Secondary reactions propylene

Table 4.43. Skeletal geometries and atomic charges of the alternative secondary-Cp (Hsec) andprimary-Cp (IIpri) propylene complexes, as well as of the transition state (IIpri ) and actual product (IIIpri) of the model propylene-polymerization reaction (4.107) cf Figs. 4.79 and4.80...

As part of the same study selectivity data were provided at 10-100 kPa partial pressures of n-butane at 0-17% conversion over HZSM-5 [90]. With increase in pressure and conversion secondary reactions started to occur. These results are also summarized in Table 13.6. The lowered selectivity to hydrogen, methane and ethane was attributed to increasingly less favorable conditions for monomolecular cracking. The dramatic increase in selectivity to propane which was absent at zero conversion, along with decrease in propylene was considered as signature for bimolecular cracking. More specifically, it was suggested that hydride transfer... 

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. 

For the kinetics we suppose that propylene reacts with adsorbed oxygen, and that a certain amount of adsorbed but unreactive propylene interferes with oxygen adsorption. Thus, propylene appears in the numerator for the primary reaction, and in the denominator for both primary and secondary reactions. If B stands for the fraction of C3H6 that is oxidized, and D for the fraction oxidized to C02, the kinetic equations for the system may be written ... 

Nor did catalytic cracking escape the probing attention of Paul Emmett. At Johns Hopkins his students used labeled molecules extensively to examine the nature of secondary reactions in the cracking of cetane over amorphous silica-alumina and crystalline zeolites. They demonstrated that small olefins (e.g., propylene) are incorporated extensively into higher-molecular-weight molecules, especially aromatics, and are the primary source of coke formation on these catalysts. 

Basing on investigations carried out, it is shown that the conjugated oxidation of propylene is a controllable process and, with respect to particular conditions, secondary reaction may display three dominant propagation directions as follows ... 

Fig. 12. Secondary reactions of primary synthesis products at low CO concentrations (Co/SiO, 2700 kPa, H2/CO = 3.0, 6.2 wt% Co, 4.8% dispersion), (a) Bed residence time effects on CO conversion and C5+ selectivity (b) CO depletion effects on propylene and propane carbon selectivity.

The high selectivities for propylene which can be as high as 45 % (12) and the low selectivities for ethylene suggest that ethylene could be a primary product in Fischer-Tropsch which could undergo a secondary reaction leading selectivity to propylene. 

The post-modification with propylene oxide gives the best catalytic results, both with Sil-GP-tacn and MCM-GP-tacn. For the latter system, methanol seems a superior solvent in comparison with acetone and acetonitrile. The epoxide selectivity in reaction 7 is limited, but this is due to secondary reactions of initially formed epoxide to phenylacetaldehyde and the diol. When these secondary products are taken into account, the selectivity for the epoxide and its derived products increases to 76 %. 

Coke formation decreases with higher gas velocities (Table 2), in the case of ZSM-5 at 500 C it may be assumed that hydrocracking is becoming a very fast secondary reaction, leading to a high selectivity towards methane and considerable amounts of coke. The nature of the maxima in the selectivities for ethylene and propylene for H -mordenite at WHSV=24 (Fig. 2) is at present not fully understood. 

In many reacting systems, the temperature of the upper steady slate ma> sufficiently high that it ts undesirable or even dangerous to operate at this t dition. For example, at the higher temperatures, secondary reactions can place, or as in the case of propylene glycol in Example. 8-8 and 8-9, evap tion of the reacting materials can occur. 

The primary products produced in isobutane cracking are propylene and isobutylene. Propane, ethylene, and ethane and methane are produced in subsequent secondary reactions as well as significant amounts of liquid products (dripolenes). 

Anthony and Singh concluded from a kinetic analysis of the methanol conversion to low molecular weight olefins on chabazite that propylene, methane, and propane are produced by primary reactions and do not participate in any secondary reactions, whereas dimethylether, carbon monoxide, and ethane do. Ethylene and carbon dioxide appear to be produced by secondary reactions. It was also shown that the product selectivities could be correlated to the methanol conversion even though the selectivity and the conversion changed with increasing time on stream due to deactivation by coke formation. 

The chief secondary reaction is the further chlorination of allyl chloride to 1,3-dichloropropane. Another side reaction is the additive chlorination of propylenes to 1,2-dichloropropane. This reaction is favored by low temperatures and, at a reaction temperature of 200 C or lower, takes place to the virtual exclusion of substitutive reactions. Dichloropropane is always present to an appreciable extent even with reaction temperatures as high as 600 C. 

Secondary reactions of propylene Radical chain dehydrogenation... 

Secondary reactions of ethylene, acetylene and propylene As ethylene accumulates. It will begin to disappear In tne dehydro-genatlon and methylatlon sequences reactions (6, 7 and 2, and 8,... 

Again, this set of secondary reactions does not result in net formation or termination of chains. However, the extra methane so formed, must be subtracted from total methane, in calculating the number of chains initiated. As with the secondary reactions involving ethylene, a propylene tends to be formed for each secondary methane. Insofar as this remains unreacted, the propylene can be used to calculate the secondary methane, from whichever source. 

As the yields of these initial products decrease with increased residence times, cyclic compounds such as cyclopentene, cyclopen tadiene, cyclohexene and benzene are produced. In the case of propylene (, 7 ), the reaction proceeds 2-4 times faster than that of ethylene and ethylene, methane, butadiene, butenes, acetylene, and methylcyclopentene are the main products during the initial step cyclopentadiene, cyclopentene, benzene, toluene and polycyclic compounds higher than or equal to naphthalene are products of secondary reactions. A remarkable fact for the thermal reaction of propylene is that the yields of five membered ring compounds are larger than those in the case of ethylene. 

The thermal decomposition of propylene involves a series of primary and secondary reactions leading to a complex mixture of products. Studies showed that the distribution of pyrolysis products varies considerably with the pyrolysis conditions and the type of reactor used. There is agreement among the studies on propylene pyrolysis that the three major products of pyrolysis are methane, ethylene, and hydrogen. However, there is disagreement on the types and amounts of minor or secondary product species. Ethane, butenes, acetylene, methylacetylene, allene, and heavier aromatic components are reported in different studies, Laidler and Wojciechowski (1960), Kallend, et al. (1967), Amano and Uchiyama (1963), Sakakibara (1964), Sims, et al. (1971), Kunugi, et al. (1970), Mellouttee, et al. (1969), conducted at different conversion and temperature levels. Carbon was also reported as a product in the early work of Hurd and Eilers (1943) and in the more recent work of Sims, et al. (1971). 

It might also be that, in certain cases, the reaction with particularly high is in reality of a chain nature. The occurrence of secondary reactions proceeding by a chain mechanism is characteristic of most unimolecular reactions. Thus, to find the rate constant of a truly unimolecular reaction unperturbed by secondary processes, measurements are usually made in the presence of foreign gases such as nitrogen oxide, toluene or propylene capable of completely suppressing the reaction. 

Figure 24.6 shows the variation of the main partial oxidation products during the oxidation of propane (Fig. 24.6a) and propylene (Fig. 24.6b) over a MoVTeNbO catalyst. It can be observed that propane is initially transformed into propylene (unstable primary product), which is then selectively oxidized into acrylic acid (a secondary reaction product). The formation of the olefin is clear, since the initial selectivity to propylene of ca. 90% is observed in effective catalysts for the partial oxidation of propane.A similar reaction network has been proposed for propane oxidation with modified VPO catalysts,but also in the propane... 

To these sets of primary and secondary reactions related to solvents, one has to add the eontributions of salt anion reduction, which usually forms metal halides and M AXy species (A is the main high oxidation-state element in the salt anion and X is a halide, such as chloride or fluoride). Most of the produets of aetive metal surface reactions are ionic compounds that are insoluble in the mother solution, and therefore, precipitate as surface films. It should be added to this picture that possible polymeric species can be formed, espeeially in alkyl carbonate solvents, whose reduction forms polymerizable species sueh as ethylene or propylene. Hence, the surface films formed on active metal electrodes are very complicated. They have a multilayer structure perpendicular to the metal surface, and a lateral, mosaic-type composition and morphology (i.e. containing mixtures and islands of different compounds and grains). Such a structure may induce very non-uniform current distribution upon metal deposition or dissolution processes, which leads to dendrite formation, a breakdown of the surface films, etc. These situations are demonstrated in Fig. 13.6 active metal dissolution leads to the break-and-repair of the surface films, thus forming mosaic-type structures. 

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