Abstract

Direct air capture (DAC) of CO2 is a promising strategy for achieving negative emissions, but the performance of DAC processes strongly depends on the thermodynamic and kinetic properties of the adsorbent materials. In this study, we investigate the impact of key step-isotherm parameters of the diamine-functionalised metal-organic framework mmen-Mg2(dobpdc) on DAC performance using a combination of temperature-vacuum swing adsorption (TVSA) modelling and variance-based global sensitivity analysis (Sobol method). Three parameters, step pressure at reference temperature (PstepO), step enthalpy (AH High), and high-loading saturation capacity (qH), were systematically varied within physically realistic ranges. The TVSA simulations under CO2 purity ≥ 98% enabled the evaluation of process productivity and specific energy consumption (SEC). The Sobol analysis revealed that ∆H High is the dominant parameter controlling both productivity and SEC, while significant interaction effects were observed between AH High and qH for productivity, and between PsteP0, and AH High for SEC. Visualisation of feasible parameter combinations highlights regions where multiple configurations achieve high productivity with manageable energy requirements. These results provide quantitative guidance for the targeted design of cooperative step-isotherm adsorbents and demonstrate a systematic framework to link material properties with process-level performance, accelerating the development of efficient DAC technologies.