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A systematically generated, pressure-dependent mechanism for high-conversion ethane pyrolysis. 1. Pathways to the minor products.

The deposition of carbon during hydrocarbon pyrolysis is part of many industrial processes. The rate and nature of deposition depend, in part, on the gas-phase chemistry of the minor pyrolysis products, which serve as deposition precursors. But the specific reaction pathways governing the formation and destruction of these minor gas-phase products are only partially known. We apply an updated version of our automated mechanism generation tool XMG-PDep to the high-conversion, pyrocarbon-depositing ethane pyrolysis system of Glasier and Pacey, to systematically uncover the likely reaction pathways governing the observed minor products acetylene, propylene, 1,3-butadiene, and benzene. Thorough examination by means of sensitivity, equilibrium, and reaction-pathway analyses reveals an extremely complex, intertwined set of reaction pathways controlling these deposition precursors, some of which are not often considered in the wider pyrolysis literature. Large, aggregated sets of disproportionation reactions, for example, appear to play an important role in the formation of benzene. The analyses motivate a companion paper (following paper in this issue) which explores in greater depth the effects of large groups of radical disproportionation reactions, omitted reaction families, and the possibility that pressure changes in the reactor could alter the distribution of the deposition precursors.