Low-Energy-Consumption CO2 Capture by Liquid–Solid Phase Change Absorption Using Water-Lean Blends of Amino Acid Salts and 2-Alkoxyethanols

Solvent regeneration for the conventional aqueous amine-based CO2 capture is very energy intensive. Development of phase-changing absorbents is an attractive solution for low energy consumption. In this work, a novel water-lean amino acid salt-based biphasic absorbent was proposed to improve CO2 capture performance and energy efficiency. Potassium prolinate (ProK) and potassium sarcosinate (SarK) with a secondary amino group were used as active components, and 2-alkoxyethanols with low volatility, low specific heat, and low viscosity were used as physical antisolvents and triggered the formation of solid phase during CO2 absorption. CO2 absorption and desorption characteristics in these systems and continuous capture cycles were investigated under ambient pressure. Relative regeneration energy consumption for solvent regeneration was also evaluated in comparison with the benchmark aqueous MEA. Phase change behavior and partition of CO2 absorbed in liquid and solid phases were characterized, and the product species in CO2-rich solid phase were identified by 13C NMR and XRD. Results demonstrated that using weak polar solvents, such as 2-methoxyethanol (EGME) and 2-ethoxyethanol (EGEE), can be favorable for the formation of solid precipitates in these systems investigated. Solid slurry with CO2 loading of 2.5–3.5 mol kg–1 can captured about 50–80% of the absorbed CO2. Ionic products such as bicarbonate and protonated amino acid salt were proved to be the main compositions in the solid precipitate. In comparison with aqueous 5.0 M MEA, the 3.0 M ProK/EGME system showed comparable cyclic capacity (about 0.80 mol kg–1) and a little higher desorption efficiency. Surprisingly, about 40–50% reduction of regeneration energy indicates that water-lean phase change ProK/EGME absorbent has a great potential for advanced CO2 capture technology.