TinSandwich
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Vigreaux column disadvantages
I'm about to buy a distillation apparatus  but I'm having some trouble making up
my mind. Most kits I have found seem to include a vigreaux column, I don't plan on doing any fractional distillation right now but it might come in
useful one day and it's about the same price with or without it. The only problem is that the column is non-removable, it is attached to the still
head and if I buy it any distillation I'll ever do will have to go trough it.
My question is are there any reasons why this might be a problem? For example is fractional distillation slower than normal distillation or does it
require more heating?
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Metacelsus
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Yes, and yes. Cleaning out the head might also be a pain if you can't remove the column.
[Edited on 5-2-2016 by Metacelsus]
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arkoma
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I'd look for a different kit. This one is only $131.
"We believe the knowledge and cultural heritage of mankind should be accessible to all people around the world, regardless of their wealth, social
status, nationality, citizenship, etc" z-lib
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aga
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Great find arky ! Wish i'd bought that one much earlier.
A vigreux adds very little time to the distillation, whilst adding a lot more separation, so definitely worth having.
The kit in that link has all you'll need for quite a while.
Liebig, Graham, Allhin condensers + a Vigreux.
It's a steal for the 2 & 3 neck flasks alone !
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XeonTheMGPony
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That is a very good kit! have to see if they have it in 20/24
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CharlieA
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According to Fieser, Research Techniques in Organic Chemistry, a typical Vigreaux column, 50 cm, operating at a reflux ratio of 5:1 has about 5
theoretical plates. This will give a pure distillate (95% pure for 2 compounds boiling 30 deg C apart. For a good separation of 2 compounds boiling 10
deg C apart, you need 22 plates.
My conclusion is that a Vigreaux column may help prevent liquid from the pot bumping over into the distillate, but is not good for much else.
@Metacelsus is right about the head/column combo being a pain to clean.
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Texium
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You mean 24/40? I've never heard of 20/24
before...
@CharlieA: Yes, Vigreux columns are certainly not the most efficient, but if you don't mind doing a few distillations for one separation and control
the temperature very carefully, separating two compounds that have a 10ºC or smaller difference in BP is certainly feasible.
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JJay
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Vigreux columns are certainly useful. I don't think they are as generally useful as Hempel columns, but they are more convenient to use and do work
well for certain distillations that need to be performed frequently (e.g. water and ethanol). I've actually seen people pack Vigreux columns before,
but I don't think it's a good idea really.
Depending on your starting concentrations, you may already have several theoretical plates in your separation. Multiple distillations will give you
more plates.
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Dr.Bob
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The other use for a Vigreux column is using it as an air condenser for refluxing higher boiling temperature solvents. I do that often now, to avoid
issues with overnight water leaks or drops in pressure. I have seen so many chemists run a reaction overnight and come back to a black tar when
their water slows down or shuts off or the hose pops off and also floods the lab. Even for shorter time frames like a few hours, I often use them.
But I would not buy a kit with one piece vigreux/head as my only dist head, that is too fixed and very hard to clean or fit into some reactions. I
have one or two of them, but they are rarely used, and I don't need a vigreux column in many cases. For most chemists, they provide sufficient
purification in distillations. Few people here are distilling isomers apart or trying to do 99.99% purity work. Most of my distillations are a
quick and easy way to remove solids, salts, and bulk impurities.
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XeonTheMGPony
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Quote: Originally posted by zts16  | You mean 24/40? I've never heard of 20/24
before...
@CharlieA: Yes, Vigreux columns are certainly not the most efficient, but if you don't mind doing a few distillations for one separation and control
the temperature very carefully, separating two compounds that have a 10ºC or smaller difference in BP is certainly feasible. |
Yes I am suffering from the effects of heat here, brain doesn't work so good once the frost melts! goat I need an air conditioner! That or bigger
freezer.
As to the OP yes they are useful but not in that iteration.
[Edited on 2-5-2016 by XeonTheMGPony]
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TinSandwich
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Thanks for all of your answers! I'll keep my eyes open, every couple of days there's something new on ebay. I was thinking of getting a basic kit with
no vigreaux, a liebig condenser and a 1000ml flask
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arkoma
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I've dealt with sam100086 SEVERAL times. Very good value for the money and prompt (less than ten days) shipping to the US.
"We believe the knowledge and cultural heritage of mankind should be accessible to all people around the world, regardless of their wealth, social
status, nationality, citizenship, etc" z-lib
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