Effect of Sodium Hydroxide Addition on Polycyclic Aromatic Hydrocarbon Emissions of Toluene Flames
2000
Wei, Yu-Ling
Addition of sodium hydroxide solution into organic flames has been extensively investigated to reduce soot formation; nevertheless, data on the effect of metal salt solution on the formation of hazardous air pollutants of polycyclic aromatic hydrocarbons (PAHs) are rather scarce. A laboratory-scale liquid-injection incinerator was used to incinerate toluene, which resembled a waste or used solvent. Solid-phase and gas-phase PAHs in the flue gases were sampled, treated, and analyzed using a high performance liquid chromatograph (HPLC). The experimental parameters included equivalence ratio and concentration of added sodium hydroxide solution. The incineration temperature was 750°C and the nominal gas residence time was approximately 2.5 s. Results indicated that particles might play a very active role in the formation of PAHs under all experimental conditions. Further, under oxygen-rich incineration, addition of sodium hydroxide solution caused a considerable increase of the sixteen solid-phase priority pollutant PAHs (pp-PAHs); while for oxygen-lean toluene flame the effect of addition of NaOH solution on solid-phase PAH was only slight. This greater solid-phase PAH content on soot of the oxygen-rich NaOH-seeded toluene flames suggested that the radical catalysis cycle of NaOH to NaO₂ to Na to NaO, then back to NaOH (Zamansky et al., 1999) might have affected the solid-phase PAH measurements. We speculate that hydrogen atoms were abstracted from hydrocarbons to form H₂O and 16 pp-PAHs by OH radicals that were produced via the sodium catalysis cycle.
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