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aliced25
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Removal of Oxygen & Carbon Dioxide from Air (Glovebox Design)
Yeah, not a newbee* trying to make a big post to begin
Ok, I was looking around at the options for working in an inert atmosphere and thought to myself, well hang on a minute, only about 22% of air is
reactive with most substrates (21% of that is oxygen), so how to remove that so as to avoid having to purchase inert gasses?
Some chemical processes exist - namely removing the oxygen (and CO2, etc.) by reacting them, thereby removing
them from the gas stream. I'm opening this topic up for ideas - quite simply, if we can get a recirculating, filtered gas stream from a hood/glovebox
(I'm trying to design a combo now - the sash comes down and a bottom sash, with the gloves built in comes up & connects to it), then we have a
workable solution for amateur chemists. I'm thinking passing it through a heated tube filled with iron/copper/zinc/etc. powder, removing the oxygen by
oxidizing the bed. The alternative is a solution which the mixture bubbles through, which contains some chemical at a low oxidation state, which
desperately grabs oxygen wherever it can find it.
I know it is possible, the removal of oxygen from Chromatographic systems is well known, but how to build something that can be replenished and reused?
The plus side of this, is that the concept requires that any reactive material in the gas stream be removed, acids are neutralized with a base, basic
material with acids, oxygen with reactive metals, etc. thereby removing the source of strange odors that make amateur chemists the target of Police.
* Some of you may know my other usernames, I'm finally comfortable with using this one again - if you know who I am keep it to yourself (there is a
bloody good reason I changed, OK?).
[Edited on 1-8-2010 by aliced25]
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stygian
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I believe those portable oxygen concentrators use zeolites to filter out N2 and CO2. Maybe with the right size/density/whatever of zeolite you could
filter the air. It is then 'regenerated' by forcing air backwards.
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densest
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Depending on where you live, it may be cheaper to buy nitrogen or argon from a welding supply house.
Oxygen concentrators don't separate all the oxygen from the feed air. AFAIK they reject 50% (more or less depending on all sorts of things).
Using a heated tube running an exothermic reaction means cooling the exit gases back down to room temperature - so you need a heat exchanger. Using
carbon means a lot of CO2 in the exit gas - will your reactions be compatible with 20% CO2? Will your carbon & air give CO2 or CO? If it's not
pure carbon, then it will outgas volatiles - hydrocarbons or complex wood derived chemicals. It will also give water (steam). If you can get iron
filings or similar finely divided iron that has solid products, but it is likely to contain oils or waxes... and zinc is pretty expensive.
This doesn't mean it can't be done, but you should sketch out the entire system including energy flows, supplies, and waste flows before going any
further.
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aliced25
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The reactions won't be compatible with 20% CO2, but Calcium hydroxide would be and running the hot gasses
through a solution gets rid of the need for a heat exchanger pretty quickly. Hang on, see the attached file and this link, it takes about half an hour - but close the system, turn on the recirculation machinery and come back, steel wool isn't exactly
expensive.
Run the off-gas from that (or a modified version) through an alkaline solution, then through sulfuric/phosphoric acid, through a short CaO column.
That will remove pretty much everything that would worry the reactions I'm thinking of. The whole system will be recirculating that same bunch of
deoxygenated air - specific reactions would require additional measures of course - but as a basic plan, that should do it.
[Edited on 1-8-2010 by aliced25]
Attachment: Oregan.Labs.Determination.Percantage.of.Oxygen.in.Air.pdf (233kB)
This file has been downloaded 1961 times
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densest
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That's all plausible. Consider it as an engineering question:
What's more fun and more important to you? Setting up a cool system to remove oxygen from air or having an air-free glove box to perform reactions in?
Do you have time to perfect both? Do you have room in your work area for your system? It's got caustics, heat, and acids in it, so it should be
protected while you're using it. What is the cost to you if your oxygen removal system fails during a reaction?
Compare the setup costs (pipes, stands, clamps, tubing, wash bottles, etc.) & consumables (CaOH, steel wool, acids, burner, etc.) against a small
cheap dewar and a couple of liters of liquid nitrogen from a welding supply store. 80 ft3 of pure N2 for $5 + a thermos bottle, a stopper, a copper
rod to control evaporation rate, and a tube. How much is your time worth?
If your goal is to perform oxygen-free reactions, I'm betting that buying N2 as pressurized gas would be cheaper *once you total all your costs* even
if you had to buy an empty cylinder for $120, a regulator for $35-50, and a fill of gas for $20. That would give you 230 ft3 of gas at the turn of a
knob *which would be guaranteed pure*.
There might be a trucking firm in your area which fills its truck tires with nitrogen (some do - it saves money...) You could get an inner-tube full
of nitrogen from them maybe even for free...
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aliced25
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Yeah, but this is only part of the system I am thinking of - recirculating the air puts the cost up there with Nitrogen gas, without the piping, the
rental on the cylinder, the refilling cost, etc. Trust me, the cheapest Nitrogen Cylinder is going to cost me WAY more than $5/fill (same with
Argon).*
The way I'm thinking of this, it is all under the Hood/Glovebox Combination. There is no need for a burner - quite simply, the gas is pumped out of
the glovebox (or sealed Hood) through the activated steel wool and then through a couple of solutions (or even better exchange columns), then over CaO
(which can be recycled by dehydration). Given the amount of air, say 1m x 0.5m x 1m, that is what 0.5 cubic meters of gas at 1atm, 21% of which is
Oxygen, some other components would need removal, so they will be removed as well. I honestly think that the steel wool (comes in boxes here for
kitchen use) is going to be cheap enough for this proposed route - then again, I've been wrong many, many times - 1 more won't hurt (I HOPE).
Simply have a switch that routes the air from the hood/glovebox either through the hydrolysis tube, then the recirculation tube, or just through the
hydrolysis tube & out. The benefit is no nasty odors, no toxic aerosols, no excessive oxidation/etc. in the immediate vicinity of your lab. I'd
like to be able to do interesting things without poisoning the neighbour's or being hassled by the Police. Designing something like this gives me that
opportunity.
Having the sash able to come down and be sealed to a flip-up panel with the gloves built in, that is the real design issue.
How much is my time worth? I am on an amateur chemistry forum trying to work out ways ordinary people can access chemicals that are otherwise
verboten, even if that means I have to spend hundreds of hours working through references to find such routes. Believe me, building something
completely self-contained as a challenge? Yeah, that works for me - there are people on here discussing how to extract caffeine, make methyl
salicylate, etc. Those chemicals aren't hard to buy, it is the making or performing that is the fun of the exercise. Engineering is just another part
of Science, an arcane art at that
*I will, of course, check the figures (and who they'll sell to) - but I've worked in metal fabrication joints before and IIRC the non-oxidizing gasses
didn't come cheap, neither did the cylinder rental (and they would only use their cylinders, quite a rort really).
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Eclectic
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An open petrie dish of sodium/potassium eutectic, maybe with mag stirrer, should scavenge any remaining reactive gasses?
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unionised
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Recirculate the air through alkaline pyrogallol. Of course you will need some sort of "make up" system to allow for the fact that you took 21% of the
air out of the box.
It doesn't do quite as good a job as the Na/K but it has the advantage that it won't catch fire on exposure to air, you may find this property
helpful.
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densest
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@aliced25 - from what you're saying, it sounds like you're not in the USA. Can you buy liquid nitrogen? In small quantities? That was my first
thought, since it doesn't require expensive tanks, regulators, etc.
Yes, it's an enormous challenge to do interesting things with OTC ingredients. That can be part of the fun!
I don't think you need or want an anaerobic system as a beginner.
I really think that keeping the odors & fumes &c away from the neighbors (and yourself!) is a very good idea. As other people have said, you
should contain & dispose of fumes and vapors at the source, in your equipment setup, rather than trying to use a hood to gather them after
release. A hood is to deal with the leftover bits and to protect you against accidental large releases.
Activated charcoal works well for scavenging vapors & reactive gases. A recirculating system with charcoal filters is a ****lot**** simpler than
what you're proposing.
I strongly suggest you get your hood working with simple absorbents before trying to work in anaerobic conditions. Once you master the lab technique,
then consider a sealed system. There are a lot of challenging & interesting projects that can be done without needing an oxygen free environment.
Look at some of the things woelen has done, for instance.
Let's look at a few numbers for the oxygen absorber:
0.5 m3 @ 21% = 105l = 4.7 mol O2
3 Fe + 2 O2 -> Fe3O4 @ 56g/mol for Fe = 400g Fe
Steel wool is pretty light - you'll need probably (guessing) 5l of it to fill your hood once.
To dry the air you'd need to remove about 5g of water (20C 50% RH).
There'd be about 4mg of CO2, so a little bit of CaO or NaOH would work.
But... the devil is in the details.
How well can you seal your box? If you have air sensitive things inside a small leak will destroy them unless you have pressurized the box, so you
need to continuously add enough N2 to keep the pressure (just a little bit, maybe 0.05 bar) up.
If any of your reactions generate gases or fumes, those must be quickly absorbed before they leak out or corrode/dissolve/react with what's in the
hood. You'd need a big absorber for them as well as the oxygen removal system.
@Eclectic - sodium/potassium eutectic is just a tiny bit reactive... a drop or two of water and watch it spatter...
"Lab Technique & Construction for the Sophisticated Amateur Chemist" is a topic that keeps coming up...
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aliced25
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Yeah, that is the idea I'm working toward - I see very little reason the drop in pressure couldn't be used with a one-way/aka non-return valve (not
exactly expensive) to draw more "air" into the system until it is equal to 1atm. Increasing it above that with ANY gas would preclude oxygen-bearing
air entering the system.
I'm thinking of this more in terms of building a system out of basic plumbing parts (for this part at least, it won't come into contact with the other
gasses - I'm looking at neutralizing them in another stage - useful for both the hood & glovebox), wherein the necessary reagents are loaded via
cartridges (normal plumbing parts with two threaded ends coupling with the relevant threaded ends of the system).
Where the off-gasses contain various contaminants - it would be prudent to put them through a system designed to remove them, amines, etc. with acid
& acids with base. The idea I had was small cartridge type containers that just screw in as bubblers, that way they can be replenished and
changed.
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microcosmicus
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> but how to build something that can be replenished and reused?
Consider Barium oxide. At lower temperatures, the monoxide
absorbs oxygen to become a peroxide while, at higher temperatures,
the peroxide gives up its extra oxygen. At one time this reaction
was used commercially for producing oxygen --- look up "Brin
process" for more information. The following article provides a
starting point:
www.che.uc.edu/jensen/W.%20B.../Reprints/162.%20Brin%20Proce...
Also, there's the patent, no. 432815, but it doesn't say much more.
Barium oxide can be prepared by calcining barium carbonate,
which is widely available and relatively inexpensive. Also, it has
the advantage of sucking up carbon dioxide (turning back into
barium carbonate) as well as water vapor (turning into the
hydroxide) so you can nab the three main non-nitrogen
constitutents of air with the same filter.
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un0me2
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Here is another option - proper pressure swing purification, such as is used in commercial operations for the production of nitrogen gas onsite. The
preparation of MnO is shown in this online paper (complete with pictures) from Manganese Oxalate (which the Author provides a preparative procedure for) via thermal decomposition
thereof, then the reduction of the same with H2 to give the bright-green MnO, which changes color when it is
used up and can then be regenerated.
I've seen other papers where the same is done with Copper Oxide, and then the regeneration via Hydrogen @ higher temperatures (the MnO requires only
300-350C).
This reduces Oxygen to the ppm level - although the Author of the online paper suggests using a liquid nitrogen trap to remove the carbon oxides and
water, CaO will remove the water and a solution of an alkali metal (in a bubbler (before the CaO column) will remove the carbon oxides.
Setting the system so that it continues to pump in air until the working atmosphere is above 1 Atmosphere shouldn't be too hard - all you need is a
pressure sensor that opens/shuts a switch/valve.
By removal of the oxygen and the other non-inert gasses from the air, you are left with virtually pure nitrogen (including several other gasses which
are inert for most purposes - xenon, argon, etc.).
Sounds like a useful way to avoid purchasing/renting gas cylinders for home use. Where other inert gasses are required (like with Lithium, which
reacts with nitrogen), helium for balloons can be purchased as well - remember it also contains a shitload of oxygen (because people tend to suck down
a lungful and then talk thinking themselves amusing). The MnO system would purify that too (and Helium has the benefit that you can actually purchase
small tanks for a lot less than argon).
quam temere in nosmet legem sancimus iniquam
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peach
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There are practical methods of handling glassware and transferring reagents and solvents specifically for running them anhydrously & minus
dissolved O2, if you're thinking of glassware chemistry.
Solvent stills, Q5 catalysts, septums, cannulas, sure seals, dry cylinder gas and more.
Densest is also correct about the use of the hoods being better suited to mopping up traces / mistakes and that a sealed glove box with scrubbers is
going to be difficult to achieve.
But, as always, it depends on what you really need it for. Glove boxes are usually used in applications where there can't be a pinhole in the entire
thing. It's not so much glassware chemistry in them as things like welding titanium for the aerospace industry, or refilling nuclear fuels, handling
germs.
They're usually set up by sucking the air out with a vacuum, then blowing dry, inert gas in from a cylinder. Some of the ones that can't withstand a
vacuum just use cylinders or dehumidifiers for biological work.
Also remember you can very easily make glove bags. I posted a link on here recently to a site that had details for playing around with all the fun,
reactive, acidic, reducing gases, by generating them in disposable syringes. The guy, very smartly, made extensive use of ziplock bags to act as
disposable, easy glove boxes. Not only to keep the gases in, but to keep the atmosphere out.
Glassware is fairly fiddly to handle without any gloves on, let alone those durt-tay thick drain gloves on the boxes. And again, there are ways to do
reactions without them every touching the atmosphere, from solvent to still to salt at the end.
[Edited on 6-10-2010 by peach]
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not_important
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Quote: Originally posted by microcosmicus  | > but how to build something that can be replenished and reused?
Consider Barium oxide. At lower temperatures, the monoxide
absorbs oxygen to become a peroxide while, at higher temperatures,
the peroxide gives up its extra oxygen....
Barium oxide can be prepared by calcining barium carbonate,
which is widely available and relatively inexpensive....
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However the monoxide-peroxide system is not a really complete reaction, free O2 is left. There's tables of the equilibrium values at various
temperatures and pressures around for the searching.
BaCO3 doesn't decompose readily, unlike MgCO3 or even CaCO3. The decomposition temperature is generally given as 1300 C or higher. See http://pubs.acs.org/doi/abs/10.1021/i560106a014 for example
Commercial preparation of BaO from BaCO3 typically mixed a carbon source such as tar with the BaCO3 and heated that, BaCO3 + C => BaO + 2 CO at a
much lower temperature (in a range more like the decomposition of CaCO3). Passing superheated steam over BaCO3, the carbonate maybe formed by the
reduction of the sulfate to sulfide and then that decomposed by passing hot moist CO2 over it.
Note that the reaction of iron+water with O2 is not real rapid. It will remove most of the O2 if given enough time, but a final polishing with
alkaline pyrogallol.
As already stated, the various oxygen 'generators' that concentrate O2 from air are also equilibrium systems that come nowhere near complete removal
of O2 from the off gases nor producing pure O2. They can be handy when you want to use O2 for an oxidation,but not as N2 or pure O2 sources.
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aliced25
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The manganese suboxide route looks feasible enough, even with reheating/reduction to regenerate the column (plus the visual indicator would be fucking
useful). CaO would grab the water from the remaining atmosphere, it would only really entail running the system for an hour or so before starting (of
course, we'll need something to check it with).
In terms of using anything for any length of time, this is used with welding, aluminium welding at that... If there was ANY oxygen it would fuck up
hot Al faster than the crap would weld.
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crazedguy
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If you want a neutral atmosphere would it be simpler to just create a vacuum, if not I would just go to a welding shop.
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vulture
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You cannot manipulate things within a vacuum, not in glovebox style.
Commercial gloveboxes use 10% H2 in N2 (formier gas) over heated Pd catalyst to convert O2 to water, which is then removed by drying train (molecular
sieve). CO2 removal usually isn't considered as it is only a few hundred ppm. If you wanted, removal by solid KOH is an option.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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benzylchloride1
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I recently purchased a glove box and a vacuum pump for around $150, I had to patch the gloves though. I plan on using helium as an inert gas at this
point since I have a cylinder of it around for my two Gow-Mac gas chromatographs. The helium I have is intended for use in balloons and I purchased it
from an automotive store and the gas chromatographs do not seem to be effected by this technical grade material since they use thermal conductivity
detectors I probably should invest in a nitrogen cylinder since nitrogen is
considerably cheaper then helium which is $55 for a cylinder refill. The dry train for my glove box is relatively simple; a column filled with
Drierite will be used to remove water, I still have not determined what I will use to remove trace amounts of oxygen. Generally a glove box is used
for weighing and transferring air sensitive chemicals; most reactions are conducted under inert atmosphere using schlenk style glassware.
[Edited on 5-1-2011 by benzylchloride1]
Attachment: Labconco Controlled Atmosphere Glove Box.pdf (1.4MB)
This file has been downloaded 1104 times
Amateur NMR spectroscopist
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jsc
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The main problem you are going to run into is generating enough oxygen-free gas that you can overpressure your system with it.
When you have a cylinder its easy: you just open the valve until the cylinder gas is flowing forcefully into the system and driving out all the
ambient oxygen.
The easiest thing to do is to get a cylinder, a compressor and the necessary valving, and then fill a cylinder with your freshly produced, oxygen-free
air. Of course, then again, you could probably just buy a cylinder of an inert gas for less than the effort to do this. Which is why gas suppliers are
in business. 
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Lambda-Eyde
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I recall reading that oxygen-free air is easily produced by passing air through a heated column of copper powder. Ideally, 63,55 g copper powder
should remove 24,5 L of oxygen from the air - which leaves us with >80 L of nitrogen left. Now that's not a whole lot of copper for a 30-40 L
glovebox!
However, I'm concerned that this method isn't that effective. It depends on column temperature, flow rate, mesh size etc. Does anyone have any
literature on this? Hands in the air if you're up for an experiment! 
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
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Melgar
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Two ideas that I've thought of myself for this purpose:
1) Melt relatively pure aluminum with a tiny bit of galinstan from a mercury-free liquid-metal thermometer. Mix the molten metals thoroughly. You
barely need any galinstan to make aluminum super-reactive with air. Over time it turns into a gray powder.
2) Get some of those chemical hand warmers and cut them open and pour the powder in a dish in your glove box. That stuff is reduced iron combined
with catalysts that make it more prone to oxidation. That seems like a pretty easy way to eat up the oxygen in your system, and you can buy those
hand warmers pretty cheap in bulk.
Calcium hydroxide, aka pickling lime or whitewash, can do a good job eating up the CO2.
[Edited on 3/18/11 by Melgar]
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kingkool
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| Quote: |
Commercial gloveboxes use 10% H2 in N2 (formier gas) over heated Pd catalyst to convert O2 to water, which is then removed by drying train (molecular
sieve). CO2 removal usually isn't considered as it is only a few hundred ppm. If you wanted, removal by solid KOH is an option.
|
I think copper catalyst is much, much more common.
| Quote: |
I recall reading that oxygen-free air is easily produced by passing air through a heated column of copper powder. Ideally, 63,55 g copper powder
should remove 24,5 L of oxygen from the air - which leaves us with >80 L of nitrogen left. Now that's not a whole lot of copper for a 30-40 L
glovebox! |
Most commercial gloveboxes use a copper catalyst (coated onto high surface area alumina) to remove oxygen. The atmosphere in the glovebox circulates
all the time, and the catalyst can go from 20% O2 to 0ppm in like 15 minutes.
After several months, the spent copper catalyst is regenerated using heating and H2/N2. The copper catalyst only needs to be replaced once every
several years.
You can buy the catalyst itself from various glove box manufacturer's websites online. Here is one source, from MBraun: http://shop.mbraunusa.com/index.php/estore-products/copper-c... .
[Edited on 24-3-2011 by kingkool]
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wxyz
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| Quote: Originally posted by aliced25 | | Yeah, but this is only part of the system I am thinking of - recirculating the air puts the cost up there with Nitrogen gas, without the piping, the
rental on the cylinder, the refilling cost, etc. Trust me, the cheapest Nitrogen Cylinder is going to cost me WAY more than $5/fill (same with
Argon).* |
Just a point of reference: I have cylinders for N2, H2, O2, CO2. They cost about $20 to re-fill at the local wending supply store, which to me isn't
much given that they last many months for me. (I use the N2 for inert gas, and the H2 for hydrogenations, all small scale. I use the CO2 to make dry
ice. And the O2 is left over from my welding days.)
Of course loading up the box the first time with N2 will use a lot, but liquid N2 is cheap and I could use that at first.
Also, I always buy a tank not rent, it's much cheaper in the long run. But you do need to have $100-$200 around to shell out for each.
Also thanks to all for the informative answers in this thread. I am interested in the same project as the original poster. I do agree that it is much
easier to run an air free experiment in the glass outside the glove box, but the glove box is great for loading up the reagents and storing them. I
happened on a great 3 by 5 foot plexiglass glove box at a industrial auction (only $100) and tips here will be a big help in maintaining an O2, water
free atmosphere inside.
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Bright Spark
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My company makes gas generators, we make hydrogen on tap with water and electricity
It sounds like the OP wants a nitrogen generator of which there are a few, some have a molecular sieve others use a membrane system which is nice as
it produces mostly oxygen as a waste product
They aren't cheap though
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Sulaiman
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Would the use of a vacuum pump to remove (almost) all of the air be viable?
Once the initial cost is overcome, the running costs would be negligible.
Such a glove box/fume cupboard may also be useful for distillations etc. ?
A possible means of justifying the cost of a vacuum pump with traps ?
(you know that you want one!)
[Edited on 14-3-2015 by Sulaiman]
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