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Thermodynamic assessment of hydrogen production and cobalt oxidation susceptibility under ethanol reforming conditions

de Ávila, C.N., Hori, C.E., de Assis, A.J.
Energy 2011 v.36 no.7 pp. 4385-4395
carbon dioxide, catalysts, cobalt, equations, ethanol, hydrogen, hydrogen production, moles, multipliers, oxidation, oxygen, steam, stoichiometry, temperature, thermodynamics
A comparative thermodynamic analysis of ethanol reforming reactions was conducted using an in-house code. Equilibrium compositions were estimated using the Lagrange multipliers method, which generated systems of non-linear algebraic equations, solved numerically. Effects of temperature, pressure and steam to ethanol, O₂ to ethanol and CO₂ to ethanol ratios on the equilibrium compositions were evaluated. The validation was done by comparing these data with experimental literature. The results of this work proved to be useful to foresee whether the experimental results follow the stoichiometry of the reactions involved in each process. Mole fractions of H₂ and CO₂ proved to be the most reliable variables to make this type of validation. Maximization of H₂ mole fraction was attained between 773 and 873 K, but maximum net mole production of H₂ was only achieved at higher temperatures (>1123 K). This work also advances in the thermodynamics of solid–gas phase interactions. A solid phase thermodynamic analysis was performed to confirm that Co⁰ formation from CoO is spontaneous under steam reforming conditions. The results showed that this reduction process occurs only for temperatures higher than 430 K. It was also found that once reduced, Co based catalysts will never oxidize back to Co₃O₄.