(480d) Materials for Sulphuric Acid Decomposition in the S-I Cycle

In 1972 the concept of Sulphur-Iodine (S-I) thermochemical hydrogen production was conceived by General Atomics. Since this time much research has investigated flowsheet design, and individual sections of the cycle, but identification of the materials required to produce a working/commercial system is still a challenge. In particular materials for the Sulphuric Acid decomposition section of the cycle; where temperatures exceed 800°C in the gas phase and >200°C for the liquid handling components. This report evaluates a range of specialized engineering materials to address the liquid Sulphuric Acid corrosion attack. At an isobaric condition of 5bar, a temperature range of 200°C to 400°C can be evaluated by adjusting the molar% of acid concentration.

Applying standard practice testing methods to the corrosion of materials in sulphuric acid can lead to erroneous results, as the acid becomes loaded with corrosion products – the level of corrosion attack depletes. To remove this affect from the analysis, a true-to-life condition, flowing system, is simulated by renewing the acid when data is collected. In addition, to ensure that the corrosion attack is maintained the level of corrosion products within the acid is also measured by titration. Intergranular boundary conditions are also given for the materials tested. Materials corrosion rates are presented in graphed form and conclusions are given for the future selection of materials for the decomposition and handling of sulphuric acid.

Conclusions of this paper are not only applicable to the S-I thermochemical cycle, but also the combining of sulphuric acid decomposition and electrolysis as in the hybrid cycle. Furthermore, the results will also be of interest to the broader sulphuric acid production industry and standards associations'.

Keywords: Sulphuric Acid, corrosion, silicon carbide, alumina, Sulphur-Iodine Cycle, hybrid cycle