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Author: Subject: sulphuric acid from SO2 problems
LostLandgull
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[*] posted on 5-4-2015 at 12:51
sulphuric acid from SO2 problems


In an attempt to make sulphuric acid from sulphur dioxide, I burnt sulphur and fed the gas into a solution of 3% H2O2 (this being the only hydrogen peroxide I have available). Following previous instructions I then bubbled chlorine gas through the solution in order to convert the remaining H2SO3 into H2SO4 (and HCl, but this would be boiled off). However after a couple hours of boiling down the solution, it turned a milky white colour, and none of the test I have tried show any signs of sulphuric acid.

Where did I go wrong?
Any help would be greatly appreciated.
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BromicAcid
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[*] posted on 5-4-2015 at 15:52


Questions:

How much sulfur did you burn and how did it go? There have been members in the past that have had serious issues with sulfur burners. Do you think you actually dissolved a significant quantity of SO2 in your peroxide solution? Do you have any numbers to help quantify that, i.e., "I went in with 200 grams of sulfur and had 150 grams of sulfur remaining after burning." What was your expected yield? Sometimes you would be surprised especially since you were only using 3% H<sub>2</sub>O<sub>2</sub>. Where did you get these instructions regarding bubbling the chlorine through your solution? Sulfur dioxide dissolves in water to make approximately H<sub>2</sub>SO<sub>3</sub>, I would assume you were using the peroxide to oxidize it to the sulfuric acid so why use the Cl<sub>2</sub>? What scale were you working at? Really the milky solution is a bit strange unless you were boiling this inside a container that could be attacked, all of your reagents should be volatile. That is unless you carried over some sulfur vapors and now have a bit of a colloid. Lots of questions, it may seem like you supplied a decent outline of your procedure but for someone who wasn't part of this decision making process or there to witness anything nearly all the critical details are missing.




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Hawkguy
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[*] posted on 5-4-2015 at 15:54


Do you have any pictures of your setup? I think that might help. I've tried what you're doing before, and it didn't work great. It would probably be better to lead the gas into a cooled test tube to condense the SO2. The produced Sulfurous Acid on exposure to Oxygen is supposed to form Sulfuric Acid.
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LostLandgull
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[*] posted on 5-4-2015 at 16:23


I burned ~50 grams (it was my first time trying it so I wanted to start small scale), it was in a closed stainless steel container so I couldn't see what was happening once I put the lid on, but it started burning well. I believed I dissolved a decent amount, near the end I could see what I presumed to be SO2 bubbling through, but instead of dissolving it just sat on top of the H2O2. When gas stopped bubbling through I opened the lid of the container and took the sulphur out (which after burning was just a large black lump), but like an idiot totally neglected to weigh it or anything. Before doing this reaction, I looked up ways to convert the H2SO3 into H2SO4 and I saw a couple posts on here saying that bubbling Cl2 through the solution would do this.
Everything except for the container where the sulphur was burnt was either made of borosilicate glass, or medical grade sulphuric acid resistant plastic.
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LostLandgull
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[*] posted on 5-4-2015 at 16:36


I don't have any pictures of it, sorry. Would an erlenmeyer or something like that in an ice bath work to cool it down to a low enough temperature?
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[*] posted on 5-4-2015 at 17:59


Wait. You burned S in a closed SS container. Dare I ask; was there adequate oxygen feed into your vessel? It might be that your milky suspension is particulate unburned elemental sulphur.
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LostLandgull
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[*] posted on 5-4-2015 at 18:23


I had a pump feeding air into the container at a pretty high rate, and all the sulphur had been burnt when I opened the container. I also had the tube from the container with sulphur to the flask with H2O2 in a slightly snake like shape in an attempt to block any unburnt sulphur being pushed through.
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[*] posted on 5-4-2015 at 18:28


Sounds alright.

I was just covering the option that you had overlooked something in the SO2 production.
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AJKOER
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[*] posted on 6-4-2015 at 03:58


I would suggest that you follow a preparation of Hypochlorous acid (note, HOCl is formed along with HCl by the action of Cl2 in the presence of water, but a little more easy to work with) that I have detailed previously on SM via the action of CaCl2 (available as DampRid) on NaOCl (active ingredient in Chlorine bleach) followed by treatment with CO2 gas (from vinegar and baking soda). Chemistry as follows:

2 NaOCl + CaCl2 = Ca(ClO)2 + 2 NaCl

Ca(ClO)2 + H2O + CO2 --) CaCO3(s) + 2 HOCl

Filter out the white precipitate and cool the Hypochlorous acid until you can add your SO2 gas:

HOCl + H2O + SO2 ---) HCl + H2SO4

What I like about this preparation is how water is consumed, thereby concentrated a bit, your acid product. Also, your starting common concentrated Chlorine bleach is around 8.25%, so your derived Hypochlorous acid is going to be a lot stronger to work with than your dilute 3% H2O2! You can also optionally distill off (into a receiver filled with SO2 to combine steps if you wish) just half of your starting amount of Hypochlorous acid as it has been reported to nearly double the strength of the product as being more volatile, most of the HOCl and Cl2O comes over first (see reference link to Watts below).
-----------------------------------------

[Edit] If your SO2 creation is still turning into a gaseous pain, you may even wish to forget it altogether (or, even a mixed route of Sulfur and SO2, by adding HOCl to a flask containing burnt and unconsumed Sulfur) and try directly using just washed Sulfur instead as per this source, Watts' Dictionary of Chemistry, Volume 2, Page 16, even dilute solution of HOCl can oxidize Sulfur all the way to H2SO4. To quote the relevant section from Watts':

"Reactions.--1. HClOAq acts generally as an oxidiser; it easily parts with 0 while HClAq remains. Thus, As is rapidly oxidised with evolution of light; P, S, Se, Br, I are converted to H3P04Aq, H2S04Aq, &c., even by dilute HClOAq; lower oxides or salts are converted into higher, e.g. SO2Aq to H2SO4Aq, FeO to Fe203, As203Aq to As2O5Aq, FeS04Aq to Fe2(S04)3Aq, Fe2Cl6Aq, and Fe2O3, MnSO4Aq to MnO2; sulphides yield sulphates, c.g. H2SAq gives" H2SO4,Aq and S; "

Link: http://books.google.com/books/reader?id=ijnPAAAAMAAJ&dq=...

[Edited on 6-4-2015 by AJKOER]
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[*] posted on 6-4-2015 at 04:22


I would add some KNO3 to the sulfur and burn it, the KNO3 is the catalyst in the lead chamber process.
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LostLandgull
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[*] posted on 6-4-2015 at 09:05


Sounds like a simple enough process. I'll have to try it.

What ratio would you use for the KNO3 to sulphur? Too little and I'm just wasting it, too much and I'm getting ripped apart by shrapnel when it explodes.
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Varmint
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[*] posted on 6-4-2015 at 09:16


try 5% and work it from there.
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[*] posted on 6-4-2015 at 13:19


Quote:
when it explodes.

Leave out the carbon and it's not gunpowder !




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LostLandgull
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[*] posted on 6-4-2015 at 17:25


You still have a fuel and an oxidizer, if placed in an airtight container with only one small tubing leaving the apparatus I would bet that the pressure would build up too fast, and the container would burst somewhere.
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AJKOER
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[*] posted on 6-4-2015 at 17:47


Quote: Originally posted by Varmint  
I would add some KNO3 to the sulfur and burn it, the KNO3 is the catalyst in the lead chamber process.


Perhaps, a little more accurate would be:

S8 + NO3- + H+ = S4O6-2 + NO2 + H2O (see, for example http://www.gregthatcher.com/Chemistry/BalanceEquation/S )

And:

SO2 (g) + NO2 (g) = SO3 (g) + NO (g) (see discussion at this link address https://www.google.com/url?sa=t&source=web&rct=j&... )

In actuality, a complex reaction where, to over simplify, the KNO3 can aid in the formation of NOx with Sulfur, which may further react with SO2 to form SO3, and eventually H2SO4 depending on reaction conditions.

Now you have some idea of the reaction pathway to make a comparable judgement on likely success, yield, cost, safety,..

[Edited on 7-4-2015 by AJKOER]
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