Pyrolysis has become a leading candidate for recovering fuels and chemicals from the plastics embedded in end-of-life vehicles (ELVs), but much of the published work has relied on automotive shredder residue — a mixed stream of plastics, metals, textiles and other materials. A new study instead characterizes plastics recovered directly from vehicle components and tests a low-cost, iron-modified clay catalyst against purely thermal processing.
The feedstock contained acrylonitrile butadiene styrene (ABS), high- and low-density polyethylene (HDPE and LDPE), polypropylene (PP), polystyrene (PS) and fiberglass, and carried substantial volatile and ash fractions. Front and rear bumpers accounted for 86.6% of the sample by weight, while fiberglass used to reinforce components contributed to the relatively high ash content. The authors note that automotive plastic waste (APW) can also contain mineral fillers, flame retardants and other additives that shape both degradation behavior and product composition.
A modified clay instead of commercial zeolites
Pyrolysis thermally decomposes polymers at elevated temperature without oxygen, breaking polymer chains into liquid, gaseous and solid products. Catalysts can improve efficiency by accelerating reactions, shifting product distributions and potentially reducing the required temperature or residence time. Commercial zeolites have been widely studied, but lower-cost clay-based alternatives are drawing increasing interest; pillared clays modified with metals such as iron, titanium or zirconium have shown potential to raise liquid yields and influence the formation of fuel-range hydrocarbons.
In this work the researchers modified bentonite clay through iron pillaring rather than using it in its original form. The process introduces iron species into the clay structure, altering characteristics such as surface acidity and pore structure that influence pyrolysis reactions. Iron-modified clays are seen as attractive because they may support oil production without relying on more expensive commercial catalysts.
Experimental design and yields
The team compared thermal and catalytic pyrolysis across temperatures from roughly 350°C to 521°C and catalyst loadings of about 6% to 34% by weight, using a statistical experimental design that let them evaluate the interaction between temperature and catalyst concentration.
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%.
Its influence on oil composition was far weaker. Thermal and catalytic runs produced similar proportions of hydrocarbons in the C8–C24 range associated with gasoline- and diesel-range compounds. In other words, the catalyst helped convert more of the feedstock into liquid product but did not substantially shift that liquid toward a higher share of diesel-range molecules. Temperature had a greater effect on 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 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 earlier 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 oil.
What would be needed next
Additional processing could therefore be required before the oil can serve as a diesel-range fuel. The researchers suggested approaches including distillation and centrifugation, as well as optimizing reaction conditions through lower temperatures and longer residence times, to reduce heavier fractions and improve fuel properties.
The study positions pyrolysis as a technically promising route for recovering value from automotive plastics while highlighting the development still required before 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.
Improved collection and sorting of automotive plastics will also matter. 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 — information researchers and recyclers need to assess feedstock availability and plan potential industrial-scale pyrolysis operations.