(633c) Molecular Recycling: Catalytic Pyrolysis of Plastic Waste | AIChE

(633c) Molecular Recycling: Catalytic Pyrolysis of Plastic Waste

Within this study, the catalytic fast pyrolysis of polyolefinic waste streams was investigated to recover valuable
base chemicals at high selectivity. We compare the energy demand and carbon footprint of this direct route
with other state-of-the-art processes. Different feeds, (virgin and post-consumer polyolefins), catalyst/feed
ratios, and reaction temperatures were tested in a micropyrolysis reactor coupled to two-dimensional gas
chromatography. HZSM-5 zeolite was used as catalyst for upgrading the pyrolysis vapors. After a steamtreatment
at 800 °C, a phosphorus-stabilized microporous HZSM-5 and its desilicated version showed high
selectivity for production of valuable base chemicals when upgrading pyrolysis vapors at 600 °C, with ~80%
C2-C4 olefins and ~5% aromatics produced from virgin PE. Increasing the reaction temperature from 600 to
700 °C, increased the aromatics yield to ~10 wt. % while producing similarly high overall yields of C2-C4
olefins. Processing post-consumer mixed polyolefin resulted in 5-10 wt. % lower olefins yield than using virgin
PE but produced ~5 wt. % more aromatics due to its contamination with PS and PET. While parent HZSM-5
rapidly deactivated for repeated runs owing to its high coking propensity, phosphorus-modified and
steamtreated HZSM-5 showed almost no deactivation during 130 runs with stable conversion towards C5+
aliphatics and high C2-C4 olefins selectivity with a 70% reduction in coke deposition. The performance of this
direct olefins production route was further evaluated in a plantwide context. It was found that it requires ~38%
lower energy input than the step-wise counterpart (plastics pyrolysis followed by pyrolytic oil steam cracking),
while it results to at least an order of magnitude lower carbon footprint as compared to peer state-of-the-art