Evaluation of materials of construction for the sulfuric acid decomposition section in the sulfur-iodine (S-I) cycle for hydrogen production: Some preliminary studies on selected materials

Water splitting by Sulfur-Iodine (S-I) cycle is one of the promising thermochemical processes for hydrogen production due to its high efficiency. The decomposition of H2SO4 to produce SO2 is the reaction with the highest energy demand in the S-I cycle and it shows a large kinetic barrier. Sulfuric acid is highly corrosive and its endothermic decomposition needs elevated temperatures (>800 degrees C). Henceforth, before the scale-up of the process plant there is a need to explore various materials of construction under very harsh acidic environments and phase changing conditions. Corrosion studies on some of the possible materials of construction (SS-304, SS-310, SS-316, Inconel-800, Alloy-20, Inconel-600, Incoloy-800H, Hastelloy C-276) were performed in detail and the most corrosion resistant material is suggested for the construction of sulfuric acid decomposition unit. The studies were performed at low temperatures (60 degrees C and 120 degrees C) as well as at high temperatures (700 degrees C, 800 degrees C and 900 degrees C). The corrosion rates were determined using weight loss method at low as well as high temperature and by using electrochemical method at low temperature (80 degrees C). The phase changing condition was more severe and resulted in higher corrosion rate. Hastelloy C-276 showed the least corrosion rate.Graphical AbstractSYNOPSIS In order to identify the suitable materials of construction for sulfuric acid decomposition in the S-I cycle, corrosion rates of different materials were determined. Materials were exposed to the various phases of sulfuric acid. The phase changing conditions had the most adverse effect on the materials.