Intergalactic_Captain
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Compressed Gases on the Cheap
After checking out this thread, I was struck with some rather dangerous thoughts considering the prospect of catalytic hydrogenation - I need
hydrogen...I can make it, but it needs to be pressurized.
https://sciencemadness.org/talk/viewthread.php?tid=4566&...
The "cylinders" used are ingeniously simple, but I'd rather have something rated a bit higher. How about a medical home oxygen tank?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=12022...
$17 shipped (empty), somewhere around 18 cubic feet at 2015 PSI. Now, I figure these would be perfect for 300-500 PSI storage of electrolytically
produced hydrogen. The post could be replaced with a ball-valve / pressure gauge / ball valve / quick connect setup akin to what was done in the
other thread.
As for compression, I'm thinking about a fridge compressor - Would this work for hydrogen? It should be electrically isolated, thus no explosion
risk, but I've never heard of anyone doing it before. The tank would also have to be purged, which could be done with either CO2, Argon, or Nitrogen
- I suppose it'll depend on which one of the three is easiest to cobble a fill adapter with on the day I do it, as my dad has standard welding
cylinders of each in his shop - Any suggestions? I'm thinking CO2 would probably be the best, but neither of us have ever had to purge a tank.
So, I suppose the question is, anyone tried compressing their own hydrogen? I figure I'll pick up four of these to take advantage of the free
shipping offer...One for hydrogen, one for oxygen, and two for whatever (possibly ammonia, if I can ever beat the clogs in my urea decomposer). Any
ideas for a compressor other than a fridge compressor would be appreciated - I've mentally designed one based on a bike tire pump, but that would
probably top out at around 200 PSI.
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vulture
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Be wary that the explosion limits of hydrogen vary with pressure and temperature. You should be able to find a chart.
No problem if you have something to scrub out the oxygen though.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Intergalactic_Captain
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I was wondering what to use as a failsafe oxygen scrubber. Would you happen to know what is used in commerce? I'd imagine that I could purge the
tanks well enough to pose a practically negligible risk from oxygen that might be in them. The hydrogen would be produced electrolytically, stored in
an oil drum (or something of the sort), then dried inline before being compressed. Not much chance for any contiminants to get in, so cleaning it
shouldn't be too exhaustive. I've seen a couple of filters meant for inline deoxygenation, but I'm wondering if I should put something in the tank
itself as well when I replace the post.
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chemrox
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You can get a small gas cylinder(s) at Harbor Freight. Cheap! I got two there and traded them up at the welding supply who also have H2 btw..the
trade-up was nominal. If the welding supply isn't available I'd like to know how the pump worked out. I have the same need with ammonia. Don't need
liquid ammonia .. just dry gas. Haven't checked local gas suppliers yet. The welding supply is pretty comprehensive though .. rent dewars and sell
liq N2.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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PHILOU Zrealone
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Hydrogen - oxygen can also become explosive once pressurized because of catalytic effect on the surface of the tank!
We had tiny explosion tests at university which happened at ambiant T° while increasing the pressure.
Tank was glass in those test and pressure was between 1 and 10 atm.
[Edited on 27-2-2008 by PHILOU Zrealone]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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evil_lurker
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I recently got a 20 cubit foot cylinder from Airgas for $93.
Took me about 4 or 5 weeks to get it in though because it was a special order item.
Got it open, cracked it open to purge before hooking up the regulator, and of course the bastard was empty.
Not all chemicals are bad. Without chemicals such as hydrogen and oxygen, for example, there would be no way to make water, a vital ingredient in
beer.
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Drunkguy
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Also consider catalytic transfer hydrogenation if you want to duck having pay for a cylinder. There's a review on this which you may know about
already. I have a variety of pdf's on the subject of hydrogenation. The ebook by Rylander is well worth having too. Additionally, hydrogen gas can be
generated by a vairiety of methods. Vogel discusses using NaBH4 as a source of H2. Various metals are also possible (foil, zinc, iron and tin) but I
cant remember if its acid or alkali that liberates H2.
Disposable cylinders of Ar are relatively easily obtained since these are used for welding. I have no clue what the purity is like. I see no reason
why they would intentionally make it dirty and technology these days means that anything under 99%+ would be sub-standard.
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Intergalactic_Captain
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The airgas and harbor freight prices aren't that bad, but for my budget I'd rather go with the medical tanks. Right now, I just need something small
and cheap to do some catalytic hydrgonation testing with various nickel catalysts. Nickel on Charcoal will probably be done first, though Raney
nickel is not out of the question if I can find a cheap graphite crucible.
Philou - What percentage of oxygen were you testing your tanks at? I figure with these, I can easily bring the O2 to 21% by pressurizing/releasing
with just air. From there, filling with enough CO2 to leave a little liquid on the bottom should bring it to a signifigantly lower
concentration...I'm not sure it would completely blow the oxygen out, but just figuring on the volume of CO2 in the cylinder compared to air, the
atmosphere left after bleeding off the CO2 should be easily brought under 1%. A few nitrogen purges could then bring down the CO2 concentration, the
O2 concentration along with it.
As long as we're talking purging, would trace amounts of nitrogen or CO2 mess with a catalytic hydrogenation procedure? I don't see anyone testing
their gases for purity before publishing a paper, and industrial H2 comes from many sources in varying levels of purity...Not really sure if they're
generally using 90%, 99%, 99.9%, etc.
I'm not that concerned with being able to fill these tanks at a gas supplier or take a full 2000psi charge, as long as I can cobble together something
that's solid at 500psi or so I'll be fine. A real hydrogen tank would be nice, but as for now I just need something to experiment with before I
decide to sink too much money into it.
EDIT
Drunkguy - I checked out the CTH procedures a while back, but for what I want to do it wouldn't be worth it. I've got some ideas on glycerine
(glycerine->acrolein->allyl/n-propyl alcohol), and for the amount I'm looking at formates and hydrides either wouldn't work or would be too
expensive. If I can make nickel work I'm set....Though I must admit some designs towards NaBH4 after reading the sodium threads and considering a
reactor for making NaH. Not sure if that one would kill me or not though, karma hasn't been on my side too much lately.
[Edited on 2-27-08 by Intergalactic_Captain]
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kilowatt
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Do not store hydrogen under pressure in a steel tank. It will absorb hydrogen, which makes the metal brittle as it forms a solid solution. The
hydrogen also reacts with carbon in the steel's structure to form pockets of methane, which damages the steel and starts cracks. In commerce hydrogen
is often stored and transported in carbon fiber or fiberglass high pressure tanks. Any steel apparatus that comes in contact with hydrogen gas,
especially at high pressure, needs regularly baked under low pressure to remove diffused hydrogen. A good example would be industrial Haber
processors; they require very high maintenance. If you can find any more info on how they are operated and maintained and what materials they use,
that would probably be most helpful.
Aluminum is also susceptible to hydrogen embrittlement and loss of tensile strength, but it absorbs hydrogen at a much lower rate than steel, so would
be more suitable but still not acceptable for anything long term. Copper alloys are probably the most resistant to hydrogen damage given its hydrogen
absorption rate is much lower than other metals. Of course I don't think you will be able to find a copper or bronze tank, but it would be ideal.
Aluminum tanks are probably your best option, and that seems to be what most medical oxygen cylinders are made of. Be weary of the valve material as
well. You should do further research on the matter before doing anything with high pressure hydrogen.
The mind cannot decide the truth; it can only find the truth.
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12AX7
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Tanks are not small shit to trifle with! If you aren't sure of your tank's integrity, get it HYDRO TESTED. The worst thing you can do is fill it
with ANY gas: compressed gas stores an immense amount of energy, and it will maim and kill when it gets loose. Water doesn't compress nearly so much,
hence hydro testing.
As mentioned, not all tanks and valves are compatible with any gas. Some gasses need special media, like acetylene. If you don't know what you're
doing, then you should consult the local welding supply company -- I KNOW there is one nearby, there is one in every town -- and talk to the guys
there.
Tim
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Intergalactic_Captain
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Hmm...Wasn't thinking about hydrogen embrittlement before, but I sure am now. I'm thinking a fiberglass/composite wrapped aluminum nitro tank for
paintball would probably be the best bet for now. They're designed for around 3000psi, and any embrittlement should be managed by the composite
shell...Anyone see a problem with this? A good gauge could be permanently attached to the tank to monitor a drop in pressure, at which point the tank
would be emptied and retired.
The oxygen tanks I linked to are steel - Obviously, they'll take oxygen...But what else could I put in them? I believe the posts are completely steel
as well, so they could at least be used for ammonia. I've been thinking about nitrous oxide as well, just for the sake of doing it.
EDIT
...I thought I remembered this;
http://www.brianb.org/images/Scuba/Homemade/Gas%20Booster/ga...
After speaking with my dad I found out that we have all the parts to piece together a hydraulic version of one of these with a drive cylinder capable
of 2500psi...Not that I need that much, but a free compressor is a free compressor. That, and his paintball connections are getting me a fiber
wrapped aluminum paintball tank at a very good price.
[Edited on 2-27-08 by Intergalactic_Captain]
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kilowatt
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Keep in mind that the aluminum will over time be converted to aluminum hydride, and baking it may leave voids in the metal. You can't rely on the
fiber wrapping to hold all the pressure. What sort of pressure are you going to be running? You can calculate how quickly the hydrogen will diffuse
through the metal given pressure differential and temperature.
If you can get a completely composite tank that would be ideal.
The mind cannot decide the truth; it can only find the truth.
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Fleaker
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What is wrong with renting cylinders? Usually one time deposit that you get back, and then monthly fee of $15. Refills are cheap as well. I suggest
you visit the welding supply house!
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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MagicJigPipe
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I bought 4 of those oxygen cylinders for $38 which includes shipping! It's great to see a business on Ebay that doesn't rape it's customers with
overpriced shipping. In fact, this shipping seems very underpriced considering the size and weight of the cylinders. Now I just have to figure out
exactly what to do with them!
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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bio2
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.......As for compression, I'm thinking about a fridge compressor - Would this work for hydrogen? It should be electrically isolated, thus no
explosion risk, but I've never heard of anyone doing it before. .............
These have a "hermetic" motor with windings directly cooled by the gas. Definitely not "electrically isolated" as you put it.
Additionally this type of compressor is only good for 200-500PSI at best, but the motor would surely overload long before that.
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Ephoton
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is it possible to do a dissolving metal reaction in one compression tank made of fiberglass and
then once it has compressed then vent the pressurised gas through a drying tube to another
tank or would the reaction stop as the tank pressurised.
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Intergalactic_Captain
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Yes, theoretically it would be possible...However, there a few caveats. First, you'd need an inline dessicant of some sort to take care of the kicked
up water vapor. Second, the amount of gas you could collect would be proportional to the size of the containers. For example, lets say you're using
two 45ci (cubic inch) paintball tanks. Since they are the same volume (I'm disregarding the liquid volume for the example), you'd only be able to
collect half the theoretical gas volume - Both tanks will be at equal pressure, so half the gas volume would be localized in one and half in the
other.
I've been doing up some quick and dirty math on the tank I'm going to use - at 45ci, the volume is around .78 liters. This equals a pressure of
around 450psi (30bar) for one mole of gas. So, keeping a "safe" range for tank pressure, that gives me 2/3 mole of availible H2 for a reaction
running at 100psi. I'm probably not going to need 100psi for what I'm doing, but the math kind of works. Figure on around 30psi to run a
hydrogenation, the tank would need to be charged to 480-500psi to deliver 1 mole of hydrogen and leave 1-2bar in the tank.
As for the tank itself, many have raised the issue of the fact that it is made of aluminum. I'm specifically getting an aluminum tank wrapped in
carbon fiber and rated at 3000psi (~200bar). The way I figure it, the aluminum will fail eventually. While it's failing, the composite shell will
keep the pressure. I'm not sure how much pressure the shell can take, but I'm guessing it'll stand up for some time considering the intended
operating pressure. There also seems to be some misunderstanding - I only intend to store the hydrogen at 500psi MAX. If I wanted a legitimate H2
tank, I'd buy one straight out.
-MagicJigPipe - Let me know the condition of the tanks when you get them in. I've decided to hold off on buying them until I know how much the
paintball tank setup is going to put me back. I'd like to have a couple floating around for oxygen, one for methyl chloride and one for a
high-temp/pressure reaction vessel....We've been going over Me3SiCl in one of my classes and it seems like one of those reagents that I'd never run
out of uses for.
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bio2
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For a low pressure (30-60 PSI) hydrogenation this is easily done in a tank say several times larger than the reaction tank as follows:
In the large generator tank (steel OK), connected through a valve manifold to the reaction vessel, add NaOH aqueous to Al turnings (or similar). When
the pressure is high enough open the line to the evacuated hydrogenation vessel until the desired pressure is attained (or equalizes) then valve off
until pressure drops due to H2 absorption and repeat.
If the generator over pressurizes open the vent line and if more NaOH is needed then vent and add with a syringe so the pressure doesn't need
to be completely relieved allowing air to be introduced.
This is easily done using a standard refrigeration manifold and there is no reason higher pressures can't be used given suitable vessels.
Refrigeration
manifolds are rated 500PSI and readily available at reasonable cost.
Worked well for me and in my application a little caustic mist was not detrimental to the reaction so a drying train was not needed.
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Intergalactic_Captain
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I was thinking about doing something like that, but using a plastic 33 or 55gallon drum as the storage tank. The ones I can get my hands one are
about 1/4" thick, so I doubt they'd have a problem handling a few bars of pressure.
Dissolving metal is one thing I'm trying to stay away from though. HCl is 40 miles away, NaOH is sold out, and sulfuric is $9/quart. Electricity is
exponentially cheaper than any of these, and my Al turnings are on hold for another purpose. Worst comes to worst it's a doable option, but
considering I've got all the hardware for an electrolysis cell as well as the power supply floating around already I'd much rather go electrolytic.
Perhaps a 2-liter bottle could be used as an intermediate. Imagine a check valve into it and a regulator out of it - I could run the cell, collect it
in a double-drum setup, compress it into the bottle...Once it hits the regulator pressure bleeds into the reaction vessel. The reaction could be
metered by monitoring the pressure in the bottle - After the reaction container pressurizes, the rate of the reaction could be derived from the rate
of pressure increase in the bottle vs. bleedoff. Once the pressure increase starts to rise disproportionately to the observed increase when it's
taken by the reaction vessel, this faster pressure rise could be noted and the hydrogen generation ceased.
A pressurized cell is yet another option, but it would be too unwieldy to move around... Very simple design principle though.
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bio2
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....... using a plastic 33 or 55gallon drum as the storage tank. The ones I can get my hands one are about 1/4" thick, so I doubt they'd have a
problem handling a few bars of pressure.........
Surely you jest. Don't even think about this.
I have a 2KW H2/O2 water generator used for a welding torch.
I am using a 5 gallon 90 mil PP bucket with threaded rod secured
reinforced lid and 3-5 PSI is plenty on the softened 70 degree
plastic.
Some bulging is evident with this setup and a little more is involved than may meet the eye at first glance. Think bubbler/scrubber/over temperature/
over pressure protection/ antisyphon/ autoventing provisions among others. A 25 foot copper cooling coil must be used in the tank to keep the temp
below 70 degrees.
Also separating the O2 and H2 is not a trivial matter if this is required. Much easier to just get any scrap Al and if you can't find lye then I feel
sorry for you.
It seems you are dreaming of some type of continuous large
capacity setup which is fun to do I quess as I also do this
sometimes.
Get your hands dirty and you will find that some little low voltage
cell to try and fill 55 gallon drums with combustible gas to several atmospheres is no small undertaking and would take days (sic) using even the
biggest computer power supply made for the consumer market.
By the time you get half your components pressure tested I could
be done with three bench scale reactions using the method just described.
Good luck and never stop dreaming, smile.
[Edited on by bio2]
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-jeffB
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| Quote: | Originally posted by bio2
....... using a plastic 33 or 55gallon drum as the storage tank. The ones I can get my hands one are about 1/4" thick, so I doubt they'd have a
problem handling a few bars of pressure.........
Surely you jest. Don't even think about this.
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A standard 55-gallon drum is 23 inches in diameter, which means the top and bottom each have an area over 400 square inches. ONE bar overpressure
would exert THREE TONS of pressure against the lid. I don't doubt that they'd have a problem handling this. 
If you must proceed with this plan, please test first by sealing your drum firmly and then parking a couple of SUVs on top of it. When it pops,
you'll know you're on the wrong track.
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Intergalactic_Captain
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Hmm... I see your point there. I'll test it out next week with compressed air anyways, I've always wanted to know how much pressure they can take
and I suppose I've got an excuse to test it.
I checked out my dads stockpile of industrial junk tonight though - The compressor parts are all there waiting to be pieced together and welded up. I
also figured out what kind of vacuum pump he had scavenged a while back...Turns out the machine the setup came from was a Varian mass-spec/leak
tester, and there are really 3 pumps - Two decent sized rotary-vane pumps and one diffusion pump. I've been checking out some specs online and it
appears that the system they came from could pull somewhere from 10^-4 - 10^-10 millitorr...Spring break is going to be interesting...
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Ephoton
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so if one was to use a reaction to pressurise any kind of gas ie HCl H2 phosphine ammonia ect
it would be best to have a large reaction tank and a small storage tank therefor making for a higher
pressure. also it would probably be a good idea to have way to much drying agent inline and to
have the agent be a very reactive one towards water not just your normal sulfuric or caustic setup.
what about if one was to use two chambers joined with a memberane so as to do electrolosis there
for only needing to add water to get pure H2 and still not needing any kind of pump. of course all
of this would have to be custom made.
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Intergalactic_Captain
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No, you're getting pressure and volume mixed up.... The pressure in both tanks will be the same in the end, so you'd want your reaction tank to be
smaller than your collection tank if you wanted to maximize efficiency. You'd need higher pressures or a boost pump, as you're always going to have a
proportional volume split between the two tanks...
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