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ABSTRACT: The use of an internal circulating fluidized bed (ICFB) is proposed for the oxidative dehydrogenation of butane. The reactor consists of two adjacent zones, separated by a wall. In the oxidizing zone the catalyst is oxidized and in the reducing zone the butane is dehydrogenated by reaction with the oxygen from the catalyst lattice. The circulation between both zones is produced by the different bed porosity, which originates a pressure difference between the two zones at the communication orifice at the bottom of the vessel. The design of this reactor is studied in a cold model. An image analysis technique was applied to measure solid circulation rates between the different regions in the reactor, by using a solid coated with a long afterglow phosphor as a tracer. The solid circulation rates through the orifices were found to correlate reasonably well with a previously developed correlation for the orifice drag coefficient. The model for solid circulation between fluidized regions was then integrated in the overall mathematical model for the ICFB reactor system to incorporate the effect of design and operating conditions on the catalyst circulation rates between compartments. A good correlation between the experimentally obtained values of conversion and selectivity and those predicted by the model is obtained. Improvements in selectivity to olefins are obtained, compared with conventional fluidized-bed reactors with cofeeding of reactants. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1510–1522, 2004
AIChE Journal 06/2004; 50(7):1510 - 1522. · 2.26 Impact Factor
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ABSTRACT: A fluidized-bed reactor with separate butane and oxygen feeds has been studied in the oxidative dehydrogenation of butane. Under suitable conditions, feed segregation allows the creation of separated oxidation and reduction zones in the same reaction vessel, between which a V/MgO catalyst is recirculated. The behavior of the reactor has been characterized, with the separation of oxidation and reduction zones as the focus of the study. The performance of the two-zone reactor has been compared to that of a conventional fluidized-bed reactor.
12/1998;
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ABSTRACT: Fluidized bed reactors where separate oxidation and reduction zones are present in the same vessel have been developed in our laboratory and applied to different processes during the last decade. This type of reactors constitutes an alternative to the use of two different reactors or of a single reactor with periodic operation. The advantages of the dual-zone fluidized bed reactor have been proven in processes such as oxidative coupling of methane, oxidative dehydrogenation of hydrocarbons, butane oxidation to maleic anhydride or dehydrogenation of hydrocarbons with simultaneous catalyst regeneration in the same vessel. In this manuscript the advantages and limitations of this type of reactor are discussed.
Catalysis Today.
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ABSTRACT: A new reactor technology is employed for propane dehydrogenation over a Cr2O3/Al2O3 catalyst. This reactor allows the continuous regeneration of the catalyst, but avoids the transfer of large amounts of solid between two reactors, since one single vessel is employed. The experimental work was carried out in a bench scale reactor using two configurations: (a) a two-zone fluidized bed reactor (TZFBR), where propane and oxygen are fed at different levels, providing separated zones for the reaction and catalyst regeneration; (b) an internal circulating fluidized bed reactor (ICFBR), where the addition of an axial dividing slab allows the partition of the vessel, giving two beds connected at the top and bottom and enabling better catalyst circulation. The effects of the main operating variables were studied: bed temperature, gas velocity, oxygen flow rate fed to the reactor, relative length between the oxidizing and reacting zones and the W/F ratio. Under suitable conditions, steady-state operation with propene yields as high as 30% can be achieved, with small requirements of oxygen to continuously regenerate the catalyst.
Chemical Engineering Journal. 106(2):91-96.
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ABSTRACT: The deactivation of bulk iron oxide during methane combustion has been studied. The observed deactivation behaviour has been explained as the result of two simultaneous deactivation mechanisms. In the initial phase of reaction both are in operation and the activity drops rapidly as a consequence of both catalyst sintering and of the depletion of lattice oxygen in the outer layers, due to a partial reduction of the catalytic surface. In later stages, catalyst deactivation is almost exclusively due to sintering under reaction conditions. A kinetic model of deactivation is presented, together with the physicochemical characterization of fresh and partially deactivated catalysts.
Studies in surface science and catalysis 139:487-494.
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ABSTRACT: Propane dehydrogenation over a Pt–Sn–K/γ–Al2O3 catalyst has been studied in the TAP reactor. Qualitative analysis of the pulse responses reveals part of the reaction network. Dissociative adsorption of propane yields propylene and hydrogen. Propylene is further converted into coke. Hydrogen and propylene compete for the same active sites.The first order rate constant for the propane conversion has been evaluated by moment analysis, the thin-zone model and regression analysis of the full pulse response for different catalyst bed lengths and temperatures. This has shown that the three methods yield comparable results for both the values of the rate constant and the corresponding activation energies. However, the expression derived from the thin-zone model is the easiest to use and gives a reasonable order of magnitude estimate of the first order rate constant.
Chemical Engineering Science.
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ABSTRACT: The kinetics of n-butane oxidation for the production of maleic anhydride (MA) over a commercial VPO catalyst has been investigated under aerobic and anaerobic conditions and at a temperature range of 400–. A kinetic model that can be applied under both aerobic and anaerobic conditions is presented. The model considers three types of oxygen: adsorbed oxygen, surface lattice oxygen and sub-surface lattice oxygen. Both adsorbed and surface lattice oxygen are considered active for the production of maleic anhydride and COx.
Chemical Engineering Science.
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ABSTRACT: The activity and selectivity of the catalysts used in oxidative dehydrogenation of alkanes results from a combination of factors related to the nature of the catalysts and to the operating conditions under which these are used. In this work, the oxidative dehydrogenation of alkanes (mainly butane) over V–Mg–O and VOx/Al2O3 catalysts has been studied. The investigation is focused on the examination of the oxidation and reduction processes that take place on the surface of both catalysts. A combination of catalyst characterization and kinetic measurements has been used, in an attempt to relate the rate of these redox processes to the catalytic performance observed under oxidative dehydrogenation conditions.
Journal of Catalysis.
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ABSTRACT: The kinetics of the oxidative dehydrogenation of butane on a V/MgO catalyst has been studied under anaerobic conditions. In these conditions the oxygen from the catalyst lattice is consumed by the reaction, and the oxidation degree of the catalyst changes during the experiment. A kinetic model is proposed in which each reaction rate is related with the oxidation degree of the catalyst. The whole kinetic model is useful for the modelling of reactors where the catalyst operates in non-steady state, i.e. where the oxidation degree of the catalyst changes with time. It has also been found that whereas the main contribution to the oxidative dehydrogenation reaction comes from the lattice oxygen, there is also a non-selective contribution from weakly adsorbed oxygen.
Chemical Engineering Science.
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ABSTRACT: Bulk iron oxide, prepared by precipitation and by the citrates method, has been studied as an alternative catalyst for methane combustion. While hematite was the dominant phase in all the samples prepared, significant differences were observed regarding the activity and stability of the catalysts, depending on the preparation method. The catalysts prepared by precipitation presented higher surface areas and lower light-off temperatures. Catalyst deactivation is due to sintering under reaction conditions, and becomes more severe if the operating temperature exceeds the calcination temperature used in catalyst preparation. The best performance in terms of stability and steady-state conversion was obtained with the catalyst prepared by precipitation and calcined at 600°C.
Catalysis Today.
