Recovering plastics from end-of-life vehicles is central to improving resource recovery and moving toward more circular use of plastics. Pyrolysis — the thermal decomposition of polymers at elevated temperature without oxygen — has emerged as a promising route to fuels and chemicals, breaking polymer chains into liquid, gaseous and solid products.
Earlier work showed that common automotive plastics such as low- and high-density polyethylene and polypropylene can be converted into hydrocarbons at relatively high yields. Much of that research, however, focused on automotive shredder residue, a mixed stream of plastics, metals and textiles. Plastics recovered directly from components such as dashboards, bumpers and headlamps are less well characterized, and automotive plastic waste can carry mineral fillers, flame retardants, fiberglass and other additives that alter degradation behavior and product composition.
Catalysts offer a way to accelerate reactions, shift product distributions and potentially cut the temperature or residence time required. Commercial zeolites have been widely studied, but lower-cost clay-based alternatives are drawing interest. Pillared clays modified with metals such as iron, titanium or zirconium have shown potential to raise liquid yields and steer the formation of fuel-range hydrocarbons, and iron-modified clays are attractive because they may improve oil production without relying on expensive commercial catalysts.
In the new study, researchers characterized plastics taken directly from end-of-life vehicles rather than mixed shredder residue. The feedstock contained acrylonitrile butadiene styrene, high- and low-density polyethylene, polypropylene, polystyrene and fiberglass, along with substantial volatile and ash fractions; front and rear bumpers made up 86.6% of the sample by weight, and the fiberglass used to reinforce components contributed to the high ash content.
Rather than using bentonite clay as received, the team modified it by iron pillaring, introducing iron species that change surface acidity and pore structure. Thermal and catalytic pyrolysis were compared across roughly 350°C to 521°C and catalyst loadings of about 6% to 34% by weight, with a statistical experimental design capturing the interaction between temperature and catalyst concentration.
The catalyst strongly affected liquid yield. Catalytic runs produced an average oil yield of about 68%, versus 41% for thermal pyrolysis alone, and the highest yield, 78.6%, was reached at approximately 416°C with a catalyst loading near 24%. Its effect on oil composition was much smaller: thermal and catalytic pyrolysis gave similar proportions of hydrocarbons in the C8–C24 range associated with gasoline- and diesel-range compounds. Temperature mattered more for composition, with lower temperatures favoring diesel-range organics and temperatures above 450°C producing a heavier, waxier oil.
The resulting oil showed properties comparable to commercial diesel in several respects — a calorific value of 49.85 MJ/kg, a flash point of 113°C and total aromatics of 3.55% by area — but density and viscosity exceeded typical diesel limits, which the researchers attributed partly to heavier, long-chain fractions. Branched heptenes and heptanes dominated the oil, compounds also seen in earlier work on polypropylene and automotive-plastic pyrolysis.
Additional processing, such as distillation and centrifugation, or optimized reaction conditions with lower temperatures and longer residence times, could reduce those heavier fractions. The study positions pyrolysis as technically promising for recovering value from automotive plastics while underscoring the development still needed before broader commercial application. Future work could test different iron concentrations, improve reactor design and heat transfer, and pair pyrolysis with downstream distillation to separate gasoline- and diesel-range fractions. Better 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.