Thermodynamic study on carbon dioxide absorption in vinyl imidazolium–amino acid ionic liquids

Abstract

Vinyl imidazolium amino acid ionic liquids (AAILs) based on seven amino acids (L-lysine [L-Lys], l-arginine [L-Arg], l-alanine [L-Ala], glycine [Gly]), l-proline [L-Pro], l-histidine [L-Hist], and l-valine [L-Val]) were synthesized and characterized as carbon dioxide absorbers. The absorption of carbon dioxide (CO2) gas in these AAILs was measured by quartz crystal microbalance sensor (QCM) at over 283.15–313.15 K temperature range and pressures up to 4 bar. According to the sorption mechanism, the experimental CO2 absorption in AAILs was correlated by the “deactivated model”. The thermodynamic parameters including the Henry's law constant, reaction equilibrium constant, and enthalpy of physical sorption were used to calculate the AAILs application potential as CO2 capture. The CO2 absorption increased with pressure and decreased with temperature. The results manifest that absorption capacities of CO2 were in the sequence of [VBIm][L-Arg] > [VBIm][L-Lys] > [VBIm][L-His] > [VBIm][Gly] > [VBIm][L-Ala] > [VBIm][L-Val] > [VBIm][L-Pro]. Amongst the studied amino acids, the highest CO2 absorption capacity was obtained for [VBIm][L-Arg] due to the availability of more amino groups. Besides, CO2 absorbed chemically was confirmed by carbamate formation using FT-IR spectroscopy.