How Would\nIdeal Sorbents Improve the Technical and\nEconomic Performance of Adsorption-Based Direct Air Capture?

Current climate policies and national pledges are insufficient\nto achieve the necessary reduction in CO<sub>2</sub> emissions, underscoring\nthe urgency of carbon dioxide removal (CDR) from the atmosphere. Direct\nair capture (DAC) is an engineered CDR process with substantial removal\npotential but also one with clear technical limits and opportunities\nfor enhancement. One such improvement is the optimization of the material,\nenabling the separation. To investigate this from a quantitative perspective,\nthis study evaluates DAC performance when replacing existing sorbents\nwith theoretical ones designed to optimize the process. In order to\ndo so, the adsorption isotherm parameters of CO<sub>2</sub> for different\nisotherm models were optimized along with process design variables\nto minimize energy and maximize productivity. Combining equilibrium\nand rate-based models, our analysis offers insights from thermodynamic,\nreactor, and economic perspectives. The results show that optimal\nsorbents have the potential to significantly improve the DAC performance\nobtained with existing sorbents, for example, Lewatit VP-OC-1065 and\nMIL-101, especially in terms of energy consumption and costs. This\nrequires that some critical sorbent characteristics are met: moderate\ncost (e.g., <30$/kg), long lifetime (e.g., >2 years), and a\nlinear\ndriving force in line with other gas separation processes (e.g., <i>k</i><sub>LDF</sub> > 0.001 s<sup>–1</sup>). Furthermore,\nour findings highlight that optimizing productivity and energy consumption\nenables the identification of minimum-cost configurations for DAC.\nThis work underscores the importance of tailored sorbent design in\nadvancing DAC toward cost-effective, efficient CO<sub>2</sub> removal\nsolutions.