New Process Turns Mixed Plastic Waste Directly Into Hydrogen Fuel Without Sorting

Plastic has become a ubiquitous part of modern life — in water bottles, shopping bags and car dashboards. But once discarded, it is among the hardest materials on earth to recycle. Most recycling processes require plastics to be sorted by type first, a step that is both laborious and costly, which is why only 9% of discarded plastic is actually recycled, while 79% is dumped in landfills and another 12% is incinerated, releasing carbon dioxide in the process.

Now, a team co-led by researchers at the UCLA Samueli School of Engineering and Ewha Womans University in South Korea has demonstrated a new chemical approach that converts a mixture of the three most common plastics directly into high-purity hydrogen fuel at temperatures far below conventional gasification. The process locks carbon dioxide away as a solid mineral without releasing the greenhouse gas into the atmosphere. 

Published in Proceedings of the National Academy of Sciences, the study shows that alkaline thermal treatment (ATT) — a process in which sodium hydroxide reacts with organic material under heat to drive hydrogen production — can efficiently handle mixed polyethylene terephthalate (PET), polyethylene (PE) and polypropylene (PP) waste in a single reactor, yielding hydrogen gas with purities exceeding 90% without requiring any sorting of plastic types.

“We are solving two urgent global problems at the same time,” said co-corresponding author Ah-Hyung “Alissa” Park, the Ronald and Valerie Sugar Dean of UCLA Samueli and a professor of chemical and biomolecular engineering. “Plastic waste is accumulating at alarming rates, and clean hydrogen is essential for decarbonizing energy. This technology tackles both of these challenges in a creative and scalable way.”

The ATT process was adapted from a method initially developed by Park and study co-corresponding author Woo-Jae Kim, a professor of chemical engineering and materials science at Ewha Womans University, as a carbon-neutral method of converting biomass such as seaweed into hydrogen gas. In laboratory experiments, the team used the modified ATT process to convert PET, PE and PP into high-purity hydrogen. The approach yielded significantly more hydrogen from PET while operating at temperatures 300-400 degrees Celsius lower than traditional steam gasification.

Unlike PET, polyethylene and polypropylene were initially less effective at producing hydrogen gas because they consist entirely of carbon-hydrogen bonds and are chemically inert under alkaline conditions. To activate them, the researchers developed a thermal oxidation pretreatment in which the plastics are briefly exposed to mild heat in air before the main reaction. That step introduces oxygen-containing functional groups into the polymer chains, creating reactive sites where the alkaline treatment can work. 

Once activated, all three plastics decompose efficiently. Carbon released during the reaction is captured by the sodium hydroxide reagent and converted to solid sodium carbonate rather than escaping as atmospheric carbon dioxide. Post-reaction analysis showed that more than 75% of the original plastic carbon ends up either as stable carbonate or liquid organic residues. Less than 13% appears in gaseous form, and direct atmospheric carbon release during the reaction is negligible. The sodium carbonate can in turn be converted to calcium carbonate using a simple recovery process, permanently fixing the carbon in a mineral widely used in traditionally carbon-intensive industries.

Previous low-temperature approaches to converting plastic waste into hydrogen, such as solar-driven photoreforming and electrochemical conversion, work only on oxygen-containing plastics like PET — leaving polyethylene and polypropylene, two of the most abundant plastics in the waste stream, out of reach. High-temperature gasification can handle unsorted mixed plastics but releases substantial carbon dioxide. ATT is the first application of the team’s own method to address all three limitations at once.

“By reducing the sorting costs and process complexity that have been major barriers to commercialization, this technology has the potential to become a next-generation core technology that supports both the hydrogen economy and the circular economy,” Kim said.

The researchers say further work is needed to optimize the process and evaluate its economic viability before it can be deployed at scale.

The research was supported by the National Research Foundation of Korea. Additional authors include Jieun Park, Hyerin Seo and Jiwon Lee of Ewha Womans University; Hyunah Kim of Korea Aerospace University; Hyung-Kyu Lim of Kangwon National University; and Wonho Jung of Sogang University.