Chemists Inspired by Plants Make Plastic Out of Carbon Dioxide

We might be able to do something useful with all that CO2 we’ve been spewing into the atmosphere—make plastic.

Capturing waste CO2 to make something useful isn’t a new idea. Over the years, chemists have devised myriad different reactions that can use the gas. There’s just one problem: None of them are very environmentally friendly, often requiring so much energy that there’s no climate benefit. But if a new, more energy efficient process pans out, waste CO2 could become a desirable commodity.

Lots_of_bottled_water
A new chemical process could produce a more environmentally friendly replacement for PET plastic, which is commonly used in bottled water.

Carbon dioxide is an incredibly abundant molecule, but also inherently stable. To make it a suitable ingredient in chemical processes, chemists first have to break its carbon-oxygen bonds, which has required gobs of energy. But scientists knew there had to be a better way. After all, plants crack CO2 and turn it into sugar using little more than sunlight and oxygen.

Chemists at Stanford University were, in fact, inspired by RuBisCo, the enzyme that plants use to pry CO2 apart, when they devised a new reaction to produce FDCA, a plastic precursor. The process mixes CO2, waste plant material, and special salts and heats them up to at least 392˚ F. With further processing, the resulting FDCA can be turned into PEF, a plastic that could easily replace PET, or the plastic that is found in everything from soda bottles to synthetic fleece jackets.

The researchers were able to crack CO2 at lower temperatures by using molten carboxylate salts as the medium in which the reaction takes place. “The idea to use molten salts in this reaction is really visionary,” Cathleen Cruden, a chemist at Queens University, Canada who wasn’t involved in the  study, told Kira Welter at Chemistry World.

Chemist Matthew Kanan and his team also found another way to use waste in the new reaction. Other processes that produce FDCA rely on the sugar fructose that’s made by plants. Before the sugar could be used, though, it had to be dried, which is an energy intensive process. The new molten salt method, though, can use already dried plant materials like grasses or corn stover.

While the new process is promising and it “seems to be much less wasteful than the fructose route to FDCA,” wrote University of Pittsburgh chemist Eric Beckman, “a comparison of the life-cycle impacts of the two routes will need to be performed to ensure that it is truly more sustainable.”