Stanford scientists have discovered a novel way to make plastic from carbon dioxide (CO2) and inedible plant material, such as agricultural waste and grasses. The researchers say the technology could provide a low-carbon alternative to plastic bottles and other items currently made from petroleum.

Many plastic products today are made from polyethylene terephthalate (PET), also known as polyester. Worldwide, about 50 million tons of PET is produced each year for items such as fabrics, electronics, recyclable beverage containers and personal-care products.

PET 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.

About 50 million tons of PET is produced annually for use in items such as beverage containers. Image credit: Pixabay.About 50 million tons of PET is produced annually for use in items such as beverage containers. Image credit: Pixabay. "The use of fossil-fuel feedstocks, combined with the energy required to manufacture PET, generates more than four tons of CO2 for every ton of PET that's produced," says Matthew Kanan, assistant professor of chemistry.

For that reason, Kanan and his collaborators focused their work on a promising alternative to PET, polyethylene furandicarboxylate (PEF), which is made from ethylene glycol and the compound 2-5-Furandicarboxylic acid (FDCA). PEF is an attractive replacement for PET because FDCA can be sourced from biomass instead of petroleum. Additionally, PEF is 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. The bottleneck has been figuring out a commercially viable way to produce FDCA sustainably.

One approach is to convert fructose from corn syrup into FDCA. But growing crops for industry requires lots of land, energy, fertilizer and water.

Rather than using sugar from corn to make FDCA, the Stanford team experimented with furfural, a compound made from agricultural waste. But, instead of making FDCA in the traditional way from furfural and CO2, which requires hazardous chemicals that are expensive and energy-intensive to make, the researchers used a far more benign compound: carbonate.

Combining carbonate with CO2 and furoic acid, a derivative of furfural, and heating the mixture to about 290 degrees Fahrenheit formed a molten salt. After five hours, 89% 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 says.

The Stanford team's approach has the potential to significantly reduce greenhouse emissions, says Kanan, because the CO2 required to make PEF could be obtained from fossil-fuel power plant emissions and other industrial sites. Products made of PEF can also be recycled or converted back to atmospheric CO2 by incineration. Eventually, that CO2 will be taken up by grass, weeds and other plants, which can then be used to make more PEF.

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