FORMATION OF PRIORITY PAHS FROM POLYSTYRENE PYROLYSIS WITH ADDITION OF CALCIUM-OXIDE

The pyrolysis reaction, which is an important source of PAH formation near the grate bed region of a waste incinerator, is the first step fo r a combustion process from the viewpoints of formation of the hazardo us air pollutants (HAPs) in the flue gas. Polystyrene (PS) pyrolyses w ith calcium oxide catalyst under an inert (100% nitrogen) and an oxida tive (10% oxygen + 90% nitrogen) atmosphere at 600, 700 and 800 degree s C were performed in a laboratory quartz reactor. The 16 priority pol yaromatic hydrocarbons (PAHs) in the pyrolysis products were analyzed with a high-performance liquid chromatograph (HPLC) equipped with a wa velength-scanning ultraviolet (UV) detector. At 600 degrees C, calcium oxide was observed to promote PAH formation; while at 800 degrees C, it reduced PAH formation. Such observed results are explained by the m echanisms involving the reaction of the gaseous hydrocarbon PAH precur sors with both free electrons and hydroxyl free radicals. In addition, as pyrolysis temperature increased, both the species number and quant ity of the priority PAHs increased. A sharp increase in PAHs was obser ved at 800 degrees C under oxidative condition, as well as at 700 and 800 degrees C under inert condition. Thus, it is suggested that the mo nitoring and control of pyrolysis parameters, which are always neglect ed during the design or operation of a commercialized incinerator, can provide some important information on the control of PAH formation fr om waste incineration because pyrolysis occurs during the earlier stag e of an incineration process. (C) 1998 Elsevier Science B.V.