Investigation of Glycolic Acid Natural Deep Eutectic Solvents with Strong Proton Donors for Ammonia Capture and Separation

The efficient and environmentally friendly recovery and separation of ammonia (NH3), as a toxic substance in the environment and an indispensable chemical raw material, has always been a challenge. In the present work, natural deep eutectic solvents (DESs) based on dual solid components of glycolic acid (GA) and xylitol (XYL) were designed and synthesized as absorbents to capture ammonia efficiently and reversibly. The results showed that DESs exhibited ideal physical properties, high NH3 absorption capacity, and high NH3/CO2 selectivity. At 303.15 K and 101.33 kPa, the absorption capacity of GA+XYL (3:1) for NH3 is as high as 0.225 g NH3·(g DES)−1, which is much higher than those of ionic liquids and DESs reported so far. DES absorbs NH3 with high reversibility and can represent high absorption performance after five absorption–desorption cycles. In addition, the intrinsic absorption mechanism was analyzed using spectral characterization and quantum chemical calculation. These protic DES-based GA and XYL with high efficiency and reversible NH3 capture are expected to be promising substitutes for ammonia absorbents.