Sustainable hydrogen production system with sulfur-water-organic materials by hydrothermal reaction

Engineered process for hydrogen generation from hydrogen sulfide ions in aqueous solution using solar energy with photocatalysis has been established. In order to design a complete closed loop of hydrogen production system, reacted sulfide ions have to be reduced to photocatalysis-active hydrogen sulfide ion. We focused on hydrothermal reaction of sulfur for reducing the reacted sulfide ions. But the oxidized sulfur species are occurred inevitably by the reaction. Thus alternative reducers are required to sulfur hydrothermal reaction for a complete closed loop of hydrogen production system. We studied sulfur-water-organic materials interaction, and particularly on the effective utilization of waste elemental sulfur. In this study, hydrothermal experiments of sulfur, water urea, and/or alcohols were carried out under atmospheric constituent condition and hypoxic condition at 200 °C. Experimental results show that maintaining solution in weak alkaline condition is important and alcohol compounds had a great role for reduction of sulfur. Elemental sulfur was completely reduced to hydrogen sulfide by the hydrothermal reaction of sulfur with urea and propanol under hypoxic condition. Those results indicate that it is possible to create sustainable sulfur cycle for hydrogen production system using hydrothermal reaction with organic compounds.