Sciencemadness Discussion Board - Low-Pressure Gas @ home

Low-Pressure Gas @ home

unome - 28-1-2010 at 03:52

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]

Picric-A - 28-1-2010 at 05:59

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

bbartlog - 28-1-2010 at 06:15

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.

ScienceSquirrel - 28-1-2010 at 06:24

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]

starman - 28-1-2010 at 11:06

Be interesting to see whether anyone could think up a suitable reaction for nitrogen...

Sulfamaic acid/Sodium nitrite

entropy51 - 28-1-2010 at 15:58

Quote: Originally posted by starman

Be interesting to see whether anyone could think up a suitable reaction for nitrogen...

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.

densest - 28-1-2010 at 17:34

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!

unome - 28-1-2010 at 18:36

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...

watson.fawkes - 28-1-2010 at 21:06

Quote: Originally posted by densest

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.

Panache - 28-1-2010 at 21:45

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.

Picric-A - 29-1-2010 at 00:04

@ 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!

ScienceSquirrel - 29-1-2010 at 06:07

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.

bbartlog - 29-1-2010 at 06:35

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!

DJF90 - 29-1-2010 at 06:42

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.

entropy51 - 29-1-2010 at 07:24

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.

ScienceSquirrel - 29-1-2010 at 08:07

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!

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.

watson.fawkes - 29-1-2010 at 10:50

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.

unome - 8-2-2010 at 03:34

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?

garage chemist - 8-2-2010 at 16:36

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.

entropy51 - 8-2-2010 at 16:50

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.

un0me2 - 8-2-2010 at 19:35

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]

bbartlog - 8-2-2010 at 21:17

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.

un0me2 - 9-2-2010 at 04:45

Hydrogenation @55psi/~4atm might be one such use?

peach - 5-7-2010 at 18:06

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]

stygian - 5-7-2010 at 19:01

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.

peach - 7-7-2010 at 14:37

H2 is a gas you can easily buy in cylinders, why would you try to generate and compress it yourself? The cylinder companies will be able to do it far more cost effectively. Hydrogen is used for glass blowing and welding, which are some of the main outputs for the cylinder gas manufacturers.

I would be willing to bet you could pressurize CO using a diving cylinder compressor. Provided it doesn't react with the greases or O-rings in the compressors. Those are hundreds each, and often thousands.

You only need to generate gas when it's things like HCl, ammonia based products or SO2, which are dangerous and odd to be renting cylinders of.

Trying to generate and compress N2 or other such everyday gases is ridiculous, they're consumed everyday in vast quantities by industry, are in no way harmful and they're cheap and dry from the cylinder companies.

[Edited on 7-7-2010 by peach]

Panache - 7-7-2010 at 18:06

i used the hcl(aqueous)/cl2 method for generating some dry HCL yesterday for the first time after reading about it here, i used a further CaCl2 bottle as a dry tubing. Controlling was problematic until i setup up a loop whereby when not in use it was flushing down the drain, when in use it was forced into the system via a small(~3inch) vacuum running from an aspirator with the tap water supply barely running,
i can highy recommend this method as cheap, very controllable and far better than h2so5/hcl methods for making HCL solutions for titrations etc whereby every thing is running at a slight overpressure.

Contrary to that method in this system it doesn't matter if you get small leaks as they leak into rather than out of your system

peach - 20-7-2010 at 11:39

Did you rent a cylinder of Cl2? If not, you were probably using a manganese dioxide Cl2 generator right? Why not just drip straight onto salt?

If I wanted to generate a large amount of hydrochloric acid, I'd use plastic containers for the HCl(g) generator; the 5l HDPE kind. I'd fill an empty one with salt and put 'jerry can' nozzles on the outlets to connect them. Then have one full of acid above and use a tube clip between the two to control the flow of acid onto the salt. I'd have another hole from the top of the bottom one to the top of the acid container to equalize the pressure between the two, which could feature a Y branch to take the HCl(g) out to the water where the acid will form.

I'd do it that way because the largest flask I have is 1l, and I've had the resulting salt cake 'pop' a glass flask when I went to rinse it out.

I'm still kind of interested in the idea of condensing the HCl(g) and running it off into a 316 stainless pressure vessel. I can buy 316 nipples that are inches long and wide and rated to 4500 psi, as well as caps and fittings of a similar kind. And I can easily line the pipe with a continuous PTFE liner, which should make corrosion next to impossible.

The steel is well resistant alone and rated to an order of magnitude more pressure than the HCl(g) can generate.

Using the longest 316 nipple I can find with a quick google, that'd store around 2.7 moles of HCl(g).

The bastardized balance;
2.7NaCl + 1.35H2SO4 → 1.35Na2SO4 + 2.7HCl

158g NaCl, 67ml H2SO4
5p salt + 51p acid

A bigger nipple would be nice, but only if it's not on a girl.

I think my budget can stretch a little further than that. To a long length of taper threaded 316 seamless tube perhaps.

The most difficult, or expensive, part would be controlling the flow of gas out of the vessel.

Store it in a long and thin piece of plastic (like a gutter pipe) and port that through some saturated KOH. You could stick that guttering inside 110mm drain pipe and fill the surrounding space with cement. You now have a 4500 psi, 316 pressure vessel charged to 400 psi inside a venting pipe attached to a scrubber and that's inside a cement lined outer pipe. All cheap and easy to put together from DIY store parts and I've never seen anyone, cylinder companies or authorities, going to that much effort.

If you filled the cement layer with cheap wire wool before pouring the cement, that'd make it even stronger (it's essentially micro-rebar and is used in reinforced cement). There no way the pressure vessel will blow it's way through all of that at 400 psi; I've seen tanks catastrophically empty at 2300psi and only go through breeze block. The worst thing that could happen is the pressure vessel entirely fell apart and dumped all of the HCl(g) instantly. The scrubber would be the first thing to be overloaded, not the walls.

The 316 alone would be enough, I'm just thinking of easy ways to make it even safer. I literally just threw out some of the fittings I'm talking about and left them sitting beside a skip at the tip; 110mm fittings.

[Edited on 20-7-2010 by peach]

Panache - 20-7-2010 at 15:41

Peach, your enthusiasm and creativity are great, keep at it, this comment is not to try to stop you from thinking about things but from someone who has tried many many things and learned over time about what potential problems will arise, without doing there is no knowing though and i'm, pretty good these days and getting my ideas to work.
There's my justification first, now your idea has a couple of potential problems, firstly, most polymers exhibit accelerated aging under the influence of gaseous HCL, they become brittle and fail many many times faster than attributable to normal oxidative processes. So your cylinder liner is going to fail fairly quickly, in the order of months, however you will not notice it until the HCl has dissolved your concrete and started leaking out, then you have a big fuck-off heavy unliftable piece of plastic and cement that one wants to go near without full respiratory and body protection.
I've posted a method for producing condensing and cylinderising Cl2, you'll find if you look, that way you can stop makign assumptions about how if done things.

Fuck i've gotta do some work, i'll finishh my critique later.

But i just may also add that using KOH to dry HCL gas seems like a novel idea!!

edit-my mistake you're not advocating dry with KOH rather just as a safety, why not use bicarb, at least it won't chew a hole in your arm if it sloshes around.

[Edited on 20-7-2010 by Panache]