Polyethylene (PE), the most widely produced plastic, can be transformed into polypropylene (PP), the second-most widely produced plastic, by application of a catalytic conversion process. By using ethylene to convert PE to propylene, the commodity monomer used to make PP, the tandem catalysis strategy offers a scalable approach to keeping waste plastics out of landfills and curbing greenhouse gas emissions.

The PE is subjected to a catalyst to remove hydrogen from the material and create a reactive location in the chain of molecules, after which another catalyst splits the molecules at this location and caps the exposedSource: J. Am. Chem. Soc. 2022 doi.org/10.1021/jacs.2c07781 ends using ethylene. A third catalyst then shifts this reactive location along the chain so the process can be repeated so that molecules of propylene remain as the end-product for use as building blocks for a virgin version of PP.

The researchers from the University of Illinois Urbana-Champaign, University of California Santa Barbara and Dow Chemical Company have engineered a reactor that supports a continuous flow of propylene for conversion into PP easily using current technology, making this development scalable and rapidly implementable.

[See also: Upcycling route cuts polystyrene reuse costs]

The study published in the Journal of the American Chemical Society establishes a proof-of-concept for upcycling PE plastic with more than 95% selectivity into propylene.