A Stanford University study has figured out a way to create recyclable plastic from carbon dioxide (CO2) plus grass or other waste from agriculture. Their idea was to come up with a renewable, carbon-based alternative to the current petroleum-based plastic which is a major pollutant of oceans and ingredient in landfills. Stanford’s Matthew Kanan said it would be possible to “dramatically lower the carbon footprint of the plastics industry” if a plastic made from CO2 could be developed.
Many plastics are currently made of PET, polyethlene terephthalate, which has two main ingredients, terephthalic acid and ethylene glycol, produced from refined petroleum and natural gas. Kanan and his team were looking for an alternative to PET, namely PEF, which is polyethelene furandicarboxylate. Kanan says “PEF is an attractive replacement for PET, because FDCA [2-5-Furandicarboxylic acid, which is used to make PEF] can be sourced from biomass instead of petroleum.”
The study, which was featured in the journal Nature, explains that a simple reaction might make it possible to use carbon dioxide for making commercial plastic products. There is an abundance of CO2, a greenhouse gas that is a major contributor to global warming, particularly since the traditional process of making plastic produces a significant amount of the gas, more than four tons of CO2 for every ton of PET produced. Worldwide, about 50 million tons of PET are produced annually in the process of making plastic.
Although PEF has many desirable qualities, the plastics industry has not yet found a low-cost way to manufacture it in quantity, mainly because there is not yet a commercially viable way to produce FDCA sustainably. One approach has been to manufacture fructose from corn syrup into FDCA, but fructose production also has a big carbon footprint, and using fructose competes with food production.
The Stanford team then started experimenting with a commonly used compound made from agricultural waste called furfural to make FDCA. The drawback with this method is that it requires expensive and energy-intensive hazardous chemicals to made.
The problem was solved when carbonate was combined with CO2 and furoic acid, which is a derivative of furfural. A molten salt was formed after heating the mixture to about 290 degrees Fahrenheit. Eighty-nine percent of the molten-salt was converted to FDCA after 5 hours. Converting that FDCA to PEF plastic was already a straightforward process that Kanan says had been worked out already by other researchers.
Products made of PEF can be burned and converted back to atmospheric CO2. They can also be recycled.