Plastic scrap could prove to be a powerful catalyst

The US Pacific Northwest National Laboratory has found a new way to tackle non-degradable polyolefin plastic scrap. It proposes a hydrogenolysis method to upcycle the polymers into selective catalysts.

The new method efficiently converts polypropylene (PP) and polyethylene (PE) into valuable commodity chemicals while reducing the need for the precious metal ruthenium. ‘The key discovery we report is the very low metal load,’ says chemist Janos Szanyi, who led the research team. ‘This makes the catalyst much cheaper.’

It is argued that 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.

Szanyi observes 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 efficient and selective catalysts to make it economically feasible.

His team discovered that reducing the amount of the precious metal ruthenium actually improved the polymer upcycling efficiency and selectivity. Szanyi explains 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,’ comments chemist Oliver Y. Gutiérrez. ‘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 it has on our system.’