Polycyclic Aromatic Hydrocarbon (PAH) and Soot Formation in the Pyrolysis of Acetylene and Ethylene: Effect of the Reaction Temperature

The formation of soot and polycyclic aromatic hydrocarbons (PM-is) has been studied during the pyrolysis of acetylene and ethylene at different reaction temperatures (1073-1423 K) in a tubular flow reactor at atmospheric pressure. The 16 PAHs classified by the United States Environmental Protection Agency (U.S. EPA) as priority compounds, together with light gases present at the outlet gas stream, were quantified by a chromatographic method. Soot formed was collected on a filter at the reactor outlet and later quantified. In this way, the relationship between PAH, gas, and soot formation can be discussed. The distribution of the target PAHs in the different phases (at the gas phase, adsorbed on soot, and/or sticked on reactor walls) is also analyzed. The speciation of the individual PAH compounds was achieved by a combination of Soxhlet extraction, extract concentration by a rotary evaporator, and gas chromatography coupled to mass spectrometry (GC-MS). The present study shows that, in the pyrolysis of both acetylene and ethylene, while soot formation is enhanced by increasing the temperature, the PAH yield exhibits a maximum in the evaluated temperature range, and such a maximum value depends upon the hydrocarbon used (ethylene or acetylene). However, the PAH distribution in the different phases does not seem to be influenced by hydrocarbon used. PAHs from ethylene and acetylene pyrolysis are seen to be mainly adsorbed on soot preferably than on other places, except for naphthalene (NAPH) in the pyrolysis of ethylene, in which case a higher concentration was found at the gas phase.