Particle volatility, size distribution and PAH/alkyl-PAH profiles during toluene pyrolysis in a flow reactor

摘要

Particle volatility, size distribution, and parent and alkylated polycyclic aromatic hydrocarbon (PAH/alkyl-PAH) profiles during toluene pyrolysis in a flow reactor were studied. The experiments were conducted under three different gas residence times (0.2, 0.5 and 0.8 s) at temperatures from 950 to 1450 degrees C. Results showed that long residence times and high temperatures led to high particle mass concentrations, low particle volatility and a significant shift of particle size distribution to larger size. Total particle number concentrations exhibited a rise-then-fall trend (peaking at a critical temperature of 1050 degrees C) with increasing temperature, indicating that increasing temperature promoted a transition from nucleation to agglomeration and coagulation which dominated the particle size distributions. Among PAHs and alkyl-PAHs, those with 2-4 rings, presented the highest concentrations at 950 degrees C for 0.2 s. They appeared at 1050 degrees C for 0.5 and 0.8 s, consistent with the critical temperature of particle nucleation at long residence times (0.5 and 0.8 s). Particle peak number concentrations and total PAH mass concentrations exhibited consistent temperature dependence, indicating soot nucleation was highly related to PAH concentrations. According to the comprehensive observations in this study, low molecular mass PAHs instead of larger PAHs appear to be the precursors of soot formation during high temperature pyrolysis processes. Copyright (c) 2021 American Association for Aerosol Research