Exploiting the hydrophilic role of natural deep eutectic solvents for greening CO2 capture

Abstract

Abstract CO2 released from fossil fuels has made a great contribution to global warming, and natural deep eutectic solvents (NADES) offer an attractive option for greening CO2 capture. Being economical natural materials, L-arginine (L-Arg) and glycerol (Gly) were used to synthesize a series of novel hydrophilic NADES (L-Arg/Gly, at mole ratios of 1:4, 1:5, 1:6, 1:7, 1:8). The L-Arg/Gly (1:6) DES showed excellent thermal stability (Tmax, 250 °C; Tf, 13.7 °C). The hydrates of L-Arg/Gly DES (at water contents of 0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%) were also prepared. The synthesis process of L-Arg/Gly DES and its hydrate were studied with FT-IR and in situ IR spectroscopy. High hydrophilicity of such solvent was demonstrated with fast and efficient capture of CO2 at a high absorption (0.511 mol CO2/mol NADES) under optimized conditions. In the gas-liquid absorption process, the hydrophilic properties of L-Arg/Gly DES and its hydrate greatly reduced the transfer barrier, and accelerated the phase transfer by increasing accessibility of active amine sites on NADES and CO2. And the dynamics for the CO2 absorption was investigated correspondingly. The absorption behaviors of CO2 in L-Arg/Gly DES and its hydrate were studied by in situ IR spectrometer and nuclear magnetic resonance (1H NMR, 13C NMR), and the characteristic infrared peaks and shifts of CO2 absorption were observed. In addition, the L-Arg/Gly DES could be reused for 5 times without obvious inactivation. Indicating the L-Arg/Gly DES would be a potential substitute of the traditional volatile amine solvents for CO2 capture.