Research by the University of California, Irvine and the Shanghai Institute of Organic Chemistry may allow millions of tons of plastic bottles, bags and other trash littering the oceans and clogging landfills could be turned into reusable fuel. Chemist Zhibin Guan and his colleagues are among those who have figured out how to dissolve the strong bonds of polyethylene plastic to re-create petroleum and other products.
The breakthrough, reported in Science Advances, means that the waste could someday be harvested and inexpensively recycled into valuable commodities. Guan said the new technique employs alkanes, specific types of hydrocarbon molecules, to disrupt the long chemical chains in polyethylene plastics. Resulting byproducts include a liquid fuel and industrially beneficial waxes. The new recycling method may have an edge on existing plastic reuse methods that rely on inefficiently heating the material to about 700 degrees Fahrenheit or breaking it down with highly reactive, toxic chemicals known as radicals.
“Synthetic plastics are a fundamental part of modern life, but our use of them in large volume has created serious environmental problems,” said Guan. “Our goal through this research was to address the issue of plastic pollution as well as achieving a beneficial outcome of creating a new source of liquid fuel.”
Guan and Zheng Huang, his collaborator at SIOC, together with their colleagues figured out how to break down the polyethylene, the most common commercially available form of plastic, using the alkanes to scramble and separate polymer molecules into other useful compounds.
Scientists have been seeking to recycle plastic bags, bottles and other trash generated by humans with less toxic or energy intensive methods. Current approaches include using caustic chemicals known as radicals or heating the material to more than 700 degrees Fahrenheit to break down the chemical bonds of the polymers.
In this newly discovered technique, the team degrades plastics in a milder and more efficient manner through a process known as cross-alkane metathesis. The substances needed for the new method are byproducts of oil refining, so they’re readily available.
Because the process requires heating at around 175 degrees Celsius (347 fahrenheit) – rather than 400 degrees (752 fahrenheit) – to break down the plastic, it uses far less energy than similar techniques. But the downsides are the process is slow – taking about four days to complete – and the catalysts are expensive to use.
Guan said the US-China joint team is still working on a few issues to make it more efficient. That includes increasing the catalyst activity and lifetime, decreasing the cost, and developing catalytic processes to turn other plastic trash into treasure.