Entropy-Driven Carbon Dioxide Capture: The Role of High Salinity and Hydrophobic Monoethanolamine

Addressing atmospheric CO₂ levels during the transition to carbon neutrality requires efficient CO₂ capture methods. Aqueous amine scrubbing dominates large-scale flue gas capture but is hampered by the energy-intensive regeneration step, sorbent loss, and consequent environmental concerns with volatile amines. Herein, hydrophobic non-volatile alkylated monoethanolamine (MEA) is introduced as a water-lean CO₂ absorbent in brine. The effects of alkylation of MEA, salinity, and aggregation of absorbents on the improved CO₂ capture process are systematically investigated. The CO₂ absorption facilitates spontaneous self-aggregation of hydrophobic absorbents, which increases the entropy of water in high-ion strength solutions. This effect is controlled by the salinity of aqueous solutions, affording comparative gravimetric CO₂ uptake performance to benchmark MEA. It is experimentally verified that the hydrophobicity of alkylated MEAs in saline water is responsible for facile absorption, and also for mild regeneration conditions. Therefore, the entropy-driven approach minimizes absorbent evaporation, corrosion, and decomposition, thus paving the way to realize energy-efficient carbon capture.