Acidity Scale in a Choline Chloride- and Ethylene Glycol-Based Deep Eutectic Solvent and Its Implication on Carbon...

Area of Science:

• Physical Chemistry
• Green Chemistry

Background:

• Deep eutectic solvents (DESs) offer tunable properties for chemical applications.
• Understanding acid-base behavior and gas absorption in DESs is critical for their industrial implementation.

Purpose of the Study:

• To establish an equilibrium acidity (pKa) scale for Brönsted organic acids in a choline chloride/EG-based DES.
• To investigate the CO2 absorption capabilities and kinetics in functionalized DESs.
• To correlate DES properties with acid-base behavior and CO2 capture efficiency.

Main Methods:

• Ultraviolet-visible (UV-Vis) spectroscopy was employed to determine pKa values.
• Acidity scales were established for 16 Brönsted organic acids in [Ch][Cl]:2EG.
• Carbon dioxide absorption capacity and kinetics were measured for various anion-functionalized DESs ([Ch][X]:2EG).

Main Results:

• An acidity scale spanning 6 pKa units was established in the [Ch][Cl]:2EG DES, comparable to aqueous systems.
• The solvent properties of [Ch][Cl]:2EG differ significantly from conventional molecular solvents.
• CO2 absorption capacity in DESs is directly correlated with the basicity of the constituent anion ([X]), with stronger basicity yielding higher absorption.

Conclusions:

• The [Ch][Cl]:2EG DES provides a versatile medium for studying acid-base equilibria.
• The anion's basicity is a key factor governing CO2 absorption in functionalized DESs.
• These findings support the development of DESs for efficient CO2 capture technologies.