Sciencemadness Discussion Board

Is it feasible to make sulfuric acid via H2O+SO3 in vapour phase?

Junk_Enginerd - 9-8-2020 at 10:49

So I've wanted a sustainable and renewable source for sulfuric acid, rather than scavenging batteries. Also it's really fascinating. SO3 + water makes sulfuric acid, but most sources state that it's too violent to be useful.

Well, me being me, I wasn't buying it without seeing it for myself. Surely it can't be that bad, at least if you keep the SO3 in vapour phase and not combine liquid SO3+water.

I set up a simple small scale experiment. I filled a test tube with water and heated it to about 80°C, above the SO3 boiling point. I took a 4 mm ID glass tube, pinched it in one end, filled it with maybe 2 ml of solid NaHSO4. Then I put a U-bend in the glass tube so that it could rest on the rim of the test tube, one open end submerged, and the other hanging outside so I could heat it.
Then I heated the pipe with a torch, starting at the top of the NaHSO4 so as to not boil the lower part first and propel the upper layers along the tube. It melted, water boiled off to form pyrosulfate... All good so far. I started seeing SO3 form, evident as mist and a yellow hint. Then, WHOOP, and apparently I had made a rocket! The little U-bend pipe flew 10-20 cm away. So it's gonna be like that huh? I put a weight on the U-bend to make it stay put. From this point on it sort of maybe worked okay, but in the end I had instead shot out half of the water from the test tube.

All in all, interesting, but indeed not very practical. It got me thinking though. Surely SO3 will just as readily react with water vapour? So that if you would boil water in one container and decompose NaHSO4 in another, route the gasses to meet in a third container, and then just allow the mist to condense... Presto?

I can't imagine water vapour and SO3 gas reacting would be so violent that a reflux column wouldn't handle it...? Hot mist, yeah, but I can't see it "exploding". Since the condensate we want to catch condenses at >250°C, it should have a quite difficult time getting out of even a poorly cooled column. Plus, if you let the condensed liquid hang around, and eventually start reducing the inflow of water vapour, you should be able to get to the oleum stage rather quickly, and get a less violent reaction.

Does this make sense? Anything obvious I'm not taking into account?

draculic acid69 - 9-8-2020 at 19:29

Is it feasible to make sulfuric acid via H2O+SO3 in vapour phase?

I'd say no.

macckone - 9-8-2020 at 19:55

Is it feasible yes, Is it a good idea no.

best methods of turning SO3 into sulfuric acid are
A) add it to sulfuric acid then add that to water very very slowly.
B) put a cup of water in a chamber containing a cup of SO3 and wait.

Method A has the advantage if you have sulfuric acid.
That is the way it is done commercially.
Method B is very slow but has the advantage if you can get sodium bisulfate but not sulfuric acid then this will give you a starting quantity for Method A.

It is very hard to condense the sulfuric acid mist.
30M packed columns were used at the turn of the century.

As for why the SO3/H2O reaction is so bad, it heats up to somewhere around 900C.

Method B avoids getting the SO3 hot by being slow.
SO3 will react with water out of the air to form sulfuric acid.
The biggest downside to method B is that the inside of the chamber gets coated in sulfuric acid.

You could use a distillation apparatus without heat to minimize the amount of clean up.
Basically let it set for a few days and the SO3 will suck the water into itself.

macckone - 9-8-2020 at 20:21

One of these adapters and two flasks should make method B very easy but you will get a vacuum in the system.
So you may want to add a way to relieve the vacuum (like a regular 105 degree vacuum adapter sealed with teflon tape).
https://www.ebay.com/itm/24-40-Both-Glass-Groud-Joint-Distil...

Junk_Enginerd - 9-8-2020 at 21:59

I like it. The vacuum should help, and self regulate the reaction too. Vacuum increases evaporation > evaporation increases reaction rate > reaction makes heat > vacuum gone > evaporation slows down...

Out of curiosity, where would the acid mostly end up? In the SO3 container?

Also, any explanation as to why exactly sulfuric acid mist is difficult to condense? To me it makes sense that such a high boiling point liquid would want to condense very quickly onto surfaces that would be relatively very cold..

Belowzero - 9-8-2020 at 22:08

Quote:

Note that directly dissolving SO3 in water is impractical due to the highly exothermic nature of the reaction. Acidic vapor or mists are formed instead of a liquid.

Oleum is reacted with water to form concentrated H2SO4.

H2S2O7 (l) + H2O (l) → 2 H2SO4 (l)


This is from wikipedia.
As mentioned above this is how the industry does it.

You need sulfuric acid to make sulfuric acid :)


Also I've seen a couple of different topics mentioning the production of sulfuric acid now and I think a sticky superthread might really help to keep all this information in one place.
We have one about nitric acid so why not, since this substance is at risk of being OTC available for the EU.
Also, a combined effort to find a way to produce this in useful quantities would be interesting and good for the spirit on this forum.

Fulmen - 9-8-2020 at 22:50

I can't see that anyone has answered the OP's question.

The SO3 + liquid water is bad as it forms a mist. I assume the reason why the mist is bad is because it can't be condensed (it already is). But if it's done in vapor phase, and the resulting H2SO4 is formed above it's boiling point it could work as it should condense onto any cold surface. In theory at least.

macckone - 10-8-2020 at 08:17

Fulmen,
Doing it in the vapor phase is EXTREMELY hot. Which I mentioned in my post, my temp may be off but it is HOT.
It is hot enough to crack borosilicate glass. The temperature differential gets too high.
This is a problem distilling sulfuric acid let alone condensing the vapor of this kind of reaction.

On boiling sulfuric acid disassociates to SO3 and H2O (not completely obviously), the recombining is exothermic enough to boil the resulting sulfuric acid. Which is why the 'mist' is hard to condense. The hotter the 'mist' is the less sulfuric acid actually exists.

I gave a method that will work and has much less problems but it is SLOW so the heat of reaction has time to dissipate.

macckone - 10-8-2020 at 08:20

Junk_Enginerd,
Most of the acid will end up in the SO3 container.
The rest will be coating the walls with a small amount where the water was.

For the why on the mist, see my answer to Fulmen.

Fulmen - 10-8-2020 at 09:41

Maccone: I do agree that the industrial method is the most sensible. Why make conc sulfuric acid when you can make conc oleum with the same effort?
But JE asked a good question that deserves a proper answer.

As I understand it the mist is caused by sulfuric acid condensing in contact with cold air. It shouldn't happen if it's condensed on a cold surface.

If SO3 and H2O is allowed to react in the gas phase, the heat of formation should simply slow down the reaction. If it's allowed to cool in a closed system the cooling would first drive the reaction to completion, then condense out the sulfuric acid. But as you point out this is a high temperature reaction that pushes the envelope for glass, and in the end you get a lower value product.

Junk_Enginerd - 10-8-2020 at 11:02

Quote: Originally posted by Belowzero  
Quote:

Note that directly dissolving SO3 in water is impractical due to the highly exothermic nature of the reaction. Acidic vapor or mists are formed instead of a liquid.

Oleum is reacted with water to form concentrated H2SO4.

H2S2O7 (l) + H2O (l) → 2 H2SO4 (l)


This is from wikipedia.
As mentioned above this is how the industry does it.

You need sulfuric acid to make sulfuric acid :)


Also I've seen a couple of different topics mentioning the production of sulfuric acid now and I think a sticky superthread might really help to keep all this information in one place.
We have one about nitric acid so why not, since this substance is at risk of being OTC available for the EU.
Also, a combined effort to find a way to produce this in useful quantities would be interesting and good for the spirit on this forum.


Oh I'm well aware. Though I think it could be feasible to endure a bit of angry SO3+water huffs and puffs just to produce a few mL of acid, which could be made oleum, diluted, and then you can keep scaling it up from there. You should only need to do it once after all.

There's quite a bit of generic sulfuric acid discussion going on in the "lead chamber process" thread, but I didn't feel this quite fit there.
Quote: Originally posted by macckone  
Junk_Enginerd,
Most of the acid will end up in the SO3 container.
The rest will be coating the walls with a small amount where the water was.

For the why on the mist, see my answer to Fulmen.


I see, thanks. I condensed some SO3 today. That's one angry substance! And holy smokes you need some serious heat to drive it out of sodium pyrosulfate. It made my borosilicate test tube all droopy. I just put in in a small jar, which I placed into a large jar with a small amount of water in it. This should work much like you proposed, if a little less elegant.

Ah, mist in general is harder to "catch" than a vapour.
Quote: Originally posted by Fulmen  
Maccone: I do agree that the industrial method is the most sensible. Why make conc sulfuric acid when you can make conc oleum with the same effort?
But JE asked a good question that deserves a proper answer.


And it's much appreciated. :)
Quote: Originally posted by Fulmen  

As I understand it the mist is caused by sulfuric acid condensing in contact with cold air. It shouldn't happen if it's condensed on a cold surface.

If SO3 and H2O is allowed to react in the gas phase, the heat of formation should simply slow down the reaction. If it's allowed to cool in a closed system the cooling would first drive the reaction to completion, then condense out the sulfuric acid. But as you point out this is a high temperature reaction that pushes the envelope for glass, and in the end you get a lower value product.


This is interesting... Didn't know sulfuric acid decomposed like that when boiled, but it makes sense. So I assume it would likely stabilize at a quite constant temperature then, as long as pressure remains constant? Sounds like a horrible monster to try and control though hah. Well, I think I understand the reasons not to pursue this route, and learned a lot from it. Thanks.

macckone - 10-8-2020 at 12:51

Yes, the inner jar, outer jar arrangement should work too.
Everything gets coated with sulfuric acid anyway because the SO3 fumes and there is water present.
Yes, SO3 is not fun to work with for this among other reasons.

As Fulmen pointed out oleum is more valuable.
It is easier to work with once it is down to H2S2O7.

symboom - 10-8-2020 at 21:45

Sounds like a reaction to do in winter in Siberia at temperatures at -40 c and f is the same that cold should make it easier to condense the sulfuric acid mist. I forgot about the vacuum occuring.

Herr Haber - 11-8-2020 at 04:35

Quote: Originally posted by Junk_Enginerd  

Oh I'm well aware. Though I think it could be feasible to endure a bit of angry SO3+water huffs and puffs just to produce a few mL of acid, which could be made oleum, diluted, and then you can keep scaling it up from there. You should only need to do it once after all.


The first time I dropwise added 20% Oleum to 96-98% H2SO4 I fully understood why H2SO4 was used in the industry instead of water.
The noise the drops made when contacting the acid were popping sounds that sounded like small explosions or sodium on water.

I hope you dont blow up / open your setup. Dealing with SO3 in a home lab is probably very unpleasant....

Mateo_swe - 11-8-2020 at 09:29

So 20% Oleum reacts that violently with 96-98% Sulfuric acid, it seems oleum really dont like water.
Is it possible to add oleum to say 60-70% sulfuric acid without a very violent reaction that might destroy the glassware?

Lets say one wants to make more sulfuric acid by adding oleum to sulfuric acid.
What concentration of the sulfuric would be optimal?
If one use very high % sulfuric its less violent but one needs to dilute the sulfuric often.
It would be hard to make a continuous process as adding water to sulfuric isnt a good idea.
Maybe some kind of cyclic process where the sulfuric is diluted in the first step then the oleum is added in the second step and repeat.
All depends on how violent the addition of oleum to sulfuric is and it would need to cool down between steps.

Belowzero - 11-8-2020 at 12:29

Quote: Originally posted by Mateo_swe  
So 20% Oleum reacts that violently with 96-98% Sulfuric acid, it seems oleum really dont like water.
Is it possible to add oleum to say 60-70% sulfuric acid without a very violent reaction that might destroy the glassware?

Lets say one wants to make more sulfuric acid by adding oleum to sulfuric acid.
What concentration of the sulfuric would be optimal?
If one use very high % sulfuric its less violent but one needs to dilute the sulfuric often.
It would be hard to make a continuous process as adding water to sulfuric isnt a good idea.
Maybe some kind of cyclic process where the sulfuric is diluted in the first step then the oleum is added in the second step and repeat.
All depends on how violent the addition of oleum to sulfuric is and it would need to cool down between steps.


My idea was to set the addition of water to a very slow drip while the vessel is submerged in a water bath (the only real danger would be if the glass breaks, however a large amount of water is probably able to buffer this in case of catastrophe)
I would also add concentrated sulfuric acid in the same fashion and rate.
Keeping the receiving solution at nearly the same concentration.

This product could then be dripped at equal rate into a final collection vessel to keep the amount of product in the receiver about the same.

Thus making continuous production possible.




[Edited on 11-8-2020 by Belowzero]

Mateo_swe - 11-8-2020 at 22:37

You plan to drip water into conc sulfuric acid to dilute it?
One should add sulfuric acid to the water, not water to concentrated sulfuric acid.
Dripping water into conc sulfuric acid is one of the first things they teach you not to do at chemistry class.
I wonder how violent it would be to drip water into conc sulfuric, anyone knows?

Belowzero - 11-8-2020 at 23:10

We are talking minute amounts here in a well buffered environment.
Example: https://www.youtube.com/watch?v=gzWG33h1QSA

If you are that worried the same idea can be reversed.
Or perhaps the water and acid can be mixed at forehand as a dilution mechanism.

[Edited on 12-8-2020 by Belowzero]

macckone - 12-8-2020 at 08:57

Do not drip SO3 into diluted sulfuric acid.
That is just asking for trouble.

Do not drip water into oleum if you aren't prepared for the outcome.
Industrially oleum is diluted with sulfuric acid with concentration above the monohydrate (84.5%).
The oleum is added to the more dilute acid as SO3 readily escapes hot oleum.

woelen - 12-8-2020 at 23:30

I have a little 65% oleum and I did the experiment of adding a single drop of this to cold water. As soon as the drop touches the water, a loud crackling noise is produced. The reaction between sodium and water is really tame, when compared to the reaction between SO3 and water. Believe me, the violence of the reaction between SO3 and water is insane, really insane.

I also mixed the 65% oleum with 96% H2SO4 in order to make 100% H2SO4 and with that mixing, still a lot of heat is produced. I did this by putting some H2SO4 in a test tube and then keeping it almost horizontal (maybe 10 degrees off) and then dripping oleum near the open end of the test tube. The oleum then slowly flows towards the acid (and while doing so, dense white fumes are produced in the test tube).

Belowzero - 13-8-2020 at 03:46

Quote: Originally posted by woelen  
I have a little 65% oleum and I did the experiment of adding a single drop of this to cold water. As soon as the drop touches the water, a loud crackling noise is produced. The reaction between sodium and water is really tame, when compared to the reaction between SO3 and water. Believe me, the violence of the reaction between SO3 and water is insane, really insane.

I also mixed the 65% oleum with 96% H2SO4 in order to make 100% H2SO4 and with that mixing, still a lot of heat is produced. I did this by putting some H2SO4 in a test tube and then keeping it almost horizontal (maybe 10 degrees off) and then dripping oleum near the open end of the test tube. The oleum then slowly flows towards the acid (and while doing so, dense white fumes are produced in the test tube).


That is some useful information woelen.
You convinced me that oleum and water is definitely not workable.

Perhaps the receiving solution can be cooled down or at least buffered with a large water bath, a condenser might be useful too to keep the fog from escaping.
From what I understand these fumes are rather hard to condense but it might be an improvement.



[Edited on 13-8-2020 by Belowzero]

macckone - 13-8-2020 at 07:50

+1 to woelen's active experiment.

A packed column works better for dealing with sulfuric acid mist.
That is how it was dealt with a century ago.

If you are worried about something breaking don't use a water bath.
Use a silica sand bed, acid washed to remove calcium carbonate.
Silica sand won't react with oleum but will contain it.
Then you can let it sit outside until it stops fuming and has absorbed enough moisture to be treated as sulfuric acid.
saw dust could be added to the sand, it will potentially ignite but if it is well mixed with sand it will not create a big fire and the oleum would dehydrate the cellulose to quickly reduce the concentration while creating an absorbing carbon foam.

Fulmen - 13-8-2020 at 11:32

Belowzero: You can't condense a mist, it's already condensed. You need a demister.

Herr Haber - 14-8-2020 at 05:15

Quote: Originally posted by woelen  
I have a little 65% oleum and I did the experiment of adding a single drop of this to cold water. As soon as the drop touches the water, a loud crackling noise is produced. The reaction between sodium and water is really tame, when compared to the reaction between SO3 and water. Believe me, the violence of the reaction between SO3 and water is insane, really insane.



20% oleum and concentrated sulphuric acid was not "insane, really insane" but, to quote you "surprising, very suprising".

I hope that these two experiments avoid a few startles, burns, holes...
It's not unlike the surprise you get the first time you mix 1/5 concentrated H2SO4 with water and see the temperature spike close to boiling point.

Mateo_swe - 15-8-2020 at 00:32

Good info.

If one would want to make more H2SO4 using H2SO4 and oleum and time isnt an issue.
Is it possible to put 2 beakers one with H2SO4, say 80%, and one beaker with oleum together in a plastic box or glass enclosure and just let time pass.
The oleum will make it into the sulfuric acid raising the concentration but it will be a slow process.
Is something like this a viable way of making H2SO4?

macckone - 17-8-2020 at 19:24

Mateo_swe,
This was covered earlier in the thread.
You can do this absorption with water and sulfur trioxide.
It is messy but workable, the water winds up in the sulfur trioxide side forming oleum but it coats the surfaces.

If you have 84.5% H2SO4 and oleum, you can mix them directly but slowly dropwise adding oleum to acid.
If your acid isn't concentrated enough heat it to drive off water.
You can use a water bath to keep it cool and use an addition funnel to add it.

symboom - 17-8-2020 at 21:42

There might be a way around it such as absorbing the sulfuric acid on activated silica gel to absorb the vapor but then your sulfuric acid is solidified

[Edited on 18-8-2020 by symboom]

[Edited on 18-8-2020 by symboom]