New Way to Recycle Plastic Waste into Fuel
Degradation of Polyethylenes into Liquid Fuels and Waxes under Mild Conditions
Millions of tons of plastic bottles, bags and other trash littering the oceans and clogging landfills could be turned into reusable fuel, thanks to research by the University of California, Irvine and the Shanghai Institute of Organic Chemistry. UCI chemists have figured out how to dissolve the strong bonds of polyethylene plastic to re-create petroleum and other products. The breakthrough means that the waste could someday be harvested and inexpensively recycled into valuable commodities.
Polyethylene (PE) is the largest-volume synthetic polymer, and its chemical inertness makes its degradation by low-energy processes a challenging problem. As reported in Science Advances , the scientists developed a tandem catalytic cross alkane metathesis method for highly efficient degradation of polyethylenes under mild conditions. With the use of widely available, low-value, short alkanes (for example, petroleum ethers) as cross metathesis partners, different types of polyethylenes with various molecular weights undergo complete conversion into useful liquid fuels and waxes. This method shows excellent selectivity for linear alkane formation, and the degradation product distribution (liquid fuels versus waxes) can be controlled by the catalyst structure and reaction time. In addition, the catalysts are compatible with various polyolefin additives; therefore, common plastic wastes, such as postconsumer polyethylene bottles, bags, and films could be converted into valuable chemical feedstocks without any pretreatment.
According to the researchers 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. A unique advantage of the new process is that the excess light alkane used for the degradation dissolves PE to form a dilute solution with low viscosity, avoiding mass and heat transfer issues encountered in the conventional catalytic pyrolysis processes involving PE melts.