Abstract
Pyrolysis of waste plastics is widely used recycling method. Owing to the end-of-life vehicles regulations, 95% of passenger cars and vehicles must reused/recovered after the dismantling. Pyrolysis of waste polyethylene and polypropylene obtained from end-of-life vehicles was investigated in a continuously stirred batch reactor using 500 and 600°C temperatures. To ensure the pyrolysis reactions the tested catalysts (5% of ZSM-5, HZSM-5, Ni-ZSM-5 and Fe-ZSM-5) were added directly to the mixtures of raw materials. Products of pyrolysis were separated into gases, pyrolysis oil and heavy oil, which was further analyzed by gas-chromatography, Fourier transformed infrared spectroscopy and other standardized methods. Based on the results it was concluded, that the catalysts significantly increase the yields of volatile products, and modify their composition. Especially the alkane/alkene ratio, the methane concentration and the concentration of branched hydrocarbon could be affected by the applied catalysts. Ni-ZSM-5 catalyst had the highest activity in methane production, while HZSM-5 catalyst proved effective in isomerization reactions. Using H-ZSM-5, Ni-ZSM-5, and Fe-ZSM-5 catalyst notably decreased average molecular weight of pyrolysis oils and significantly higher aromatic content was observed.
Highlights
Waste polymers could be transformed into valuable hydrocarbons by pyrolysis
Regarding waste plastics from ELV, polyethylene, polypropylene and polystyrene are the mostly favored for pyrolysis, because the chemical structure build up only from carbon and hydrogen; their pyrolysis oil free of unwanted components
Wet impregnation was used for Ni-ZSM-5 and Fe-ZSM-5 synthesis, using Ni(NO3)2x6H2O and Fe(NO3)3x9H2O, respectively, while 1M NH4NO3 was used for HZSM-5 synthesis at 80°C
Summary
Waste polymers could be transformed into valuable hydrocarbons by pyrolysis. E.g. higher gas and oil yields are obtained using higher temperature and catalyst. Another important parameter is the kind of raw material, because it has a dominant effect on the product yield and compositions. Especially the decomposition of virgin polymers was investigated and less information is available related to the pyrolysis of real wastes. Modern cars and vehicles contain approximately 1015% plastics, depending on their type. Regarding waste plastics from ELV, polyethylene, polypropylene and polystyrene are the mostly favored for pyrolysis, because the chemical structure build up only from carbon and hydrogen; their pyrolysis oil free of unwanted components
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