PAH emissions from high-temperature oxidation of vaporized anthracene

The presence of polycyclic aromatic hydrocarbons/compounds (PAH/PAC) in the exhaust of combustion equipment as well as their growth to soot particles depends on the balance of formation and depletion reaction pathways. Detailed understanding of PAH oxidation is necessary for a correct quantitative description of combustion processes. This study focuses on the high-temperature oxidation of anthracene, a 3-ring PAH, by molecular oxygen. By reacting this already formed PAH, under non-sooting conditions, its oxidative depletion processes were isolated from its formation processes, as well as from soot formation pathways. Anthracene powder, fluidized in nitrogen, was introduced into a two-stage electrically heated laminar-flow drop-tube furnace. In the first stage, kept at 900 °C, anthracene was vaporized. Thereafter, upon mixing with preheated oxygen-containing gases in a venturi, gaseous anthracene was oxidized in the second furnace at oxygen mole fractions of 1–5% and gas temperatures of 950–1050 °C. Gas temperature and velocity profiles in the furnaces, as well as anthracene particle vaporization trajectories were obtained with a computational fluid dynamics code. Sampling, followed by chemical analysis, was conducted at three locations within the oxidizing furnace. Trends with residence time show increasing CO and CO2 yields in the furnace and gradually decreasing O2. CO increased with higher oxidizing temperatures and oxygen concentrations. Acetylene was the most abundant light hydrocarbon, followed by methane, ethylene, benzene, propylene and ethyl acetylene. Prevalent PAC included fluorene-9-one, 9,10-anthracenodione, biphenylene, dibenzofuran, fluorene, indene, naphthalene, anthrone, xanthone and 2-naphthalenecarboxaldehyde. Most species’ yields increased with rising oxidation temperatures. A global anthracene reaction rate with oxygen was deduced, and an activation energy of 71 kJ/mol was calculated. An anthracene oxidation reaction scheme was proposed.