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One Step Closer to Turning Plastics Into Fuel

Researchers in California and China have discovered a new method for breaking polyethylene into liquid fuel and solid wax

(Wikimedia Commons)
smithsonian.com

Plastic. The world produces some 300 tons of it each year. But when we’re finished with our milk cartons, shopping bags and electronics packaging, most is simply thrown away—the U.S. only recycles about 9 percent of post-consumer plastics. It can sit in landfills for up to 1,000 years, leaching chemicals into the soil. There are as many as 240,000 metric tons of it floating in our oceans, creating “garbage patches” thousands of miles from human habitation. Whales, seals, sea turtles and birds accidentally eat it, becoming sick or dying.

Now, researchers have figured out a way of not only recycling plastics, but recycling them into something entirely different: fuel.

Chemist Zhibin Guan at the University of California, Irvine, and his collaborators have discovered how to break down the bonds of polyethylene. Polyethylene, the most commonly produced plastic on Earth, is found in everything from soda bottles to cling wrap, children’s toys to cosmetics containers. Since these plastics are petroleum-based, the team figured it might be possible to turn them back into fuels.

The work was a collaboration between Guan’s lab and the lab of Zheng Huang at the Shanghai Institute of Organic Chemistry.

“The serious pollution in China, including the so-called ‘white pollution’ by plastic wastes, has triggered us to develop new approaches to address this issue,” Guan says. “[At] the same time, the huge energy needs from China and other developing countries call for new fuels.”

Normally it’s extremely difficult to break down polyethylene, as its molecules are extremely stable. Previous ways of breaking it down have involved high heat, which is inefficient and hard to control. Guan’s work focuses on using alkanes, a type of hydrocarbon molecule, to separate polymer molecules into different compounds at lower temperatures. The product of the broken down polyethylene is liquid fuel and solid wax. How much of each depends on the catalyst and the reaction time. The process also seems to work on post-consumer plastic waste, such as soda bottles, which have additives beyond “pure” polyethylene that could have proved problematic in the breakdown. This means waste plastic could be processed directly into fuel without any other treatments. The team’s work was recently published in the journal Science Advances.

Guan and his colleagues are currently working on increasing the efficiency of the catalysts in order to reduce the cost of the process.

“I hope that with further research and discovery of more efficient and cheaper catalysts, this process can be commercialized,” Guan says. “This will hopefully help us to save our environment from plastic pollution.”

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