(511i) Effect of Dopant Modification in Iron Sulfide-Based Sulfur Carrier for Hydrogen Production from Hydrogen Sulfide in a One-Reactor Cyclic Sulfur Looping Scheme

Hydrogen sulfide (H₂S) is a hazardous pollutant, responsible for undesired material corrosion and catalyst poisoning. Emissions from industrial activities, especially in the oil and gas processing industries primarily contribute towards H₂S generation. Claus process is a widely adopted technology that decomposes H₂S into sulfur and steam. However, it is constrained by various drawbacks such as reduced sulfur recovery due to unfavorable thermodynamics, huge capital cost, and low energy efficiency. More importantly, the process consumes Hcontent of H₂S into low-value steam due to its oxidative chemistry.

In this work, a one-reactor cyclic sulfur looping scheme is developed for decomposition of H₂S into valuable hydrogen (H₂) and elemental sulfur (S) using iron sulfide (FeS) as a sulfur carrier. It consists of two sub-steps—sulfidation and regeneration wherein FeS simultaneously decomposes H₂S into H₂, producing sulfur rich phase–FeS_x (where, x>1) and the captured sulfur is then removed during regeneration step by decomposing FeS_x into FeS in inert atmosphere. The scheme significantly reduces the requirement of processing units and overall energy requirement as compared to the Claus process. To improve upon the low reactivity of the sulfur carrier, FeS is modified by incorporating a low percentage (2%) of molybdenum (Mo) dopant which induces electronic structural changes while preserving phase integrity of FeS. The reactivity and recyclability performance of the sulfur carriers is tested using thermogravimetric analyzer and fixed bed setup and solid characterization techniques such as X-ray diffraction (XRD) and Scanning electron microscope (SEM) are used to understand the changes in the solid phases. With dopant modification, a dramatic increase of ~24% in sulfur uptake is obtained as compared to undoped sulfur carriers. Density functional theory (DFT) calculations are performed to investigate the reaction pathways, energetics, and electronic structures. Results from DFT pointed out that surface hydrogen diffusion is the rate-determining step for sulfidation of FeS, which can be significantly promoted through Mo dopant modification. Our findings demonstrate a novel approach for H₂S utilization and guide the future sulfur carrier design.