Oct 22 2019
An efficient process for breaking down any discarded plastic to a molecular level has been formulated by a research team from Chalmers University of Technology, Sweden. The resulting gases can then be changed back into new plastics—possessing the same quality as the original. The new process could change present-day plastic factories into recycling refineries, within the setting of their current infrastructure.
Henrik Thunman, Professor and Head of the Division of Energy Technology at the Department of Space, Earth, and Environment. (Image credit: Chalmers University of Technology)
The fact that plastics do not degrade, and thus accumulate in ecosystems, is one of the biggest environmental problems. But at Chalmers, a study team headed by Henrik Thunman, Professor of Energy Technology, appreciates the resilience of plastic as an advantage. The fact that it does not degrade makes it a promising candidate for circular usage, forming a true value for used plastic, and thus an economic motivation to collect it.
We should not forget that plastic is a fantastic material—it gives us products that we could otherwise only dream of. The problem is that it is manufactured at such low cost, that it has been cheaper to produce new plastics from oil and fossil gas than from reusing plastic waste.
Henrik Thunman, Professor of Energy Technology, Chalmers University of Technology
Presently, through experimenting with chemical recovery via steam cracking of plastic, the team has come up with an efficient process for converting used plastics into plastics of original quality.
“Through finding the right temperature—which is around 850 degrees Celsius—and the right heating rate and residence time, we have been able to demonstrate the proposed method at a scale where we turn 200 kg of plastic waste an hour into a useful gas mixture. That can then be recycled at the molecular level to become new plastic materials of virgin quality,” says Henrik Thunman.
The experiments were performed at the Chalmers Power Central facility in Gothenburg.
In 2015, about 350 million tons of plastic waste was created across the globe. In total, 14% was collected for material recovery—8% was recycled into plastic of lower quality, and 2% to plastics of comparable quality as the original. About 4% was lost in the process.
On the whole, about 40% of worldwide plastic waste in 2015 was processed after collection, mostly through incineration for energy recovery or volume reduction—discharging carbon dioxide into the air.
The rest—approximately 60%—ended up in landfills. Only about 1% was left uncollected and leaked into natural surroundings. Though just a small percentage, this, however, signifies a substantial environmental problem, since the amount of plastic waste is very high in general, and since the natural degradation of plastic is very slow, it accumulates as time goes by.
The present-day model for recycling plastic tends to fall under what is called the “waste hierarchy.” This means the plastic is repetitively degraded, to lower and lower quality before being burned up for energy recovery in the end.
“Instead of this, we focused on capturing the carbon atoms from the collected plastic and using them to create new plastic of original quality—that is, back to the top of the waste hierarchy, creating real circularity.”
Nowadays, brand new plastics are created by shattering fossil oil and gas fractions in a device called a “cracker” in petrochemical plants. Within the cracker, building blocks comprising basic molecules are formed. These can then be integrated into many diverse configurations, resulting in the huge variety of plastics found around the world.
To achieve the same from collected plastics, new processes have to be created. What the Chalmers scientists currently present are the technical steps of how such a process could be engineered and incorporated into current petrochemical plants, in an economic way. Ultimately, this kind of development could facilitate a vastly important transformation of current petrochemical plants into recycling refineries of the future.
The team is pursuing its work on the process.
We are now moving on from the initial trials, which aimed to demonstrate the feasibility of the process, to focusing on developing more detailed understanding. This knowledge is needed to scale up the process from a few tonnes of plastic a day, to hundreds of tonnes. That is when it becomes commercially interesting.
Henrik Thunman, Professor of Energy Technology, Chalmers University of Technology
More About: The Chalmers Researchers' Method and its Potential
The process is relevant to all kinds of plastic that result from the waste system, including those that have traditionally been dumped in landfills or at sea.
What renders it currently viable to utilize collected and sorted plastics in large-scale petrochemical plants is that an abundant volume of material is collected, meaning that the plants can ideally maintain the same output. These plants need about 1 to 2 million tons of sorted plastic waste each year to convert to equal the production levels they presently derive from oil and fossil gas.
Sweden's total amount of plastic waste in 2017 was about 1.6 million tons. Only about 8% of that was recycled into lower quality plastics.
Therefore, the scientists see a prospect to develop a circular use of plastic in society, as well as provide an option to replace the need for oil and fossil gas to create different high-quality plastics.
Circular use would help give used plastics a true value, and thus an economic impetus for collecting it anywhere on earth. In turn, this would help minimise release of plastic into nature, and create a market for collection of plastic that has already polluted the natural environment.
Henrik Thunman, Professor of Energy Technology, Chalmers University of Technology
End-of-life bio-based materials such as wood, paper, and clothes could also be employed as raw material in the chemical process. This would mean the team could slowly minimize the amount of fossil materials in plastic. Net negative emissions can be created, if carbon dioxide is also trapped in the process. The vision is to develop a sustainable, circular system for carbon-based materials.