Abstract

As Direct Air Capture (DAC) becomes essential for climate mitigation, optimising process-level performance for advanced adsorbents is critical. This study investigates the impact of cycle configuration on the performance of mmen-Mg2(dobpdc), a metal-organic framework with a unique cooperative, step-shaped adsorption mechanism. A one-dimensional temperature-vacuum swing adsorption (TVSA) model was developed in Aspen Adsorption V14 and validated against experimental breakthrough data (R2 = 0.9756). The study compares a standard 5-step TVSA cycle with a modified configuration incorporating a preheating stage before the vacuum stage to enhance product purity.

Contrary to established trends for conventional adsorbents, results indicate that preheating is counterproductive for this phase-change MOF. The modified cycle resulted in significantly lower CO2 recovery and higher specific energy consumption (SEC) without improving purity. This degradation is attributed to the material’s steep temperature sensitivity; heating before evacuation triggers a rapid shift in the step position, causing premature CO2 desorption and loss at atmospheric pressure. These findings suggest the need for specialised cycle strategies tailored to the unique thermodynamic characteristics of phase-change materials.