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Process Devised for Plastics from Carbon Dioxide, Plants

Aanindeeta Banerjee and Matthew Kanan

First author Aanindeeta Banerjee, left, and Matthew Kanan (Stanford University)

10 March 2016. Producing common plastics like polyester today often needs large inputs of fossil fuel derivatives. A chemistry lab at Stanford University in California developed a low-carbon alternative to polyester that combines recycled carbon dioxide with inedible plant matter, such as agricultural waste, as reported in today’s issue of the journal Nature.

Matthew Kanan and colleagues at Stanford study the synthesis of renewable fuels with new types of catalysts that operate more efficiently and reduce the carbon footprint of fuels and their derivatives. Among the derivatives of fossil fuels is the widely used plastic polyethylene terephthalate, commonly known as polyester, found in an array of bottles, containers, fibers, and consumer goods.

Polyethylene terephthalate, or PET, is made of terephthalic acid and ethylene glycol, which are derived from refined petroleum and natural gas. “The use of fossil-fuel feedstocks,” says Kanan in a university statement, “combined with the energy required to manufacture PET, generates more than four tons of CO2 for every ton of PET that’s produced.”

The Stanford team sought an environmentally-friendly alternative to PET that would meet user needs and still be economical to produce. One such alternative is polyethylene furandicarboxylate, or PEF, which Kanan notes is even better than PET at sealing out oxygen — an important criterion for packaging — and can be made with biomass as its feedstock instead of petroleum.

The plastics and packaging industries are aware of PEF, but producing it sustainably is a challenge. PEF, like PET, is made of ethylene glycol, plus the compound 2-5-furandicarboxylic acid, or FDCA. The biochemical company Avantium, in the Netherlands, is partnering with Coca-Cola and others to develop a sustainable technology for producing FDCA. So far, however, their process converts sugars from corn to make FDCA, which calls for large quantities of energy and water, as well as competing for land needed to grow food.

In their article, the authors report on a process for making FDCA from inedible biomass, such as waste agricultural residues like corn stalks, and grasses. The team investigated a furfural, a building-block chemical made from agricultural waste as a feedstock for FDCA, which could be combined with carbon dioxide to make FDCA. Making FDCA with those components, however, requires strong high-energy reagents, and the researchers sought a more benign method.

That more benign approach, devised by graduate student and first author Aanindeeta Banerjee, combines carbonate, a salt derived from carbonic acid, with carbon dioxide and furoic acid, a derivative of furfural. The researchers cook carbonate, carbon dioxide, and furoic acid into a molten salt, which requires heating at temperatures of 200 to 350 degrees centigrade. After 5 hours, a large proportion of the molten salt (89%) converts to FDCA.

The authors believe their process could recycle carbon dioxide generated by power plants or other industrial sites to make FDCA for producing PEF, which would otherwise enter the atmosphere, thus reducing its carbon footprint even further. But more needs to be done. “This is just the first step,” says Kanan. “We need to do a lot of work to see if it’s viable at scale and to quantify the carbon footprint.”

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