Researchers turn carbon dioxide and plants into renewable plastic

Researchers at Stanford University on the U.S. west coast have found a way to turn carbon dioxide (CO2) and inedible plant material, such as agricultural waste and grasses, into plastic.

"Our goal is to replace petroleum-derived products with plastic made from CO2," said Matthew Kanan, an assistant professor of chemistry.

In a study published by the online edition of the journal Nature, the Stanford team described their work on polyethylene furandicarboxylate (PEF), a promising alternative to polyethylene terephthalate (PET), also known as polyester.

Many plastic products now are made from PET. Worldwide, about 50 million tons of PET are produced each year for items such as fabrics, electronics, recyclable beverage containers and personal-care products. It is made from two components, terephthalic acid and ethylene glycol, which are derived from refined petroleum and natural gas.

Manufacturing PET produces significant amounts of CO2, a greenhouse gas that contributes to global warming.

In comparison, PEF is made from ethylene glycol and a compound called 2-5-Furandicarboxylic acid (FDCA).

"PEF is an attractive replacement for PET, because FDCA can be sourced from biomass instead of petroleum," Kanan said. "PEF is also superior to PET at sealing out oxygen, which is useful for bottling applications."

Despite the many desirable attributes of PEF, the plastics industry has yet to find a low-cost way to manufacture it at scale. One approach is to convert fructose from corn syrup into FDCA. But growing crops for industry requires lots of land, energy, fertilizer and water.

"Using fructose is problematic, because fructose production has a substantial carbon footprint, and, ultimately, you'll be competing with food production," Kanan said. "It would be much better to make FDCA from inedible biomass, like grasses or waste material left over after harvest."

The researchers have been experimenting with furfural, a compound made from agricultural waste that has been widely used for decades. About 400,000 tons are produced annually for use in resins, solvents and other products.

But making FDCA from furfural and CO2 typically requires hazardous chemicals that are expensive and energy-intensive to make. "That really defeats the purpose of what we're trying to do," Kanan said.

The Stanford team solved the problem using a far more benign compound: carbonate. Graduate student Aanindeeta Banerjee, lead author of the Nature study, combined carbonate with CO2 and furoic acid, a derivative of furfural. She then heated the mixture to about 290 degrees Fahrenheit (200 degrees Celsius) to form a molten salt.

The results were dramatic. After five hours, 89 percent of the molten-salt mixture had been converted to FDCA. The next step, transforming FDCA into PEF plastic, is a straightforward process that has been worked out by other researchers, Kanan said.

The new technology, the researchers claimed, could provide a low-carbon alternative to plastic bottles and other items currently made from petroleum and dramatically lower the carbon footprint of the plastics industry. Endit