In this work, a complete thermodynamic study of the first step of the Mn 2O 3/MnO thermochemical cycle for solar hydrogen production has been performed. The thermal reduction of Mn 2O 3 takes place through a sequential mechanism of two reaction steps. The first step (reduction of Mn 2O 3 to Mn 3O 4) takes place at teomperatures above 700 °C, whereas the second reaction step (reduction of Mn 3O 4 to MnO) requires temperatures above 1350 °C to achieve satisfactory reaction rates and conversions. Equilibrium can be displaced to lower temperatures by increasing the inert gas/Mn 2O 3 ratio or decreasing the pressure. The thermodynamic calculations have been validated by thermogravimetric experiments carried out in a high temperature tubular furnace. Experimental results corroborate the theoretical predictions although a dramatically influence of chemical kinetics and diffusion process has been also demonstrated, displacing the reactions to higher temperatures than those predicted by thermodynamics. Finally, this work demonstrates that the first step of the manganese oxide thermochemical cycle for hydrogen production can be carried out with total conversion at temperatures compatible with solar energy concentration devices. The range of required temperatures is lower than those commonly reported in literature for the manganese oxide cycle obtained from theoretical and thermodynamic studies.
Áreas temáticas de ASJC Scopus
- Energías renovables, sostenibilidad y medio ambiente
- Tecnología del combustible
- Física de la materia condensada
- Ingeniería energética y tecnologías de la energía