Propylene oxide oxidation— rate expression

Assuming that only the reactions shown in Fig. 5.1 operate for the hydroformylation of propylene to n-butyraldehyde with 5.1 as the catalyst, and oxidative addition of dihydrogen is the rate-determining step, what should be the rate expression What is the implicit assumption ... 

For the oxidation of ethylene, propylene, 1-butene, and cia- and froms-2-butene, Henry 286, 287) has shown that the rate expression is... 

One of the first comprehensive kinetic analyses over Au/TS-1 concerned the oxidation of H2 to form water [65]. DPT calculations [63,65] showed the RDS to be the formation of adsorbed H2O2 which ultimately decomposes to form water [65]. In the presence of propylene, the generated H2O2 is expected to perform the epoxidation, therefore similarities between the production of PO and water can likely be drawn. Traditional kinetic analysis [65] produced a power rate law for water production of rn o = h exp[-(37.1 1.1 kj mol- )/RT][H2]° 0.02jqj0.17 0.02 Development of a series of elementary steps [Eqs. (11.1-11.5)] capable of reproducing the observed experimental orders and consistent with DPT calculations proved to require two active sites one capable of nondissociative adsorption of O2 and dissociative adsorption of H2 and a second available for only dissociative adsorption of H2 [65]. The resulting rate expression [65] is presented as Eq. (11.6). 

The deep oxidation rates of propylene to COx (i.e. CO2 as well as CO ) are deseribed by the rate expression ... 

At the present time, the fuels which can be described by this modeling approach include hydrogen, carbon monoxide, methane, methanol, ethane, ethylene, acetylene, propane, and propylene. The reaction mechanism used to describe the oxidation of these fuels has been developed and validated in a series of papers (3-7). The elementary reactions and their rate expressions are summarized in Reference (7) and are not reproduced here due to space limitations. Reverse reaction rates are computed from the forward rates and the appropriate thermodynamic data (8). This mechanism has been shown to describe the oxidation of methane (3,A), methanol (5), ethylene (6), and propane and propylene (7) over wide ranges of experimental conditions. It has also been used to describe the shock tube oxidation of ethane (4,9), and acetylene (10). 

Complex reactions with consecutive or parallel steps are commonly encountered in catalytic slurry reactors, e.g. in hydration of propylene oxide, ethynylation of formaldehyde to bu-tinediol or hydrogenation of unsatturated oils [35, 36, 37, 38, 39]. If one can assume in a simplified analysis of these reactions that the concentrations of the liquid reactants are in excess, compared to the gaseous one (Aj ) the rate of reaction of the gaseous reactant (in the absence of intraparticle diffusion) can be expressed as... 

Catalytic activity is expressed in terms of the temperature at which the combustion of propylene occurred at a given rate. Catalysts below the straight line showed enhanced activity over the component oxide due to the formation of a perovskite structure. Conversely for catalysts above the line activity was reduced. Although there is a degree of scatter most catalyst are generally distributed close to the line indicating that the activity of the unsubstituted perovskite oxides are primarily determined by the nature of the B component oxide. The most active catalysts being based on the oxides of Co and Mn. 

The oxidation of propylene and of the four butenes over bismuth molybdate is first order in olefin and independent of oxygen and products (131). For higher olefins, however, the rate drops off markedly with increasing conversion, and a positive oxygen dependence appears 132). The oxidation of 1-pentene was studied in detail by Adams (132) by feeding various mixtures of olefin, oxygen, and pentadiene to a flow reactor under conditions of low conversion (<10%). The rate of oxidation was found to fit the following expression ... 

Ethylene oxidation over five CuO catalysts prepared with various amounts of KOH was found to have a rate equal to A(C2H4) by Koutsoukos and Nobe 172). They used 0.02-0.1% C2H4 in air at 217-340°, and observed activation energies of 20-27 kcal/mole. In related work, Accomazzo and Nobe 173) used a supported copper catalyst (50 % CuO, 50 % AlgOj) for the oxidation of ethylene, propylene, and other hydrocarbons at low concentrations in air. The rate was expressed as equal to l (olefin) . Activation energies for ethylene and propylene were 18 and 17.5 kcal/mole, respectively. Propylene could be oxidized to an equal extent at about 20° lower temperature than for ethylene. The products were essentially only COg and HgO. Diffusion effects and conversion equations were discussed. 

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