Solubility and Thermodynamic Parameters of H₂S/CH₄ in Ionic Liquids Determined by ¹H NMR

Natural gas remains an important global source of energy. Usually, sour gas from the well or refinery stream contains H₂S among other contaminants that should be removed to fulfill permissible standards of use. Despite the use of different gas-liquid sour gas upgrading technologies, ionic liquids (ILs) have been recognized as promising materials to remove H₂S from sour gas. However, data concerned with thermodynamic solution functions of H₂S in ILs have scarcely been reported in the literature. In this work, solution ¹H NMR spectroscopy was employed for quantifying H₂S soluble in [BMIM][Cl] and for gaining a better understanding of the H₂S-IL interaction. Experiments were carried out in a Young-Tap NMR tube containing a saturated solution of H₂S/CH₄/[BMIM][Cl] and recording spectra from 298 to 333 K. The thermodynamic solution functions, determined from the Van't Hoff equation, showed that solubility of the H₂S in the [BMIM][Cl] is an exothermic gas-liquid physisorption process (Δ_solH° = -66.13 kJmol^-1) with a negative entropy change (Δ_solS° = -168.19 JK^-1 mol^-1). ¹H NMR spectra of the H₂S/[BMIM][Cl] solution show a feature of strong solute-solvent interactions. However, solubility enthalpy is a fifth of the H-S bond energy value. Results from ¹H NMR spectroscopy also agree with those from the bench dynamic experiments.