aonomus
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Air free technique without a nitrogen tank?
So I've been struggling with handling air-sensitive compounds such as FeCl2 without the nitrogen supply I'm used to at work... what are other forum
members solutions for handling air-sensitive reactions without the nitrogen tank?
I don't want to handle a nitrogen tank in an enclosed basement with only 1 exit in an enclosed space. Any accident would be catastrophic/fatal from
valve failure (even if the tank is secure).
Edit: I suppose a nitrogen separation membrane could be used, but where would I find one without paying a fortune?
[Edited on 9-7-2010 by aonomus]
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Contrabasso
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Proper ventilation in the lab would help. then even if the nitrogen leaks the vent fans should be pushing fresh air IN and also pulling stale air OUT.
Work out where the flow should go and fix it with two fans and hoses.
Nitrogen asphixiation is bad as is flammable or toxic or inebriating fume from organics, even dust from powders should be vented out of your vicinity
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densest
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A typical "K" (1.5m high) tank holds 200-250 cubic feet of gas. That's about a 2m cube. Unless your basement is very small and has no ventilation,
nitrogen wouldn't be a problem. Two small vent fans as mentioned above would make sure. Flammable gases and heavier-than-air gases might be something
more to worry about - propane, for instance.
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Lambda-Eyde
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Try looking for small 1L argon cylinders at welding stores:
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aonomus
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My main concern with compressed gasses is the unlikely but possible valve/regulator failure which can displace a sizable amount of air. I have enough
air exchange to negate small constant leaks (eg: improperly seated regulator, dirt in regulator, etc), however I'd want to avoid having a small tank
with high cost with such risk. Regardless I'll check into how much small K cylinders of N2 or Ar cost.
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densest
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Using the evidence of how safety regulations are written in industry, if the valve or regulator fails catastrophically your big worry is the ballistic
characteristics of a 50+Kg cylinder propelled by a 150bar gas stream! If your basement is 5m x 4m x 1.5m = 30m3, displacing 8m3 of the air with
nitrogen gives a 15% oxygen concentration. That's plenty to sustain consciousness & activity though I wouldn't want to do anything energetic or
think deep thoughts. I stipulate that any catastrophic failure will cause full mixing of all the air in the room. Nitrogen is lighter than oxygen and
will fall upwards.
The "K" size tank is the most common one found at welding supply stores - about 5 feet high and 9 inches in diameter.
I'd say get the tank, use industry standard tiedowns and tipover protection, and put something substantial over the regulator so nothing heavy falls
on it. Mostly because good regulators are expensive.
Events of suffocation in the news universally have in common a denser-than-air gas in a stagnant unventilated tank-like structure. If I were to worry
about gas in the basement, a slow CO2 leak from a really big liquid CO2 tank and a day-long power failure (fans stopped) would be the deadly scenario.
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entropy51
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Given the number of us who use chlorine, bromine, HCl, HBr, AlCl3, benzene, phosgene, ether, chloroform, etc etc in our basements, am I the only one
who thinks all this hand-wringing over nitrogen (! for gosh sakes) quite amusing?
And all this time I thought I was a chemistry wuss.
Find some nice safe hobby like wood working if you're afraid of nitrogen. I'm pretty sure that the air you're breathing right this minute is 80%
nitrogen.
Get your doctor to write you a prescription for some testosterone cream and rub it all over your body.
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Magpie
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Would this make one irresistible to women, or would they run in terror?
Here's a picture of my small 40 ft3 argon cylinder.
http://www.sciencemadness.org/talk/viewthread.php?tid=10366#...
Even with all the junk in my garage (mostly my wife's) I probably have an air volume of 3500 ft3. If this argon only mixed with the lower 6 ft of air
it would be diluted with 2000 ft3. This would still only give a 2% concentration of argon.
I do feel better having done this calculation.
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devongrrl
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I've seen the K type cylinders of argon in my local B & Q hardware store but I've never seen the regulators there.
Can anyone give me tips about the best places to look for them and what to ask for ?
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Contrabasso
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If you are bothered about the catastrophic failure of your nitrogen cylinder, where are you getting them from? Where are the regulators coming from.
Normal service gas fittings are long term stable, if the cylinder is secure and in date then it should be fine, the regulator likewise. Plastic piping
could be suspect if you overpressure it.
Put the cylinder outside if you want to be sure.
Some ventilation helps, so turn on the fume extractor.
Lots of places sell the gasses used for MIG and TIG welding, fewer places sell the fittings, try a welding equipment supplier.
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Magpie
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Quote: Originally posted by Contrabasso  |
Lots of places sell the gasses used for MIG and TIG welding, fewer places sell the fittings, try a welding equipment supplier. |
....or a brewing supplies distributor like:
http://www.micromatic.com/
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entropy51
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It increases one's lung capacity so that you can hold your breath while running from that toxic cloud of
nitrogen!
[Edited on 11-7-2010 by entropy51]
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Contrabasso
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Search ebay UK for argon regulators there was a page of them from 99p some with flow rate meters too.
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zed
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Sometimes air can be excluded in unusual ways.
My buddy Dr. Death, used to load up the thimble of his soxlet extractor with LAH, to do reverse addition reductions, using diethyl ether as a solvent.
Now, seeing that LAH, sitting there suspended in the atmosphere, without a buffer of inert gas.......with a liter of hot diethyl ether boiling under
it......Well, frankly, it gave me the heeby jeebies.
Dr. Death, never encountered problems during the procedure. He explained it to me like this: Ether vapor is quite heavy. After an initial
evacuation of air.....Once, the ether starts refluxing, the interior of the reaction apparatus IS full of an inert gas........ Ether vapor! As
long as reflux is maintained, and as long as there is a slight positive pressure within the reaction vessel, air will be excluded.
Likewise, in the absence of an inert gas buffer, many air sensitive reactions can be performed, by applying a vacuum to the reaction vessel. If you
have a good vacuum pump, vacuum is a lot cheaper to generate that argon.
[Edited on 11-7-2010 by zed]
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peach
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I loled. 
I'm all for safety around cylinders, but N2 isn't going to be an issue. And, as someone has already said, if the valve catastrophically fails, oxygen
displacement is the least of your worries. You'll know if it goes, I can assure you of that; it's going to make a horrendous whistle / scream.
Mythbusters did an episode on this, where they purposefully tried to smash the valve / regulator stem by dropping about 25lbs of metal on it from 6ft.
At the start, they couldn't get it to catastrophically fail.
BOC rent cylinders with plastic hand grips around the valve which are there, partly, to stop the stem suffering an impact.
If you're worried about it going, put the cylinder outside. It's actually in the health and safety guides, at least in the UK, that industrial users
have to do this with all their spare cylinders; so they're all in one place and visible if there's a fire (and they're away from potential sources of
damage inside the work environment) - that why you see a lot of metal fabrication yards with steel cages outside full of cylinders.
I was handling oxygen / acetylene tanks entirely on my own by the age of 14 and have never had a problem with a cylinder. My dad was dead by the time
I was 10 and I was the oldest guy in the house, so no one taught me how to do it. Just read up on what can go wrong and how to deal with them
responsibly.
Speaking of responsibility. I have seen videos of Hazmats teams unscrewing the valve stems on commercial HCl(g) / Ammonia tanks, whilst they're
pressurized.
With home made HCl(g) generators, they usually try to drain them into an alkaline wash first. If the valve is corroded shut, they'll shoot them.
Why in the fuck someone would purposefully unscrew the valve stem on a commercial cylinder of that kind, with it pressurized, is beyond me; I'm a
gimp, and I wouldn't do that. Not only is it environmentally poor practice, it's poor in terms of the safety of people around with regards to the gas
and it's asking for problems mechanically. If the tank has been back filled with something other than the marked gas, it could ignite or explode when
they do that. Hydrogen can ignite when you do something like that.
I've had the pressure disc burst on a liquid CO2 cylinder for a paintball gun pop in the car. We weren't driving. It wasn't an issue (and I had hold
of it in my hand the entire time it was emptying), but the noise it makes is loud, and there were clouds of white gas everywhere as it boiled. That
was their fault. It had literally just been filled (a minute ago), it was a very hot day and I suspect they overfilled it or the disc was a dud.
No BOC cylinder has ever done that. If it was going to empty through the burst disc, it'd have done it at the factory when it warmed up, on the bumpy
ride to the yard or in the yard. And burst discs opening isn't an issue either with gases like these.
It used to be funny at university when BOC turned up to refill the cryogenic tanks. They'd turn up in a small liquid tanker and pump it out as a
liquid, through something like a petrol pump, into the dewars. Whenever they were doing it, the car park would look like the end of Terminator 2,
because some of it would inevitably boil off and float around the tarmac; the dewars aren't pressurized and don't seal like normal gas tanks, they
'pour' liquid into them.
A zeolite generator isn't going to be good enough, the atmosphere won't be anywhere near oxygen free in terms of chemistry. My BOC tanks cost £15 for
one about waist height, it's 99.998% pure and dry.
I drag the cylinders around the house. I've had them in my bedroom beside my bed. Hospital patients at home routinely have O2 tanks beside them. The
industrial users beat the shit out of tanks, evidenced by how beaten up some of them look.
But if you're renting from someone like BOC, they've been hydrostatically tested and endoscope inspected before you got them. They're not going
anywhere. Divers carry higher pressure cylinders strapped to their spine.
Argon is unnecessary and far too expensive for a lot of chemistry.
Simple advice, DO NOT swap regulators and hoses between reactive gases, such as oxidizers and fuels. If you stick a fuel regulator on a tank of
oxygen, the metals, greases and seals aren't designed for it, and the regulator may have traces of fuel left in it. Combined with oxygen at 230 bar =
spontaneous, explosive combustion. Buy the right regulator for the right cylinder and get one new.
When I screw the regulator on, I finish it with a jerk with the wrench to make sure it's fully seated; but that's like dealing with micrometers, too
much force will damage the threads, 99% of the work has already been done. I open the cylinder valve a tiny bit at first, to check it registers on the
regulator properly. If there's a problem, I can easily shut it off that way. I also take care that the cylinder can't fall and bang it's regulator. A
simple length of chain, or standing it in a specific place and in a specific way, can solve that.
Countless numbers of people use cylinders everyday, and the failure rates are vanishingly low. And even smaller once stupidity is taken out of the
equation.
Read the guides and advice people like BOC publish.
As much as I want to big up the safety talk to feel important, I've got to agree with entropy, you are being a wuss.
Saying this, I am interested in the kind of logic you're getting at. I have to filter things without oxygen around, under vacuum. Combining that with
an N2 cylinder and long filtration times wastes cylinder gas and risks popping something. I would prefer to simply suck air into the funnel via an
aggressive oxygen scrubber; e.g. hot coke, hot alkaline earth metal etc (I'm sure there are safer alternatives, I just haven't thought about it much).
You could pump air in through those instead, but I'd still say go for a cylinder 99% of the time.
You want to question things around oxygen, high pressure fuel gases and the severely corrosive or explosive gases (like Silane, which you'll likely
never have a use for). Noble gases are blind folded, one hand behind the back by comparison.
For a chemist, the most annoying thing about renting N2 is the cost of renting the cylinder. The gas is cheap, the cylinder it's self, for an X waist
height, is about £45 - 50 a year.
Look after your regulators and put the caps back on when it's not on a cylinder.
Respect, yes. Fear, no.
[Edited on 14-7-2010 by peach]
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aonomus
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Well, having seen the calculations on volume vs displaced volume, I agree that its not too big a deal to have a properly restrained N2 tank indoors.
Now I just need to find a reasonable price on one...
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Magpie
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In chemistry argon may at times be more desirable as nitrogen can be reactive forming nitrides, etc.
When you say that argon is far too expensive, that may be true where you live but not for everyone. My distributor charges $20/fill for a 40 ft3
cylinder for either gas.
I likewise had a person from Sweden, I think, tell me aluminum was far too expensive vs stainless steel. That certainly is not true in the US.
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densest
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In the US, retail argon, nitrogen, etc. can be bought for between $25-60 for 240CF depending very much on the supplier. It pays to shop around. The
biggest thing determining your cost of gas is how much you throw away vs. how much you actually use.
That is: how clean the threads are on the regulator and tank and how carefully you tighten it. The quality of the regulator is a close second.
Remember that the tank valve must be opened fully for the valve stem seal to work. And how well you set the flow rate once the system is running.
240CF of any gas should last quite a while if you're using it as a purge or cover gas in a closed or nearly closed system. If you're using to carry
reaction products around that's another story. I've heard of (insane) people connecting to a natural gas stove and using that to save money! Not my
idea of a good time, though leading it outside and flaring it off via an anti-flashback device might be viable.
If you're intending to use a gas for more than a few months, "buy" a tank from your supplier. It'll cost between $100-$150 and it'll be good for ten
years. You can have it refilled or you can simply exchange the empty for a full one at most gas retailers. That way you have it for as long as you
want. If you buy it from your retailer you can sell it back when you're done with it - often at exactly the same price as you paid for it.
Most of the refill price is handling cost - large tanks cost relatively little more than small ones to refill. Balance the usage you anticipate
against the cost of the tank itself.
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peach
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You've said this before. He's asking specifically about removing oxygen and using nitrogen. I don't understand how you're being charged the same price
for two gases that are on the opposite ends of the spectrum to each other with regards to availability from liquefied air. It's more than twice as
expensive from BOC. But congratulations if you're getting them for the same price.
If you buy a tank, you care about it popping and you're having it filled by one of the big names, they won't refill it without it's routine test
certificates. And I wouldn't want one around without them either. Which you'll have to send it off for and pay for. Although, that's every five years
I think in the UK.
The rental price goes down the longer you agree to keep it.
From one of BOC's old price lists, the rental rate for an X cylinder (waist height and the smallest they do these gases in) is about £6 a month. Rent
it for a year, save £13, three years £55, five years £105. Rent a party balloon helium cylinder, get fucked in the ass.
Turning the cylinder off when you're not using it might be a better idea if you're concerned about gas leaking out or the regulator being knocked off.
[Edited on 15-7-2010 by peach]
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densest
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At least here, the test date & tester is stamped into the metal of the tank, so no certificate is needed. And apparently the bulk gas is so cheap
here that the cost of administration and handling is most of the retail price.
I could get liquid oxygen for about 1/3 as much as oxygen gas per mole if I got a 200 liter tank. 1/3 of that price is the hazmat license for the
truck to come to my house and refill my tank! I think LN2 is 1.50/l in very small quantities, decreasing very quickly in bulk.
I'm sure bulk argon is much more expensive than bulk oxygen, and bulk nitrogen is much cheaper than bulk oxygen. Retail pricing is funny.
I'm -not- buying from Airgas. I'm buying from an independent local gas dealer. The national companies charge whatever they feel like.
One alternative to a tank of compressed gas is buying liquid gas. A good dewar is -very- expensive ($100s) new but they do come available
surplus/used. My dewar will keep a liter of LN2 for about 2 weeks with about 50% loss. If all he needs is a stream of gas, that might do. A thin metal
rod which could be lowered in as a controlled heat leak controls the flow rate. Then he could buy gas only when he needed it in small quantities.
[Edited on 15-7-2010 by densest]
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peach
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That's an interesting reply, because I have been wondering about renting corrosive or liquid tanks.
You're also right that it's the handling costs that usually outweigh the gas it's self for a lot of this. It's £15 to have a cylinder delivered from
BOC, but I pick them up since it's £2.60 that way, in tunnel tolls. In theory, I'm supposed to have a compressed gas cylinder sticker in the car
window when I do that. I did call the tunnel operators and they had no real idea what I was talking about. I then called the house insurance people,
who told me I had to have the fire services come out to review my setup, storage and use methods. I did call them. Again, no one had any real idea
what I was on about. And there was no way they were coming out to have a look at my garage.
Liquids are only worse, as you say, because they have to send 'the special truck' that only does one gas at a time, needs a special tank and a special
pump with special hoses and nozzles.
I was thinking of getting one of the dip tube liquid CO2 tanks to make my own dry ice on demand. It's far too expensive buying it by the bag or block,
particularly when I'm not going to use all of it and might not need it again for weeks. Still, I don't need dry ice that often anyway, so I haven't
bothered.
The only time I've seen normal people using liquid oxygen tanks was at a CHAMPS Flameoff, there's a video in this link. You think that's enough gas? 
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aonomus
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For dry ice you could always make a cone adapter for a paintball CO2 tank and just invert it into a sandbag sack (those plastic weave types, not the
fabric type). Fills are cheap, they take the tank, weigh, and fill by mass of liquid CO2. From that point you can just invert and open your valve up.
As for the N2, a small size cylinder rental sounds like a good idea once I clear enough space to put it down. I'm tempted to strap it to a steel load
bearing column in the basement, though that carries a certain amount of risk in the worst case scenario.
The one air sensitive reaction I've done (not really a reaction) is drying out FeCl2 by pulling vacuum on the distillation setup, and allowing water
vapor to fill the setup, and repeating this purge-fill cycle till the entire apparatus is mostly water vapor. Not bad for trying to make do with what
I had, but there are a few air sensitive reactions I want to try (within reason).
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