Catalytic decomposition, paraffins

In considering the chemical reactions based on the light olefins it is obvious that natural gas liquids are at a disadvantage in comparison with the corresponding refinery cuts. These contain varying but substantial percentages of olefins as such—the results of thermal and catalytic decomposition of the heavier petroleum molecules. But refinery olefins are also in demand for synthesis to premium motor fuels. It is fortunate that there are abundant supplies of natural gas paraffins for conversion to provide adequate raw material for our olefin chemistry. 

As an example of a unimolecular decomposition reaction, we study the monomolecular catalytic cracking reaction of //-paraffins in high-silica acid zeolites or other crystalline or ordered acid porous materials, in this section [97-102],... 

The main task of thermal and catalytic cracking is decomposition of large (long) hydrocarbon molecules into smaller ones. High-molecular feedstock, such as paraffin hydrocarbons and plastic chains produces lower molecular paraffins and a-olefins [5] ... 

The decomposition of pure phase carbonate minerals has been extensively studied and reviewed (17). The influence of these minerals on oil shale pyrolysis kinetics has not been extensively studied, but the studies of Jukkola et al. (18) and Campbell (15) are notable. The results of both these studies indicate that the major calcite decomposition step is through reaction with silicate minerals in shale to produce Ca- and Ca-, Mg-silicates. The observed enhancement in pyrolysis yield after carbonate removal may be indicative of the catalytic role of silicate minerals in paraffinic and aromatic compound decompositions. In effect, an apparent preference for calcite-silicate interactions in raw shale limits silicate-catalyzed organic reactions which would presumably result in enhanced oil yields. It should be noted, however, that the silicate/carbonate ratio is increasing with net pyrolysis yield for the raw shales, Table I. This may reflect excess silicates becoming free to catalyze organic decomposition. 

The next step in the catalytic cracking of paraffins is the decomposition of the activated molecule, or carbonium ion. The rules governing that particular phase are relatively clear. The primary rule involved is that the carbon-carbon cleavage occurs at the position one carbon atom away from the carbonium-ion carbon atom. 

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