Release of PAHs during pyrolysis of Pingshuo coal

A flash pyroprobe combined with GC-MS was used to investigate the effects of temperature on the release property of PAHs (polycyclic aromatic hydrocarbons) during pyrolysis of Pingshuo coal. The formation mechanism of PAHs was also discussed. The results indicate that the total amounts of the 16 PAHs released increase obviously with increasing temperature during pyrolysis, reach the maximum at 800℃, and then decrease. The ring distributions of PAHs have a notable dependence on the pyrolysis temperature. The different species of PAHs reaches the maximum yields at individual temperature. With increase in pyrolysis temperature, the total amount of PAHs increase observably, which is attributed to cracking of the bridge bonds, the fat side chain on aromatic ring, the methyl and phenolic group in the coal macrostructure. With further increase to 1 000 and 1 200℃, the amount of high-ring PAHs increases due to the occurrence of condensation reaction. Thermal cracking of macromolecular compounds concentrated during 600~800℃, and condensation are the main reactions occurred at high temperatures. The PAHs during coal pyrolysis are generated from the volatilization of aromatics structure in coal, the cracking reactions of macromolecular compounds and the condensation reactions of radicals at high temperature; meanwhile, the last one is the major source of high-ring PAHs during coal pyrolysis.