MECHANISTIC INVESTIGATION INTO THE FORMATION OF POLYCYCLIC AROMATIC HYDROCARBONS FROM THE PYROLYSIS OF TERPENES

Introduction Currently, there is interest in utilizing renewable energy resources, such as wood and agriculture waste, for power generation, production of liquid fuels, and specialty chemicals as a consequence of the environmental benefits. However, pyrolysis, gasification, and combustion of biomass produces polycyclic aromatic hydrocarbons (PAHs), which are environmental pollutants and soot precursors. , , , , 3 4 5 6 7 In pyrolysis, PAHs are proposed to be formed by pyrosynthesis, in which radicals undergo a series of bimolecular reactions with alkenes, alkynes, and aromatics to form larger ring structures. The yield of PAHs are found to increase with temperature and gas phase residence times. 9 In gasification and combustion, it has been postulated that PAHs arise from pyrolysis reactions in oxygen-deficient regions. A better fundamental understanding of the initial pyrolysis reactions that occur in the thermochemical processing of biomass, and subsequent reactions of the vapor phase products could provide insight into reducing PAH emissions from biomass combustion, reducing tar formation from gasification, and enhancing production of specialty chemicals from the fast pyrolysis of biomass. As a consequence of the chemical complexity of biomass and its pyrolysis products, it has been difficult to gain detailed information on the formation pathways of specific products. Thus, to gain fundamental kinetic and mechanistic information on product formation in biomass pyrolysis, efforts have focused on the pyrolysis of key chemical constituents found in biomass. In our previous investigations, we have focused on the pyrolysis of plant steroids as potential precursors to PAHs. It was shown that the native ring structure of the steroid was maintained to form PAHs, such as phenanthrene and chrysene, and the yield of PAHs was dependent on the steroid structure. PAH yield and ring size were also shown to increase with residence time, temperature, and concentration. In this investigation, the pyrolysis of plant terpenes was investigated at 600800 °C and at short residence times (≤1 s). This study focused on the pyrolysis of solanesol, squalene, phytol, and β−carotene. These terpenes are