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Author: Subject: Synthesis of Sulfur Trioxide and Oleum: The persulfate method
DJF90
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[*] posted on 22-3-2008 at 02:29


Thanks gc, I now have something to look forward to reading next week. It's a shame I can't read german :(
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[*] posted on 20-5-2008 at 07:53


Quote:
Originally posted by garage chemist
In the meantime I have succeeded in making SO3 from NaHSO4.
It worked extremely well, I got 23,8g SO3 from 100g pool pH-minus.
It's simply a matter of enough heat.
From 680-880°C, plain sodium pyrosulfate (from NaHSO4 at 480°C) gives off all its SO3.
And the best part: not a bit of it is decomposed to SO2. Because decomposition of SO3 requires a catalyst, like for example iron compounds, which are lacking here.

I just have to write a documentation.
Oleum has now become a simple OTC preparation.

[Edited on 22-3-2008 by garage chemist]


EDIT: I found the writeup, very impressive! I have 400g of NaHSO4 and look forward to doing this as a project.

[Edited on 20-5-2008 by ADP]




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[*] posted on 20-5-2008 at 08:04


Yes, of course, it's in Prepublication- has been for a long time.



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[*] posted on 20-5-2008 at 12:23


Quote:
Originally posted by ADP
Quote:
Originally posted by garage chemist
In the meantime I have succeeded in making SO3 from NaHSO4.
It worked extremely well, I got 23,8g SO3 from 100g pool pH-minus.


I have 400g of NaHSO4 and look forward to doing this as a project.


Without wishing to detract, in any way, from what must have been a pretty sustained effort, garage chemist, IMO, a yield of 23.8g from 100g looks somewhat skimpy for the amount of work expended.

If ADP gets a corresponding yield from his 400g he'll end up with less than 100g of product for his pains.

And I know this could be the maximum obtainable under the conditions.

I've seen a patent fairly recently which stated "The electrolysis is stopped at the point concentration of ~98%, since proceeding past this point would result in the production of oleum."

It's not quite verbatim, and the patentee could, let's face it, be mistaken, for all anyone knows, but if he's right, it could be another grail, if that's not a contradiction.

'One slight problem, I can't for the life of me, find it, or remember
which friggin' site I found it on.

It's frustrating, but I'm still looking.

If anyone else has come across something similar, I'd be most
interested?

I can't actually set up any kind of electrolysis at the moment, but might be able to have a go in a few weeks.

In the meantime, I want to look at the, so far, fugitive patent to see how authoritative it looks as I only skimmed through it the one time I saw the blasted thing.

(sigh)Someone else must have seen it!

P
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[*] posted on 24-5-2008 at 17:32


Quote:
Originally posted by garage chemist
Yes, of course, it's in Prepublication- has been for a long time.
Forgive my ignorance... but where exactly is the write up? A link maybe?
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[*] posted on 24-5-2008 at 18:12


Go to prepublication, press Ctrl + F, enter hydrogen, there it is.



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[*] posted on 25-5-2008 at 09:20


Ahh, fein dank. I didn't exactly know what the prepublication was. Found it.
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[*] posted on 21-7-2014 at 08:19


I have been off and on working on building a small electric furnace for the last several weeks so that I could produce SO3 among other things. The furnace was made from kiln bricks (2.5 inches thick), angle iron (2" X 2"), an old clothes dryer heating element (ca. 15 gauge nichrome wire) and an infinite switch from an old kitchen range for temperature control. The infinite switch was rated for 240V, but seems to work fine at 120V. It is the current rating, in this case, which is of greater importance I think. I have a decent digital thermocouple meter but the best probe I have has insulation rated to only 500C. I have ordered a probe that is rated for up to 1250C, but I don't have it yet. The 5000 or 6000W at 240V dryer heating element was reduced in length slightly (cut) and was run at 120V instead of 240V. The current to the element was measured as about 9.5A when the infinite switch was in the on state. This means the furnace element is putting out about 1140W (P=IV). With the infinite switch turned to the maximum setting and the cover on the furnace an internal air temperature of 500 Celsius could be reached in about 2 minutes. I didn't actually time it, but the temperature rises very quickly. Until I have the higher temperature thermocouple probe I won't know exactly how high the temperature can go. I used the following video as a guide to build my furnace, but I also read David J. Gingery's book, "LI'L BERTHA, A Compact Electric Resistance Shop Furnace", which had in it a lot of useful information.
http://www.youtube.com/watch?v=en4yhzLuD9A

Below are pictures of a trial run. I did two trial runs and led the SO3 into a Florence flask which contained what was left in the bottom of a bottle of drain cleaner sulfuric (91% H2SO4). I obviously still need to do some work on the collection part of the apparatus, as some SO3 was escaping and water was undoubtedly getting in and being absorbed, but the furnace works wonderfully and produces SO3 from NaHSO4 with ease. I have read enough to know that I need a moisture protection tube with anhydrous calcium chloride or some other suitable desiccant in it.

The quartz tube that a glass blower made for me is 30mm id. I had the side arm made rather long so as to avoid troublesome connections and also to act as an air condenser. About 130-140g of sodium bisulfate (pool pH down) was put into the tube for each run. It was just a trial run as I said before, but after the first run the 91% sulfuric acid in the flask was ~94% and after the second ~97% as measured by titration. I didn't measure the volume at the start because I was mostly focused on the furnace for the initial runs, but the final volume of 97% sulfuric acid was 166mL. This is likely not the best use of SO3, since the acid could be brought up to at least 95% reasonable efficiently by distilling off water. I also have a much bigger quartz tube on the way. I am trying for a 50mm tube, with a little greater length also, which would allow me to make about 3 times as much SO3 per run.

Air temperature in the furnace was kept between 300 and 400C for about an hour where it seemed mostly water came over. Once the air temperature in the kiln got up over 500C is was not long until much more dense white fumes appeared and the drops coming out of the side arm made hissing sounds that could be heard from 50 feet away when they hit the lawn below. The drops instantly carbonized the lawn they fell on. This is when I moved the collection flask into place and began collecting SO3.

Current To Element.jpg - 262kB Start up.jpg - 237kB Water Coming Over.jpg - 258kB Carbonized Lawn.jpg - 310kB Start SO3 Collection.jpg - 245kB SO3 Collection.jpg - 265kB SO3 Collection 2.jpg - 468kB


[Edited on 22-7-2014 by Hennig Brand]




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[*] posted on 21-7-2014 at 09:43


Nice! Did you calculate the % yields?
Surly they could have been increased by using a ground glass joint to a RBF rather then a Florence flask.
I doubt there'd be any pressure buildup, as the SO3 would dissolve quickly into the sulfuric acid.
How much 91% sulfuric acid did you start with?




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[*] posted on 21-7-2014 at 11:09


I didn't have it all thought through when I gave the specifications to the glass blower for the quartz tube. I think the larger tube I am about to have made will have the same design though, just a larger reaction tube. I think the long side arm/air condenser was a good addition and that by the time the vapor makes it to the collection flask it will have cooled enough that a Teflon bushing could be used to connect the side arm to the flask and the vent line to the flask. According to "Small Scale Synthesis of Laboratory Reagents", by Leonid Lerner, the maximum distillate temperature is about 340C, even when the melted reaction mixture is at 860C. I may do something similar to what I did here, http://www.sciencemadness.org/talk/viewthread.php?tid=15676&... , but with a moisture protection tube connected to the vent line.

It is the non-condensable gases (air), in the system, that would be most responsible for building up pressure if the system was sealed. Maybe it could be sealed once it was up and running, but I would feel a lot better about it being vented especially given the fact that the SO3 and sulfuric acid are pretty dangerous materials to have an accident with.

I actually didn't measure the sulfuric acid volume started with, which is a real shame. It would have taken me 10 or 15 minutes to go get a graduated cylinder and I was mostly just keen to test out the furnace and associated equipment. It turned out that the apparatus works really well and it is actually a trivial matter to produce SO3 with a bit of equipment by this method. I wish I had measured the sulfuric acid volume at the start because it would have told us how much SO3 was absorbed as well as how much water was absorbed. I suppose I could always do another run in the same way.


[Edited on 22-7-2014 by Hennig Brand]




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[*] posted on 22-7-2014 at 11:10


Well Done, Henning Brand. It's nice to see that my work is still an inspiration to members.
For your next batch, try to condense the SO3 directly instead of absorbing it in H2SO4. Do not use a CaCl2 tube, the SO3 vapors will violently react with every bit of moisture that it already contains. Instead, tightly stopper the neck of the flask with glass wool stuffed around the tube from the condenser. This prevents circulation of moist air into the receiver. Cool the receiver with ice, immersing the flask in it.
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[*] posted on 23-7-2014 at 05:06


Thanks Garage Chemist, I will definitely use your suggestions on my next batch.



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