In a breakthrough upcycling technique, researchers have turned polyethylene (PE) – one of the world’s most widely used plastics – into polypropylene, one of the world’s most common plastics.
In the current day and age, a great deal of PE is not recycled, so it accumulates in landfills. Combustion is used to recycle the collected fraction into energy. An email message from Damien Guironnet to indianexpress.com suggests that this recycling strategy is not really sustainable. An article published in the Journal of the American Chemical Society on Friday was co-authored by Guironnet, a professor of chemical and biomolecular engineering at the University of Illinois Urbana-Champaign.
This method could reduce greenhouse gas emissions by as much as three million cars if only 20 percent of the world’s PE plastic production could be recovered and converted.
They created a proof-of-concept reactor for upcycling PE plastic, which creates a flow of propylene that can be converted into PP. Using a reactor, PE molecules are cut into small pieces of propylene molecules many times. By removing hydrogen from the PE chain, a catalyst creates a location for a reaction to occur.
A second catalyst then splits the chain in half before a third catalyst moves the reaction up the PE chain so that the first catalyst can repeat the process. It is estimated that 95 percent of the final product will be propylene at the end of the process. The remaining 5 percent of the chemical is butene, which is used in plastic production, gasoline production, and rubber production.
An article published in the journal Science on Thursday documents a similar process. Researchers say the Science article was authored by a team that used an energy-intensive process.
Despite Guironnet’s confidence that the technology is scalable, it faces several obstacles before it can be applied on a large scale. It is the catalyst stability that poses the greatest challenge. In order to scale up such a process, we will need catalysts that are extremely robust. Impurities are always present in PE waste. Guironnet explained that scalable catalysts would need to be unaffected by the impurities.
If the researchers find a catalyst that is stable enough, the PE that is being upcycled doesn’t need to be as pure, but if the catalyst is sensitive, then the PE will have to be cleaned, which will increase the cost.
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