Samusan
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H2SO4 distillation with rubber gasket?
Hello, when distilling sulphuric acid (from drain cleaner, it's cheaper for me currently) with a thermometer adapter, do I need to worry about the
acid reacting with the little red rubber gasket that seals around the thermometer or should i use just a normal curved joint and omit the thermometer?
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SWIM
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If it's the kind of adaptor I'm thinking of (they're like a red rubber cap with a hole in the center. Common in 19/22 sets they use in some
colleges.), then it won't take hot nitric or sulfuric well.
I'm also pretty sure it would melt even if it did survive the acid.
If it's a little gasket like an O-ring then you may be able to get a PTFE replacement, but even this will start to degrade before you hit the BP of
sulfuric acid.
There isn't that much need for precise temp readings when distilling sulfuric acid, so many just use the curved joint.
Nurdrage has a good video on this and it includes advice on judging when the acid starts coming over fairly pure.
If you really want to use a thermometer a glass jointed thermometer with a glass joint topped distillation head would probably be the way to go. They
come in 10/30, 10/18, and 7/12 (easy to find equipment in 7/12, but damned hard to find used thermometers for it)
New thermometers with glass joints are expensive, but Laboy has ones for $20 to $25 (USD) sometimes.
Most of the other guys seem to want $60- $80.
I really don't see much need for one for H2SO4, but they do come i handy for many uses.
The big drawback with them is that you need several different immersion depths for different equipment because a 75mm immersion thermometer with a
ground joint has a set immersion depth and won't work in your 25mm immersion short path head.
If you've got both 10/30 and 10/18 equipment you'll need a few more most likely.
There's an old kind of distillation head where the thermometer port is a tube a few cm long that closely fits the thermometer. These were made so you
could use rubber tubing to seal thermometer to head without the tubing getting too hot and melting. The close fit in the tube would limit heat
transfer to the seal from hot vapors, and the tube also acted as a little air condenser cooling the vapors that got into it.
One of these with Teflon tape might survive the hot acid.
I don't think a regular PTFE thermometer adaptor would.
I think it would either break down or break the joint from expansion.
[Edited on 27-1-2020 by SWIM]
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Abromination
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It will degrade quickly, buy a glass thermometer adaptor piece/jacket for a thermocouple, and use whatever thermometer you want in it.
List of materials made by ScienceMadness.org users:
https://docs.google.com/spreadsheets/d/1nmJ8uq-h4IkXPxD5svnT...
--------------------------------
Elements Collected: H, Li, B, C, N, O, Mg, Al, Si, P, S, Fe, Ni, Cu, Zn, Ag, I, Au, Pb, Bi, Am
Last Acquired: B
Next: Na
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rockyit98
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make a mold of what you like to resist acid or alkali with POP.mix up talcum powder with silicone rubber ( normal sealing tube) 2:1 by mass mix them
well to make a putty and fill the mold. i'm thinking of giving the full procedure in a new post.
"A mind is a terrible thing to lose"-Meisner
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rockyit98
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make a mold of what you like to resist acid or alkali with POP.mix up talcum powder with silicone rubber ( normal sealing tube) 2:1 by mass mix them
well to make a putty and fill the mold. i'm thinking of giving the full procedure in a new post.
"A mind is a terrible thing to lose"-Meisner
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Tsjerk
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Boiling sulfuric acid temperatures are really close to Teflon decomposition temperature. Any rubber will be ripped to shreds by boiling sulfuric.
But what is your goal? Do you want to purify or just concentrate? If the latter you don't need a thermometer, just boil down till you think the acid
is thick enough. Also when really distilling you don't need a thermometer. There is nothing boiling higher than the acid, not without breaking the
glass anyway.
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Samusan
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Thank you everyone for your advice, I’ll go with the plain bend adapter
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unionised
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Quote: Originally posted by rockyit98  | | make a mold of what you like to resist acid or alkali with POP.mix up talcum powder with silicone rubber ( normal sealing tube) 2:1 by mass mix them
well to make a putty and fill the mold. i'm thinking of giving the full procedure in a new post. |
Silicone rubber will not even stand up to cold sulphuric acid for long (and for a while, I had the scars to prove it).
I don't think talc would be much better.
Wiki concurs
"Talc is not soluble in water, but is slightly soluble in dilute mineral acids."
https://en.wikipedia.org/wiki/Talc
So, if you are going to post a write up, you need to show that the stuff works.
On the other hand, silicone and cornflour makes a good putty rubber.
Not much long term stability though.
Talc would probably do better.
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woelen
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Just a word of caution when you want to distill H2SO4. The 98% azeotrope boils well over 300 C and that is VERY hot. Be absolutely sure that your
glassware withstands that kind of temperatures. Also try to imagine what happens if the glass breaks and 300+ C hot acid is flowing freely over your
equipment, workbench, or even worse, parts of your body. Acid at that temperature is increadibly corrosive and will char organic matter in a fraction
of a second and many other materials are attacked like crazy as well.
If you want to concentrate the acid, then I would put the acid in a glass beaker and heat that, until it starts fuming densely (much more so than when
just boiling water). Then you should stop. The acid in that case is well over 90% concentration. You can also clean the acid somewhat by adding a
little H2O2 to the acid, prior to boiling it down. Do not add a lot of concentrated H2O2, due to the risk of violent explosion or decomposition, but
slowly adding a few ml of 12% H2O2, while stirring, to 100 ml of acid makes it purer. On heating, the H2O2 will destroy organic impurities and on
stronger heating to drive off the water, any remaining H2O2 will decompose slowly and boil off as water. Do all of this outside, you don't want the
white fumes of H2SO4 in your house. The fumes lead to slow corrosion of materials inside.
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SWIM
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The stuff can do some pretty major bumping too.
When I concentrated battery acid it'd boil smoothly to a certain point and stop, then would bump hard enough to send a large spurt up out the top of
the flask. (an Erlenmeyer though, not a beaker)
If you've got a glass magnetic stirbar put that in and stir the hell out of it.
If not, use lots of good boiling chips/stones/boileezers or whatever they call them in your neck of the woods.
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morganbw
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I have yet to distill H2SO4 but have concentrated it.
Before I would feel comfortable distilling H2SO4, I think I would need/want/(or be very careful) quartz glassware.
A note to the unwary, boiling chips do not work well with some high specific gravity liquids, an ebulliator is usually a better choice.
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Tsjerk
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A quartz distillation setup? That would be insanely expensive and unnecessary. Borosilicate is perfectly fine at boiling sulfuric temperatures. Just
do as Woelen suggested, and make sure that if something breaks you don't directly have a disaster at hands.
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SWIM
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Yeah, quartz also has that problem that joining it to a glass joint can cause stuck or broken joints too. (worse if quartz is the outer joint).
Yukangquartzglass (on Ebay) does custom quartz work.
Probably $400 or $500 dollars to get some basic quartz still out of them.
($300 if you'll settle for 2 distilling flasks and set them up with 1 sitting in water. Kinda dopey looking, but ought to work.)
But plenty of people on here have distilled it in Pyrex, and I can only think of 2 who bothered to use quartz or Vycor.
I do believe I'd use a new flask if possible.
The minor banging around flasks endure sooner or later produces tiny spots of damage on the surface which reduce the flask's resistance to thermal
shock.
I've seen some old research from the 40s where they found a brand new flask took a 50 to 75 degree greater temp difference without breaking than a
flask which had been subjected to ordinary use in the lab.
This makes me wonder if it would be worth having 1 flask dedicated to really hot work which you just treat like it was made of gold: Always stored in
its own little padded box and washed and handled with great care to avoid any of those little impacts which might compromise the pristine surface.
Never put down on a hard surface unless there's a cork ring under it.
@Morganbw: Yeah, an ebulliator. I NEVER think of those things for distillations at atmospheric pressure because I always associated them with vacuum
work. Just some weird mental block...
[Edited on 29-1-2020 by SWIM]
[Edited on 29-1-2020 by SWIM]
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Dr.Bob
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I worked with boiling surfuric acid years ago, when it was used to clean silicon wafers before they were lithographed. The process removed any
traces of dirt, skin, oils, goo, sharpie marker, and nearly anything from the wafer. The only common items that lasted long in there were quartz,
PTFE (special high temp version), and tantalum. If it got on the double layered, heavy rubber gloves, they gave you enough time to remove them
before they failed. So it is really that bad at 300 C. Not that it cannot be worked with safely, but you do need to plan for fumes, eye and
splash protection, gloves and what happens if the flask breaks.
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Sulaiman
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I have two ground jount thermometers,
after calibration has been checked at least once they are reliably accurate for many years,
I really like using them,
but they are costly and fragile.
To read the temperature I need to get my face quite close to the glassware,
which is a little too close for comfort with boiling sulphuric acid.
A thermometer well/pocket with a (e.g. cheap eBay) thermocouple is sufficient,
it is more rewarding to see the temperature stabilise
(not necessarily at precisely the expected tempereature reading, but close enough)
and know that the azeotrope is distilling over.
______________________________________________
In my opinion, using an adapter without a thermometer is MUCH better than putting your thermometer in a sitiuation where it could fall into and crack
the flask of boiling sulphuric acid.
P.S. joint-size adapters have been no use to me in using say a NS14 thermometer in NS24 glassware
as the adapter puts the bulb in the wrong place and 'shields' the thermometer.
So usage is quite restricted. (but I still love the look)
CAUTION : Hobby Chemist, not Professional or even Amateur
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