Use of Hydrophobic Coatings on Direct Air Capture Sorbents for Carbon Dioxide Removal from Air
The environmental concerns surrounding increasing carbon dioxide levels in the atmosphere have driven extensive research into containment methods. One solution involves employing sorbents to remove carbon dioxide from the air directly using an anionic exchange membrane. The process of adsorbing and releasing carbon dioxide from this membrane is governed by the moisture swing process: As humidity rises, the sorbent samples will give off carbon dioxide while adsorbing water vapor; as humidity drops, carbon dioxide is adsorbed as water vapor is released. Hence, consumption of water is required to release carbon dioxide for sorbent regeneration.
Ionic contaminants in the water, specifically chloride, can impair the active sites of the sorbents and lead to marked decreases in sorbent capacity over time. Therefore, a method that can shield these active sites from contaminating ions will help to preserve their performance and may confer the efficiency increases needed for widespread adoption of sorbents for carbon dioxide removal.
Researchers at Arizona State University have developed a new method for protecting anionic exchange membranes of carbon dioxide capture systems while also minimizing the amount of water consumed by the moisture swing process. By topically treating the membrane with a hydrophobic coating, contamination of the membrane’s functional groups is reduced, as is the amount of entrained water that must be evaporated away sorbent regeneration.
Two different hydrophobic treatment types were demonstrated on Snowpure Excellion™ I-200 anionic exchange membranes. Versus an untreated membrane, the first treatment type saw a 34.5% reduction in water retention while maintaining 90% of sorbent performance. The second treatment type resulted in a 97.5% reduction in water retention, and although sorbent performance was reduced by half, this level of performance was preserved despite exposure to contaminants through a 1M sodium chloride solution wash.
• Carbon capture
• Sorbent regeneration
Benefits and Advantages
• Efficient – Significantly reduces water consumption and thus evaporation times during the moisture swing process
• Protective – Enables high-level resistance to chloride contaminants
• Practical – Does not require sorbent design modification since coatings are applied topically