Propane Oxidative Dehydrogenation to Propylene

Figure 1 is the catalytic behavior of VSU545 in propane oxidative dehydrogenation to propylene. Selectivities to propylene in the range of60-80% are obtained up to propane conversions of about 20-25% and reaction temperatures up to around 450- 500 C. For higher reaction temperatures and conversions the selectivity decreases due both to the formation of carbon oxides and of aromatics. As compared to pure silicalite, a significant increase in both the selectivity to propylene and the activity in propane conversion is observed. 

Figure 1. Propane oxidative dehydrogenation to propylene on VSil545. Exp. conditions flow reactor tests with 2.8% C3, 8.4% O2 in helium. 4.2 g of catalyst with a total flow rate of 3.1 L/h (STP conditions).

Figure 2. Comparison of the catalytic behavior of VSil samples in propane oxidative dehydrogenation to propylene. Conversion of propane and selectivity to propylene at 470 C. Exp. conditions as in Fig. 1.

Phase Ml (propane oxidative dehydrogenation to propylene function) Phase M2 (propylene ammoxidation to acrylonitrile function) ... 

Pdrez-Ramiirez, J. and Gallardo-Llamas, A. (2005). Framework composition effects on the performance of steam-activated FeMFI zeolites in the N20-mediated propane oxidative dehydrogenation to propylene, J. Phys. Chem. B, 109, pp. 20529-20538. 

Figure 4. Comparison of the behavior of VSil545 in propane oxidative dehydrogenation using N2O or O2 as oxidizing agents. Exp. conditions as in Fig. 1. The dotted lines represent the propane conversion and propylene selectivity observed in the absence of the catalyst (homogeneous gas phase). The activity of the catalyst in the absence of O2 or N2O is similar to that observed in the homogeneous gas phase, but the selectivity to propylene (around 50-60%) is lower.

Dehydrogenation processes in particular have been studied, with conversions in most cases well beyond thermodynamic equihbrium Ethane to ethylene, propane to propylene, water-gas shirt reaction CO -I- H9O CO9 + H9, ethylbenzene to styrene, cyclohexane to benzene, and others. Some hydrogenations and oxidations also show improvement in yields in the presence of catalytic membranes, although it is not obvious why the yields should be better since no separation is involved hydrogenation of nitrobenzene to aniline, of cyclopentadiene to cyclopentene, of furfural to furfuryl alcohol, and so on oxidation of ethylene to acetaldehyde, of methanol to formaldehyde, and so on. 

Catalytic oxidative dehydrogenation of propane by N20 (ODHP) over Fe-zeolite catalysts represents a potential process for simultaneous functionalization of propane and utilization of N20 waste as an environmentally harmful gas. The assumed structure of highly active Fe-species is presented by iron ions balanced by negative framework charge, mostly populated at low Fe loadings. These isolated Fe sites are able to stabilize the atomic oxygen and prevent its recombination to a molecular form, and facilitate its transfer to a paraffin molecule [1], A major drawback of iron zeolites in ODHP with N20 is their deactivation by accumulated coke, leading to a rapid decrease of the propylene yield. 

Besides ODH processes, a few reports about non-oxidative dehydrogenation (DH) over carbon catalysts also exist. At the reaction temperature of 823-873 K, propane is reported to react to propylene and hydrogen in high yield (30-40 %) over ordered mesoporous carbon, which was shown to be much more active than graphitic and/or nanostructured carbon (CNTs) [66], On the other hand, a hybrid catalyst system for... 

Smits, Seshan and Ross have studied the selective oxidative dehydrogenation of propane to propylene over Nb20s and Nb2C>5 supported on alumina.32 Vanadia supported on MgO has typically been used in these reactions, although reduced surface vanadyl ions can give rise to decreasing selectivity to propylene. Niobia on the other hand, is much more difficult to reduce than vanadyl but there have been few studies with this oxide in such reactions. 

This generates opportunities to use new reaction pathways not feasible in conventional macroscale reactors. For example, Sadykov et al. utilize rapid thermal quenching in conjunction with short residence times in a microreactor to suppress undesired side reactions in propylene production by the oxidative dehydrogenation of propane. 

The physicochemical properties of potassium-, bismuth-, phosphorous- and molybdenum-doped (MeA7 atomic ratios of 0 to 1) V2O5/Y-AI2O3 catalysts and their catalytic behavior in the oxidative dehydrogenation of propane have been compared. The incorporation of metal oxides modifies the catalytic behavior of alumina-supported vanadia catalysts by changing both their redox and their acid-base properties. In this way, the addition of potassium leads to the best increase in the selectivity to propylene. This performance can be related to the modification of the acid character of the surface of the catalysts. The possible role of both redox and acid-base properties of catalysts on the selectivity to propylene during the oxidation of propane is also discussed. 

Propylene demand will grow to the 11-billion lb level by 1973. Propylene from either heavier ethylene feed stocks or European imports will not alleviate the shortage completely. On the other handy it is not expected that price will exceed 3.1 cents/lb. In spite of decreasing propylene availability, refiners will consider release of alkylate stocks at this level. Development of an economic process for direct propylene production is in the future. Dehydrogenation or iodinative partial oxidation processes for propylene from propane are neither commercially proved nor have they been demonstrated to have economic promise. Dehydrogenation in the presence of sulfur may bypass propane dehydrogenation equilibrium limits, and preliminary experimental data are presented. 

There is one exception in these results using propane relative to those obtained when propylene was used to represent the hydrocarbon in extremely lean conditions, the HC activity was enhanced by the presence of SO2 this effect has been reported in previous laboratory studies of propane oxidation [26], We suggested previously that SO2 promotes acid catalysis of propane dehydrogenation, only in this case, the carbonaceous material may be more easily removed from Pt-Rh than from Pd under oxidizing conditions, thus complete oxidation of propane dominates over coking. Other factors, however, may also be... 

When propane is oxidized, the dehydrogenation and C-C bond splitting occurs to yield propylene and acetaldehyde in considerable amounts. The oxidation of the latter is accompanied by the appearance of so-called cool flames [32]. The mechanism proposed for the propane oxidation is presented in Table II.8 [32c]. 

The distributed-reactant membrane reactor has also been studied for several oxidative dehydrogenation reactions ethane to ethylene, propane to propylene and butane to butene. The results for these reactions have shown more promise, with higher yields for the membrane reactor when compared with a fixed bed, over certain ranges of the operating parameters. 

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