Design of Ionic Liquids for Fluorinated Gas Absorption: COSMO-RS Selection and Solubility Experiments

Area of Science:

• Environmental Chemistry
• Materials Science
• Chemical Engineering

Background:

• Fluorinated gases (F-gases), particularly hydrofluorocarbons (HFCs), pose significant risks to the atmosphere due to their high global warming potential.
• Efficient separation and recycling technologies for HFCs are crucial for climate change mitigation and managing end-of-life refrigeration and air conditioning equipment.
• Difluoromethane (R-32) and 1,1,1,2-tetrafluoroethane (R-134a) are key HFCs requiring effective capture strategies.

Purpose of the Study:

• To investigate the potential of ionic liquids for capturing R-32 and R-134a.
• To analyze solute-solvent interactions and predict Henry's constants for these F-gases in various ionic liquids using the COSMO-RS method.
• To experimentally validate the absorption capacities of the most promising ionic liquids.

Main Methods:

• Utilized the COSMO-RS method to screen over 600 ionic liquids for interactions with R-32 and R-134a, predicting Henry's constants.
• Selected the top three performing ionic liquids based on COSMO-RS calculations.
• Measured F-gas absorption equilibrium isotherms using gravimetric and volumetric experimental techniques.

Main Results:

• COSMO-RS predictions showed good agreement with experimental absorption equilibrium isotherm data.
• Tributyl(ethyl)phosphonium diethyl phosphate, [P2444][C2C2PO4], exhibited the highest absorption capacities in both molar and mass units among the tested ionic liquids.
• Trihexyltetradecylphosphonium glycinate, [P66614][C2NO2], and trihexyl(tetradecyl)phosphonium 2-cyano-pyrrole, [P66614][CNPyr], demonstrated competitive absorption capacities.

Conclusions:

• Ionic liquids are effective absorbents for capturing R-32 and R-134a, contributing to F-gas mitigation strategies.
• The selected ionic liquids, particularly [P2444][C2C2PO4], offer high absorption capacities for targeted F-gas separation.
• Future research should focus on industrial-scale process simulations to evaluate the performance of these ionic liquids, considering properties like viscosity and heat capacity.