Design and Demonstration of a Direct Air Capture System with Moisture-Driven CO2 Delivery into Aqueous Medium

Two direct air capture (DAC) systems were designed and demonstrated to passively capture CO2 from ambient air and use moisture to release the CO2 into an alkaline medium. A bench-scale system delivering ∼1 g CO2 d-1 was demonstrated in a laminar flow hood, and a small pilot-scale system that could deliver ∼100 g CO2 d-1 was operated outdoors in a 4.2 m2 raceway pond. Novel elongated mesh-tube packets containing anion-exchange resin (AER) beads were found to reduce drying and CO2 loading time 4.3-fold compared to larger mesh bags. Technoeconomic analysis (TEA) estimates the cost of capturing CO2 into an alkaline solution, suitable for cultivating photosynthetic microorganisms, to be $229 per tonne for a practical scenario based on current results and $72 per tonne for an aspirational scenario considering improvements to sorbent capacity, hydrophobicity, and sorbent lifetime. TEA further estimates an additional $110 per tonne to extract CO2 from solution, purify it, and compress it to 15 MPa, suitable for sequestration. Moisture-driven processes have the potential to use up to 87% less energy than thermal and/or vacuum swing DAC by using energy from water evaporation.