Corrosion resistance of structural materials in high-temperature aqueous sulfuric acids in thermochemical water-splitting iodine–sulfur process

• Published in: International journal of hydrogen energy 2013-05, Vol.38 (16), p.6577-6585
• Main Authors: Kubo, Shinji, Futakawa, Masatoshi, Ioka, Ikuo, Onuki, Kaoru, Yamaguchi, Akihisa
• Format: Article
• Language: English
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Corrosion; Energy; Exact sciences and technology; Fuels; High silicon iron; Hydrogen; Silicon carbide; Sulfuric acid; Sulfur–iodine process; Thermochemical process
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2013.01.106

Very harsh environments exist in the iodine–sulfur process for hydrogen production. Structural materials for sulfuric acid vaporizers and concentrators are exposed to high-temperature corrosive environments. Immersion tests were carried out to evaluate the corrosion resistance of ceramics and to evaluate corrosion-resistant metals exposed to environments of aqueous sulfuric acids at temperatures of 320, 380, and 460 °C, and pressure of 2 MPa. The aqueous sulfuric acid concentrations for the temperatures were 75, 85, and 95 wt%, respectively. Ceramic specimens of silicon carbides (SiC), silicon-impregnated silicon carbides (Si–SiC), and silicon nitrides (Si3N4) showed excellent corrosion resistance from weight loss measurements after exposure to 75, 85, and 95 wt% sulfuric acid. High-silicon irons with silicon content of 20 wt% showed a fair measure of corrosion resistance. However, evidence of crack formation was detected via microscopy. Silicon enriched steels severely suffered from uniform corrosion with a corrosion rate in 95 wt% sulfuric acid of approximately 1 g m−2 h−1. Among the tested materials, the ceramics SiC, Si–SiC, and Si3N4 were found to be suitable candidates for structural materials in direct contact with the considered environments. ► We carried out immersion tests to evaluate the corrosion resistance of materials. ► SiC, Si–SiC, Si3N4, high-silicon irons, and silicon enriched steels were examined. ► Test samples were exposed to aqueous H2SO4 at 2 MPa and near bubbling points. ► A broad range of concentrations, 75 wt%, 85 wt% and 95 wt%, of H2SO4 were used. ► Silicon containing ceramics showed excellent corrosion resistance.