A quantum chemistry study for ionic liquids applied to gas capture and separation

Area of Science:

• Computational Chemistry
• Environmental Science
• Materials Science

Background:

• Greenhouse gas emissions drive global climate change.
• Carbon capture and storage (CCS) using amine-based solvents is a key mitigation strategy.
• Ionic liquids (ILs) are increasingly explored as advanced solvents for CCS applications.

Purpose of the Study:

• To evaluate the interactions between various gases (CO2, SO2, H2S) and the components of ionic liquids (cations and anions).
• To investigate the influence of cation-anion interactions on gas binding affinity.
• To identify promising ILs for efficient gas capture.

Main Methods:

• Quantum chemical calculations were performed using the B3LYP/6-311+G** level of theory and the M06-2X functional.
• Dispersion effects were explicitly considered in the calculations.
• Various IL systems were studied, including imidazolium, tetraalkylammonium, and tetraalkylphosphonium cations with different anions, with a focus on [THA][Tf2N].

Main Results:

• The availability of the anion for gas interaction increases as the cation-anion interaction weakens.
• Tetrahexylammonium bis(trifluoromethanesulfonyl)imide ([THA][Tf2N]) exhibited a significant binding energy of -274.89 kJ/mol.
• The study analyzed interactions between gases and diverse IL structures, including variations in alkyl chain length.

Conclusions:

• Weakening cation-anion interactions in ILs can enhance their gas capture capabilities.
• [THA][Tf2N] demonstrates strong energetic potential for gas capture applications.
• Computational analysis provides valuable insights into designing effective ILs for CCS.