Hydrophobic Amines for CO₂ Capture: Entropy-driven CO₂ capture and development of CO₂ -responsive organic crystals

The transition to carbon neutrality necessitates efficient CO2 capture methods to address atmospheric CO2 levels. Aqueous amine scrubbing is the predominant method for large-scale flue gas capture, but it faces challenges such as energy-intensive regeneration, sorbent loss, and environmental concerns due to volatile amines. Alternative porous solid-state adsorbents are complex and difficult to scale up, expensive, and have low water tolerance.
In Chapter 2, a hydrophobic, non-volatile alkylated monoethanolamine (MEA) is introduced as a water-lean CO2 absorbent in brine. A systematical investigation of the effects of MEA alkylation, salinity, and absorbent aggregation on CO2 capture efficiency was performed. CO2 absorption induces spontaneous self-aggregation of hydrophobic absorbents, increasing the entropy of water in high-ion strength solutions. This process, controlled by solution salinity, yields CO2 uptake performance comparable to benchmark MEA. Experiments confirm that the hydrophobicity of alkylated MEAs in saline water enhances absorption and allows for mild regeneration conditions. The entropy-driven method reduces absorbent evaporation, corrosion, and thermal and oxidative decomposition, enabling an energy-efficient carbon capture process.
Chapter 3 presents a novel solid-state material that captures CO2 through a unique structural transformation of the crystal structure of the organic molecules. This amphiphilic hydrogenbonded organic framework (HOF) based on a small-molecular weight organic molecule rapidly reorganizes upon CO2 exposure, achieving high capture capacity (2.5 mmol/g) and easy release at low temperatures (60 °C). Using solid-state NMR spectroscopy and electron diffraction, these materials' molecular structures and behaviors were determined. The method offers significant energy efficiency, promising reduced costs and improved sustainability in industrial CO2 capture, providing a simpler and more effective solution for emissions management.