Obtaining/producing oleum, how to make SO2

[Dhzugasvili]

I was just wondering, since over here seemingly it is quite hard to get oleum/sulfuric acid with 10% dissolved So2, can this be easier to make?

[c0deblue]

Wrong forum - this belongs in Miscellaneous.

Oleum is formed by dissolving Sulfur Trioxide (SO3) in concentrated Sulfuric Acid. SO3 is obtained by reacting SO2 with oxygen over a catalyst (e.g. Vanadium). SO2 is produced from burning sulfur.

None of these processes are for the faint of heart (or stomach). Doing this sort of chemistry in populated areas is sure to make you personna non grata.

[Mr Cool]

If you really want to make it, you can get the catalyst (vanadium pentoxide) from ceramic suppliers as a pigment or something. I think it's a pigment.
But if an explosive requires oleum, then it probably isn't worth making because there are loads of excellent explosives that don't require it. If you're making TNT then just make TNP instead, it's more powerful, easy to make and easier to set off.

[CodeMason]

Couldn't you just obtain oleum by simply boiling less concentrated H₂SO₄, such as car battery acid or instant drain opener?

For that process, iron oxide (rust) can be used as the catalyst instead of vanadium oxide, and you need a platinum catalyst near the end I hear. It's a very tricky process, and you won't see me trying it.

[Jumala]

Oleum is concentrated sulfuric acid with 10-30% dissolved SO3.

It is no problem to make SO2. It is simply made by burning sulfur.
The problem is to oxidize it to SO3. There are two methods. One is the lead chamber proceed where SO3 is made from SO2 and nitric acid. the other is the catalyst proceed where is used platinum.

Oleum cannot be made by boilind H2SO4.

[CodeMason]

But I thought, that when you heat H₂SO₄ to the boiling point, it decomposes into H₂O and SO₃, the SO₃ staying in the solution but the H₂O blows away as steam, hence making oleum... Or am I way off here?

[PHILOU Zrealone]

And what if the SO3 is a volatile solid with a low melting point and that as soon it has separated from H2SO4 it combines with the H2O!Learn or read some chemsitry before reinventing it!Encyclopedias, internet, libraries gives good infos...you just need a little search!

All you need is an hermetic acid-heat-pressure resistant reactor, SO2, O2, a catalyst, heat and a cold trap to condense the solid SO3!!!SO2 and O2 are gases while SO3 is not!

------------------
"Life that deadly disease sexually transmitted".
"Chemistry is all what stinks and explode; Physic is all what never works! ;-p :-) :o)"

[Lagen]

The SO3 for oleum can be produced by thermal decomposition of anhydrous iron(III) sulfate, or ferric sulfate. This substance is comparatively much more expensive than the common iron(II) sulfate, and is difficult to obtain in the anhydrous form. It forms various hydrates (mono-, penta-, nona-, dodeca-), the monohydrate is a grayish white powder, the higher hydrates are yellow. The anhydrous form is a grayish crystalline substance. The ferric sulfate can also be obtained from the commercially available 40% solution by evaporation (sold under the name "Prefloc" in my country), this is a somewhat cheaper source. If you aren't absolutely sure the ferric sulfate is anhydrous, it must be calcined first to remove all water. This can be done in the very same vessel in which the decomposition will be carried out afterwards, a stainless steel retort is suitable for this purpose. The volume of the retort must be sufficient to accommodate the material at a density of 0.2 g/cm3. Heat the sulfate at 450-460°C for a sufficient period of time, until no water vapour is given off. This is best done in a gas furnace with thermostatic temperature control, or a similar enclosure where the temperature can be equalized. The temperature must not exceed 470°C, at which point the sulfate might start decomposing. After the calcination of the sulfate is finished connect the outlet of the retort to a suitable receiving bottle containing 1.53l (2.8kg) of 98% H2SO4 for every 2kg of ferric sulfate used. The gas inlet should be through a piece of thin glass tubing extending below the surface of the acid, the outlet can be vented out or alternatively you can attach a second smaller receiving bottle in series to improve efficiency. Increase the temperature in the retort to 480-500°C and maintain this temperature until the evolution of SO3 stops. The temperature of the acid should be maintained at 45-50°C by cooling with flowing water. The theoretical concentration of the oleum after connecting the solutions is 30% (d=1.925). Do not cool below 45°C, otherwise the SO3 will condense in the tubing and on the walls of the apparatus. Also, do not use water as the receiving medium, the reaction of SO3 with water is very violent and difficult to cool down.

[10fingers]

I came across a process awhile back for making TNT which does not use oleum. It was a three step process using mixed sulphuric/nitric acid. Supposedley you could use nitric as low as 70% concentration.
According to the text oleum only increases the efficiency of the process and is not absolutely necessary.

[Mr Cool]

I also read that, I seem to remember that in total it used a LOT of acid. Shouldn't be too hard to recycle though.

[10fingers]

Yes it did. It says you mix up three batches of acid for the mono, di, and trinitration. You take the spent acids and recycle the mono, use the di for the next mono and use the tri for the next di.
To recycle you mix with some more sulphuric and distill off the nitric.
My friend tried this process once out of curiosity. He got a product that had all the properties of TNT , melted at around 80 degrees C, formed pale yellow needle like crystals and burnt with a black sooty smoke. For some reason though this stuff would not detonate. He even tried putting it in a pipe with a compound detonator consisting of HMTD and MHN but there was maybe only a slight detonation of the TNT. I know that TNT is hard to set off but I wouldn't think it is that hard.

[Tony Montana]

There is a much, much easier way! Why dont you download Paladin Press's Black Book Revised/ State of the art improvised munitions, from:
http://members.optusnet.com.au/~hand/montana/and read the chapter about making Oleum! HINT: You only need, Sulfur, Iron Oxide and concentrated H2SO4.

[This message has been edited by Tony Montana (edited August 25, 2001).]

[Lagen]

After doing some very quick and dirty calculations (the book gives no weights or ratios), I can see some fundamental flaws in that method. Firstly, I doubt that a piece of rust from "rusting iron" would work as catalyst. Catalysts like copper and iron oxides must have a very high specific surface to work - at least tens of square meters per gram, so must be specially prepared for this purpose. Then they suggest to drive all the gas through that little pyrex tube. Let's do some calculations first. The receiving "flask" looks like a ketchup bottle, and it is half full of H2SO4. Say they have 250ml H2SO4 there, or 457g. To convert it to 30% oleum, one would need 196g SO3 (assuming 100% efficiency...), that's almost 55 liters of SO3. 79g of sulfur would be needed. Say the sulfur would burn in 10 minutes (shorter burning times would be even more problematic) and the inner diamater of the tube is 7mm. That results in a speed of 238 cm/s. How could the gas get 100% reacted with such a small amount of catalyst at such a speed? How would you make the gases bubble at this speed through those several centimeters of (rather dense) conc. sulfuric acid? Can you imagine that the gas could get absorbed? Say that the driving force would be the tremendous heating of the little metal dish, undoubtedly a great amount of gases from the torch would enter the reaction, further increasing the total volume and speed of flow, the plastic tubing probably wouldn't take it and non heat-resistant ketchup bottles could crack. The gases from the torch would contain LOTS of water from the combustion of the hydrocarbon fuel, so any SO3 formed would be immediately converted to H2SO4 vapour, and no oleum could be made. The H2SO4 would condense on the catalyst, clogging it, unless there was a gaping hole in it (then the catalyst wouldn't work). There is no heat dissipation means between the pyrex tube and the receiving flask, which would be necessary to cool down the gases from a few hundred down to 45°C - safe for oleum). They do not tell us to cool the receiving bottle. A lot of the oleum would decompose as soon as it was made, creating a cbp solution of 98.33% H2SO4 at 338°C. The candle in the picture would hardly heat the tube to 200°C, while for the catalyst the temp. would have to be in the range 400-800°C. A much larger torch would be necessary.
*sigh...* Okay, enough bitching, but I seriously doubt the authors have actually tried it. Has anybody else tried this method?

[DogOfWar]

I have been trying to produce oleum by pyrolysis of sodium bisulfate.

Step one, dehydration;

2NaHSO4 --> Na2S2O7 + H2O @ 315*C

Step two, cracking;

Na2S2O7 --> Na2SO4 + SO3 @ 460*C

And bubbling the SO3 through concentrated (98%) H2SO4.

I believe this should work. Anyone have suggestions or comments?

I have had some problems with the temperature required for cracking, stoppers and tubing etc. are melting! I have switched to ground glass hardware now, but have not yet cranked up the rig to see if it works.:D

[Enkidu]

What is your reference for this procedure's use in the production of sulfur trioxide? Has it been successfully performed?

I suppose you've seen garage chemist's member publication about sulfur trioxide and it's accompanying thread over at SM? He used sodium persulfate instead of sodium bisulfate. I can see why you'd want to use sodium bisulfate; it's much cheaper. However, as you mentioned, the decomposition of the bisulfate produces both water and SO3. GC had trouble only getting rid of the water before further decomposition. Of course, SO3 + H2O <---> H2SO4. You'd only be getting 100% sulfuric acid (fuming sulfuric acid).

A catalyst is another aspect you need to take into account. Na2S2O7 does not decompose and give off SO3 without a catalyst (according to GC). I'd suggest MgSO4 rather than H2SO4, as I imagine that a catalytic amount of H2SO4 would be evaporated at the high temperature you have listed.

I'd advise some tests before bubbling your SO3 directly into conc. sulfuric acid. Because of the likely small yields of your experiment, it's even less likely that you could tell if you're bubbling SO3 or H2SO4 into your sulfuric acid. Why not use the high MP of SO3 (16*C) to your advantage? Cool your receiving flask and see if the proposed SO3 solidifies.

Whether you use sodium bisulfate or sodium persulfate, your yields will probably be pitiful. I don't know what your use for the oleum is, but you're going to need a heck of a lot of starting material to get any quantity of oleum with a significant dissolved SO3 content. That means many small batches. I looked into producing sulfur trioxide for thionyl chloride (and in turn thionyl chloride for acetic anhydride) and I decided it wasn't worth it.

I hope I haven't discouraged you.

As a final word of warning (from GC),

Sulfur trioxide is extremely corrosive. It instantly carbonizes any organic matter it touches, including skin. A drop placed on wood instantly makes a black spot, under strong fizzing and fuming. The same happens when a drop falls on the skin.

Sulfur trioxide also reacts with water with explosive violence. When a drop of water falls into a flask containing SO3, the flask usually shatters because of the violent reaction and localized heating. [I.e., wait until your glassware stops fuming before washing it out and neutralizing with a base. Also, when adding your SO3 to sulfuric acid, use good stirring and 0*C acid.]

SO3 fumes in air very strongly. The synthesis must be carried out outside or under a fume hood.

[DogOfWar]

Cranked up my still this afternoon, no doubt about it... this stuff IS SO3!
Ate the cover right off of the end of the tubing!

Tried your suggestion as well and cooled flask... bingo solid SO3.

I am trying to find a way to fully use the gas stream, possibly by bubbling through two beakers in series. Can I cool the SO3 down and keep it cool to store it? Can it be added directly as a solid by some method to the H2SO4?

I wouldn't try to manufacture oleum this way, but for personal use it looks like it's going to be cheaper and easier than buying it!

Reference is from old (1957) college textbook on general chemistry.
Also I found a ref in Wikipedia to same process.

[DF90]

Sodium bisulphate can be used to produce Sulphur trioxide.

The bisulphate is heated to about 320C at which point it is dehydrated to Sodium pyrosulphate, Na2S2O7. This is then heated at about 460C to produce Sulphur trioxide and Sodium sulphate by thermal decomposition. The Sulphur trioxide can be condensed and collected (its boiling point is 45C).

I assume this can be added carefully to conc. sulphuric acid, first reacting with any water present to produce more sulphuric acid until 100% concentration is achieved. At this point any sulphur trioxide added will be used to produce oleum.

As a word of warning the addition of sulphur trioxide to conc sulphuric acid should be cooled as the reaction between the SO3 and the water present is very exothermic. It is also more efficient if you start with the highest conc. of acid you can to prevent wasting precious SO3 to make H2SO4

[Azido]

Could SO3 be used to double, triple, even quadruple (etc) your supplies of H2SO4?

::1

A small amount of H2SO4 is turned into Oleum with the addition of SO3.

The resulting Oleum is then very carefully diluted into a stoichiometric amount of distilled water, resulting in more concentrated H2SO4.

goto 1

Handy if you have a lot of CuSO4 and not a lot of H2SO4..

[megalomania]

Indeed, Azido, that is how sulfuric acid is made industrially. Sulfur trioxide gas is mixed with sulfuric acid of moderate concentration until it forms oleum with a maximum percentage of dissolved sulfur trioxide. The oleum is then added to water to make more sulfuric acid, some of which goes back into the system to be reacted with sulfur trioxide.

[penguin6636]

I wouldn't try to manufacture oleum this way, but for personal use it looks like it's going to be cheaper and easier than buying it!


I also tried making SO3 this way but had a zero to terrible yield. I was a bit too liberal with my glass grease and I think most of the SO3 produced went to work on it instead of making a happy little deposit in the collection flask. I ended up with black shit everywhere and some very acidic liquid. My bisulfate probably wasn't fully decomposed yet. Could you describe your setup and process in a little bit more detail, maybe some pictures too? :)