Aromatic Hydrocarbon Emissions from Burning Poly(styrene), Poly(ethylene) and PVC Particles at High Temperatures

Abstract

A study on the semi-volatile aromatic hydrocarbon emissions from the pyrolysis/combustion of poly(styrene) (PS), poly(ethylene) (PE) and PVC particles was conducted. Dispersions (aerosols) or batches (fixed beds) of the above types of polymer particles, 90-300 μm in diameter, were burned in bench-scale, drop-tube or muffle-type electrically-heated furnaces, respectively. In the drop-tube furnace, pyrolysisis/combustion took place at gas temperatures ranging from 900 to 1200°C and particle heating rates were in the order of 10 3 -10 4 °C/s. The total residence times of the gases in the furnaces were 1 or 2 s ; envelope flames surrounding the particles lasted for 6-130 ms, while residence times in the post-flame region were 0.3-1.8 s depending on the polymer. Semi-volatile organic emissions were captured from the gas and solid phases using XAD-4 adsorbers and glass fiber filters, respectively, and analysis was conducted with gas chromatography coupled with mass spectrometry (GC-MS). The combustion characteristics of single particles of the three plastics were studied in earlier experiments using optical pyrometry and high-speed cinematography. Gaseous diffusion, chemical kinetics and pyrolysis kinetics were inferred, therein, to govern combustion of PS, PVC and PE particles, respectively. The types of the aromatic hydrocarbon emissions were found to depend on the polymer burned, while their relative amounts were influenced by combustion parameters such as temperature, residence time, etc. Substituted poly-aromatic hydrocarbons (PAHs), oxygenated compounds and chlorinated aromatics were detected in the combustion products of PVC. PAHs with fused rings were emitted from the combustion of PE. PAHs, either substituted or with fused rings were emitted from the combustion of PS. As the gas temperatures and residence times increased, the amount of PAH emissions from all polymers decreased. The results indicated that as the size of PVC sample decreased, in the presence of oxygen, the amount of PAHs decreased. However, as the size of PE sample decreased, or when oxygen was present, the amount of PAHs did not necessarily decrease. The behavior of PS was found to be between that of PVC and PS.