Thermodynamic analysis of temperature-swing adsorption for CO2 capture based on PVT differentiation of adsorbed phase on adsorbents

Adsorption-based carbon capture is a mature technology for carbon reduction, but energy consumption during desorption limits its development. Temperature-swing adsorption (TSA) captures CO2 during adsorption and uses heat during desorption to release the gas. However, the adsorbed phase absorbs heat during desorption, leading to additional energy consumption, which is often overlooked in studies. This study analyzes adsorption isotherms, derives the molar volume of the adsorbed phase, and creates a PVT relationship model based on the Virial equation. It also evaluates the enthalpy of the adsorbed phase to assess the performance of three adsorbents in CO2 capture cycles and further clarify their energy consumption in TSA. The study finds that the N2 adsorbed phase of all adsorbents follows the five-order Virial equation. The CO2 adsorbed phase behaves differently for each adsorbent: Zeolite 13X follows the first-order equation, activated carbon follows the five-order equation, and Mg-MOF-74 switches from first-order to five-order in different temperature regions. Adsorbed phase-based energy consumption analysis demonstrates that Mg-MOF-74 exhibits the lowest total energy demand, with 44 % of its energy attributed to sensible heat arising from adsorbed phase thermophysical propertie. In contrast, activated carbon shows the highest energy consumption, with negligible sensible heat contribution due to its limited adsorbed phase thermal response. Mg-MOF-74 exhibits the highest exergy efficiency, approaching 20 %, whereas activated carbon demonstrates the lowest value of approximately 2 %. The study emphasizes the significant impact of sensible heat of adsorbed phase on system efficiency, suggesting future work to optimize the PVT model for better energy consumption assessment.