ENVIRONMENT
When we think of recycling plastic we usually think it means turning the waste into new plastic, albeit downgraded material. But now there’s another option: turning it back into the oil from which it was made.
Every year, more than 380 million tonnes of plastic is produced worldwide, more than 100 times the weight of the entire blue whale population. Just 9% of all plastic ever made has been recycled into new plastics; today, only 16% of plastic waste is recycled to make new plastics, while 40% is sent to landfill, 25% incinerated and 19% is dumped. Efficiently recycling plastic by conventional means is notoriously difficult, not the least because it has to be sorted into categories. At the moment, plastics are usually recycled mechanically: they’re sorted, cleaned, shredded, melted and remoulded. Each time plastic is recycled this way, its quality is degraded. That’s because when plastic is melted, the polymer chains are partially broken down, decreasing its tensile strength and viscosity, making it harder to process. The new, lower-grade plastic often becomes unsuitable in food packaging and, besides, most plastic can be recycled a very limited number of times before it is so degraded it becomes unusable.
Instead of a system where some plastics are rejected because they’re the wrong colour or made of composites, what if all types of plastic could be fed into an “infinite” recycling system, where the plastic is broken down into its chemical building blocks, which can then be used for fuels or be made into new plastics?
It’s called chemical recycling and it’s been around for a few decades, but only now beginning to emerge.
The process is fairly simple: each plastic product is washed, shredded and melted down, then fed into a pyrolysis reactor where it’s heated enough to turn it into a gas that is then cooled to condense into an oil-like liquid, and finally distilled into fractions that can be put to different purposes.
A number of chemical recycling trials are currently underway across the world. UK-based Recycling Technologies has developed a pyrolysis machine that turns hard-to-recycle plastic such as films, bags and laminated plastics into Plaxx. This liquid hydrocarbon feedstock can be used to make new virgin-quality plastic. The first commercial-scale unit was installed in Perth, Scotland in 2020.
Plastic Energy has two commercial-scale pyrolysis plants in Spain and plans to expand into France, the Netherlands and the UK. Its plants transform hard-to-recycle plastic waste, such as confectionery wrappers, dry pet food pouches and breakfast cereal bags into what’s called “tacoil” — a feedstock that can be used to make food-grade plastics.
In the US, the chemical company Ineos has become the first to use a technique called depolymerisation on a commercial scale to produce recycled polyethylene, which goes into carrier bags and shrink film. Ineos also plans to build several new pyrolysis recycling plants.
In the UK, Mura Technology has begun building the world’s first commercial-scale plant to handle mixed plastic; coloured plastic; plastic of all composites; plastic at all stages of decay, even plastic contaminated with food or other kinds of waste. And there’s just about no down-cycling, meaning the plastics can be infinitely recycled. With a conversion rate of more than 99%, nearly all the plastic turns into a useful product.
The hot, excess gases generated during the process will provide about 40% of the energy to run the plant. “We want to use as much renewable energy as possible and will be seeking, wherever practical, to aim for 100%,” Mura’s CEO Steve Mahon told the BBC’s Future Planet.
The plant, due for completion in 2022, aims to process 80,000 tonnes of previously unrecyclable plastic waste every year, as a blueprint for a global rollout, with sites initially planned in Germany and the US. By 2025, the company plans to have one million tonnes of recycling capacity in operation or in development worldwide.
“[Our] recycling of waste plastic into virgin-equivalent feedstocks provides the ingredients to create 100% recycled plastics with no limit to the number of times the same material can be recycled — decoupling plastic production from fossil resource and entering plastic into a circular economy,” Mahon adds.
Sharon George, senior lecturer in environmental science at Keele University, has welcomed Mura’s efforts, saying, “This overcomes the quality challenge by ‘unmaking’ the plastic polymer to give us the raw chemical building blocks to start again. This is true circular recycling.”
Mura argues its plant will fill a much-needed niche. “[Chemical] recycling is a new sector, but the scale at which it is developing, specifically for Mura, shows both the urgent need for new technology to tackle the rising problem of plastic waste and environmental leakage, and an opportunity to recycle a valuable ready-resource, which is currently going to waste,” Mahon says.
He also notes such a system is another way to shift the balance in favour of plastic recycling by producing an oil that can be sold at a profit. Mura has recently announced partnerships with the plastic manufacturers Dow and Igus GmbH, and the construction firm KBR.
“The interesting thing here is that Mura can find value in plastics that aren't usually economically viable to recycle mechanically,” says Taylor Uekert, researcher at the Cambridge Creative Circular Plastics Centre, University of Cambridge.
However, as Paula Chin, sustainable materials specialist at the conservation organisation WWF, notes, “These technologies are in their infancy and they are by no means the silver bullet solution to the plastic waste problem. We should focus on increasing resource efficiency as a way to minimise waste through greater reuse, refill and repair systems — not relying on recycling to be the saviour.”
Paving roads with recycled plastic
Meanwhile, Scottish company MacRebur is using recycled plastic waste to part-pave roadways.
Company engineer Toby McCartney says he drew on three sources of inspiration for the initiative.
One was the poor quality of the road outside his home in Lockerbie, Scotland, “which was full of potholes”.
The second was a trip to southern India, where he spent time with a charity to help landfill pickers identify and resell potentially useful items that were being discarded. McCartney “noticed some of the waste plastics retrieved by the pickers was put into potholes and set alight until it melted to form a makeshift plastic pothole filler.” This spurred him to further engineer a process to pave roads in the UK.
The third driver came from his own daughter, he told the BBC. When her teacher asked her what lives in the world’s oceans, she responded, “Plastics, Miss.” He felt he should make it part of his mission to change that.
“We take the polymers, the plastics that you and I throw away every single day — the bottles, the bags, the nappies — and we pelletise them,” McCartney told CNN.
Typical roads are made out of several different materials, including rocks, gravel and limestone; MacRebur’s roads replace some of the least environmentally-friendly component, bitumen, with a combination of plastic pellets.
While it replaces just 6% of the bitumen, it’s enough to make a difference to durability: when combined with asphalt, plastic pellets help it last longer, forming a stronger seal, like a kind of superglue. Also, every tonne of asphalt produced would use around 18,000 single-use plastic bottles or around 63,000 single-use plastic bags.
At first, there was skepticism in official circles, and it took some time to convince governments and asphalt manufacturers alike that plastic could do the job. But after testing, the product was found to be “60% stronger” than regular asphalt.
MacRebur is now trialling its recycled plastic pavement in the US, Canada, Bahrain and Saudi Arabia. And it is also partnering with corporations, neighbourhood associations, and even private homeowners to find solutions for all sorts of paving projects.
BOTTOM MacRebur’s team inspecting bitumen with recycled plastic contentplant
PHOTO MacRebar