Micro-Scale Catalytic Reactor for Syngas Production

This paper presents both experimental and modeling investigations of a catalytic wall fuel processor consisting of coupled methane reforming and methane combustion sections. The reacting systems are both catalytic and the latter generates the heat required for the occurrence of the former. The catalytic wall reactor was examined for light-off behavior and for steady-state product distribution. On one hand, the analysis of the reaction products distribution after catalyst ignition indicated that in both combustion and reforming sections catalysts undergo to a relatively long transient (about 40 min) before reaching steady state conditions. On the other hand, a much longer reactor thermal transient was observed and the two transient behaviors appear independent of each other. Analysis of the reactor operating under real conditions (nonadiabatic) showed that a 3D model is needed to accurately predict the reactor performance because a 2D model, although much more convenient, cannot allow for the whole heat loss thereby yielding unreliable results

Modelling of a Catalytic Micro-Reactor Coupling Endothermic Methane Reforming and Combustion

In this study the mathematical modelling of a catalytic microstructured plate reactor for the production of hydrogen was performed in 2D and 3D geometry. The proposed reacting system uses the heat generated by an exothermic reaction (combustion) to sustain endothermic reforming reactions. Therefore, it pertains to those devices useful for producing the feed for fuel cell system for the remote generation of electrical power. However, because of the compactness of the reacting system it can also be considered in the context of apparatus aiming at process intensification. Within this frame the catalytic contribution of both exothermic and endothermic reactions was modeled considering the classic Langmuir- Hinshelwood surface kinetic theory. The advantage of using a real 3D geometry configuration consists in the possibility of considering the importance of the entering and boundary effects with particular attention to fluid stagnation and heat hot spots. The trade off of such a choice is certainly the huge increase of computing time and/or of the power of the computing facility. With respect to other works performed with similar reactor geometry and reacting systems this does not use simplifying assumptions such as catalyst layers modeled by one-dimensional approach, fully developed laminar flow or transverse heat and mass transfer taken into account through lumped heat and mass transfer coefficients. Results of simulations presented here concentrates on the comparisons between results of: countercurrent (CTC) and concurrent (CNC) flow patterns of the reactant streams; of simulations carried out with 2D and 3D models and of the influence of the thickness of the catalytic layers on the reactor performance. Simulations indicates that CNC flow pattern of reactants streams allows a better performance of the reactor since positive temperature differences between the catalyst layers and the gas in the channels maintain along the whole reactor and, consequently, there are not heat flux inversions, which occur under CTC flow pattern. Results also showed that as concerns an adiabatic reactor, whatever the operating conditions, 2D and 3D models yield substantially the same results. Finally, modelling demonstrated that for a realistic catalyst layer configuration thicknesses larger than 50 _m are useless for enhancing the reactor performance. The feasibility of the model proposed may show its potential in fast and easy implementation of several combustion and reforming fuels so to significantly enhance the performance prediction of real processes

Improved Performances of a Fluidized Bed Photoreactor by a Microscale Illumination System

The performances of a gas-solid two-dimensional fluidized bed reactor in photocatalytic selective oxidation reactions, irradiated with traditional UV lamps or with a microscale illumination system based on UV emitting diodes (UVA-LEDs), have been compared. In the photocatalytic oxidative dehydrogenation of cyclohexane to benzene on catalyst the use of UVA-LEDs modules allowed to achieve a cyclohexane conversion and benzene yield higher than those obtained with traditional UV lamps. The better performances with UVA-LEDs are due to the UVA-LEDs small dimensions and small-angle emittance, which allow photons beam be directed towards the photoreactor windows, reducing the dispersion outside of photoreactor or the optical path length. As a consequence, the effectively illuminated mass of catalyst is greater. We have found that this illumination system is efficient for photo-oxidative dehydrogenation of cyclohexane to cyclohexene on sulphated and ethanol to acetaldehyde on

Mechanical characterization of individual polycrystalline carbon tubes for use in electrical nano-interconnects

Polycrystalline carbon tubes were generated by CVD inside electrochemically prepared nano-porous anodic aluminium oxide membranes. This method produced nano-tubes without catalyst, featuring polycrystalline and a few layer thick walls. Individual tubes could be isolated and suspended on microfabricated substrates such that they formed single-side clamped beams. These beams were then used to investigate their mechanical properties employing electrostatic forces for bending the tubes beyond their mechanical stability where pull-in occurs, which could be detected by monitoring the current flowing from the tube to the substrate