engleski

Soot formation during plastic waste pyrolysis in an entrained flow reactor at 1273-1573K

Plastic materials are widely used in household applications, packing, electrical and vehicle equipment, and the global production of plastics has reached 500 million tons per year in 2016. The high-temperature pyrolysis is one of the advanced technologies for plastics waste treatment, because the high-temperature pyrolysis of plastics not only produces a high yield of combustible gas but also produces a high yield of soot, a high-value product. Currently, the mechanism of soot formation during plastic waste utilization at high temperatures has not been reported. In this study, soot was produced in a temperature controlled lab-scale entrained flow reactor at 1000, 1100, 1200, and 1300 oC. The soot formation mechanism were analyzed based on the yield and composition measurements of gas and soot. The properties of soot were characterized by various methods including scanning transmission electron microscopy (STEM), elemental analysis, Fourier transform infrared analysis (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Results show that with the temperature increasing from 1000 to 1200 oC, the yield of soot increases from 12.2 to 26.5 wt.%, when the temperature further increases to 1300 oC, the change of soot yield is slight and a maximum soot yield 26.5 wt.% is obtained. H2 and CO are the dominant in gas products, accounting for 80-98% of gas products by volume depending on temperatures, and with the temperature increasing, the contents of H2 and CO increases, while the contents of minor species (C2H2, CH4, C2H4, and CO2) decrease. The morphology analysis by TEM indicates the inception of soot particles start at ~1100 oC, when the onion layered structure of spherical particles (20-50 nm) is observed, below 1100 oC, fine particles exist as the amorphous carbon substance of a larger size (>100 nm). With the increase of temperature, the particle size becomes smaller and more uniform. XRD patterns and FTIR spectrums show that with the increase of temperature, more C=C functional groups are formed in soot particles, while the C-H and C=O functional groups are destroyed. Based on these physical-chemical analyses above, the soot formation mechanism during plastics pyrolysis is proposed At last, the kinetic analysis on soot oxidation activity by TGA show that a higher producing temperature decreases the starting temperature, the apparent activation energy, and the pre- exponential factor of soot oxidation.

plastic waste ; pyrolysis ; soot formation ; gas product ; high temperature

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