Amine functionalized deep eutectic solvent for CO₂ capture: Measurements and modeling

Deep eutectic solvents (DESs) have gained a great interest among researchers owing to their inherent advantages to become an adaptable alternative to ionic liquids (ILs) and common amine solutions for CO₂ capture. In the present study, we prepared five new three-component DESs by functionalization of choline chloride-ethanolamine (1:7, mol:mol) DES using different types of amines: diethanolamine (amine type 2), methyldiethanolamine (amine type 3), piperazine (amine type 2) as well as 1-(2-aminoethyl)piperazine (amine type 1 and 2). All of the prepared DESs are liquid at room temperature and their melting points were in the range of 265–276 K. The solubility of CO₂ in the studied DESs was measured at pressures up to 2 MPa and 298.15 K. The obtained experimental data were analyzed by the use of generic Redlich-Kwong equation of state (RK-EOS) model and Henry's law constant have been calculated from the obtained experimental data through the EOS correlation. All the studied DESs show chemical absorption of CO₂ which can be approved based on the excess enthalpy and Gibbs energy functions. FT-IR spectroscopy and ¹³C NMR verified the formation of carbamate in the CO₂ absorption process which revealed the chemisorption of CO₂ in the studied DESs. The ideal association model has been utilized to describe the excess thermodynamic functions and two different types of the chemical association have been detected AB2 and AB, (A refer to DESs and B to CO₂). Based on the obtained solubility data, the amines that enhanced the absorption capacity of choline chloride-ethanolamine (1:7) follow the trend as follows: piperazine > aminoethylpiperazine > methyldiethanolamine > diethanolamine. Therefore, piperazine can be considered as an absorption enhancer. The viscosity of DESs before and after CO₂ absorption as well as the thermal behavior of the DESs were also investigated.