Propane, dehydrogenation

In this application, the separated hydrogen is fed to a gas turbine and to a post-combustion chamber using its exhausts to supply the dehydrogenation reactor thermal duty. The plant is designed for a propylene capacity of 

Palladium-based Selective Membranes for Hydrogen Production 

Another important process in which catalyst deactivation by coke deposits plays an important role is propane dehydrogenation, which can be performed with a variety of materials, including metal and metal oxide catalysts. Different in situ and operando spectroscopies have been applied to these catalysts, including UV-vis, Raman, electron paramagnetic resonance (EPR), and X-ray absorption spectroscopies [4, 115, 140], 

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The oxidative propane dehydrogenation is well investigated and also a highly exothermic reaction. In a fixed-bed reactor, steep temperature gradients are ob-servableandtheconversionofpropaneandselectivityofthereactionarestrongly determinedbytemperatureandtotalflowrate[133]. 

The pulse experiments demonstrated that active sites for propane dehydrogenation are formed upon exposure of the oxide form of gallium modified ZSM-5 to propane itself. A constant 1 1 ratio of hydrogen produced to propane consumed is attained after a number of pulses with little propene formation, which suggests that, after propane dehydrogenation to propane, aromatization proceeds through hydrogen transfer reactions. 

Since it is now well accepted that the role of the additive in the H-ZSM-5 based catalysts is to Increase the rate of propane dehydrogenation it is clear that the additive should be sufficiently active to establish rapidly the thermodyneunic equilibrium propane-propene. Ga203 or ZnO exhibits with respect to Pt catalysts lower dehydrogenating properties. Nevertheless, when supported on H-ZSM-5, they were found to promote more efficiently the aromatization of propane, and also the... 

The nickel-containing sample showed no detectable activity up to a reaction temperature of 650 °C within the short residence times applied for the tests. Increasing the reaction temperature to 750 °C led to a conversion of 6% for this sample. However, the catalyst was mostly active for propane dehydrogenation (44% selectivity) and had a selectivity of 28% towards both carbon dioxide and carbon monoxide [52]. 

Van Sint Annaland [28] proposed a four-step process for propane dehydrogenation coupled with combustion of methane or propane the phases of the process are illustrated in Fig. 1.15. Different process schemes are possible, depending on the sequence of the phases within one cycle. In any case, the complete cycle is symmetric, which is favorable with respect to heat recovery. 

Fig. 1.15. Coupling of propane dehydrogenation and methane combustion in a four-step catalytic fixed-bed process [28].

Y. Yildirim, E. Gobina and R. Hughes, An Experimental Evaluation of High-Temperature Composite Membrane Systems for Propane Dehydrogenation J. Membrane Sci., 135 107-15 (1997). 

The use of the H2-D2 equilibration reaction as a probe reaction to study the deactivation on Pt/Al203 and Pt-SnMl203 catalysts during propane dehydrogenation... 

The amounts of catalyst were about 10 mg and the pressure about 1.3 bar in all runs. The catalyst was reduced in flowing hydrogen. First during a temperature ramp from room temperature to 516 C. Thereafter the sample was kept at this temperature for 4 h. The reaction mixture used for the propane dehydrogenation was 20 cm3/min propane, 6 cm3/min hydrogen and 40 cm3/min nitrogen (flows at 0 C, 1 atm). 

The results from the H -D2 experiments are shown in Figures 2 and 3. In Figures 4 and 5 the propane dehydrogenation conversion just before an H2-D2 experiment have been related to the HD formation rate. Experiments from all the runs were used. The TOF, based on the number of hydrogen chemisorption sites on a fresh catalyst, were calculated from the rate... 

The continuous decrease in the propane dehydrogenation activity, with constant HD formation rate can have different origins. Calculations indicate that diffusion limitations may play a role in the propane dehydrogenation, but not in the H2-D2 reaction, when the amount of coke in the pores of the catalyst is high. Different structure sensitivity for the two reactions might also contribute to this effect. Somorjai [8] showed that the H2-D2 reaction is structure sensitive. For the propane dehydrogenation, on the other hand, fiiloen et al. [9] found that only one Ft atom is necessary for the reaction to proceed. 

The H2-D2 equilibration reaction was shown to be useful as a probe for measuring the metal area not covered by coke, on Pt/Al203 and Pt-Sn/AL03 catalysts deactivated during propane dehydrogenation. Problems with the method are the effect that the repeated stops have on the dehydrogenation deactivation profile, and the difficulties in correlating the HD formation rate to free metal area. 

An isotope labelling study of the deactivation of a Pt/alumina catalyst used for propane dehydrogenation. 

Activity, selectivity and extent of carbon laydown during propane dehydrogenation at 873 K... 

The composition and reactivity of the carbon laid down during the initial stages of the propane dehydrogenation reaction was examined by transient isotope labelling experiments using [2-]3C]-C3HgandC3JHs as tracers in a series of reactions in a pulsed flow microcatalytic reactor. In these experiments alternate series of labelled and unlabelled propane pulses were passed over the catalyst sample and the products analysed by glc and mass spectrometry. 

The activity and selectivity of the Pt/alumina catalyst for propane dehydrogenation is critically dependent on the extent of formation of a carbonaceous deposit, which contains both carbon and hydrogen, on the catalyst. 

Only a relatively small fraction of the carbon laydown on the surface can be removed by high temperature dioxygen treatment. After regeneration carbon continues to build up on the catalyst surface in subsequent propane dehydrogenation reactions. 

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