Db33
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is there an ideal size for a liebig condenser for distillations?
when i first bought my initial first piece of glassware equipment, it was a distillation kit on ebay and came with a 200mm liebig. I personally think
its way to small. So anyways i thought a 300mm would be alot bigger. And it is alot more useful i think but im still not sure its ideal. I have seen
400mm and even 500mm and 600mm liebigs on ebay and im wondering what would be the ideal.... im guessing since its about right in the middle, that most
people will say the 400mm and thats what im pretty much decided on i just wonder if i shouldnt maybe go a bit bigger.
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Sulaiman
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don't buy until you try !
the condenser has to remove heat at about the same rate of heating of the boiler,
the cooling power of a condenser depends upon;
cooled surface area
water temperature and water flow rate (if too small the exit temperature will be too high)
so set up your kit, get a good water flow through the condenser
increase boiling rate until the first 3/4 has condensing vapour and the last 1/4 just has a few drops.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Tsjerk
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I never did any distillation where the distillate didn't condense in the first ten centimeters of the liebig. I guess 20 cm is fine for most
distillations, otherwise cool your coolant further.
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JJay
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I've overrun my condenser a few times when using a single 30 cm Liebig. You can get more efficiency out of a long Liebig, but other types of
condensers are more efficient at shorter sizes compared to a Liebig and have greatly diminishing returns per unit length. You can always stack
condensers if necessary: http://www.sciencemadness.org/talk/files.php?pid=446891&...
[Edited on 28-1-2017 by JJay]
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Praxichys
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It's all a balance. Remember that the heat input you give the still pot has to be removed by the condenser. You can distill very low BP solvents with
a very short condenser (which is considered a bad combo) as long as you're very gentle with the heating. However, this situation is far from ideal and
is going to take forever.
On the other hand, if you're distilling something with a high MP like t-butanol, phenol, DMSO, etc, a long condenser will give you problems because
even cool tap water will cause these things to freeze in the condenser and block it up.
My personal preference for general use is a 400mm 24/40 liebig coupled with a 300W mantle. In general, if it's good for water, it'll be good for 80%
of the things you'll need for typical amateur organic chemistry as long as you're gentle with low-BP solvents.
That said, you will eventually acquire an array of various condensers for specific purposes. For instance, when I'm dealing with 2 liters of solvent
at a time, I use a coil pre-condenser leading into a Friedrichs which allows me to strip low-BP solvents at something like 60ml/min.
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Db33
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i currently have
200mm Liebig
300mm Liebig
300mm Dimroth/reflux
300mm Graham
i also have another 300mm liebig but its part of a steam distillation setup so the top isnt 24/40 but fits a special piece.
im considering a 300mm Allihn and like the topic says, some sort of longer version of a liebig, which i always thought was the most ideal for slanted
distillations. Whereas i use the Dimroth for refluxes.
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JJay
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I have
300mm Liebig
300mm air condenser
300mm Vigreux
300mm Graham
300mm Dimroth
Short path distillation apparatus
The Graham condenser can easily handle 1100 watts of steam at a full boil and has never given me any problems with ether, bromine or pyrolysis
products, which like to shoot half-condensed through Liebigs. It's a pain to clean and probably isn't suitable for reflux, and I'd be afraid to see
what would happen when doing a high-temperature pyrolysis over a flame if it clogged, but so far, nothing like that has happened.
I've been thinking about getting another 30 cm Liebig with indentations for packing so I could use it as a Hempel column or put it inline with my
existing Liebig.
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Texium
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I use my 300 mm Liebig for most applications. I have a 400 mm Graham that I use for bromine, ether, and fractional distillations, since it pairs well
with my 400 mm Vigreux. I also have a 200 mm Liebig with a larger diameter that works well for distilling high boiling/melting compounds like phenol
when warm water is run through it.
When it comes to 14/20 glassware, all I have is a 100 mm Liebig, but on that smaller scale, it's perfect. I would like to get a fractionating column
and a 14/20 Graham at some point though.
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Chemetix
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My personal fave is a 200mm Double Davies 19/26. 1liter per hour of ethanol
A 300mm Graham for Soxhlet, handles ether extractions well.
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Db33
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graham condenser for distillation? would liquid be able to flow down those coiled tubes easily?
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JJay
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Quote: Originally posted by Db33  | | graham condenser for distillation? would liquid be able to flow down those coiled tubes easily? |
If it's standing straight up and down with condensable vapor flowing in through the top, yes.
In other configurations, I've read mixed reports. I've used a Graham condenser for distillation in a vertical configuration on numerous occasions but
haven't tried anything else with one. If you want to practice chemistry and only have one condenser, it should be a Liebig.
[Edited on 28-1-2017 by JJay]
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Praxichys
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Yeah, it's not good to use a graham on an angle. It causes pressure swings which lead to bumping, leaking/separating joints, and poor head temperature
control resulting in impure products.
Also, if you get some sort of runaway, the inertia of the liquid sitting in the graham coils acts like a stopper and can cause the flask to explode.
Normally you would leave a stopper unclipped in the still head to prevent this, but the backpressure an angled graham exerts would cause it to pop out
during normal distillation, causing the inexperienced to stick a clip on it. It's a recipe for disaster.
The double Davies is also a great choice. It basically has twice the surface area per unit length as a Liebig, and almost no backpressure. The
drawback is that they are not very easy to clean.
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alking
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A 200mm should be fine for most applications if you can keep it near freezing, even low boiling solvents it should be fine with ime. I have a 200mm
liebig, a 300mm liebig, and a 300mm coil/reflux. I use the 200mm for most things. If I'm distilling a low bp solvent like DCM I'll use the 300mm, but
it's still all condensed within the first 30-50mm or so, but why not have the extra assurance? I've never needed to use the coil condenser, but it's
very efficient. If you have a coil and a liebig I see no reason to get an allihn, it's about halfway in between the two in regards to efficiency.
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Amos
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When distilliing a high-boiling/melting compound that is traditionally used with a short-path condenser, I just distill directly into a 2-neck flask
and set a condenser up on the other joint, vertically. The flask does most of the cooling and almost nothing gets stuck/coated onto the condenser
interior, meaning less cleanup and fewer mechanical losses.
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JJay
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| Quote: Originally posted by Amos | | When distilliing a high-boiling/melting compound that is traditionally used with a short-path condenser, I just distill directly into a 2-neck flask
and set a condenser up on the other joint, vertically. The flask does most of the cooling and almost nothing gets stuck/coated onto the condenser
interior, meaning less cleanup and fewer mechanical losses. |
I think that might work well for preparing aluminum chloride from zinc chloride and aluminum.
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Chemetix
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| Quote: Originally posted by Praxichys | Yeah, it's not good to use a graham on an angle. It causes pressure swings which lead to bumping, leaking/separating joints, and poor head temperature
control resulting in impure products.
Also, if you get some sort of runaway, the inertia of the liquid sitting in the graham coils acts like a stopper and can cause the flask to explode.
Normally you would leave a stopper unclipped in the still head to prevent this, but the backpressure an angled graham exerts would cause it to pop out
during normal distillation, causing the inexperienced to stick a clip on it. It's a recipe for disaster.
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I had to think about this...what I know as a graham condenser has coolant running through a central coil and the condensate on the outside. It sounds
like you are describing what I know as an inland revenue condenser; condensate runs down a central coil with coolant in the outer jacket. Which must
be run vertically as you said.
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Magpie
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I got along fine with a 19/26 200mm West condenser for many years. A West is very similiar to a Liebig and seems to have replaced it (pretty much) in
the US. Member Organicum explains why the West was invented - had to do with WWI or WW2.
A few years ago I broke down and bought some 24/40 glassware from Dr Bob. I suppose the West for this size is ~300mm.
I also have a Graham, which I never use. It was a gift. It doesn't have ground glass fittings.
Then I have 2 large 5 bulb Alihn's, which were bought for soxhlet extractions, which I have never done in my home lab. I have used one of these a
time or two, however.
Sometimes I think I should own a Friedrichs, but I'm not sure why. Mostly because Len1 and garage chemist have one, I suppose. 
The single most important condition for a successful synthesis is good mixing - Nicodem
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