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unome
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Low-Pressure Gas @ home
I was just thinking (yeah I know, I should really warn people), but the idea behind the bicarbonate/acid fire extinguisher (ie. invert it and they
mix, forming CO2 and a shitload of pressure) could be applied to the preparation of HX gases (alkali metal halide solid mixes with H3PO4 liquid),
Sulfur dioxide (sodium metabisulfite (s) mixes with HCl (or other acid)), Hydrogen by mixing solid aluminium flakes with STRONG NaOH solution.... For
that matter, what about MeNH2 and or ammonia from the hydrochloride salt and ammonium fertilizers & NaOH respectively...*
Be interesting to see whether anyone could think up a suitable reaction for nitrogen... That would also be useful...
Just think about it, no acquiring lecture bottles, etc. Just build/acquire the relevant tanks (either get the old ones or copy the plans for new ones,
make sure there is a pressure relief valve). Best of all, when it is exhausted, simply wash the whole thing inside & out - then reload it with the
part A (solid) Part B (solution) and/or Part C (see below - the drying agent).
*It really isn't too hard to envision building in a fairly long, specially tailored drying train between the start of the tank outlet (nb. inside the
container) to a point outside the tank, where the delivery tube/hose connects.
[Edited on 28-1-2010 by unome]
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Picric-A
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Sounds like the method cooks use to make HCl., essentially a potential bomb releasing a shit load of toxic, explsoive or corrosive gasses.
Stick to the LB's
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bbartlog
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I think what you want is a Kipp generator. If the pressure is low, a tank just makes things complicated.
Ammonium nitrite decomposition via acid would serve to produce nitrogen. And I'd rather use zinc and HCl to make hydrogen gas than Al/NaOH.
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ScienceSquirrel
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There is a piece of equipment for doing this called a Kipps Apparatus.
As long as they are used correctly they are perfectly safe.
http://en.wikipedia.org/wiki/Kipp%27s_apparatus
This is also a good example of a good Wikipedia article.
A concise description with references that work if you need to know more
[Edited on 28-1-2010 by ScienceSquirrel]
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starman
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Be interesting to see whether anyone could think up a suitable reaction for nitrogen...
Sulfamaic acid/Sodium nitrite
Chemistry- The journey from the end of physics to the beginning of life.(starman)
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entropy51
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A NITROGEN GENERATOR.
Chas. van. Brunt
J. Am. Chem. Soc., 1914, 36 (7), pp 1448–1450
DOI: 10.1021/ja02184a012
Publication Date: July 1914
Passing air over hot copper filings or flakes (from steel wood + CuSo4) works pretty good, too, if you don't mind a trace of CO2 and inert gases.
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densest
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I'd add my vote to avoid storage & tanks. A compressor suitable to put anything even slightly reactive into a tank gets very expensive. One good
enough to pressurize to 2500+ PSI/170 bar is $5000 or more. Hydrogen leaks through the smallest hole (only helium is worse), oxygen requires cleaning
to remove anything remotely combustible, Cl is war gas, HCl, well..., and so on.
A possible engineering solution for nitrogen if one happens to have the equipment.
The discard vent of an oxygen separator (generator, medical oxygen generator) is depleted in oxygen and argon. I have only seen one mention of how
much oxygen those units actually extract from air. The "efficiency"quoted is 50% or so, giving an exhaust gas of 80% nitrogen or so. That would cut
the amount your absorber would have to deal with. The exhaust would still (AFAIK) have most or all of the CO2, H2O, Xe, etc. as well. I don't know
which way the Ne goes - at a guess it leaves with the O2.
Any substantial back pressure (> 1 PSI, .07 bar) would probably cause the gas separation to decrease substantially.
Membranes are used in commercial nitrogen separators. High pressure air passing over one side, N2 out. I have no idea what the membrane is; my
interest has always been in getting the largest amount of oxygen at the lowest possible price for my flameworking torch!
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unome
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No compressor needed - the liquid & solid parts are added at STP, maybe with an evacuation & purge once they are in place, but no compressor
is needed still. The reaction between the solid & the liquid forms the gas required, but it continues to form it even under pressure, resulting in
medium pressure gas. Such as is provided by the CO2 extinguisher, where sodium carbonate/bicarbonate as a solid, is allowed to mix (by inverting the
cylinder) with an acid, producing CO2 - the pressure of which is sufficient to force it some distance from the tank when the valve is opened.
It is VERY similar to the Kipps Apparatus, except it would provide for pressurised gases, whereas a Kipps cannot do that. I have attached a picture of
a sectioned Soda-Acid fire extinguisher - the idea is pretty simple...
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watson.fawkes
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Quote: Originally posted by densest  | | The discard vent of an oxygen separator (generator, medical oxygen generator) is depleted in oxygen and argon. I have only seen one mention of how
much oxygen those units actually extract from air. The "efficiency"quoted is 50% or so, giving an exhaust gas of 80% nitrogen or so.
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If you change out the adsorbent material inside of one of these units, you can change what it is you're
extracting. There are materials that preferentially extract nitrogen, so you get a pretty pure nitrogen stream and a raffinate stream depleted in
nitrogen. Look for books on pressure swing adsorption for a more thorough treatment, including how to calculate an optimal set of cycle times for your operating parameters. I
don't recall off the top of my head what it is they use for nitrogen. It's a zeolite that's in there for oxygen.
Of rather wider interest, silica gel is used for extracting water vapor, at which it is enormously effective, easily getting it down to < 1 ppm in
a single stage unit.
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Panache
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i'd always wondered why those birch meth cooks didn't just dump some ammonium salt and NaOH into a steel cylinder followed by a few hundred ml's of
H2O then simply close the valve. When then want their ammonia they can then open the valve, dry and condense.
Then again i'm sure there is a very good reason, my phys chem being what it is however i'm not surprised that i'm unaware of any obvious potential
problems with this methodology. Anyone care to have a stab, obviously leaving out super obvious like appropriate valves etc.
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Picric-A
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@ Panche- Earlier down the post i called these things bombs for good reason.
I read an article about how these meth cooks store gasses like this. They used them to make HCl and of course to do this they would pour salt + conc
H2SO4 in a steel(!) propane cylinder, screw on lid and heat.
Things wrong with this -H2SO4 + Fe --> nice big hole in the tank
-hole in the tank + compressed corrosive gas --> disaster!
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ScienceSquirrel
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I seldom agree with Picric-A but mixing up chemicals that react to produce a gas in a sealed container fails in to the category of insanity science,
unless you want to produce a bomb.
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bbartlog
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It is VERY similar to the Kipps Apparatus, except it would provide for pressurised gases, whereas a Kipps cannot do that.
Modifying a Kipp generator to produce more positive pressure wouldn't be especially hard, within the limits of whatever materials it was made of. What
I don't understand (and I'm not convinced you do either...) is what the point of providing the gas supply under pressure (more than the few kPa needed
to bubble it through a solution) is. Obviously we *store* things like CO2, Cl2, propane under pressure for convenience; but then we have regulators on
the tanks to ensure that the supplied gas comes out under tight control.
mixing up chemicals that react to produce a gas in a sealed container fails in to the category of insanity science, unless you want to produce a
bomb.
I have a spent aluminum-casing fire extinguisher, the top of which can be unscrewed. And I've put in baking soda and vinegar, quickly closed it, and
let my kids use the resulting extinguisher off my back porch. But you can be sure that I looked at the pressure limits (it's been tested to 300psi),
calculated how much gas the extinguisher could hold, added a large safety factor, and carefully weighed the reagents before doing this. So I don't
agree that this is *necessarily* so dangerous as to be off limits; I just fail to see the point when it comes to lab chemistry!
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DJF90
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I'm going to argue that if one knows what he is doing then this is not so troublesome. The issue arises not from the creation of gas, but from the
chemicals used in creating it. To show my perspective, ammonia, chlorine, and sulfur dioxide cylinders (amongst others) are filled with liquid
reagents, and sealed. Obviously the chemical equilibriates between the liquid and gaseous phase, producing a vapor pressure. The reason why this is
ok, is because a) the filling company knows the mechanical capabilities of the tank, and b) the volume of reagent is carefully calculated as to not
avoid overpressure.
Now, assuming the amateur is capable calculating these two critical points, the only reason why this is not possible is due to chemical
incompatabilities with the tank, either of the reagents used to produce the gas, or the gaseous chemical itself. This is where the downside is; any
gas that is useful chemically, as a low-medium pressure source, will be incompatible with most tanks used for storing compressed gases such as propane
or butane, or the chemicals for the production of the gas will be incompatible with the tank material.
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entropy51
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Some of the older chemistry books, especially the ones describing lecture demonstration experiments, tell how to make all sorts of Kipp-like
generators for generating NH3, H2S, Cl2, etc. on demand. I'd be more inclined to go with one of these designs rather than guess about the stress
limits and chemical incompatability. In particular the cylinder valve may not stand up to the new gas and you have a leaking cylinder when you least
expect it.
I'm reminded of a problem that occurred when ether was used as an anesthetic. An empty O2 cylinder connected to the ether vaporizer would cool
overnight and siphon ether back into the cylinder, which was returned to the vendor and refilled with O2 under pressure. The explosions killed a lot
of workmen until they learned to first put a little air in the empty cylinders, and slowly let it back out while sniffing for ether fumes.
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ScienceSquirrel
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| Quote: Originally posted by bbartlog |
mixing up chemicals that react to produce a gas in a sealed container fails in to the category of insanity science, unless you want to produce a
bomb.
I have a spent aluminum-casing fire extinguisher, the top of which can be unscrewed. And I've put in baking soda and vinegar, quickly closed it, and
let my kids use the resulting extinguisher off my back porch. But you can be sure that I looked at the pressure limits (it's been tested to 300psi),
calculated how much gas the extinguisher could hold, added a large safety factor, and carefully weighed the reagents before doing this. So I don't
agree that this is *necessarily* so dangerous as to be off limits; I just fail to see the point when it comes to lab chemistry!
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But you are using vinegar and baking soda and you have enough skill to do some calculations as well.
There are quite a few that struggle with molarity and gas laws and they might be thinking of doing it with concentrated sulphuric acid and sodium
chloride to make hydrogen chloride under pressure.
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watson.fawkes
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| Quote: Originally posted by entropy51 | | In particular the cylinder valve may not stand up to the new gas and you have a leaking cylinder when you least expect it. |
You get leaking cylinder even when you take adequate precautions with properly specified gear. The valve and regulators can fail
through material defects, accidents, etc. It's evidently common enough that tanks of hazardous materials are often stored in cabinets with dedicated
ventilation lines (think fume cabinet), although I've never seen one personally. On the other hand, it seems relatively easy to do and cheap insurance
for what easily could be a fatal accident.
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unome
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I was merely writing up a method whereby people could access gasses at medium pressures for immediate use... I "assumed" those doing so would ensure
that the containers used were (a) capable of withstanding the pressure(s) involved and (b) chemically inert to the ingredients thereof.
Yes, it is very little more than a pressurised Kipps apparatus, I made no claim to the contrary, useful for when various gases are needed under
slightly more, even 3 or 4 times more, than atmospheric pressure. I wouldn't suggest trying for anything more than that without properly made pressure
equipment. As to valves, at 3-4 atm, valve design is still relatively simple, that is beer keg type pressure, actually, those screw-top beer kegs
(stainless steel ones) would be just about perfect for a lot of gasses.
PS Why the fuck do people continue to argue incessantly about the obvious?
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garage chemist
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Nitrogen can be made by dripping a solution of sodium nitrite into a hot solution of ammonium chloride (or any other ammonium salt).
NaNO2 + NH4Cl ---> NaCl + N2 + 2 H2O
At room temperature the reaction is very slow, it needs to be heated to go at a useful rate.
Whether this is useful depends on how cheaply sodium nitrite is available to the experimenter.
Solid ammonium nitrite is explosive, btw.
Making N2 by chemically removing the oxygen from an air stream is certainly cheaper for larger amounts.
Or one could get some liquid nitrogen, acquire an old 200 bar gas bottle, screw off the valve, add a carefully calculated and weighed amount of LN2,
screw the valve on again and let warm up: a N2 bottle for very cheap.
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entropy51
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| Quote: | | NaNO2 + NH4Cl ---> NaCl + N2 + 2 H2O |
A useful source of N2 for sure. But careful with the heating, this
one can get out of hand. Heat gently and remove heat when it starts foaming.
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un0me2
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As to the point where it comes to lab chemistry, try going into BOC Gasses here (Oz) and ordering H2, SO2, NH3 or Cl2 gas, you'll have a warrant sworn
on the delivery address before the bloody thing arrives.
That said, I have NOTHING to hide, I just dislike having to replace walls, furniture, light fittings, electrical wiring, tiles, etc. not to mention
having my partner and children woken up and thrown around by armed men. That is what a raid is, anyone who doesn't fear that outcome obviously has yet
to encounter it and/or is truly retarded.
[Edited on 9-2-2010 by un0me2]
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bbartlog
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As to the point where it comes to lab chemistry
I don't question the utility of the gases per se, I question the marginal utility of producing them at some moderate yet poorly controlled pressure
vis a vis using a Kipp generator (or other similar source). Gas at (say) 3 bar is still enough to fling apart my glassware in all directions, unless I
take a lot of trouble to seal, fasten and so on. And if I do go to this trouble... I get what? Slightly different equilibria compared to STP?
Marginally faster chlorination? I don't get it.
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un0me2
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Hydrogenation @55psi/~4atm might be one such use?
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peach
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First of all, go to google and type in "hcl gas generators clandestine".
Read the whole document. Carefully.
Forget using metallic tanks. That's a bad idea.
Note that the authorities have suggested a better idea, plastic PVC piping with a pressure release valve. I'll improve on their idea, check the burst
pressure of the pipe you use (over pressurize it with air first once assembled), have at least one blow off valve and have it blow off down a
restricted outlet through a solution of strong base to neautralize the HCl(g) etc. You could also double wall the generator, put one section of
smaller pipe inside a bigger section, so if the generator pops, the doesn't spray everywhere.
I'd say those are fairly easy and worthwhile safety features. Kind of odd that document didn't bother with any of them. They have hazmat suits, but
spraying HCl(g) around for fun isn't exactly environmentally friendly. They're
mainly bothered about it popping and hitting them with bits of plastic, but the pressure relief won't work if the plastic fails for some other reason.
I find generating HCl(g) using an addition funnel is kind of annoying, as the reaction fizzes a lot at the start, but will then trickle along for
another 6 or more hours. I'd prefer it to be done and for me to be able to vent it in a controlled manner. It's not about pressure, but about
producing a known flow rate and quantity.
I'm using HCl(g) to dry FeCl3 and things like that, not pressurize reactions or anything fancy.
As for generating N2 at home, jesus no. It's dirt cheap and you need it oxygen free if you're using it for an inert atmosphere. Buy a zeolite based
separator (oxygen generator). They can filter air quite well. But it'll still be relatively thick with oxygen, you'd need to chemically scrub it out
on the way to the reaction. Maybe you could fill a glass tube with some carbon and roast it, to reduce it to CO2; although, you'd probably get more CO
doing that. You could heat some magnesium or something like that maybe. I go straight to a cylinder for N2, I have one here right now. The cylinders
are cheap, tons of industrial guys use them, the oxygen has been scrubbed and the gas is dry.
But reactive gases are another story. Things like HCl(g) will rot the shit out of normal gas handling equipment, there's a reason scientific
regulators cost a lot.
The burst pressure of schedule 40 PVC pipe is remarkably high, 600-800 psi I think. That will drop, drastically, if the plastic warms up. Plastics
also have a nasty tendency to become brittle around certain reactive gases. If you went over 100 psi with a home made pressure vessel, I would
personally sign you in as clinically insane.
[Edited on 6-7-2010 by peach]
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stygian
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Hmm a bit diametric, but what about high pressures? Can any sort of ordinary compressor be used for H2/CO? Some F-T or MTG is really interesting to
me at this point.
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