Experiments with catalytic oxidation of acetone vapor via heated copper

[Anonymous]

I did some experimentation with the above earlier on.  Learned some interesting things. But first, some pretty pictures in the next post.  : )

[Anonymous]

[Anonymous]

Learned a couple interesting things.  I thought the oxidation process might spread eventually to other parts of the coil after heating for awhile.  Not that I’ve observed.  I think this is 6 copper wire, and I wrapped the coil somewhat densely. Since I was heating it with a micro butane torch, it took awhile to heat up a good portion of the coil. Sticking it over a canister stove should work better at heating more of it and more uniformly.

Another interesting thing is that putting a pretty air porous, pre filter with activated charcoal in it, over the top of the container was enough to slow down the evaporation, and thus oxidative burning, which heats the copper.  It basically stops the process if kept on there.  Wasn’t quite expecting the latter.

A further surprise is how long the acetone lasts (I thought it would evaporate much more quickly, especially with the heat of the copper coil interaction with same).  I put less than a half ounce in an aluminum bottle shortly after the above pics were taken (quickly transferred it from glass container to Al), and it’s still going strong about 45 minutes later.

The aluminum container (a Al water bottle, with a somewhat narrow top), is getting hot, but not near as hot as the glass container got.  I think it’s because the Al bottle is reflecting the IR radiation, and more heat is being vented up through the top opening, rather than directly conducting through the Al (except for where it’s directly touching the bottle).

If I black, hard anodize the bottle, it should conduct and radiate the heat out via the Al material itself a lot more.

So far, I think this does have some potential of being a heater within an insulated tent (especially if combined with a couple to few small beeswax candles), provided it’s flue vented.

[Anonymous]

Ok, now I’m confused. I just re-checked it, and surprisingly the Al bottle was cool to the touch.  I thought that all the acetone must have evaporated.  Took the coil out and looked, and there was still some liquid in there.  There was some orange powdery coating on some parts of the coil. I guess copper oxide?

If enough copper oxide (or whatever it is) builds up on the surface, I guess that stops the process?  In that case, might not have that much potential to be a good heater.

 

[R]

https://backpackinglight.com/forums/topic/50655/#post-1759979

Seems acetone may only produce 30% more energy than methanol. Will that offset the weight of your catalyst for the output you’re interested in? Maybe try a copper dish scrubber?

Paraffin has a higher energy density than gasoline. Maybe experiment with carbon felt wick? Also, try searching BPL on paraffin stoves to get up to speed on the current state of that art. Since you’re not cooking on it you may be able to relax some constraints.

 

[Anonymous]

It might be worth trying a copper dish scrubber Rene.  I went with the heavier, thicker copper initially because I had read some Y.T. comments indicating that experiments with thin wire, indicated the copper got hot enough to melt.  That’s why I did the long coil of thicker wire, to better distribute the heat.  It’s hard to see in the pics, but only about 40% of the coil was being directly heated via the oxidative process.

Yes, been doing some testing with wax as well.  My first one was with an alcohol stove that’s based on the general fancy feast/tomato can design, but a little fancier than same.  I put a carbon felt piece vertically around the outside ring, and another piece inside.  It does burn pretty hot and technically works, but the combustion is less efficient than I would like–primarily yellow flame, pretty sooty, and no doubt produced plenty of CO.  I used primarily soy wax for it.

I’ve already started building a new heater specifically designed for wax.  It’s a round, thin walled tin with a screw top lid.  I bent some copper tubing into an inverted U. I plan to drill a few small holes at the top of the Cu tubing.  The tubing will be placed through the lid and sealed in.  Some carbon felt will be threaded through the tubing, to hang a bit out of same on both sides. Wax will be placed in container body, the lid screwed on tight. Some insulation will be placed over the top and sides of the tin (probably wool).

The tin will be lifted up to place a couple small beeswax candles under it as a pre heater of the wax in the tin.  I’m hoping that as the wax heats up, it builds some pressure, and the vapors are channeled up the tubing to the top holes, mixing with the outside air in a controlled manner to get a more clean and complete combustion.  I really like beeswax candles–especially their smell, and meanwhile they will provide some light and a little heat that I can warm my hands on at least.

I’m going to try it like this first, and if it doesn’t work so well, I may modify it with another hole drilled into the copper tubing, but near the base, a small nozzle placed in pointed up, connected to some tubing that will have a simple control valve towards the beginning of the tubing, and a large blown up balloon attached on the end (with an extra balloon handy to blow up when the other one gets low).

I’ll post a pic when I’m done building the initial design.

 

 

 

[DAN-Y]

You’re on a scientific roll :-) look forward to the outcome.

[Anonymous]

Thanks, but might not be, did you see this?  “If enough copper oxide (or whatever it is) builds up on the surface, I guess that stops the process?  In that case, might not have that much potential to be a good heater.”

This occurred about an hour into heating the copper, and there was still some acetone left. There might be a way to slow down the formation of copper oxide or whatever formed on the surface, which apparently stopped the process, but I don’t know how.  Maybe soak it in some vinegar and let it dry without rinsing it off?

I’m looking forward to the wax stove testing though. If it works decently, it will solve some the main problems of wax–inefficient combustion, flaring up and popping.

[DAN-Y]

You have the “determination” for the wax stove to succeed, stick with it…..nothing ventured, nothing gained!

[R]

https://backpackinglight.com/forums/topic/another-wax-stove/

In particular, last post on page one.

Edit: just saw your post on this thread.

[Anonymous]

So far the prototype does not work at all.  I think it’s just not getting enough air within the body, or at the top, and the wick is not exposed, and I didn’t get it hot enough (I didn’t have a lot of time to fiddle with it today).  The carbon felt thread through the copper tubing probably slows down the circulation of air and wax vapors (might try for a much thinner piece).  I think I need to make the top holes bigger, pull some of the carbon felt through, and make the air intake hole on the side wall of the container larger–right now it’s like a pin hole (you can’t see that from the pic).  I also think the container is too small, and the copper tube might be too large/wide.

If I’m relying on converting the liquid wax into gas vapor within the container and using pressure to direct it up, maybe I don’t need a wick to begin with?

I’m not sure this heat-pressure to concentrate and push the wax vapors up the tube to top holes is even tenable (without serious machining and engineering above my pay grade).  I’m waiting on a larger container and some smaller copper tubing.

If further modifying and prototypes don’t work–I’ll move on to a type more similar to Jon’s.

A note about the pic, since this was a prototype and I wanted to able to re-use or modify the tubing, to make it temporary I just hot glued it in–which is part of the problem since it melts before the wax reaches vaporization temps.  For paraffin wax, it’s around 700*F.  I’m not sure about soy wax (I’ve just generally read that “vegetable oil” is about 570*F).

[Anonymous]

I’m not sure the above design is practical.  Even if it’s well insulated, it will take a long time and a lot of energy to heat the soy wax up enough to vaporize it, I think.

The idea was to use my canister stove to start the heating process since I’ll be bringing that to primarily heat water/food (it’s pretty efficient, albeit somewhat expensive heating/energy source), and then keep it going with some beeswax candles, which will have the added benefit of some light, nice smell, and a little extra heat.  Once the process is jump started and the top burners are lit, then hopefully the copper tubing would conduct heat back down into the wax to keep it going. Might have to keep a candle under it though.

(For those who haven’t read the other threads,this is meant to be a tent heater in a small, insulated tent, not a cook stove. Hence it’s meant to run longer, at lower output to combine heat with a couple to few smaller regular candles).

Still plan to do some experimentation and tweaking with it, but leaning to think it’s too energy intensive of a process to be practical.

When I get the larger “tin” (steel) container and smaller copper tubing, I plan to just braze bond it, then run it at higher temps and for longer, both with wicks and without wicks through the burn holes.  Problem with that though, is if the burn holes are too big, it won’t provide correct pressure and mixing of gas vapors to air, and if too small–can’t use wick material.

Might just have to build two different types and see which one works best.

[R]

Justin,

Try plumbers solder to seal the copper pipe. Everything you need should be at your local hardware store. You might also find luck with compression fittings.

Are you familiar with the alcohol stoves of similar design? The challenge in attempting this with wax is liquifying the fuel in the reservoir. Priming with another stove may get you started, but you still need to transfer enough heat down from the wax flame to keep it liquid. You could extend the copper pipe down in to the reservoir, but this would present a problem opening a screw top canister when the wax is solidified. Maybe a metal reservoir will do the trick?

All of your vaporization should be happening in the pipe at the flame ports, where the heat is. If your wick can’t draw the fuel that far up, it won’t work. You could easily verify this by dipping various sample wick materials in your candidate liquid fuels, holding the wick vertical, and measuring how far up the fuel climbs.

I don’t see a place for an air inlet in this type of stove. An inlet requires a negative pressure, generally achieved with a Venturi. That requires a fluid stream, generally achieved with a thermal updraft. And that requires a duct extending above a heat source. Your stove has the heat source at the top. No draft, no Venturi, no negative pressure to draw air in.

The alcohol versions of this design put a loop in the pipe with the flame port at the bottom pointing up. They might be called coil stoves. The port directs a stream of gaseous fuel at the upper portion of the coil. That acts as a flame holder generating a lot of (loud) turbulence, mixing air in to the fuel stream for an efficient burn. It would be interesting to see if this process is sufficient for the heavier lipid molecules to burn completely.

[Anonymous]

I’m pretty new to cooking type stoves in general  Up until about a couple years ago, I did mostly no cook. Then I bought two alcohol stoves and tried them out for a bit, then two canister stoves, which I’ve stuck with more.

So I’m very much still in a learning phase with trying to figure out how these actually work and how best to build them, cause I didn’t ever give it much thought up until very recently (let alone wax)..

I appreciate the different suggestions, tips, and explanations of concepts.  .Likely I’ll have to read and re-read, and ponder it some.

Agree that the copper tubes down into the wax could be problematical, but since this will be a run  long time heater and not a cook stove, I’ll likely run mostly out of fuel most of the time, and/or have to get into the habit of remembering to take off the top, shortly after, so I don’t run into that.  But with this design, you’re right, I most likely would need the thermal feedback from the copper tube to help keep the process going.

I think it could possibly help the whole process by insulating the main body, and part of the tubes pretty well. An alcohol stove wouldn’t need that, but it might be a lot more crucial for a wax stove?

I’ll look up coil alcohol stoves, etc.  Thank you.

[R]

Ya know, if you only inserted one end of the pipe in to the lid and reservoir, sealing the other end, you could center it in the lid, which would make it much less of a problem to unscrew the lid when the wax is solid.

Minimizing the region that reaches the vaporization temperature means a quicker cool down for a cleaner snuff.

[Anonymous]

Good points Rene.

[Author]

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