Formation mechanisms of PAHs for the low temperature pyrolysis of cellulosic materials
The formation and yields of PAHs from the pyrolysis of cellulosic materials over the temperature range of 300 to 650 °C were investigated. At a temperature of 300 °C, no detectable amounts of PAHs were observed from the pyrolysis of cellulose, glucose, and pectin. Detectable amounts of 2-4 ring PAHs were observed at and above 400 °C. B[a]P and B[a]A were observed at and above 500 °C. Gas phase residence time (2-18 sec) and sample size (200-500 mg) did not show any significant effects on the yield of PAHs over this temperature range. Addition of oxygen to the gas stream reduces the yields of PAHs. The pathway to PAH formation in the 300-650 °C temperature range is believed to be the carbonization process where the solid residue undergoes a chemical transformation and rearrangement to give a more condensed aromatic structure via a host of dehydration, decarbonylation, decarboxylation, depolymerization, dehydrogenation, and cross-linking reactions. The experimental data was used to estimate a set of global kinetic parameters for the formation of PAHs in this temperature range.