Turning plastic into fuel profitably was a pipe dream. A new process just made it possible

A team from the Oak Ridge National Laboratory, in the United States, has achieved convert plastic bags and kitchen boards into gasoline and diesel without having to resort to high temperatures or expensive materials. The discovery, published in the Journal of the American Chemical Society, has raised some eyebrows and below we tell you all the details.

The problem they are trying to solve. The plastic is one of the most difficult materials to recycle profitably. Specifically, polyethylene (the polymer that makes up supermarket bags, white plastic containers or kitchen cutting boards) accumulates millions of tons in landfills each year. Until now, the only technically viable way to turn it into fuel was through a process called pyrolysis, which requires heating the material to temperatures between 450 and 500 degrees Celsius. An expensive, energy inefficient process that is difficult to scale to an industrial level.

What does the new method consist of?. Researchers at Oak Ridge National Laboratory (ORNL) have opted for a different path: introduce the plastic into a mixture of molten salts with aluminum chloride, which acts both as a solvent and as a catalyst. These salts are inorganic compounds that remain stable even under demanding reaction conditions.

The key is that the aluminum atoms in the mixture bind to the polymer and generate areas of high acidity that break the long molecular chains of the plastic into smaller fragments, which are transformed into molecules typical of gasoline or diesel. And all this at less than 200 degrees Celsius, a temperature comparable to that of a conventional domestic oven.

Why it represents a relevant technical leap. Beyond the reduction in temperature, the process dispenses with three elements that make traditional methods more expensive and complicated: noble metal catalysts (such as platinum), organic solvents and external contribution of hydrogen. According to Zhenzhen Yanga scientist at ORNL and one of the lead authors of the study, “this is the first time that molten salts have been used as a means to produce high value-added chemicals from waste without any catalytic initiators or solvents, and at a temperature below 200 degrees Celsius.”

Gasoline efficiency reaches approximately 60% in moderate conditions, a result that the researchers themselves describe as promising for its future industrial application.

As they verified that worked. To understand exactly what happens during the reaction, the team used a combination of advanced analysis techniques, including soft X-ray spectroscopy, nuclear magnetic resonance, neutron scattering, and gas chromatography.

Thanks to isotopic labeling, they were able to track how carbon behaves during the process and confirm that the simplest polymer chains produce gasoline-like fuel, while the more complex ones derive into diesel molecules. By having this level of detail, the process could be optimized depending on the type of fuel you want to obtain.

What remains to be resolved. The system is not ready to scale immediately. The main obstacle is that the aluminum salts used are hygroscopic, that is, they absorb moisture from the environment, which compromises their long-term stability. The team working now on ways to confine or protect these saltspossibly using halides or carbon materials, to make them more durable under real industrial conditions.

Mbeyond the laboratory. If the process manages to scale successfully, the implications are considerable. Polyethylene is the most produced plastic in the world, abundant and cheap to obtain as a raw material. Aluminum salts, for their part, are low-cost commercial materials. According to Liqi Qiua postdoctoral researcher at the University of Tennessee, “the starting material is abundant in consumer waste, and our catalyst system, molten aluminum salts, is very cheap.”

The result could be a cost-effective route to converting plastic waste into high-quality transportation and industrial fuels, while also clearing up our landfills. At the moment the patent is pending, so we will have to wait to find out if this remedy ends up coming to fruition.

Cover image | Elbert Lora and Marek Studzinski

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