Chemgineer
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Cool glassware
I appreciate the short path distillation apparatus is an extremely useful bit of kit, are there any other really useful things I should have a look
into from places such as Aliexpress?
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RustyShackleford
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snyder column, great distillate separation efficiency (also makes a very pleasing sound when used).
Dean stark apparatus/clevenger apparatus for collecting heavy or light phases from azeotropes that separate upon condensation, former is particularly
useful in drying reagents or removing water from reactions when using toluene.
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Sulaiman
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Quote: Originally posted by Chemgineer  | | I appreciate the short path distillation apparatus is an extremely useful bit of kit, are there any other really useful things I should have a look
into from places such as Aliexpress? |
I bought one of the common 'short path' distillation heads.
Very nice.
Can be used for simple distillation with or without reduced pressure,
but to me, the term 'short path' implies molecular distillation, pressures so low that the mean free path is comparable to equipment path lengths.
The inbuilt Vigreux section of the unit that I bought would block most of the path.
I would have preferred a unit without the puny Vigreux section as it would be easier to clean.
So it's really cute, but not as useful as it looks.
Mine is still unused 
(I called the Vigreux section puny because I guess/think that it would not even add one theoretical plate)
As cute as it looks,
I think that investing in individual components is better long term as it gives flexibility of design/upgradeability/replacement. (glass is fragile)
Members that have actually used one of these may have other opinions?
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Keras
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I do a lot of things with my short path distillation apparatus, it is especially well-suited for steam distillation, with minimal amount of losses.
It, however, isn't particularly well suited for either difficult distillations (unless put atop a Vigreux column, but that defeats its purpose), or
under reduced pressure, because bumping would sometimes splash liquid up to the built-in short condenser part and down into the receiving flask,
ruining the operation.
That being said, it is also ideal when you have no rotovap and want to remove solvent.
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Fery
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Recently I've bought these Snyder columns cheaply here:
https://sklep-chemland.pl/en/kolumna-vigreux-model-1100dl600...
The 600 mm length variant has 10 plates.
There are 29/32 ground glass joints, the size which is commonly used in my country.
They are not insulated, I wrap few layers of newspapers around (if temperature during distillation above 100 C) or put on tubular plastic insulation
for water pipes (if temperature below 100 C).
They are even harder to clean than Vigreux, I usually reflux acetone through them for cleaning them.
As RustyShackleford already pointed out, the sound of jingle glass is beautiful.
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Texium
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Yep. I’ve found it to be far
superior to an apparatus of assembled components when working on very small scales (a few mL or less). When working on a larger scale, you don’t
have to worry about how much material you lose just from stuff getting into joints, or being stuck to the surface of the glassware in a film too thin
to coalesce and roll down the condenser.
On a small scale, these factors become very important and could impact your yield significantly. You want to minimize surface area of glass along the
distillation path, and use as few joints as possible. The short path only has 3 joints, if you count the thermometer. An assembled apparatus would
have at least 5, possibly more depending on your setup, and the surface area would be much larger.
They’re also good for distilling high-boiling compounds, because it’s less glass that needs to heat up and stay hot in order for distillate to
pass to the condenser. You may still have to wrap up to the side-arm with foil, but the path the vapor has to take is, well, shorter. Thus, you’ll
enjoy a speedier distillation and spend less time sitting around waiting for the vapor to even reach the condenser.
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Keras
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| Quote: Originally posted by Texium |
They’re also good for distilling high-boiling compounds, because it’s less glass that needs to heat up and stay hot in order for distillate to
pass to the condenser. You may still have to wrap up to the side-arm with foil, but the path the vapor has to take is, well, shorter. Thus, you’ll
enjoy a speedier distillation and spend less time sitting around waiting for the vapor to even reach the condenser. |
However, the reduced condenser size means you can’t really distill too fast lest the vapour passing the condenser have no time to return to the
liquid state. There is definitely a trade-off here between speed and efficiency.
[Edited on 7-8-2023 by Keras]
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Rainwater
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Kepps appratus, used to generate gasses. My personal favorite
"You can't do that" - challenge accepted
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Texium
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| Quote: Originally posted by Keras | | Quote: Originally posted by Texium |
They’re also good for distilling high-boiling compounds, because it’s less glass that needs to heat up and stay hot in order for distillate to
pass to the condenser. You may still have to wrap up to the side-arm with foil, but the path the vapor has to take is, well, shorter. Thus, you’ll
enjoy a speedier distillation and spend less time sitting around waiting for the vapor to even reach the condenser. |
However, the reduced condenser size means you can’t really distill too fast lest the vapour passing the condenser have no time to
return to the liquid state. There is definitely a trade-off here between speed and efficiency.
|
I’m more so referring to the time it takes for stuff to even start distilling. Once it does, the rate can
be reasonably adjusted. Having a higher capacity condenser isn’t worth anything if you can’t keep the hot side of your apparatus hot enough to
prevent the vapor from just condensing in the still head.
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Chemgineer
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| Quote: Originally posted by Fery | Recently I've bought these Snyder columns cheaply here:
https://sklep-chemland.pl/en/kolumna-vigreux-model-1100dl600...
The 600 mm length variant has 10 plates.
There are 29/32 ground glass joints, the size which is commonly used in my country.
They are not insulated, I wrap few layers of newspapers around (if temperature during distillation above 100 C) or put on tubular plastic insulation
for water pipes (if temperature below 100 C).
They are even harder to clean than Vigreux, I usually reflux acetone through them for cleaning them.
As RustyShackleford already pointed out, the sound of jingle glass is beautiful. |
Is the Snyder column worth using then, is it massively better than a Vigreux?
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Sulaiman
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I've not used a Snyder column but I believe that each stage can add close to one theoretical plate,
so it should be several times more efficient (hetp) than a Vigreaux.
I consider Vigreux columns to be multiple times less efficient than a packed column of the same height.
eg
typical Chinese 300mm Vigreaux, 1 to 2 theoretical plates(at low throughput)
300 mm plain column packed with 3mm dia. glass spheres, 5 to 6 plates.
A plain column can also be used as an air condenser for higher bp liquids (eg H2SO4)
A reasonably good choice is a packed Vigreaux column.
The condensed liquid is directed towards the centre of the column/packing,
away from the wall which is where most channeling occurs.
I have done this but I did not estimate the hetp for it as that was a 'quick' distillation.
My Vigreaux column is of the typical cheap Chinese type,
with a side arm near the top for a condenser.
- less pieces/joints required for a simple setup.
but again, less long term flexibility.
PS
A Vigreux column that is thermally insulated will add approximately zero theoretical plates.
A packed column without a reflux condenser will give minimal fractionation,
An insulated packed column with a reflux condenser is optimal.
___________________________________
Cool glassware:
Snyder column
Kipp's apparatus
Soxhlet extractor
Coil condenser (if mis-used, bubbles, dyes etc.)
A set of various size Beakers down to 5ml...cute (and actually useful)
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Keras
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| Quote: Originally posted by Sulaiman | I've not used a PS
A Vigreux column that is thermally insulated will add approximately zero theoretical plates.
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I thought that, on the contrary, thermodynamic equilibria at each stage (‘plate’) required the column to be properly insulated. Failure to do so
results in very poor performance.
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Keras
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| Quote: Originally posted by Texium |
I’m more so referring to the time it takes for stuff to even start distilling. Once it does, the rate can be reasonably adjusted. Having a higher
capacity condenser isn’t worth anything if you can’t keep the hot side of your apparatus hot enough to prevent the vapor from just condensing in
the still head.
|
Fair enough. You can even distill products under their boiling point, if you’re not in a hurry.
I found that adjusting the rate is not an easy task, given the propensity of my heating mantle to overshoot somewhat, then backing off, etc.
But anyway, I agree.
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Sulaiman
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| Quote: Originally posted by Keras | | Quote: Originally posted by Sulaiman | I've not used a PS
A Vigreux column that is thermally insulated will add approximately zero theoretical plates.
|
I thought that, on the contrary, thermodynamic equilibria at each stage (‘plate’) required the column to be properly insulated. Failure to do so
results in very poor performance. |
you are correct - if a reflux condenser is used.
Vigreaux columns are commonly used without a reflux condenser, relying on cooling via the wall to produce reflux.
Insulated wall = no cooling = no reflux.
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Chemgineer
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Thanks for the tips guys, I got myself a snyder column and I like it so much i've ordered another so I can stack them.
It's doing a great job of separating alpha and beta pinene from turpentine at the minute.
[Edited on 20-8-2023 by Chemgineer]
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Fery
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The difference between b.p. of alfa pinene 156 C and beta pinene 165-167 C is only 10 C. You need also a distillation head with adjustable reflux
ratio, e.g. taking 1 drop of distillate and returning 5-10 drops back into the column.
If you need chemically pure alfa pinene, then you can further process your alfa pinene fraction by a reaction into its nitrosyl chloride where only
alfa react while beta doesn't. The alfa pinene nitrosyl chloride is solid so crystallizes. You can process it further into your desired products or
regenerate back the alfa pinene by a reaction with alcoholic solution of aniline.
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Chemgineer
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| Quote: Originally posted by Fery | The difference between b.p. of alfa pinene 156 C and beta pinene 165-167 C is only 10 C. You need also a distillation head with adjustable reflux
ratio, e.g. taking 1 drop of distillate and returning 5-10 drops back into the column.
If you need chemically pure alfa pinene, then you can further process your alfa pinene fraction by a reaction into its nitrosyl chloride where only
alfa react while beta doesn't. The alfa pinene nitrosyl chloride is solid so crystallizes. You can process it further into your desired products or
regenerate back the alfa pinene by a reaction with alcoholic solution of aniline. |
I seemed to get pretty stead temperature at 155 deg C with the snyder column, there was then a definite drop in temperature and then it increased to
165 deg C as the heating mantle brought the flask up to temperature. I admit though I have no clue of the purity of the alpha. It smells a little
sweeter than the beta.
I've not seen a an adjustable reflux still head, sounds expensive?
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Fery
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If you heat only moderately so most of the condensate returns back and only little passes into receiver it could work somehow. But better is thermally
insulated column and adjustable reflux ratio distillation head.
The more reflux returns back the better separation.
Imagine there is no reflux back and everything passes into receiver. The difference in b.p. is 10 C and the 2 compounds are in ratio 1:1. You distill
off e.g. 3/4 of the content. There is still some % of the compound with lower b.p. in the distillation flask. If there is reflux ratio 10 : 1 (10
drops return back and 1 is taken into receiver) then there is almost no compound with the lower b.p. in the distillation flask (the volatile compound
has more time to distill off and the condensate poorer on the more volatile compound returns back in big volumes). When 2 compounds have such a small
b.p. differences like 10 C, the difference of their partial pressure is not too much different (e.g. something like 2:1) that means that a lot of
compound with lower b.p. still stays in the distillation flask even after distilling off half of the content if there is no condensate returning back.
The more condensate you return back the better separation.
Also at the beginning, you should wait for few minutes (e.g. like 10 - 20) with variable reflux ratio head as during this period the temperature drops
because lower b.p. compound concentrates in the upper part of the column. Imagine that during these 20 minutes the volume of the condensate returned
back into the flask could be comparable to the volume in the distillation flask (I always distill at maximal power at which the column does not choke
yet, the power is initially set to max and later reduced until column stops to flood and the condensate manages to flow into distillation flask). See
what happens on thermometer - after 20 minutes the T drops by 2 C when not taking off any condensate yet and returning everything back into the
distillation flask:
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
It was separation of methanol, ternary mixture ethyl acetate : ethanol : water from food pharma grade azeotropic ethylalcohol made by fermentation,
the b.p. differences somewhat at the similar range as in your case (about 10 C).
time 11:10 AM T=76,0 C https://www.sciencemadness.org/whisper/files.php?pid=658651&...
time 11:31 AM T=74,0 C https://www.sciencemadness.org/whisper/files.php?pid=658651&...
Btw if you have Pinus Jeffreyi you can obtain also very pure n-heptane.
[Edited on 22-8-2023 by Fery]
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