High temperature, short residence time pyrolyses of n-decane (NDN), cyclo-decane (CYDN), and decahydronaphthalene (DNH aka decalin) were experimentally investigated using a coiled tube flow reactor 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 high severities.  Decomposition kinetics at T = 1125 K provided apparent first order rate constants keff ~15 s<sup>-1</sup> for each of NDN, CYDN, and DHN, insensitive to the presence and number of rings.  Corresponding Arrhenius parameters [log A (1/s), E* (kcal/mol)] were, respectively, NDN[8.2, 36.3] and DHN[8.2, 36.6].  The selectivities of specific products relevant to olefin plant operations , in mol/100 mol substrate converted, at T= 1125 K, from each of (NDN, CYDN, DHN) were: CH4 (85, 66, 77), Ethylene (211, 159, 111), Propylene (67, 56, 22), Butadiene (18, 30, 14) and Benzene (4, 9, 26).  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 substrate.  Graph-theory suggests that mono-cyclo-alkane Cn pyrolysis should yield only ethylene and butadiene, with respective selectivities 100*(n-4)/2 and 100. Actual experimental pyrolysis of CYDN (n = 10) provided ethylene ~1/2 and butadiene ~ 1/3 of theoretical.  These diminished selectivies relative to theoretical are likely due to Rice-Kossiakoff isomerizations that render mono-cyclo-alkane pyrolysis pathways akin to those of the corresponding n-alkanes.

Severe pyrolyses of n-decane, cyclodecane, and decahydronaphthalene, with graph-theoretic interpretations

255th National Meeting (2018)

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