Butanol Production Process

In my previous job, I worked for a major chemical company for seven years. For six of those years, I worked on various processes to produce butanol. This included roles in R&D, process, and production, and I received a patent while working in Germany for devising a novel process for making butanol. Butanol is an alcohol like ethanol, but whereas ethanol has 2 carbon atoms, butanol has 4.

The most common industrial process to produce butanol involves a few steps. First, synthesis gas is produced. Synthesis gas is a very important raw material. It is composed of hydrogen and carbon monoxide, and is produced by burning a feed at a high temperature while limiting the oxygen available for the reaction. The feed material for producing synthesis gas can be natural gas, fuel oil, coal, or even biomass. Once synthesis gas is produced, it can be used to make a wide variety of chemicals, including diesel (via the Fischer-Tropsch reaction), methanol, ethanol, propanol, or butanol.

If the desired end product is butanol, the synthesis gas is reacted under pressure with propylene to first produce butyraldehyde, and then this is reacted with hydrogen under pressure to produce butanol. The crude product contains butanol, isobutanol, and water, and must be distilled to obtain specification butanol, which has a wide variety of end uses.

The energy return on investment (EROI) for producing butanol in this way is certainly less than 1. I have never bothered to calculate it, but there are a number of energy intensive steps involved in butanol production. However, given the end uses for butanol, the EROI was never a major concern. Sure, saving energy during the production of butanol was always a priority, but since it typically is not used as a fuel, there was no requirement that the EROI be greater than 1 in order to have a viable process.

Bio-Butanol versus Bio-Ethanol

I have made clear in several of my essays on ethanol that my primary objection to using ethanol as fuel is the poor EROI. Ethanol production consumes large quantities of natural gas via fertilizer for corn and then distillation of the ethanol. (If coal is used instead of natural gas, you may have an economic process, but certainly not a green one). The reason so much distillation energy is required is that ethanol is completely soluble in water. The end product of the fermentation results in something like an 8% ethanol/92% water solution. It takes a lot of energy to heat water up, so the distillation of ethanol into a pure form uses up a lot of energy and contributes to the poor EROI.

Butanol, on the other hand, has a more limited solubility in water. According to the Material Safety Data Sheet (MSDS) for butanol, it is only 7.7% soluble in water. What does this mean? There is a much less energy intensive method of separating butanol from water, and that is by letting it phase out (just like oil and water). Therefore, you would expect the EROI for producing butanol from corn would be much better than for producing ethanol from corn.

Until this weekend, I didn’t realize that anyone was producing butanol from corn or biomass. During my graduate school studies, we produced butyric acid as a very smelly byproduct of our biomass process, and this can be converted into butanol. But one of the editors over at Omninerd pointed me to a site this weekend that demonstrates the viability of producing butanol from biomass. I encourage you to check out the claims at, which are based on the work of a chemical engineering professor at Ohio State.

The entire site is worth a read. Here are a few excerpts:

How does butanol compare with ethanol as an alternative fuel?

Butanol has many superior properties as an alternative fuel when compared to ethanol. These include:

· Higher energy content (110,000 Btu’s per gallon for butanol vs. 84,000 Btu per gallon for ethanol). Gasoline contains about 115,000 Btu’s per gallon.

· Butanol is six times less “evaporative” than ethanol and 13.5 times less evaporative than gasoline, making it safer to use as an oxygenate in Arizona, California and other states, thereby eliminating the need for very special blends during the summer and winter months.

· Butanol can be shipped through existing fuel pipelines where ethanol must be transported via rail, barge or truck

· Butanol can be used as a replacement for gasoline gallon for gallon e.g. 100%, or any other percentage. Ethanol can only be used as an additive to gasoline up to about 85% and then only after significant modifications to the engine. Worldwide 10% ethanol blends predominate.

They claim the process is competitive with ethanol on a per gallon basis. Given that butanol has substantially more BTUs than ethanol, the price per BTU would be much lower than for ethanol:

Our preliminary cost estimates suggest that we can produce butanol from corn for about $1.20 per gallon, not including a credit for the hydrogen produced. This compares with ethanol production costs of about $1.28 per gallon. Taking into account the higher Btu content of butanol, this translates to 105,000 Btu per dollar for butanol and 84,000 Btu per dollar for ethanol with corn at $2.50 per bushel. As a further point of reference, butanol produced from petroleum costs about $1.35 per gallon to manufacture.

The economics of the EEI process will be even more attractive when waste material is used as feedstock instead of corn and the price to produce a gallon is $0.85. In such cases the need and cost to grow and prepare the corn for fermentation, by far among the major cost items, are eliminated.

A couple of other claims are worth noting. They say that they can produce 2.5 gallons of butanol for every bushel of corn. On a BTU basis, that is 30% more BTUs than can be produced if ethanol is the end product. Second, they also claim that butanol can be used in biodiesel applications, and can be blended with diesel. If true, that would give butanol a significant advantage over many other alternative fuel options. Finally, they note that the process produces a significant amount of hydrogen as a byproduct.

What’s the Catch?

I need to spend some time going over the patents and linked reports more closely to see if anything suggests a problem that has been glossed over. I can think of one possible issue off the top of my head. One of the knocks on methanol is the toxicity. Ethanol is considered non-toxic for the most part. If trace quantities of ethanol entered the groundwater, it would not be as alarming as methanol getting into our water supplies. Butanol is less toxic than methanol, but more toxic than ethanol, and it is somewhat soluble in water. Therefore, the one thing that should be addressed is the potential for butanol to find its way into our water supplies.

Other than that, this looks worth pursuing. Butanol has a number of clear-cut advantages over ethanol, and it should have a superior EROI. The authors of the site indicate that they need to complete testing on a demonstration plant and a pilot plant. I look forward to the results of their testing.

72 thoughts on “Bio-Butanol”

  1. Mr. Rapier,

    Since the butanol is produced by bacteria in a fermentation tank, it will likely be produced at a fairly dilute concentration, below the butanol solubility limit. As the butanol concentration rises, the bacteria will find it energetically harder to work against the concentration gradient. Thus, since the butanol is likely present in the fermentation water below the butanol solubility limit, I don’t think it would separate out of the aqueous phase unless you changed the conditions – i.e., distilled the butanol out, or used a pervaporation separation process (membrane/evaporation combination – a schematic I saw showed vacuum pumps and condensation chambers). So, it may still take significant energy to separate butanol from the fermentation solution. That’s one reason I think algal vegetable oil may be the easiest biofuel to produce (not to use), because it really does separate out by itself without energy input, once you have crushed the algal cells. Whaddaya think?

    Brother Kornhoer from the TOD

  2. Last time I looked at algae, theey claim was the seperation process was ‘not worked out’ and the high yields are based on a rich CO2 environment.

    I’m not convinced the capitol costs of large algae tanks works out VS growing a starchy plant.

    No matter which approach is used, it won’t be like sticking a hi-tech straw in the ground and sucking on sweet crude.

    And I thought butanol had a higher boiling point than water….Guess I’ll have to go check that again.

  3. Yeah, I thought about that possibility as I was writing (that it might be produced at less than 7.7%). However, even if it is, you wouldn’t have to distill it to purity. All you have to do is distill it until the concentration is above 7.7%, and then you send it a vessel and allow the butanol phase to separate, while recycling the aqueous phase back to the distillation column. It would still require much less energy than a full blown ethanol distillation.

    I am still enthused about the possibility of biodiesel from algae, though. I would like to see a full-blown energy balance on this process. I know the separation portion is going to have a decent energy balance since the biodiesel will phase out. I just wonder about growing, collecting, and processing the algae.


  4. Eric,

    Butanol does have a higher boiling point than water. My thinking is that you don’t have to do a full-blow distillation in order to start separating out a butanol stream by phasing. You just need to concentrate it up a bit.


  5. This is good news. The promotion of ethanol is a farm subsidy boondoggle in Wisconsin. Ethanol is a terrible thing to do to good gasoline.


  6. Mr. Rapier,

    An issue you didn’t raise when considering butanol as an additive for gasoline is the octane number. I have no idea what that number is (although I know for butane it is much lower than for propane or methane). One reason ethanol is attractive as a gaoline additive is that it acts as an octane booster. Butanol may not be similarly attractive.

    The converse issue for butanol as a diesel additive would be cetane number, which typically works in the inverse to octane number. This is why ethanol is not at all attractive as a diesel additive. Again, I have no idea what the cetane number of butanol is.

  7. R^2,

    Check out:


    Apparently butanol is an inhibitor of bacterial growth, so it generally stays well below 7% concentration (25 g/L = 2.5% concentration “rarely achieved”). So distillation would have remove most of the water anyway. However, a silicalite absorption / desorption process that use much less energy than distillation is cited in the first link.

    Brother Kornhoer from TOD

  8. I assume they are suggesting the use of Butanol in place of methanol/ethanol for the esterfication of fatty acids to produce biodiesel? Wouldn’t that have undesirable effects on the viscosity of the fuel?

  9. terrible exhaust and bad EROEI

    butanol only phase separates after the ethanol/butanol/acetone in the fermenting liquid is distilled from it. That’s when it’s possible to phase separate, not before. It still does not avoid the energy of distillation.

    algae can be used for ethanol, BTW. Corn shouldn’t be seen as a good source. Monoculture’s time has passed.

    to the one blogger “good gasoline” is an oxymoron. Gasoline is toxic waste.

  10. This report:
    (Sorry, don’t know how to do links) lists various forms of butanol (1-butanol, 2-butanol, 2-methyl-1-propanol and tertiary butyl alcohol) as potential octane enhancers for petrol (gasoline). No actual octane numbers are given, but I guess the octane number concern is not an issue.

    Nontheless, a high octane number almost certainly means a low cetane number, which would make butanol a lousy additive for diesel.

    Robert Fry

  11. My recollection is that butanol (at least n-butanol) smells pretty gross. Not in the same league as butyric acid, of course, but still it makes me wonder, would there be serious consumer acceptance issues?

  12. Responses to several people here:

    You might also look at this process:

    MixAlco: Biofuels and Chemicals from Biomass

    Check page 23 of that presentation. You will find my name listed there. This was my graduate school research.

    An issue you didn’t raise when considering butanol as an additive for gasoline is the octane number.

    Butanol boosts octane just like ethanol.

    Apparently butanol is an inhibitor of bacterial growth, so it generally stays well below 7% concentration (25 g/L = 2.5% concentration “rarely achieved”).

    I encountered the same problem in graduate school. The bugs would work very well when the concentration was zero, but they would slow down as the products built up. You really need a series of reactors, each of which has bacteria optimized for higher and higher levels of product.

    terrible exhaust and bad EROEI

    The butanol site said:

    In ten states Butanol reduced Hydrocarbons by 95%, Carbon monoxide to 0.01%, Oxides of Nitrogen by 37%, this in a 13 year old car with 60,000 original miles.

    I don’t know what the EROI is, but I can see it being better than for ethanol. Dissimilar molecules have lower energy requirements for distillation. It should require less energy to separate butanol from water than for ethanol from water. Due to the phasing, you also don’t have to distill to a high level of butanol purity. You can accomplish a lot of this by phasing the butanol once the concentration is high enough. That is how butanol is separated from water in the chemical industry.

    My recollection is that butanol (at least n-butanol) smells pretty gross.

    Pure butanol isn’t bad. If it has a little butyric acid in it, then it is horrible.


  13. Regarding groundwater contamination, the link I gave above:
    (did not come out properly before. If you only get to the main publications page, it is paper 2a) states the following:
    “None of these alcohols are expected to bind strongly to soil and would be expected to move into the water compartment where they would biodegrade. As linear alcohols, n-propanol and n-butanol are likely to degrade quickly. Isobutanol and sec-butanol are expected to degrade more slowly than ethanol but faster than TBA”

    ALthough no numbers are given, it sounds like n-butanol (if that’s what they are making) would biodegrade much faster than an ether like MTBE, so likely not a problem.

  14. Because of its low vapor pressure, a vehicle powered by 100% butanol would probably have cold starting problems. One solution would be to add some lighter components to the fuel (e.g. ethanol).

  15. Correction to above – ethanol won’t help cold starting. This is why E85 is sold, but not E100. Needs something lighter yet, like pentane.

  16. RR –

    This butanol stuff has been buggin’ me a bit…I haven’t been able to stop thinking about it. OK, let’s say you have a 2.5% butanol solution coming out of your bioreactor. You want to roughly triple the butanol concentration so it will phase out. Butanol has a higher boiling point than water, so you can’t distill it out first. You still have to distill out 2/3 of the water to triple the butanol concentration, ignoring the fact that some of the butanol will leave as well as an azeotrope with the water. That stuff you will likely phase-sep once it condenses, but it’s probably not much better than ethanol, overall, I think (please point out if/where I’m wrong).

    I started thinking along other lines…what about a liquid-liquid extraction with something like pentane, or a freon that’s liquid at room temperature but boils just above? You could insulate your reactor tank, have it operate at a temperature above the boiling point of pentane, using the bacterial activity to generate as much of the heat as possible. Then, take a constant stream of fluid from the bioreactor at say 120 F, use a heat exchanger with the pentane to cool it to room temp (boiling the pentane), then have the liquid-liquid extraction with the pentane at room temp (assuming alcohol & hydrocarbon are miscible). The water could be recycled for nutrients, etc. The pentane would go in a loop, starting as a liquid in the liquid-liquid extraction, then to the heat exchanger with the warm water, boiling the pentane & leaving the butanol behind as a liquid residue. The pentane would then flow to an outside condenser, and then to a small pump. The thing I like about this is that it uses the heat generated by the bacteria to power the separation.

    Another option: take the water from the bioreactor, run it down a well-insulated counter-current heat exchanger with it’s own return flow. At the end of the heat exchanger, when the water should be close to O C, freeze most of the water. Latent heat of fusion is 15% of latent heat of vaporization, and room temperature is closer to freezing anyway. Butanol will phase out of the water/ice slush, separate it, and use the slush to cool the incoming water. Then allow the now-melted ice to go back up the heat exhanger in the counter-current. In the Midwest, for part of the year your freezing would be done courtesy of Mother Nature.

    What do you think? Am I full of it, or does this make some sense?

    Brother Kornhoer, occasional poster on The Oil Drum.

  17. A liquid extraction is possible, and I know people who are working on such schemes. My research advisor in grad school was working on a liquid-liquid extraction scheme.

    But if the bioreactor is only producing 2.5% butanol, it is going to be tough to economically separate it. I know places where a 3% butanol solution is sent to the wastewater ponds, because it isn’t economical to extract.


  18. Just thinking on this a little more tonight. What is really needed is bio-pentanol. I bet it has similar fuel properties to butanol, but its water solubility is negligible. Therefore, it phases out as it is produced. I just can’t find much information on bio production of alcohols higher than butanol.


  19. Hi,

    I think Butanol could be separated with supercritical CO2, maybe one could get bacteria strains that could trive under supercritical conditions at about 60 C. It would make the process even more efficient.

    I’m an organic chemist working as an environmental consultant at

    I think biofuels should be so easy to make that just about any farmer could make a nice income from it.


    G. Nilsen

  20. I have a great interest in n-butanol as a fuel, and as a solvent in combination with CO2 and water. Has anyone out there attempted separation of butanol-water with supercritical or liquid CO2? ( I think it would go into the CO2 phase quite readily)

  21. Phil,

    I have never heard of anyone doing that, and I have been around a lot of butanol separation units. Since it phases out of water at fairly low concentrations, the separation is not all that energy intensive.



  22. butanol is a no-brainer. i don’t understand why it hasn’t been approached before, except for specialized use.

    for fuel purposes what about n butyl n butyrate (as a diesel substitute) or di-n-butyl ether (for use as a gasoline substitute)?

    i have no idea what cetane/octane values these compounds have (nor have i been able to find the values), but once you have a butanol process set up (specialized clostridiums), (you make butyric acid, then continue it to butanol), these other butanol deriviatives are easily manufactured.

    i’ve got to think these are drop in the tank replacements.

    you could use sewage sludge or other raw biomasses as the feed material and get out of the food loop. EROI would be … attractive.


  23. RR,

    Enlightening discussion about butanol, which wasn’t on my radar until BP/Dupont and Chevron started talking about it publicly.

    A few more questions, after this fruitful thread:

    1. Is butanol produced only through thermochemical process (gasification, FT), or can it be done with biochemical processes, like enyzmatic hydrolysis? Are the enzymes required any different than those being tested for cellulosic ethanol?

    2. Are there any biomass sources that would be especially conducive to butanol conversion, such as pine, prairie grasses, wheat straw, etc.? What properties would the feedstock need to be more favorable?

    3. Do you know anything about the air emission impacts of combustion? You mention lower evaporative emissions, which is the main issue with ethanol. What about NOx or other combustion products?


  24. 1. Is butanol produced only through thermochemical process (gasification, FT), or can it be done with biochemical processes, like enyzmatic hydrolysis? Are the enzymes required any different than those being tested for cellulosic ethanol?

    Yes, it can be done biochemically. At, they describe some biochemical processes in detail and link to some research.

    2. Are there any biomass sources that would be especially conducive to butanol conversion, such as pine, prairie grasses, wheat straw, etc.? What properties would the feedstock need to be more favorable?

    The link above describes them using corn, and getting the same per gallon yield. Better would be to use a biomass gasification process, which would have a higher conversion. But it will probably be tough to turn syngas directly into butanol.

    3. Do you know anything about the air emission impacts of combustion? You mention lower evaporative emissions, which is the main issue with ethanol. What about NOx or other combustion products?

    There are significant reductions of CO and NOx versus gasoline, but not sure how that stacks up against ethanol.



  25. no info on di-n-buytl ether or n butyl n butyrate?

    the new biomass systems use clostidrium that doesn’t process thru the acetone-ethanol-butanol and produce just butanol. at that point, it shouldn’t matter what biomass you’d use, just that any lignin be digested first

  26. no info/comment on di-n-butyl ether or n butyl n butryate?

    the new clostridium bio process avoids the old acetone-ethanol-butanol and just produces n butanol.

    it shouldn’t matter what biomass you could use, as long as the lignin was destroyed.

  27. Thank you for the great information on this page. I have recently acquired a bio-butanol fever, dreaming of driving a car with a bio-butanol bumper sticker on it. Does anyone know of someone making a home reactor? Think it can be done? The only attempts I have read are of Ohio State’s- anyone know of others?

    The gears are turning,
    M Cameron

  28. Floating an organic, non-water-soluble solvent or oil on top of a bio-reactor solution would probably remove quickly much of the butanol that was produced from the fermentation water solution. Mixing and then allowing the solvent to separate would do it much faster. The solvent would be centrifuged to remove any trace of water, like a cream separator, and then butanol could be evaporated directly from the solvent at low temperatures with vacuum distillation.

    Solar energy could be used at the low temperatures required for vacuum distillation. Carbon Dioxide produced by the fermentation is removed at fermentation, solvent mixing and solvent centrifuging stages and will not interfere with the vacuum distillation. Vacuum insulated solar collectors can be used to produce high temperatures even in the winter for distillation. Multiple effect distillation has reduced the energy needed to extract water from sugar solutions, by a factor of four to eight times, for more than a hundred years, and it is also likly that it will also work in butanol production.

    One very significant advantage of butanol is that there are far fewer government taxes and laws controlling its production and distribution. Thus it is likely that a small plant that produced a few tens of gallons a day from cornmeal could be owned and operated by a farmer, and the unit would be factory produced at mass production prices like tractors. It would be automatically computer controlled for much of its operation as are modern cars. The other oganics produced by fermentation might not interfere much with butanols use as a fuel in some uses, but may have to be separated and sold or used on site for fuel purposes.

    A German maker of Steam Engines has a division that sells long running, packaged internal combustion engine-generator-waterheaters for getting both electricity and heat from fuels. Honda is selling a similar small system for homes that run on natural gas, but both could be used with any fuel including biogas from the waste products of fermentation and any volatile liquid fuels that cannot be sold with the butanol. The heat may be used by the farm and the butanol producer as can the electricity.

  29. I occasionally revisit the wikipedia butanol resources to see what new has come up, which is how I arrived here.

    It should be practical to make a small home-scale fermenter using a simple water filtration trick. That involves putting an inverted plastic basin on top of the sludge, running a tube up into it through the sludge, and drawing off the liquid from there – the sludge becomes the filter.

    The simple but wasteful way of getting the butanol out is asperging, blowing warm dry air through the filtered liquid to evaporate water and other impurities enough for the remainder to separate out. Freeze distilling is also a possibility.

    However the most promising method looks like vacuum distilling, with a pump drawing vapour off and the recondensed liquid returning the heat to the boiler through a heat exchanger. The theorteical energy cost is much lower that way, and much less butanol would be boiled off at the lower operating temperatures. Again, the increased concentration would do the final work of butanol separation.

    I have sometimes wondered if the school experiment for methane synthesis could be extended to higher hydrocarbons. That involves destructively distilling acetic acid with soda lime. what would happen with higher fatty acids, e.g. sebacic acid? Though even if it works I doubt if it would be economic.

    I have also wondered if you could synthesise hydrocarbons by pulling oxygen out of formaldehyde in the presence of lower hydrocarbons or even hydrogen. For instance, what would happen if you had a reactor full of hot zinc vapour with a trace of hydrogen and then trickled formaldehyde into it? If it worked the zinc oxide would be removed faster than oxygen could be extracted from that, and then it could be recycled to recover the zinc.

  30. BP & DuPont have signed an agreement to convert an existing Ethanol plant in England to produce Bio-Butanol.
    What I cannot find out though is what they need to change in order to produce bio-butanol and how much it will cost to convert an average sized plant: 55-100 million gallons.
    Anyone know the answer?

  31. I’m glad to see progress in commercial biofuels, but what I’d really like to know is whether it would be feasible to set up a butanol still using yard wastes (primarily grass, but leaves and the occasional dog deposits as well)?

    Besides cost, there’s the issue of complexity (it would help if you didn’t have to be an engineer & chemist to set up and run it), smell, energy usage (solar seems like a good idea, but cost is sure to be a factor), and of course, not blowing oneself up in the process.

    Is this possible for suburban home use, or is this better left to commercial plants and large farms?

    Brian Merta

  32. Brian,

    Because butanol fermentation requires special microorganisms, and my bet would be that they are not that easy to maintain, it is probably not something that one could do at home. In addition, the purification of the butanol is quite a bit different than that for ethanol, so you might be looking at a more complex distillation train.

    Cheers, Robert

  33. Robert,
    Regarding what you said:

    “… I can think of one possible issue off the top of my head. One of the knocks on methanol is the toxicity. Ethanol is considered non-toxic for the most part. If trace quantities of ethanol entered the groundwater, it would not be as alarming as methanol getting into our water supplies. Butanol is less toxic than methanol, but more toxic than ethanol, and it is somewhat soluble in water. Therefore, the one thing that should be addressed is the potential for butanol to find its way into our water supplies.”

    Alcohols, ranging from Ethanol, propanol, butanol, pentanol, all the way to fatty alcohol, are extremely biodegradable. So soon after they hit the soil after a spill and get in contact with water (say from rain) and get diluted enough, they will biodegrade.

    So there is NO problem in using any of these alcohols as fuels.

    MTBE, on the other hand, is not biodegradable under normal conditions.


    Cesar Granda

  34. Robert,

    Regarding what you said here:

    “I need to spend some time going over the patents and linked reports more closely to see if anything suggests a problem that has been glossed over. I can think of one possible issue off the top of my head. One of the knocks on methanol is the toxicity. Ethanol is considered non-toxic for the most part. If trace quantities of ethanol entered the groundwater, it would not be as alarming as methanol getting into our water supplies. Butanol is less toxic than methanol, but more toxic than ethanol, and it is somewhat soluble in water. Therefore, the one thing that should be addressed is the potential for butanol to find its way into our water supplies.”

    Alcohols, ranging from ethanol all the way to possibly octanol, are extremely biodegradable. So after a spill, as soon as they hit the soil and get diluted with water enough, they will biodegrade.

    MTBE, on the other hand, is not biodegradable under normal conditions.


    Cesar G.

  35. Cesar G,
    You seem to have fallen for the “corn lobbies” propaganda. Your statement regarding MTBE is not correct – MTBE will biodegrade – but over time frames measured in weeks to months dependant upon the environment into which it is released. Ethanol is claimed to be biodegradable within days/weeks, however a lot of information is left out of this statment when the ethanol is mixed with petrol.

    When petrol containing MTBE escapes from underground storage tanks (seemingly very common in the USA) MTBE will flow with underground water movements and “contaminate” water supplies with a “plastic taste” at levels of 5 to 20 parts per billion depending on your palate, whilst the nominated harmful level is above 250 parts per billion (depending on whose water quality standards you use). Most importantly, MTBE leaves the BTEX in the soil around the tank and does not carry it down to the drinking hole.

    On the other hand, ethanol does exactly that. BTEX (Benzene, toluene, Ethyl Benzene and Xylene) are mobilised when Ethanol is in the equation – particularly where petrol/ethanol has phase-separated (ie when water contamination exceeds 0.3 to 0.7% by volume) contamination plumes have been shown to expand 2 to 3 times further than would otherwise have been the case. All of these unsavoury products are more effective at killing you than MTBE without anything like the taste tingle you’d get as a warning. Benzene, the product linked to cancers and identified as a liver and reproductive toxin, is probably the most insiduous of all given it was used as an aftershave in the early 1900’s.

    To make matters worse, the expanded plume experiments also showed that the biodegrading of the Ethanol in the petrol slowed down the biodegradation of the BTEX, extending the opportunity for injestion. Alcohols are extremely effective in killing many bacteria at certain concerntrations (guess where we kept snakes we caught as kids) and Ethanol in plumes was shown to not just kill some of these helpful biodegrading bacteria, but of the ones remaining it was consumed in preference to the BTEX.

    “Economic arguements” hold up one variable for experimentation whilst all else is held constant – you can’t argue like that here. Yes Ethanol on its own (particularly in a good scotch) might be better than MTBE on its own – but not when they’re in petrol.

    Correspondingly, Butanol looks good on a number of fronts, particularly relative to ethanol, but don’t bring up irrelevant details that really apply to all these products added to petrol – they all need SECURE STORAGE!

    If you don’t believe me check out the Euro 4 and 5 standards that leave Europe requiring MTBE to reach the 95 octane levels required in sufficient quantities to supply their demand.
    Their reaction to the removal of “legislated protection” over MTBE in the US was simply to ask “what’s the petrol doing in the ground in the first place?”

  36. I have been developing a technique that continuously depleates and extracts the butanol from the digester. I need 1.2% concentration to make it viable from the extraction process. This looks like it has already been achived with the new strains. I think within 10 years bio-butanol will exceed ethanol production. The economics are shifting the goal post that quickly.

    Bob H (Australia)

  37. Just some information for you guys on Butanol as a fuel. I have access to the non bio produced butanol. It smells similar to rubbing alcohol, so not a bad smell to deal with. I have run the butanol in various engines to see how it does. The exhaust from the butanol run engines smells much less than does a gasoline fired engine and as you might have read is said to produce much less emissions. I have found that in a fuel injected car it does well and have run it at levels as high as 85% with no major problems. I did however, as was posted on this forum, have some issues in cold weather. The car would start but I had to let it warm up about 30 seconds before putting it in gear if not the car would kill. I have also tried the butanol on some small carburated engines. The smaller low compression engines didn’t run so well but would run with the engine slightly choked. I ran it pure in one and put it in while the engine was warm from running on regular gasoline. The engine would run but required it to be somewhat partially choked. I later tried to start the engine after it was completly cooled down and it wouldn’t start at all. I had to hit the carb with a little gasoline to get it going.
    Due to butanols higher octane levels and lower vapor pressure I feel that increasing the compression ratio on the engines would make the engines run all around better.
    Hope this was usefull information.

  38. Manufacture of Bio-Butanol through distillation will produce a Bacterium laced waste stream. If so, what will a production plant do to satisfy the environmentalists and DEQ?

  39. I like the idea someone posed earlier about trying a real-time liquid-liquid extraction using a solvent that is only sparingly soluble in water and thus may not harm the bacteria? Remember that solubility in a medium may be fine, but relative solubility in a pair of media is determined by a calculation based on the ‘free energy’ calculation of having a particular concentration in each, such that the free energy is the same in either… I do not know if something like Pentane would harm bacteria, but at 20*c it has a solubility of 0.01g/100ml in water (Sited: wikipedia ^.^) or 0.1mg/g. However if the butanol disolves well enough in it, one might be able to get very concentrated before even having to suck off the pentane… and meanwhile you are removing the bacterially hindering butanol… And I pick pentane for the delightful boiling point properties the guy mentioned. Almost no energy input to get pretty pure butanol ^.^

  40. Mr. Rapier,

    I’m a student at Caltech and I have been trying to sort through the feasibility of using butanol as a fuel in the aviation transportation sector. It seems it’s a pretty good candidate to replace gasoline but what about kerosene since jet fuel is the predominant fuel type consumed for air travel? One issue relating to the feasibility is the production of toxic byproducts at lower power settings (I had read that for example methanol produces acetaldehyde). Is the chemistry of butanol combustion similar enough to methanol or ethanol to potentially have this problem?

    Your blog has been a neat source of links and information, thanks!

    -Ghyrn Loveness

  41. It seems it’s a pretty good candidate to replace gasoline but what about kerosene since jet fuel is the predominant fuel type consumed for air travel?

    AS far the fuel characteristics go, yes, it is a good candidate. It might even function OK as jet fuel, as I have seen reports that it functions OK in a diesel engine. The problem is going to be producing it economically from biological sources. Right now, they only get about 1.5% butanol and about 98.5% water. That is not going to be economical to distill. I have to finish the essay that I started a month ago detailing this. I just haven’t wanted to finish it.

    Cheers, Robert

    P.S. I had a friend in grad school at A&M that graduated from Cal Tech. Incredibly sharp guy.

  42. I am trying to find out about relative water consumption among manufacturing processes — ethanol vs. butanol, dry milling ethanol vs. wet milling ethanol vs. enzymatic fermentation of ethanol.

    Do you know? Or can you refer me to a source?

  43. Hey guys,
    I just found this blog and find it extremely interesting. I have a potential eye-opening process to produce biobutanol from lignocellulosic materials. Check out

    So, some thoughts on my process would be appreciated as well as thoughts on a grass roots campaign to raise capital.

    Glad to be a part of this blog thread.


  44. excellent forum here!
    Please checkout my upcoming film “Running on Fumes?”

    In the film we test butanol in various non flex cars, and we are actually testing butanol with The D.O.E…this is the first time our government is actually testing the fuel and getting real data. We’re testing in both spark and diesel engines.

  45. I have only recently become aware of the potential of butanol vice ethanol and do not know if it can be produced from all the typical sources for ethanol production, but, at least for ethanol, corn is probably the least efficient crop from which to produce a biofuel. It is variously reported that ethanol from corn returns 1.07 to 1.25 times the energy used to produce it (some sources claim as high as 1.3, but are not generally accepted) as compared to an 800% return on energy for sugar cane based ethanol production. Some studies indicate that ethanol production from corn actually requires more energy to produce than is yielded.

    The “corn mafia” has co-opted the ethanol for biofuel movement with heavy subsidies that have doubled the price of corn recently. Ethanol from corn is still uncompetitive even with all the subsidies and makes no sense at all.

    Not only that, but corn based ethanol also has a much smaller reduction of exhaust emissions than sugar cane based ethanol.

    Although vehicles can be adapted to run on ethanol, no such modification is supposed to be required for butanol which is an advantage difficult for the ethanol proponents to overcome.

  46. Where can I license bio-butanol technology to produce my own bio-butanol? Can anyone assist me with this please?

    I also see a company called ButylFuel developed such a process, but there are no contact details of them on the web, just a postal address. Does anyone have their direct contact details?


  47. A couple of quick comments on biobutanol.
    Microbes — The microbes for biobutanol are not impossible to maintain, biobutanol was a commercial product before WWII. However it got out competed by oil derived butanol. See for an interesting history.

    Dual distillation processes like the ones described by EEI allow higher butanol yields. Initial ABE fermentation yield butanol,acetone and ethanol; however microbial mixes and GM microbes appear to be able to push that towards butanol and hydrogen as the two primary end products.

    Although the primary discussion here has been about the final distillation:
    GM’s that survive in higher butanol concentrations seem like a good way to go to make butanol more economically viable. If you can get them even close to 7.7% then extraction becomes extremely cheap.

    I’ve been wondering: can you run a butanol sludge over a molecular sieve that size excludes butanol to remove the water (and cause the butanol to separate out) then dry the sieves using solar energy and recycle them at an industrial level.

    Finally: grassroots funding… A group of us (mostly at UCSD) who got really excited about butanol as a potential fuel are trying using ad based funding to generate revenue to research butanol. If it fails we will donate the revenue we have generated to some research group but we’d be happy to have people come to our site and at least take a look! (Shameless plug)

    Thanks Mr. Rapier for running the awesome blog/discussion board on all things energy.
    Mike Hannon

  48. It seems some people are not fully understanding all the issues of butanol production and use.

    Can I make this it home?


    Reason 1: Butanol isn’t smelly, but one of the steps on the metabolic pathway, butyric acid, is one of the smelliest things on earth (it smells like someone ate four pounds of blue cheese and then puked into old running shoes).

    Reason 2. The only people getting reasonable yields are using two step, complicated fermentations, using two different fussy bacteria. This isn’t like brewing a batch of homebrew.

    Reason 3. Butanol boils at 117 degrees C, water at 100. In a home built batch process you are likely only going to get 1.5 to 2 % butanol and you would have to boil the rest. Building a different method of separation is difficult, expensive or impossible for the home builder.

    Can I use butanol in my car now?

    Sort of.

    Reason 1. The heat of vaporization is a bit high. This means it is fine if you have fuel injection and you live in Texas. Carb in Canada is not going to work. Newer vehicles with higher compression and direct injection should work great with butanol. Octane is between 94 and 104 depending where you read.

    Is it economic?

    Sort of

    The current state of the art: multi stage fixed bacteria continuous flow reactor, some concentration with pervaporation, then distillation, is not economic. You cant get the concentration higher than about 3%, not because of any concentration gradient, but because butanol and acetone are toxic to the bacteria above those concentrations.

    However, there are some very interesting recent developments.

    Some researchers at UCLA have tricked E.Coli into producing butanol. This has huge potential as E.Coli culture and production is very well understood. Also, it uses an amino acid pathway as opposed to metabolic pathway, also good. As well, E. Coli is easily grown in the lab, easily genetically modified, just a much better target organism than Clostridia.

    But, … the biggest hurdle remains the separation. Freezing may work (butanol freezes at -117), it may be some liquid liquid extraction (not likely though, the inside of bio reactors is very frothy and mucky, not very conducive to l-l extraction) membrane pervaporation, vacuum distillation (still expensive, energy and capital) or some totally different method.

    In any event these are big ticket research items. I have not heard of any grass roots funding drives that have managed to raise the several millions of dollars this kind of research requires. I don’t want to discourage anybody from trying, but if you want to do something now, try investing in some venture funds that are funding these kinds of ventures.

    Clarity on some other points. Butanol is not a good direct replacement for diesel, but can be used for esterification of fatty acids for biodiesel. the product is not much different than methanol or ethanol based biodiesel.

    Algae oil is a few years out due to massive capital requirements to build ponds, lack of effective separation technology, and researchers still searching for the best organism, but it could have some other great spinoff benefits if diverting polluted agriculture run off for the ponds.

    I think everyone agrees corn based ethanol is not the answer, but fuel produced from corn waste is worth pursuing. In fact we have to pursue all alternatives. Ethanol, biodiesel, butanol, hydrogen, batteries, hybrids, even nuclear fission and maybe fusion will all have a role to play.

    In terms of biomass you can use, it does matter. Very few organisms can digest cellulose or lignin, and those that can do so very slowly. If someone is to use woody biomass sources, it either has to be chemically broken to sugar or enzymatically changed to sugar.

    Hope this helps, Sorry for the verbage.

    Jake from

  49. If BP can produce the genetically engineered microbes required to withstand the higher toxicity of butanol than it might be possible. I think EROI is a big part in the production of any alternative fuel and where you save in one area hidden costs arise in another. Large scale agriculture is going to use a lot of fuel. Transporting the biomass is also going to use fuel. What do farmers do with the left over biomass from energy crop production now? Is it plowed back into the fields as a natural fertilizer? If we use the cellulose byproducts to produce butanol then the actual grain can be used for other purposes and some associated costs might be recouped from the sale of said grain. I think the problem will be finding enough arable acreage in the U.S to produce enough butanol to satisfy the US demand for fuel. One source I read stated that we would need about 6 times the available cropland acreage in the US in order to produce the needed 140 billion gallons a year of fuel that the US currently consumes. That same source stated that the US currently has about 434 million acres of cropland.

    Alternatively, the algae biodiesel process can be accomplished in deserts where crops normally can’t be grown without significant costs associated with irrigation and fertilizers.

    The algae to biodiesel fuel process is still in the R&D stage anyway but Solix Inc has a pretty big setup out in the desert already. Biodiesel research goes back to the Carter administration and I think the government has sunk about $25 million dollars into it with little to show.

    Overall, I think the biodiesel process may be the better choice.

  50. Another question I have in regards to switching over from gasoline to a biofuel is the overall effect on the US economy.

    If it is given that there is a finite supply of crude oil remaining in the world and that if we (the world) continue to use crude oil for fuel then the supply will eventually deplete and an alternative fuel must be found.

    What are the components that alter the price we pay for a gallon of gasoline at the pump?
    – The price per barrel of crude
    – Federal and state taxes
    – Refining costs and profits
    – Distribution and marketing
    – Octane rating of the fuel

    But I also think that supply and demand factor into the price of a barrel of crude oil.

    It is hard to calculate how many vehicles are in the United states and which use gasoline and which use diesel fuel. I think a rough number would be about 250 million registered vehicles in the U.S.

    One source I read stated that the U.S. consumes 20 million barrels of oil per day. That is a large demand and should influence the price we pay at the pump. If biodiesel is only viable for diesel engine vehicles, then what will we use or do to power gasoline engines?

    If demand on the world market dropped by 20 million barrels per day, what would happen to the price for a barrel of oil?

    Say the U.S takes the lead on switching to biofuel and shoulders the cost of doing so. This may include hidden costs such as requiring consumers to purchase a new car or a new engine for a car in order to use this fuel. The infrastructure may also require a significant investment of capital to transport, store, and distribute bio fuels.

    While the U.S or another country is doing this would the price of oil fall and be of benefit to the ecconomy of a country that has not shifted over? It seems to me that our ecconomy could take a massive hit from any rapid shift to biofuel while actually improving the ecconomy of counrties that dont.

    Therefore there should be a gradual shift with several varieties of biofuel at comparable prices so that each fuel price stabalizes at a reasonable price and give consumers the chance to migrate over to the biofuel of choice in a more progressive manner which would be more palatable to the consumers wallet.

  51. I have read all of the comments of this blog. Many of you are barking up the correct tree.

    I am doing research on conversion of cellulose to sugar and the subsequent collection of hydrogen using an enzymatic process here at FSU-FAMU College of Engineering.

    When our research is finished there will be an abundance of sugar. Sugar is the feed stock of alcohols.

    Our cars will run on alcohols and this is our future.

    Butanol is very promising, but what is the deal with the conversion. Which bateria do we use? I know butanol is not the only product of the fermentation. What are the other products. It seems that if ethanol and butanol were the products the seperation would be more painful than if they were seperate.

    How well does a mixture of butanol and ethanol work as a replacement for gasoline?

    A problem with doing research in fuels is that the inflation and value of the dollar is not given when explaining the price of fuel.

    What is the price to make ethanol today?!?

    If you are looking for a biofuel educated soon to be ChE for research this summer contact me at

  52. This may be a stupid question, but..

    If butanol will essentially separate it’s self at 7.7 percent, then why don’t you just add butanol to the solution until you reach 7.7 percent?

    Then remove both the “old” and “new” butanol.

    The engineering of a bacteria that can tolerate, and continue to produce, butanol when the solution reaches more then 7.7 percent seems the best long term solution to me.

  53. There are no stupid questions. Only silly ones. 🙂

    I kid. The reason that won’t work is what would actually happen is that as you added butanol, the pure butanol is now lost to the dilute solution, until as you say equilibrium is reached. Now, as dilute butanol continues to be produced, it continues to pull more and more pure butanol into the solution. You would find yourself having to re-distill butanol that you have already separated.


  54. what if an enzyme is used to seperate the butanol. an enzyme that requires two products of which one is butanol. make is hydrophilic and not keep the other product in the solution. the probably heating the enzyme may make it release butanol. and then cooling would restructure the enzyme

  55. I was watching an interesting show on brewing. Specifically a non-distilled beer called utopias caught my attention. It has an alcohol content of 25%. Meaning that the makers have a yeast capable of surviving in extremely high alcohol content environments.

    Considering the chemical similarity of alcohol and butanol wouldn’t it make sense that such a resistance would be likely to extend to butanol as well? If that is the case I would think this would be a perfect base organism to engineer to produce butanol. As another lab has already coaxed a yeast to produce butanol this would seem to be a relatively easy thing to do.

    Granted there are a huge number of if’s in this scenario, but the potential payoff would be enormous.

    Even if engineering of butanol resistant production organisms is a failure it demonstrates that selecting for tolerance to a similar chemical is possible, and is likely to be possible with butanol as well.

  56. There seems to be a lot of discussion of the production of butanol via the fermentation of corn. However, has anyone considered the production of butanol from enzyme-catalyzed synthesis, using grasses such as switch grass and hemp as feed stock? Articles I’ve read online seem to suggest that it is possible to obtain higher yields for ethanol using these feeds, and so I’m compelled to think that the same would be true of the production of Butanol. What is more, if there exists a means of developing reasonably-priced enzyme production, the EROI of production in this fashion would be much lower (since feedstocks like switch grass and hemp require little irrigation and almost no fertilizer).

  57. You make a good argument that bacteria, water, and butanol make an un-economic combination. You go on to say that this means butanol is uneconomic. The comments generally discuss how the bacteria could be hardier. That ignores the third factor, water; can a bacterial culture medium be chosen that has a lower butanol solubility water? I’m reminded of a picture in my high school chemistry book of a rat swimming in perflourocarbon.

  58. Hi All, does anyone has any informations about the chinese bio butanol industry? there should be already 5 bio butanol factories in production. what kind of butanol/water separationtechnology they are using there? thanks for any infos

    indi jones

  59. Aren’t we missing the notion that if all we need to do is increase butanol ratios to achieve phase seperation that we could accomplish that by doseing the mixture with pure butanol base? Get the ratio about 7-8% seperate and move on. We might hurt the bacterial processes with high doses but dodge the energy bullet associated with distallation…

  60. If you use pure butanol, then you have the problem that already purified butanol is now mixed with water and needs to have energy spent on it to purify it. Lots of people think this is a solution, but if you look at what happens, you actually waste good butanol.

    The same is true if you try to use pure butanol to extract the produced butanol. What actually happens is that the pure butanol will travel into the water, and some water into the pure butanol.


  61. Dear RR,

    Congrats !

    This is one of the most commented article I have seen and continues for 3 years.

    Good info overall…. but solution seems a far away….



  62. It’s not that we don’t have a solution. It’s that it would cost to much. Take a good look around the algos site for one possibility.

  63. What I want is a clear cut argument:
    Methanol Vs Butanol

    How are they different and which is more likly to be fueling our vehicles in the very near future?

  64. Considering the recent developments in cellulosic ethanol, probably ethanol. I’m not a chemist though, so don’t ask me what the advantages/disadvantages are of either.

    Last I heard a plant for producing cellulosic ethanol was slated to be built this year. Projected price at pump was 1$ per gallon.

  65. Jake Gray wrote “…the biggest hurdle remains the separation. Freezing may work (butanol freezes at -117)…”

    In case anyone thinks that one would freeze out the butanol itself, that’s not what would happen. I wrote about freeze distilling, but I didn’t spell out that I was thinking of the process Brother Kornhoer described, freezing out just enough water to raise the butanol concentration in the liquid enough for phase separation.

    Perhaps it’s labouring the obvious, but the hydrogen, ethanol and acetone byproducts could be used towards fuelling the separation process(es), with equipment designed to use them. That is, if it were cost effective to ferment butanol for its own sake at all, those would provide an effectively free energy source, cheap enough to justify purifying those byproducts out enough to burn too (if they had a market worth selling them on, that could pay for other biomass as fuel, e.g. wood chips). The only questions I can see are whether the additional separation would reach an EROI break even and whether there would be enough byproducts to fuel all the separation on their own. However, if you could integrate the whole production process start to finish, you would literally have crop waste to burn anyway; for renewability you would recycle the ash through settling ponds growing nitrogen fixing pond scum to get green manure. And there’s always sparging to fall back on, for a simple but wasteful way to reach concentrations where phase separation would work (I remembered the term wrong in my previous comment). But I digress…

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