Let’s Go Round Again: Closing the Loop on Problem Plastics

Article by Adam Duckett

Jess Gregson stands in front of the process plant she is helping to build, which is set to start recycling problem plastics later this year

With today’s Earth Day campaign calling for action on plastic production, Adam Duckett talks to Jess Gregson, a chemical engineer building a plant in the UK that will allow tricky to recycle plastics to be used over and over again

YOU PROBABLY don’t pay much attention to the plastic film that covers your block of cheddar or the one you pierce with a fork before you pop a ready meal into the microwave. But Jess Gregson does.

Those plastic films are typically made of multiple layers of different plastic, including high density polyethylene and polypropylene – and are one among many forms of plastic that are currently difficult or impossible to recycle. Once you discard them in the bin, their ultimate fate is landfill or incineration, but perhaps not for much longer. Jess and her colleagues at Mura Technology are creating a new route – one that involves turning that discarded plastic into the raw materials to make fresh plastic.      

Jess, who is a process engineer for Mura, is engineering a huge recycling plant in Teesside which is set to show that supercritical steam can break these materials back down into the chemicals they were originally made from. Her work could help bring about a circular economy for problem plastics. The plant is scheduled to begin operations in the coming months, producing 20,000 t/y of hydrocarbons from plastic waste. In doing so it could help reduce our demand for fossil fuels, cut emissions, and divert plastics away from polluting the environment.  

“It's nice to know that you're involved in something that will make a difference,” she says. “It's not just technology for the sake of technology. It's actually got a benefit for the community and the world.”

Jess is calling me from her company’s Teesside office. Once she’s finished our call, she needs to get down to the plant floor and run trials of the equipment that separates the raw waste arriving at the plant. The material preparation plant – or MPP as it’s known – must remove any contaminants from the large bales of waste arriving at the plant. This is to ensure that only the right sorts of plastic are fed into the next stage where the chemistry happens, turning the plastic back into its constituent molecules.

Choosing engineering

It could have been so different for Jess. She originally studied chemistry and went to work as an analytical chemist in the pharmaceuticals industry. But the work wasn’t challenging enough.

“Once you knew what you were doing, it was the same day in, day out, which is completely opposite to now.”

In 2017, Jess chose to return to university and study chemical engineering.

“I've always been more interested in the engineering side,” she says. “What we're doing here, yes, it's engineering, but within the reaction itself, that's chemistry. Having a mix of both appealed to me.”

The MPP, though, is a mechanical engineering project. The process engineering bit starts later.

First, the unsorted waste is fed into a shredder, then through stages to remove metals, dirt, and grit, and finally an infrared optical sorter picks out the type of plastics that Mura doesn’t want, leaving behind only those that it wants to process and can’t be mechanically recycled. These include those films mentioned earlier, along with polyethylene used to make bread bags and bleach bottles, plus the polypropylene pots that your yoghurt and margarine come in.

Jess says she’s excited for tests to start on the “chemical engineering stage” of the plant – the one that chemically recycles the plastics. It begins with an extruder.

“It basically pressurises and heats up the plastic into a toothpaste consistency,” Jess explains. It then gets mixed with supercritical steam which Mura uses as the solvent for its so-called Hydro-PRT process.

“There's nothing else that's added into the reactor other than the molten plastic and the steam.”

It takes about 30 minutes for the plastic to be “cracked” back into its hydrocarbon components. It’s then depressurised and moves on to more traditional chemical engineering technologies including a distillation column that separates out the chemical components.

“Those four products are naphtha, a distillate gas oil, a heavy gas oil, and a heavy wax residue. And these will then go forward into storage tanks for shipment to petrochemical companies.”

These are drop-in replacements of fossil feedstocks that can be put through existing chemical processes to make new virgin-grade plastics and construction materials.

If Mura and other companies developing similar chemical recycling techniques can successfully demonstrate these processes and prove them profitable then they could help wean plastics production off fossil fuels. Industry trade group Plastics Europe published a report last year outlining how this production might change in the coming years. In 2021, European industry made 57m t of plastic, but 50m t of it was produced using fossil fuels. Just 5m t was made from mechanically recycled plastics.

This involves shredding waste plastics into small pellets that can be turned into new plastic products. However, the act of doing so downgrades the plastic, meaning it can’t typically be used to remake the same product it came from.

A second option is chemical recycling – the sort of technique that Mura is developing – which converts the waste back into the same raw materials it was originally made from, allowing it to make the same product once again. None of Europe’s plastics were produced using these processes in 2021, but it’s estimated they could reach 12m t by 2050, and alongside mechanically recycled plastics and those made from biomass could reduce fossil-based plastics to 22m t by 2050. It’s not the whole solution to Europe’s plastics problem but it could certainly play a part.

“Obviously at the minute we wouldn't be at the scale where you cut out all crude oil plastic, but it would be a reduction of that crude oil and therefore it’s more efficient and it’s better for the environment. It’s a lot more beneficial to be able to do that. Not just reducing the plastic that ends up as waste, but also to reduce the emissions that come from the actual processing of new plastic.”

What next for Jess?

The lessons that Jess and her team learn from running the plant in Teesside will shape the development of the larger-scale plants that her colleagues are currently designing. Mura has plans for plants in Germany and the US that each could produce at least 50,000 t/y of recycled hydrocarbons.

“I want to be involved in that scale-up process,” Jess says.

“I want to stay within sustainable projects…develop my skills broadly and see where it takes me.”

But for now, she’s focused on working with her colleagues and their contractors to get the Teesside plant ready for operations. She feels a sense of wonder at seeing what they’ve created. What started out as rough land, is now home to a huge plant.

“It’s come on a massive way. It’s still hard to see because there’s a lot of scaffolding on it. Once that scaffolding is down…we’ve got it.”

Article by Adam Duckett

Editor, The Chemical Engineer

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