1 research outputs found
Online Study on the Pyrolysis of Polypropylene over the HZSM‑5 Zeolite with Photoionization Time-of-Flight Mass Spectrometry
The production of hydrocarbons through
the pyrolysis of polyolefins
is a promising way of fuel recycling. In this work, online single-photon
ionization time-of-flight mass spectrometry (SPI–TOFMS) was
used to study both thermal and catalytic decompositions of polypropylene
(PP) in a tubular furnace. SPI produces few or no fragments of molecular
ions, making the identification and interpretation of complex pyrolysis
products in real time possible. The mass spectra at different reaction
temperatures and time-evolved profiles of selected species during
the pyrolysis processes were measured. The pyrolysis products can
be classified into three groups: alkenes, dienes, and aromatics. As
the coke precursors, aromatics mainly composed of benzene, toluene,
and xylene (BTX) were observed at a very low temperature of 300 °C
with the presence of HZSM-5, which cannot be detected for pure PP
until 700 °C, indicating that HZSM-5 can accelerate the coke
formation. Because of the secondary reactions, different tendencies
of product intensities were exhibited as the reaction temperature
increased. In addition, in comparison of the time-evolved profiles
of the alkenes and BTX under high temperatures, a two-stage catalytic
degradation process taking place on the external surface and the micropores
of HZSM-5 was verified. A degradation mechanism was also proposed
for the pyrolysis of PP with a low HZSM-5 content based on the time-evolved
profiles performed at a low temperature. This work demonstrates the
good performance of SPI–TOFMS for the online study of the polymer
pyrolysis as well as the evaluation of the catalyst