Hydrogen production from a chemical cycle of H_2S splitting

摘要

The sulphur-iodine thermochemical water-splitting cycle (S-I cycle) developed for hydrogen production from water is fundamentally based on the following three chemical reactions:rnH_2SO_4 → H_2O + SO_2 + 0.5O_2, 2H_2O + SO_2 + I_2 → H_2SO_4 + 2HI, 2HI → H_2+I_2.rnThis paper proposes to replace the H2SO4 decomposition with a reaction between H_2S and H_2SO_4 and the replacement gives rise to a H_2S-splitting cycle that produces H_2 and elemental S from H_2S, shown as follows:rnH_2S + H_2SO_4 → S + SO_2 + 2H_2O, 2H_2O + I_2 + SO_2 → H_2SO_4 + 2HI, 2HI → H_2 + I_2.rnCombined with the reactions such as O_2 + S → SO_2,rnSO_2 + 0.5O_2 → SO_3, SO_3 + H_2O → H_2SO_4,rnthis new cycle cannot only produce more H_2 and extra H_2SO_4 but also facilitate flexible H_2 to H_2SO_4 production ratio. Thermodynamic analysis shows that the new cycle is more energy-efficient than the S-I cycle of water-splitting because a series of endothermic reactions in H2SO4 decomposition have been replaced with an exothermic reaction between H_2S and H_2SO_4. Technologies to be developed from this chemistry will be able to convert H_2S from sour or acid gas into H_2 and elemental S or H_2SO_4, which are more valuable than elemental S only, the product of the Claus process. In upgrading and refinery, the H_2 produced can be returned to use in hydrotreating; and in gas plants, H_2 from H_2S splitting is an alternative clean fuel. Environmentally, H_2 production based on this H2S-splitting cycle is carbon free.