(27g) Severe Pyrolyses of Methylated Cyclohexanes, With Rice-Herzfeld and Graph-Theoretic Interpretations

High temperature, short residence time pyrolyses of cyclohexane, methyl-cyclohexane, 1,2- dimethyl-cyclohexane and 1,4- dimethyl-cyclohexane were experimentally investigated using a coiled tube flow reactor with outlet temperatures 1100-1200 K, residence times ~0.3 s, and steam/hydrocarbon ratios ~1, to simulate commercial steam cracking of naphthenic feedstocks at severities from 1.5 to 4.   Decomposition kinetics and product selectivities were interpreted two ways.  First by the classical Rice-Herzfeld types of free-radical pathways, initiated by substrate bond fissions and containing the requisite H-abstraction, beta-scission, isomerization, combination and disproportionation types of elementary steps, and second by taking graph-theoretic excursions upon the A(djacency) matrices of each of the monocyclic substrates.  The  influence of either the absence or presence of methyl substitution, and of the number of methyl substituents, and their peripheral proximities, upon the pyrolysis pathways of each substrate was discerned from the observed yields of specific products, namely, ethylene, propylene, butadiene, isoprene and benzene, of interest in olefin plant operations.