OCR Text |
Show transformed by two reactions, cracking and addition reactions. The cracking reaction occurred types of dominantly at 500 - 700 °C in the second stage incinerator. When the incinerationtemperature was greater than 1200 °C, the addition reaction occurred dominantly and the major products were soots which are more thermally stable. From the analysis results in the 14 PAHs, as shown in Figure 1, it indicated that the critical temperature for the maximum yield of 14 PAHs was shifted from 1000 °C to 900 °C. when metallic chloride (BaCh or NaCl) was added into the incineration system. The yields of 14 PAHs and soots were more with BaCh or NaCl additive than those without metallic chloride additives. This indicated that metallic chloride additives could promote the reaction sequence towards the growth and cogulation reaction of soots from PS pyrolysis. When the second stage temperature increased to the critical temperature, black tar formed and the concentration of 14 PAHs was 104-105 ug/g-p.s.. Pha, Flu and Pyr were major specils found among the 14 PAHs, as shown in Figure 2. When the stage-two temperature was increased, the 14 PAHs formed were decreased. The reason was that the thermal temperature provided enough energy for the low-ring PAHs to grow to high-ring PAHs and soot particulates. At incineration temperature above 1000 °C, the soot particulates of black powder formed and the weight of soot particulates formed to be increased as the stage-two pyrolysis temperature increased. The above results also indicated that PAHs would effectively react with phenyl, biphenyl, naphthyl, binaphthyl, and C2H2 and grow to larger PAHs when the pyrolysis temperature was increased to the higher temperature of 1000 °C. Reactions of soot formation such as nucleation, condensation coagulation, aggregation mechanisms occurred effectively. Because the change in free energies caused by the series reactions of PAHs and soot formation were so large, reactions became practically irreversible. This, in turn, had the effect "of pulling" the reaction sequence forward twords formation of larger PAHs and soot particles. It had been postulated that mechanism for coagulation is through the reactions of aryl radical + PAH and molecule and soot active site + soot[7]. Of the 14 species of PAHs, only Pha, Flu and Pyr were always found to be in the gas phase in the PUF sample. The reason may be that the boiling points and vapor pressures were low. The various distributions of 14 PAHs between the gas and solid phases resulting from the polystyrene incineration - 4 - |