Reaction kinetics isobutane dehydrogenation

In contrast to the results obtained for dehydrogenation reactions, kinetic energy release distributions for alkane elimination processes can usually be fit with phase space theory. Results for the loss of methane from reaction 9 of Co + with isobutane are shown in Figure 10b. In fitting the... 

Kinetic Parameters for the Horiuti-Polanyi Reaction Scheme for Isobutane Dehydrogenation and Isobutylene Hydrogenation... 

The paraffins dehydrogenation on platinum-alumina catalysts proceeds with constant rate up to some time-on-stream after which a slow deactivation of the catalysts takes place Since relative changes of the catalyst activity ( characterized by reaction rate) are proportional to relative amounts of the deposited coke it can suppose that coke formation is the main reason of deactivation. Deactivation can be related with an attainment of a threshold in coke concentration (Co) on catalysts. The threshold amounts are 1.8 wt.% for A-I, 6,8% and 2.2% for A-II and A-IXI catalysts respectively. The isobutane dehydrogenation in non-stationary region (C > Co) is described by the following kinetic equation ... 

Ter-butanol dehydration and n-hexane cracking were studied on samples in H form, isobutane dehydrogenation was studied on dried samples activated in situ. Reactions were carried out on st.steel or pyrex integral, fixed bed, plug flow reactors at atmospheric pressure. Catalyst (1-2 cc) was crushed to 20-40 mesh size. On-line chromatographic analyses were carried out. Experimental conditions are outlined in Table 1. Kinetic constants were evaluated by applying eq.(1). 

A quantitative kinetic model, denominated TC4, for the catalytic conversion of n-butane is proposed. The model considers 56 elementary reactions, six of them were chosen to occur in heterogeneous phase. The TC4 model can be used to predict the product distribution and the heterogeneous rate constants for a wide range of conditions and on different catalyst types. The model can fit also the experimental data from the isobutane dehydrogenation reaction. A plot, that we have denominated "the graphic s performance of a catalyst", is proposed for the evaluation of the maximum yield of a catalyst with a minimum of experimental data. 

Catalytic activity for isobutane dehydrogenation was measured in a conventional flow reactor at atmospheric pressure and 550°C, with a feed flow of pure isobutane of 50 cm min. The composition of the reaction products was analyzed using a Carlo Erba Fractovap series 2150 gas chromatograph on line with the reactor. In all the tests, conversion was kept below 10% to assure kinetic control conditions (equilibrium conversion for these experimental conditions is around 55%). 

Figure 10. Comparison of experimetnal kinetic energy release distributions to phase-space calculations for (a) dehydrogenation of n-butane by Co+ and (b) loss of methane in reaction of Co+ with isobutane. Data from reference 38.

The activity of the catalyst is also important, as reflected in the value of Da. If the reaction rate is slow, equilibrium will not be approached and the removal of a product by a membrane will not affect the ultimate yield. This was demonstrated by Raich and Foley, who showed that the very promising results of early studies using the dehydrogenation of cyclohexane to benzene were achieved due to the fast reaction rate which quickly attained equilibrium. Slower reactions, such as the dehydrogenation of isobutane to isobutene, are not helped by a membrane reactor as they are kinetically limited (low Da). 

A detailed kinetic study of oxidative dehydrogenation of propane, isobutane, n-butane (23 runs) and LPG (27 runs) was conducted over a wide range of partial pressures of pure and mixed hydrocarbons (0-0.3 atm), oxygen (0-0.2 atm) and steam (0.2-0.7) atm and temperature 600-670°C. Oxidation of Hj, CjHg, C H, CH and CO was also tested at 600-650°C. A set of reactions was selected based on the distribution of products ... 

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