Hydrogen Generation from Hydrogen Sulfide Decomposition

We propose a new method for the processing of hydrogen sulfide to create elemental sulfur and hydrogen gas. The process is based on a thermochemical cycle that leverages differences in temperature and reaction conditions to accomplish the thermodynamically unfavorable hydrogen sulfide decomposition over two reaction steps. First, hydrogen sulfide is reacted with iodine in aqueous conditions to produce dissolved hydroiodic acid and elemental sulfur. The sulfur is filtered out and the concentrated hydrogen iodide and water mixture is vaporized. The hydrogen iodide is then catalytically decomposed to hydrogen gas and iodine, which are flash separated. Overall, the two reaction and separation steps combine to accomplish the decomposition of hydrogen sulfide to hydrogen and elemental sulfur. This proposed process is similar to ideas put forth in the 1980s and 1990s by Kalina, Chakma, and Oosawa, but makes use of more recently discovered thermochemical hydrogen iodide decomposition methods and catalysts rather than electrochemical or photoelectrochemical methods.

This process is especially useful when the hydrogen sulfide was created by the reaction of hydrogen with sulfur-rich hydrocarbons during hydrodesulfurization. By recovering and recycling the hydrogen gas originally used to desulfurize the hydrocarbon, the amount of hydrogen gas needed to treat a sulfur-rich hydrocarbon is dramatically reduced. As larger quantities of sulfur-rich resources are extracted, methods to efficiently desulfurize hydrocarbons are increasingly important. Further, this process is inherently carbon neutral which is an advantage over steam reforming, the current main source of hydrogen gas.

A process model was created to explore the viability of the process. The model suggests that hydrogen could be profitably generated in processes with a maximum temperature of just 300 degrees Celsius. This implies that the heat required for the decomposition of hydrogen sulfide could be supplied by solar concentrators or heat integration with other process units. Process units in the model were defined by literature and experimental results.