UCLA and Ewha Womans University convert mixed plastic waste into hydrogen

UCLA and Ewha Womans University convert mixed plastic waste into hydrogen

A research team co-led by Ewha Womans University in South Korea and the UCLA Samueli School of Engineering has developed a chemical process that converts mixed plastic waste into high-purity hydrogen fuel without the need for sorting. The method, known as alkaline thermal treatment (ATT), addresses the high costs and labor associated with separating plastics by type, a barrier that contributes to only 9% of discarded plastic being recycled according to a 2025 European Environment Agency report.

The study, published July 7 in the journal Proceedings of the National Academy of Sciences, demonstrates that a single reactor can handle a mixture of the three most common plastics: polyethylene terephthalate (PET), polyethylene (PE), and polypropylene (PP). The process yields hydrogen gas with purities exceeding 90%.

Traditional steam gasification can handle unsorted plastics but requires extreme temperatures and releases substantial carbon dioxide. In contrast, the ATT process operates at temperatures 300–400 degrees Celsius lower than conventional gasification. This shift reduces energy demand and helps mitigate greenhouse gas emissions.

The ATT method was adapted from a carbon-neutral process previously developed by Professor Woo-Jae Kim of Ewha Womans University and Professor Ah-Hyung "Alissa" Park of UCLA to convert biomass, such as rice husks, waste wood, and seaweed, into hydrogen gas.

While PET is naturally reactive, PE and PP are chemically inert under alkaline conditions because they consist entirely of carbon-hydrogen bonds. To resolve this, the researchers implemented a thermal oxidation pretreatment. By briefly exposing these plastics to mild heat in air, the team introduced oxygen-containing functional groups into the polymer chains. This creates reactive sites that allow the alkaline treatment to function on fossil-based polymers similarly to how it works on biomass.

"We are solving two urgent global problems at the same time,"

Ah-Hyung "Alissa" Park, Ronald and Valerie Sugar Dean of UCLA Samueli and professor of chemical and biomolecular engineering, via newsroom.ucla.edu

The process also incorporates inherent carbon storage. Rather than releasing carbon dioxide into the atmosphere, the sodium hydroxide reagent captures the carbon and converts it into solid sodium carbonate. Post-reaction analysis revealed that more than 75% of the original plastic carbon is converted into liquid organic residues or stable carbonate. Less than 13% appears in gaseous form, and direct atmospheric release is described as negligible.

The team further identified a recovery process to convert this sodium carbonate into calcium carbonate. This permanently fixes the carbon in a mineral used by traditionally carbon-intensive industries.

The researchers noted that previous low-temperature methods, including electrochemical conversion and solar-driven photoreforming, only work on oxygen-containing plastics like PET. ATT is the first application to address the limitations of temperature, sorting, and carbon emissions simultaneously.

"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,"

Woo-Jae Kim, professor of chemical engineering and materials science at Ewha Womans University, via newsroom.ucla.edu

The research was supported by the National Research Foundation of Korea. Contributors to the study included researchers from Korea Aerospace University, Kangwon National University, and Sogang University, alongside Jieun Park, Hyerin Seo, and Jiwon Lee of Ewha Womans University.

The team says further work is now required to evaluate economic viability and optimize the process before the technology can be deployed at scale.