Researchers used a calcium bentonite clay catalyst to convert shredded end-of-life vehicle plastics into oil containing diesel-range hydrocarbons and exhibiting several properties comparable to commercial diesel.
Recycling plastics from end-of-life vehicles (ELVs) is an important part of improving resource recovery and supporting more circular use of plastics. Among the available technologies, pyrolysis has emerged as a promising route for recovering fuels and chemicals from waste polymers.
The process thermally decomposes plastics at elevated temperatures without oxygen, breaking polymer chains into liquid, gaseous, and solid products.
Previous studies have shown that pyrolysis can convert common automotive plastics such as low-density polyethylene (LDPE), high-density polyethylene (HDPE), and polypropylene (PP) into valuable hydrocarbons at relatively high yields. However, much of the existing research focuses on automotive shredder residue, a heterogeneous mixture containing plastics, metals, textiles, and other materials.
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That leaves less information 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.
Catalysts can improve pyrolysis efficiency by accelerating reactions, altering product distributions, and potentially reducing required temperature or residence time. 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.
In the study, researchers characterized plastics recovered directly from ELVs rather than relying on mixed automotive shredder residue. The feedstock contained acrylonitrile butadiene styrene (ABS), high- and low-density polyethylene (HDPE and LDPE), polypropylene (PP), polystyrene (PS), and fiberglass. It also contained substantial volatile and ash fractions.
Front and rear bumpers accounted for 86.6% of the sample by weight. Fiberglass, commonly used to reinforce automotive components, contributed to the relatively high ash content.
Researchers addressed a gap in previous work by characterizing automotive plastic waste before performing pyrolysis. Courtesy of Thermal and catalytic pyrolysis of automotive plastic wastes to diesel range fuel.
Rather than using bentonite clay in its original form, the researchers modified it through iron pillaring. The process introduces iron species into the clay structure, changing characteristics such as surface acidity and pore structure that can influence pyrolysis reactions.
The team compared thermal and catalytic pyrolysis across temperatures ranging from approximately 350°C to 521°C and catalyst loadings of roughly 6% to 34% by weight. A statistical experimental design allowed the researchers 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 approximately 416°C with a catalyst loading of about 24%.
The modified clay significantly increased oil yield during catalytic pyrolysis. Courtesy of Thermal and catalytic pyrolysis of automotive plastic wastes to diesel range fuel.
However, 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. 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 had a greater effect on product composition. Lower pyrolysis temperatures favored diesel-range organics, while temperatures above 450°C produced a heavier, waxier oil.
The resulting pyrolysis oil showed several properties comparable to those of 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. These values were 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. However, not all properties met diesel specifications. Both density and viscosity exceeded the limits typically specified for diesel fuel. The researchers attributed this partly to heavier, long-chain hydrocarbon fractions remaining in the pyrolysis oil.
Additional processing could therefore be required before the oil could be used as a diesel-range fuel. The researchers suggested approaches such as 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 also highlighting the additional development 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.
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.
Better information on these waste streams would help researchers and recyclers assess feedstock availability and plan potential industrial-scale pyrolysis operations.
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