Portal de Periódicos da CAPES

Formation of polycyclic aromatic hydrocarbons and their radicals in a nearly sooting premixed benzene flame

2000; Elsevier BV; Volume: 28; Issue: 2 Linguagem: Inglês

10.1016/s0082-0784(00)80679-7

1873-2704

Henning Richter, Timothy G. Benish, Oleg A. Mazyar, William H. Green, Jack B. Howard,

Catalytic Processes in Materials Science

Polycyclic aromatic hydrocarbons (PAH) are associated with health hazardous effects, and combustion processes are major sources of their presence in atmospheric aerosols. In the present work, chemical reaction pathways of PAH formation have been investigated by means of the modeling of a nearly sooting, low-pressure, premixed, laminar, one-dimensional benzene/oxygen/argon flame (equivalence ratio =1.8, 30% argon, gas velocity at burner at 298 K v=50 cm s−1, pressure=2.67 kPa). This flame has been investigated by Bittner and Howard using molecular-beam sampling coupled to mass spectrometry. More recently, Benish extended the set of available data for radicals up to 201 amu and for stable species up to 276 amu using nozzle-beam sampling followed by radical scavenging with dimethyl disulfide and subsequent analysis by gas chromatography-mass spectrometry. An existing kinetic model has been refined. Density functional theory computations were used to update the thermodynamic database, while transition state theory followed by a bimolecular quantum Rice-Ramsperger-Kassel analysis allowed for the determination of kinetic data relevant for the present study. The reaction of phenylacetylene radicals with acetylene is shown to be limiting for the concentration of 1-naphthyl radicals, while naphthalene is formed mainly by self-combination of cyclopentadienyl. The insufficient consumption of PAH as well as acetylene beyond the reaction zone gives some evidence of the need of additional PAH growth pathways involving acetylene but thermodynamically more favorable than subsequent hydrogen-abstraction/acetyleneaddition reactions. A new pathway for acenaphthylene formation is suggested and consists of benzyne recombination followed by hydrogen attack and isomerization.