RogueRose
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H2SO4 from sulphur candle
I was unaware of sulphur candles and their use for fumigation so when I found out about them I read up a little more and found some interesting
stories about sulphur one of which was that solid chunks would burn once lit. I figured sulphur needed something in addition to O2 to burn in normal
atmospheric conditions but some reported lighting piles or chunks on a plate and allowing the fumes to fill the structure.
Candles were made with various proportions of wax and sulphur but it would seem that the sulphur may burn with a wick alone in a regulated manner
(with wick and candle shape/size). This could allow for SO2 production in a steady consistent manner. Even if some wax is needed the only addition
to output would be CO2 which shouldn't be an issue.
The idea I have is to take a pipe of 3-4" diameter and maybe 4-10' long, capped on both ends. Have a hole on both ends, one to allow the SO2 to flow
in and the other to pull air out. lay pipe flat on floor and fill 1/2 full with water. Ideally there would be a few misters positioned at the top of
the pipe in a few locations for the SO2 to pass through as it flows through the pipe - so the water re-circulates within the pipe. A small fan will
be placed on the far end of the pipe (opposite the candle) and pull air. As the candle burns and SO2 is released it is pulled into the tubing leading
to the pipe where it passes through the misters and over the surface area of the water, forming H2SO3 and H2SO4. I guess adding a bubbler would be a
good idea to oxignate the water to help convert to sulfate.
What I'm most curious about is how quickly sulphur dioxide will absorb into water and if there is anything else that can be done to speed absorption
in the water.
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j_sum1
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This is a route to H2SO3 and sulfites. You need an additional oxidation step to get H2SO4. This is not trivial. There is a thread on the lead
chamber process that may interest you. Industrially, V2O5 is used as a catalyst along with high temperatures to form SO3. Ultimately, H2SO4 is
tricky to make for the home chemist. There are a huge number of different routes but they all have their drawbacks.
Burning sulfur does have its uses. Nurdrage shows effectively how it can be done to produce quite pure manganese sulfate. I have made sodium sulfite
from it which has been a useful chemical o have around. (mostly for cleaning up hexavalent chromium and other things that are undesirable to leave in
a high oxidation state.) I use a tin can and cardboard for a wick following Nurdrage's example but there are probably cleaner methods.
If you are after sulfuric acid, I recommend buying it. Nothing you can do can beat big industry at their game. OTOH, if H2SO4 is not available where
you are (which happens) then IMO, the most accessible method is electrolysis of copper sulfate using a piece of lead as an anode. Do a search on my
name: I have described the procedure I use(d) several times.
Edit
To answer your big question, SO2 is extremely soluble in water. If you bubble it through a tall enough column at a low rate you will find that few
bubbles make it to the surface. And bubbling it through an alkaline solution is even better (and will likely get you the product you are after.)
[Edited on 29-12-2016 by j_sum1]
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RogueRose
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Thanks for the reply. I have read a good number of the threads (large portions, some not in entirety as they are long). I guess my question now
would be what conditions need to be present for the H2SO3 to transform into the SO4. The idea wasn't so much out of necessity or the acid being
unavailable.
As with so many things on the internet, I see other sites stating that the H2SO3 easily converts into H2SO4 when enough O2 is introduced into the
water.
The thing about dissolved O2 in water (from what I can tell from research) is water will only retain a small amount of the O2 that passes through it,
less than 1% from what I have read - so even if bubbling 21% O2 through water, very little of that will be absorbed by the water.
What made me think this might be possible is from when I replaced H2O2 with a bubbler during copper acetate or copper sulfate production.
If 100g of sulfur was burnt and absorbed in 1L of H2O giving a mix of mainly H2SO3 and a much smaller amount of H2SO4, can the rest of the H2SO3 be
converted into H2SO4 by bubbling air through the water or would this somehow release the SO2 from the H2SO3 (SO2 + H2O = H2SO3). Having the dissolved
O2 in the water would allow the 2(H2SO3) + O2 = 2(H2SO4).
The thing is that while reading about sulfurous acid is that the wiki states it doesn't exist in solution - but it also states it is the intermediate
in the formation of H2SO4.
The problem with figuring this stuff out, especially from the amateur's point of view is different sources state different results or properties of
various chemicals (stated properties may be slightly different but still different).
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Herr Haber
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Just out of curiosity, what are the candles used for normally?
I know you can get wicks pretty easily if you are in a wine making region as they are used to fumigate the barrels but that might be different from
place to place because of regulations.
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unionised
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Fumigating greenhouses to get rid of insect pests in Winter.
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AJKOER
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Actually for paths to H2SO4, the H2O2 treatment of SO2/H2O is well known along with the use of chlorine Cl2 or just hypochlorous acid, HOCl (see, for
example, https://books.google.com/books?id=0W1mAQAAQBAJ&pg=PA365&... ).
Lesser known is that one may be able to turn SO2/O2 treated tap water rich in transition metals (including manganese, or even trace amounts of
cobalt) salts into dilute H2SO4 with a manganous impurity. The radical based chemistry path is outlined by one source as follows, to quote:
"The manganous ion is a powerful catalyst for the chain reaction of bisulfite ion with O2: 2HSO3- + O2 → 2SO42- + 2H+. At relatively high
manganous ion concentrations (∼10-4 M, pH 4.5), the rate does not depend on oxygen or bisulfite ion concentration but is proportional to the square
power of the manganous ion concentration. In the mechanism for the uncatalyzed reaction a simple replacement of the propagation reactions b and c by
reaction 3 accounts for the [Mn2+]2 dependence in the three-term rate law. This term combined with the term for the uncatalyzed reaction leads to the
quantitative prediction of the third term which contains [HSO3-][Mn2+]. It is proposed that SO5•- oxidizes the manganous ion to Mn(III) and Mn(III)
is rapidly reduced back to Mn2+ by HSO3- with the formation of the chain carrier SO3•-. The ratio of the bimolecular rate constant of (3) to the sum
of the rate constants of (b) and (c) is 124. The addition of the initiator catalyst S2O82- to the manganous ion catalyzed reaction confirms that
manganese enters the reaction mechanism through a propagation step"
Source: "Kinetics and Mechanism of the Oxidation of HSO3- by O2. 2. The ...", link: http://pubs.acs.org/doi/abs/10.1021/ic951141i?src=recsys&...
More background on sulfite radical chemistry, see https://www.researchgate.net/publication/19330636_Free-Radic... and also https://www.google.com/url?sa=t&source=web&rct=j&...
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Note, one can prepare HOCl by the action of CO2 on a mixture of aqueous NaOCl (chlorine bleach) and CaCl2. Remove the CaCO3 precipitate leaving dilute
HOCl and NaCl. One way to remove the NaCl from the HOCl and concentrate the hypochlorous acid is to distill half of the volume of the HOCl/NaCl and
discard the remaining half. Per Watts Dictionary of Chemistry, the more volatile than water HOCl/Cl2O is driven largely off first, so the
concentration of the hypochlorous acid is nearly doubled and the NaCl is removed. Note, concentrated HOCl is increasingly unstable and should be
cooled, free from strong light and used promptly. Link to sources: https://www.sciencemadness.org/whisper/viewthread.php?tid=17...
[Edited on 29-12-2016 by AJKOER]
[Edited on 29-12-2016 by AJKOER]
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