Novel Fe-Mn-Zn-Ti-O mixed-metal oxides for the low-temperature removal of H2S from gas streams in the presence of H2, CO2, and H2O

The efficiency of Fe-Mn-Zn-Ti-O mixed-metal oxides of varying composition prepared by sol-gel methods toward removal of H2S from a gas mixture containing 0.06 vol% H2S, 25 vol% H2, 7.5 vol% CO2, and 1-3 vol% H2O was studied in the 25-100 °C range. In particular, the effects of the Fe/Mn molar ratio in the Fe-Mn-Zn-Ti-O solids on the H2S uptake and regeneration performance of the solids were studied. The nominal chemical composition (metal mol%) of the Fe-Mn-Zn-Ti-O solids was found to strongly influence the chemical composition, particle size, and morphology of the crystal phases formed. It was found that the 5 Fe-15 Mn-40 Zn-40 Ti-O mixed-metal oxide provides the highest H2S uptake as fresh and after regeneration in 20% O2/He gas mixture in the 500-750 °C range compared with the other solids investigated. It was also found that 5 Fe-15 Mn-40 Zn-40 Ti-O exhibits higher H2S uptake than a commercial Ni-based H2S adsorbent in the 25-50 °C range. In particular, a three times greater H2S uptake at 25 °C compared with that on the commercial adsorbent was found. The effectiveness of the regeneration procedure of 5 Fe-15 Mn-40 Zn-40 Ti-O solid after complete sulfidation was found to be in the 48-82% range, depending on the sulfidation temperature and regeneration conditions applied. A detailed characterization of the fresh, sulfided, and regenerated 5 Fe-15 Mn-40 Zn-40 Ti-O and 20 Fe- 40 Zn-40 Ti-O solids, which exhibited the best and worst H2S uptake performance, respectively, using BET, XRD, Raman, XPS, and Mössbauer techniques revealed important information on the sulfidation mechanism. The present work provides new fundamental knowledge that could trigger further research efforts toward the development of alternative mixed metal oxides not based on toxic chromia (Cr2O3-Fe2O3/α-Al2O3), which is used today in several industrial plants for the catalytic oxidation of H2S (Claus process).