Mechanistic investigation into the formation of polycyclic aromatic hydrocarbons from the pyrolysis of plant steroids

There have been many studies on the pyrolysis of biomass model compounds bu t most have not been performed under the high heating rate, short residence time conditions currently used in the thermochemical conversion of biomass . In this investigation, the pyrolysis of plant steroids is investigated by flash vacuum pyrolysis (FVP) and flow pyrolysis at residence times of 0.1- 2.0 s and temperatures of 550-800 degreesC to determine if the native cycli c ring structure in the steroid leads to the formation of polycyclic aromat ic hydrocarbons (PAHs) or whether PAHS are formed by pyrosynthesis. FVP of stigmasterol, stigmasterol acetate, beta -sitosterol, and stigmasta-3,5-die ne at 700 degreesC showed that PAHs, such as acenaphthylene, phenanthrene, anthracene, pyrene, chyrsene, benz[a]anthracene, and their monomethylated d erivatives were formed in the absence of bimolecular reactions, and the yie ld of PAHs was dependent of the structure of the steroid. Similar products were found in the flow pyrolysis of stigmasterol, and the yields of PAHs we re found to increase with increasing temperature and residence time. Thermo chemical kinetic estimates were used to postulate pathways for the formatio n of the primary pyrolysis products. (C) 2001 Elsevier Science Ltd. All rig hts reserved.