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Oxidative Dehydrogenation Of Butane Over V-Mg-O Catalyst And Selective Oxidation Of Lower Hydrocarbons Using Inert Inorganic Membrane Reactor

Posted on:2001-02-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:S H GeFull Text:PDF
GTID:1101360002952011Subject:Chemical process
Abstract/Summary:PDF Full Text Request
There are large amount of lower alkanes (C2-C5) in the petroleum gas and natural gas. Oxidative dehydrogenation of lower alkanes offers an alternation as a route for the production of dienes and alkenes. Oxidative dehydrogenation reaction is a complex process. The selectivity and yield can increase using correct reactor and catalyst. In this work, a reactor was developed in which a partially coated inert porous ceramic membrane was used as an air distributor to the catalytic bed. In this case, the oxygen partial pressure is low in the membrane reactor. The oxidative reaction process is controllable and the selectivity to desired products increases. The studies are as follows: 1. V-Mg-O catalyst was prepared by impregnation and citrate method. The catalysts were characterized by X-ray diffraction (XRD), temperature- programmed reduction (TPR), temperature-programmed desorption (TPD), Thermogravimetry (TG) and BET technology. The crystal phases of MgO, Mg3(V04)2 and V205 were detected in 24-V-Mg-O catalyst prepared by impregnation method. The active component for the oxidative dehydrogenation of butane was identified by tests to be tetrahedral Mg3(VO4)~,. The are two kinds of active sites in the surface of the catalyst. It was observed that the Mg3(V04)2 content imcreased as the calcination temperature increaseed. 2. The performances of catalyst prepared by impregnation and citrate method for oxidative dehydrogenation of butane were compared. The existence of MgV2O6 in the V-Mg-O catalyst prepared by citrate method leads to low selectivity to C4 dehydrogenation products (butene and butadiene). 24-V-Mg-O catalyst prepared by impregnation method is very active and quite selective to C4 dehydrogenation products. The effect of V205 content, calcination temperature and calcination time of V-Mg-O catalyst on the conversion and selectivity was studied using the conventional fixed-bed reactor (FBR). The effect of operation conditions such as reaction temperature, contact time (W/F), molar ratio n02/nC4HIO and the extent of delution on the performance was investigated.3. It was observed that the selectivity and yield to C. dehydrogenationproducts increased using CO= as dilutent gas fOr oxidative dehydrogenation ofbutane. At high temperature and in the presence of oxygen, the radica1s arefOrmed in butane decomposition or oxidative pyrolysis on the surface of thecatalyst and the homogeneous reactions are accelerated. But the homogeneousreactions is greatlj reduced probably through chain termination reaction of theradicals with the surface of inert quartz chips. The deposition of coke on 24-V-Mg-O catalyst used fOr oxidative dehydrogenation of butane was studied usingTG and XRD technology. It was observed that the total amount of coke wasn'thigh and the catalyst deactivation was 1ow. The content of coke deposited on thecatalyst depended on the oxygen partial pressure. The crystal phase of usedcatalyst changed and V,O, crystal phase disappeared.4. The kinetic of the oxidative dehydrogenation of butane over V-Mg-Ocatalyst was first studied. The parallel-consecutive network was described bythree power law equations. The kinetic parameters of oxidative dehydrogenationreaction of butane (equation r,) and deep oxidative reaction of butane (equationr,) were calculated from linear regression of initial reaction rates. The kineticparameters were adjusted from integral conversions. Then the equations of rl, r2and deep oxidative reaction of C. dehydrogenation products (equation r,) wereobtained. The variance between calculated values and experimental values islow. The power law equation can correctly be used to describe test results. It...
Keywords/Search Tags:butane, propane, butene, oxidative dehydrogenation, kinetics, ceramic membrane, membrane reactor, magnesium orthovanadate
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