Tetraalkylammonium-based dicationic ionic liquids (ILs) for CO2 capture

Abstract

This investigation includes the synthesis and characterization of a new series of ionic liquids (ILs) based on the tetraalkylammonium dication for the absorption of CO₂, a step towards the development of more efficient and sustainable technologies. It was possible to synthesize amine-substituted PEG diacrylate by modifying poly(ethylene glycol) (PEG), which was then quaternized with 1-bromopentane to produce the IL PDBr. The other IL products, PDNTf₂, PDBF₄ and PDPF₆, were synthesized via the metathesis of PDBr with the appropriate salt. The synthesized products were characterized using various techniques, such as FTIR, ¹H and ¹³C NMR, elemental analysis, and density and viscosity meters, and evaluated as potential sorbents for CO₂ capture. DSC and TGA were used to examine the thermal properties of the ILs. As observed from their thermal degradation behavior, the ILs exhibited two-stage disintegration with thermal stability up to 150 °C. The pressure drop method was used to study the sorption capacity of the ILs towards CO₂. The sorption investigation showed that when the pressure is increased, the CO₂ absorption increases. Equilibrium is reached in 40 minutes, demonstrating a rapid absorption rate. The IL with the [BF₄]⁻ anion (PDBF₄) demonstrated a maximum sorption capacity of 0.577 mole fraction of CO₂, and can be regenerated and reused efficiently with less than 0.5% variation from its original absorption capacity. The CO₂ absorption capacity for the ILs with other anions follows the trend: Br ≈ NTf₂ < PF₆ < BF₄. This work shows that tetraalkylammonium-based dicationic ILs are adaptable, making them a suitable material for many applications, including sustainable CO₂ capture technology.