Severe Pyrolysis of the C12 Hydrocarbons n-Dodecane, Cyclododecane, and 2,6-Dimethyl-Decalin, with Rice-Herzfeld and Graph-Theoretic Interpretations

High temperature, short residence time pyrolyses of n-dodecane, cyclododecane, and 2,6-dimethyl-decalin were experimentally investigated. A coiled tube flow reactor was used, with outlet temperatures 1050-1150 K, residence times ~0.3 s, and steam/hydrocarbon ratios ~1, to simulate commercial steam cracking of naphthenic feedstocks at severities from 0.8 to 3.3. Experimental selectivities Sj = (mol j produced/100 moles of substrate decomposed) were calculated for j = methane, ethylene, propylene, butadiene, isoprene and benzene, the products of special interest in olefin plant operations. 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 graph-theoretic methods based upon the A(djacency) and C(ycle) matrices of the substrates. These revealed the influence of both the size and numbers of rings within each substrate upon their pyrolysis pathways and also the profound influence of either the absence or presence of methyl substituents.