Sustainable and enhanced hydrogen production from biomass through sulfur redox cycle using georeactor

This study proposes a new method of producing hydrogen which uses organic compounds as raw material and involves sulfur redox cycle, through utilization of georeactor as direct application of geothermal energy. This method consists of two sections of a cycle: (1) hydrogen production from an alkaline aqueous solution at subcritical conditions of water, where sulfide anions, HS ^- and S ^2- act as reducing agents of water, and (2) sulfide anions regeneration at much lower temperatures, where an organic compounds derived from biomasses act as reducing agents of oxidized sulfur-containing- compounds formed in the first section. Hydrogen production was observed at ≥280°C and corresponding saturated vapor pressure in a 60 minutes reaction of sodium sulfide aqueous solution. Sulfide anions were able to be regenerated from the solution after hydrogen production at 300°C, at ≥60°C in a 10 minutes reaction, using glucose as the reducer. A hydrogen production through the sulfur redox cycle was also demonstrated by following procedure: 1 ^st hydrogen production - sulfide anions regeneration - 2 ^nd hydrogen production, where the hydrogen production and sulfide anions regeneration were conducted at 300°C and 105°C, respectively. Considering glucose as the raw material, results indicated that hydrogen production from 1 mol glucose was greater than that by hydrothermal gasification at much higher temperatures up to 500°C.