Scientists have developed a new chemical process that can convert mixed plastic waste into high-purity hydrogen fuel while capturing most of the carbon instead of releasing it as carbon dioxide.
The study was carried out by researchers from the UCLA Samueli School of Engineering and Ewha Womans University in South Korea. The findings were published in the Proceedings of the National Academy of Sciences.
Plastic waste remains one of the worldโs major environmental problems. Many plastic products, including bottles, bags, packaging, and vehicle parts, are difficult to recycle once discarded. Traditional recycling often requires plastics to be separated by type, which increases cost and complexity.
As a result, only a small portion of plastic waste is recycled. Much of it ends up in landfills or is burned, releasing carbon dioxide and contributing to environmental pollution.
The new method offers a different approach. It can process a mixture of three common plastics: polyethylene terephthalate, polyethylene, and polypropylene. These plastics are widely used and often appear together in waste streams, making them difficult to recycle through conventional methods.
The process is known as alkaline thermal treatment. It uses sodium hydroxide and heat to break down organic materials and generate hydrogen. Unlike traditional gasification, which requires very high temperatures, this method operates at much lower temperatures.
In laboratory tests, the process produced hydrogen with more than 90% purity without requiring the plastics to be sorted first.
One major advantage is that the method captures much of the plasticโs carbon. During the reaction, sodium hydroxide traps carbon and converts it into sodium carbonate, preventing it from escaping as carbon dioxide.
The researchers found that more than 75% of the carbon originally present in the plastic was retained in stable carbonate compounds or liquid organic residues. Less than 13% entered the gas phase, and direct carbon dioxide release during the reaction was negligible.
The sodium carbonate can also be converted into calcium carbonate, a stable mineral form that can permanently store carbon.
The researchers originally developed the alkaline thermal treatment method for producing hydrogen from biomass, such as seaweed. In this new study, they adapted it to handle plastic waste.
While PET responded well to the treatment, polyethylene and polypropylene were initially more difficult to break down because they are made mainly of strong carbon-hydrogen bonds. To solve this, the team added a mild thermal oxidation pretreatment, briefly heating the plastics in air before the main reaction.
This step introduced oxygen-containing groups into the plastic chains, making them more reactive and easier to decompose during alkaline treatment.
The breakthrough could help address two major challenges at once: the growing burden of plastic waste and the need for cleaner hydrogen production.
Hydrogen is considered an important fuel for decarbonizing energy systems, but many current production methods still release carbon dioxide. A process that produces hydrogen from plastic waste while storing carbon could support both the hydrogen economy and the circular economy.
The researchers caution that the technology is still at the laboratory stage. More work is needed to improve efficiency, reduce costs, and determine whether the process can be scaled for commercial use.
If successfully developed, the method could provide a cleaner way to treat unsorted plastic waste while producing valuable hydrogen fuel and keeping most of the carbon locked away.
Journal Reference:
Park, J., Kim, H., Seo, H., Lee, J., Lim, H.-K., Jung, W., Park, A.-H. A., & Kim, W.-J. (2026). Selective and direct hydrogen generation from mixed plastic waste via alkaline thermal treatment with inherent carbon storage. Proceedings of the National Academy of Sciences, 123(28). https://doi.org/10.1073/pnas.2537552123