Sciencemadness Discussion Board - Generating, Drying and Liquifying SO2 -> SO2Cl2 etc

Generating, Drying and Liquifying SO2 -> SO2Cl2 etc

Sauron - 28-8-2008 at 23:17

What is the best substrate for generating SO2? Vogel and Merck Index are mum on this. Vogel just says "Go get a cyclinder" while Merck 12th says nothing. I have not yet looked in Brauer, or Ullmann but I do not have high hopes.

Also I am soliciting advice on the drying train.

SO2 condenses easily at -10 C and freezes at -78. I want to liquify it and store it in lecture bottles with and without dip tubes.. I cannot purchase SO2 where I am.

I want to use SO2 to prepare SO2Cl2 and SOCl2. Dry ice is readily available for cooling.

The no-brainer choice would be sodium sulfite or bisulfite. Generating with dil H2SO4 and scrubbing with conc H2SO4 are what come to mind. I am looking for anything more efficient, if possible.

[Edited on 29-8-2008 by Sauron]

not_important - 29-8-2008 at 00:03

Silica gel or alumina could be used for drying, although H2SO4 works well. Also, if you freeze the SO2 and then allow it to just barely melt, I believe water will remain frozen (possibly as a SO2-H2O mix) and so could be filtered off to give quite dry SO2.

I've always burned sulfur for making much SO2, for cost reasons.

Sauron - 29-8-2008 at 00:12

Cost is not really an issue and I'd just as soon not get into a DIY sulfur burner. SO2 from a burner is fine for making SO3 over V2O5 but that is not what I am after.

Thanks for the input.

Brauer has no prep for SO2 but he does have drying procedure to use in prep of SO2Cl2 from SO2 and Cl2. He recommends conc H2SO4 for both gases, washed seperately then mixed before passing through the reaction tube, which is a 6-bulg (or longer) Allihn condenser mounted vertically. The bulbs are about half packed loosely with glass wool and about half of the remaining upper space is then filled with granular activated carbon. This setp produces c.150 g sulfuryl chloride per hour. The product is quite pure and requires a single distillation only.

His setp using coarse camphor as catalyst is even simpler but the product requires two fractionations to rid it of camphor. IMO the GAC catalyst is better.

[Edited on 29-8-2008 by Sauron]

not_important - 29-8-2008 at 04:40

Getting a sulfur burning that worked and keeping it working was trouble, but cost was a large enough issue to be worth the trouble.

The charcoal catalysed method did seem better to me as well. I've tried it, but used a simple plain tube fractionation column with a loose alternating layering of glass wool and charcoal, in this case freshly prepared sugar charcoal.

Klute - 29-8-2008 at 05:53

Very interesting topic.

I have used the bisulfite method when trying to produce dimethyl sulfate via MeOH/SO2/CuCl2, and found it pretty satisfying: very controlable flow, no excessiev frothing or foaming, and not too excessive volumes, although this wasn't on a very large scale.

Please let us know how it goes!

woelen - 29-8-2008 at 06:18

I also used bisulfite + sulphuric acid for making SO2. The yield of gas was good, but I suffered from excessive foaming. The entire erlenmeyer and even the tubes going from the erlenmeyer were filled with foam.

Klute, can you elaborate on your method of making SO2, which does not suffer from excessive formation of foam?

Sauron - 29-8-2008 at 07:12

Yes, please, Klute, we are all ears. Kindly let us know all the details of your SO2 prep.

smuv - 29-8-2008 at 07:34

I have used sodium metabisulfite and acid in the past to generate small amounts of SO2; no problems with foaming but this was all on a small scale.

kilowatt - 29-8-2008 at 07:42

If you can do high temperature (around 1200°C or a bright yellow heat) a mixture of coke or coal with gypsum or gypsum and silica will do. It can be cast into pellets and loaded into a steel or refractory retort. With excess carbon (more than 4:1 carbon to CaSO4 molar) calcium sulfide is formed instead.

Sauron - 29-8-2008 at 08:06

@KW I have no idea what you are on about. We are talking about generating SO2 chemically. Smuv mentioned decomposing sodium metabisulfate thermally. I looked at that and related thermal decompositions and concluded they are uneconomical and rather low yield.

Please explain. Assume I know nothing which is not overstating the case.

I am just after a nice chemical process to make SO2 gas I can dry then condense with dry ice-acetone to bottle in LBs as vapor over liquid. No semi-industrial processes please.

If I can make 500 g liquid SO2 in 8 hours I will be happy. This is only about 8 mols. Enough for a standard lecture bottle IIRC. I think those are 440 cc and SO2 has a d of c.1.5. A quick look at old Aldrich catalog will remind me how much is normally in a LB. (Answer is 454 g so about 300 ml, LB is 2/3 full.)

[Edited on 30-8-2008 by Sauron]

Magpie - 29-8-2008 at 09:19

The idea of having SO2 on tap in a lecture bottle has intriqued me for some time although I have no immediate plans for its use. I know that the wine industry in my locale buys or rents small cylinders of SO2 on a regular basis. It perturbs me that I could probably not just buy one of these although I admit not having tried. I'm just suspecting that one would have to be in business to buy one.

This is putting the cart before the horse, but Sauron, where do you purchase lecture bottles?

ScienceSquirrel - 29-8-2008 at 09:31

I have used liquid liquid sulphur dioxide as a reaction medium back in my professional days.
It has a high boiling point so the gas normally comes in a little bottle a bit like a butane gas cylinder but with a small brass fitting to go on top.
Something like this;

http://www.sigmaaldrich.com/catalog/search/ProductDetail/FLU...

[Edited on 29-8-2008 by ScienceSquirrel]

Sauron - 29-8-2008 at 09:45

Aldrich sells mild steel and stainless steel lecture bottles. If I recall the mild steel bottles have a choice of thread sizes. They also sell valves, regulators if you have to get fancy, holders and carriers, systems for connecting LBs in series and so on.

In this country I have found no local source. The Thai industrial-gases company does not sell lecture bottles (filled or emptry) though they will fill them for you if you have the bottles. But they cannot do that for SO2 due to MOD restrictions.

Photo from Aldrich attached, mild steel LB 3/8" NPT

In USA you probably have a number of choices as to suppliers. Note that lecture bottles are not same as "sample boms" the latter normally have threaded necks at both ends although sometimes they can be had flat on bottom. (Lecture bottles have a rounded bottom and so can only stand erect when in a holder.) In general lecture bottles are less costly than sample bombs.

Aldrich also sells mild steel Kilo Lab cylinders in larger sizes than 440 ml LBs.

My intention is not long terms storage but merely making what SO2 I need "JIT" (Just in Time" If using it as a solvent, no problem, a Dewar will do. If using it in a reaction it is better to put it in a LB and control the flow, so a constant flow rate is attainable, something just about impossible to get out of a generator.

Under these conditions mild steel is fine. Bone dry SO2 does not attack mild steel. If I wanted to keep a LB of it on the shelf I would be inclined to put it in a SS LB even though they are a lot costlier, as I do not fancy a SO2 leak.
But if I can generate 500 g a day why should I need to store any on the shelf? That's just asking for trouble.

As an aside, SO2 dissolves in methanol to extent of 32% w/w (according to Merck).

ScienceSquirrel, I am looking at a 13 ywar old Aldrich catalog and they still listed SO2 in 454 g lecture bottles. At that time this was $150.

Vogel describes SO2 being available commercially in heavy walled glass bottles with a valve on top.

I am quite certain that SO2 is available commercially/industrially in cylinders, as it is widely used in industry and agriculture, for example for preserving fruit, bleaching textiles, and so on. It is almost certainly available in industrialized countries in lecture bottles. In this country it is proscribed for no good reason that I can see.

[Edited on 30-8-2008 by Sauron]

e030095.jpg - 104kB

SO2 preparation

Formatik - 29-8-2008 at 13:06

Gmelin in S[A] and S[B] covers a variety of reactions for SO2 formation. Some basic information: By dry heating of sodium dithionite Na2S2O4 at 190ºC there is suddenly a large amount of SO2, but the reaction occurs exothermically and explosively (Z. anorg. Ch. 191 [1930] 340/81, 342). SO2 will form by thermal decomposition of sulfites: Z. anorg. Ch. 139 [1924] 261/92, and pyrosulfites as well as by heating of their solutions. For suitable preparation: by the addition of acids onto sulfites or aqueous sulfites. More about this under the sulfites themselves. There are other methods covered ie, decomposition of sulfates, H2SO4, sulfide roasting, reaction of S with metal oxides, etc. but the reaction of sulfites seems to me to be most suitable for the lab preparation.

I've used several grams of a metabisulfite and hyposulfite mixture then letting moderate HCl drip in through a separatory funnel to generate SO2 in the sulfuric acid thread, but eventually had violent blow offs of the cork, maybe starting out using the sulfites in solution and better stirring could have avoided these.

[Edited on 29-8-2008 by Schockwave]

Klute - 29-8-2008 at 13:47

I dripped a conc. solution of sodium metabisulfite into 50% H2SO4 with good stirring. Maybe the reverse addition causes foamign because bisulfite is in excess at all times, and the SO2 is evolved on a larger surface/volume, where as with excessa cid the recation si very quick and somewhat located. But obviously after a while the whole solution is bubbling, but no excesisve foam (hardly more than 1/2 cm at max.)

Here is the thread wher ei decribed the (failed) attempt at preparing (MeO)2SO2 with SO2/CuCl2/MeOH.

A attempt at Halfapint's DMS synthesis

the resulting waste water still contains appreciable amoutns of SO2 (saturated). Heating it to reflux should expel a certain amount of SO2, and the solution could then be kept as a reducing agent to quench other oxidative wastes before disgarding the two.

[Edited on 29-8-2008 by Klute]

panziandi - 29-8-2008 at 14:29

I would use sodium metabisulphite, very cheap commercial chemical with high quantity of SO2 in it. I would add reasonably concentrated H2SO4 to it, that way minimising volume of wastes. Dry by a wash bottle of H2SO4 then into a dry ice-acetone dewar condenser with an adaptor at the bottom to lead the liquid into the lecture bottle (chilled in dry ice) then just close it off once filled suitably.

I was looking at those lecture bottles myself but not for SO2. I was not sure about the threading, you just literally thread on a valve once filled with your liquified gas and the valve acts as the regulator? It looks like that from the pictures etc. Although the entire set up is a little off budget for now until my student funds come through!

ScienceSquirrel - 29-8-2008 at 14:39

As you say there are lecture bottles and larger cylinders of sulphur dioxide on the market.
The 'tins' of sulphur dioxide that I referred to are still available. I was not doing a huge run of experiments using sulphur dioxide so a few tins were enough.
I am surprised that sulphur dioxide is so restricted in Thailand. I would have expected it to have been fairly freely available.
I would guess that there is a substantial agricultural and food processing sector and round here they tend to throw sulphur dioxide in everything.

Formatik - 29-8-2008 at 14:43

Quote:

Originally posted by panziandi
I would use sodium metabisulphite, very cheap commercial chemical with high quantity of SO2 in it. I would add reasonably concentrated H2SO4 to it, that way minimising volume of wastes. Dry by a wash bottle of H2SO4 then into a dry ice-acetone dewar condenser with an adaptor at the bottom to lead the liquid into the lecture bottle (chilled in dry ice) then just close it off once filled suitably.

For a freezing mixture, I would use alcohol/CO2 mixes which should stop just short of the freezing point of SO2 (from the freezing mixture thread), also better is that alcohol is more readily available.

Sauron - 29-8-2008 at 22:16

Aldrich's Kilo-Lab sylinders re larger sizes 18 and 90 L mild steel and I believe rated at 1800 psig.

Their smaller steel storage are called Sure/Pac and run from 2.2 L down to 25 ml I think.

They have only a few sizes of stainless steel double ended sample bombs, I think largest is 500 ml to approx same as a LB (440 ml)

The SS lecture bottles they were showing in their online catalog last year are now gone. Sole remaining Aldrich LB offering is mild steel.

I have a lot of material about other sample bomb manufacturers in USA, such as Parker and Swagelok. Some single ended types are made with flat bases in SS.

Picric-A - 30-8-2008 at 02:33

If you have easy acess to conc sulphuric this reaction works extremly well.
Simply add pices of copper to a flask followed by conc sulphuric acid and simlpy heat to produce a steady stream of SO2, quite dry. This method works well when you have plenty of drain opener. Of cours it is pointless when using it to make sulphuric acid via contact process...

Klute - 30-8-2008 at 04:53

Funny, I had a pretty bad view of this reaction: it was very irregular, violently bumping at times, and hard to control (can't add more Cu without opening the setup and getting gassed).

I suppose on a very small scale it can be practical, but I would hardly recommend that to produce 8 moles of SO2

Picric-A - 30-8-2008 at 05:02

I find it very smooth and easy... hmmm what size copper do you use? powder or granules?
If you add an exess of Cu to the flask then add the H2SO4 with a dropping funnel it can be easily monitored and topped up.

Sauron - 30-8-2008 at 06:05

Sorry, kid, I don't muck around with drain cleaner or battery acid, just reagent grade H2SO4. I'm a chemist not a plumber or an auto mechanic. And this thread has nothing to do with making sulfuric acid.

[Edited on 30-8-2008 by Sauron]

Klute - 30-8-2008 at 07:11

Granules, from finely cut Cu wire. I wanted to get some SO2 and coulf have used with some CuSO4, but I finally stuck to metabisulfite and made CuSO4 seperatly.

panziandi - 30-8-2008 at 08:14

Sauron: I think the confusion about the contact process was from further up the board when somebody posted about a sulphur furnace which is not a suitable method for you. He didn't mention drainer opener from what I can see just said "if you have access to plenty of sulphuric acid" which I assume you do.

To be clear Sauron wants a chemical method of making clean SO2 gas quickly in the lab not industrial methods just methods which work and a quick and easy. He then wants to dry and liquify and store this gas in a cylinder.

I'd say acid + sulphite/bisulphite/metabisulphite. I think the last is easier to get in larger quantities cheaply. Copper may work, I read it does, I haven't tried it but if I was doing this I'd go with teh acid+sulphite method myself for convenience.

Picric-A - 30-8-2008 at 15:54

You know what Sauron? i dot realy care...
sorry for the confusion, i did mention drain cleaner as it is a fairly cheap source of impure conc sulphuric.
if the product is SO2, why use pure, lab grade H2SO4 when drain opener grade works just as well?

chloric1 - 30-8-2008 at 17:24

Quote:

Originally posted by Picric-A
You know what Sauron? i dot realy care...
sorry for the confusion, i did mention drain cleaner as it is a fairly cheap source of impure conc sulphuric.
if the product is SO2, why use pure, lab grade H2SO4 when drain opener grade works just as well?

Yeh I second that. Reagent or lab grade should be saved for important synthesis not menial task such a SO2 production. If the drain cleaner sulfuric acid is readily available in your neighborhood then why not use it for SO2, HCl, or drying gases instead of paying hazmat charges.

Doing such does not make one a punk. Actually, your derogatory tone diminishes your professional image in my eyes.

Klute - 30-8-2008 at 20:10

This whole second page is uselessly unconstructive... Could we go back to topic and avoid such worthless bitterness? Please?

..Could a mod clean this up?...

ScienceSquirrel - 30-8-2008 at 20:40

Quote:

Originally posted by Sauron
The entire forum is being polluted by the likes of Picric-A and is becoming well nigh uninhabitable.

Why shy away from the truth? That is not courtesy, it's cowardice.

It is not that bad.

Posters come and go.

I view posting here as a night down the pub.
If you do not get on with someone then ignore them. Move on and chat to someone else.
If someone gets offensive then the mods will tell them to 'drink up'

Sauron - 30-8-2008 at 20:58

I just requested quotation on lecture bottles, stainless control valves and CGA110 PTFE sealing washers. The control valves are knob type with 1/4" hose barbs.

I'll report what they quote. Doubtless it is a lot less in USA with S-A Singapore and their agent in Thailand out of the loop.

[Edited on 31-8-2008 by Sauron]

chloric1 - 31-8-2008 at 04:23

Ok anywho- Just as a helpfull tip, I heated dry sodium metabisulfite in a test tube a year ago because an Advanced Inorganic Chemistry text had a list of solids that evolved dry gases. Sodium Metabisufite was recommended for SO2 generation. What I found was part of the sulfite reduced itself and I got polysulfides and the test tube cracked by being exposed to a strongly alkaline melt. IRC the Bisulfite can exist in more than one configuration with one of those having a hydrogen bonded directly to the sulfur. I realize that metabisulfite is supposed to be the pyrosulfte but I am considering partial hydration here. Now my metabisulfite was technical grade and it might of had sulfite as an impurity.

This is just something to consider. One might try mixing metabisulfite with and inert filler, like aluminum oxide. had heat dry. Another thought is heating sodium metabisulfite with a monobasic phosphate salt and removing moisture.

Sauron - 31-8-2008 at 05:14

A quick look at the stoichiometry of such reactions the other day led me to conclude that they were not the best way to get the most SO2 out of a given amount of substrate, even without considering unexpected side reactions like yours. Add to that the energy input, and it's just not a good tradeoff for the sole advantage of not having to dry the SO2 stresm, which is after all, easy.

According to Ullmann's SO2 is somewhat soluble in H2SO2, varying with concentration of the acid, minima being at 85%. I will have to look up this reference to see how much SO2 gets lost this way. It can't be much as this is almost universally the drying agent of choice for SO2.

Chart is attached. At ordinary temperatures and concentrations of H2SO4, 20-40 g SO2 dissolve in a Kg of acid. SO2 is 64 g/mol. However, as the solubility drops way off at elevated temperatures, dissolved SO2 can be recovered at the end of a prep run by warming the H2SO4. Adjusting the acid to 85% first would be helpful.

[Edited on 31-8-2008 by Sauron]

[Edited on 31-8-2008 by Sauron]

SO2.jpg - 24kB

panziandi - 31-8-2008 at 05:39

looking back over this thread it appears there are two options: sulphites + acid, or reducing the sulphuric acid with copper... you seem to have dismissed the sulphite method on grounds of not a good trade-off substrate:SO2 and energy input. But sulphites are cheap so you are saving there. Reducing sulphuric acid with copper is the other suggestion, Cu(s) + 2H2SO4(aq) → CuSO4(aq) + SO2(g) + 2H2O(l), looking at that and seeing as you want to fill several lecture bottles with SO2 and not being bothered to do the math, I'd say it'll cost a lot more in copper metal (expensive at the moment) and also cost more in acid consumption and you will have a large volume of copper (II) sulphate to dispose of, because I can't imagine you wanting to keep a simple lab made chemical like that. Large quantities of copper (II) compounds constitute an environmental hazard and would require professional disposal, although having the Chao Phraya running cupric-blue may be interesting!

p.s not to mention the copper method requires hot concentrated H2SO4 certainly not the nicest but you also have energy input there for heating a large volume of acid.

[Edited on 31-8-2008 by panziandi]

Sauron - 31-8-2008 at 05:56

Come now, I said no such thing. I dismissed only the thermal decomposition of sulfites, not their reaction with moderately dilute H2SO4 (like 50%) to generate the SO2, preferably dropping the sulfite as saturated soln into the acid. Then, passing the SO2 through a wash bottle or two of conc H2SO4 before passing it into a large Dewar condenser with integral collecting flask (1 liter) and taking that liquid SO2 off to fill lecture bottles 300 ml at a time.

I accept Klute's bad experience with the copper method, and therefore will not consider it further. The only one who recommended copper was someone I would not believe if he told me the sun was shining and I had a window open. In the category of BURN BEFORE READING.

[Edited on 31-8-2008 by Sauron]

panziandi - 31-8-2008 at 06:08

Ah I see! Well I certainly think sulphite method is the best. In fact I may try this next week if I get a chance I'm thinking along similar lines of preparation then drying through H2SO4 (only one wash bottle as the quantities will be minimal) then through a coldfinger and I will attempt to store the liq SO2 in a glass pressure vial closed with a HiVac teflon tap (basically it looks like a schlenk solvent tube but with a constriction so you can ampuole off the bottom if required) ... but I have molecular genetics exams this week so chemistry is put on the back burner for now!)

chloric1 - 31-8-2008 at 08:03

What about using a drying tube filled with pumice stones moistened with H2SO4. That way less H2SO4 s used and less of your SO2 will be dissolved on drying.

My unexpected results in regards to the pyrolisis of metabisulfite are really a reminder that what you think should be straight forward in chemistry is often much more complex and involved. I still might someday try another dry pyrolisis of metabisulfite but I will try different conditions and additives so that SO2 can come off at lower temperatures to limit side reactions.

Sauron - 31-8-2008 at 08:05

Also, as we will be generating the SO2 from 50% H2SO4, which will gradually become more dilute as the satd sulfite solution is added, significant amounts of SO2 will remain dissolved in the generator flask and will have to be driven off by heating at the end, just as with the wash bottle acid.

The amounts of dissolved SO2 in the wash bottles are relatively trivial. The amount of dissolved SO2 in the generator is not. It is well worthwhile to replenish the acid in the generator to maintain it at the maximum practical concentration (probably more than 50% but not more than 85%) to minimize this. Alternatively, or additionally, the generator can be externally heated throughout the run to a temperature between ambient and 100 C, consistent with minimizing production of water vapor. 60-70 C perhaps. Keeping the temperature up and the acid concentration up will keep SO2 solubility at or below 20 g/Kg acid.

Panziandi, you just restated Murphy's Law without attribution.

Sauron's Law: Murphy was an optimist.

Now let's talk about practical matters so far unmentioned.

Let's suppose we want to use 1 Kg Na2SO3 to generate SO2.

MW 126, solubility 230 g/L water ambient. Very roughly therefore 4.3 L and concentration a little under 2 M.

Stoichiometry:

Na2SO3 + H2SO4 -> SO2 + Na2SO4 + H2O

So that Kg of sulfite gets me 8 mols SO2, slightly over 500 g

For the reaction I need 8 mols H2SO4 = 800 g 100%, 640 g 95% acid, d 1.85 so how many mls?

Dissolve in 800 ml water. (USUAL CAUTIONS).

So we are going to react 4.3 L satd sodium sulfite soln by dripping it into 50% H2SO4 about 1300 ml so at end, reactants volume is 5.6 L. If we let this alone the resulting H2SO4 concentration at the end will be low (actually if we stick to stoichiometry, nil, because all the acid will have reacted and now will be sodium sulfate.) So clearly we need to add conc H2SO4 slowly through the reaction or intermittently anyway, in amounts calculated to keep the acid concentration where we want it (50%) and preferably at the end we want to hike that to 85% and drive off all dissolved SO2. External heating may not be required because the heat of dissolution of the conc H2SO4 will be considerable.

The product 8 mols SO2 is exactly what I want to load into a standard LB.

[Edited on 1-9-2008 by Sauron]

[Edited on 1-9-2008 by Sauron]

Klute - 31-8-2008 at 08:34

I like the idea of adding concentrated acid to keep the concentration up. That way you can start with a minimal amount of water in the acid at the beggining.

P2O5 might be a good option for drying the acid too, perhaps after a small H2SO4 washbottle to avoid consuming the P2O5 quickly: very little SO2 in the wash bottle, efficient drying and no absorption from the P2O5. The used P2O5 coudl then be neutralized with water to form conc. H3PO4 with possible traces of SO2, which could be used to generated more SO2 from bisulfite, instead of H2SO4?

panziandi - 31-8-2008 at 13:52

By adding H2SO4 towards the end would generate enough heat perhaps to avoid requiring external heat?

I expect you will actually get NaHSO4 and not Na2SO4 so perhaps just bare that in mind and adjust accordingly if you are aiming for 500g SO2 adjust to generate an excess to ensure you'll have plenty.

I would use as high a % of H2SO4 as possible, in fact I'd prefer to use 98% neat onto the sulphite and in a larger flask (so as foaming is not an issue) just to keep waste minimal, and flash the larger flask with air or etc at the end to ensure all SO2 is flushed into the Dewar and collected. With an excess you'll be sure to have enough to fill a LB and any not bottled can be discarded or used.

I like the idea of H2SO4 on pumice actually - never has occured to me as a drying wash agent more of a dessicator dryer but would work well I'd imagine! P2O5 maybe overkill? I imagine two washes with H2SO4 would be plenty but mild steel does rust so perhaps P2O5 to remove trace moisture before bottling. But will you simply be decanting the liq SO2 into a LB or will u vac out the LB and attach via adapter to the base of Dewar etc? if you are decanting forget P2O5 as the SO2 could attract trace moisture whilst decanting. I'd only use P2O5 if the system was closed. Does that make sense or too waffly?

Sauron - 31-8-2008 at 14:33

I have two large dewar condensers as cold traps with integral 1 L receiving flasks and bottom drains. I was planning to run a tuve from that drain into the dry, unclosed, chilled LB and after filling, quickly screw on the control valve with ptfe sealing washer - valve open, then once the valve is well started in the thread, close the valve and tighten thread (it takes a wrench.) Then the closed LB can come out of the cold bath and slowly come to ambient, I can use some soap soln to check for leaks.

If reacting reagent conc H2SO4 and dry sulfite (anhydrous as it usually is these days) the SO2 would not need drying. I agree P2O5 is overkill. Woelen just quoted Vanino's book saying CaCl2 is a good drying agent for SO2, as well. (See parallel thread.) P2O5 is flocculent and a mess. I only handle it in a glove box, no breezes and no moisture. The bottle once opened stays in the dry box. Otherwise it turns into expensive H3PO4.

------------------

OK so we worked out the stoichiometry for sodium sulfite.

Na2SO3 + H2SO4 -> SO2 + Na2SO4 + H2O

How about sodium bisulfite?

NaHSO3 + H2SO4 -> SO2 + NaHSO4 + H2O

MW 104 so almost 10 mols/Kg and solubility 300 g/L water at ambient. Conclusion: sodium bisulfite is better choice than sodium sulfite, and should produce >600 g SO2 per Kg.

Next up, sodium meta-bisulfite.

Na2S2O5 + H2SO4 -> 2 SO2 + Na2SO4 + H2O

2 mols SO2 per mol metabisulfite but the MW is almost 2X that of bisulfite so yield SO2 per Kg is no better (c. 600 g/Kg).

Solubility:

I have not been able to find this quantified, most describe this salt as "freely soluble" but surely there's a limiting amount?

[Edited on 1-9-2008 by Sauron]

panziandi - 1-9-2008 at 02:49

OK! Well bisulphite looks the best candidate then. All the sulphites dissolve in cold water BUT I only speak from the experience of Na2S2O5 as it's cheapest for me to get, it dissolves in cold water but you get small lumps which remain stubborn and need stirring or breaking up to dissolve. On the solubility front:

Na2SO3:
Solubility in water:
23 g/100 mL (20°C)
Solubility in other solvents:
soluble in glycerol
practically insoluble in alcohol

NaHSO3:
Solubility in water:
300 g/l water
Solubility in other solvents:
SOLUBLE IN 2 PARTS BOILING WATER
SOLUBLE IN ABOUT 70 PARTS ALCOHOL

Na2S2O5:
Solubility in water:
540 g/L (20°C)
Solubility in other solvents:
Freely soluble in glycerol
Slightly soluble in alcohol

So maybe metabisulphite would be better due to its higher solubility?

[Edited on 1-9-2008 by panziandi]

chloric1 - 1-9-2008 at 03:33

The metabisulfite is indeed highly soluble. On two occassions at least I remember making a 40% solution. Once
to clean up permanganate stains and secondly for react with ketones.

Never tried 98% H2SO4 directly on a sulfite. Concentrated sulfuric acid is a strong oxidizer. You might get a mess. It might oxidize your sulfite to dithionate while itself be reduced to SO2. You would still get SO2 but at what yields? What would be the stoichometry of this redox? I feel there would be several species involved here much like 98% added to potassium iodide crystals.

Sauron - 1-9-2008 at 04:01

Oleum is a strong oxidizer. Conc H2SO4 is a strong dehydrating agent but not a strong oxidizer. The Vanino procedure cited by woelen employs conc H2SO4 with calcium sulfite admixed with calcium sulfate as diluent.

Now that's his procedure not mine but while I think acid somewhere in the 50% to 85% range is best, I do not think any oddball redox reactions are going to happen with conc H2SO4 (95-98%).

Sounds like metabisulfite gets the mix down to <2 L fot the metanisulfite soln containing >5 mols (1 Kg, MW 190) and only 750-800 ml or so of 50% H2SO4. So very compact, well under 3 L total and a 5L flask is fine. Very nice as the metabisulfite is also cheapest of the three salts. I'd still add the solution to the acid to minimize foaming.

[Edited on 2-9-2008 by Sauron]

ScienceSquirrel - 1-9-2008 at 04:08

I don't suppose you have any home brew shops out in Thailand?

The stuff is used as a sterilant / final wash for equipment so a few pounds buys 500g in the UK.

Klute - 1-9-2008 at 07:44

I'd think it's even cheaper as a technical industrial product, 2E/kilo... Hard to get lower.

Sauron, in order to insure your SO2 satys well anhydrous, you ould add a little (non-agressive) dessicant in the receiver? CaCl2?) Do you plan on distilling the SO2 from the first Dewar to the LB? Or just transfering?

ScienceSquirrel - 1-9-2008 at 08:07

Quote:

Originally posted by Klute
I'd think it's even cheaper as a technical industrial product, 2E/kilo... Hard to get lower.

Sauron, in order to insure your SO2 satys well anhydrous, you ould add a little (non-agressive) dessicant in the receiver? CaCl2?) Do you plan on distilling the SO2 from the first Dewar to the LB? Or just transfering?

My local home brew shop sells food grade 97% for a third of the price of Sigma Aldrich's 97%. It does not come in a nice Sigma Aldrich tub but it probably comes from the same factory in China!
Of course if Sauron is buying a 25kg drum he is going to get it cheaper...

Sauron - 1-9-2008 at 08:11

No home brew shops (illegal but popular.)

Anyway plenty industrial chemical suppliers and lab chemical suppliers.

Klute - 1-9-2008 at 08:11

That's what's called selling a name......

Sauron - 1-9-2008 at 08:22

I doubt I will buy a 25 Kg drum, at least initially. The 2.5 Kg packing looks attractive. Food grade is really overkill for this application.

The dewar will be terminated with a drying tube. I was just going to drain the receiver into the LB, distilling the SO2 ought not to be necessary, IMO.

Remember this is short term storage only. The SO2 will get turned into SOCl2 or SO2Cl2.

Sauron - 2-9-2008 at 04:45

I have now been quoted c.$150 for a mild steel 440 ml lecture bottle. I'd guess this is $75 in USA, the rest being shipping, duty, VAT and middleman greed.

A 900 ml Sure/Pac cylinder is half that price. But rated 240 psi vs 1800 psi for the LB.

The real shock however is the quote on the control valve. A simple SS316 control valve, nothing fancy, not a regulator, no gauges, is $275. So probably $140 in USA.

I think this is ridiculous. An empty LB and a simple control valve >$400??

NUTS!

I'm not going to put up with this. I will generate the SO2, pass it through drying train and use it directly. If I need intermediate storage I will put it in a dewar flask.

panziandi - 2-9-2008 at 05:12

Could you not get hold of an old lectue bottle cylinder that has been disposed of at a salvage yard etc and fill that with SO2?

Sauron - 2-9-2008 at 06:08

The valve for SO2 needs to be stainless steel, or monel. Brass would not be wise. So the odds of finding a LB with a serviceable SS control valve are slim. Anyway there are no such salvage yards in Thailand.

In USA LB users must dispose of empty LBs as hazardous waste. It costs about $300 per LB to do that. Linde has inaugurated a LB return program for customers to get around that (and to steal a competitive march on Matheson, Air Products etc.)

I have been to the Thai industrial gases people and they do not stock LBs. They told me they can fill them once I have them and offered to import Matheson LBs prefilled for me (hugely expensive.) The LBs are not so pricey, I can live with $75 in USA or $150 delivered here. But I barf on the notion of having to pay big money for a dinky little needle valve. That is really outrageous and renders the whole affair uneconomical and unattractive.

It does not kill the project, just the LB storage aspect. That was a luxury and as such is dispensible.

panziandi - 2-9-2008 at 09:55

Is that from an Aldrich office? Perhaps eBay could get one? There are often regulators etc on ebay (OK usually for N2, O2, Fuel) but sometimes you find specialtiy ones. I'm obviously not in Thailand and have NO EXPERIENCE WHATSOEVER in getting equipment from SE asia but... I know that you can often jump to the country next door, could a Chinese gas company supply cheaper LB and regulators? I asked about the salvage yards as my local council dump has a metal cage which people recycle cylinders at. I had empty disposable Ar cylinders and took them there to dump and noticed smaller lecture bottles were there... I couldn't pinch one tho (mind I don't know what was / had been in them!)

Sauron - 2-9-2008 at 10:22

I detest eBay and have not been active on LabX for some time.

I don't think I'd care to muck around with Chinese or Indian control valves.

But thanks for the suggestions.

Sauron - 3-9-2008 at 12:20

Now I have quotes from two other sources, Fisher in USA and Argo in UK, for stainless steel lecture bottle manual control valves. Both quotes are in the $170 range ($160 Fisher, 80 GBP Argo) so I think my guestiamte of a 2X factor in my local Aldrich agent's quote ($275) is about right.

What I can do is buy the LBs and/or Sure/Pac bottles from the local agent but circumvent them for the valves and buy those directly from S-A in USA via one of my colleagues there, then have him trans-ship to me from his US location. The valves are small and light. The bottles, not so small and not so light.

Brass valves are in the $100 range but useless for SO2 and other corrosives.

These damned valves have tripled in price in the space of 12 years. Ridiculous!

On the premise that dealing with an OEM might be more reasonable I have requested a quote from RMI Manufacturing in Livermore CA. They have a LB control valve in 303SS, 3/8 NGT to CGA 180/110. NGT is I guess, newer nomenclature for Natl Pipe Thread. I will look it up.

NGT is National Gas Taper thread. NPT is National Pipe Taper thread. Apparently NGT is a newer standard which has a simplified gaging system (go/no-go measuring tools for threads are called gages not gauges). I will have to look up what difference there might be between 3/8 NPT and 3/8 NGT and if they are a mismatch then this RMI product may not be compatible (at least without an adapter) with the Aldrich LB which has a 3/8 NPTF thread. Fortunately because of some of my former engineering work I am familiar with thread forms and this is not terra incognita.

[Edited on 4-9-2008 by Sauron]

Natures Natrium - 7-9-2008 at 18:56

https://sciencemadness.org/talk/viewthread.php?tid=4061&...

Only thing I have to add to this is that my bottle is still holding up after several years, despite having a brass control valve. Where the SO2 was flowing across the surface it initially discolored, then did not appear to react any more. I suspect passivization.

-NN

Sauron - 7-9-2008 at 19:42

That's interesting.

But the price difference between a brass control valve and a SS one is only about $50. They have gotten to be expensive, too.

I'm more interested in how you make use of your bottle. Is it a LB or more of the Sure/Pac type? Mild or stainless steel? Do you liquify your own SO2 or do you have it refilled commercially?

garage chemist - 7-9-2008 at 19:45

I have made sulfuryl chloride via the camphor method recently, using Sartori's procedure, and it did work nicely.
A single fractionation affords a pure product, and a quite small amount (ca. 10g) of camphor can make an almost infinite amount of SO2Cl2 if you just keep bubbling SO2 and Cl2 into the liquid simultaneously.
I found that it is very important that the reaction mixture be cooled with cold water or ice during the synthesis, as the solubility of gases in liquids decreases with increasing temperature. If the liquid gets warm, both Cl2 and SO2 partially bubble through without reacting.
If it stays cold, the gases both get completely absorbed.

The SO2 was generated by dripping 30% HCl on potassium bisulfite, which is available extremely cheaply from ebay here (EUR 3,20/kg).
This gas generator gets very cold during operation- the SO2 evolution seems to be an endothermic process. It should be placed in a warm water bath to counteract this and increase the rate of gas production.
If the gas generator is not warmed, only a part of the theoretical amount of SO2 is released even after all the HCl has been added- and upon swirling or warming, suddenly very large amounts of SO2 are released, which is a bad thing.
After all the HCl has been added to the bisulfite, the gas generator should be slowly heated to about 80°C in order to release all SO2 that is still dissolved in the aqueous KCl solution, which really is a lot.
The SO2 was dried by a CaCl2 tube. H2SO4 could be used as well.

Chlorine was produced via the usual TCCA method, and also dried with CaCl2.

I find that the camphor method is superior to the GAC method because of the simpler apparatus and visual control of the gas streams- you can see the SO2 and Cl2 bubbles getting smaller while dissolving in the reaction mix, and the color of the head space over the reaction mix tells you if you have chlorine in excess, which is to be avoided.

Sauron - 7-9-2008 at 21:12

Welcome back, old friend! Good to see you posting again.

Natures Natrium - 14-9-2008 at 16:32

Quote:

Originally posted by Sauron
That's interesting.

But the price difference between a brass control valve and a SS one is only about $50. They have gotten to be expensive, too.

I'm more interested in how you make use of your bottle. Is it a LB or more of the Sure/Pac type? Mild or stainless steel? Do you liquify your own SO2 or do you have it refilled commercially?

I don't know the difference between LB and Sure/Pac. I'm fairly certain it is stainless steel, since it used to contain pure oxygen. The walls of the vessel appear to be extremely thick, a cm or more.

I liquefied my own as detailed in that thread I linked to. Haven't used it much, except for a few mild reductions, and producing SO2Cl2 via activated carbon in a 300mm leiberg condenser with water circulating. Always wanted to try the camphor method, heard from a reputable source it works extremely well.

I only used the brass valve because it came with one, at the shop where I bought it. Had to rig a hose barb to it via some pipe clamps and some braided PVC hose, since I couldn't find a suitable, official adapter. Works good with no leaks, under the weak ~15PSI that the SO2 generates at 25C.

-NN

[Edited on by Natures Natrium]

Sauron - 14-9-2008 at 20:11

LBs are DOT rated for 1800 spi so can handle highly compressed gases. Sure/Pac are rated 240 spi so are only suitable for for condensed gases (vapor over liquid (with or without a dip tube). In both cases as sold by Aldrich they are mild (carbon) steel. Last year or earlier this year Aldrich also offered stainless steel LBs but no longer. They still offer SS sample cylinders, double ended, in a variety of sizes up to 500 ml (comparable to a LB, smaller than Sure/Pac that goes to 2.2 L.)

The SS sample bombs are much costlier.

watson.fawkes - 15-9-2008 at 10:32

The Compressed Gas Association publication CGA G-3 is their monograph on SO2. The table of contents is available for free online.

The refrigerant designation of SO2 is R-764. It was one of the first refrigerants used in residential freezers. It should be clear that an ordinary refrigeration compressor can liquefy it and that a standard refrigerant recovery system can move it around.

All the material compatibility charts I've seen distinguish between wet and dry SO2. I seem to recall that brass is acceptable for the dry gas.

NGT is the same basic thread form as NPT, except with more threads engaged and tighter tolerances on roots and crests. See this page for more information from a gage vendor. I presume the purpose is to allow dry assembly of the joint, avoiding spiral leaks without thread sealing compounds.

panziandi - 15-9-2008 at 10:53

Slightly off topic but slightly related and apologies for posting here... Please keep it to a single post reply if possible or U2U so as not to cause a branchng thread:

The disposable Argon and CO2 cylinders for mig welding such as: http://www.welduk.com/Details.asp?ProductID=90

I was studying an empty cylinder I had lying around and it looks possible to remove the non-return valve and possibly fill with liquified gas.

It does clearly state "NON-REFILLABLE" but... any ideas on whether it would be ok to open the cylinder and fill with another gas...?