Coskata Refutes Energy Analyst’s Critique, Says It’s On Track to Make Ethanol for Under $1 Per Gallon

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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.

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Wade Roush is a freelance science and technology journalist and the producer and host of the podcast Soonish. Follow @soonishpodcast

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7 responses to “Coskata Refutes Energy Analyst’s Critique, Says It’s On Track to Make Ethanol for Under $1 Per Gallon”

  1. Curt Fischer says:

    The quality of Robert Rapier’s blog post is stunningly bad. Of course, this doesn’t mean his conclusions are wrong, just that they’re unsupported.

    First: A well-known approximation to chemical engineers is that costs scale as the 0.6 power of the capacity.

    In equation terms, where C is cost and P is capacity: (C_big / C_pilot) = (P_big / P_pilot)^0.6.

    If we accept the 0.6 as gospel for a second, that would give a extrapolated cost for a 150 MMgal / yr plant of $356 per daily barrel, not $9.6 million. That’s still ~2x higher than EIA Annual Energy Outlook 2006’s estimate for biomass-to-liquids capital costs. I’m confused why R. Rapier would quote both the $9.6 million number and the EIA number in the SAME POST, without noting the huge inconsistency.

    Second, the correlation is known to be inaccurate when making giant extrapolations. Our extrapolation here is indeed gigantic, by at least a factor of 3000 or so. A lot will depend on what the right value for the exponent turns out to be. For example, changing it from 0.6 to 0.55 reduces the capital cost by a third. Raising it to 0.65 makes the costs surge. But whatever the exponent might be, we know for sure that it won’t even be close to 1.0, which is what Rapier assumed.

    Third: Rapier says: One final thing I would point out is that the selectivity of these processes generally favors methanol over ethanol. They may be able to push the selectivity toward ethanol, but they will almost certainly end up producing mixed alcohols that will have to undergo purification to ethanol.

    This is ridiculous, as the selectivity for ethanol relative to methanol of the bacteria Coskata plans to use is virtually infinite. Bacterial metabolism is not the same as Fischer-Tropsch (no relation to me).

  2. I always find it extremely ironic when someone is critical of a piece of work, and then completely botches the math when trying to demonstrate it. Check your numbers, Curt. $356 per daily barrel? And then you note that you are confused?

    Further, I have to presume the Curt didn’t actually read the post, since he is confused about a quote and states that I didn’t note a huge inconsistency. Yet that post states “Caveats are that the graphic is for full-sized plants, and the numbers are a couple of years old.” So the very issue that Curt is complaining about was addressed in the post. Curt is taking exception to something that he has misinterpreted in one case and overlooked in another.

    The issue in focus in the original post was how far out of the stratosphere the numbers were for their pilot plant – and I gave a specific example of another pilot plant (GTL). When comparing pilot to pilot, the numbers were $9.6 million to $188,000 – and the $188,000 plant didn’t go to commercialization because it was too expensive. It is known that the $9.6 million will fall as the process scales (Curt seems to believe this would be a revelation to me, despite the fact that I have actually been closely involved in the scale up of facilities), but the point was that they wouldn’t fall enough (based on the $25 million which Coskata now says includes things other than the plant) to be competitive.

    So, I am left to conclude that Curt thought the quality was bad because of his misinterpretations of what I ‘really meant’ instead of what I actually wrote.

    Cheers, RR

  3. Curt Fischer says:


    Thanks for the response. First, thanks for catching my typo: instead of $356 per daily barrel, I meant $356k per daily barrel. The discrepancy between this number and the chart on your blog post, like I mentioned, was about twofold.

    Second, I fail to see how your caveat that the “graphic is for full-sized plants” explains away my objection on your use of the $9.6 million number.

    Third, your comparison of “pilot to pilot” is still not a fair comparison. The GTL pilot plant you mentioned was 400 bbl/d of capacity. The Coskata pilot is only 2.6 bbl/d. See the equation in my earlier comment? If we use that to scale down the GTL pilot to 2.6 bbl/d in size, the cost per daily barrel of the hypothetical super-small GTL plant would be $1.4 million. That’s still much lower than Coskata’s pilot, but not nearly as low as your comparison would (mis)lead one to believe.

    You seem to reject the idea that plant costs do not scale directly with capacity. Although I recognize that the 0.6 value for the scaling exponent is not universal, it is surely closer to the truth than the 1.0 you implicitly assume.

    Fourth, you have not responded to my criticism of your claims about selectivity vs. methanol.

  4. Curt, that’s just the thing. I stated several times in my post “of course this is just pilot scale.” What do you think I mean by that? So when you suggest that I seem to reject the scale issue, or that I am “implicitly assuming” something – and that was the gist of your initial post – you have skipped over multiple instances of me indicating that I did not expect costs to scale directly with size. The $9.6 million number was not significant because I expected a full-sized plant to come in at that number. It was significant because it was so far away – even with scaling (and your own numbers above show this) from competing with corn ethanol, oil refining, GTL, or even CTL that it is a nonstarter. Thus, the ‘Dead Man Walking.’ Now, Coskata has since indicated that there is much more in that estimate than just a pilot plant. So maybe that’s a valid answer. It’s really hard to say when someone has only done lab-scale experiments.

    If you have kept up with the conversation – which has continued following the initial post – you will see exactly what my issues are. First, you can’t make any sort of reasonable plant estimate based on lab scale experiments. You are probably aware of this. You can’t reasonably extrapolate mass and energy balances from a few hundred gallons a year in a lab (their current pilot scale) to a hundred million gallons a year.

    Regarding the selectivity issues, most (alcohol) gasification processes do result in mixed alcohols (or at least have significant by-products). Coskata indicated to me – and I reported it in my followup – that their microbes produce no byproduct alcohols. This was your only legitimate criticism, but I had already reported that in my follow-up. This will simplify the purification step, but they also indicated that the alcohol coming off the fermenter is at 3 or 4% ethanol. If you have access to HYSYS, run a separation at that level of ethanol and see how much net energy is lost due to the BTUs required for removing water.

    To conclude, I actually hope they deliver on their claims. For that matter, I would help them in any way that I could. I have long been on the record that I think gasification is the future. I just see some areas that warrant a good investigation.


  5. Sven Arunogen says:

    Wish it was true. Just another scam. Next.