Secondary reactions ethane

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 product yields by carbon number are plotted in Figure 6. At all except the most severe conditions studied,the major component in the gas phase was n-butane. This observation is consistent with the a-ring opening and dealkylation mechanism proposed for tetra-and octa-hydrophenanthrene cracking. At the most severe conditions ethane was present in the greatest quantities. This can be explained by side chain cracking of n-butylbenzene according to the Rice-Kossiakoff mechanism or by secondary reactions of the n-butane. 

Apart from the products mentioned, secondary reactions also form various amounts of trichlorosilane, silicon tetrachloride, as well as gases (hydrogen, ethylene, ethane, etc.) and carbon. They also form compounds with fragments containing... 

This overall reaction, however, does not show all the stages of the process, since apart from the substances mentioned it forms hexaethyldilead, ethylene, ethane and butane, which demonstrates some secondary reactions. In particular, at the first stage of the reaction ethylchloride seems to interact with metallic sodium forming free ethyl radicals, i.e. the reaction uses the radical mechanism and ethyl radicals are responsible for further synthesis. 

The oxidative dehydrogenation reactions over these catalysts are similar to the gas phase result of shock tube experiments determined by Skinner et al. (ref. 6). This observation supports the fact that the recombination reactions of methyl radicals in the gaseous phase are an important source of ethane and that the ethene is a secondary product derived from ethane. This secondary reaction proceeds in the gaseous phase as well as the catalyst surface. The major role of the MgO surface is to produce the methyl radical efficiently. The active sites for cleaving the H-CH3 bond should be moderated by Li to enforce C2 selectivity. In addition to gas phase oxidation, the direct surface oxidation of the hydrocarbon adsorbate is very significant especially for acidic materials. 

The secondary reactions of ethane via unimolecular decomposition can be written as ... 

The fixed sulfur is bound to the tungsten as a surface layer with the average composition WgS. Secondary reactions subsequently produce ethyl mercaptan, ethane and H2S, and the average composition of the solid surface changes to W S. 

The products were the same as those obtained from propane but the distributions were different. In particular the production of butenes and of C5-C7 non aromatics (C5 ) was greater whereas that of methane, ethane and aromatics was smaller. The percentage of ethylene, butenes and Cg went through a mwximum showing that these conq>ounds underwent secondary reactions. The product distributions were different on HZSM5 and on ZnHZSMS ... 

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. 

For reaction B (Table 3) the observed ratio of ethanol to ethene is higher than the predicted ratio. This indicates that alcohols are probably not formed by the hydration of alkenes in secondary reactions. The reverse reaction is more likely. The data for reaction C show that the ratio of ethanol to ethane is much higher than expected and so from cases B and C, it appears possible that alcohols could be primary products. 

Secondary reactions of ethane Initially, reactions 1, 2 and 3 describe the course of the decomposition, but as ethane accumulates it begins to disappear in the dehydrogenation sequence, reactions 4, 5 and 2, and should reach a steady-state concentration if no other processes intervene. At the steady state,... 

Surface effects were also Investigated by experiments In a reaction vessel filled with quartz tubes which Increased the sur-face/volume ratio by a factor of 10. Initial rates of ethane formation were quite unaffected, and the early stages of the decomposition were undoubtedly homogeneous. Formation of secondary products and of ethane. In the autocatalytic stage showed some surface enhancement, suggesting a small surface component In the secondary reactions, probably less than 10% of the whole. This relative lack of sensitivity to surface/volume ratio again Indicates that surface deposits of carbon are not very Important In the reaction mechanism. 

At partial pressures near one atmosphere, ethane decomposes by a simple Rice-Herzfeld mechanism, with combination or disproportionation of ethyl radicals as the predominant chain-ending step. However, at a total pressure ot 100 mm., or at a partial pressure of 0.01 atm. another chain-ending step predominates. Unlike butane formed from ethyl, the products of this step cannot be distinguished analytically from the major products of the reaction chain. It is therefore believed to involve reaction of H and C2H5, either homogeneously or at the reactor wall. Quantitative rate and yield data are given, as are methods of correction for secondary reactions and of extrapolation to zero reaction time. 

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