NETL team converts CO2 into acetate: Project can reduce greenhouse gas while supplying useful commercial raw material

Aug. 27—PITTSBURGH — As greenhouse gas and global warming worries continue around the world, a three-person team of researchers at the National Energy Technology Laboratory have found a means to turn carbon dioxide into a useful commercial product — acetate — and are working to grow their discovery to commercial scale.

Djuna Gulliver, federal principal investigator ; Sam Flett, research associate with the Oak Ridge Institute for Science and Education ; and research engineer Dan Ross, with NETL's Lidos Research Support Team, explained their work and provided a tour of their Pittsburgh lab.

Acetate is a semi-synthetic liquid with wide-ranging uses: It can be spun into fibers for fabric or molded into shapes for eyeglass frames or jewelry or used for cleaning supplies or such things as nail polish remover (acetone).

Their discovery of turning CO2 gas into liquid acetate was a happy happenstance, the three scientists said. It involves the intervention of microorganisms that act as biocatalysts.

A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. A biocatalyst is a natural substance that use enzymes from biological sources to accomplish the same purpose for biochemical reactions. NETL has filed for a patent on the technology.

Ross had been working on a different project to convert coal into methane using microbiology and had access to coal bed methane wells. The idea of converting CO2 into value-added products using electricity is nothing new, so they decided to try enriching these methane samples in the lab for conversion into acetate.

"We figured that it would be a good source of those microorganisms and we had a very unique ability to get these samples because we do work in these systems a lot, " Gulliver said.

Not every little critter is suitable, of course. They started with a highly diverse community and through a series of experiments enriched for a community that has the highest abundance of four to five microorganisms that catalyzed the conversion of carbon dioxide to acetate.

And they don't have to keep going back to the well to harvest more organisms, they said. They continue to propagate from the original sample — a lay person might roughly compare it to sourdough starter.

The next phase of their project, they said, is figuring out how to produce more. Right now, they can produce about 8 grams per liter of solution — a gram being about.28 ounce or 1.9 teaspoons — in test tubes. They want to titer that up — titer is a measure of concentration — to 40 grams per liter and go from producing liters of product to gallons. "Our goal is always to increase that concentration."

"Scale up is going to be more an issue, I think, in terms of the material costs to make sure we're able to have the logistics of that, " Gulliver said. They should, in theory be able to grow the microorganisms into a biomass big enough for significant amounts of conversion.

They began work on this project back in 2017-18, they said, but COVID interrupted, so by the end of 2020 and into 2021 they started expanding the testing process, Ross said. "In the past few years, we've been optimizing and now that we've kind of narrowed it down, we want to work more on the bioreactor side — so engineering that to get it to maximize our products."

A bioreactor is not some kind of monstrous machine producing stuff with all kinds of noises and frightening effects. Their bioreactors are 1-liter tubes. They put combine the propagation liquid with culture in the tube, gas it up with CO2 and let it work to produce the acetate.

Right now, when they reach the titer they want, they have to stop and remove the material. This is called a batch reactor.

So, they're working to develop a flow-through reactor, where a fluid stream comes in and hits the biocatalyst, and as it works acetate comes out of a different outlet. This means they could increase the residence time — the amount of time in the reactor — and double or triple the concentration, and constantly pull out product rather than constantly stopping the process.

As they scale up, where will they get the CO2 ? Not from the directly, Gulliver said, but probably from waste gas off an industrial facility.

When they scale up and find a commercial partner, what the market might do with the acetate is open for exploration, they said. Maybe sell it as pure acetate, maybe sell it as a drop-in feed for something like biofuels. "We feel like this might be a good target for the first product to then be converted later on, " Ross said.

But, they said, that is still some years away.

Email: dbeard @dominionpost.com