Plastic upcycling: from waste to fuel for less

Petroleum-based plastic waste presents an untapped source of carbon-based chemicals that can serve as the starting material for useful durable materials and fuels. Very little plastic is currently recycled, mainly for economic and practical reasons. But Pacific Northwest National Laboratory (PNNL) scientists are trying to change the dynamic by applying their expertise in efficiently breaking chemical bonds. Their plastics recycling innovation was recently presented at the American Chemical Society fall meeting in Chicago.

The new method is designed to upcycle plastics to valuable commodity chemicals and simultaneously increase conversion to useful products while using less of the precious metal ruthenium.

“The key discovery we report is the very low metal load,” said Pacific Northwest National Laboratory chemist Janos Szanyi, who led the research team. “This makes the catalyst much cheaper.

“This research shows the opportunity to develop effective, selective and versatile catalysts for plastic upcycling.”

It’s well known that adding hydrogen — a reaction known as hydrogenolysis — to difficult-to-recycle plastics like polypropylene and polyethylene presents a promising strategy to convert plastic waste into value-added small hydrocarbons. This process requires catalysts to make it economically feasible and that’s where the PNNL-led research excelled.

The research team discovered that reducing the amount of the precious metal ruthenium actually improved the polymer upcycling efficiency and selectivity. In a study recently published in ACS Catalysis, they showed that the improvement in efficiency happened when the low ratio of metal to support structure caused the structure to shift from an orderly array of particles to disordered rafts of atoms.

To make the method practical for use with mixed plastic recycling streams, the research team is now exploring how the presence of chlorine affects the efficiency of the chemical conversion.

“We are looking into more demanding extraction conditions,” said chemist Oliver Y Gutiérrez, an expert in industrial applications for catalysis. “When you don’t have a clean plastic source, in an industrial upcycling process, you have chlorine from polyvinylchloride and other sources. Chlorine can contaminate the plastic upcycling reaction. We want to understand what effect chlorine has on our system.”

This fundamental understanding may help convert waste plastic that would usually end up as pollution in the environment into useful products.

Image credit: iStock.com/sutiporn