Recycling plastics from end-of-life vehicles (ELVs) sits at the intersection of two difficult problems: recovering value from a complex mixed waste stream, and doing so in a way that supports more circular use of plastics. Pyrolysis — the thermal decomposition of polymers at elevated temperatures in the absence of oxygen — has become one of the more closely watched routes for turning waste polymers back into fuels and chemicals, splitting polymer chains into liquid, gaseous and solid products.
Most published work, however, has examined automotive shredder residue (ASR), a heterogeneous mix of plastics, metals, textiles and other materials. Far less is known about how plastics recovered directly from specific components — dashboards, bumpers and headlamps — behave during pyrolysis. That distinction matters, because automotive plastic waste (APW) can carry mineral fillers, flame retardants, fiberglass and other additives that change both degradation behaviour and the composition of the resulting products.
Characterising the feedstock first
The research addressed that gap by characterising automotive plastic waste before subjecting it to pyrolysis, rather than relying on mixed shredder residue. 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 the fiberglass commonly used to reinforce automotive components contributed to the relatively high ash content.
A catalyst that lifts yield, not composition
Catalysts are one lever for improving pyrolysis: they can accelerate reactions, alter product distributions and potentially reduce the temperature or residence time required. Commercial zeolites have been widely studied, but lower-cost clay-based alternatives are drawing increasing interest. Among them, 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. Iron-modified clays are particularly attractive because they may improve oil production without relying on more expensive commercial catalysts.
The researchers modified bentonite clay through iron pillaring, introducing iron species into the clay structure and changing characteristics such as surface acidity and pore structure that can influence pyrolysis reactions. They 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 had a strong effect on liquid yield. Catalytic pyrolysis produced an average oil yield of approximately 68%, against 41% for thermal pyrolysis alone, with the highest oil yield — 78.6% — achieved at about 416°C and a catalyst loading of roughly 24%.
Its influence on oil composition was much weaker. 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, by contrast, had a greater effect on product composition. Lower pyrolysis temperatures favoured diesel-range organics, while temperatures above 450°C produced a heavier, waxier oil.
Fuel properties: close, but not yet diesel
The resulting 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 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 every property met diesel specifications. 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 would therefore be required before the oil could be used as a diesel-range fuel. The team pointed to approaches such as distillation and centrifugation, and to optimising reaction conditions through lower temperatures and longer residence times, as ways to reduce heavier fractions and improve fuel properties.
What would still have to change
On the evidence presented, pyrolysis reads as a technically promising route for recovering value from automotive plastics — and one that still needs development 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. The condition of the feedstock is equally important: better collection and sorting of automotive plastics will be needed, because 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. Better information on those waste streams would help researchers and recyclers assess feedstock availability and plan potential industrial-scale pyrolysis operations.
The work thus frames the technology as a credible option with a clear set of remaining constraints — yield and composition respond to different variables, and the fuel produced still requires upgrading — rather than a finished answer to automotive plastic waste.