Page 63 - Plastics News November 2019

teChnoLogy

All plastic waste could become new, high-quality plastic through

advanced steam cracking

research group at Chalmers University of Technology, is so high overall, and since the natural degradation of
A Sweden, has developed an efficient process for breaking plastic is so slow, it accumulates over time. The current
down any plastic waste to a molecular level. The resulting model for recycling plastic tends to follow what is known as
gases can then be transformed back into new plastics -- of the 'waste hierarchy'. This means the plastic is repeatedly
the same quality as the original. The new process could degraded, to lower and lower quality before finally being
transform today's plastic factories into recycling refineries, burned for energy recovery. "Instead of this, we focused
within the framework of their existing infrastructure. on capturing the carbon atoms from the collected plastic
The fact that plastics do not break down, and therefore and using them to create new plastic of original quality
accumulate in our ecosystems, is one of our major -- that is, back to the top of the waste hierarchy, creating
environmental problems. But at Chalmers, a research group real circularity."
led by Henrik Thunman, Professor of Energy Technology, Today, brand new plastics are made by shattering fossil
sees the resilience of plastic as an asset. The fact that oil and gas fractions in a device known as a 'cracker' in
it does not degrade makes it possible for circular usage, petrochemical plants. Inside the cracker, building blocks
creating a true value for used plastic, and therefore an consisting of simple molecules are created. These can then
economic impetus to collect it. "We should not forget that be combined in many different configurations, resulting in
plastic is a fantastic material -- it gives us products that the enormous variety of plastics we see in our society. To
we could otherwise only dream of. The problem is that it do the same from collected plastics, new processes need to
is manufactured at such low cost, that it has been cheaper be developed. What the Chalmers researchers now present
to produce new plastics from oil and fossil gas than from are the technical aspects of how such a process could be
reusing plastic waste," says Henrik Thunman. Now, through
experimenting with chemical recovery via steam cracking
of plastic, the researchers have developed an efficient
process for turning used plastics into plastics of virgin
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 carried out at the Chalmers Power
Central facility in Gothenburg. In 2015, around 350 million designed and integrated into existing petrochemical plants,
tonnes of plastic waste were generated worldwide. In total, in a cost-effective way. Eventually, this kind of development
14 per cent was collected for material recovery -- 8 per could enable a hugely significant transformation of today's
cent was recycled into plastic of lower quality, and 2 per petrochemical plants into recycling refineries of the
cent to plastics of similar quality as the original. Around future. The researchers are continuing their work on the
4 per cent was lost in the process. Overall, around 40 per process."We are now moving on from the initial trials,
cent of global plastic waste in 2015 was processed after which aimed to demonstrate the feasibility of the process,
collection, mainly through incineration for energy recovery to focusing on developing more detailed understanding.
or volume reduction -- releasing carbon dioxide into the This knowledge is needed to scale up the process from a
atmosphere. The rest -- about 60 per cent -- went to few tonnes of plastic a day, to hundreds of tonnes. That
landfill. Only around 1 per cent was left uncollected and is when it becomes commercially interesting," says Henrik
leaked into natural environments. Though only a small Thunman. The process is applicable to all types of plastic
percentage, this nevertheless represents a significant that result from our waste system, including those that
environmental problem, since the amount of plastic waste have historically been stored in landfills or at sea.

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