Novel phase-change deep eutectic solvents: Experimental investigation of physicochemical properties and CO₂ capture performance

Efficient carbon capture technologies are crucial for mitigating climate change amid escalating CO₂ emissions. Traditional solvents like monoethanolamine (MEA) suffer from limitations such as high energy consumption and degradation. This study synthesized eight novel phase-change deep eutectic solvents (DESs) via a one-step process, combining 2-amino-2-methyl-1-propanol (AMP) as hydrogen bond donor (HBD) with acetamide, tetraethylammonium chloride, tetrabutylammonium bromide, and tetrabutylphosphonium bromide as hydrogen bond acceptors (HBAs) at 1:4 and 1:6 ratios. It addresses the critical challenge of developing absorbents concurrently featuring high CO₂ capacity, excellent stability, and environmental benignity. DES density decreased linearly while viscosity declined exponentially with temperature, with negligible toxicity as predicted by ECOSAR. Acetamide-based DESs exhibited the highest thermal stability (132.67 °C). Dual absorption mechanisms were observed: chemical reaction dominated at low pressures (0–0.2 MPa), while physical absorption governed by Henry's law prevailed at high pressures (0.2–0.7 MPa). The acetamide/AMP (1:6) DES achieved a maximum capacity of 3.29 mol·kg −1 at 323.15 K, significantly outperforming MEA. Cyclic absorption-desorption experiments confirmed the excellent regenerability of the solvents, particularly the acetamide-based DES, which maintained a regeneration efficiency of over 80% after three cycles. Fourier Transform Infrared Spectroscopy (FTIR) confirms the occurrence of chemical reactions during the absorption process. When deep eutectic solvents absorb CO₂, insoluble carbamates are formed, which leads to phase change. Phase-change deep eutectic solvents are promising candidates for next-generation materials in the field of efficient and sustainable industrial CO₂ capture.