gasification reactors, and the resulting hydrogen- and carbon-monoxide-rich syngas is siphoned off and sent through pipes lined with bacteria-coated membranes; the bacteria absorb the gas and churn out ethanol, which is flushed out using water.
Bolsen won’t say exactly how much ethanol this process produces, in terms of grams of ethanol per liter of syngas per hour—he says publishing that number would give away too much about the company’s proprietary technology. But “where we are today, we can get more than 100 gallons of ethanol from 1 dry ton of biomass,” he says. By breeding stronger microorganisms that are more tolerant of impurities, the company has improved the efficiency and throughput of its process 600-fold since it acquired the rights to the original Oklahoma State bacteria in 2006, he adds.
But “we still have a lot of learning to do,” Bolsen says. “That’s why we’re spending as much as we are on the commercial demonstration plant.” The individual pieces of Coskata’s process work well in the lab: gasification technology is well understood, and the bacteria produce the expected amount of ethanol when fed lab-produced syngas, and the company has figured out how to extract the ethanol in a water bath. But when the company hooks up its fermentation chambers to the Westinghouse plasma gasification system in Madison, the bacteria will be feeding on real industrial syngas for the first time. And “there are always integration challenges,” Bolsen says. “But you can’t sell a biomass-to-ethanol solution without showing the whole thing working together.”
Bolsen says he contacted Rapier on Wednesday and had a “very cordial” conversation that dug into technical questions about gas-to-liquids conversion, one of Rapier’s areas of expertise. “I’m always happy to talk about what we’re doing,” says Bolsen. “I’m hoping he’ll come out with another article with some additional understanding.”
That remains to be seen. Last night I talked with Rapier, whose company specializes in wood acetylation, a non-toxic process that can make pine as hard as teak and even steel. He said he agreed that economies of scale would probably kick in when Coskata moves beyond the pilot phase. But he remains skeptical about some of Coskata’s numbers.
“I told [Bolsen] I thought the $1-per-gallon claim was misleading,” Rapier says. “The reason—and he will tell you this himself—is that the production cost doesn’t include any capital recovery.”
Rapier also doubts whether Coskata will be able to build its 100-million-gallon-per-year plant for the $400 million figure projected by Bolsen. “At pilot scale and commercial scale, they will find that issues that didn’t seem to be much of a problem at lab scale suddenly become real problems,” Rapier predicts. “You can’t just go from a lab scale to full scale plant and expect to catch everything; that’s why you build a pilot plant. That will add on to that $400 million estimate, and that’s where a lot of these projects die, when it becomes obvious that the capital costs will be a killer.”
He does think, however, that gasification is a better way to create input for ethanol production than enzymatic approaches. Rapier says that in his next post about Coskata, he’s likely to be “neutral” about the technology. “I think it’s promising—but I think there are signs of overpromising, which is a pet peeve of mine,” he says.
