Synthesis and Characterization of Amino Acid-Based Ionic Liquids for Selective Absorption of CO₂ Using Liquid Foam Bed and Semi-Batch Reactors

Carbon dioxide (CO₂) emissions are produced by the combustion of fossil fuels for power generation, automobiles, and other major industrial processes. Hence, there is a need for efficient CO₂ absorption using advanced materials and reactor systems within the framework of carbon capture and storage technologies. This work emphasizes the synthesis and characterization of amino acid-based ionic liquids (AAILs) for CO₂ (99.99% pure) absorption via a liquid foam-bed reactor (FBR) and semi-batch equilibrium studies (SBES). Seven different AAILs, namely [TETA][ALA], [TETA][LYS], [TETA][GLU], [TETA][ASP], [TETA][GLN], [TETA][MET], and [TETA][PHE], were newly synthesized. The AAILs were characterized using FTIR and Raman spectroscopy and ¹H and ¹³C NMR spectroscopy to confirm their formation. Physical properties such as viscosity and density were also presented. The highest and lowest densities of 1.1709 and 1.0646 g cm⁻³ were observed for [TETA][ASP] and [TETA] [ALA], respectively, among the synthesized AAILs. The application of AAILs in FBR and SBES for CO₂ absorption was evaluated under different experimental conditions. Parameters such as initial concentration, surfactant, pH, and AAIL regeneration were studied. [TETA] [LYS] gave the highest moles of CO₂ absorbed per mole of [TETA][LYS] used; the highest mole ratios of 0.442, 0.172, and 0.112 (dry basis) were observed at initial concentrations of 500, 300, and 100 mmol CO₂, respectively. Finally, the highest mole ratio of CO₂ per mole of [TETA][GLU] was 0.166, followed by 0.133 for [TETA][ALA], during desorption studies.