(706d) Sub-Ambient Direct Air Capture of CO2 Using MIL-101(Cr) Monoliths

Current carbon drawdown scenarios require deployment of direct air capture (DAC) technologies to reduce atmospheric CO₂ concentration. Supported amine materials based on zeolite, silica, and metal-organic frameworks (MOFs) have been demonstrated as promising adsorbents for DAC, but the shaping and structuring of these materials into sorbent modules for practical processes have been inadequately investigated compared to the extensive research on material development.

In this work, we demonstrate the successful fabrication of adsorbent monoliths composed of cellulose acetate and the highly porous chromium MOF, MIL-101, by solution based additive manufacturing (SBAM). These monoliths feature macroporous interpenetrated polymeric frameworks where nano MIL-101 crystals are evenly distributed. Branched polyethylenimine was successfully immobilized in these monoliths to impart CO₂ uptakes of 1 mmol g(monolith)^-1 at both ambient (25 °C) and sub-ambient (-20 °C) conditions. Temperature controlled desorption (TPD) experiments reveal two CO₂ sorption mechanisms depending on the amine loading in the monoliths and CO₂ sorption conditions. The DAC performance under both ambient and sub-ambient conditions of these monoliths were further evaluated by dynamic breakthrough experiments, and the system pressure drops and mass transfer kinetics are benchmarked with systems where adsorbents of other forms like powder and pellets are deployed. In summary, our work showcases the excellent CO₂ capture performance of PEI-loaded MIL-101 monoliths under both ambient and sub-ambient conditions, suggesting the versatility of these monoliths in DAC applications regardless of climate conditions.