Superbase‐Added Choline Chloride‐Based Deep Eutectic Solvents for CO2 Capture and Sequestration

Abstract

AbstractDeep eutectic solvents (DESs) have emerged as inexpensive and environmentally‐benign liquid media for potential usage in chemical sciences. CO2 capture and sequestration by various substances is an active area of research in green chemistry. CO2 capture ability of DES‐based systems composed of salt choline chloride mixed with hydrogen bond donors urea (named reline), ethylene glycol (named ethaline), and monoethanolamine (named MEACC), are assessed in the absence and presence of three superbases: 1,5‐diazabicyclo[4.3.0]‐non‐5‐ene (DBN), 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), and 1,5,7‐triazabicyclo[4.4.0]‐dec‐5‐ene (TBD), respectively. Addition of superbase is found to significantly increase the CO2 capture ability of the DESs reline and ethaline; for the DES MEACC, the CO2 capture ability is not changed much as monoethanolamine and MEACC on their own exhibit appreciable CO2 capture efficiency. It is found that the overall efficiency of CO2 capture is the best with superbase DBN as compared to DBU or TBD due to the lower steric hindrance around the imine structure. Presence of glycerol in the superbase‐added DESs results in decrease in CO2 capture ability due to significantly lower solubility of CO2 in glycerol. 13C NMR, FTIR and Raman spectroscopic measurements reveal that major part of the captured CO2 binds covalently to the electron‐rich functionalities present on the components of the DES with superbase assisting this association. The reversibility of the captured CO2 is assessed by introducing N2 gas into the CO2 captured superbase‐added DES system; it is found that only 21–25% CO2 by weight could be removed from the system through five cycles. Heating the CO2 captured superbase‐added DES system to 60 °C and 100 °C results in loss of only 23% and 35% CO2 by weight, respectively. Intramolecular excimer intensity of 1,10‐bis(1‐pyrenyl)decane and steady‐state fluorescence anisotropy of rhodamine 6G fluorescence probes effectively monitor the CO2 capture process as viscosity of the superbase‐added DES increases as more‐and‐more CO2 is captured. Efficiency, effectiveness, and robustness of superbase‐added DES‐based systems towards CO2 capture and sequestration is amply highlighted.