Emission of polycyclic aromatic hydrocarbons from the pyrolysis of liquid crystal wastes.
A liquid crystal display can be described as a panel consisting of two plates of glass with liquid crystals in the space between. Generally, the liquid crystal wastes are extracted and separated into various fractions. Some recyclable materials, i.e., metals, glass, plastics, etc., are recycled, but the liquid crystals are incinerated. The emission factors for 16 U.S. EPA priority polycyclic aromatic hydrocarbons (PAHs) from the combustion of liquid crystal are approximately 390 and 1520 times higher than that of waste terephthalic acid and biological sludge combustion, respectively. In this study, we determined the emission of PAHs from the liquid crystals pyrolysis. We also investigated the fragments and gas compositions using on-line thermogravimetry-mass spectrometry (TG-MS). A temperature series of 14 fragments was analyzed in nitrogen, and was found to include m/z: 30, 32, 42, 44, 55, 57, 67, 81, 95, 109, 128, 166, 178, and 202. The fragments at m/z 32 represents formaldehyde and the fragment at m/z 44 is carbon dioxide. The fragments at m/z 55, 57, 67, 81, 95, and 109 represent hydrocarbon components, all of which may be liquid crystal by products. The TG-MS as analyzed above can offer a better understanding of the mechanisms of byproduct formation in liquid crystal waste pyrolysis. Experimentally, not detected (n.d.) -5.98 and n.d. -20.2 microg/g of 16 PAHs, in the particulate and gas phases, respectively, are determined from the emission of liquid crystal waste pyrolysis. The PAH profiles showed a predominance of naphthalene (42.6%) and phenanthrene (13.5%). The total PAH emissions for the 16 species were 7.75 and 44.05 microg/g in the particulate and gas phases, respectively, significantly lower than the values associated with liquid crystal combustion. From the viewpoint of PAH emission control, our results suggest that the pyrolysis is a better option for the disposal of liquid crystal wastes than that of combustion.
Chien
Yi-Chi
YC
Department of Environmental Engineering and Science, Fooyin University, Kauhsiung County 831, Taiwan. pl036@mail.fy.edu.tw
Liang
Ching-Ping
CP
Shih
Pai-Haung
PH
D008401:Gas Chromatography-Mass Spectrometry; D017745:Incineration; D007220:Industrial Waste / Q000032:analysis*; D050866:Liquid Crystals / Q000032:analysis*; D013058:Mass Spectrometry; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis*; D013696:Temperature
D007220:Industrial Waste; D011084:Polycyclic Aromatic Hydrocarbons