New plastic upcycling technology can potentially reduce greenhouse gases equivalent to those of 3 million cars

Researchers have developed a breakthrough upcycling process that can help convert polyethylene (PE) – the world’s most common plastic – into polypropylene, which is among the top five most common types of plastic in the world.

“Today, unfortunately, a large part of the PE is not recycled and ends up in landfills. The collected fraction is reused in the form of energy through incineration. This recycling approach isn’t really sustainable,” Damien Guironnet said in an email to Guironnet is Professor of Chemical and Biomolecular Engineering at the University of Illinois Urbana-Champaign and co-principal author of the research article published in the Journal of the American Chemical Society on Friday.

According to the researchers’ preliminary analysis, if only 20 percent of the world’s PE plastic production could be recovered and converted in this way, the equivalent of saving greenhouse gas emissions would be equivalent to taking three million cars off the road.

Researchers developed a proof-of-concept for upcycling PE plastic – a reactor that produces a stream of propylene that can be converted to PP using current technology. The reactor does this by cutting PE molecules many times into small pieces of propylene molecules. The process begins when a catalyst removes hydrogen from the PE chain and creates a place for a reaction to take place.

Thereafter, a second catalyst splits the chain before finally a third catalyst shifts the reaction up the PE chain so that the process can be repeated by the first catalyst. When the process is complete, the finished product is 95 percent propylene. The other 5 percent is butene, a chemical that has many uses in the plastics, gasoline, and rubber industries.

A similar process was documented in a research article published in the journal Science on Thursday. According to the researchers, the research team that wrote the Science article used a process that is more energy-intensive.

Guironnet is confident that the technology is scalable and adaptable to current industry needs, but the research faces some obstacles before it can be applied on a large enough scale. “The biggest challenge is the stability of the catalyst. To scale up such a process, we need to identify catalysts that are extremely robust. PE waste is always contaminated. To remain scalable, we would need to find catalysts that are unaffected by these impurities,” explained Guironnet.

If the researchers manage to find a sufficiently stable catalyst, the PE being upcycled doesn’t have to be as pure, but if the catalyst is delicate, that would mean the PE had to be cleaned, making the solution more expensive.

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