Vapor-liquid equilibrium of carbon dioxide solubility in a deep eutectic solvent (choline chloride: MDEA) and a mixture of DES with piperazine-experimental study and modeling

In recent decays, many investigators have carried out the CO2 absorption in ionic liquids, but these green solvents are expensive and hard to prepare. In recent years, researchers have introduced deep eutectic (DES) solvents composed of a hydrogen bond donor and a hydrogen bond acceptor. DES melting point is usually lower than the ideal solution of its constituents' components and is in the liquid phase at room temperature. In this work, we have measured CO2 solubility in a deep eutectic solvent composed of choline chloride and methyldiethanolamine (MDEA) in a molar ratio of 1–6. We carried out experiments at 323.15, 333.15, and 343.15 K within the 1–50 bar pressure range. Besides, we added piperazine (Pz) as a physical solvent at 5, 10, and 15 wt% to the DES. Based on the obtained results, we observed enhancing pressure and reducing temperature led to increasing CO2 absorption. Also, increasing piperazine caused to intensify the CO2 absorption in the mixture of the DES + Pz system. Finally, we used a thermodynamic approach for the computation of the vapor–liquid equilibria of the present systems. We applied the Peng-Robinson (PR) equation of state to calculate the gas fugacity coefficient in the vapor phase. The non-random two-liquid (NRTL) activity coefficient model was used to compute the non-ideality of the liquid mixture. The modeling results were in very good agreement with the experimental data.