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Manufactured from petroleum, plastic shopping bags, a source of litter on land and at sea, can be converted back into diesel, natural gas and other useful petroleum products, Illinois researchers report.
The conversion produces more energy than it requires and results in transportation fuels such as diesel that can be blended with existing ultra-low-sulfur diesels and biodiesels.

Other products, such as natural gas, gasoline, the solvent naphtha, waxes, engine oil and hydraulic oil also can be derived from shopping bags.

The new study appears in the current issue of the journal “Fuel Processing Technology.”

There are other advantages to the approach, which involves heating the bags in an oxygen-free chamber, a process called pyrolysis, said Brajendra Kumar Sharma, a senior research scientist who led the research at the Illinois Sustainable Technology Center.

“You can get only 50 to 55 percent fuel from the distillation of petroleum crude oil,” Sharma said. “But since this plastic is made from petroleum in the first place, we can recover almost 80 percent fuel from it through distillation.”

Previous studies have used pyrolysis to convert plastic bags into crude oil, but Sharma’s team took the research further by fractionating the crude oil into different petroleum products and testing the diesel fractions to see if they complied with national standards for ultra-low-sulfur diesel and biodiesel fuels.

A mixture of two distillate fractions, providing an equivalent of U.S. diesel #2, met all of the specifications required of other diesel fuels in use today, after addition of an antioxidant, Sharma said.

“This diesel mixture had an equivalent energy content … and better lubricity than ultra-low-sulfur diesel,” he said.

The researchers were able to blend up to 30 percent of their plastic-derived diesel into regular diesel, and found “no compatibility problems with biodiesel,” Sharma said.

“We can just use it as a drop-in fuel in the ultra-low-sulfur diesel without the need for any changes, ” he said.

Americans throw away about 100 billion plastic shopping bags each year, according to the Worldwatch Institute. The U.S. Environmental Protection Agency reports that only about 13 percent of plastic bags used are recycled. The rest end up in landfills or escape to the wild, blowing across the landscape and entering waterways.

Plastic bags make their way into giant ocean garbage patches, killing wildlife and littering beaches as far north and south as the poles.

“Over a period of time, this material starts breaking into tiny pieces, and is ingested along with plankton by aquatic animals,” Sharma said. Fish, birds, ocean mammals and other creatures have been found with a lot of plastic particles in their guts.

Whole shopping bags also threaten wildlife, Sharma said. “Turtles, for example, think that the plastic grocery bags are jellyfish and they try to eat them,” he said. Other creatures become entangled in the bags.

The research paper, “Production, Characterization and Fuel Properties of Alternative Diesel Fuel From Pyrolysis of Waste Plastic Grocery Bags,” is available online or from the University of Illinois News Bureau.