Kinetic and mechanism of CO2 adsorption by ionic liquids (ILs) were studied, theoretically. The studied ILs are composed of 1-ethyl-3-methylimidazolium [Emim] as the cation with a general formula of the [Emim][X] (X=Gly-, Ala-, Lys-, Arg-). To investigate the alkyl chain length and the number of the amine group effects on the CO2 adsorption, different amino acid anions were chosen. On the basis of the enthalpy changes during the CO2 capture, a chemisorption nature is confirmed. An increase in the number of the amine (-NH2) groups in the ILs structures, accelerates the CO2 adsorption (Ea[Emim][Arg]=125.72 kJ.mol-1). On the other hand, a comparison between the activation energies, obtained in the cases of the [Emim][Ala] and [Emim][Gly], shows only a small difference due to alkyl chain length increment (3.21kJ.mol-1). This behavior may be related to an enhancement in the steric hindrance of the alkyl chain because of its interferences with CO2. Donor-acceptor interactions and C-N bond formation were investigated by natural bond orbital analysis. Moreover, topological studies shows a covalent nature for the C-N bond critical point showing that CO2 capture is a chemisorption process. Finally, on the basis of different analyses, [Emim][Arg] is proposed as the best candidate for CO2 adsorption form the kinetic and thermodynamic viewpoints.

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