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Author: Subject: The Synthesis of Sulfur Trioxide and Oleum: the vanadium (V) oxide-catalyzed method
einstein(not)
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[*] posted on 22-6-2009 at 13:11


Excellent idea! This is the reason I post here. I'm using a small lindburg furnace and this tube is about 12 inches longer than the box is wide so I'm think heat transfer my not be an issue. Won't be able to use it vertically though. Thanks again for the excellent insight.
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[*] posted on 23-6-2009 at 03:06


Will the sulfur not be oxidized by the SO3?

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[*] posted on 23-6-2009 at 05:16


Quote: Originally posted by 12AX7  
Will the sulfur not be oxidized by the SO3?
Probably. I am under the impression, and I very well may be mistaken, that this is pretty slow when the sulfur is cold. Honestly, I'm not sure even why I have this impression, and while I did do a fair amount of reading on sulfuric acid last year, it was by no means exhaustive.

Anybody?
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[*] posted on 24-6-2009 at 10:26


This is rather off topic however I thought it was important enough to mention.
I know I don’t have any picture to prove hover come the 2nd August I will post a thead in pre-publication on my contact plant.
Interested in research into various catalysts into the oxidation of SO2 --> SO3, I went out and bought 5g of ‘Platinised Kaowool’ This stuff cost £39.99 however you get surprisingly a lot and I thought it would be a great catalyst for a variety of other projects.
I took out the V2O5 cat. Tube from my mini plant and replaced it with 0.8 gram (again this is quite a lot, it just sounds little ) of platinised kaowool.
The result was far more efficient than my V2O5 cat. The Pyridine test showed very very little SO2 present at all! And the 0.8g of catalyst covered only 5cm of 14mm bore tubing.
Now how quickly does a Pt. Catalyst spoil and is there any way of re-activating the spent catalyst?
Will post pics asap!


[Edited on 24-6-2009 by Saber]
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[*] posted on 24-6-2009 at 11:12


Some asides!
Great work for making it possible.

I'd been thinking of fabricating a glassware venturi aspirator pump, and a glass magnetically coupled pump. Now I think could one use a mag pump to drive an aspirator pump, could one use an aspirator pump to draw the gasses through a sulphur burner and a V2O5 tube.

This would mean that the process ran at a slightly reduced pressure drawing in SO2 and air and in the final stage water was recycled through the aspirator and pump with surplus gas passing via the sump pot and scrubbers to atmosphere.

You would start with dissolving SO3 into water to make sulphuric acid then dissolving further SO3 to make oleum. All done in glass pumped with a spinning magnet well sealed into a glass tube driven by a mag stirrer.
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[*] posted on 24-6-2009 at 12:49


Dont try dissolve SO3 directly into water! it just leaves you with fumes of extremly corrosive H2SO4.
Instead Dissolve it into H2SO4 to form H2S2O7 then dilute this to reform more H2SO4.
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[*] posted on 11-6-2011 at 14:13


I built a double chamber sulfur burner similar to what is described in the following patent chain.

... 4039289, 4526771, 4966757

It is a bit smaller and simpler than described in the patents but seems to work fairly well. I'm not sure exactly what the SO2 concentration is using this method, but you can make a lot of it when you turn up the feed air volume (tested up to 100 SCFH). I constructed it as follows:

1) Start with a 2" diameter, 10" long steel pipe.
2) Weld a 1/4" thick metal disk inside of the pipe about 2.5" in from one end.
3) Drill a 3/8" hole in the disk with a drill press.
4) Drill/Tap two 1/8" NPT holes in the side of the pipe about 1" to each side of the disk welded inside of it. This provides the two compartments with separate feed air.
5) Put an end cap on the end of the pipe with the larger compartment.
6) Drill/Tap the other end cap with 1/8" male NPT and 1/2" standard thread for a plug, and put this end cap on the other end of the pipe (the end closest to the metal disk). This is the top end of the assembly.
7) Wrap the bottom 5" of the pipe with high temperature silica cloth for electrical insulation.
8) Wrap 2 twisted strands of 30AWG nichrome wire around the silica cloth with 0.25" spacing. This ends up being about 13 feet of wire, which will deliver about 300W of power when connected to 120VAC.
9) Thread in all three 1/8" NPT to tube compression fittings. The two on the side are for the two feed air lines and the one on the top end is for SO2.
10) Place a thermocouple near the heating element and insulate the whole assembly. I used kaowool.

Hook the the heater element and thermocouple to a temperature controller and the feed air lines to air flow regulators. When filling, I set the temperature controller to about 300C and heat the whole assembly. I then melt about 1 lb of sulfur an pour it through the 1/2" threaded plug hole and it flows down into the bottom chamber. There are much better ways of setting this up, but did not want to deal with the complexity of a hopper and continuous feed line for the sulfur now.

I put a plug in the 1/2" plug hole and set the temperature to about 410C (just below boiling point). After heating up, I push air through both feed lines at about equal rates. The air entering the sulfur chamber burns some sulfur, and the gases pass into the next smaller chamber and are combined with more air to finish the burn and provide surplus oxygen. This seems to work fairly well, and is capable of producing lots of SO2. You just have to get the feed rates right... if you don't provide enough air in the second burn chamber, not all of the sulfur vaporized in the first one will burn and this will fowl/plug the exit tube and the SO3 reactor. You also won't have enough spare oxygen to produce the SO3.

Also, use stainless steel fittings and tube. Copper tube reacts with sulfur and will not last long.


[Edited on 12-6-2011 by Evanescent]
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[*] posted on 11-6-2011 at 14:31


Nice work. I had always assumed an atomizer of some type would be necessary for an efficient sulfur burner.



The single most important condition for a successful synthesis is good mixing - Nicodem
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[*] posted on 11-6-2011 at 16:21


Yeah, while researching I saw several examples of sulfur burner products that used an atomizer, but these were for very large industrial SO2 producers (many kG per hour)... not really necessary for lab scale production. Sulfur ignition point is somewhere around 230 to 260C (depending on the source), so heat it up and introduce oxygen and it will burn.
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[*] posted on 12-6-2011 at 08:09


Fleaker, you have been doing a great job with the SO3 reaction, so I have duplicated some of your work and am trying to produce methods for SO2 production (see above) and the absorption of SO3 in H2SO4. I've been following your work for a while, so decided to join in and share what I have been doing...

A single H2SO4 bubbler is not very efficient, an absorption tower with bubble caps would be better. However, this is a bit large and expensive for lab scale production. I have a small 0.5" diameter column that I packed with glass beads. I installed this vertically on a reservoir holding H2SO4, and used a peristaltic pump with Viton tubing to pump the H2SO4 to the top of the column where it would bubble through the packing material with the SO3/air mixture passing vertically through it. The 0.5" diameter was much too small for the flow rates. I could not go much over 10 SCFH gas before I had issues. At 20 SCFH, the H2SO4 would bubble and splatter out the top of the column because of the high vertical flow rate of gas and the heat of reaction causing splattering. I would like to have a much larger diameter column with more open space for passage of gas. I have been thinking of using a Vigreux column (instead of packing) with a diameter of 1" or more. Some cooling would also help...
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[*] posted on 12-6-2011 at 08:42


That's interesting work, and it's nice to see someone taking this approach. I presume you are trying to make oleum.

One word of caution, when you get some oleum, how strong I don't know, I doubt if any plastic or polymer like Viton is going to hold up, except possibly perfluoros like ptfe, Kalrez, etc. I accidently threw a large drop of strong oleum onto the epoxy coating of my hood wall. It turned it brown. Even when I wiped this off it has left a permanent stain. Glass is good, and stainless steel is OK, for short term at least.

Also, any oleum, even 15%, is going to fume profusely when exposed to ambient air. This is a valuable visual indicator of its presence in the vapor state. Adequate ventilation is mandatory.




The single most important condition for a successful synthesis is good mixing - Nicodem
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[*] posted on 12-6-2011 at 09:37


Actually, I looked this up before using Viton fluoroelastomer. According to Dupont's chemical resistance guide, it has an "A" rating for 20% oleum. I attached a screen shot below. Cole-Parmer says the same. I have not had any problems with it yet, and hopefully won't since the number of elastomers with oleum compatibility is almost non-existent. It is nice to use these with peristaltic pumps.


[On second thought, I removed the screen shot from DuPont's chemical resistance guide. I don't want to draw any unwanted attention to the forum... just take my word for it or look for yourself.]

[Edited on 12-6-2011 by Evanescent]





[Edited on 12-6-2011 by Evanescent]
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[*] posted on 12-6-2011 at 19:01


Hey all!

I'm glad to see someone finally going for it! Any questions, ask! I made a few modifications that I never posted about. In my other thread on this, you can see that it pretty nastily charred FEP tubing that I had connected to the stainless via compression fittings.


I can say with some certainty that you cannot use FEP/PFA/Viton/Kalrez whatsoever if the SO3 is hot. At room temperature to about 180*C, FEP, PFA, and PTFE all tolerate it well. PVDF not so much at these high temps. Kalrez is better than Viton, but it won't take it forever, especially if it's hot.

Are you making oleum successfully?


I'll be back at it soon. I have some Cs (and Rb) to show you guys :-)
I'd also like to re-visit the ketene plant proper. I now have a much, much, much bigger tube furnace with a 2 m long quartz tube to use.




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[*] posted on 12-6-2011 at 21:09


Quote: Originally posted by Evanescent  


I have a small 0.5" diameter column that I packed with glass beads. I installed this vertically on a reservoir holding H2SO4, and used a peristaltic pump with Viton tubing to pump the H2SO4 to the top of the column where it would bubble through the packing material with the SO3/air mixture passing vertically through it. The 0.5" diameter was much too small for the flow rates. I could not go much over 10 SCFH gas before I had issues. At 20 SCFH, the H2SO4 would bubble and splatter out the top of the column because of the high vertical flow rate of gas and the heat of reaction causing splattering. I would like to have a much larger diameter column with more open space for passage of gas. I have been thinking of using a Vigreux column (instead of packing) with a diameter of 1" or more. Some cooling would also help...


This is called "flooding" the column. I agree that a 0.5" column diameter seems a bit small. But you might try a more open packing like tiny stoneware saddles, broken glass, or even a stainless steel scrub pad loosely packed. If it still floods you will have to cut the gas flow rate, or as you say, get a larger column diameter.

It seems that applying some ice-water cooling to the column would help alot also.

In my 1956 version of Shreve's Chemical Process Industries it only mentions making 20% oleum using an absorbtion column. Do you have information suggesting higher % oleum is being made this way?





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[*] posted on 13-6-2011 at 20:02


There have been two things keeping me from being successful at making oleum yet:

-My air supply is much too wet (as you discovered in your experimentation, Fleaker). A lot of my SO3 appears to react with the water vapor from the air feed and turn into H2SO4 mist. Right after the SO3 reactor, I pass the stainless steel exit tube for a little ways through warm water to reduce the temperature before it goes into the column. Quite a bit of sulfuric acid condenses in the tube because of the cooling water, and will actually start to gurgle after running for a little while. I put a flask at the end of the beaker and turned the gas flow up enough to push the liquid out (thinking it might be liquid SO3), and all I got was H2SO4 contaminated with metal compounds it stripped from inside the stainless steel tube. I got some molecular sieve and built a drying chamber I am going to attach in line with my air source before my flow regulators. Just a 1.25" diameter PVC pipe with a screen at the bottom and hose barbs at each end that stands vertical.

-The column diameter was too small and/or the packing material too dense. I had to run at very low flow rates to keep from flooding the column (as Magpie pointed out). There appeared to be a rather energetic reaction in the tube (more than just the bubbling of gas), as it appeared that the liquid was boiling/spattering in some places. It was going to take a long time to accomplish anything with the low flow rate I was running at and the exit tube from the SO3 reactor was gurgling again with H2SO4, so I just shut it down until I could improve the setup.

I have an air dryer now, so can insert that into the system. I also ordered a 1" diameter column I am going to try out. I would prefer to have an even larger diameter, but this is the largest one I could find without building something custom and spending lots of money. This hobby seems to greatly reduce my spare funds...

You can use a packed column as an absorption column... your goal is just to have a lot of liquid-to-gas surface area to enhance absorption. The same types of column construction used for distilling can be used for absorption. I may still have issues with flooding, but should be much better than before. I'll try some other packing materials as well if I still have problems.

My biggest success so far was in getting the sulfur burner to work reliably. I've heated it up and run it a few times already and have not had any issues with it. Once it gets hot enough for the sulfur to ignite, it produces more than enough SO2 for my experimentation.
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[*] posted on 13-6-2011 at 20:28


It looks like you are making steady progress. I think you have set quite an ambitious goal: going from elemental sulfur to oleum in one continuous train. Getting everything tuned to run in harmony will be quite an achievement. This also, as you say, takes some funds. I find that once you get beyond the textbook experiments it seems like you always need some new, expensive equipment.



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[*] posted on 3-12-2011 at 20:25


Just to make sure I understand what's gone before, I just sketched this:



The bubbler/absorption tower on the right should be about 2-3" across, I think, to ensure that evolved heat can't cause unpleasant consequences. The tap above it for H2SO4 replenishment ought probably be left open, or else it looks like a sealed system.

The cooling coil is within a 'bucket' of water, which might as well start out from the hot tap, about 40 Celsius. This should have a cone full of ice or similar above it so that the water doesn't all evaporate.

Air is added to the combustion chamber to make sure there is sufficient oxygen around. CO2 and moisture are removed in hopes of avoiding having too many other things going on - as is stated in the top-left note box, an oxygen generator would be far better.

What do you think of smashed pumice as the substrate? Glassy, porous, light, and as far as I know it shouldn't mind 600 Celsius.

Have I missed anything?

[Edited on 4-12-2011 by Gammaray1981]
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[*] posted on 3-12-2011 at 20:55


Quote: Originally posted by Gammaray1981  

Have I missed anything?


How does N2 leave the system? If you simply leave the absorbtion tower vent open you will lose the recycle SO2 and O2, as well as bleeding off the N2.




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[*] posted on 3-12-2011 at 21:05


Hm. The O2 isn't really an issue, if the N2 is - it's just coming from the air. I suppose the recycle line could be run through a dry-ice/acetone bath and the O2 and N2 vented afterwards. The then-liquid SO2 would have to be allowed to return to gaseous form before it was recycled, though.

That's an additional layer of complication, of course, but the alternative is venting SO2 to atmosphere - or attempting to convert it all in one pass, which by the looks of this thread and the relevant patents isn't possible, or would take a much longer tube furnace.
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[*] posted on 4-12-2011 at 09:17


I checked a flow diagram for the contact process in Shreve's "Chemical Process Industries." It shows the vent at the top of the absorbtion tower. So industry is just venting the N2 and any other unreacted/absorbed gases, at least back in the '50s.

You might want to check Shreve and/or the process descriptions in Ullman's or Kirk-Othmer. The key phrase is "Contact Process for Sulfuric Acid."




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[*] posted on 4-12-2011 at 10:48


I don't have Shreve, though I suppose I could go to the Library, but I do have Kirk-Othmer handy. It states there that two-stage converters were initially used, with a conversion rate of about 95% SO2-SO3. Given the rate of increasing efficiency from thereon, I would put the one-stage efficiency at about 87%, so perhaps 80-85% for a home-built tube furnace and catalyst setup. Given the source is burning sulphur, that's an acceptable loss economically, but there remains the serious question of polluting the air and annoying the neighbours.

It is suggested that ammonia is used to scrub SO2 from the exhaust gasses, which would negate that problem.

Given these problems, I'm in favour of buying a used oxygen generator for this sort of purpose - it's not like a torch, where huge flow rate is important, and the output is dry. Efficiency savings all round, I think.
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[*] posted on 6-12-2011 at 21:01


Quote: Originally posted by Gammaray1981  
It states there that two-stage converters were initially used, with a conversion rate of about 95% SO2-SO3. [...] Given the source is burning sulphur, that's an acceptable loss economically, but there remains the serious question of polluting the air and annoying the neighbours.
[...]
Given these problems, I'm in favour of buying a used oxygen generator for this sort of purpose
Commercially, the typical way of scrubbing the exhaust gasses from a contact process plant is to build a second contact process plant. The exhaust gas from the first is used as the feed gas for the second. Conversion efficiency is a nominal 95%. After two stages, you're down at 0.25% of feed sulfur left in the final exhaust gas, small enough for a regular scrubber.

Rejection of non-reacting gasses is the main emissions problem in any small scale contact process plant. I've convinced myself that tank oxygen is the right way to deal with the problem for a first prototype, essentially eliminating the problem except at shutdown. Make O2 the limiting reagent and you can get a gas-sealed system that doesn't build up non-reacting gasses. There are enough problems to work out for such a plant that it's prudent to eliminate emissions issues on the first round of development entirely.

The problem with an oxygen concentrator is that the Ar goes over with the O2, so that you have an approximately 95% O2 + 5% Ar mixture. That 5% Ar will still need venting, yielding all the SO2 emissions problems that you have just burning in air, except they take longer to show up.
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[*] posted on 24-1-2013 at 08:18


Thread bump!

How about using sodium metabisulfite to generate SO2 for this reaction? The source of SO2 is really a matter of convenience. The partial pressure of water is negligible at room temperature, but a drying tube can still be used for comfort of mind if the atmosphere is humid.




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[*] posted on 24-1-2013 at 23:15


I just bought some V2O5 the other day and have been doing some research along the lines of SO2 production etc.. It sounded like a viable route to me but I was wondering how it would play out? I haven't heated the stuff to decomp yet.(no fume hood or ground glass) so I was wondering if it would all try to come out nice and steady or whoosh? you may have to use your air supply to blow it through to the cat, or matching air/O2 flow rate mixer just prior depending on SO2 production rates. proper cooling could be difficult also.
also if it decomps like wiki says the similar K version does, K2S2O5(s) → K2O(s) + 2SO2(g), you would be left with Na2O. lye for your trouble is a decent bonus.
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[*] posted on 25-1-2013 at 03:21


Quote:
I just bought some V2O5 the other day and have been doing some research along the lines of SO2 production etc.. It sounded like a viable route to me but I was wondering how it would play out? I haven't heated the stuff to decomp yet.(no fume hood or ground glass) so I was wondering if it would all try to come out nice and steady or whoosh? you may have to use your air supply to blow it through to the cat, or matching air/O2 flow rate mixer just prior depending on SO2 production rates. proper cooling could be difficult also.
also if it decomps like wiki says the similar K version does, K2S2O5(s) → K2O(s) + 2SO2(g), you would be left with Na2O. lye for your trouble is a decent bonus.

Your post doesn't seem to make much sense ─ is it me, or are you talking through your hat?
V2O5 is reduced, reversibly, to VO2 on heating!
And where does lye, the old name for NaOH, come in?

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