Polycyclic aromatic hydrocarbons in combustion residues from 1,3-butadiene

Abstract

Residues from combustion of 1,3-butadiene in vapor and pool fires under normal air were extracted and analyzed by GC and GC-MS. Typical chromatograms showed some 60 major resolved peaks, about 145 minor peaks, and unresolved mixtures. Resolved compounds included aromatic (e.g., C₂-benzenes, indene, C₁- and C₂-indenes) and PAH compounds from 2 to 6 rings along with extended PAH series containing five membered rings (e.g., benzoindenes, cyclopentaphenanthrenes, acephenanthrylene, acepyrene, cyclopentapyrenes, indenopyrene). These PAHs were primarily unsubstituted. The presence of labile pentacyclic rings in prominent compounds suggested that low temperature (400–500°C) pyrolytic processes were operating in the butadiene flames. On the other hand, assemblages of ortho-peri condensed PAHs (mass 202 −276; e.g., pyrene, benzopyrenes, perylene) with limited amounts of alkyl substitution indicated a higher temperature provenance (> 750 °C). Measurements indicated significant thermal gradients (430 °C to > 900 °C) in the vapor flames. The concentration of benzo(a)pyrene generated per gram butadiene burned in vapor fires was estimated between 20 – 58 μg. Total concentration for all resolved compounds was c. 9000 μg PAHs/g butadiene burned. The pool fire PAH yields were 50% - 70% of those observed for the vapor fires but the measured flame temperatures were lower (350 – 500 oC). Nevertheless the PAH compound distributions were similar in many ways to those of the vapor fire, including the presence of the “high temperature” PAHs identified in the vapor fires. These and other compositional features of residues from both flames suggested that Diels-Alder reaction mechanisms were important and that relative flame temperatures did not fully account for observed PAH distributions.