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Making cheep oxygen

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john bunsenburner

Thu Apr 09 2009, 08:46PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

I am building a small oxy-hydrgen welding torch. It will be fed with hydrogen from a small reactor which uses Na2CO3 and Al to produce hydrogen. It will be kept at a temperature of about 80Â°C using a waste vegtable oil burner through which the solution will be pumped.
My problem is that I donot wish to invest in expensive canisters and regulators for oxygen, nor do i wish to have to make chlorate candles. That is why i am askign you, dear 4hv community, for help:

How could one produce a fair amount of oxygen cheeply and without the use of special equiptment?

P.S. I am happy to answer any questions you might have about the set up of said welding torch, and I am even more happy if you could give me tips and suggestions for my little project.

Chris

Thu Apr 09 2009, 11:14PM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Potassium chlorate can be made in an electrolysis cell from KCl and then decomposed thermally to produce oxygen. The decomposition of pure KClO4 starts at around 400Â°C and can be catalyzed by a few percent manganese dioxide to improve yield and lower the decomposition temperature apparently below the melting point (I have not done it myself though). This reaction is exothermic, so you will need to monitor it with a thermocouple to ensure that it does not run away, but really it is quite safe compared to many other exothermic decomposition reactions (for example the decomposition of NH4NO3 to H2O and N2O, which could probably also work for your purposes). For additional safety you should run this reaction in a long narrow vessel or vessels with high surface area, with the option of forced cooling. A steel or more preferably stainless steel pipe can be used for this. It will be more preferable to keep the reaction in the solid phase, but that could prove difficult.

The oxygen produced by this reaction may contain a small amount of chlorine, and so that will need removed if it is a problem.

Bored Chemist

Thu Apr 09 2009, 11:57PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

If you generate both the O2 and the H2 electrolytically then you have a fairly simple system that should work.

Chris

Fri Apr 10 2009, 01:37AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Electrolytic hydrogen would be many orders of magnitude cheaper than that generated from aluminum too (the oxygen is going to be electrolytic in source either way though), but I seriously doubt that he has enough electrical power to make an electrolyzer that could run a decent torch.

john bunsenburner

Fri Apr 10 2009, 07:44AM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
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Posts: 53

Yes that is my main problem. I do not wish top medle with expensive electronics equiptent, nor high voltages. therefore my best bet was to use washing soda(very cheep) and aluminium(free if from scrap) and make hydrogen from the two.
@Chris: How much potassium chlorate would I need to have a good supply of oxygen? Or how much oxygen do I get per 100g of potassium chlorate?

Oh and just out of curiousity, what kind of power would I need to run a decent torch?(I have 240V AC here, if I find or make an AC-DC converter...?)

Bored Chemist

Fri Apr 10 2009, 03:03PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

This torch

runs up to 500,000 BTU/Hr and 1 BTU/Hr is equivalent to about 0.3W so the torch runs at something like 150Kw.
Some of these burn roughly 20 times less.

What do you count as a decent torch?

100g of KClO3 would give about 40g of oxygen assuming it decomposes fully to oxygen and KCl.

Hawever, unless you can be in two places at once so that you can keep an eye on whatever you are doing with the torch and also on the hot chlorate oxygen generator I'd not recommend this approach.

And while I'm at it, steel burns nicely in oxygen, if you overheat the oxygen generator you will have a very dangerous reaction.

[Edit: Fixed link]

john bunsenburner

Fri Apr 10 2009, 07:46PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

And how good/bad would results be if I used air? Would make things alot easyer. Also, i consider a decent torch one which can make small welding joints.

The first link you provided burns propane not hydrogen, the second one does not seem to work

Bored Chemist

Sat Apr 11 2009, 09:29AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

I'm sure there are plenty of welds made using gas/air torches so air works OK.
I know the link was to a propane torch, but, for a given size of torch, the power will be similar. You would get a higher temperature with an oxy hydrogen torch but the power won't be that different.
I don't know what's wrong with the seond link but it was just some site I found googling BTU/Hr and torch to give some idea of what was on the market.

john bunsenburner

Sat Apr 11 2009, 02:42PM

Registered Member #1937 Joined: Sun Jan 25 2009, 12:28PM
Location:
Posts: 53

Oh, we have totally misunderstood each other, i ment what kind of power do I need in electricitcal terms inorder to run a decent torch of an electrolosis cell. I knew something was wrong/confusing.

EDIT:
I just found out about air purification using zeolite to filter out impurites and nitrogen and leaving you with nearly pure oxygen and argon, that sounds like a really good alternative for me, do you think it is buildable for a reasonable price(30$?)

Steve Conner

Sat Apr 11 2009, 08:45PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I remember a friend of my mom's who made silver jewellery. For delicate silver soldering work, she used a tiny oxy-hydrogen torch powered by an electrolyzer, something like this:

It probably takes about as much power to run the electrolyzer as it would to run an electric arc welder, plasma torch, soldering iron, etc. of the same heat output. Maybe a bit more.

The major hazard with these things is if the flame blows back inside it and explodes the whole apparatus. Pieces of tank and caustic potash solution everywhere.

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