Pyrolysis of plastic waste recovered directly from end-of-life vehicles can produce oil with several properties comparable to commercial diesel, according to a study that characterized automotive plastic waste before processing it. The research examined how an iron-modified clay catalyst affects both the yield and the composition of the resulting oil.
Recycling plastics from end-of-life vehicles (ELVs) is seen as an important part of improving resource recovery and supporting more circular use of plastics. Pyrolysis thermally decomposes plastics at elevated temperatures without oxygen, breaking polymer chains into liquid, gaseous, and solid products. Earlier studies have shown that common automotive plastics such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) can be converted into valuable hydrocarbons at relatively high yields, but much of that work has focused on automotive shredder residue, a heterogeneous mixture of plastics, metals, textiles, and other materials.
Less is known about how plastics recovered directly from components such as dashboards, bumpers, and headlamps behave during pyrolysis. Automotive plastic waste (APW) can also contain mineral fillers, flame retardants, fiberglass, and other additives that affect degradation behavior and product composition.
Feedstock and catalyst
In the study, researchers characterized plastics recovered directly from ELVs rather than relying on mixed shredder residue. The feedstock contained acrylonitrile butadiene styrene (ABS), HDPE, LDPE, 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.
Instead of using bentonite clay in its original form, the team modified it through iron pillaring. That process introduces iron species into the clay structure, changing characteristics such as surface acidity and pore structure that can influence pyrolysis reactions. Iron-modified clays are of particular interest because they may improve oil production without relying on more expensive commercial catalysts such as zeolites.
Yield versus composition
The team compared thermal and catalytic pyrolysis across temperatures of roughly 350°C to 521°C and catalyst loadings of about 6% to 34% by weight, using a statistical experimental design to 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%.
The catalyst had much less influence on the composition of the oil. Thermal and catalytic pyrolysis produced similar proportions of hydrocarbons in the C8–C24 range associated with gasoline- and diesel-range compounds, meaning the catalyst helped convert more feedstock into liquid but did not substantially shift that liquid toward a higher proportion of diesel-range molecules. Temperature had a greater effect: 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, including 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 oil. Additional processing could therefore be required before the oil can be used as a diesel-range fuel; the researchers suggested distillation and centrifugation, as well as optimizing reaction conditions through lower temperatures and longer residence times to reduce heavier fractions.
The study positions pyrolysis as a technically promising route for recovering value from automotive plastics, while highlighting the development still needed 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 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 in turn constrains assessments of feedstock availability and planning for industrial-scale pyrolysis operations.