Tuning CO₂ Absorption in Hydrophobic Protic Ionic Liquids via Temperature and Structure

Area of Science:

• Chemical Engineering
• Materials Science
• Environmental Science

Background:

• Conventional amine-based solvents (e.g., MEA, DEA) for CO2 removal face challenges like high energy demand, degradation, and corrosion.
• Developing alternative CO2 capture solvents is crucial for mitigating greenhouse gas emissions.

Purpose of the Study:

• To investigate novel hydrophobic protic ionic liquids (HPILs) for efficient CO2 absorption.
• To evaluate the performance of HPILs as alternatives to traditional amine solvents.

Main Methods:

• Synthesis of HPILs with ammonium cations and bis(trifluoromethane)sulfonylimide ([Tf2N]-) anion.
• CO2 absorption measurements using the pressure-drop method.
• Analysis of CO2 solubility, selectivity over methane (CH4), and recyclability.

Main Results:

• CO2 solubility is pressure-dependent (increases with pressure) and temperature-dependent (decreases with temperature).
• [BEHA][Tf2N] demonstrated the highest CO2 capacity at 298.15 K (1-20 bar), correlating with its free volume.
• All studied ILs showed superior CO2 selectivity over CH4, and [BEHA][Tf2N] maintained structural integrity over two absorption cycles.

Conclusions:

• Hydrophobic protic ionic liquids are effective for CO2 capture, offering improved performance over conventional solvents.
• [BEHA][Tf2N] is a promising candidate for CO2 removal applications due to its high capacity, selectivity, and recyclability.