Waste Drink Cartons Turned Into Catalysts That Strip Sulfur From Tire Pyrolysis Oil

Researchers in Turin have converted discarded Tetrapak drink cartons into an iron-tailored catalyst that removes up to 57 percent of the sulfur from pyrolysis oil made from scrap tires, one of the most stubborn impurities standing between waste-derived fuels and everyday use. The study, published open access in Discover Catalysis on 20 October 2026 by Valentina Tamborrino, Luca Lavagna, Sergio Bocchini, Alberto Tagliaferro and Mattia Bartoli, describes a single thermal route that transforms a notoriously difficult packaging waste stream into a working heterogeneous catalyst for oxidative desulphurization.

Tire pyrolysis has reached a high level of technological readiness, allowing industrial-scale conversion of end-of-life tires into a liquid oil fraction whose hydrocarbon distribution is comparable to that of conventional transportation fuels. The problem is sulfur. Tires are vulcanized with sulfur, and the pyrolysis oils they yield are dominated by thiophenic and benzothiophenic compounds that resist conventional hydrodesulphurization, the industrial benchmark for sulfur removal. Hydrodesulphurization is also energy intensive and hydrogen demanding, which sits awkwardly with decentralized, waste-based tire conversion schemes. The oil examined in this study contained 7139 ppm sulfur, far above any limit for use as a drop-in fuel.

The team’s answer was oxidative desulphurization, a process that selectively converts organosulfur compounds into sulfoxides and sulfones, which can then be removed by extraction or phase separation without altering the hydrocarbon matrix. Rather than using soluble metal salts, ionic liquids or metal-organic frameworks, the researchers built a Fenton-like system on a solid carbonaceous support, an approach that promotes interfacial electron transfer and stabilizes the mixed-valence iron species needed for sustained catalytic activity. Their feedstock for that support was contaminated Tetrapak packaging collected in Turin, washed with water and dried at 105 degrees Celsius for 72 hours.

The preparation was deliberately simple. One hundred grams of Tetrapak was pyrolyzed in a tubular furnace under a nitrogen flow at a heating rate of 15 degrees Celsius per minute and held at 800 degrees Celsius for 30 minutes, yielding a carbon-aluminum composite the authors call TC. Ten grams of this solid was then suspended in water with iron nitrate at an iron-to-TC weight ratio of 0.1, dried overnight, and subjected to a second carbothermal treatment under the same conditions. During this step, the iron nitrate released NOx species, and the resulting iron, mainly as oxide, reacted with the carbon matrix above 800 degrees Celsius, partially consuming the carbon and anchoring reduced iron nanoparticles onto the surface.

Characterization showed how much that second firing changed the material. The raw pyrolyzed Tetrapak had a very low specific surface area of 8.3 square meters per gram, with carbon flakes of 100 to 200 nanometers mixed with aluminum flakes of 100 to 200 micrometers. After carbothermal reduction, the composite, Fe@TC, displayed a more homogeneous morphology of particles 20 to 100 micrometers across, with iron nanoparticles of 10 to 20 nanometers uniformly distributed on the surface, and its specific surface area rose to 42.5 square meters per gram. Energy-dispersive X-ray analysis indicated that roughly 20 weight percent of iron was anchored to the catalyst. Raman spectroscopy gave an ID/IG ratio of 1.3, corresponding to a volumetric crystallite size of 12.9 nanometers, and detected peaks attributed to Al2O3 and Fe2O3 at 371 and 809 wavenumbers respectively.

X-ray photoelectron spectroscopy revealed the chemical state of the metals before catalysis. The iron fraction was mostly metallic, with an Fe(III) content of only 11 weight percent, consistent with a core-shell structure in which a metallic iron core is covered by a thin passivating oxide layer formed during post-synthesis air exposure. The aluminum fraction told a different story: Al(III) accounted for up to 47 weight percent, indicating massive oxidation of the metallic aluminum layer during thermal conversion, plausibly driven by small organic acids released from the radical decomposition of the cellulosic fraction of the carton. This native aluminum matters, because Al(III)/Al(0) couples are reported to participate in Fenton-like chemistry, boosting the effectiveness of iron species through highly reactive aluminum-based radical species.

The catalytic tests used a deliberately recalcitrant feed: two grams of tire pyrolysis oil suspended in 15 milliliters of a 10 percent hydrogen peroxide solution with the catalyst, sealed in vials and heated in an oil bath at 60, 80 or 100 degrees Celsius for 2, 4 or 6 hours at catalyst loadings of 2, 5 and 10 weight percent. Sulfur content was measured by ICP-OES after microwave-assisted acidic digestion, and each test was run three times with relative deviations below 3 percent. Thermogravimetric analysis confirmed the oil’s fuel-like character, with more than 67 weight percent of C6-C10 hydrocarbons boiling between 120 and 180 degrees Celsius.

The results mapped out a clear performance landscape. Under the harshest conditions tested, 6 hours at 100 degrees Celsius with 5 weight percent Fe@TC, desulphurization reached 56.1 percent, cutting the sulfur content to 4005 ppm with a turnover number of 328. Controls were unambiguous: the unmodified carbon support and hydrogen peroxide alone achieved only 33.2 and 34.5 percent removal under identical conditions. Lowering the temperature to 80 and 60 degrees Celsius dropped performance to 47.0 and 46.0 percent, a threshold-like effect above 80 degrees that the authors attribute to reaction kinetics. Time mattered even more: 2 hours gave only 28.7 percent removal while 4 hours reached 53.1 percent, behavior consistent with slow conversion of recalcitrant sulfur species. Catalyst loading showed a plateau, with 2 weight percent giving 35.4 percent, close to the support alone, and 10 weight percent improving only marginally to 57.0 percent, likely because of transport limitations and particle aggregation at high loading.

Recyclability data added an unexpected twist. After three consecutive catalytic cycles, Fe@TC showed no significant loss of activity, with desulphurization actually edging up to 56.9 percent. Microscopy revealed that the iron particles had grown to hundreds of nanometers, yet XPS of the recovered catalyst showed the Fe(III) fraction had risen from 11 to 51 weight percent and Al(III) from 47 to 74 percent. Since both Fe(III) and Al(III) are far more active than their zero-valent counterparts in Fenton-like processes, the authors argue that this progressive surface oxidation explains the maintained or improved performance despite particle growth. Raman spectra of the spent catalyst showed minimal changes in the carbon support, with the ID/IG ratio shifting slightly to 1.1.

The authors note that the starting sulfur level of 7139 ppm posed a serious obstacle for a simple water-to-oil biphasic approach, because the water phase saturates rapidly with the sulfones produced during oxidation. Even so, Fe@TC performed close to systems previously reported for oxidative desulphurization of tire-derived oils with lower sulfur contents. The broader significance, they argue, lies in the self-consistent platform: the same pyrolysis conversion route that turns scrap tires into fuel oil also turns hard-to-dispose-of beverage cartons into the multi-metal catalyst needed to clean that oil, closing a waste-management loop in which one problematic stream helps upgrade another.

Subject of Research: Catalytic oxidative desulphurization of scrap tire pyrolysis oil using a catalyst made from waste Tetrapak packaging

Article Title: Upgrading of scrap tire derived pyrolytic oils through catalytic oxidative desulphurization over iron tailored Tetrapak® based catalyst

Article References: Tamborrino, V., Lavagna, L., Bocchini, S., Tagliaferro, A., & Bartoli, M. (2026). Upgrading of scrap tire derived pyrolytic oils through catalytic oxidative desulphurization over iron tailored Tetrapak® based catalyst. Discover Catalysis, 3(1), Article 20. https://doi.org/10.1007/s44344-026-00051-w

Image Credits: AI Generated

DOI: 10.1007/s44344-026-00051-w

Keywords: tire pyrolysis oil, oxidative desulphurization, Tetrapak recycling, iron catalyst, carbothermal reduction, Fenton-like catalysis, hydrogen peroxide, waste-derived fuels, heterogeneous catalysis, sulfur removal, carbon support, catalyst recyclability