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Sulphuric acid decomposition is the high temperature (850–900 °C) reaction step of sulphur based water splitting processes (Iodine–Sulphur and Hybrid-Sulphur processes) for hydrogen production. In this work, reaction kinetics and mass transfer data are generated experimentally, for sulphuric acid decomposition using chromium doped iron oxide, Cr–Fe2O3, catalyst in a packed bed reactor (PBR). Experiments are performed using catalyst powder, less porous catalyst particle (pellet) and high porous catalyst particle (foam), between 700 and 850 °C and 0.1–10 ml min−1 liquid feed flow rate. Activation energy and frequency factor of Cr–Fe2O3 catalyst obtained from the powder catalyst study are 74 kJ mol−1 and 183 m3 kg−1 s−1. Internal effectiveness factor ( η ) of pellet and foam, two industry types of Cr–Fe2O3 catalyst (5 mm size) are calculated from the experimental studies performed at external mass transfer resistance free regime. Internal effectiveness factor of pellet and foam obtained are 0.12 and 0.26 respectively, which shows strong pore diffusion resistance in these catalyst types. Overall effectiveness factor ( Ω ) for both the catalyst types (pellet and foam) are also obtained for the investigated range of temperatures and flow rates. Further, catalyst particle (pellet and foam) is modeled in COMSOL MULTIPHYSICS® simulation software to get an insight into concentration and temperature profiles. Significant concentration drop and smaller temperature drop are seen in less porous pellet. Small concentration drop and significant temperature drop are observed in porous foam, through simulation studies. Focus of future R&D is to optimise the size and porosity of Cr–Fe2O3 catalyst, for maximum effectiveness factor and thereby maximizing the reaction rate and conversion.

HIx processing section of Iodine-Sulphur (IS) thermochemical cycle dictates the overall efficiency of the cycle, which poses extremely corrosive HI–H2O–I2 environment, coupled with a very low equilibrium conversion (~22%) of HI to hydrogen at 450 °C. Here, we report the fabrication, characterization and operation of a 4-tube packed bed catalytic tantalum (Ta) membrane reactor (MR) for enhanced HI decomposition. Gamma coated clay-alumina tubes were used as supports for fabrication of Ta membranes. Clay-alumina base support was fabricated with 92% alumina (~8 μm particle size) and 8% clay (~10 μm particle size), sintered at a temperature of 1400 °C. An intermediate gamma alumina coating was provided with 4% polyvinyl butyral as binder for a 10% solid loading. Composite alumina tubes were coated with thin films of Ta metal of thickness 80% single-pass conversion of HI to hydrogen at 450 °C. The hydrogen throughput of the reactor was ~30 LPH at a 2 bar trans-membrane pressure, with >99.95% purity. This is the first time a muti-tube MR is reported for HIx processing section of IS process.

Bunsen reaction is one of the three reaction steps of iodine-sulfur process. In present study, Bunsen reaction is carried out in co-current reactor to identify effect of different operating conditions on concentrations of Bunsen reaction product mixture. Bunsen reaction studies have been done in tubular reactor, which is made of tantalum tube and stainless steel jacket, in 50–80 °C temperature range, 2–6 bar (g) pressure range. Feed flow rates are varied for HIx (mixture of hydroiodic acid, water and iodine) 1.2 l/h - 3 l/h, SO2 0.02 g/s – 0.24 g/s and O2 0.008 g/s −0.016 g/s. It has been observed that, increasing SO2 feed flow rate and pressure results in increased mole fraction of HI in HIx phase and H2SO4 in sulfuric acid phase. Increase in temperature increased the mole fraction of HI in HIx phase but decreased the mole fraction of H2SO4 in sulfuric acid phase. Increase in feed I2/H2O ratio and HIx feed flow rate, decreased the mole fraction of HI in HIx phase. Higher pressure improved the conversion of Bunsen reactants to products.

In iodine-sulfur (I-S) thermo-chemical process for hydrogen production, Bunsen reaction is studied to identify the role of different operating conditions on purity of Bunsen reaction product phases. The focus of this work is to find out the level of contamination in each of the Bunsen reaction product phases. Hydroiodic acid and iodine are contaminants in sulfuric acid phase and sulfuric acid is contaminant in hydroiodic acid phase. Enhancing the level of purity in two product phases will reduce the burden on purification steps in downstream of I-S process. Bunsen reaction has been studied in continuous co-current reactor made of tantalum in the range of 50–75 °C, 2–6 bar (g) with HIx (mixture of hydroiodic acid, water and iodine) flow rate of 0.8 l/h - 3.3 l/h, sulfur dioxide 0.06 g/s – 0.24 g/s & oxygen 0.008 g/s −0.016 g/s. At 4 bar (g), 70 °C with HIx and SO2 flow rates of 1.8 l/h and 0.24 g/s respectively, purity of sulfuric acid phase is maximum i.e. 99.85 mol percent. At 4 bar (g), 60 °C with HIx and SO2 flow rates of 1.5 l/h and 0.12 g/s respectively, purity in HIx phase is maximum i.e. 99.66 mol percent.

The iodine-sulphur (IS) thermo-chemical process is being studied as a potential process for production of hydrogen by water splitting. It consists of three chemical reactions: 1) Bunsen reaction, which is the acid production step, 2) sulphuric acid decomposition to produce oxygen; 3) hydrogen iodide decomposition to produce hydrogen. In this work, a detailed parametric study of the Bunsen reaction is presented, which was carried out in agitated reactor (ABR) in counter current mode of operation. Experiments have been carried out in the reactor at different temperatures by varying the sulphur dioxide (SO2) flow rate and partial pressure of SO2. Bunsen reaction rate and SO2 conversion are calculated experimentally from feed rate and scrubbing rate of SO2. It has been observed that the reaction rate and SO2 conversion increase with increase in SO2 flow, increase in SO2 partial pressure and decrease in temperature. 'Tanks-in-series' model, one of the non-ideal reactor models, has been proposed to describe the ABR reaction system. The model has been validated with experimental results. This approach can be useful for the design and scaling up of the agitated reactor.