Evaluation of Mmen-Mg2(dobpdc)-MOF and Lewatit Adsorbents for Direct Air Capture by a Modular Vacuum Temperature Swing Adsorption (VTSA) Process

This draft publication presents results from dynamic process simulations of a Climeworks-type vacuum-temperature-swing adsorption (VTSA) process using two very different sorbents. One of the chosen sorbents is a commercially available solid amine, Lewatit, for which the CO₂ sorption can be described by Langmuir formalism, while the second sorbent is a metal-organic framework (MOF), mmen-M2(dobpdc), for which CO₂ sorption follows an S-shaped isotherm. For both sorbents, the VTSA cycle is optimized at typical Norwegian ambient conditions (278K, 80% relative humidity) with respect to minimum energy consumption and maximum productivity with constraints on the CO₂ purity (> 95%) and recovery (>80%). We find that the Lewatit adsorbent has a higher energy requirement than mmen-Mg2(dobpdc), which is mainly a consequence of the higher capacity of the latter. Nevertheless, a higher temperature must be used during regeneration for the MOF than for Lewatit and the S-shaped isotherm of the MOF resulted in the use of a less deep vacuum pressure during the product extraction step compared to Lewatit.