Propylene, formation

Figure 3. Specific rate of propylene formation at 500 C per vanadium atom in VSil samples as a function of the Si02A 203 ratio. Exp. conditions as in Fig. 1...

V gave poorer results than III or IV. The result with Reactor IV fell between those of Reactor III and V. Reactor II gave almost the same yield of hydrogen peroxide as Reactor III with somewhat lower selectivity for propylene formation. Therefore, the effect of reactor pretreatment on selectivity for hydrogen peroxide formation is ... 

At the reaction temperatures ranging from 430° to 450°C. and residence time 6-8 sec. under atmospheric pressure the reaction proceeded with fairly high selectivity for hydrogen peroxide and propylene formation. 

For the reaction of the propyl chlorides, the possibility of dehydro-halogenotion followed by hydride abstraction from propylene to produce propane, while remote, cannot be discounted (Scheme 9). We believe, however, that propylene formation would produce oligomerization and polymerization products and thus is not consistent with fully one-third of the product going to propane. 

Thermal deazetization of pyrazolines results in the formation of cyclopropanes and alkenes, illustrated in Figure 44 for the parent compound (18). This reaction is of interest in that one could imagine that it would involve the same trimethylene biradical (19) proposed to be an intermediate in cyclopropane stereomutation (Section III.A). Supporting this notion is the observation that the parent pyrazoline gives 89% cyclopropane and 11 % propylene at 250° C. If one took this product ratio as a reflection of the branching ratio from a common trimethylene intermediate, it should then be possible to compare these figures with the relative rates of stereomutation and propylene formation from cyclopropane-d2 . Interestingly, they are identical. 

Figure 5. Reaction Orders for Propylene Formation from Propane a. Oxygen Dependence, b. Propane Dependence [12].

Propylene Formation. It has been reported (20) that no C3H6 was observed as a radiolysis product of pure CH4. We, however, observe about 2.2% of this product, 44% of which is produced by ion-molecule reactions (Table III). The only precursor ion we observe is CH2+ however, excited methane molecule is also a precursor (Figure 5 and Table... 

Olefinic bonds are only reduced by nitrogenase when they and —C=N are in conjugation. Ethylene and 1,3-butadiene are not reduced. Acrylonitrile is reduced by six electrons to propylene and ammonia and by eight electrons to propane and ammonia (68). Double bond migration occurs in propylene formation. No 2- or 4-electron products have been found. 

Ethylene production is maximized at temperatures of 700° to 750°C and residence times of about 6 sec, whereas propylene formation is favored by lower temperatures (650°C) and shorter residence times (2 sec). 

Fig. 5.14 Differential electrochemical mass spectrometry measurements in half-cells containing TIMREX SFG6 and SFG44 as electrodes and 1-M LiPF in ethylene carbonate/propylene carbonate 1 1 (w/w) as electrolyte. The mass signal miz = 27 and miz = 44 corresponding to the ethylene and propylene formation, respectively, was monitored as a function of the potential applied to the graphite electrode at a scan rate of 0.4 mV...

Matkovskyi, E E., Chemgya, L. 1., and Russiyan, L. N., Cationic oligomerization of propylene. Formation of active centers, Izv. Akad. Nauk. SSSR, Ser Rhim., 1984, 643 (Russian). 

According to Froment [119], the propylene formation is very fast, but this olefin is very reactive on the nondeactivated catalyst. 

The kinetic constants of olefin formation at 350°C follow the order kC > kC > C2 activation energy for propylene formation is lower than it is for other olefins [133]. 

Detailed kinetic studies performed by Froment s group shows an extrapolation of the propylene yield to initial times [101]. This proves that propylene might be at least one of the primary products in MTO reaction after the initiation step, which is formed directly from MeOH/DME. This result is consistent with [61,103]. According to Froment [119], the propylene formation is very fast, but this olefin is very reactive on the catalyst. With progressive deactivation by coke, the reactor zone in which the propylene yield reaches its maximum moves further downstream [101]. 

Lesthaeghe et al. [134], based on the theoretical studies available in the literature, claimed that no ethylene can be formed through direct mechanisms in MTO. However, the trimethyl oxonium and ethyldimethyloxonium ions are distinctly stabilized by the surrounding ZSM-5 framework, which does not impose steric constraints on further intermolecular reactions. This means that the potential intermediates for propylene formation are more probable. 

At low temperature, propylene is mostly formed by DME propagation as well as ethylene methylation. In conditions of reduced DME conversion, propylene formation occurs nearly exclusively and via methylation of the added ethylene with selectivity close to 100% on SAPO-34 and H-ZSM-5. It was also demonstrated that DME propagation does not proceed via ethylene, on both topologies. The addition of ethylene to the DME feed switches the MTO mechanism toward a mechanism where propylene is a true primary product from DME. At higher temperature, the propylene is a product of the ethylene methylation, aromatic/ coke and olefins cycles. 

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