Propylene reaction paths

When hydrocarbons are present in the gas mixture, NO removal by oxidation to NOz occurs at much lower input energy and the reaction paths change significantly as compared to the case without hydrocarbons. Numerous works analyze the reaction mechanism of NO. conversion in non-thermal plasma with addition of hydrocarbons, especially ethylene [33,37,77,79,81-83], propylene [35,76,81,83-87], and propane [76,81,85,87],... 

The surface reactions of graphite electrodes in many nonaqueous solutions have been investigated intensively,29 30 and the major reaction paths in a variety of alkyl carbonate solutions seem to be quite clear. Both EC and PC decompose on graphite electrodes, polarized cathodically, to form solid surface films with R0C02Li species as major components,31 and ethylene or propylene gases, respectively, as co-products. 

Much of the recent work on the cyclopropane-propylene isomerization has had one of two objectives, either to try and determine which of the two reaction paths suggested by the early workers is involved, or to test the various theories of unimolecular reactions. Comer and Pease (1945), using catalytic hydrogenation to analyse their reaction product, but otherwise working under similar conditions to Chambers and Kistiakow-sky, suggested that all the results obtained could be represented just as well by the reaction scheme... 

The rate constants were determined at a series of pressures in the fall-off region, and the fall-off curve was very similar to that obtained for the structural isomerization to propylene. The similarity of the two sets of data suggests that both reactions may proceed through similar reaction paths. One obvious possibility is that once again the trimethylene biradical is formed, which can undergo internal rotation followed by recyclization. An alternative transition state has been suggested which involves, as an activated complex, a much expanded cyclopropane ring in which hindered internal rotation occurs (see also Smith, 1958). 

The reaction paths can be confirmed simply by adding intermediates to reacting mixtures of H2 + 02. Thus, when 2-butene is added, the primary products are propylene, acetone, isobutyraldehyde, CH4, and HCHO. Propylene gives C2H4, C2H5CHO, HCHO, CH3CHO, and CH4 as primary products. 3,3-Dimethyloxetane has not been added to date, and its oxidation products are thus not clear. Its structure would be consistent with acetone and isobutyraldehyde as major oxidation fragments. 

The use of isotopic tracers has demonstrated that the selective oxidation of propylene proceeds via the formation of a symmetrical allyl species. Probably the most convincing evidence is presented by the isotopic tracer studies utilizing, 4C-labeled propylene and deuterated propylene. Adams and Jennings 14, 15) studied the oxidation of propylene at 450°C over bismuth molybdate and cuprous oxide catalysts. The reactant propylene was labeled with deuterium in various positions. They analyzed their results in terms of a kinetic isotope effect, which is defined by the probability of a deuterium atom being abstracted relative to that of a hydrogen atom. Letting z = kD/kH represent this relative discrimination probability, the reaction paths shown in Fig. 1 were found to be applicable to the oxidation of 1—C3He—3d and 1—QH —1 d. 

Fig. 7. Reaction path of the two-step addition of a single propylene unit to a growing...

Three operation variables, benzene-to-propylene ratio (Rg), temperature (T), and space time (t) are of prime concern to a reactor designer. Since alkylation reactions are so fast, the controlling performance of the reactor is determined by the reaction selectivity. At a constant average temperature, examination of the reaction paths and kinetics models indicated that selectivity Increased with Increasing benzene-to-propylene ratio regardless of the space time applied. The temperature effect was slightly more complicated. Since most of a process reactor... 

The relative contributions of the three proposed reaction paths remain to be determined. The products from both the retro-ene and the addition reactions can be predicted with some quantitative certainty. For dodecene, the former produces only 1-nonene and propylene. The product distributions from the addition paths should be identical to those from the cracking of the corresponding paraffins. These product distributions can be predicted using the method of Rice and Kossiakoff (16). This approach parallels excellently with experiments (16,17). (From available data we estimate its accuracy as d=10%.) For dodecene, the addition of hydrogen atoms, methyl radicals, and ethyl radicals will produce Ci2H25, Ci3H27, and Ci4H29 parent radicals. The product distributions predicted by the Rice-Kossiakoff method for the decomposition of these radicals at 525°C are shown in Table IV. 

Trim-ethylene is a moiety with a shallow potential energy well on the reaction path connecting cyclopropane and propylene. Its very short unimolecular lifetime, following different types of initial excitations, has been calculated from classical trajectories [343,344] and compared with both experiment [391] and quantum dynamics [392]. Excellent agreement is found. This is an example of a rather large molecule, for which classical mechanics accurately describes the unimolecular dissociation because of the shallow potential energy minimum and, thus, very short lifetime. 

Just as in chemical catalysis, electrocatalysis provides a reaction path which lowers the energy of activation (see Fig. 3.1) and hence increases the rate of reaction, i.e., the current density for a given overvoltage. We can distinguish between the situation when a species in solution acts as a catalyst and a process where the reactive intermediate has to be adsorbed on the electrode. We have already met an example of the former in Section 3.1.3, namely the catalysis of the epoxidation of propylene by means of bromide ions. 

The / -radical 2-Cg// 3 disappears through isomerization and decomposition with formation of ethylene and new radicals. The reaction path is developed until a stage at which only relatively stable olefins are obtained. Specific reactions of ethylene and propylene may have to be added, though. 

Finally, an additional reaction pathway exists and this does not seem to be operative with SAPO-34 and Beta under regular processing conditions. This path seems to be operative with ZSM-5 and that may involve successive methylations of propene, followed by cracking to yield higher alkenes [111]. A similar mechanism that involves successive methylations of ethylene followed by cracking to yield higher alkenes over ZSM-5 does not seem to be as important [125]. It is conceivable that this mechanism may be partly operative during the MTO experiments over SAPO-34 described above that used co-fed ethylene or co-fed propylene [126]. 

The specifically formulated CGP-1 catalyst plays a vital role in the MIP-CGP process. Unique catalyst design, such as metal promoted MFl zeolite, phosphorus modified Y zeolite, and a novel matrix with excellent capability to accommodate coke [12] were involved to ensure the primary cracking and secondary reactions to proceed within a defined path. The commercial trial results of the MIP-CGP process in SINOPEC Jiujiang Company showed that, in combination with CGP-1 catalyst, the propylene yield was 8.96 wt%, which increased by more than 2.6% as compared with FCC process. The light ends yield and slurry yield are basically equal. The olefin content of the gasoline produced by MIP-CGP process was 15.0 v%, which was 26.1% lower than that of FCC gasoline. The sulfur content of gasoline was decreased from 400 to 270 pg/g. 

The latter complex undergoes CO loss to generate coordinatively unsaturated 4.28. Conversion of 4.28 to 4.30 is the crucial step that is responsible for the formation of the branched isomer. Obviously this reaction is possible only when propylene is present as one of the reactants, or under reaction conditions where propylene from //-propanol is generated in situ. Conversion of 4.28 to 4.30 is an example of alkene insertion into an M-H bond in a Markovnikov manner (see Section 5.2.2 for a discussion on Markovnikov and anti-Markovnikov insertion). The anti-Markovnikov path leads to the formation of 4.29, which is in equilibrium with 4.24. Complexes 4.25 and 4.26 are analogues of 4.4 with //-butyl and /-butyl groups in the place of methyl. They reductively eliminate the linear and branched acid iodides. In the presence of water the acid iodides are hydrolyzed to give //-butyric and / -butyric acids. 

Mechanistically, two pathways are logical (Scheme 3). The ethyl cation can directly alkylate methane via a pentacoordinated carbonium ion (Olah) (path a), or alternatively, although a less favorable pothway (b), the ethyl cation could abstract a hydride ion from methane. The methyl cation thus formed, which is less stable by 39 kcal/mole (26), could then react directly with ethylene. In the latter case, propylene and/or polymeric material would probably be formed since the hydrogen required for a catalytic reaction has been consumed by the formation of ethane. 

---