blended butane failure

[Bob Gross]

I had one Coleman 3250-702T blended butane canister, 220 gram size, to fuel my Gnat stove. We used it without problem on the first and second evenings, and the second and third mornings. The temperature had been a little cool, 30-35 F, so the blended fuel separated somewhat (at least according to the theory) and the lighter fraction burned off. On the third evening, the flame reduced to a fizzle and then stopped completely, even with the temperature around 40 F. As I shook the canister, it seemed to be almost half full by weight, yet there was no feel of liquid sloshing. We set it aside and tried it again on the fourth morning, but it wouldn't do anything. A different butane canister carried us along for cooking.

In all cases, I had a simple aluminum foil windscreen around this, tall enough for the top of the cook pot. I would think that some warmth was projected down to the ground to slightly warm the canister.

Once I got it home and allowed it to assume a warm ambient temperature, it worked fine. I think that helps prove the theory.

What can I do to avoid a similar problem in the future?

–B.G.–

[Greg Mihalik]

Put a new canister in the 'fridge (it should be about 38°) overnight.

Then test it with the gnat.

[Bob Gross]

"Put a new canister in the 'fridge (it should be about 38°) overnight.

Then test it with the gnat."

This helps me avoid a future problem how, exactly?

–B.G.–

[Jerry Adams]

1 – use iso-butane instead – good maybe down to 20 F

2 – use inverted canister stove

3 – warm up the canister in your pocket/sleeping bag, then wrap a 1.5 foot aluminum or copper #18 or #16 wire around the canister and up into the flame so heat is conducted to canister

[Bob Gross]

The Coleman blend is about 80% isobutane.

The canister was warmed in the foot of my sleeping bag overnight. Still, when the burner was attached and fuel control turned, nothing flowed.

I do have a remote canister stove, but it is much heavier than the Gnat. I suppose that I can stand up the canister to be inverted.

–B.G.–

[Greg Mihalik]

"This helps me avoid a future problem how, exactly?"

You will know if the mix is sub-par for cold temps.

Or maybe I don't understand what you mean by "future problem"?

[Bob Gross]

Nearly all of the blended butane fuel is either 70% or 80% isobutane, so I have little choice beyond that in fuel. Is there one brand that works better?

I'm sure that if I refrigerator tested it in a similar fashion to last week's situation, I would get about the same result.

The only way that I can see to avoid the same result in the future is to heat the canister with a lighter or candle in advance of each use. That would keep the fuel mix more evenly blended as the first half is used.

We used lighters and candles this way thirty years ago before blended fuel was popular. You just have to make sure that you don't heat a seam, and if it gets too hot to touch, then you've gone too far.

–B.G.–

[Stuart R]

Bob – with propane/butane blend on an upright canister stove, the propane gets burned off quickly regardless of the temperature of use. When the canister is half empty there will be practically no propane left, just butane. However, if the blend really contained iso-butane, it should continue to work down to 25-30F. I don't know what Coleman canisters in the US contain but over here it is definitely propane/n-butane which is not good below 40F.

Another thing that happens in the cold – rubber washers and o-rings get harder, so when you screw the stove onto the canister the rubber does not compres as much and sometimes the pin on the stove does not depress the valve in the canister sufficiently. The Pocket Rocket is particularly bad for this, but the Gnat has only a small o-ring so I wouldn't expect this to be a problem, but something to check…

[Jerry Adams]

That doesn't make any sense

I used something that was cheap ("Burton" for $2.50 at Fred Meyer for 220g) and I think was butane, maybe with propane, and it worked down to 32 F, but pretty slow.

I've used Giga Power and MSR isobutane down to almost 20 F and it gets slow but works.

Maybe something wrong with that canister or Coleman in general? Maybe it's butane, not iso-butane?

[Jerry Adams]

Google says Coleman 3250-702T is butane/propane, not iso-butane – that should just barely work at 32 F

[Jerry Adams]

And warming it ahead of time will work for a while, but as it burns and the butane evaporates inside the canister, it quickly cools off.

[Bob Gross]

I grabbed one of my Snow Peak Gigapower GP-500G (450 gram) canisters off the shelf to see how different it was according to the label. All of the labeling is in Japanese!

–B.G.–

[Bob Gross]

It sounds like this Coleman fuel is a poor choice for freezing temperatures.

So, what is the best choice? Snow Peak or other?

–B.G.–

[Jerry Adams]

Google says it's iso-butane (and 15% propane).

Never made any sense to me to have any propane, because it you're at the lower temperature limit, the propane will outgas first leaving just the iso-butane – that's what's important, to have iso-butane not butane.

If you had just iso-butane, theoretically, the pressure would be a little less so you have a lighter weight canister.

[Jerry Adams]

I've used Giga Power and MSR. I think they work the same. The Giga Power may be a little cheaper. Or whichever one is available. Or other brand that says iso-butane.

The "Burton" brand said "high performance fuel" and said "butane" on the checkout receipt. Don't buy that. And don't buy Coleman.

[Bob Gross]

I think I may have purchased the Coleman fuel at a small shop. I usually purchase Snowpeak or MSR at the bigger REI stores which commonly stock more than one brand.

There are some small differences in the weight of the contents, so the cheapest canister may not be the best buy.

–B.G.–

[Roger Caffin]

Hi Bob

Coleman is n-butane/propane, and n-butane boils at 0 C. When the stove has been burning for a few minutes the canister is likely to be sub-zero. What you are burning then is mainly the 30% propane.

Options (which may be all used together):
* use a canister which is labelled 'isobutane/propane'
* use an inverted canister stove, with the canister inverted
* put the canister in a dish of luke-warm water
* put a windshield around the stove so the canister gets warm to the touch (but NOT 'hot')
and of course:
* subscribe to BPL and read our many comprehensive technical articles on all aspects of this subject.

Cheers

[Stuart R]

Oh no Roger, not you as well!
n-butane boils at 0 C… What you are burning then is mainly the 30% propane.

The vapour pressure vs temperature of butane is a smooth curve, 0C just happens to be 1013mB. Similar smooth curve for propane, just higher pressure at any given temperature. For any blend of propane/butane, the partial pressure of each component is the same smooth curve of the pure companent just reduced by its mole weighted fraction. The net result is that the ratio of the two partial pressures is almost independent of temperature, meaning that the ratio of propane/butane in the gas mixture is almost independent of temperature.

The ratio of propane/butane in the gas state depends on the ratio of propane/butane in the liquid state (vapour pressure), but NOT on temperature.

So, if the GAS is say 50% propane at 10C, it will still be 50% propane at -10C

I'll forgive if you plead advancing years ;-)

[James Marco]

Stuart, this explanation is wrong.
Vapour pressure, while describing a smooth curve as you say, does not quite act like that at the boiling point of materials, nor, the freezing point. This is why ice is found in a vacume, yet we know that it can melt to water and boil off as steam. But that is a single component system.

The boiling point of the n-butane is higher than for propane. This is where the actual problem lies. On Bob's stove, he boiled off the propane in the fuel mix and never recovered enough heat to boil off the n-butane. He should have applied more heat to the system, somehow. Inverted canisters simply supply liquid fuel to a stove. They provide "heat" to the canister by increasing the pressure locally, in the preheat tube. This pressure cannot be supported in a cold canister so it "condenses" in the fuel, causing the temperature to raise. Not really by conduction. But a remote canister will get warm, anyway. Like making capuchino, steam is used to cook the milk by raising the temp of the milk. Boiled fuel heats the entire canister, not just the preheat tube.

What you describe is incorrect in that you say the ratio of components in the gas remains the same. Not true. The difference in ratios for boiling off liquids changes quite a lot. A good example is distilling alcohol. In a water/alcohol mix, it would be impossible to distill alcohol acording to your explanation. Pressure and temperature are RELATED, indeed, numbers are usually given for STP, standard temperature and pressure. In a closed system, such as a canister, it is no more complicated than making moonshine. About the best that can be done is 95% alcohol and 5% water even though you never boil the water. The vapour pressure increases enough to carry over in the distalate at about 5%. The same for gas canisters, propane boils off but the vapour pressure of the n-butane is high enough to burn off some. So, you might burn off 95% (sorry, I never looked up the vapour pressures for n-butane) propane. Roger said "mainly the 30% propane". Quite correct.

It is possible to have one component liquid but not boiling and the second component at, or slightly above, it's boiling point. This will change the ratio of the gas mix a LOT. Conversly, by dropping the temperature to below the boiling point of one component (n-butane in this instance,) it is possible to boil off the other (propane.) Of course, they will form a euctectic at some point, so you will likely not be able to boil ALL the propane off. Also, by reducing the temperature below the boiling point of n-butane, you CAN force some of the gas back into the base solution, again changing the ratio of the gas mixture compared to the base mixture.

[Stuart R]

Sorry James, I disagree.
"The boiling point of the n-butane is higher than for propane."
That much is true. The vapour pressure of pure n-butane is 1013mB at -0.5C : that is the definition of boiling point. For propane it is -42C.
Now, when you have a mixture of propane and n-butane, you don't have two boiling points, you have only one and it will lie between the two temperature given above, depending on the ratio of the two components of the liquid. Specifically, it depends on the molar weighted fraction.

"What you describe is incorrect in that you say the ratio of components in the gas remains the same" and "propane boils off but the vapour pressure of the n-butane is high enough to burn off some"
I think you misunderstood me. Of course the ratio changes as the gas is used up by the stove, that is the entire reason the stove stopped working. What I was trying to explain was that at any point in time, the ratio of the gasses does NOT depend on temperature. A new canister with 30% propane and 70% n-butane as liquid will have around 65% propane in the gas mixture, regardless of the temperature. The % propane will go down as the fuel is used so that at some time later there may be 25% propane in the gas (and a lower % in the liquid), but that will not be a function of temperature.

"It is possible to have one component liquid but not boiling and the second component at, or slightly above, it's boiling point. This will change the ratio of the gas mix a LOT."
No, the liquid that is below the boiling point of the pure substance (butane) will still be evaporating due to its vapour pressure. There will LESS of it in the gas state than the other component (propane), but not none. Same as with your alcohol example: you always get water vapour coming off the mixture (as well as alcohol), even at temperatures well below 100C

[Kevin Babione]

Come on – be a man and shake the canister while you're using it to keep the fuel blended.

Sorry – couldn't resist…

[Jesse Anderson]

"Now, when you have a mixture of propane and n-butane, you don't have two boiling points, you have only one and it will lie between the two temperature given above, depending on the ratio of the two components of the liquid. Specifically, it depends on the molar weighted fraction."

I don't mean to be too blunt, but this is completely wrong. You do indeed have two very different boiling points. That is the very basic premise of refining oil. If a variety of combined hydrocarbons had a singular boiling point, the entire distillation process would not function and you would never have the two separate products in the first place.. No amount of mixing will ever change the boiling point of either component. They will always work off of their own unique curve.

[Stuart R]

So Jesse, you are saying that crude oil can be heated to the boiling point of some particular chemical, octane say, and then that chemical and no others will boil off?

How do you think mixtures of chemicals such as naptha are produced?
By mixing together all the constituent chemicals after they have been separated?

[Jerry Adams]

If you use a propane/butane mixture at high temperatures like 50 F or whatever, will it maintain the propane/butane ratio more than if you use it close to 30 F?

The "accepted wisdom" is the opposite – if you use it close to minimum temp then most of the propane will be used up first so you're stuck with just butane which then doesn't work so good.

If the percent propane drops as you use it regardless of temperature, then the only thing that will work is to use a full canister if you're close to the minimum temperature.

[James Marco]

"…Now, when you have a mixture of propane and n-butane, you don't have two boiling points, you have only one and it will lie between the two temperature given above, depending on the ratio of the two components of the liquid. Specifically, it depends on the molar weighted fraction."

Sorry, I still don't see it except as a special case, ie eutectic. This defines the composition of the gas ratio's in a two part mixture at any given temperture/pressure and can be calculated. In a closed system, NONE of the components actually boils, soo, I do understand what you are trying to say.

But, this contradicts what you stated earlier:
"The vapour pressure vs temperature of butane is a smooth curve, 0C just happens to be 1013mB. Similar smooth curve for propane, just higher pressure at any given temperature. For any blend of propane/butane, the partial pressure of each component is the same smooth curve of the pure companent just reduced by its mole weighted fraction. The net result is that the ratio of the two partial pressures is almost independent of temperature, meaning that the ratio of propane/butane in the gas mixture is almost independent of temperature.

The ratio of propane/butane in the gas state depends on the ratio of propane/butane in the liquid state (vapour pressure), but NOT on temperature.

So, if the GAS is say 50% propane at 10C, it will still be 50% propane at -10C"

Temperature and pressure are HIGHLY and DIRECTLY related, not independent of eachother. To say that the composition of the gas in the canister is the same at 10C and -10C is incorrect. The pressure exerted on the can, from each component, can be calculated for each temp.

However you are correct in that the propane will burn first, but not exclusivlely, in most canisters. Above the boiling point of the n-butane, it will add a considerable portion to any flame. But they will still form a balance at any given pressure (or temperature if you prefer, nearly indistinguishable.) However, below the boiling point of n-butane, it will add only a small amount to the flame. This assumes a wide open jet, of course, as in Bob's case…not enough to burn.

" A new canister with 30% propane and 70% n-butane as liquid will have around 65% propane in the gas mixture, regardless of the temperature."

This is incorrect. At temps below the boiling point of n-butane, we might see a lot more propane. At temps above that we might see a lot less, since there WILL be a difference between raw vapour pressure at -10C and raw vapour pressure at 10C for n-butane. (Since propane is always assumed to be at or above the boiling point, I am ignoring that and calling it a one. We just add a bit of pressure to a highly compressible gas/or vapour pressure if you prefer to look at it that way.)
Again, temperature and pressure are related. The molar fraction of vapour pressure will only change slightly for propane. Burn it at those two temps, I will garantee you that in the lower temp case the propane will be the primary component and the canister will burn normally at the higher temp. The open valve, of course, reverts the system to a more STP like system, I sort of doubt there is ever any actual boiling inside the cannister, though.

[Author]

Posts