In situ regeneration of the Ni-based catalytic reformer of a 5 kW PEMFC system

The paper reports the results of on-site regeneration catalytic bed of the natural gas reformer in a 5 kW PEM fuel cell system. The Ni catalyst previously poisoned by sulphur from the available natural gas, could be re-activated by injection of pure water steam, following the method developed for industrial reformers using the same metal catalyst: this method was shown to be perfectly efficient, provided no natural gas was fed during the operation. Results of the tests conducted are presented and discussed in relation to published data on S-sorption on Ni surfaces.     

Competition between the gas and surface reactions for the oxidative coupling of methane 1. ‘Non-isothermal’ results in catalytic jet-stirred reactor

A catalytic jet-stirred reactor (CJS reactor) has been developed to investigate the interaction between gas-phase and surface reactions for the oxidative coupling of methane. This reactor allows the modification of the number of catalyst pellets (La₂O₃) for a fixed gas-phase volume. It permits also to set different temperatures for the gas-phase volume and the catalyst. The results of these ‘nonisothermal’ experiments are presented; they suggest that the contribution of the gas-phase reactions is rather significant and that the C₂₊ selectivity is improved by an increase of the gas-phase temperature up to 850°C.     

Photocatalytic degradation of gaseous 1-propanol using an annular reactor: kinetic modelling and pathways

Photocatalytic oxidation of airborne contaminants appears to be a promising process for remediation of air polluted by Volatile Organic Compounds (VOCs). In the present work, the photocatalytic oxidation of gaseous 1-propanol has been investigated by using an annular photoreactor. The annular photocatalytic reactor was modelled by a cascade of heightened elementary continuously stirred tank reactors. The influence of several kinetic parameters such as pollutant concentration, incident light irradiance, contact time and humidity content has been studied. The photocatalytic degradation by-products of 1-propanol has been identified in the gas-phase by GC/MS. Propionaldehyde and acetaldehyde were found to be the main gaseous intermediates. Propionaldehyde and acetaldehyde have been taken into account in a "two-site model" to evaluate the possible competition of adsorption between 1-propanol and its by-products of degradation. A mechanistic pathway is then proposed for the photocatalytic degradation of 1-propanol.     

Direct conversion of methane in formaldehyde at very short residence time

To obtain new kinetic data, a quartz annular flow microreactor was chosen for the experimental investigation of the gas phase partial methane oxidation to formaldehyde under high temperature (1173–1273 K) and short residence time (20–60 ms). High formaldehyde selectivity (up to 80%) is achieved, but the yield remains low. For a single pass operation, the best HCHO experimental yield is 2.4%. The kinetic simulation using GRI-Mech 3.0 shows an overall good agreement with the experimental data, though there does exist some discrepancies for some conditions. The general pathways of the reaction show that HCHO is formed mainly from direct oxidation of methyl radical CH₃ by O₂, and partly from dehydrogenation or oxidation of methoxy radical CH₃O.     

Kinetic modeling of surface reactions involved in CVI of pyrocarbon obtained by propane pyrolysis

A detailed heterogeneous kinetic mechanism based on elementary surface reactions has been developed to model pyrocarbon deposition obtained by propane pyrolysis on carbon fibers. The model contains 275 elementary steps involving 66 surfaces sites. It is combined with a homogeneous model in order to reproduce both deposition kinetics and gas phase composition. Deposition reactions are assumed to occur on the edges of basic structural units on both zig-zag and armchair sites. The kinetic parameters of surface reactions are estimated by analogy with a chemically similar gas phase “prototype” reaction. Simulated results are compared with experimental results obtained in a perfectly stirred reactor at low pressure (2.6 kPa) with temperature ranging from 1173 to 1323 K and residence time ranging from 0.5 to 4 s, using propane diluted in nitrogen as carbon precursor. Results show good agreement between simulations and experiments for both deposition kinetics and gas phase composition. In the chosen conditions, pyrocarbon precursors are mostly small unsaturated species (acetylene and ethylene) and methyl radicals.