Aromatics Pyrolysis Kinetics

The decomposition of pure phase carbonate minerals has been extensively studied and reviewed (17). The influence of these minerals on oil shale pyrolysis kinetics has not been extensively studied, but the studies of Jukkola et al. (18) and Campbell (15) are notable. The results of both these studies indicate that the major calcite decomposition step is through reaction with silicate minerals in shale to produce Ca- and Ca-, Mg-silicates. The observed enhancement in pyrolysis yield after carbonate removal may be indicative of the catalytic role of silicate minerals in paraffinic and aromatic compound decompositions. In effect, an apparent preference for calcite-silicate interactions in raw shale limits silicate-catalyzed organic reactions which would presumably result in enhanced oil yields. It should be noted, however, that the silicate/carbonate ratio is increasing with net pyrolysis yield for the raw shales, Table I. This may reflect excess silicates becoming free to catalyze organic decomposition. 

E. 1. Shin, M. Nimlos, and R. 1. Evans, The formation of aromatics from the gas-phase pyrolysis of stigmasterol Kinetics, Fuel 80(12 Special Edition SI), 1681-1688 (2001). 

E. B. Ledesma, N. D. Marsh, A. K.Sandrowitz, and M. J. Womat, Global kinetic rate parameters for the formation of polycycUc aromatic hydrocarbons [PAH] from die pyrolysis of catechol A model compound representative of soUd fuel moieties. Energy Fuels 16(6), 1331—1336... 

Electrophilic replacement constants crXr have been obtained for all the positions of benzo[6]thiophene from the solvolysis of isomeric l-(benzo[ >]thienyl)ethyl chlorides in 80% ethanol-water. These constants signify replacement of the entire benzene ring by another aromatic system (74JOC2828). The positional order of reactivity was determined to be 3>2>6>5>4>7, all positions being more reactive than benzene. The same order was also derived from the kinetic data for pyrolysis of the isomeric l-(benzo[6]thienyl)ethyl acetates (78JCS(P2)1053). A modified extended selectivity treatment has been developed to correlate electrophilic substitution data in benzo[Z> ]thiophene, which assumes a dual activation mechanism (79JOC724). 

To begin the exploration of actual reaction pathways in complex pyrolyses of aromatic substances, we have carried out a detailed experimental and theoretical analysis of the liquid-phase pyrolysis of bibenzyl. This pyrolysis system has been studied by others (44,45,46), and the general kinetic features of this reaction system are now rather well agreed on. Complete details of this work will appear elsewhere (38a) and a few implications of this work of particular relevance to coal reactions will be discussed here. 

Naphtha feed is treated as a single pseudo species. Naphthas, used as pyrolysis feedstocks, are mainly composed of paraffins and naphthenes, with lesser amounts of aromatics. Olefin content is usually very small. Consistent with observed pyrolytic behavior of paraffins and naphthenes (15,16,26,27,28), feed decomposition is assumed to follow first-order kinetics. Equation 3 of the reactor model can be simplified as follows. 

A patented process has been developed for the production of electrode binder pitch from petroleum-based materials. Carbon anodes produced from the petroleum-based pitch and coke have been used successfully on a commercial scale by the aluminum industry. One stage of the process involves the pyrolysis of a highly aromatic petroleum feedstock. To study the pyrolysis stage of the process a small, sealed tube reactor was used to pyrolyze samples of feedstock. The progress of the reaction is discussed in terms of the formation of condensed aromatic structures, defined by selective solvent extraction of the reaction product. The pyrolysis of the feedstock exhibits a temperature-dependent induction period followed by reaction sequences that can be described by first-order kinetics. Rate constants and activation energies are derived for the formation of condensed aromatic structures and coke. 

Shin, E.-J., N. Mark, and R.J. Evans Gas phase kinetic studies of the formation of aromatics in the pyrolysis of... 

The use and importance of aromatic compounds in fuels sharply contrasts the limited kinetic data available in the literature, regarding their combustion kinetics and reaction pathways. A number of experimental and modelling studies on benzene [153, 154, 155, 156, 157, 158], toluene [159, 160] and phenol [161] oxidation exist in the literature, but it would still be helpful to have more data on initial product and species concentration profiles to understand or evaluate important reaction paths and to validate detailed mechanisms. The above studies show that phenyl and phenoxy radicals are key intermediates in the gas phase thermal oxidation of aromatics. The formation of the phenyl radical usually involves abstraction of a strong (111 to 114 kcal mof ) aromatic—H bond by the radical pool. These abstraction reactions are often endothermic and usually involve a 6 - 8 kcal mol barrier above the endothermicity but they still occur readily under moderate or high temperature combustion or pyrolysis conditions. The phenoxy radical in aromatic oxidation can result from an exothermic process involving several steps, (i) formation of phenol by OH addition to the aromatic ring with subsequent H or R elimination from the addition site [162] (ii) the phenoxy radical is then easily formed via abstraction of the weak (ca. 86 kcal moT ) phenolic hydrogen atom. 

Sakai, T., et al. A Kinetic Study on the Formation of Aromatics During Pyrolysis of Petroleum Hydrocarbons, in Albright, L. F. und Crynes, B. L. Industrial and Laboratory Pyrolyses. ACS Symposion Series 32, Washington 1976, p. 152-177. 

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