A research group at Chalmers University of Technology, Sweden, has developed an efficient process for breaking down any plastic waste to a molecular level. The resulting gases can then be transformed back into virgin plastic – the same quality as the original, according to Science Daily.
The technology is not only transformational, but the system makes the circular use of plastics possible, connecting all carbon-based materials of both fossil and biogenic origin. Today’s plastic factories could become recycling refineries, within the framework of their existing infrastructure.
The research team, led by Henrik Thunman, Professor of Energy Technology, says plastics are a major environmental problem because they don’t break down. But he says this also makes all that plastic waste an asset. The fact that it does not degrade makes it possible for circular usage, creating value for used plastic and an economic incentive 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,” Thunman said in a statement, according to The Engineer.
Chemical recovery through steam cracking
The researchers experimented with chemical recovery through the use of steam cracking – developing an efficient process for turning used plastics into plastics of virgin quality. The experiments were carried out at the Chalmers Power Central facility in Gothenburg, Sweden.
In steam cracking, a gaseous or liquid hydrocarbon feed-like naphtha, LPG (low-pressure gas) or ethane is diluted with steam and then briefly heated in an oxygen-free furnace, Generally, the reaction temperature is very hot (around 850 °C) but the reaction is only allowed to take place very briefly.
After the cracking temperature has been reached, the gas is quickly quenched to stop the reaction in a transfer line exchanger. The products produced in the reaction depend on the composition of the feedstock, on the hydrocarbon to steam ratio and on the cracking temperature and length of time in the furnace.
“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.
Thurman says that the current process for recycling plastic follows what he calls a “waste hierarchy.” In other words, plastic is repeatedly degraded into a lower and lower quality until it can be burned for energy recovery.
“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,” Thurman says.
“We are now moving on from the initial trials, which aimed to demonstrate the feasibility of the process, to focusing on developing a 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,”
According to the researchers, 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 minimize the release of plastic into the environment, and create a market for the collection of plastic that has already polluted the natural environment.
This most interesting research was published in the Science Direct journal Sustainable Materials and Technologies on October 18, 2019.
