Scientists have created a ground-breaking method to convert the second-most produced plastic, polypropylene (PP), from the most prevalent plastic, polyethene (PE), which could lower greenhouse gas emissions (GHG). According to co-lead author Susannah Scott, Distinguished Professor and Mellichamp Chair of Sustainable Catalytic Processing at UC Santa Barbara, “the world needs more and better choices for extracting the energy and molecular value from its waste plastics.” The mounds of plastic garbage that have collected over the past few decades do not have much incentive to be recycled because conventional plastic recycling techniques produce low-value plastic molecules. But Scott continued, “The way we start to develop a circular economy for plastics is by turning polyethylene into propylene, which can then be utilized to make a new polymer.”
Co-lead author Damien Guironnet, a professor of chemical and biomolecular engineering at Illinois, said, “We started by conceptualizing this approach and demonstrated its promise first through theoretical modeling — now we have proved that it can be done experimentally in a way that is scalable and potentially applicable to current industry demands.” According to a recent study published in the Journal of the American Chemical Society, a series of coupled catalytic reactions convert PE, the #2 and #4 plastics that account for 29% of the world’s plastic consumption, into propylene, the essential component needed to make PP, also known as the #5 plastic and responsible for close to 25% of it.
With more than 95% selectivity, this work establishes a proof-of-concept for upcycling PE plastic into propylene. This discovery is scalable and quickly implementable thanks to the reactor the researchers have developed that generates a constant supply of propylene that can be readily transformed into PP using current technology.
According to Garrett Strong, a PhD student working on the project, “our preliminary study implies that if just 20% of the world’s PE could be recovered and converted via this pathway, it may represent a potential savings of GHG emissions similar to removing 3 million automobiles off the road.”
In order to produce several small pieces, or propylene molecules, it is necessary to repeatedly slice each extremely long PE molecule. In order to create a reactive site on the chain, a catalyst first eliminates hydrogen from the PE. At this point, a second catalyst divides the chain in half before capping the ends with ethylene. In order to repeat the process, a third catalyst finally advances the reactive site along the PE chain. Eventually, just a huge number of propylene molecules are left.
Think about slicing a baguette in half, then taking exactly measured pieces from the ends of each half. The size of each slice depends on how quickly you cut, Guironnet suggested.
Now that the proof of concept has been established, Scott said, “we can start to increase the efficiency of the process by inventing catalysts that are faster and more productive, allowing for scaling up.” “Better catalysts will enable speedy implementation of this innovation because our end-product is already compatible with current industry separation techniques,” says the researcher.
The research given in this article greatly enhances a paper that appeared in Science last week. Both teams made use of brand-new polymers and comparable chemistry. The Science team, on the other hand, employed a different procedure in an enclosed batch reactor that required significantly higher pressure and more ethylene recycling.
“We need solutions that are very scalable if we are to upcycle a large portion of the approximately 100 million tonnes of plastic waste we generate each year,” Guironnet added. “Our group showed the chemistry in a flow reactor we designed to constantly and extremely selectively generate propylene. This is a crucial step towards solving the enormous scale of the issue we are dealing with.
Ivan Konstantinov, a Dow senior scientist and co-author, stated that the company is “taking a leading role in promoting a more circular economy by designing for circularity, building new economic models for circular materials, and partnering to reduce plastic waste.” We are committed to exploring new solutions to decrease plastic waste and are encouraged by this approach as a project funder.
(source: ANI)
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