1,721,013 research outputs found
Modelling of continuous reactors for flow chemistry
Full text linkFlow chemistry is gaining increasing attention as a mean to achieve process intensification in the fine chemicals synthesis field. Furthermore, it can overcome heat and mass transfer limitations thanks to more efficient mixing, allowing applications characterised by insufficient yield or safety issues, when carried out in the traditional batch mode. Despite their spreading use, micro- and meso-reactors are complex systems that require some detailed modelling in order to achieve the desired process intensification effect. In this review, some examples will be provided dealing with three main modelling items. On one hand, kinetic modelling is needed in order to correctly size the reactor and to estimate its productivity with time-on-stream under different conditions. Then, fluid dynamics issues have to be carefully modelled to predict heat and mass transport properties, which are ultimately related to fluid flow inside micromixers and microreactors. All these topics will be discussed, to review the current developments in continuous microreactors modelling and design, together some examples of process simulation
Tecnologie per la produzione di idrogeno da fonti rinnovabili : siamo pronti per la sfida?
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Continuous flow (micro-)reactors for heterogeneously catalyzed reactions : main design and modelling issues
Full text linkContinuous flow chemistry is a rapidly developing branch in organic and drugs synthesis, whereas it is common practice in heterogeneous catalysis for base chemicals production. Heterogeneously catalysed synthetic protocols are being developed and can take advantage of the reaction and reactor engineering experience at the macro-scale, provided that suitable models are applied to the micro- and meso-reactors in use. The main process parameters that define possible mass, heat and momentum transport limitations in heterogeneous catalytic reactors are reviewed. Specific models applying such concepts to microreactors are proposed. Finally, examples are reported of heterogeneously catalysed reactions carried out in microreactors for different applications
H2 production by steam reforming of bioethanol
No full textDifferently supported Ni-based catalysts, with variable metal loading, have been synthesized by means of an innovative prepn. procedure. This technique, named Flame Spray Pyrolysis, allows the continuous one-step prodn. of nanosized particles, characterized by high thermal stability due to a flash calcination for a few milliseconds into a flame. The morphol. and structural features of the as prepd. supports and of activated catalysts are here summarized, together with catalyst performance for the steam reforming of bioethanol at 750°C, atm. pressure. Alumina, chosen for comparison with com. catalysts for this application, did not show a suitable support due to its high surface acidity, which leads to faster coking with respect to other supports. Increasing Ni loading allowed to increase H2 productivity and the best results were achieved with the sample 15 wt.% Ni/La2O
Carbon based materials for H2 storage
No full textWe set up a volumetric method to quantify the amount of H2 “delivered” after saturation of porous solids at high pressure. A complementary dynamic method has been also developed to take into account the reversibility of adsorption and to assess in at least a semi-quantitative way the strength of interaction between H2 and the adsorbent. The method has been applied to compare the H2 storage capacity of very promising carbon-based materials, as supplied, after thermal/chemical treatments or functionalized with metals. The best results, ca. 7 wt% H2 “delivered”, were achieved after saturation at 77 K, 20 kgf/cm2 with an active carbon with ca. 3000 m2/g of apparent specific surface area
Flame-spray pyrolysis preparation of perovskites for methane catalytic combustion
Full text linkA flame spray pyrolysis apparatus was set-up and optimised for the preparation of perovskitic mixed metal oxides in nanoparticle-size powder form. LaCoO3 was chosen as test catalyst, aiming at correlating crystallinity, surface area, particle size, catalytic activity and durability with some fundamental operating parameters of the apparatus. In particular, feeding rate of precursors solution, flow rate of the O2/CH4 mixture for the igniter and flow rate and linear velocity of the main dispersing-oxidising oxygen have been thoroughly analysed. The activity of the prepared samples was tested for the catalytic flameless combustion of methane, a reaction requiring a proper combination of activity and thermal stability of the catalyst. Provided a crystalline perovskitic phase forms, activity increases with increasing surface area of the powder. By contrast, the higher the initial sintering of catalyst particles within the flame, the higher is thermal stability. Tuning up of operating parameters allows to properly address the desired catalyst properties
Steam reforming of ethanol over Co and Cu based catalysts
No full textCo- and Cu-based catalysts prepared by flame pyrolysis (FP) technique are proposed as possible substitutes for Ni-based catalysts, very active for the Ethanol Steam Reforming reaction, but showing poor stability towards coke formation when operating at relatively low temperature. The FP method allowed to achieve a partial incorporation of the active phase into the support, leading to high dispersion and lower reducibility. The best results were achieved with 10wt% Co/SiO2, which led to higher activity, good C balance and low CO/CO2 ratio. This was ascribed to the high initial dispersion of Co into the silica matrix, which led to available Co particles well dispersed and stable
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