• Energy Research

Abstract The inhibiting effect of the presence of CO 2 (15 vol.%) in the reaction mixture of CO-PROX reaction on the performance of CuO/CeO 2 catalysts has been investigated; CO 2 depresses CO oxidation up to 160 °C, its effect being negligible at higher temperatures. The CO 2 coverage of both ceria support and catalysts has been quantitatively determined by CO 2 TPD experiments and the distribution of adsorbing sites has been modeled. Two sites for CeO 2 (one modified by the strong interaction between Ce and Cu when copper is added) and an additional site associated to less interacting copper for CuO/CeO 2 catalysts have been identified by the mathematical model. Although ceria gives a large contribution to CO 2 adsorption, the sites present in larger amount rapidly desorb CO 2 in the typical temperature range of CO-PROX reaction (80–150 °C), especially when copper modification induces a decrease of desorption activation energy, thus suggesting that these centres are involved in CO oxidation. Adsorption sites attributed to copper less interacting with the support still keep a fraction of adsorbed CO 2 in this temperature range and the higher selectivity suggested that they can be mainly related to the H 2 oxidation activity.

Abstract In recent works, we have demonstrated both experimentally and theoretically the occurrence of strong pressure shocks due to Rapid Phase Transition of water produced by combustion, if oxygen-enriched fuel mixtures are exploded in a non-adiabatic reactor. Indeed, peaks of hundreds of bars, although with very short duration, are observed if ultra-high-frequency acquisition system is adopted. In this work, experimental tests were performed, in a non-adiabatic 5 dm 3 cylindrical vessel, for methane explosion in oxygen varying fuel concentration and inert concentration and type (CO 2 , N 2 ). Both flammability limits, following the classical definition, and limits of fuel concentration for the combustion-induced Rapid Phase Transition (cRPT) phenomenon have been found experimentally and justified theoretically. Results are relevant to a range of applications and surely to mitigation/prevention measures. Reconsidering fuel hazards in real process is also mandatory.

The effect of pressure on the flash point (FP) of various fuels (methanol, ethanol, acetone, ethyl acetate, n-hexane, n-octane, benzene, toluene) and their binary mixtures (ethanol-acetone, ethanol-n-octane, methanol-hexane) has been quantified. It has been found that the FP significantly decreases with decreasing pressure. In particular, in going from 1 atm to 0.4 atm, the FP decreases of about 10 °C for all the pure substances investigated. This means that, when dealing with industrial processes operated at pressure lower than 1 atm, the FP present on the material safety data sheet is not conservative since it is measured at 1 atm. A unique equation for evaluating the FP at different pressures starting from the value at atmospheric pressure has been proposed and validated. This equation applies to both pure substances and their binary mixtures, both ideal and non-ideal.

In this paper heat and mass transfer phenomena are studied in a catalytic monolith with a fast exothermic reaction taking place at the walls at fully developing laminar flow for different values of the kinetic parameters. A two-dimensional model has been adopted to simulate the behaviour of the monolith reactor. The unsteady Navier-Stokes equations have been discretized by adopting the control volume approach and solved by means of the CFD-ACE+ package. The model surface reaction is parametrically varied to account for the effects of the perturbation generated by heat production associated with the reaction on flow field, temperature and concentration profiles and then on transport. Results show that Nu and Sh trends are not monotonic functions but that there exists a transfer enhancement due to the perturbation of the flow field. This increase is shown to be dependent on the kinetics parameters of the surface reaction. We show that the definition of the new driving force we previously proposed, which relates the transfer coefficients to the adiabatic temperature rise, is also able to describe the effect of the kinetic parameters if the pre-exponential factor and the activation energy are included in the correlation.

In this work, a mathematical model of fuel conversion and energy balance has been developed to study the dynamic behavior of a lean premixed pre-vaporized combustor fed with ethanol/air and ethanol-hydrogen/air mixtures. The combustor was modeled as a well stirred reactor (WSR). Results show that, for a simplified model reaction, Hopf bifurcations occur. Spontaneous oscillations have been found, suggesting that the combustion reaction plays an important role in the development of dynamic regimes. Hydrogen addition stabilizes ethanol combustion, damping the oscillations. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.

The laminar burning velocities of hydrogen-methane/air mixtures at NTP conditions were calculated using the CHEMKIN PREMIX code with the GRI kinetic mechanism. The equivalence ratio and the fuel composition were varied from lean to rich and from pure methane to pure hydrogen, respectively. The results show that the values of the blends laminar burning velocities are always smaller than those obtained by averaging the laminar burning velocities of the pure fuels according to their molar proportions. Moreover, in lean mixtures the hydrogen addition enhances the methane reactivity slightly, while a strong inhibiting effect of the hydrogen substitution by methane is observed at rich conditions. These findings are attributed to changes of both, the H radicals concentration and the reactions involving such atoms. It was attempted to correlate the calculated laminar burning velocities by means of a Le Chatelier's Rule-like formula. A good prediction is obtained, except for rich mixtures With high hydrogen contents. With this limitation, the proposed formula is Successfully applied also to mixtures at higher than normal values of initial pressure (up to 10 atm) and temperature (up to 400 K).

Glycerol is the main by-product of biodiesel production; its upgrading to more valuable products is a demanding issue. Hydrogenolysis to 1,2-propanediol is one of the most interesting processes among the possible upgrading routes. In this study, we propose novel copper/zirconia catalysts prepared by advanced preparation methods, including copper deposition via metal–organic framework (MOF) and support preparation via the sol–gel route. The catalysts were characterized by N2 physisorption, X-ray diffraction, Scanning Electron Microscopy, H2-TPR and NH3-TPD analyses and tested in a commercial batch reactor. The catalyst prepared by copper deposition via MOF decomposition onto commercial zirconia showed the best catalytic performance, reaching 75% yield. The improved catalytic performance was assigned to a proper combination of redox and acid properties. In particular, a non-negligible fraction of cuprous oxide and of weak acid sites seems fundamental to preferentially activate the selective pathway. In particular, these features avoid the overhydrogenolysis of 1,2-propanediol to 1-propanol and enhance glycerol dehydration to hydroxyacetone and the successive hydrogenation of hydroxyacetone to 1,2-propanediol.