Hydrogen from bio-fuels by 'steam-iron' process: Modelling and kinetics

摘要

Steam-iron process, directly related to chemical looping, can produce high purity hydrogen from liquid bio-fuels in a single vessel taking advantage of its reductive behaviour. It comprises two steps: reduction of an iron oxide with additives with aid of the fuel, and oxidation of the previously produced metallic iron by steam producing PEMFC quality hydrogen. Since it takes place in the same reactor, the process can be described by a single mathematical model in which multiple thermodynamic equilibria and elemental composition of the inlet streams are taken into account. Three stages have been identified in reductions according to the different oxidation states of the solid. Last two are repeated along cycles. Oxidation passes in a single stage. Synthetic bio-fuels have been produced taking into account representative compounds of the different fractions present in such fuels: alcohols, aldehydes/ketones and acids. Kinetics has been obtained by fitting experimental results acquired in a lab-scale fixed bed reactor operating in isothermal mode at several temperatures and reactant partial pressures. An anti-Arrhenius behaviour has been found that can only be explained from a sintering perspective. Accordingly, a model has been included for accounting that issue. Optimization of the cycle time length has also been studied. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.