Phase separation characteristics of the Bunsen reaction when using HIx solution (HI–I2–H2O) in the sulfur–iodine hydrogen production process

•Bunsen reaction using the HIx solution was investigated on several parameters.•The amount of H2SO4 that separated into the H2SO4 phase was very small.•A method to improve the separation of the H2SO4 phase solution was proposed.

To continuously operate an integrated sulfur–iodine (SI) hydrogen production process, the HIx solution (HI–I2–H2O) could be recycled from the HI decomposition section as a reactant in the Bunsen reaction section. In this study, the temperature, iodine content and water content were varied to identify the phase separation characteristics of products from the Bunsen reaction using the HIx solution with SO2. Increasing the temperature increased the volume of the H2SO4 phase solution and decreased the impurity content in each phase. Increasing the iodine feed concentration somewhat decreased the volume of the H2SO4 phase solution, although the density difference between the phases increased. The amount of H2SO4 that separated into the H2SO4 phase was very small under most of these conditions, which significantly hindered the continuous operation of the integrated SI process. The feed of additional water in the separation step was suggested to improve the separation performance of the H2SO4 phase solution while minimizing side reactions.