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Concentrating Hydrogen Peroxide

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LAN_403

Conundrum

Thu Apr 05 2012, 07:53AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Sterilise things? OAUGDP is the other variant.
Also its handy for generating UV, someone suggested making a PCB etcher that way.
Its a lot cheaper and easier to build than a UV tube based unit, apart from needing an ignition coil to generate the 150Hz or so at 10KV+ it needs.
The lack of tubes also means it doesen't lose emission over time, and the ozone generates also starts to develop the image on the board so you can tell if something went wrong BEFORE wasting expensive developer/etchant.

There are ways around that though

One of the guys on the homemade fuel forums suggested using a glow discharge sheet immersed in the SVO as a way to modify it into fuel, without the other steps.
Just add the hydroxide and methanol, and use a small pump to circulate the mixture through the cell.
Still needs titration but should work..

Bored Chemist

Thu Apr 05 2012, 04:30PM

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

klugesmith wrote ...

Wastrel wrote ...
If you can buy "30 volume" peroxide and have to concentrate, I recommend starting from that, it's about 9%.

I came to understand the "volume" rating of diluted H2O2 in pre-Internet days, but was probably older than the median reader of this forum today.
It's based on a simple assay method: 1) Bring a sample of H2O2 solution together with a catalyst. 2) capture all the resulting oxygen gas at atmospheric pressure, and take the ratio of its volume to that of the original liquid solution.

Oh no it isn't.
You don't use a catalyst, you use an oxidant like KMnO4
This gives you twice as much oxygen so it makes your product look twice as good.

cbfull

Thu Apr 05 2012, 04:54PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

I don't think the freezing idea will work. Mixtures of H2O2 and water are eutectic, meaning the mixtures will have a lower freezing point than either component alone.

I store my 35% H2O2 in a freezer that is well below zero, and it shows no sign of freezing. There is a popular website that sells the food grade stuff that claims that storing it in a freezer is dangerous. I'm not sure I follow their logic but I am fairly certain it's incorrect. Here is a quote from their page:

"There is a false view commonly taken that H202 should be stored in the freezer. If H202 is frozen at too cold a temperature, it will separate (decompose) as the water and H202 freeze at different temperatures. Do not store H202 in a freezer."

What do you think? Is this just a case of a poorly communicated real safety issue? The company I bought it from (Eagle Enterprise) states in numerous instances to store it in the freezer. There was even a big sticker on the box when I received it that said to store in the freezer immediately! Anyway, I think this "Pure Health Discounts" website is just trying to sound very confident and knowledgeable as a marketing technique. That claim likely has no basis in reality.
I have been buying it and storing it in the freezer for several years now without a problem, and I see no reason to stop.

Did I just rant? Maybe a little...

Conundrum

Fri Apr 06 2012, 08:07AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Keeping it cold would stop it degrading as quickly.

Gas buildup = pressure = Big BadaBOOM.
Which would be a "Bad Thing" (tm)

-A

Forty

Fri Apr 06 2012, 04:06PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

Hmm. I read in several places that that was one way of concentrating it. It would also explain that warning, since if it separated out you'd have high concentration h2o2 in your freezer which could be dangerous.

I guess I'll just have to try it. I don't think 60%+ would be very easy to make that way, but taking 3% up to ~20% should be doable.

Also read about adding table salt to it. supposedly separates into an h2o2 layer and a salt water layer. not sure I buy that one though, but it's simple enough to test.

edit: yea salt doesn't seem to do anything. I also learned how not to heat up peroxide: microwave.
I've got another beaker in the freezer. So we'll see how passively freezing it works out. I wonder how many government flags I've collected by looking up h2o2 concentration methods... hmm.
Also upgraded the DBD device to a cylindrical design. Works beautifully and makes a ~1/16" thick by ~1.25" long cylinder of plasma. Next step will have to be an open ended one that air could be pumped through. Better cooling will be required for extended run times. Still haven't checked on the nitrogen oxide production of it, but it smells only of ozone. Of course if ozone bubbling turns out to not be a good way of making h2o2, then I don't know what the heck i'll do with the thing besides show it to people.

cbfull

Fri Apr 06 2012, 08:33PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

I should add something to my comment before that freezing wouldn't work. I have read that it actually can work, just at much much lower temperatures than most of our freezers can go.

I got interested in this again recently because I am working for a company that makes digital density meters, and that's typically how the concentration is determined. I contacted Solvay which I think is the largest manufacturer of H2O2 in the US (probably in the world). They were kind enough to send me a table of density vs. concentration and temperature. I'll gladly send it to anyone interested.

Forty

Fri Apr 06 2012, 09:39PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

My freezer works just fine. went through two cycles of freezing it and then taking out the ice and adding more peroxide. Left it in too long on the 3rd time though, so now I've got to let it thaw (all turned to slush/ice)

I was looking at the graphs of freezing temperature vs h2o2 concentration and it doesn't go all that low until you're at like 60% concentration.

klugesmith

Fri Apr 06 2012, 10:08PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Good work, Forty. (reporting the result of an experiment rather than a literature search).

Not long ago, there was a thread here about concentrating alcoholic solutions by freezing.

As a definite non-expert, I thought that freezing does not generate a pure H2O phase.
Isn't it like boiling or freezing of other fluid mixtures, to produce a partly enriched phase and a partly depleted phase?
Has anyone found a phase diagram showing the eutectic point of H2O with H2O2 (or EtOH?)

[edit] FWIW: fractional freezing in Wikipedia.

cbfull

Tue Apr 10 2012, 01:39PM

Registered Member #187 Joined: Thu Feb 16 2006, 02:54PM
Location: Central Ohio
Posts: 140

Forty wrote ...

My freezer works just fine. went through two cycles of freezing it and then taking out the ice and adding more peroxide. Left it in too long on the 3rd time though, so now I've got to let it thaw (all turned to slush/ice)

I was looking at the graphs of freezing temperature vs h2o2 concentration and it doesn't go all that low until you're at like 60% concentration.

Do you have a thermometer to check your freezer temperature? That should be a somewhat reasonable indicator of what concentration you could theoretically achieve using this technique. I am curious now to find out what the temp of my freezer is.

Conundrum

Sat Apr 14 2012, 05:13AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Come to think of it, my freezer seems to be on a lot of the time.
What I need to do is make a remote temperature reader, that reports the system temperature at several locations and provides an average on an external display.

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