Answers for your biofuels questions: Coskata, LanzaTech, butanol

August 5, 2012 |

Here in Digestville, we debut this week a content collaboration with Consumer Energy Report, a must-see content site that we recommend you check out and bookmark. Twice a month, we’ll check in with CER and excerpt their latest and greatest – including contributions from CER and Energy Trends editor and noted biofuels commentator Robert Rapier.

In our first collaborative, RR answers some questions from readers. One is on Lanzatech, and the other is about the feasibility  of filtering for butanol separations. The questions were slightly edited for brevity.

Q. I am interested if the decision by Coskata shall flow on to Lanzatech and their purchase of Range Fuels in regards to ethanol?

We are currently developing a project that incorporates a number of pieces, however we are considering the use of natural gas as a dual feedstock to produce critical volume likely producing methanol as a fuel and chemical base. Our view is to follow the lead by China and to develop technologies and processes around methanol to fuel. Currently we are are undertaking research and developing a possible business model.

Do you think we are going to see a vhs (ethanol) vs beta (methanol) situation develop in the future?

RR answers: Lanzatech has technology that was close to Coskata’s technology, so this is certainly a good question. In my opinion, Lanzatech is going to have a tough time making cost-competitive ethanol for many of the same reasons that caused Coskata to shift to natural gas. If you don’t want to make a full commitment to natural gas, I think a low-risk approach (but probably higher capital) is the one you describe in which you would have a capability of feeding natural gas into the process.

Natural gas should work fine in Lanzatech’s process, and would certainly be a lower capital option than wood waste. I know they would ideally like to process waste streams that contain a lot of carbon monoxide, but they are going to need the capability of building greenfield plants that provide their own feedstock. Natural gas could be a path forward.

As far as ethanol versus methanol, in my view methanol and di-methyl-ether (DME) produced from methanol are likely to gain a stronger foothold in China before they do so in the U.S. The U.S. agricultural lobby has not looked favorably upon methanol in the U.S., and I believe they will fight hard to keep it out of the fuel supply and protect ethanol’s market share. After all, there is already a large supply of cheap methanol in the U.S. and approximately none of it ends up in the fuel supply. I don’t expect that situation to change soon, but if you are thinking about China as a target market then your chances may be better there.

Q: This may be a dumb question (chemistry is not my area), but has anyone looked at simply filtering the butanol from the water?  What are the relative molecular sizes?

RR answers: This particular issue is in reference to the energy-intensity of separating a solution containing low levels of butanol. For reference, I have written in some detail about this issue in Butanol 101 .

It’s not a dumb question; in fact membranes can be used to separate butanol from water. The membranes I am familiar with don’t work on the basis of size differences (although some gas membranes do) but rather the relative polarity of butanol and water. Since butanol is a less polar molecule than water, some membranes such as polydimethylsiloxane (PDMS) that present a hydrophobic surface allow butanol to migrate into the membrane while excluding water.

This sort of separation can allow low-concentration butanol that is generally produced from biological processes (perhaps 2% to 6% butanol) to concentrate up to above the phasing concentration (~8% for n-butanol). Once the phasing concentration is reached, the energy requirements are far lower because the mixture separates into a butanol-rich phase containing maybe 20% water and a water-rich phase containing about 8% butanol. Therefore, instead of distilling off a mixture of 95% water and 5% butanol — which is extremely energy-intensive — you would distill a mixture that contains only 20% water.

The disadvantage is that the total costs of operating a membrane system are still not cheap. Chemical companies that produce billions of gallons of butanol each year are well aware of such systems, and have taken a look at the economics many times. But a fundamental difference between the petrochemical process and the biological process is that the former does not have to remove copious amounts of water as is the case in the latter. Therefore, the economics may be more compelling to utilize membranes for those pursuing the biological route.


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