Reactivity and stability of different pyrites as sulfur carriers for chemical looping decomposition of H2S into H2 and S

Direct decomposition of H2S into H2 and S offers an attractive approach for the simultaneous recovery of H2 and S from an abundant and toxic waste gas. However, it still encounters challenges related to the thermal equilibrium limitations. Chemical looping decomposition of H2S into H2 and S presents a promising alternative, utilizing metal sulfides as sulfur carriers. This approach decouples the direct H2S decomposition into two-step reactions as the decomposition of sulfur carrier for S production and the sulfurization for H2 production, effectively overcoming the inherent thermodynamic constraints. Natural pyrite, a widely available mineral primarily composed of FeS2, is a potential candidate as the sulfur carrier. In this study, two low-cost pyrites were explored as sulfur carriers in the chemical looping decomposition of H2S. The decomposition, sulfurization and cyclic performance of different pyrites were experimentally investigated. During the decomposition process, pyrite converts into the FeS phase, releasing elemental sulfur gases and resulting in a more porous structure. Higher temperatures can promote pyrite decomposition and enhance sulfur production. During the sulfidation process, the influence of temperature is much stronger than the type of pyrite sulfur carriers on H2S conversion. Increasing sulfidation temperature significantly enhances H2S conversion, while higher H2S concentrations result in a decrease in H2S conversion. The sulfidation reactivity of pyrite sulfur carriers may be hindered by mass transfer resistance and mild kinetic activity. Additionally, both pyrite samples demonstrate stable performance during consecutive 20 cycle. Inert supports, such as SiO2 in natural pyrites, play a crucial role in maintaining structural stability and mechanical strength.