n-Butyl / Butanol – Stove Fuel?

[Dan @ Durston Gear]

I'm sure this would have been thought of by now if it worked, but does anyone know if butanol (aka n-butyl or butyl alcohol) can be used as a fuel in an alcohol stove?

I've done some reading today, and the big appeal with this fuel is the energy density is almost 50% higher than ethanol (29.2MG/L vs. 19.6 MG/L), while only being about 3% heavier. It's almost double the density of methanol (16MG/L) which myself lots of hikers are using.

[EDIT: The above numbers are comparing energy/volume, not energy/weight. Energy/weight is 20% higher than ethanol and 85% higher than methanol).

Some can be found on eBay.

Lots of info on this fuel:
http://en.wikipedia.org/wiki/N-Butanol
http://en.wikipedia.org/wiki/Butanol_fuel

[Dan @ Durston Gear]

Check out 0:12 of this video. They show butanol burning in a dish:

[Roger Caffin]

I have never tried butanol.
However, Tony Beasley (see our articles) has tried methanol (1 carbon), ethanol (2 carbons) and propanol (3 carbons). Butanol has 4 carbons.

What Tony found was that ethanol is OK but propanol gives off nasty fumes – quite bad. Working from the chemistry, I would predict that butanol would be even worse, but I might be mistaken. (I doubt it.)

Cheers

[Dan @ Durston Gear]

Thanks Roger. I haven't been able to find any record of anyone actually trying this fuel, which seems surprising to me since it has the potential to significantly lower fuel weight if it burns cleanly.

The only info on burning butanol that I can find is in the context of using it in your car. Apparently you can toss it in a car with zero modifications and it will give you about 10% better MPG than gasoline and it will lower your emissions.

Article on automotive use:
http://nabc.cals.cornell.edu/pubs/nabc_19/NABC19_5Plenary2_Ramey.pdf

Key excerpts:
"In comparison to gasoline and ethanol, butanol is hard to ignite and it burns with a cleaner flame; it is combustible but not dangerously flammable as is gasoline"

"I drove to the EPA station in Springfield, OH, using butanol I had made in the lab from sugar and corn. They were amazed by the test results: butanol reduced hydrocarbons by 95%, carbon monoxide to 0.01%, and oxides of nitrogen by 37% compared to gasoline."

Picture of butanol burning from YouTube still:

Obviously an internal combustion engine is a pretty different than an alcohol stove, which is why I'd love to try some.

There a few bottles of it on eBay, but none of the sellers will ship it to Canada due to hazmat regulations. If anyone wants to be so kind as to relay a bottle up to me (just leave off the return address to cover your butt) send me a PM and I'll fund everything.

http://www.ebay.com/itm/N-BUTYL-ALCOHOL-99-5-Glass-Bottle-500ml-REAGENT-/120711460848?pt=LH_DefaultDomain_0&hash=item1c1af6b7f0#ht_500wt_922

http://www.ebay.com/itm/1-Butanol-Reagent-ACS-99-9-500-ml-/390372846775?pt=LH_DefaultDomain_0&hash=item5ae408ecb7#ht_500wt_1021

[Dan @ Durston Gear]

I got an email back from one of the major butanol producers. It sounds really promising….especially with an easier lighting wicking stove like the Starlyte that I'm using. I've possibly found a place that will sell me some butanol for testing. Hopefully they don't cancel my order.

"Butanol packs more energy than methanol or ethanol, so use for camping might be easier in some ways as you would have to carry less fuel.

The issue with butanol is that it is harder to ignite. The flash point is 35C compared to 14C for ethanol and 11C for methanol. The enthalpy of combustion (energy released) is 2670 kJ/mol compared to 1370 for ethanol and 715 for methanol (this is due to the extra carbon bonds that you can break) so you will generate more heat energy if you can get the butanol lit. Once burning you will not generate anything more dangerous than you would with methanol or ethanol – the combustion products are exactly the same.

Bottom line – don't know exactly how it would work in your stove, but the best way to find out would be experimentally to see if the difficulty in lighting the alcohol overrides the benefits that you would get in carrying less fuel, and also if the slightly harder procurement for butanol is worth the effort.

If you try it and it works, let me know."

Tim

Dr E. Tim Davies
Chief Technical Officer
Green Biologics Ltd

[James Klein]

From his own numbers, it appears that butanol would be ~20% better than ethanol.

Butanol has a molar mass of 74g/mole
Ethanol has a molar mass of 46g/mole

Therefore enthalpy of combustion would be:

36kJ/g for Butanol
30kJ/g for Ethanol

Also, I didn't check to see if he provided the lower or higher heating value for them but the lower value factors in heat required to turn the water formed during combustion into vapor and therefor is a better value for comparing fuels….

[Dan @ Durston Gear]

Thanks James.

After a bit of background reading, I understand how you're converting from MJ/mol to MJ/gram, and that MJ/gram is really the most important number as it tells us how much heat we are getting out of the weight.

So butanol is 36.6 MJ/gram, whereas ethanol is 30.5 and methanol is 19.7, for a theoretical advantage of 20% over ethanol and 86% over methanol.

It seems some actual testing is needed to see how this stuff burns.

Here in Canada, it's virtually impossible to buy ethanol. Butanol is tough to get because it needs to adhere to hazmat regs, but pure ethanol (even methylated spirits/denatured alcohol) is actually illegal, so short of smuggling some across the border you can't get it. So far this has left me using methanol, which burns nice but is at a huge theoretical disadvantage.

American's can buy pure butanol here for $10/pint:
http://www.enasco.com/product/KM00551M

[Bob Gross]

If this is impossible to buy in Canada, and if it is super expensive to buy in the U.S., then why do you bother to consider it?

–B.G.–

[Dan @ Durston Gear]

Ethanol is illegal to possess in Canada, while butanol is just expensive and tricky to ship (must go ground).

I've come across online stores that sell a one gallon jug of butanol for about $25. It sounds expensive compared to methanol (about $10/gallon locally) but it's still cheap compared to using a canister stove. A gallon would do me for the summer.

The main attraction is those week or longer hikes where I'm carrying a full quart of methanol for my wife and I. If I could carry pint of butanol instead (which would weigh about 60% as much) that would be a big gain. It would also make even longer trips possible. With the fuel weight I save, I could add an extra day of food.

[Roger Caffin]

> Once burning you will not generate anything more dangerous than you would with methanol
> or ethanol – the combustion products are exactly the same.
That statement is VERY suspect. One could use exactly the same argument with propanol – but we know that it produces real nasties. I suspect the guy is just ignorant of this as he is focused on car use. Also, not a lot of research has been done on the toxic combustion byproducts of butanol.

"Consumer acceptance may be limited due to the offensive smell of butanol."
Wikipedia.

http://www-personal.umich.edu/~mswool/publications/Karwat%20J_Phys_Chem_A%202011%20115%204909-4921.pdf
Research into burning butanol – note that there are four isomers of this btw. I quote:
"butanol is more attractive for application to aviation,
transport, and storage as compared to ethanol, although toxic
pollutants such as aldehydes and ketones, which are harmful to
health, are formed as combustion byproducts from both ethanol
and butanol."
"Osswald et al.6 studied fuel-rich (φ = 1.7), low-pressure flames
of the four isomers of butanol using molecular beam mass
spectrometry. The authors were able to identify 57 chemical
species, including radical and isomeric species, at various heights
above their porous plug burners using a combination of electron
ionization and photoionization mass spectrometry. The authors
were able to characterize pollutant emissions and soot precursors
from the flames of the four isomers, with fuel structure significantly
influencing the concentrations of these products; high
concentrations of formaldehyde and acetaldehyde were detected
in n-butanol flames, and while tert-butanol flames produced low
concentrations of oxygenated intermediates, they did produce
higher concentrations of propargyl and benzene"

Guinea pig stuff if you ask me.

Cheers

[Dan @ Durston Gear]

Yeah it is guinea pig stuff…it seems like such a hard thing to really figure out.

"Consumer acceptance may be limited due to the offensive smell of butanol."
I've read conflicting things on the smell. This quote says it smells offensive, while other sources have said it smells pleasant like a sweet wine.

I didn't want to pay $12 to get the full article, but this paper below tested the intensity and pleasantness (or unpleasantness) of butanol on a subject group. The abstract says that the smell was generally pleasant below 300ppm, neutral at 300pm and then unpleasant above that.

http://psycnet.apa.org/index.cfm?fa=buy.optionToBuy&id=1975-00150-001

[Ryan Smith]

Everything I've read makes it sound like it's no more toxic than ethanol which many already use currently. Keep in mind I'm not a chemist however. Colin Krusor seemed pretty sharp on alternative fuels in a thread about 6 mos ago. You should PM him for his opinion.

http://www.dow.com/productsafety/finder/nbut.htm#HealthInfo – says it smells like bananas.

Ryan

[Dan @ Durston Gear]

"n-Butanol occurs naturally as a minor product of the fermentation of sugars and other carbohydrates,and is present in many foods and beverages.It is also a permitted artificial flavorant in the United States,used in butter, cream, fruit, rum, whiskey, ice cream and ices, candy, baked goods and cordials. It is also used in a wide range of consumer products."

Not to say that nasties aren't produced when it burns though….

[Colin Krusor]

Dan, I agree that longer-chain alcohols seem to be a promising alternative fuel for alcohol stoves. I think they merit a bit of experimentation, at least. I won't bother posting the link to the other thread I started on this topic a while ago because the content is the same as this one.

Why do you consider butanol but not the higher alcohols? The heat of combustion goes up more or less linearly with the number of carbons. I was considering doing some experimenting with hexanol or heptanol. Both of these have very low toxicity and their odors are not unpleasant. They are used extensively in consumer products, including widespread use in perfumes. Hexanol smells a bit "green" or woody to me, a bit like broccoli. I think heptanol smells like mown grass. They are more oily and less volatile than the short-chain alcohols, so a spill is a bit more of a mess, but they are less toxic than HEET. Octanol and nonanol could be considered, but in winter they might solidify, and even in warm weather it might be difficult to get them to vaporize in a conventional alcohol stove.

If I remember right, I think I calculated that a backpacking trip requiring 6 ounces of HEET would require 3.3 ounces of hexanol. If an alcohol stove can be modified to achieve and maintain a good hexanol or heptanol flame and minimize soot at a range of temperatures and elevations, then I would use them routinely. They are more costly than HEET, but still cheaper than gas fuels in canisters.

[Dan @ Durston Gear]

"Why do you consider butanol but not the higher alcohols?"
Honestly I don't know much about chemistry but I thought I'd look into other alcohols to see if one had a higher energy density than ethanol. Butanol was the first one I came across that sounded promising.

EDIT: Now that I look into this a bit more. The flash point might be a bit of a concern with the higher alcohols. Butanol is supposed to be kinda hard to light with a flashpoint of 35C (vs. 11C for Ethanol). Hexanol and Heptanol are 59C and 70C respectively, so it might be hard to get them going. Maybe you'd need a bit of methanol/ethanol to light the stronger alcohols.

"I was considering doing some experimenting with hexanol or heptanol."
I'm surprised there's fuels out there that have huge theoretical gains that seemingly no one has tried. Perhaps responsible testing is just too hard to evaluate safety? I'm going to do some more reading on hexanol and heptanol and see what I can dig up. I'll also try to buy some. My possible lead on getting butanol fell through, so I'm not sure how to get it in Canada. Lots of it for sale in the USA but no one will ship international. I'll see about these other fuels….(EDIT: They seem pretty darn hard to get too here in Canada).

[James Marco]

Dan, I think you will run into the incomplete combustion problem I have with anything longer than one or two carbons in a non-presurized stove. Even propanol never quite reaches the full efficiency it could because of this.

Basically, oxygen and carbon hydrogen alcohols form all sorts of strange shapes. Isopropanol is one that is widely known. Butanol is a longer chain. As a somewaht incorrect model for conceptulizing it, the oxygen can only attach at the outer ends, then these react, then there is an odd carbon hanging around that needs another oxygen. So think of this as a two stage burning process…it doesn't happen instantly. Propanol takes some time to burn. In a pressurized stove a small amount is mixed with a LOT of air then burned. In a regular alcohol stove there is just not enough air mixing to complete the combustion, soo, you get free carbon comming off…soot.

With methanol (HEET) and ethanol you get pretty clean burns. One carbon burns in one shot (again, not really correct.) Ethanol has two ends, and no middle…it burns in one shot too. Anything longer will require a delayed and ionized flame to be maintained for longer to complete the burn. Longer chains like hexanol could require up to three passes by my poor model. It does help to predict that you will get soot, lots of it, without some sort of super mixing. This super mixing is usually accomplished with pressure and a small jet. Just my two cents…

Remember, it is really only a model and works up to a point, only.

[Colin Krusor]

It occurred to me that one could mix hexanol or heptanol with a low boiling alcohol like methanol. I did a bit of looking and couldn't find any information about azeotropes of binary alcohol mixtures, so I don't know exactly what vapor composition you'd get, though.

Does anyone know the azeotrope for methanol and heptanol? I don't have a copy of the CRC or any other good physical chemistry reference books and the tables online are very limited. If your mixture is 10% methanol and 90% heptanol, and the vapor above the pool is predominantly methanol, then the stove would light about as readily as a pure HEET-filled stove. The initial methanol flame would gradually bring up the temperature and pressure of the stove, and by time the heptanol begins to boil, the methanol should be just about gone. This all depends on the composition of the vapor.

This would take care of the lighting problem, but would not address the issue of incomplete heptanol combustion. I wonder if very tiny jets might help to introduce more oxygen…

[Dan @ Durston Gear]

"I think you will run into the incomplete combustion problem I have with anything longer than one or two carbons in a non-presurized stove."

This could well be the case. From the brief video of butanol burning on Youtube (0:14 @ http://www.youtube.com/watch?v=s09ujb35w4s) it looks like it's burning pretty well (ie. non-smokey) just sitting in a dish, but the clip is really too short to judge and visuals aren't everything. Your explanation sounds reasonable, although I'd still like to try and burn some. Have you actually burned alcohols with more than 3 carbons before? It could be that thee carbon IPA simply burns poorly for other reasons, but if lots of higher carbon fuels combust incompletely, then that's a bad trend.

[Dan @ Durston Gear]

Well it's been nearly a year, but I've finally got some butanol ordered by someone who isn't going to cancel my order. I spoke with them on the phone today. Delivery is still 4-5 weeks out, but I'm just thrilled that it's coming.

First, I'm going to see how well it burns in my existing stoves, and I'll try it with a little methanol mixed in to see if there's any advantage to that. Most likely I'll need to design some sort of pressured stove – I've got a few neat ideas.

[Franco Darioli]

Just a quick comment about lack of availability for Ethanol in Canada ( I also see sometimes comments from the US too…) I suspect that sometime folk don't look in the right place.
For example a quick search found a product called PHAB Marine Alcohol (90% Ethanol, $20 for 4 liters) but I would think if you look where industrial cleaning products are sold you will also find something similar to that.

[James Marco]

Hi Dan…yeah, keep us informed.
I suspect you will simply corrupt the methanol/ethenal. It really doesn't matter about the blends. The molecular combustion will remain pretty much unimpaired. The butinol componet will still burn sooty.

I mixed all sorts of stuff in an open alcohol burner. There is simply too much fuel for the air. Some sort of presurized jet, a lot like a cannister stove, is needed to really pump air into the fuel/air mix.

I tried WG, parafin, kero, benzene, some fairly pure octane, acetone, etc… lots of mixes with plain old petrocarbons. All have a similar problem. If you add more than about 1-3% of these, they all burn sooty. That isn't enough to boost fuel heat. Even ispropinol does about the same, but I have never gotten it to burn efficiently even though there are some commercial stoves out there. After the alcohol is burned off you simply burn the carbon/hydrogen. This is the same with all longer chained alcohols and simplistic petrochemicals(butane, propane, etc.) Follow? Note that is is NOT really what is happening, but fairly well approximats alcohol's burning.

I think I would research a platinum catalyst, similar to the platinim coated meshes found in labs. This is expensive as hell, though. But this would lower the energy needed for complete combustion…sililar to those found on kerosene heaters. (Note that the coatings on that stuff is extreamly thin, 2-3 molecules thick electroplate. Even touching them will damage the coating…never try to clean them mechanically.) Once the catalyst gets hot enough, it will produce good heat. But, if you are going to use a catalyst, why bother with alcohol? Even WG has much higher heat…

[Dan @ Durston Gear]

Thanks for the comments guys.

Franco: Yeah I have found a source for ethanol here in Canada. It did take a while because even though it's not restricted a lot of places will only sell to schools or industry to cover their butts. This place that is selling me the butanol seems reasonable and happy to sell me other stuff as well.

James: Good comments. I suspect some sort of a pressured design is what I might end up with. I've got a few wild ideas for a self pressuring alcohol stove. It'll probably not work out, but it'll be fun to try.

The idea with a methanol mix would just be to get it started if butanol proves tough to light. I don't think it will be tough to light, but in cold conditions having some methanol in the mix to get some extra vapor might be good. I think I'll have bigger problems than this though.

[Dan Yeruski]

Hey Dan, did you ever get your butanol?

Have you tried a "coil" type burner? Using an alcohol primer might get it to working for you. Ebay has some nice ones. The Taykit comes to mind.

I'm doing some research on butanol and came across your thread.

[Dan @ Durston Gear]

No. The company that was going to sell to a Canadian like me ended up not being able to order it (or some lame explanation like that). Colin (Kursor?) did manage to get some, but as I recall it burned quite smokey.

As you mentioned, a self heating / coil stove might do it. There was one stove on YouTube where a lower stove heated the upper stove, which ended up getting super pressurized (and also maybe dangerous). The key would be a design where the added complexity/weight don't offset the gains from butanol.

[Author]

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