Pyrolysis is emerging as a promising route for recovering fuels and chemicals from waste polymers, and a new study examines how plastics recovered directly from end-of-life vehicles (ELVs) behave under both thermal and catalytic processing. The work focuses on automotive plastic waste (APW), which can carry mineral fillers, flame retardants, fiberglass and other additives that influence degradation behavior and product composition.
Much of the earlier research had concentrated on automotive shredder residue, a heterogeneous mix of plastics, metals, textiles and other materials. The new study instead characterized plastics taken directly from vehicle components before pyrolysis, addressing what the authors describe as a gap in previous work.
Feedstock drawn from vehicle components
The feedstock contained acrylonitrile butadiene styrene (ABS), high- and low-density polyethylene (HDPE and LDPE), polypropylene (PP), polystyrene (PS) and fiberglass, along with substantial volatile and ash fractions. Front and rear bumpers accounted for 86.6% of the sample by weight, and fiberglass, commonly used to reinforce automotive components, contributed to the relatively high ash content.
An iron-pillared clay catalyst
Rather than using bentonite clay in its original form, the researchers modified it through iron pillaring. That process introduces iron species into the clay structure and changes characteristics such as surface acidity and pore structure, which can influence pyrolysis reactions. Iron-modified clays are of interest because they may improve oil production without relying on more expensive commercial catalysts.
The team compared thermal and catalytic pyrolysis at temperatures ranging from roughly 350°C to 521°C and catalyst loadings of about 6% to 34% by weight. A statistical experimental design allowed the researchers to evaluate the interaction between temperature and catalyst concentration.
Higher oil yield, little change in composition
The catalyst strongly affected liquid yield. Catalytic pyrolysis produced an average oil yield of approximately 68%, compared with 41% for thermal pyrolysis alone. The highest oil yield, 78.6%, was achieved at about 416°C with a catalyst loading of roughly 24%.
The catalyst had much less influence on the composition of the resulting oil. Thermal and catalytic pyrolysis produced similar proportions of hydrocarbons within the C8-C24 range associated with gasoline- and diesel-range compounds. In other words, the catalyst helped convert more of the plastic feedstock into liquid product but did not substantially shift that liquid toward a higher proportion of diesel-range molecules.
Temperature had a greater effect on product composition. Lower pyrolysis temperatures favored diesel-range organics, while temperatures above 450°C produced a heavier, waxier oil.
Fuel properties and remaining gaps
The resulting pyrolysis oil showed several properties comparable to those of commercial diesel. The researchers reported a calorific value of 49.85 MJ/kg, a flash point of 113°C and total aromatics of 3.55% by area, values within or comparable to ranges specified for conventional fuels. Branched heptenes and heptanes dominated the oil, compounds also identified in previous studies of polypropylene and automotive-plastic pyrolysis.
Not all properties met diesel specifications, however. Both density and viscosity exceeded the limits typically specified for diesel fuel, which the researchers attributed partly to heavier, long-chain hydrocarbon fractions remaining in the pyrolysis oil. Additional processing could therefore be required before the oil can be used as a diesel-range fuel. The team suggested approaches such as distillation and centrifugation, as well as optimizing reaction conditions through lower temperatures and longer residence times, to reduce heavier fractions and improve fuel properties.
Outlook
The study positions pyrolysis as a technically promising route for recovering value from automotive plastics, while also highlighting the additional development required before the process can move toward broader commercial application. Future work could investigate different iron concentrations in the catalyst, improve reactor designs and heat transfer, and combine pyrolysis with downstream distillation to separate gasoline- and diesel-range fractions.
The researchers also note that improved collection and sorting of automotive plastics will be important. Without systematic removal and classification of plastic components from end-of-life vehicles, reliable data on the volume and composition of available automotive plastic waste remain limited, which would hamper efforts to assess feedstock availability and plan potential industrial-scale pyrolysis operations.