Seeking top-performing absorbents with excellent structural stability and renewability to realize efficient removal of H 2 S from natural gas is of great importance. Here, the H 2 S absorption thermodynamic and kinetic properties by a non-aqueous liquid binary blend of monoethanolamine (MEA) and ethylene glycol (EG) was systematically studied. The addition of solvent EG not only improves the thermal stability but also reduces the viscosity of the system especially after H 2 S absorption. The absorption mechanism was revealed by the combination of experimental characterization and Density Functional Theory (DFT) calculations, which show that the absorption process is a proton transfer reaction. In addition, a quasi-primary kinetic model was used to describe the absorption kinetic behavior, with rate constants increasing with temperature and pressure. Reaction equilibrium thermodynamic model (RETM) fitting thermodynamic results showed that the enthalpy (ΔH) and entropy (ΔS) of the interaction of the absorbent with H 2 S was −40.72 kJ/mol and −114.71 J/mol/K, respectively. Most importantly, the optimum absorption temperature was calculated to be 287.80 K and the optimum desorption temperature was 386.62 K. Moreover, the desulphurization rate was verified to increase with decreasing temperature and increasing H 2 S partial pressure. Five cycles of absorption-desorption experiments were conducted at 313.15 K for absorption and 373.15 K for desorption in order to verify the good reuse properties of the absorbent. Considering the excellent thermal stability, low viscosity after H 2 S absorption, acceptable absorption capacity as well as good reversibility, it is believed that the MEA/EG blend has a significant potential in the field of desulfurization.
CO 2 and H 2 S are considered impurities in natural gas that moderate the pace of environmental health. Developing highly efficient and cost-effective absorbents is of significance for sweetening natural gas. Herein, four superbase protic ionic liquids (SPILs) were prepared in this study. Typical physical properties (density, viscosity, and decomposition temperature) were also examined at ambient pressure. These SPILs show low viscosity values at ranging from 5.1 cP to 18.3 cP at 313.2 K. The solubility of H 2 S (0–1.0 bar), CO 2 (0–1.0 bar), and CH 4 (0–5.0 bar) was systematically measured at temperatures in the range of 298.2 K to 333.2 K. Impressively, the absolute solubility of H 2 S under 0.1 bar was found to be located at 4.31–5.15 mol/kg at 313.2 K, which is the highest value obtained among the reported results in the literature. The ideal selectivity of H 2 S/CH 4 and CO 2 /CH 4 (H 2 S or CO 2 solubility at 0.1 bar vs CH 4 solubility at 1 bar) at 313.2 K are in the ranges of 367–653 and 92.4–240, respectively. The interaction mechanism we explored was characterized by NMR and FT-IR spectroscopy. Thermodynamic parameters, such as enthalpy, Gibbs free energy, and entropy of dissolution were calculated from the temperature dependent solubility using the “deactivated model”. These SPILs are promising alternative candidates for the simultaneous removal of H 2 S and CO 2 in natural gas upgrading.
Developing environmental benign and efficient solvents for the natural gas sweetening is of great significance to the development of green chemistry. However, there is no task-specific deep eutectic solvents (DESs) for H 2 S absorption so far. Herein, we have for the first time developed a series of task-specific DESs for the selective separation of H 2 S, in which quaternary ammonium salts with free tertiary amine groups are designed as hydrogen bond acceptors (HBAs) and azoles as hydrogen bond donors (HBDs). Density, viscosity, and thermal decomposition temperature, as well as the solubility of H 2 S (0–1.0 bar), CO 2 (0–1.0 bar), and CH 4 (0–5.0 bar) were systematically determined. NMR paired with theoretical calculations are applied to characterize the interaction mechanism of H 2 S and DESs. A reaction equilibrium thermodynamic model (RETM) with a 1:2 stoichiometric reaction mechanism was screened to correlate H 2 S solubility data. It is found that [C 4 -TMHDA][Cl]-Im could achieve up to 0.996 mol H 2 S per mol DES at 303.2 K and 1.0 bar. Moreover, the captured H 2 S can be easily stripped out at elevated temperature and reduced pressure, with negligible loss in H 2 S capacities during four absorption–desorption cycles. The results obtained in this work indicate that these DESs are promising candidates for efficient and selective separation of H 2 S and CO 2 from natural gas. This work provides novel insights into the future design of high-performance task-specific DESs for the capture of H 2 S.
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