New Chemical Process Transforms Unsorted Plastic Waste Into High-Purity Hydrogen at Low Temperatures

Plastic is ubiquitous, but recycling it remains a logistical and economic bottleneck. Because different polymers melt and react at vastly different temperatures, recycling facilities must meticulously sort polyethylene terephthalate (PET) from polyethylene (PE) and polypropylene (PP) before processing. This sorting requirement is so labor-intensive and costly that only 9% of discarded plastic is actually recycled globally, while the vast majority is landfilled or incinerated. High-temperature gasification can handle mixed plastics without sorting, but it requires massive energy inputs and releases substantial carbon dioxide into the atmosphere.[4]

A team of chemical engineers from UCLA and South Korea's Ewha Womans University has demonstrated a chemical workaround that bypasses the sorting bottleneck entirely. Writing in the Proceedings of the National Academy of Sciences, the researchers detail a process that converts an unsorted mixture of PET, PE, and PP directly into high-purity hydrogen fuel. The method, known as alkaline thermal treatment (ATT), operates at temperatures 300 to 400 degrees Celsius lower than conventional steam gasification, drastically reducing the energy required to break down the waste.[1]

The ATT process relies on sodium hydroxide reacting with the organic material under moderate heat. As the plastic breaks down, it releases hydrogen gas. Crucially, the sodium hydroxide also acts as a built-in carbon capture mechanism. Instead of allowing the carbon from the plastic to escape as carbon dioxide, the reaction traps it, converting it into solid sodium carbonate. Analysis of the reaction outputs showed that more than 75% of the original carbon in the plastics was successfully locked away in stable carbonate compounds or liquid organic residues, with less than 13% entering the gas phase.[1][2]

While the ATT method works seamlessly on oxygen-containing plastics like PET, the researchers faced a significant hurdle with polyethylene and polypropylene. These two plastics—which make up the bulk of shopping bags, food containers, and automotive parts—consist entirely of stable carbon-hydrogen bonds. Under alkaline conditions, they are chemically inert, meaning they initially produced very little hydrogen. Previous low-temperature hydrogen conversion methods, such as solar-driven photoreforming, have similarly failed to break down these stubborn polyolefins.[1][2][4]

To overcome this chemical resistance, the engineering team introduced a thermal oxidation pretreatment step. By briefly heating the PE and PP plastics in air before they enter the main reactor, the researchers forced oxygen-containing functional groups to attach to the long polymer chains. These newly introduced oxygen groups act as chemical footholds, creating reactive sites where the sodium hydroxide can successfully attack and dismantle the polymer backbone. Once activated by this mild heating step, all three plastic types decomposed efficiently in the single reactor.[1][2]

The optimized process yielded impressive results for all three major plastic types. The researchers reported hydrogen yields of 43.7 millimoles per gram of plastic for PET, 51.9 millimoles for PE, and 30.2 millimoles for PP. When the plastics were mixed together and processed simultaneously, the resulting hydrogen gas exceeded 90% purity. The sodium carbonate byproduct generated during the reaction can also be easily converted into calcium carbonate, a stable mineral widely used in construction and manufacturing, ensuring the carbon remains permanently sequestered.[1][4]

The ATT method was not originally designed for plastic waste. The research team initially developed the process as a carbon-neutral way to extract hydrogen from wet, salty biomass. In a 2020 study published in Nature Communications, the same researchers demonstrated that ATT could successfully convert brown seaweed into high-purity hydrogen while suppressing carbon dioxide formation. Adapting the technique from organic seaweed to synthetic, chemically inert plastics represents a major leap in the technology's versatility.[3][4]

While the chemistry is proven, the evidence for its real-world viability remains thin. The current data comes exclusively from highly controlled laboratory experiments using small-scale reactors and pure plastic samples. It remains unknown how the ATT process will perform when exposed to the severe contamination typical of municipal waste streams, such as food residue, paper labels, and toxic chemical additives. Furthermore, the energy required for the thermal oxidation pretreatment and the continuous supply of sodium hydroxide must be factored into a full lifecycle analysis to determine if the process is genuinely net-positive for energy and emissions at an industrial scale.[1][4]