Pyrolysis of plastic waste recovered directly from end-of-life vehicles (ELVs) can yield oil in the gasoline and diesel range, and an iron-modified clay catalyst sharply raises the amount of liquid produced, according to a new study. The work compares thermal and catalytic pyrolysis of automotive plastic waste (APW) and reports oil properties alongside the processing steps still needed before the product could be used as a diesel-range fuel.
From shredder residue to component plastics
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. Much of that work, however, has centered on automotive shredder residue, a heterogeneous mixture of plastics, metals, textiles and other materials, leaving less information on plastics recovered directly from components such as dashboards, bumpers and headlamps.
Automotive plastic waste can also contain mineral fillers, flame retardants, fiberglass and other additives that affect how the material degrades and what products form. In this study, the researchers characterized plastics taken directly from ELVs rather than relying on mixed shredder residue. The feedstock contained acrylonitrile butadiene styrene (ABS), HDPE, LDPE, PP, polystyrene (PS) and fiberglass, 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.
Iron-pillared clay as catalyst
Catalysts can improve pyrolysis efficiency by accelerating reactions, altering product distributions and potentially reducing the temperature or residence time required. Commercial zeolites have been widely studied, but lower-cost clay-based alternatives are drawing 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 attractive because they may improve oil production without relying on more expensive commercial catalysts.
Instead of using bentonite clay in its original form, the researchers modified it through iron pillaring, introducing iron species into the clay structure and changing characteristics such as surface acidity and pore structure. The team compared thermal and catalytic pyrolysis across temperatures from about 350°C to 521°C and catalyst loadings of roughly 6% to 34% by weight, using a statistical experimental design to evaluate the interaction between temperature and catalyst concentration.
Yield gains, limited shift in composition
The catalyst strongly affected liquid yield. Catalytic pyrolysis produced an average oil yield of about 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%. However, the catalyst had much less influence on the composition of the resulting oil: thermal and catalytic pyrolysis produced similar proportions of hydrocarbons in the C8–C24 range associated with gasoline- and diesel-range compounds. In other words, the catalyst converted more of the feedstock into liquid 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.
Fuel properties and remaining gaps
The resulting pyrolysis oil showed several properties comparable to 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, 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 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 could serve 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 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 broader commercial application. Future work could examine 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 matter: without systematic removal and classification of plastic components from ELVs, reliable data on the volume and composition of available automotive plastic waste remain limited, information that would help researchers and recyclers assess feedstock availability and plan potential industrial-scale operations.