Sorting through different plastic recovery processes
From incineration and mechanical recycling to chemical recycling and gasification, operators aren’t short of options on how to recycle plastic waste. They aren’t short of challenges either. Each pathway comes with its own problems that hinder plastic producers and recycling companies from adopting them.
The simplest and most common form of plastic recovery in many regions is incineration. It produces heat and energy by incinerating plastic. So, shouldn’t it be a viable plastic recovery process?
“It’s not that straightforward,” explains Mitchell.
“While you’re getting rid of the plastic waste and generating energy, the emissions are high, particularly greenhouse gases. You’re basically solving some problems while creating other challenges. It’s a short-term solution and sadly not a circular one.”
Mechanical recycling is another conventional plastic recovery process. It involves sorting plastics and ends with compounding them, with wasting and granulation steps in between. It’s a common polymer recycling process. But only certain plastics such as polyethylene terephthalate (PET) result in a high-grade end product suitable for applications like food packaging. With most of the other plastics, the process downcycles them to lower grade formulations.
“Compared to the plastics they originate from, downcycled plastics aren’t cost-competitive,” explains Mitchell. “They’re a couple of steps down quality-wise. So, they may not be suitable for applications like food packaging. That means there’s less demand for them.”
Chemical recycling could help create a circular economy
To make plastic recycling competitive, the industry needs to produce recycled plastics that meet the quality demands of end users at a competitive price. The answer may be chemical recycling. This process produces higher quality recycled plastic and can emit lower GHG emissions.
Mitchell says, “By converting the plastic to a useful product, we are getting closer to full circularity. This is why we’re working with SABIC and Plastic Energy on the Geleen project in the Netherlands to develop an advanced recycling unit that will use a pyrolysis process.”
The Geleen project is promising. As an industry first, the proof of concept will go a long way to increasing uptake and buy-in. But what exactly does pyrolysis produce and how does it work?
“Pyrolysis can produce an oil-like material. It uses heat to break down long polymer chains, in plastic, into shorter chains. This results in a synthetic oil that has a high energy density. As a result, it can become a drop-in replacement for the conventional fossil fuels market.
“Alternately, it can be part of the petrochemical value chain as a fossil-based oil replacement. Once in the value chain, many products can have a recycled plastic element. It’s not a perfect solution, but it’s a start.”
The circularity of gasification – from plastic to olefins and back to high-grade plastic
While pyrolysis is promising, the conversion process isn’t 100 percent efficient. This means it can still emit GHGs. The end product is also potentially a combustible fuel, which produces high emissions in its various applications. As a result, it’s not fully circular.
“To achieve something close to a fully circular economy, we can use gasification,” explains Mitchell.
Because the process produces olefins that are of the same quality as fossil-based olefins, you can transform olefins back into high-grade plastic polyolefins. These include polyethylene and polypropylene. This time the process doesn’t downcycle them, so they’re suitable for applications such as food packaging.
While it promises a fully circular economy, gasification emits GHGs from the chemical reactions and heating that happen during the process. This is because gasification is a high-temperature, energy-intensive process that’s not 100 percent efficient. But with the right technology and processes, it can be better overall than pyrolysis, which also produces GHG emissions directly or indirectly.
So, beyond making it fully circular, we need to decarbonize the recovery process, too. Renewable energy could be a solution. Sources like green hydrogen could power the process, while carbon capture, usage and storage (CCUS) could solve the emission challenges.
Mitchell says, “You can capture the CO2 from the gasification process and combine it with green hydrogen to create green methanol. This green methanol can be converted into olefins, which then create high-grade plastics.
“If we go further and use renewable sources like solar and wind as energy sources to power the entire process, we eliminate our dependency on carbon intensive fuels. This gets us even closer to full, decarbonized circularity.”
Scaling up plastic recovery for a net-zero future
With innovations like gasification, the rate of plastic recovery could increase to compete with conventional plastic production. But how do we reassure producers and governments that this is the most sustainable solution?
“Simply put, we need to prove it works. And we are,” says Mitchell. “We’re working on projects that bring the individual building blocks of the gasification-to-olefins process together. This includes Velocys’ Altalto Immingham waste-to-jet fuel facility which relies on gasification. And Liquid Wind’s first green methanol flagship facility – a CO2-to-eMethanol development.”
Projects like these are what the industry needs to go from recycling just nine percent to keeping up with growing plastic demand. With enough investment, innovation, increased incentives and support, the industry can create a fully circular economy around plastic recovery.