(174a) A Graph Theoretic Moiety Hypothesis for Olefin Yields from High Severity Pyrolyses of C6 to C12 Cyclo-Alkanes

A graph-theoretic “moiety hypothesis” is proposed wherein the selectivity to a particular olefin product is a linear function of the unsubstituted and methylated moieties in a cycloalkane substrate. This is applied to the yields of ethylene, propylene, butadiene, isoprene, and mono-aromatic products experimentally obtained from the high temperature, short residence time pyrolyses of cyclohexane, methyl-cyclohexanes, decalin and methyl-decalins. A coiled tube flow reactor was used at outlet temperatures about 1100 K and residence times of order 300 milliseconds with steam dilution to simulate commercial steam-cracking conditions at severities from 1 to 4. Decomposition kinetics and the major and minor product selectivities obtained from selected substrates were also interpreted in terms of conventional Rice-Herzfeld free-radical pathways, for comparison with the graph-theoretic approach. An attempt was made to apply the present results to the steam-cracking of heavy naphthenic feedstocks.