Design and thermophysical characterization of betaine hydrochloride-based deep eutectic solvents as a new platform for CO 2 capture

• Published in: New journal of chemistry Vol. 46; no. 11; pp. 5332 - 5345
• Main Authors: Jangir, Anil Kumar, Bhawna, Verma, Gunjan, Pandey, Siddharth, Kuperkar, Ketan
• Format: Journal Article
• Language: English
• Published: 14.03.2022
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/D1NJ05373F

Deep eutectic solvents (DESs) are emerging as a new generation of sustainable and green media. Concerning the same, the present work outlines the synergistic information provided from the thermophysical assessment on new betaine hydrochloride (BHC)-based DESs. In order to acquire stable and convenient DESs, BHC as a hydrogen bond acceptor (HBA) is combined with urea (U) as a primary hydrogen bond donor (HBD) and ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and glycerol (GLY) as secondary HBDs. A series of four different DESs, namely DES 1 (BHC : U : EG), DES 2 (BHC : U : DEG), DES 3 (BHC : U : TEG), and DES 4 (BHC : U : GLY) were optimized by a capricious molar ratio (1 : 4 : 2.5), which offers satisfactory liquid stability. Comprehensive spectral studies were used to investigate the molecular structure and the hydrogen bonding of the prepared DESs, while the important thermophysical properties viz. , thermal stability ( T dec ), density ( ρ ), speed of sound ( u ), viscosity ( η ), electric conductivity ( κ ), and refractive index ( n D ) were investigated at different temperatures. The effect of temperature on the measured thermophysical findings was correlated using a thermodynamic model. The viscoelastic and rheological findings revealed a considerable shift in the flow regime with varying HBDs in the prepared DESs. Furthermore, from an application viewpoint, these task-specific DESs were used for CO 2 capture, where the outcomes indicated that DES 2 (BHC : U : DEG) showed a high uptake of CO 2 at 0.0200 mol of CO 2 /mol DES, which increased to 0.0319 mol of CO 2 /mol DES in DES 2 in the presence of superbase (1,5-diazabicyclo[4.3.0]-non-5-ene (DBN)). Spectral studies indicated that CO 2 reacts with the -NH 2 /-OH centers of DES via R–O–COO − /–R–NH–COO − formation during CO 2 capture. Overall, the prepared DESs exhibit long-term performance in CO 2 capture, which qualifies them as prospective and suitable alternatives to ILs.