The impact of co-adsorbed water on energy consumption and CO2 productivity in direct air capture systems

• The impact of atmospheric moisture on adsorption-based DAC was analyzed. • Co-adsorbed water enhanced CO 2 desorption from solid amine sorbents. • Desorbed water limited CO 2 partial pressure during sorbent regeneration. • Energy consumption and CO 2 productivity were assessed at varying humidities. • The optimal humidity for direct air capture operation was identified. Adsorption-based direct air capture (DAC) of CO 2 , using solid amine sorbents, is among the most promising negative emission technologies for achieving net-zero emissions. Given the high atmospheric water content, reaching up to 4%, solid amine sorbents also adsorb a substantial amount of water from the air. However, a comprehensive understanding of how the co-adsorption of water affects the energy consumption and CO 2 productivity of a DAC process has not yet been obtained. Here, employing a polyethylenimine-impregnated sorbent, we investigated the impact of co-adsorbed water on a temperature vacuum swing adsorption process designed for DAC. Both experimental and simulated results indicated that co-adsorbed water could enhance the desorption of CO 2 by limiting the CO 2 partial pressure inside the column during sorbent regeneration. The promotion of co-adsorbed water on CO 2 productivity was significant, especially at low desorption temperatures lacking sufficient desorption driving forces. Optimal relative humidities for achieving the lowest energy consumption at various desorption temperatures were also identified. This study provides valuable insights into how co-adsorbed water affects CO 2 desorption from solid amines, which aids in designing CO 2 sorbents and associated DAC processes with reduced energy consumption.