Solving the Water Loss Challenge in Potassium Hydroxide-Based Liquid Direct Air Capture Systems by Tolerating Concentration Fluctuations

High Resolution Image Download MS PowerPoint Slide Water evaporation driven by weather variability represents a critical and underexplored limitation in KOH-based liquid direct air capture (L-DAC) systems that absorb atmospheric CO 2 . Thus, we develop a pseudo-steady-state model using year-round climate data from Denmark and Los Angeles, representing cold–humid and hot–dry conditions, to evaluate daily water balance and identify sorbent compositions that minimize annual water loss while preserving system operability. Model assumptions are evaluated through experiments evaluating model assumptions under idealized air-contactor and pellet-reactor conditions. Air contactor tests show that outlet air equilibrate with the sorbent water activity independent of inlet humidity, and that variations in K 2 CO 3 concentration do not highly affect CO 2 capture provided the KOH concentration remains >1 M. Pellet reactor experiments demonstrate that KOH concentrations predicted for dry climates inhibit CaCO 3 formation, whereas KOH concentrations at or below 2 M enable over 80% conversion of Ca(OH) 2 or CaO to CaCO 3 . These results define a feasible KOH operating range of 1–2 M. By adjusting K 2 CO 3 concentration to local climates, simulations show that net water loss can be avoided while maintaining KOH levels in the feasible range, enabling sustained capture and regeneration. These findings indicate that L-DAC systems can be engineered to support more sustainable deployment.