Characterization of southern Taiwan red soils as a regenerable sorbent for sorption of hydrogen sulfide from coal gas with spectroscopic techniques

The purpose of this research is to use red soils as a high-temperature regenerable sorbent for sorption of hydrogen sulfide from coal gas and collocates with a series of spectroscopic apparatuses in order to investigate the structure changes after multiple sorption/regeneration processes. Results indicate that red soils could be reused after 10 multiple sorption/regeneration cycles and maintain approximately 80% sorption efficiency. With EDS and EA analyses, residual sulfur species are detected in the 10th regenerated red soils and exist with values of 0.6 and 0.33%, respectively. Undesired sulfur species including sulfide, sulfate and elemental sulfur are further identified by XPS spectroscopy. With the best regression fitting results, sulfate species is the dominative sulfur species, which occupies approximately 71% of residual sulfur. It is believed that these residual sulfur species are the major cause to result in red soils' deterioration after regeneration and reduce the sorption efficiency. Appreciable amounts of regeneration gases CO, CO₂ and SO₂ are detected by on-line FTIR spectroscopy. Their formation mechanisms are attributed to the different gas-solid reaction, one is the reaction of carbon and oxygen, and the other is FeS and oxygen. From the analysis of solid-state nuclear magnetic resonance spectroscopy (SSNMR), a significant change for ²⁷Al and ²⁹Si and it is established that a portion of aluminum is reformed into pentacoordinated structure. Formation of aluminosilicate is maybe another reason to result in deterioration as a result of the loss of surface area.