Researchers report that pyrolysis of plastic waste recovered directly from end-of-life vehicles (ELVs) can yield a liquid product with properties comparable to commercial diesel, and that an iron-modified clay catalyst can raise oil yields well above those of purely thermal processing. The work characterized automotive plastic waste (APW) before pyrolysis rather than relying on mixed automotive shredder residue.
Feedstock and process
Pyrolysis thermally decomposes plastics at elevated temperatures in the absence of oxygen, breaking polymer chains into liquid, gaseous and solid products. Earlier research has 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 centred 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. APW can also contain mineral fillers, flame retardants, fiberglass and other additives that influence degradation behaviour and product composition.
In the study, 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 used to reinforce automotive components contributed to the relatively high ash content.
Catalyst compared with thermal pyrolysis
Rather than using bentonite clay in its original form, the researchers modified it through iron pillaring, introducing iron species into the clay structure to alter surface acidity and pore structure. Commercial zeolites have been widely studied as catalysts, 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 increase liquid yields and influence the formation of fuel-range hydrocarbons.
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, and the highest oil yield — 78.6% — was achieved at about 416°C with a catalyst loading of roughly 24%.
Oil composition and fuel properties
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, meaning the catalyst converted more of the plastic feedstock into liquid product but did not substantially shift that liquid toward a higher proportion of diesel-range molecules.
Temperature played a greater role. Lower pyrolysis temperatures favoured diesel-range organics, while temperatures above 450°C produced a heavier, waxier oil.
The pyrolysis oil showed several properties comparable to those of commercial diesel: a calorific value of 49.85 MJ/kg, a flash point of 113°C and total aromatics of 3.55% by area, values reported as 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. However, both density and viscosity exceeded the limits typically specified for diesel, which the researchers attributed partly to heavier, long-chain hydrocarbon fractions remaining in the oil.
Upgrading and next steps
Additional processing would therefore be needed before the oil could be used as a diesel-range fuel. The researchers suggested approaches such as distillation and centrifugation, as well as optimising 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 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 noted 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 APW remain limited, which would constrain assessments of feedstock availability and planning for potential industrial-scale pyrolysis operations.