Impact of adsorption kinetics on the integration of temperature vacuum swing adsorption-based direct air capture (TVSA-DAC) with e-methanol production

Understanding the integration potential of direct air capture (DAC) with carbon utilisation processes can help pave the way for DAC to become an essential part of the solution towards carbon neutrality. In this study, we provide a detailed technical assessment of an integrated system using direct air capture based on temperature-vacuum-swing-adsorption (TVSA-DAC) as the carbon source for e-methanol production. The integration potential is evaluated in terms of technical compatibility, heat integration, water management, and overall energy efficiency. A specific focus is given to the TVSA-DAC process considering the uncertainty of the available adsorption mass transfer kinetics. It is found that the CO₂-productivity ranges from 0.23-13.35 kg_CO2 m⁻³ h⁻¹ given an interval for the CO₂ mass transfer coefficient of 0.0001-0.1 s⁻¹ in which the highest productivity is obtained using a steam sweep during desorption. The potential to achieve a steady CO₂ output from the TVSA-DAC is proven; however, the complexity of the integrated design configuration depends greatly on the adsorption kinetics. Generally, a well-aligned heat integration with no external heat demand for the combined system can be achieved using high-temperature heat pumps to facilitate favourable heat recovery from the electrolysis. Furthermore, the integrated system can be water self-sufficient and even net producing at a relative humidity above 50% due to the co-capture of water in the TVSA-DAC process. The overall energy efficiency can reach up to 52% for the integrated system.