[Mubirin]

Im trying to make a fireless portable heat source and hit a brick wall on the chemistry side of things. I am looking for chemical combinations that can achieve a heat of at least 150ºC (302ºF) in under 8 seconds and maintain temperature for at least 2minutes.

Also, I have tried experimenting with calcium oxide and water. While the maximum temperature is sufficient, it takes about 5minutes to heat up. Are there any catalysts that can drastically speed up the reaction?

[Jasim]

What about oxidizing an alcohol, like potassium permanganate and glycerol?

[Honclbrif]

Is there any way to juice up one of those iron based hand warmer packs? Reduce the amount of inert binder, or include a mild oxidant instead of utilizing atmospheric oxygen? I wouldn't use too strong an oxidizer otherwise a fire could result.

[Jasim]

Sodium acetate recrystallization isn't going to get the temperature you want, but that might be a way to go. I wasn't thinking with regards to the fireless requirement, as stated oxidizing an alcohol has risk of fire...but not if it's in inert atmosphere. But I don't know how you are planning on containing this reaction.

[Arkcon]

I am looking for chemical combinations that can achieve a heat of at least 150ºC (302ºF) in under 8 seconds and maintain temperature for at least 2minutes.

Also, I have tried experimenting with calcium oxide and water. While the maximum temperature is sufficient, it takes about 5minutes to heat up. Are there any catalysts that can drastically speed up the reaction?

You want a temperature above the boiling point of water, from a solution in water?  Presumably not contained in a pressure vessel, but instead open, or in some sort of plastic bag?  Sorry, but your needs are simply not realistic.  You will have to rethink this from the ground up.  If the calcium oxide in water reaction is adequate, then you've decided to go with a different temperature, so you may need to restate the problem.

[Mubirin]

What about oxidizing an alcohol, like potassium permanganate and glycerol?

Yea, I'll give that a try. Thanks

Presumably not contained in a pressure vessel, but instead open, or in some sort of plastic bag?

I am using an air tight vessel.

[Arkcon]

I am using an air tight vessel.

The laws of physics dictate that a reaction in water reaches 100 C and then stops, until the water completely boils into steam, then it can get hotter (which of course, it won't since the water is no longer available) as the vessel fills with high pressure steam.  You will not achieve 150 C with an aqueous reaction.

[Mubirin]

I was using about one part water to 4 parts CaO. I think you'll find that the temperature goes above 100 degrees celcius. But you are right, for my purposes CaO is inadequate.

Either way, I intend to try potassium permanganate instead.

[fledarmus]

Have you looked at the total energy flow of your problem to find out just how many calories (or BTUs, or whatever your favorite unit is) you are trying to generate and what time scale you need to generate it on?

For instance, you want your reaction to generate a temperature of 150C. I can do that by spraying a solution of t-butyllithium through the air. Instant ignition, much higher than 150C. How much of what material are you actually planning on heating? What is the heat capacity of that substance?

Then you want it to maintain it's temperature for 2 minutes - once again, I can do that by pouring it into a vacuum flask. Apparently, however, you want this heat to be transferred into another object. In that case, it isn't the temperature of the object you should be concerned about, but the energy flux from the object. How much energy are you trying to transfer across what surface area, over what amount of time?

I could see the potential for a two-part reaction system in your process - one that generates a lot of heat very rapidly to bring your temperature up quickly, and another that generates heat more slowly, to maintain the temperature by adding energy at the same rate that energy is being radiated from your object. But the actual energy flows that you desire would be necessary before making any predictions about what reactions might be useful.

[Mubirin]

I apologize for not being 100% clear earlier but basically my goal is to heat 3-4 grams of a substance which has an approximate heat capacity (Cp) of 250 J/(mol K) at 25°C. So to heat up that substance to around 180-200 degrees, I'll need about 0.05 moles so I need about 2000 J of heat transfer delivered to the substance. This is not including compensation for irreversibilities so let's say around 2400 J will be required. Then I need to maintain it at 180-200 degrees for several minutes so a constant release of around 200-400 J/s would be ideal to counter irreversibilities.

So I'm looking for a chemical reaction which can do such a thing. You don't have to worry about the surface area since I've already given you the approximate energy requirements. I hope I've been helpful

[orgopete]

Im trying to make a fireless portable heat source and hit a brick wall on the chemistry side of things. I am looking for chemical combinations that can achieve a heat of at least 150ºC (302ºF) in under 8 seconds and maintain temperature for at least 2minutes.

Also, I have tried experimenting with calcium oxide and water. While the maximum temperature is sufficient, it takes about 5minutes to heat up. Are there any catalysts that can drastically speed up the reaction?

If I understand this correctly, it sounds as if the rate is limited by the mixing. Flour will explode as a dust, but you may have a hard time lighting a bag of flour. If your calcium oxide were of infinitely small particle size, then the reaction rate should be limited by the mixing rate shouldn't it? 

[billnotgatez]

I thought that the original post was looking for some reaction that was exothermic and not produce a fire.
We have mentioned CaO plus water, but the boiling point of water limits the temperature.

Would any other liquids react with CaO exothermically and do so at a higher temperature. Would it be safe to do that sort of reaction. Below is a link to a list of boiling points of common liquids.
http://www.engineeringtoolbox.com/boiling-points-fluids-gases-d_155.html

< >
By the way when Mubirin eventually posted specific parameters, I knew that my guess that he was trying to cook hamburgers without a fire was not what he was doing.
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[Mubirin]

So after a few weeks of experimentation with potassium permanganate and glycerin I still haven't got the results I really wanted. After putting the mixture in a pressure vessel I wasn't getting enough heat transfer. I could get a thinner copper vessel, but I'm worried I might end up winning a Darwin award. Infact, i think I might forget about using a pressure vessel altogether. We'll see.

fledarmus, you mentioned a 2 stage reaction. Maybe you could give a few suggestions. Here are the details you asked for just in case you missed it:

I apologize for not being 100% clear earlier but basically my goal is to heat 3-4 grams of a substance which has an approximate heat capacity (Cp) of 250 J/(mol K) at 25°C. So to heat up that substance to around 180-200 degrees, I'll need about 0.05 moles so I need about 2000 J of heat transfer delivered to the substance. This is not including compensation for irreversibilities so let's say around 2400 J will be required. Then I need to maintain it at 180-200 degrees for several minutes so a constant release of around 200-400 J/s would be ideal to counter irreversibilities.