Efficient capture of low partial pressure H2S by tetraethyl ammonium amino acid ionic liquids with absorption-promoted solvents

Abstract

To capture H₂S from gas mixtures, ionic liquids (ILs), especially functional ILs, are regarded as novel absorbents and can absorb a large amount of H₂S at high pressures. However, the solubility of dilute H₂S in functional ILs is still very low and the viscosities of H₂S-absorbed ILs are very high resulting in long absorption equilibrium times. To enhance the solubility and reduce the equilibrium time, we designed mixtures of functional ILs, tetraethyl ammonium amino acids, and ethylene glycol (EG) to capture dilute H₂S of 0.005 MPa. It has been found that these mixtures can absorb a large amount of H₂S from mixed gas, and EG content, temperature, H₂S mole fraction and type of ILs have significant influence on the absorption. At 40 °C, the solubility of H₂S in the mixture can reach up to 2.36 mol H₂S per kg mixture. EG in the ILs mixtures not only decreases the viscosity of ILs before and after the absorption, but also enhance the absorption capacity of H₂S in ILs. Low temperatures, high H₂S partial pressures and low pK_b of –NH₂ (or –NH) in amino acids formed the anion of ILs have positive effects on H₂S absorption in the mixtures. The mechanism of H₂S absorption by functional IL and EG mixtures has also been proposed.