Microwave catalyst in recycling PET

By Paul Gander

- Last updated on GMT

Products of depolymerisation: EG on the left and PTA on the right
Products of depolymerisation: EG on the left and PTA on the right

Related tags Polyethylene terephthalate

A new EU project aims to construct a demonstration plant for the depolymerisation of polyesters, including polyethylene terephthalate (PET), applying microwave technology.

This could potentially be used on those coloured and laminated plastics typically not processed by mechanical recycling.

Chemical recycling, or depolymerisation, breaks polymers down into their component monomers which, in turn, can be used to synthesise new polymer for food-grade packaging.

Since the 1990s, chemical recycling has been largely eclipsed by mechanical recycling in Europe, with food-grade, post-consumer recyclate now available in larger quantities.

“Over the past few years, people have started to work on low-cost chemical recycling, reducing the break-even point in economic terms, but also in terms of the amount of feedstock required,”​ said Maurizio Crippa, chief executive of Swiss company gr3n.

‘Low-cost chemical recycling’

Crippa is the inventor of the technology now being scaled up by the consortium behind Demeto (Depolymerisation by Microwave Technology), funded under the EU’s Horizon 2020 programme (grant agreement 768573).

The process, which can also be applied to polyester textiles and laminates, uses sodium hydroxide to trigger alkaline depolymerisation.

But, crucially, it uses microwave energy as a catalyst, cutting the reaction time from one or two hours to just 10 minutes, Crippa claimed.

Because it is a flow-through rather than a batch system, there are no interruptions for loading or unloading the reactors. This process breaks PET down into the monomers ethylene glycol (EG) and purified terephthalic acid (PTA).

The 13 partners in the three-year project aim to start building an Italian demonstration plant before mid-2019 and run it for a year to fine-tune the technology. It will have a 1,000–1,500t capacity, but a full-size production plant would be 10 times this size.

Fine-tune the technology

Crippa estimated that commercial break-even would come at around 5,000–8,000t a year.

He rejected the idea that production-scale plants using the Demeto technology could compete with mechanical recycling for PET feedstock.

“When mechanical recyclers buy bottles, they tend to focus on clear and light-blue PET, even though up to 50% of what they buy can be mixed colours,”​ said Crippa.

“They make very little money out of this. A typical capacity for mechanical recycling plants is around 30,000t. One of our 15,000t capacity plants could be located close by, allowing both parties to benefit.”

Around two-thirds of the polyester produced worldwide goes into making fabric, said Crippa. Clothes retailer H&M is part of the consortium, as well as Petcia, a Spanish mechanical recycler of PET.

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