Manganese sulfate effect on PAH formation from polystyrene pyrolysis

Polystyrene (PS) was pyrolyzed with/without manganese sulfate addition in a 100% N2 environment at 600, 700 and 800°C in a laboratory quartz reactor. The mole ratio of carbon (in PS) to Mn was 40/1. The gas-phase and liquid-phase polycyclic aromatic hydrocarbons (PAHs) were extracted with dichloromethane (DCM) and subsequently prepared for further analysis with an HPLC equipped with a wavelength-scanning ultraviolet (UV) detector and a fluorescence (FL) detector. Virtually no char or coke residue was observed in the reactor at the end of the pyrolysis reaction. The addition of MnSO4 into the high-temperature pyrolysis of PS reduced PAH formation in all liquid and gas products. The transition metal-chelating oxidation mechanism previously used to explain soot reduction during combustion was not adequate for explaining the results of PAH reduction via MnSO4 addition into the inert pyrolysis. Furthermore, it is suggested that soot reduction via manganese salt addition into oxygen-rich combustion might not result only from the well-accepted chelating oxidation mechanism; rather, it might result from the reduction of hydrocarbon species in the locally fuel-rich environment via manganese salt addition, as inferred from the reduction of PAH formation during inert pyrolysis with/without MnSO4 addition observed in this study.