How is CO₂ absorbed into a deep eutectic solvent?

Area of Science:

• Physical Chemistry
• Materials Science
• Environmental Science

Background:

• Deep eutectic solvents (DES) are promising for carbon dioxide (CO2) capture.
• Sustainable CO2 reduction is vital for preventing global climate change.
• Understanding CO2 solvation mechanisms in DES is key to optimizing their performance.

Purpose of the Study:

• To investigate CO2 absorption in choline chloride: ethylene glycol DES.
• To elucidate the roles of anions, cations, and hydrogen bond donors in CO2 solvation.
• To compare DES CO2 absorption mechanisms with those of ionic liquids.

Main Methods:

• Ab initio molecular dynamics simulations were performed.
• Simulations used the isothermal-isobaric ensemble.
• Studies were conducted at 1 MPa and 5 MPa at experimental densities.

Main Results:

• CO2 solvation is influenced by anion and hydrogen bond donor effects, with a minor cation effect.
• A competition exists between the anion (chloride) and hydrogen bond donor (ethylene glycol) for CO2 interaction.
• At lower pressures, ethylene glycol-CO2 interaction dominates; at higher pressures, chloride-CO2 interaction is dominant.

Conclusions:

• Choline chloride: ethylene glycol DES show potential as effective CO2 absorbents.
• The interplay between anions and hydrogen bond donors can be exploited for tunable CO2 absorption.
• DES offer advantages similar to ionic liquids for CO2 capture, with added benefits from hydrogen bond donors.