Parametric study and kinetic testing for ethanol steam reforming

An experimental kinetic investigation has been carried out for ethanol steam reforming (ESR). The selected catalyst was a K-promoted Ni/ZrO2 sample prepared by flame pyrolysis, which revealed particularly active and stable for this application based on previous investigation. Ethanol conversion, selectivity to the main possible byproducts (methane, ethylene and acetaldehyde), hydrogen productivity and the CO/CO2 ratio, as a measure of the contribution of the water gas shift reaction, were correlated to the temperature, water/ethanol ratio and space velocity in a central composite experimental design. The parametric dependence of the reaction outcomes helped the qualitative assessment of the best operating conditions and suggested hypotheses on the reaction mechanism. A more quantitative parametric analysis was carried out by multivariate analysis. Particularly dramatic experimental conditions have been adopted in order to highlight the formation and further evolution of possibly critical intermediates, such as ethylene and acetaldehyde. To keep ethanol and intermediates conversion below 100% at sufficiently high temperature to guarantee coke free operation, the space velocity and feed dilution were increased. This will enable drawing a kinetic model accounting for the detailed evolution of such species. An increase of temperature did not adequately improved H-2 selectivity, whereas the water/ethanol ratio was an effective parameter to push H-2 productivity. The reforming reactions of ethanol and of acetaldehyde/ethylene byproducts were dependent on the three parameters (kinetically controlled), whereas the CO/CO2 ration was substantially independent on the space velocity, indicating that the water gas shift reaction reached an equilibrium value.