Manufacturing of PET produces large amounts of CO2. What if there is a better way to serve the demand for plastics?

Inedible plant waste and CO2 could replace PET in plastics

Inedible plant waste and carbon dioxide have been used to create a renewable plastic material that could in future replace petroleum-based PET.

The discovery, made by Stanford University researchers, could help reduce greenhouse gas emissions. First of all, the production of the new material, called PEF, for polyethylene furandicarboxylate, doesn’t generate as much emissions as the manufacturing of PET (polyethylene terephthalate) - the current number one material for making plastic bottles. Moreover, the CO2 needed for the production of PEF could be taken from power plant emissions.

"Our goal is to replace petroleum-derived products with plastic made from CO2," said Matthew Kanan, an assistant professor of chemistry at Stanford. "If you could do that without using a lot of non-renewable energy, you could dramatically lower the carbon footprint of the plastics industry."

PEF has already been known before. However, the existing production method did not allow large-scale manufacturing due to the limitations in production of one of the two major components of PEF – the 2-5-Furandicarboxylic acid (FDCA).

Previously, researchers experimented with using fructose from corn syrup to make FDCA, but that has proved problematic due to the high energy, water and land requirements of growing fructose rich crops.

"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."

That is exactly what the Stanford team managed to achieve. In an article published in the journal Nature, they described a method to make FDCA from furfural, a compound in agriculture waste, and carbonate.

Stanford graduate student Aanindeeta Banerjee, lead author of the Nature study, combined carbonate with CO2 and furoic acid, a derivative of furfural, and heated the mixture to approximately 200°C to form a molten salt. After five hours, 89 per cent of the molten-salt mixture had been converted to FDCA.

Furfural had been experimented with to make FDCE in the past. However, the process required toxic and expensive chemicals that are energy-intensive to make. "That really defeats the purpose of what we're trying to do," Kanan said.

Using carbonate is cheap and safe by comparison. Furfural is also abundant and easy to make - around 400,000 tons of the material are produced every year from agricultural waste for use in resins, solvents and other products.

The resulting PEF can be recycled or simply burned. That returns the CO2 locked in the plastic back into the atmosphere, from where it can be absorbed by crops, which in turn produce furfural. PEF, the researchers said, is also superior to PET at sealing out oxygen, which is useful for bottling applications.

"We believe that our chemistry can unlock the promise of PEF that has yet to be realised,” said Kanan. “This is just the first step. We need to do a lot of work to see if it's viable at scale and to quantify the carbon footprint."

The team is attempting to use the method also for production of renewable fuels and other compounds from hydrogen and CO2.

Currently, some 50 million tons of PET are produced every year for items such as fabrics, electronics, recyclable beverage containers and personal-care products. Manufacturing of every ton of PET results in more than four tons of CO2 escaping into the atmosphere, which makes the technology a significant contributor to global warming.

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