Scientists Turn Mixed Plastic Waste into Clean Hydrogen

by Arlene Karidis (Waste360) Mixed plastic waste is nearly impossible to recycle, with billions of tons choking landfills and incinerators worldwide. Now scientists in California and South Korea have developed a unique, experimental method to manage this problematic stream. It’s designed to deliver another advantage: converting the trash into clean hydrogen while trapping carbon before it’s released to the air.

Study co-author Woo-Jae Kim, a professor at Ewha Womans University, Korea, believes the thermal technology could achieve a $4-per-kilogram (kg) hydrogen cost. This would put it in line with North American subsidized rates for green hydrogen (produced via water electrolysis), which costs $3.50 to $6.00 per kg.

According to Kim, the competitive edge comes down to a few efficiencies. The process uses half the operating temperature of conventional gasification, requiring less energy. And it’s a fairly simple, one-step method. But the true differentiator is the use of sodium hydroxide (NaOH) as a catalyst—this chemical compound rapidly breaks down plastics, requiring almost no sorting, while boosting hydrogen yield.

In answer, the team put the plastic-busting NaOH to work on a second task: capturing the CO2 released during the reaction and turning it into stable, solid sodium carbonate.

At the end of the process, all that’s left is two outputs: the sodium carbonate, which has some industrial applications, and high-purity hydrogen, potentially used for clean fuel, power, or to make chemicals.

Keith D. Patch, an independent consultant specializing in hydrogen, confers that a robust life-cycle evaluation assessing environmental impact of hydrogen production, use, and disposal will be important. He points, for instance, to a reference in the UCLA/Ewha U study to calcium carbonate as a potential application. It’s widely used in cement.

This presents a challenge for carbon reduction goals, Patch explains, because when kilns turn calcium carbonate into quicklime, the stored CO2 is released, while burning kiln fuel also adds more emissions.

In the U.S., clean hydrogen producers can emit no more than 4 kg of CO2 for every 1 kg of hydrogen produced. This new process hits that 4 kg limit while yielding hydrogen with over 90% purity. For comparison, green hydrogen reaches 99.5% to 99.9% purity.

Kim and Park’s early steps took them in a slightly different direction, though ultimately laid the groundwork for how they would branch out. Their current process was adapted from a method they developed years ago to convert seaweed into hydrogen gas.

Preliminary work suggests their adapted method effectively handles polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), bioplastics, and food-contaminated plastics—as well as paper packaging and biomass beyond seaweed.

From their own lab, Kim and Park are working to advance to the next stage. Their most immediate hurdle is figuring out how to run an uninterrupted production workflow. READ MORE