Oxygen effect on PAH and PM formation in low temperature benzene pyrolysis

Abstract

Carbonaceous particulate matter (PM) is formed by combustion of hydrocarbon fuel. PM contains SOF (soluble organic fraction) and vapor phase hydrocarbons, and the main component of PM is soot. Soot formation process is considered to start from pyrolysis of the fuel, but needs more detail analysis. Then, formation processes of PAHs (polycyclic aromatic hydrocarbons) and PM in a benzene-oxygen-nitrogen mixture were experimentally investigated using a flow reactor. The effects of temperature, especially low temperature, and oxygen on these processes were analyzed by independent control of them. To analyze growth processes from single-ring aromatics to PAHs, mass concentrations of naphthalene, biphenyl, phenanthrene, anthracene, and pyrene were measured by GC-FID. Furthermore, the total mass concentrations of single-, two-, three-, and four-ring aromatics were evaluated to clarify temperature and oxygen effects on these processes. Experimental results showed that concentration of biphenyl formed from benzene pyrolysis with no oxygen was higher than the naphthalene concentration, however concentration of naphthalene formed from benzene pyrolysis with oxygen was higher than the biphenyl concentration. As for the PM formation, small fraction of PM was formed under lower temperature than 1173 K even though the mixture contained no oxygen. Its formation ratio increased with oxygen addition. Temperature of 1280 K was a valley where yield PM showed the minimum. Beyond this temperature, much of PM than in low temperature pyrolysis was formed. However, the low concentration PM valley did not appear under ϕ = 2.80 and 1.83 conditions. At lower temperature than 1170 K, PM mass concentration increased with the addition of oxygen. On the other hand, at higher temperature than 1300 K, PM mass concentration decreased with the addition of oxygen. Under low temperature condition, it suggested that PM formation mechanisms was different depending on the without- and with oxygen.