Sciencemadness Discussion Board - Storage of pressurized liquid SO2 in plastic containers

Storage of pressurized liquid SO2 in plastic containers

garage chemist - 26-2-2011 at 08:37

Today I liquefied some SO2 (around 20g) in a flask, using my lab cryostat for cooling. I poured it into a clean, dry, heavy walled 300ml PET softdrink bottle and capped it, to test the chemical resistance of the PET plastic. After warming up, there was no smell of SO2 around the cap, and the bottle was nicely pressurized.
Two hours later the liquid SO2 was gone, and the bottle smelt very strongly of SO2 on the entire outside. Upon releasing the residual pressure, I found that the plastic had softened uniformly and not just where the liquid SO2 was in contact with it.
While PET is technically resistant against SO2 (I found this info in at least one chemical resistance chart), it seems like diffusion through it is extremely rapid and there also seems to be some swelling and softening of the material due to SO2 takeup. So a PET bottle is, unfortunately, not suitable as a container for liquid SO2 despite the relatively low pressure (4-5 atmospheres).

Has anyone done similar experiments, or devised ways of storing SO2 under pressure without using metal containers?
I don't have suitably heavy-walled PE or PP containers, nor do I have any idea where such could be found.

watson.fawkes - 26-2-2011 at 10:22

Quote: Originally posted by garage chemist

I don't have suitably heavy-walled PE or PP containers, nor do I have any idea where such could be found.

It used to be that outdoor equipment stores carried PE or HDPE water bottles.

peach - 26-2-2011 at 11:57

Absolutely tons of plastic bottles are PP or PE, they're a major section of all the plastics used for packing domestic commodities. If you search eBay.co.uk for 'plastic bottles' you'll find a large amount of them. You want to avoid any that look crystal clear, as they are likely PET. The rest will be PP or PE. They do tend to be the thinner walled kind, the heavy walled ones are out there. When I buy bottles of drain sulphuric, it comes in a solid white PE bottle with a thick wall. I'd post you mine actually, but it's still pretty much full. If I find an almost empty one I'll let you know; but I've likely thrown it out if it was near empty.

I'm looking at a graph for the vapour pressure of SO2 now, and it appears to be around 3-4 bar at room temperature; 40 to 60psi.

Things like fizzy drinks bottles are usually rated to burst at about 200psi. But I wouldn't feel too happy storing any serious quantity of SO2 in a plastic bottle at 40-60psi. If it doesn't burst, it's probably going to try making it's way through the plastic or around the seal anyway.

Store it in the freezer and the pressure drops to around 0.7 bar.

{edit}As watson suggests, have a look at plastic water bottles for camping, hiking or running. They are quite often much heavier walled than others due to them getting beaten up in rucksacks or out in fields. The stores hardly ever list what they're made from, so check the bottle for the recycling symbol. 2 in a triangle for HDPE, 5 for PP.

{edit2}I want to see your cryostat.

[Edited on 26-2-2011 by peach]

hissingnoise - 26-2-2011 at 13:00

Quote: Originally posted by watson.fawkes

It used to be that outdoor equipment stores carried PE or HDPE water bottles.

I don't know which polymer is used for the ordinary, small water bottles but they're readily chewed up by H2SO4

garage chemist - 26-2-2011 at 15:18

Nevermind, I found an old drinking bottle made of sturdy aluminium that appears quite perfect for the purpose once I replace the crumbling old rubber gasket with one made of PTFE.
It appears quite ideal for ammonia too, since aluminium is completely resistant against both wet and dry ammonia.
Now I only need to drill a hole for the connector into the cap and find some kind of valve.

OK, I'll make a pic of my cryostat. It goes to -60°C and I've liquefied ammonia in it. I call it the "no more dry ice machine" since I'll never have to buy dry ice again as long as it works.

Magpie - 26-2-2011 at 15:59

That's a nice project GC, and I too would like to see your cryostat.

Quote: Originally posted by garage chemist

Nevermind, I found an old drinking bottle made of sturdy aluminium that appears quite perfect for the purpose once I replace the crumbling old rubber gasket with one made of PTFE.

I'm surprised that you found a drinking bottle with a screwed cap that could give you a good enough seal for 3-4 bar. But I suppose you can tolerate a tiny bit of leakage. PTFE does seem to give a pretty good seal on my glass bottles for ether.

Quote: Originally posted by garage chemist

Now I only need to drill a hole for the connector into the cap and find some kind of valve.

Is the cap thick enough to allow you to screw in a nipple or will it have to be welded? A needle valve with PTFE seat and packing would seem good but might be expensive too. Maybe even an HDPE seat and packing would be OK too.

peach - 26-2-2011 at 16:43

Quote: Originally posted by hissingnoise

Quote: Originally posted by watson.fawkes

It used to be that outdoor equipment stores carried PE or HDPE water bottles.

I don't know which polymer is used for the ordinary, small water bottles but they're readily chewed up by H2SO4

If it's crystal clear and 'crackles' as you scrunch it up, it'll be PET. Pretty much all the disposable drinks bottles are PET.

The kind I'm thinking of, and I expect watson, are the ones you're supposed to reuse; that are usually opaque and thick walled.

Eclectic - 26-2-2011 at 18:45

Why the need for plastic container? What about used empty propane cylinders for low pressure gasses? (gas over liquid)

Magpie - 26-2-2011 at 19:04

Quote: Originally posted by Eclectic

Why the need for plastic container? What about used empty propane cylinders for low pressure gasses? (gas over liquid)

That was my first thought also. In fact it seems that you could use the Schrader type valve already built into the gas bottle both for filling (with gas), using, and sealing. Attach a regular propane nozzle and you have a needle valve for use and filling (with gas) too. Compatibility of the soft parts in the valves with SO2 (dry, and a little wet) would need to be verified. I'm not sure if these valves could be used to fill the tank with liquid, but I don't see why not. Anyone know?

For an easy fill with a liquid a larger fill port would work well.

[Edited on 27-2-2011 by Magpie]

[Edited on 27-2-2011 by Magpie]

Eclectic - 26-2-2011 at 19:44

I'm pretty sure the "Schrader" valve is spring loaded pressure relief, but there are adapters available for refilling from the main port.

Magpie - 26-2-2011 at 20:10

I just went out to the lab and checked my 400g propane bottle. It appears to have a small Schrader looking valve on the dome - but I guess this is a pressure relief valve. However, the externally threaded discharge port does have a Schrader valve which is opened when the valved nozzle or regulator is screwed on to the port.

[Edited on 27-2-2011 by Magpie]

[Edited on 27-2-2011 by Magpie]

garage chemist - 27-2-2011 at 00:40

I can't use empty propane cylinders since I want to pour the liquefied SO2 into the cylinder and then seal it. The types of valves in use here can't be removed, and I don't have a compressor that I could use for SO2.

condennnsa - 27-2-2011 at 01:41

how did your setup for liquefying SO2 look like? did you make it from burning sulfur? and yes, please if you can, take a pic of your cryostat

garage chemist - 27-2-2011 at 02:03

I added 30% HCl from a dropping funnel to solid potassium metabisulfite, and gently heated the flask with a bunsen burner to liberate the gas. The SO2 passed a washing bottle with a little H2SO4 and then went on to the cooled condensation flask.

Conc. H2SO4 for drying SO2 is not an ideal choice, the solubility of SO2 in this is quite high (100g/kg) and increases with sinking concentration. A CaCl2 drying tube would be better, but I wanted a visual indication of gas flow, and the H2SO4 in the wash botle was already saturated with SO2 from a previous batch so there were no losses.

You can't use burning sulfur as a SO2 source for this.
If you burn sulfur with air to use up most of the oxygen, you get around 13% SO2 in nitrogen plus residual oxygen.
When this gas is cooled to -50°C, only half of the SO2 condenses out, giving an offgas with around 6% SO2.
In industry, this offgas is fed to a contact process H2SO4 plant.
At home, losing half of the SO2 to the atmosphere would be unacceptable. Also, -50°C is not easily reached with a freezer.
At the -20 to -30°C that I was working at, nothing would condense from sulfur burner offgas.
You need to prepare pure SO2 from a sulfite salt or by reduction of H2SO4 with e.g. copper turnings.

gsd - 27-2-2011 at 09:27

Quote: Originally posted by garage chemist

You can't use burning sulfur as a SO2 source for this.
If you burn sulfur with air to use up most of the oxygen, you get around 13% SO2 in nitrogen plus residual oxygen.
When this gas is cooled to -50°C, only half of the SO2 condenses out, giving an offgas with around 6% SO2.
In industry, this offgas is fed to a contact process H2SO4 plant.
At home, losing half of the SO2 to the atmosphere would be unacceptable. Also, -50°C is not easily reached with a freezer.
At the -20 to -30°C that I was working at, nothing would condense from sulfur burner offgas.
You need to prepare pure SO2 from a sulfite salt or by reduction of H2SO4 with e.g. copper turnings.

Actually in industry, the liquid SO2 is made by SO2 from burner gas but not by direct cooling / condensation process.

The burner gas containing about 10-12 % SO2 is first scrubbed with water to absorb most SO2. (IIRC the solubility of SO2 in water is about 20% at 30 Deg C.) Inert gasses are let-off from scrubber and the water laden with SO2 is stripped by steam heating. The gas released now is almost pure SO2 with some water vapours - which are removed by H2SO4 wash and the SO2 is compressed and liquified in Compressor and Chiller.

gsd

garage chemist - 28-2-2011 at 13:00

Pics!

The Cryostat itself, a Haake Q combined with recirculator and thermostat F3.

Instead of using the thermostat F3, I added a selfbuilt controller that switches the cooling on and off at adjustable temperature limits (-20 and -30°C for this application). The controller is actually a PID controller but I use it as a two-point thermostat since PID control is totally incompatible with compressor cooling. I also added an overhead stirrer since there is no stirring when the recirculator is switched off.

The original method of temperature control was that the cooling was running the whole time, and the thermostat was heating against it to keep the bath temperature constant. Extremely wasteful of electricity. I changed this as soon as I got it. Now, the cooling only runs 10% of the time.

The SO2 gas generator. I am heating sulfuric acid with sulfur. This is a very cheap and convenient method. The acid has to be above 300°C to react with the sulfur, and the water has to be constantly distilled off. The SO2 stream is quite slow.

The condensation flask. The inlet tube runs down to the bottom.

You can see the droplets of liquid SO2 on the walls of the flask here.

And here's the stirrer shaft covered with frost, since it's made of aluminium and conducts heat very well.

[Edited on 28-2-2011 by garage chemist]

NurdRage - 28-2-2011 at 13:28

Can i ask what you want to use your SO2 for?

This is not a perfect all around solution, but for some things this is pretty good: Store the SO2 as a solution in methanol.

SO2 has a VERY high solubility in methanol (i think 40%+ by mass), and at room temperature the SO2-methanol solution is very convenient to handle and can be added directly to various reactions where the methanol isn't a problem.

I've done it personally and have used it to make sodium dithionite and reduce manganese dioxide.

[Edited on 28-2-2011 by NurdRage]

garage chemist - 28-2-2011 at 15:08

I eventually want to develop a catalytic reactor for SO3 production from SO2 and air, and in order to have a gas stream of constant and finely adjustable composition I want SO2 gas "on tap", meaning from a gas cylinder.
Also, I need it for gold and platinum group metals refining, and not having to set up a gas generator every time I want to precipitate gold would be an advantage.

Dissolving SO2 in an alcohol is an idea I also had, in order to wash it out of the offgas from a sulfur burner. Ethanol, which I had in mind, dissolves 200 times its own volume of SO2 at 0°C.
But I now found that the reduction of H2SO4 with sulfur works so well that I will produce all of the SO2 for the cylinder that way.
I will use "recycled" sulfuric acid for this, which is mostly spent nitrating acid from various aromatic nitrations that I have boiled down to density 1,8. Reduction with sulfur is a good way to turn it into something useful.

NurdRage - 28-2-2011 at 15:22

Interesting,

yeah the alcohol method is probably not good for a catalytic gas reactor.

Good idea with the reduction method. Sounds like you're all set.

I look forward to your future setup

peach - 28-2-2011 at 16:50

First of all, NICE setup.

What are you thinking of using for the cylinder?

The commercially available ones usually rot around the valve stem, where they're in contact with moisture. Or the tap jams because moisture has gotten into there as well. So, if it's going towards a cylinder, it may help extend it's lifespan if all of the glassware is blown out with anhydrous cylinder gas before the generation starts. And the cylinder it's self. Blowing the cylinder out may be harder work. The typical method for getting all the damp air out of something is to first put it under vacuum and then backfill, sometimes a few times over. Argon is expensive compared to air, but has the added advantage that it should more easily displace the air given that it's heavier than it.

There's a picture of a HCl(g) cylinder on curly arrows blog with the stem corroded shut. The cylinder has a very, very basic setup on it, which is just a brass flow control stuck on the valve stem.

The really expensive Matheson manifolds for corrosive gases will have a purge feature, to blow the gas out and displace any damp air as well, before it's all turned off. But with any setup, blowing the corrosive material out and replacing it with dry, inert gas around the controls is going to help.

I expect you may already know some or all of this, I'm only mentioning it to save any future 'urgh!' moments if not.

Eclectic - 1-3-2011 at 02:07

GC, have you tried to find any catalysts for the H2SO4 + S8 reaction? Copper, iron, vanadium? We had a thread on this a while back, with a lot of "it will never work" attitude, much like the making potassium thread.

garage chemist - 1-3-2011 at 08:00

No, the reaction goes sufficiently fast at reflux temperature, and with the bunsen burner, this is very simple to do.
I made about 40g SO2 (weighed as liquid) in 3 hours using 100g H2SO4 and 15g sulfur (obviously, a lot was left over as I had to stop since it was getting late).
The sulfur melts into a large viscous blob that floats around in the boiling acid, evolving gas at the interface between sulfur and acid. I think that the reaction rate depends on the area of contact between these liquids. Stirring should help, but it's entirely too hot for PTFE.
I think that using a larger amount of reagents should increase the speed of gas generation.
One should also use more than the theoretical amount of sulfur, since it tends to get volatilized and settle as a thick yellow dust coating in the condenser.
The acid, however, is consumed practically without losses. Only the reaction water distills, provided one doesn't boil needlessly intense.

garage chemist - 13-3-2011 at 08:10

I was not able to get the aluminum drinking bottle sufficiently gastight- there always was too much leakage around the cap to tolerate.
Instead of this, I now acquired an old 1L medical oxygen cylinder in order to fill it with SO2.
Upon disassembly of the cylinder valve, I found that the inside parts were made of brass. Experiment will have to show how much this is attacked by SO2.
Chemical resistance databases contradict each other, but in one book, "Handbook of corrosion data" I found that most brass types resist anhydrous SO2 and are corroded by it in presence of moisture. So the situation is similar to chlorine, which needs to be perfectly dry to be bottled in steel cylinders.

Does someone know where to look up the density of liquid SO2 at 50°C? All sources just give the density (1,46 g/ml) at the boiling point (-10°C), but the liquid obviously expands upon warming, and if there is insufficient headspace in the cylinder, the incompressible liquid can rupture the cylinder upon expanding despite the 150 bar rating.
I found the information that commercial 2L SO2 cylinders contain 2kg, and 10L ones contain 12kg. So I should be able to safely fill 1kg into my 1L cylinder.
Any thoughts about that?

ElectroWin - 13-3-2011 at 10:00

maybe measure expansion coefficient and tell us?

H2SO4 + S reaction is catalyzed by iron!

garage chemist - 13-3-2011 at 11:15

Today I set up a larger SO2 generator, using 120ml H2SO4 and 55g sulfur, and this time I added 2g Fe2O3 in the hope of getting a more rapid gas stream. This made a huge difference!
The SO2 evolution began at a much lower temperature, and by the time the sulfur had become black and viscous, the mixture was bubbling vigorously and the gas stream was so fast that the bubbles in the washing bottle could not be counted any more (estimate 6-8 bubbles per second).
The bunsen burner did not have to be set as high as without the Fe2O3- the acid was nowhere near boiling.
The gas stream was so brisk that solid sulfur aerosol was carried into the washing bottle and even into the liquid SO2, making it turbid. I need to add a gas filter the next time.
Also, at -20°C bath temperature, there was a significant amount of SO2 escaping from the cold trap, and I had to lower the temperature to -30°C to condense it all.

After one hour, I stopped the reaction, and 35g liquid SO2 had accumulated. The last time, I had to wait 3 hours for this amount, and the flask was much hotter.

This iron catalysed H2SO4 + S reaction has now suddenly solved the question of "how do I make 1kg pure SO2 in one day, with cheap materials".

If 1L H2SO4 costs EUR 15 and 1kg sulfur EUR 7, then the price for 1kg SO2 (from 566ml acid and 167g S) would be EUR 9,66.
Refilling the 1kg SO2 cylinder for less than EUR 10 raw material cost, that's seriously cheap!

Eclectic - 14-3-2011 at 07:12

I found a old patent or reference in Muspratt or the like from late 1800's where they used pumice stone for added area too. This in a cast iron reactor.

Do you know if CPVC is resistant to liquid SO2? The pressures seem fairly low and you could overcoat it with fiberglass.

garage chemist - 15-3-2011 at 15:20

I filled a test quantity of SO2 (around 50g) into my oxygen cylinder, which has a nickel (?) plated brass valve, with the inner moving parts made of bare brass. It seems to hold up very fine so far. After I've used up the SO2, I will open the cylinder again and disassemble and inspect the valve. Then I can prepare for filling the cylinder to its full capacity.

I found some bits of possibly useful information in some old chemistry books. In "Elements of chemistry" by Sir Robert Kane:
http://books.google.de/books?id=IYEEAAAAQAAJ&pg=PA1020&a...
a method for production of SO2 is given, consisting of heating a mixture of MnO2 with sulfur:
MnO2 + 2 S ---> MnS + SO2
This could be useful for those wishing to use only elemental sulfur as the sulfur source.
Also, for preparation of SO2 on a larger scale, heating charcoal with H2SO4 is recommended, giving a gas mixture of 2 parts SO2 with 1 part CO2, but I see no reason to do this when sulfur with a little Fe2O3 can be used instead of charcoal.

I order to prepare 1kg of liquid SO2, I realized that I have to liquefy it in portions as my cryostat is too small to accomodate a 1L round-bottom flask. Thus, there is a need for intermediate storage of the liquid SO2. Although possible, I would rather not place glass flasks of liquid SO2 next to the frozen food in our freezer.
I have a 2L glass dewar vessel into which I could pour the liquid SO2 to pool the portions. It would obviously have to be located outside while being filled. What worries me is the possible ingress of atmospheric moisture, which would promote corrosion of the steel and brass. Do you think that a styrofoam cover (if it isn't softened by SO2 like PET) provides enough protection against that?
The dewar vessel is cylindrical with a wide mouth, with no lid.
Better ideas for intermediate storage of SO2?

watson.fawkes - 15-3-2011 at 21:09

Quote: Originally posted by garage chemist

I order to prepare 1kg of liquid SO2, I realized that I have to liquefy it in portions as my cryostat is too small to accomodate a 1L round-bottom flask. [...] Better ideas for intermediate storage of SO2?

You're farther ahead than I am in working on this project, although I did just acquire a lecture bottle for the purpose. My solution, which I'm in the middle of acquiring gear for, is to liquefy with a refrigeration compressor. SO2 is refrigerant R-764 and was commonly used before the freons. One of the advantages of this approach is that you evacuate the storage bottle before filling, and then you're generating and pumping with a fully sealed system, so assuming your drying train is working right, you get good-and-dry SO2.

Apropos of the question you posed, the compression stage isn't a batch process, so there's no need for intermediate storage. The main disadvantage of this method is that the generation stage needs to have a fairly small waste gas volume, or else there's more work to be done to deal with that.

garage chemist - 17-3-2011 at 15:13

I would probably do it that way too, if I could cheaply obtain expendable old fridge compressors. But I can't.
All old fridges are brought to the scrapyard and get recycled by special companies that also dispose of the CFC refrigerant in an environmentally friendly way.
The scrapyard doesn't let anyone near the old fridges, and asking doesn't help.

The refrigeration compressors are also quickly destroyed by pumping corrosive gases like ammonia and SO2. The compressors of the old-time SO2 refrigerators were built completely different (openly accessible motor and shaft).
Also, air in the system is a big problem as it collects in the gas cylinder, raising the pressure required for liquefaction.
One can evacuate the cylinder beforehand and purge the compressor with the gas to be liquefied, but during the unavoidable refilling of the gas generator, air will get into the system again.

Air in the system is not a problem with pressureless liquefaction by cooling. Here, ingress of moisture is the issue, along with the question of intermediate storage of the cold liquid. A freezer dedicated for lab use would solve the second problem.

The ultimate gadget for filling gas cylinders at home would be the "Universal oil-free laboratory compressor for corrosive gases". Motor openly accessible, pistons sealed with PTFE, all exposed parts made of steel, capable of compressing chlorine.
Perhaps someone who is really good at machine-building may one day construct something like this.

Fleaker - 22-3-2011 at 22:21

This is an interesting thread. It's also scary. Liquid sulfur dioxide is not something I'd ever with to have a spill of without being far away!

garage_chemist, on my 70 kg tank, it has a siphon tube and the liquid expands in the stainless tubing once outside of the bottle.

Bulk LSO2 is about $1.05/kg so making it for 10X that price on the small scale certainly isn't bad.

Natures Natrium - 31-3-2011 at 19:43

Wow, I am so jealous of your cryostat. I can think of dozens of fascinating uses just off-hand.

As for SO2 in an old, small, stainless steel lecture bottle (previously used for oxygen) with a brass valve, I can report that my bottle is still holding up to this day. That is around 5 years, I believe. The gas was mostly dried by the precipitation of ice crystals as I recall (since I was using dry ice/acetone, temp near -60C).

Your method of generating SO2 sounds so much more convenient and controllable than HCl on metabisulfite, particularly since you seem to have found a suitable catalyst.

Good stuff, I just had to come out of lurkdom and drop my two pennies. :-)

MnO2 + 2S ---> MnS + SO2

tetrahedron - 3-11-2012 at 15:09

Quote: Originally posted by garage chemist

I found some bits of possibly useful information in some old chemistry books. In "Elements of chemistry" by Sir Robert Kane:
http://books.google.de/books?id=IYEEAAAAQAAJ&pg=PA1020&a...
a method for production of SO2 is given, consisting of heating a mixture of MnO2 with sulfur:
MnO2 + 2 S ---> MnS + SO2
This could be useful for those wishing to use only elemental sulfur as the sulfur source.

those old sources gladly understate the dangers involved in the experiments..how vigorous is this reaction? up to what scale is it a safe prep? i have a feeling you tested it yourself..do you have any detailed data on apparatus, yield, etc?

unionised - 4-11-2012 at 05:07

Re the original posting and title (and I realise it's a bit late)
http://www.tandfonline.com/doi/abs/10.1080/00028896709342519
SO2 leaks through (at least some) plastics

garage chemist - 4-11-2012 at 12:42

Quote: Originally posted by tetrahedron

Quote: Originally posted by garage chemist

No, I haven't tested it. Try it out yourself and report your findings. The original text recommends to heat this mixture in glass flasks, so it definately isn't a pyrotechnic mixture.
Personally I would trust these old texts any day in contrast to the bullshit that can be seen on some youtube videos and wikipedia articles. If there's one thing that these old-time chemists were really good at, it's experimental technique.

I have switched to burning sulfur in a stream of pure oxygen in my quartz reaction tube. This is far less dangerous than the method using boiling concentrated H2SO4 and sulfur and produces a much faster stream of SO2, saving lab time.
It also fills my garage with the most beautiful and brilliant blue light from the flame.
The only problem with this process is that the intense heat of the sulfur-oxygen flame vaporizes a part of the unreacted sulfur, which condenses into a fine sulfur aerosol upon cooling in the downstream section of the tube. So much of this aerosol is produced that a glass wool filter is very rapidly clogged, producing so much backpressure that the joints of the quartz tube pop open despite clamping them.
If no gas filter is employed, then the aerosol deposits on the glass coil of the condenser that is being used to liquefy the SO2, fouling up the heat transfer and necessitating labor-intensive cleaning of the condenser after each production run.
Additionally, the sulfur aerosol is also suspended in the liquid SO2, necessitating a redistillation of the crude liquid to obtain a clear SO2 product.
I need to develop a gas filter that can hold a large amount of solids before becoming saturated.
Adding to the problem, the sulfur aerosol deposits as a rubbery, sticky layer of "plastic" sulfur, not as a dust. This is what blocks the glass wool filter so quickly.

On the bright side, this process gives an excellent yield.
I repeatably obtain an 85% yield of liquid SO2 after the redistillation.

tetrahedron - 4-11-2012 at 17:04

Quote: Originally posted by garage chemist

No, I haven't tested it. Try it out yourself and report your findings.

thanks for the input. i might.

Quote:

the aerosol deposits on the glass coil of the condenser that is being used to liquefy the SO2

have you tried a room-temperature precondenser? also, do you have a lot of unreacted oxygen?

garage chemist - 4-11-2012 at 21:58

Quote: Originally posted by tetrahedron

have you tried a room-temperature precondenser? also, do you have a lot of unreacted oxygen?

There is almost no unreacted oxygen, that's the beauty of the process and the reason for the high yield upon direct liquefaction of the burner offgas. The reaction is arranged so that the hot flame contacts (and vaporizes) plenty of excess sulfur, consuming all oxygen. If I had excess oxygen in the offgas then I wouldn't have the aerosol problem, because the aerosol would burn up.
But since oxygen is the more valuable precursor (I'm using a high pressure cylinder) I choose to work under conditions of excess sulfur. Also, without excess sulfur, I would face the problem of significant co-production of SO3, which would require special purification of the crude SO2 to remove it.

Yamato71 - 5-12-2012 at 13:26

I have used epoxy coated aluminum paintball CO2 cylinders to store gases and liquified gases up to 1800 psi without leakage. The black 1/2 to 1 liter bottles have an "O" ring where the cylinder valve seals into the aluminum body so that you can condense liquified gases such as SO2, NH3, etc directly into a chilled bottle and then screw the valve back on before allowing the bottle to warm up to RT. This is especially effective for the collection and storage of anhydrous ammonia using an ammonia generator and a dry ice/acetone "cold finger" condenser. I have an assortment of these bottles charged with Ar, N2O, H2, O2, N2, CO, CO2, NH3, H2S, etc for lab use similar to the "lecture bottle" sized cylinders we remember from college. Standard CGA gas pressure regulators can be fitted to to the paintball cylinder valves, usually with a 1/8" NPT nipple for low pressure gas delivery.

[Edited on 5-12-2012 by Yamato71]

garage chemist - 5-12-2012 at 13:44

Are the valves of the paintball cylinders made of steel? They would be perfect for ammonia if they were.
The valves of the 1L medical oxygen cylinders that I'm using are nickel plated brass. They hold up perfectly with sulfur dioxide, but aren't suitable for ammonia.

I don't have a cheap source for dry ice. I'm using my selfmade compressor cooler for condensing gases.
Well done on condensing and bottling all those different gases!
My SO2 cylinder now contains about 700g and that should be enough for my planned experiments. I always chilled the bottle in my -30°C methanol bath, unscrewed the valve and poured in the prepared batch of redistilled liquid SO2.
That way I have accumulated this amount of SO2, preparing batches of about 200g and collecting them in my cylinder.

Yamato71 - 5-12-2012 at 16:29

Actually, most of the valves I've seen on paintball cylinders are brass, which rules out their use for moist ammonia. I have also seen stainless steel valves. As to using brass valves for ammonia, if your NH3 is anhydrous, you shouldn't have any problems.

In my case, I generated NH3(g) using an ammonium salt (nitrate or chloride) and NaOH. The moist NH3 was then passed through a column of sodium amide (NaNH2), which converted any residual water into more NH3 and NaOH. This pre-dried ammonia gas was then passed to a large insulated RBF containing sodium metal shot, a stirbar and topped with a large dry ice/acetone reflux condenser vented with a CaCl2 drying tube. As the NH3 condensed into the RBF, the sodium dissolved into the liquid ammonia and destroyed any residual traces of water. As long as the solution was dark blue, the ammonia was sufficiently anhydrous.

When the flask held enough anhydrous ammonia, the open paintball cylinder was screwed to a homemade adapter that threaded into the cylinder and mated with the taper on the end of the condenser. The paintball cylinder was then lowered into a dry ice/acetone freezing mixture and a vent tube carried NH3(g) from the RBF to the condenser atop the cylinder. As the anhydrous NH3/Na mixture warmed up, the gaseous ammonia was again condensed into the aluminum cylinder.

This step was essentially a final distillation as the metallic sodium was left behind in the flask, together with a bit of NaOH from the dehydration. When the anhydrous liquid ammonia finished distilling into the paintball cylinder, the valve was screwed into place and the cylinder was removed from the freezing mixture.

One of these ammonia cylinders with a brass valve sat on the shelf more than 3 years before it was used. After it was emptied, the valve was removed and inspected closely. Even after three years, the brass was still bright and shiny without a trace of corrosion. As long as the ammonia is strictly anhydrous, having brass fittings shouldn't be an issue.

garage chemist - 6-12-2012 at 11:29

Yes, drying liquid ammonia with sodium is what Brauer recommends too. Since I don't have any sodium amide, I predried the gas with KOH flakes.

How do you unscrew the valve from the paintball cylinder?
With my medical oxygen cylinders this was always a big problem, requiring excessive use of force. I still have two cylinders on which I haven't been able to unscrew the valve at all.

watson.fawkes - 6-12-2012 at 11:53

Quote: Originally posted by garage chemist

With my medical oxygen cylinders this was always a big problem, requiring excessive use of force. I still have two cylinders on which I haven't been able to unscrew the valve at all.

If you've got a friend with a chain vise, of the kind used by pipefitters, they'll clamp a cylinder well enough to change the valve. Use a brass shim around the cylinder if you don't want to mar it. Also, use a large wrench with a long handle.

garage chemist - 6-12-2012 at 13:14

Can you link me to a picture of the device that you're writing about? Never seen anything like this, and google turns up nothing that seems right for the job.

Yamato71 - 6-12-2012 at 13:57

Since the valve on the paintball CO2 cylinder is sealed with an "O" ring, it can be unscrewed by using a simple 1" open-end wrench (spanner for our EU friends) and resealed the same way with only moderate hand torque. GC, what device are you asking to see, the paintball cylinder or the chain vise? BTW, a strap wrench will work to secure the cylinder as well. Normally, I just wrap an old towel around the cylinder and clamp it into a bench vise.

garage chemist - 6-12-2012 at 14:00

I'm asking to see the chain vise. Though I am also unsure about which paintball cylinder Yamato means, the CO2 kind or the nitrogen kind.

Yamato71 - 6-12-2012 at 14:19

I am only familiar with the liquid CO2 variety. They use an O-ring sealed valve so that they can be recharged in the field using dry ice and an open end wrench. They are powder-coated aluminum, rated to 1800 PSI (12,410 kPa).

watson.fawkes - 6-12-2012 at 16:01

Quote: Originally posted by garage chemist

I'm asking to see the chain vise.

In the USA, RIDGID makes a quality, popular line of pipefitting tools. Here's their bench-mounted chain vise. You can't see it that well in that product photo, but the pins holding the links of the chain together stick out on each side of the links. There's a pair of recesses in the vise body, on the left, where the two ends of pins on the chain catch in the body of the vise. The handle on the right tightens the chain. All but the smallest have a 4" / 100 mm diameter capacity, plenty big enough for lecture bottles or paintball cylinders.

There are other ways of rigging up a strap or chain around a cylinder to hold it while torquing on the head. This is by far the most direct way.

Natures Natrium - 11-12-2012 at 20:09

Well, crap. I recently tried to use my 6 or 7 year old bottle of SO2, only to find that the valve is completely frozen shut. At some point in the future, I will chill the bottle and unscrew the valve from the bottle to see what the deal is. I am supposing that the culprit here is inadequate drying of the SO2 gas before storage.