Effect of pyrolysis conditions on the formation of polycyclic aromatic hydrocarbons (PAHs) from polyphenolic compounds

Abstract

Effect of pyrolysis conditions, such as temperature and substrate composition, i.e. inorganics, on the formation of polycyclic aromatic hydrocarbons (PAHs) from polyphenolic compounds, chlorogenic acid (CA) and lignin, was studied under inert atmosphere. Two routes for the PAH formation were investigated: primary volatile tar and the solid residue, i.e. char. The reactor consisted of a quartz tube with two zones. Zone 1 was used to first pyrolyze the substrate at 250–400 °C to produce a low temperature tar (LTT) and then to pyrolyze the char at 625 °C to produce a high temperature tar (HTT), The LTT and HTT were then passed through zone 2 maintained at temperatures between 700 and 920 °C. Yields of most PAHs increased with temperature, except in a few cases where the yields of two- and three-ring PAHs exhibited a maximum at 870 °C. The maximum may be due to the growth of these PAHs into heavier PAHs. The partial removal of sodium and potassium from lignin decreased the formation of char and PAHs, co-pyrolysis of CA and lignin also altered the PAH distribution. Preliminary analysis of the data from CA gave high activation energies for the PAH formation, with activation energy generally increasing with the PAH size.