Plastic Recycling Reimagined

Will Simpson takes us on a tour of some of the most groundbreaking plastic recycling technologies on the horizon, offering hope that today’s material mess might become tomorrow’s material manna.

Plastic recycling remains one of the biggest conundrums in the recycling world. Whilst plastic bottles, pots, tubs and trays have been a feature of kerbside collections for well over a decade in the UK, the actual amount of plastic that actually gets recycled still remains low – just 44 per cent of the UK’s total plastic packaging waste in 2021.

Due to the lack of facilities in the UK, far too much still ends up being exported – some 540,000 tonnes of it in 2020 – much of that effectively ‘dumped’ on the other side of the world, in Turkey and Malaysia in particular. For the 44 per cent that is picked up, the vast majority goes to mechanical recycling. Here PET is sorted, cleaned and granulated so it produces plastic ‘flakes’ which can be used in a number of non-food grade applications.

But that means that there is still a huge amount of virgin plastic coming onto the market each year – effective closed-loop plastic recycling is still some way off. And this at a time when there is an increased demand for recycled plastic: the Plastic Packaging Tax came into effect in April this year, meaning that packaging with a recycled content of less than 30 per cent now comes with a surcharge of £200 per tonne.

Enzymatic RecyclingSo, action is needed. Urgently. However, there are a number of new developments that, combined, could move the dial on plastic recycling. As yet, none resemble a silver bullet. But they could mean that in a few years’ time there will be a range of options for end-of-life plastic beyond mechanical recycling.

Enzymatic recycling

This is an intriguing new process, developed by the French company Carbios. Essentially, it involves purified bacteria feeding on the bonds that hold polymers together, breaking them down to their essential building blocks. This breakthrough was announced back in 2019, when Carbios produced the first PET bottle using this process. “We take plastics or polyester fibres, process them in our plant and inject them with enzymes we have developed – one kilo of them per 100 kilos of plastic waste,” explains CEO Emmanuel Ladent. “The enzyme acts like a pair of scissors, cutting through the molecules until we have monomers, with which we are able to assemble virgin plastic.”

The advantage of the Carbios method is that it is not energy-intensive. “We use some energy, of course,” says Ladent. “But generally we work at pretty low temperatures – 70 degrees – while traditional recycling technologies use a lot of heat.” Enzymatic recycling also scores high in its circularity. “The current mechanical recycling techniques are not circular in the sense that you reproduce a plastic, but it works three or four times and then it is waste: it doesn’t have the same quality as virgin plastics – the rigidity – and the plastic gets darker and darker. The advantage of enzymatic recycling is that you can recycle over and over, using the same monomers. So you end up using far fewer resources.”

The major drawback is that, so far, PET is the only polymer they can recycle. “Our ambition is to continue this development and find enzymes that could recycle all the plastics. Today we are starting with PET, but we don’t want to stop there.” Ladent claims that there is a “huge appetite” from plastic manufacturers to invest in the Carbios process. Indeed, their partners at launch were the Thai group Indo Rama Ventures, which produces over six million PET bottles per year.

Whilst he admits that enzymatic plastic recycling is still in the ‘pre-industrial’ phase, he is convinced that within a decade it will present a viable alternative to using virgin material. Carbios’s first plant is to be opened in the North East of France in 2025, but the firm has a long-term strategy of partnering with plastics producers, setting up facilities close to existing plants, thus cutting down on costly and inefficient transport costs. Ladent mentions one possible partnership with a PET producer “somewhere in the North of England”.

“We believe that by 2035, 50 per cent of the plastics will be recycled. So there is going to be a huge need for increased capacity. And we are not going to do investment by ourselves – we are going to use the plastics producers who are going to invest in our technology. We will license our technology to them so that they can produce recycled products from our technology.”

Supercritical water

This is a new hydro-thermal process that converts non-recyclable plastics into their base components so they can be used to construct new plastics. It has been developed by the Cheshire-based firm Stopford in partnership with the University Of Birmingham. Their method – patented as CircuPlast – uses water at a very high temperature (above 375 degrees celsius) and high pressure (220 bar; more than 200 times the atmospheric pressure at sea level) to fray chemical bonds. “When you do that to water, its thermophysical properties – its polarity, its density, its viscosity – all those things change significantly,” explains William Thom, Stopford’s Senior Technology and Innovation Consultant. “It behaves very differently.”

“It’s more able to solvate organic molecules so it can act as a solvent to things that wouldn’t normally dissolve in it. Also, by virtue of the temperature, it has a huge amount of thermal energy in the molecules – they are moving around very, very fast. What that allows it to do is act as an effective heat transfer medium, so it breaks apart the carbon bonds in the polymeric feedstock and converts that into monomeric units – your light oils – that can then, in principle, be used to make fresh plastic.”

“Currently when you make plastic you drill oil out of the ground and some of the components will get upgraded – they’ll get treated in certain ways, cracked, to get broken down more. And then when you have your natural feedstock, that goes through a polymerisation process and it converts short hydrocarbon molecules into long polymeric chains.”

Supercritical water, he explains, essentially flips that process around. “We’re starting with our long chains and we’re breaking them into small molecules and in principle – this is the real advantage over mechanical recycling – what you end up with is the same as what was initially drilled out of the ground. So this is potentially truly circular – you can really close the loop. With this process, you can start off with food-grade plastic. It can then go through a chemical recycling process and be used to produce food-grade plastics again.”

Supercritical water as a method of plastic recycling also has an edge in that – in theory – it can be used with any kind of polymer, from PET to polyethylene and polypropylene. “Each plastic or each type of polymer will have its sweet spot in terms of optimal reaction conditions,” says Thom.

However, there are downsides. “It’s not easy engineering,” he admits. “With supercritical water not only do you have high temperature but you also have very high pressure, and that means that everything is more expensive to design and build and operations are more challenging. Also, although you’re getting rid of having to deal with nasty organic solvents, you need to clean up the water after you’ve used it and recycle it.”

CircuPlast is still at a relatively early stage of development: Stopford currently has a demonstrator which they hope to complete by September. “Realistically, I think we’re a few years away,” says Thom. “There may well be other supercritical water processes that come on the market sooner. It does have significant potential – the higher scale you operate at, the easier your utility integration, your temperature integration and those engineering challenges become easier to overcome.” Certainly, there is some industry interest in the process. Trade organisation PlasticsEurope is investing over seven billion Euros in chemical recycling, a proportion of which, according to Stopford, will be used to develop hydro-thermal techniques such as supercritical water.

Chemical recycling

Chemical recycling is, in effect, the umbrella term for a number of plastic recycling processes, including hydro-thermal methods such as supercritical water and gasification, a process whereby plastics are heated to around 1,000-1,500 degrees celsius with a limited amount of oxygen. This breaks the molecules down to their simplest components to produce syngas, a combination of hydrogen, carbon monoxide and CO2. The syngas can then be used to produce a variety of chemicals (methanol, ammonia etc) for plastics production.

One of the more established chemical recycling methods is pyrolysis. Not a new innovation by any means, it’s one whose time may well have arrived.

“I think in the past when it’s been tried on larger scales the economics haven’t quite stacked up,” says Sophie Gilham, Head of Sustainability at Recycling Technologies, a Swindon-based firm that is spearheading the process. Plastics are broken down into a range of hydrocarbons by heating them (without oxygen) to temperatures of around 550 degrees celsius.

“This vapourises them and after that, there is a distillation process that you’d probably be familiar with from GCSE science. That leaves three fractions that range from a heavy, quite waxy hydrocarbon material to a lighter liquid fraction. The lighter one is similar to a crude type oil that can then go into refineries, into the petrochemical industry.”

One of these fractions can be used to make feedstock for polyethylene and polypropylene, which could fill a gap in the market as those two polymers cannot be de-polymerised directly into monomers. The plastic produced would be of virgin quality and could be used in applications such as food packaging.

Recycling Technologies has a strategy of using a ‘modular distributed model’, which also aims to get around the huge inefficiencies associated with transporting a light material like plastic hundreds of miles. “What we’ve done is develop a modular mass-producible type plant, which can take 7,000 tonnes of plastic per year and you’ve got these at sites where the infrastructure already exists. You’ve got mechanical recycling happening so they are taking all the clean stuff and all the residual material comes to us.”

This article was taken from Issue 103

The downside is that pyrolysis cannot accept all plastics – PVC, for example, is a no-no. It is also very energy-intensive. “It’s very much a trade-off between that and the closed-loop nature of the recycling,” says Gilham. “But as with any new technology – I’m sure I speak for other chemical recyclers as well – we’re trying to prove the technology and demonstrate that you can turn plastic back into plastic. We have a roadmap for improving our technology and a plan to broaden the specification of plastics that we can take.”

Gilham suggests it will take a few years before these problems can be ironed out. “The way we intend to move forward is that we’ll roll out a number of version one machines, Then we’re looking at the next stage – version two. What we’d also like to do is come back and retrofit all the earlier versions that aren’t as energy-efficient.”

What next for plastic recycling?

All of these methods are still some way off from becoming a viable alternative in themselves to mechanical recycling or using virgin plastic. But there is a general recognition within the sector that, looking forward, innovation is essential. “There is an awful lot of vying from petrochemical and plastic manufacturers,” says Gilham. “They know they have to hit targets of 30 per cent recycled content and mechanical alone is not going to meet that. But with the conversations that we’ve had, we feel that those companies are adapting their upfront technologies to accept pyrolysis and other methods. The whole chain is beginning to adapt and there is a recognition of the need for change.”

“There is no one solution to this,” she insists. “It has to be the FMCGs (Fast Moving Consumer Goods), the retailers, the plastic manufacturers, the petrochems, us. Everybody has to be looking at this as a full system. None of this can work in isolation.”