Chemical recycling based on pyrolysis could help turn all plastics and their mixtures into oil, contends a new VTT study.
All collected plastic waste don’t qualify for mechanical recycling. About 40 to 60 percent of separately collected plastic waste in Finland ends up incinerated.
Mechanical recycling suits only the most common plastic bottles, bags and wraps. They are sorted, washed, melted and molded into new products.
It has often proven difficult and occasionally even impossible to separate various types of plastics used.
The quality of plastic will also weaken and so too the number of recycling loops, making the material unfit for further use.
Now VTT – as part of the Business Finland WasteBusters’ project – has found a solution to this problem in the form of chemical recycling.
“By chemical recycling, plastics and their mixtures can be broken down into separate raw materials, whose quality is equal to that of respective virgin materials,” explains Anja Oasmaa, Senior Principal Scientist at VTT.
In the WasteBusters project, long polymer chains of plastics and their mixtures were pyrolysed – heated in the absence of oxygen – and thus chopped into shorter chains and in part even to monomers.
According to the scientists, the resulting pyrolysis wax or oil can be processed with traditional methods at oil refineries.
“Pyrolysis oil can be distilled into separate monomers, diesel and other fractions, some of which can be used directly as fuels and some as raw material for plastics and other chemicals,” says Oasmaa.
The project focused on pre-treatment and pyrolysis of plastic waste, and also somewhat on post-treatment of the product.
According to Oasmaa, improvements of pre-treatment in particular are decisive for a cost-effective concept.
“There are all kinds of films as well as both dense and porous pieces together in plastic waste, which makes it difficult to handle.”
“We managed, however, to make it homogenous with the Modix-extruder developed by VTT.”
Image copyright and content: Randy Olson-National Geographic/VTT