Mitigating Water Evaporation in Aqueous Liquid-Based Direct Air Capture Using Supported Ionic Liquid Membranes

The stability and efficiency of direct air capture (DAC) processes using liquid absorbents are significantly influenced by solvent volatility. This study investigated CO2 recovery performance and absorbent weight loss of aqueous potassium hydroxide (KOH)-based DAC incorporated with SILMs through two types of experimental studies. Semi-batch membrane contactor modules were employed and a 1 M aqueous KOH solution was selected as the liquid absorbent. The semi-batch modules were exposed to the atmosphere for seven days to examine water transport between the feed and permeate sides for different membrane types. Hydrophobic SILMs, particularly [ThtdP][NTf2], effectively suppressed water evaporation compared with other IL-impregnated and blank membranes. In addition, we conducted 2-hour semi-batch CO2 absorption experiments with 120 L/min of the air inflow to quantify the CO2 recovery performance of a DAC system using aqueous KOH and SILMs. Comparing the SILMs cases with a blank membrane case, it was revealed CO2 recovery and apparent permeance for SILMs cases decreased by approximately 15% from the blank membrane case,whereas IL types and relative humidity did not affect CO2 recovery performance. These findings highlight the use of SILMs can stabilize the process operation of liquid-based DAC at various humidity conditions.