engleski

Soot formation during polyurethane (PU) plastic pyrolysis: The effects of temperature and volatile residence time

Soot is an undesired co-product during thermal- chemical disposal (incineration, pyrolysis, etc.) of plastic wastes at high temperatures, while also regarded as a valuable nanoscale carbon- based material if with proper production and post-treatment methods. In this paper, the pyrolysis of polyurethane (PU) plastics, a major composition of plastic waste, was conducted in a fixed-bed reactor to investigate the soot formation mechanism in depth. The effects of pyrolysis temperature (1000–1300 °C) and volatile residence time (0.2–2 s) on the yield, micro- morphology, composition and reactivity of soot were studied. Results show that the initialization and growth of soot particles during PU pyrolysis requires a certain high temperature and long volatile residence time. With a volatile residence time of 2 s, the soot yield is 11.0 wt.% at 1000 °C and increases to 24.5 wt.% with the pyrolysis temperature increasing to 1300 °C ; while when the volatile residence time decreases to 0.2 s, the soot cannot be observed until 1200 °C. When the pyrolysis temperature increases 1000–1100 °C, the X-ray diffraction (XRD) patterns indicates an enhanced graphitization thereby a lower reactivity of soot oxidation, which is approved by onion-like layered structures initially observed by the high-resolution transmission electron microscope (HR-TEM) at 1100 °C and 2 s. When the pyrolysis temperature increases from 1100 °C to 1200–1300 °C, NaCl is observed in soot particles, which catalysis promotes the reactivity of soot oxidation. Gas chromatography and mass spectrometer (GC–MS) was used to measure the gas and tar compositions, especially the polycyclic aromatic hydrocarbons (PAHs), are proved essential for the formation of soot precursor. A large number of PAHs with ring number ≥4 start to form at 1100–1200 °C. Based on the soot characterization and gas-tar compositions, a pathway from light fragments and mono-ring aromatics to heavier aromatic compounds is proposed aiming to explain the chemical evolution of soot precursor particles.

Polyurethane, Pyrolysis, Soot, Volatile residence time, High temperature

nije evidentirano