Experimental Measurement and Modeling of Methane Solubility in a Deep Eutectic Solvent (NaCl + Ethylene Glycol)1:16

Nowadays, deep eutectic solvents (DESs) are being investigated as environmentally friendly alternatives to traditional solvents. The solubility of methane in a DES plays a fundamental role in determining the overall methane/CO2 separation efficiency. Despite its significance, experimental data on methane solubility in DESs are limited. This study aims to experimentally determine the solubility of methane in a DES composed of 1 mol of NaCl and 16 mol of ethylene glycol using a high-pressure solubility apparatus. Solubility measurements were conducted at four isotherms, under pressures up to 3 MPa. For thermodynamic modeling, the Soave–Redlich–Kwong (SRK) equation of state (EoS) and the Peng–Robinson (PR) EoS were employed in conjunction with two mixing rules, namely, the conventional van der Waals (vdW) and the more advanced excess Gibbs energy mixing rules of Wong–Sandler (WS). Furthermore, the cubic plus association (CPA) EoS was applied in combination with the vdW mixing rules for thermodynamic modeling of methane in the investigated DES. Among all the thermodynamic packages, the combination of the PR EoS + WS mixing rules gave the best results with an average absolute relative deviation of 4.52%. Finally, Henry’s constant was determined from the experimental data, allowing for the subsequent calculation of the standard entropy, enthalpy, and Gibbs energy of the dissolution process.