Metathesis is a degrading experience for plastics

Researchers have developed a cross-alkane metathesis process that breaks down polyethylene waste into liquid fuels and waxes under mild conditions. Polyethylene is the largest-volume plastic worldwide and a major source of plastic waste. One option for addressing the waste problem is to convert polyethylene to useful breakdown products, but it is chemically inert and difficult to degrade efficiently. High-temperature pyrolysis works, but it’s expensive and forms complex mixtures of hydrocarbon gas, oil, wax, and char. Mild recycling reactions have been developed, but they use reactive radical reactions that are hard to carry out or generate mostly methane and ethane, demand for which is limited. Zhibin Guan of the University of California, Irvine, Zheng Huang of the Shanghai Institute of Organic Chemistry, and coworkers have now developed a mild cross-alkane metathesis process that degrades polyethylenes into more useful liquid fuels and waxes (Sci. Adv. 2016, DOI: 10.1126/sciadv.1501591). In the process, polyethylene and a readily available light alkane are dehydrogenated to form olefins. An olefin metathesis reaction then scrambles those olefins and breaks down the long chains. Finally, hydrogenation forms alkanes. Multiple cycles of the reactions degrade polyethylene into short alkanes appropriate for use as transportation fuels and waxes.