Abstract
The potential of 1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]Fe(III)Cl4) for replacing an iron(III) chelate catalytic solution in the catalytic oxidation of H2S is attributed to its no side reaction and no degradation of the chelating agent. The catalytic oxidation product of water in non-aqueous [bmim]Fe(III)Cl4 possibly has an influence on the oxidative absorption of H2S. Water and hydrophobic [bmim]Fe(III)Cl4 mixtures at water volume percents from 40% to 70% formed separate phases after srirring, without affecting the oxidative absorption of hydrogen sulfide. Then, studies on the properties of homogeneous [bmim]Fe(III)Cl4–H2O mixtures at water volume percents in the range of 5.88–30% and above 80% reveal that these mixtures are both Brønsted and Lewis acids at vol % (H2O) ≤ 30%, and only Lewis acids at vol % (H2O) ≥ 80%. Raman spectra showed that [bmim]Fe(III)Cl4 was the dominating species at vol % (H2O) ≤ 30%, in contrast, [bmim]Fe(III)Cl4 decomposed into FeCl3·2H2O and [bmim]Cl at vol % (H2O) ≥ 80%. Further research on oxidative absorption of H2S by homogeneous [bmim]Fe(III)Cl4–H2O mixtures demonstrated that [bmim]Fe(III)Cl4 was reduced by H2S to [bmim]Fe(II)Cl4H and FeCl3·2H2O was reduced to FeCl2, at the same time, H2S was oxidized to S8. In addition, the decrease in acidity caused by increasing the water content increased the weight percent of absorbed H2S, and decreased volatile HCl emissions. However, it is difficult to prevent the suspended S8 generated at vol % (H2O) ≥ 80% from the formation of sulfur blockage. Therefore, oxidative absorption of H2S by [bmim]Fe(III)Cl4–H2O mixtures is feasible at vol % (H2O) < 80% without sulfur blockage.
Highlights
The potential of 1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]Fe(III)Cl4 ) for replacing an iron(III) chelate catalytic solution in the catalytic oxidation of H2 S is attributed to its no side reaction and no degradation of the chelating agent
The acidity of homogeneous [bmim]Fe(III)Cl4 –H2 O mixtures may change with the increment of water
As the x(H2 O) in homogeneous mixtures was increased from lower concentrations (5.88–30%) to higher concentrations (≥80%), the colour of the mixture changed from dark brown to brownish yellow
Summary
The potential of 1-butyl-3-methylimidazolium tetrachloroferrate ([bmim]Fe(III)Cl4 ) for replacing an iron(III) chelate catalytic solution in the catalytic oxidation of H2 S is attributed to its no side reaction and no degradation of the chelating agent. [bmim]Fe(III)Cl4 (1-butyl-3-methylimidazolium tetrachloroferrate) is an ionic liquid with unusual properties, including low volatility, high thermal stability, high hydrophobicity [1], low viscosity [2], and low surface tension [3]. There has been a considerable recent interest in the use of [bmim]Fe(III)Cl4 as an alternative to an iron(III) chelating solution for catalytic oxidation of H2 S. Iron(III) chelating solutions have several disadvantages that are associated with liquid phase oxidation processes, including degradation of the chelating agent [7] and sulfur oxo-acid salt formation [8]. Catalytic-oxidation of H2 S by [bmim]Fe(III)Cl4 differs from other heterogeneous catalytic reactions in that it is comprised of two simultaneous reactions that occur in the same or a separate vessel [10]
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