Asus3
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Micro Short Path Apparatus Fractional Distillation at Reduced Pressure - What we need
Laboy micro short path apparatus, and a 100mm vigreux column. It has been a learning experience setting everything up, it is hard to clamp it down and
have it in the oil bath, without the sides touching / unaligned fitment.
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25x200mm test tubes with side arm, a glass straw, a couple of stoppers, a thermometer - etc., not sure hear about the best heat source? I'd like to
stay mobile. Any comments on the usages of a heat gun? What about the battery powered mobile heat guns? Are these real nice? or would a moving bic
flame that creeps up the sides of the glass, suffice???
I've had troubles getting temperature and vacuum down, have been using a hand vacuum pump.
I've learned this, as far as I know,
"✔ Vapor density determines how well vapor climbs and interacts with a distillation column.
✔ Running hotter (less vacuum) gives the vapor enough energy and velocity to engage the Vigreux plates.
✔ A taller Vigreux column requires adequate vapor density and momentum—otherwise the column does nothing.
✔ Too much vacuum makes vapor too “thin” and weak to climb → poor or no separation.
✔ Moderate vacuum + higher temperature + tall column = effective fractional distillation.""
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I had always thought more vacuum would mean the vapor is going to come across more. According to A.I. there is an optimal range, to engage the
fractionating column.
Been using peanut oi or sand has a heating bath.
I've reached about 350f in oil bath, and at about 22.5 inches of mercury, as far as conditions go for the micro short path apparatus / fractionating
column. I got vapor about halfway up the fractionating column, but no condensing vapor. I use a SH-2 hotplate stirrer, wondering about the 300w 100mm
110v soldering pot, and peanut oil? Or perhaps using a crystallization dish, for these more volatile compounds. (234c at sea level).
I'm worried about bumping in the micro short path apparatus, I'd like to use stirring, but I'm afraid my hotplate stirrer wont get the oil bath hot
enough.
Would making an air bath suffice? Will I need an air bleed tube?'
Also, as far as the second setup goes, with the 25x200mm test tubes with side arms, I wonder how much vacuum these can hold? Additionally, I'd like to
use them as miniature fractional distillation at reduced pressure apparatus'
Thank you sciencemadess!!!
It seems that if one of those side armed flasks had 3 side arms, and some sort of vacuum cut off on the barbs, it could be used similar to a cow/pig
adapter...
Might be an interesting job for the glassblowers?
P.S. viton tubing is supposedly better resistance than silicone
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How can I make a glass tube fit into the brake bleeder case?
[Edited on 30-11-2025 by Asus3]
[Edited on 30-11-2025 by Asus3]
[Edited on 30-11-2025 by Asus3]
[Edited on 30-11-2025 by Asus3]
[Edited on 30-11-2025 by Asus3]
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bnull
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Welcome to the forum. LaTeX works, html does not, and images can sometimes appear rotated because of the forum software.
Two things. One: what are you distilling? It is one of those intrusive questions, like when a fire starts somewhere and you need an extinguisher and
the other guy asks what is burning. Because you don't want to use water on electrical equipment, right? It helps to narrow down the options. Two:
there is a book on semimicro chemistry in the Library (link below in my signature) that may help you with your test-tube-with-side-arm sort of thing.
It is by Cheronis or Heidelberger, I forgot which one.
By the way, take AI suggestions with a pinch of salt.
[Edited on 1-12-2025 by bnull]
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Dr.Bob
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One big issue is that the Vigreaux is being cooled by air. The best solution is a vacuum jacketed column, as that allows good reflux, without acting
as a condenser also and cooling the vapors too much. If you can find one, that would be great, but you can also just wrap it with fiberglass
insulation and some Al foil instead. For heat, either a oil bath or heat gun can work. Even better is a heating mantle on a stir plate, as mantles
can go pretty hot, especially if the flask is under vacuum, which helps to insulate the system even more.
The vacuum is also critical, using a stronger vacuum pump almost always helps, you can always put a valve in the vacuum line to limit it if it is too
string a vacuum. You can use a piece of Tygon or rubber tubing to link the vacuum source to the short path inlet, but that hand vacuum pump is going
to be tought to get much vacuum, more importantly, you need a consistent vacuum level to get a good distillation, I would find a small HVAC vacuum
pump or other small pump. For lower BP compounds, a lower vacuum like an aspirator can work, but not well for BPs about 100 C or more.
Test tubes are mostly not designed for vacuum. Most jointed ones are also poor quality in my experience. I would stick to rbfs, they come in many
sizes, and are cheap to buy.
Good luck, you are close to the right setup, but will need either more heat, better insulation, or higherr vacuum, or some combination of them all.
But if the compound is high enough BP, you might need all three. I have done a few of those, and for example, diethyl malonate needs a rotary vacuum
pump, insulated dist column, and a heating mantle on a stir plate. The mag stir bar makes a great boiling chip, as it stirs, it helps the mix boil.
But even my setup took almost 25-30 minutes under vacuum to heat up enough to start boiling, and did allow some traces of other impurities to come
over with the diethyl malonate.
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BromicAcid
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A Vigreux does offer some separation but in order to due a real fractional distillation you need a controllable return to the column to get a steady
state. A variable takeoff head is an expensive investment but it's critical to get the best separation.
Distillations are fun, having been in industry for nearly 20 years I've run well over 1000 distillations of different compounds and they all seem to
have their own little eccentricities. What you learn on one compound might not be applicable to another.
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Asus3
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Another project,
59mL Tobassco bottles, I bought some epoxy, goes by the name of JB - weld. JB weld original, and JB water weld. I'm wondering if I can break the
bottle, insert glass tubing, and seam the bottle together again with the epoxy.
Advice?
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bnull
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A few things. One: you don't break bottles. You cut or drill them with the appropriate tools. Breaking stresses and cracks the glass. You may not see
all the cracks but they're still there. Two: these bottles are appropriate for room temperature work only, such as storage of compatible chemicals, as
measuring devices, to perform suitable reactions and crystallizations. Submitting them to hotter or colder conditions is not a good idea. Third: these
"welds" are not compatible with all chemicals. They're fine for everyday use, which does not include constant contact with solvents or reactive
substances, with or without the application of heat.
I recommend you use them only as reagent bottles. Find a good cap and bingo! they're ready.
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Asus3
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Well guys still trying to dial it in, so far I've get my vapor "front" to reach the top of my 100mm vigreux, this is on full blast heat.
I can:
Install a gauge near the vacuum port of the apparatus (since the gauges before the check valves don't tell the pressure of the apparatus (essentially
making sure vacuum is in check, might be kinda hard to mail it with the hand vacuum pump for a range of B.P.s*)
Use a heat gun: increase temperature on the round bottom heating flask
Use a crystallization dish: this will allow me to use less oil and have better fitment of the apparatus into the oil bath, greater heat.
Use a claisen dapter with an air bleed tube and a hoffman clamp or better yet, as I've heard, a needle valve in line to slowly let air in through the
bleed tube.
I've had problems apparently, getting the heat high enough, getting the vacuum low enough (really it's a guess what my vacuum pressure is in the
system *
A lot of variables here, or things I can do to affect how the systems heats ups.
Will need to get a thermometer for my oil bath, as I cooked my hobby lobby candle thermometer 
I'm looking for advice and suggestions, preferably I'll have my cow/pig LABOY micro short path apparatus dialed in, and then start working on the
24x150mm test tube with side arms, I have 10 of them + 10 lab thermometers. I'm wanting to attach a couple together with some glass tubing, having an
air bleed hole a thermometer hole and the sidearm is connected by tubing to a tube going through a stopperee 24x150mm side arm test tube, where vacuum
is applied and glass wool is packed. (Read glass wool could be used for preventing bumping in vac distillation setups as well as packing for
fractionating column material / or a blocker that broken glassa pieces cna be stacked atop
I tried using broken glass to provide nucleation sites, as I've had problems forking a steady, rolling boil.
I've read a few things on AI that have been misleading, causing time and financial setbacks. Kind of interesting stuff.
[Edited on 11-12-2025 by Asus3]
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Asus3
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Here you can see how I'm kind of dependent upon the vigreux column to get a good angle clamping down on the apparatus.
Since my pump doesn't use any electricity, I'm intrigued by the idea of running the whole fractional distillation at vacuum apparatus without any
electricity.
I'm a little unsure which needle valve would provide the best flow control and whatnot for my air bleeds, if at all necessary.
Here are some items I'm looking at to upgrade my current system, and develop the 24x150mm side arm test tubes into fractional distillation apparatuses
of there own.
[Edited on 11-12-2025 by Asus3]
[Edited on 11-12-2025 by Asus3]
             
Attachment: 71xBoOMoQqL._AC_SY300_SX300_QL70_FMwebp_.webp (11kB)
This file has been downloaded 25 times  
[Edited on 11-12-2025 by Asus3]
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Asus3
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edit it is a 200mm vigreux.
My dilemma is wondering if I knock out the large segment of fractionating column, (whilst still retaining sum theoretical plates..*) and use hotter
oil temperature if I can successfully get this fractional distillation at vacuum to go.
Or will I then need a larger heat source, to upgrade to a solder pot. Then, if that is the case, I may be requiring an air bleed tube to help with
stirring. We will see.
[Edited on 11-12-2025 by Asus3]And, if that is the case, what kind of needle valve is needed for the slow bleed end tube regulator?
[Edited on 11-12-2025 by Asus3]
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Sulaiman
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I have never performed fine fractional distillation at reduced pressure, these ideas are extrapolations of my experiences.
I sometimes used side-arm test tubes with vacuum, as scrubbers.
The thickness of the glass compared to its overall dimensions gives great strength.
I would have no worries using test tubes at any vacuum level.
At low pressures there is not a lot of heat transferred by the gas
so fractional distillation under vacuum would, I expect
need an insulated column, so a reflux condenser and variable take-off head would also be required.
Even at atmospheric pressure, a Vigreaux column gives poor fractionation.
A packed 200mm Vigreaux may add about three theoretical plates,
I used 600mm of column packed with 3mm glass spheres and got about ten theoretical plates, which is ok for near azeotropic ethanol.
You could progressively add insulation to your column until vapour passes over to the condenser,
but that would defeat the purpose of the column.
Try just a simple distillation under vacuum,
the fractionation will be poor, but you will get nearer to your goal.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Dr.Bob
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This is not accurate:
"You could progressively add insulation to your column until vapour passes over to the condenser, but that would defeat the purpose of the column."
The internal reflux of the vapors and liquid equilibrating is what creates the theorectical plates. Insulating the column prevents the premature
condensation of the vapors so they interact mostly with the liquid dripping off the column. So an insulated column will work much better for both
theoughput and final purity. Vacuum jacketted columns are routinely used for large scale distillations, I sold a 6-7 foot one on this site about
10-15 years ago from my friend Ed, and have since sold a few smaller ones, and might still have one or two left scattered around. They were used to
fractionate Freons into 1-2 C fractions, which could provide up to 98-99% pure fractions of some isomers and mostly pure batches of others, which
would be combined and then redistilled one more time to get to 99+%.
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Sulaiman
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Dr. Bob
I agree that to achieve fine fractional distillation the column should be well insulated ... if you have a reflux condenser.
In this case it is a 200mm Vigreaux with no reflux condenser.
If you insulate it then you will just have an insulated vapour path with negligible reflux.
I believe.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Zoe_LaboyGlass
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From a purely glassware standpoint, the setup is asking some fairly slender pieces to do double duty.
Joints and Vigreux columns are meant to handle flow and separation, not to act as structural supports or alignment tools.
Once you start hanging multiple components off each other, any small misalignment or thermal expansion tends to show up as stress, especially under
heat and vacuum. In practice things usually behave better when long sections are supported independently and unnecessary air-exposed length is kept to
a minimum. This is more about mechanical and thermal behavior of glass than about chemistry.
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