacuum swing adsorption (TVSA). The results show that TVSA is a promising process for DAC, and amine-modified adsorbents perform better than metal-organic frameworks in most situations.