Solubility of CO2 and CH4 in sterically hindered amine-based deep eutectic solvents

Decarbonization of methane is essential in many applications such as biogas and natural gas. Solvents with high selectivity towards CO2 are required for the upgradation of biogas and natural gas. Deep eutectic solvents (DESs) sharing green properties of ionic liquids have shown the ability to capture CO2 selectively. In this work, we have synthesized four novel secondary amine-based DESs using quaternary ammonium salt as hydrogen bond acceptor. The CO2 and CH4 uptake of the synthesized DESs were experimentally investigated. The viscosities of DESs were also evaluated and correlated with the Vogel-Fulcher-Tammann (VFT) and the Arrhenius equation. The modified Lydersen-Joback-Reid method was used for the critical properties estimation of synthesized DESs. All the synthesized DESs have shown high CO2 absorption and relatively very low CH4 absorption indicating their high selectivity towards CO2. The experimental DES-CO2 and DES-CH4 vapor-liquid equilibria were successfully correlated with the NRTL model and Peng-Robinson equation of state.