Absorption performance and reaction mechanism study on a novel anhydrous phase change absorbent for CO2 capture

Abstract

• A novel phase change absorbent was proposed for CO 2 capture with low energy consumption. • Ethanol promoted phase change behavior and increased CO 2 loading. • Reaction of CO 2 capture with [N 1111 ][Gly]/ethanol was a three-step reaction. • Intramolecular hydrogen bonds affected products’ solubility, causing phase change. Carbon capture and utilization technologies are urged more than ever due to the excessive emissions of CO 2 that could lead to serious environmental problems. Phase change absorbents are quite competitive in reducing the energy consumption of carbon capture. In this work, tetramethylammonium glycinate ([N 1111 ][Gly]), an efficient absorbent, was dissolved in ethanol and 1-propanol, respectively, to absorb CO 2 . After CO 2 absorption, the saturated solution separated into two phases. CO 2 was enriched in the lower phase, so that only the CO 2 -rich phase needed to be regenerated and the energy consumption of regeneration could be thus reduced. Under the optimal conditions, the CO 2 loading of fresh absorbents could reach 0.85 mol CO 2 /mol IL. On the basis of the 13 C NMR analysis and quantum chemical calculation, a three-step reaction mechanism of CO 2 capture with [N 1111 ][Gly]/ethanol was proposed. CO 2 reacted with [N 1111 ][Gly] to form carbamate, which was similar to the two-step Zwitterionic mechanism of MEA with CO 2 . Then the formed carbamate could react with ethanol to form ethyl carbonate and [N 1111 ][Gly], which resulted in higher CO 2 loading. Moreover, hydrogen bond characteristics were analysed to clarify the phase change mechanism. The number and bonding energy of intramolecular hydrogen bonds were increased after capturing CO 2 , leading to the formation of precipitation.