Kinetic study and modeling of sulphuric acid decomposition using Cr–Fe2O3 catalyst for sulphur based water splitting processes

Abstract

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.