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