Turning plastic into diesel fuel instead of trash

(credit: Kevin Krejci)

Plastics are great. They can take any shape and serve an endless variety of roles. But... the beginning and end of a plastic’s life are problematic. While some plastics are made from renewable agricultural products, most are derived from petroleum. Plastics are not as easy to recycle as we'd like, and a huge percentage ends up in landfills (or the ocean), where they can be virtually immortal.

The easy way to recycle plastic is to just rip it up, melt it down, and pour a new mold. But that only works when the plastic is all the same chemical type, which is a level of purity you rarely find in a recycling bin. Without separating plastics precisely into different types, you get a mixture that is much less useful than pure plastics. We’re limited in what we can make out of it. Other methods for recycling plastics require serious energy input, like high pressure and temperatures over 400°C. That can produce a variety of hydrocarbon compounds, but they can be difficult to work with.

Recently, a team led by Xiangqing Jia of the Shanghai Institute of Organic Chemistry decided to try some chemical tricks to turn some of these plastics into something useful, even if it’s not more plastic. They worked with polyethylene, which makes up the majority of the plastic we use. Polyethylenes are essentially long chains made of repeating links of carbon, with hydrogen hanging off the side. The challenge is to break that resilient chain into shorter pieces so we can use the pieces to make other compounds.

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