Pyrolysis of n-Butylbenzene at Various Pressures: Influence of Long Side-Chain Structure on Alkylbenzene Pyrolysis

Abstract

This work investigates the pyrolysis of n-butylbenzene, which widely exists in transportation fuels and their surrogate mixtures. Both reactive and stable pyrolysis products were comprehensively detected with synchrotron vacuum ultraviolet photoionization mass spectrometry. Their mole fractions versus temperature were also evaluated at 30, 150, and 760 Torr. A kinetic model of n-butylbenzene pyrolysis was developed, and new data were used to validate the model. On the basis of the modeling analysis, the benzylic C–C bond dissociation that forms the benzyl radical and the propyl radical was found to be a key decomposition reaction of n-butylbenzene at all investigated pressures, whereas H abstraction provided increasing contributions with increasing pressure. Compared with small alkylbenzenes, such as toluene and ethylbenzene, n-butylbenzene demonstrates different pyrolysis characteristics and chemistry because of the existence of its long alkyl side chain. n-Butylbenzene has a higher pyrolysis reactivity and lower decomposition temperature regions, which inhibit the further decomposition of the benzyl radical and the formation of highly unsaturated C2–C4 products. As a result, conventional combination reactions between aromatic radicals and highly unsaturated C2–C4 species are only minor formation pathways for indene and naphthalene in n-butylbenzene pyrolysis, while fuel-specific pathways become crucial instead. Furthermore, combination reactions involving the benzyl radical and the phenyl radical are crucial for the formation of many PAHs, especially phenanthrene and fluorene. The results in this work reveal the strong influence of side-chain length on the pyrolysis chemistry of alkylbenzenes and indicate a further need for exploring the influences of other structural features.

Unraveling chemical structure of laminar premixed tetralin flames at low pressure with photoionization mass spectrometry and kinetic modeling

“…As a result, tetralin is almost totally consumed by bimolecular reactions via the attack of small radicals, while the unimolecular decomposition reactions show only minor contributions to the consumption of tetralin in both the lean and rich flames. This is similar to the case in the pyrolysis of tetralin, 14 which indicates that tetralin has quite different decomposition characteristics to alkylbenzenes like ethylbenzene, 29,40 n ‐propylbenzene, 33,41 and n ‐butylbenzene 42,43 . Among the unimolecular decomposition reactions, the H 2 ‐elimination reaction producing H2A2 and H 2 and the simultaneous cleavage of two benzylic CC bonds producing o ‐xylylene (o‐C 8 H 8 ) and C 2 H 4 are the dominant ones in both the lean and rich flames, while the total contribution of unimolecular decomposition reactions to the consumption of tetralin is enhanced in the rich flame, as shown in Figure 5.…”

“…This is similar to the case in the pyrolysis of tetralin, 14 which indicates that tetralin has quite different decomposition characteristics to alkylbenzenes like ethylbenzene, 29,40 n-propylbenzene, 33,41 and n-butylbenzene. 42,43 Among the unimolecular decomposition reactions, the H 2 -elimination reaction producing H2A2 and H 2 and the simultaneous cleavage of two benzylic C C bonds producing o-xylylene (o-C 8 H 8 ) and C 2 H 4 are the dominant ones in both the lean and rich flames, while the total contribution of unimolecular decomposition reactions to the consumption of tetralin is enhanced in the rich flame, as shown in Figure 5. It can be found that both of the two dominant unimolecular decomposition reactions are not producing any radicals, indicating the negligible roles of the unimolecular decomposition reactions in the chain reaction system of tetralin flames.…”

A functional-group-based approach to modeling real-fuel combustion chemistry – I: Prediction of stoichiometric parameters for lumped pyrolysis reactions

“…The present work first investigated the temperature, pressure and reaction time dependencies of the yields of CH4, C6H6 and C7H8, based on detailed kinetic models [23][24][25]. Three C10 fuels, n-decane, decalin and n-butylbenzene, were selected to represent paraffinic, naphthenic and aromatic fuel classes.…”

“…were initially collected from experiments on the pyrolysis of 44 neat fuels, covering wide temperature, pressure and reaction time conditions. They were obtained in different labs with various experimental apparatus, such as shock tubes [26][27][28][29], flow reactors [22,25,30,31] and jet-stirred reactors (JSR) [32,33]. All of these collected speciation data included experimental uncertainties, so they were evaluated to establish consistency across different datasets.…”

Exploring pyrolysis and oxidation chemistry of o-xylene at various pressures with special concerns on PAH formation

“…The flow reactor pyrolysis experiments were performed at the National Synchrotron Radiation Laboratory. Detailed introduction to the beamline and the flow reactor apparatus have been introduced elsewhere [16][17][18][19]. o-Xylene (purchased from Sinopharm Chemical Reagent Limited Co., Shanghai, China, with purity≥99%) was gasified in a home-made vaporizer.…”