Recovery of elemental sulfur direct from nonferrous flue gas by a low-temperature Claus process with H2S as the interim reducer

Abstract

Direct reduction of high concentrations of SO2 from flue gases with oxygen to produce elemental sulfur (S8) is a promising pathway, that can realize sulfur resource recycling economically and storage avoiding the expensive SO2 pre-separation procedure. However, the process is significantly restricted by the O2 oxidation in flue gas and the traditional reducing gases can hardly work efficiently because of the excessive consumption by O2. In this study, we developed a low-temperature Claus process (LTCP) to reduce SO2 to S8 in the presence of O2 (5 vol%), and the interim production of H2S was employed as the reducer carrier, which can be efficiently re-produced by the reaction of S8 with H2 or CO thereafter. Results indicated that LTCP exhibited 97.2% S8 yield with the stoichiometric ratio at 150 °C and 5 vol% of oxygen content, which were both far higher than those for H2 or CO as the reducing gases at 350 °C. Further increasing the SO2 to H2S ratios to 1:1, almost 100% of H2S can be used to selectively reduce SO2 by Claus reaction at lower temperatures, and the slip H2S can be completely suppressed. As the catalyst and the temporary storage for S8 deposit, Al2O3 shows the best performance compared with other supported metal oxide and sulfide catalysts, and the sulfur capacity even achieves 432 mg(S)/g(Cat) with only 15% breakthrough. Meanwhile, LTCP also demonstrates excellent off-line temperature-swing regeneration performance, and part of the recovered S8 can be readily used to produce H2S. These promising results can officiously resolve the intractable problem of O2 oxidation and enable sulfur recovery directly from any nonferrous smelting and other flue gases with high concentrations of SO2.