Author Topic: Fractional Distillation Review  (Read 4083 times)

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Quicksilver

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Fractional Distillation Review
« on: July 10, 2001, 09:06:00 PM »
Animated step-by-step review for beginners.  If you've never done it before, it's worth the watching. (even with a slow dialup)

Animated Fractional Distillation:

http://www.indiana.edu/~issgraph/crandall.html

    (Requires quicktime.)

For the impatient...
Selected Setups for Organic Chemistry Labs:

http://www.cornell-iowa.edu/tlt/teach/chem/fractional_distillation/fractional_distillation1.html



-quicksilver-

Chromic

  • Guest
Re: Fractional Distillation Review
« Reply #1 on: July 10, 2001, 10:52:00 PM »
Good show.

Obviously, the most common technique used here is vacuum fractional distillation using an oil bath and magnetic stirring. Why hasn't anyone ever taken any good pics of a running vacuum distillation setup before? SWIC knows that was one hard thing to visualise before gaining wings.

goiterjoe

  • Guest
Re: Fractional Distillation Review
« Reply #2 on: July 12, 2001, 11:26:00 PM »
SWIM took pictures of his setup several times, but unfortunately he never posted them on the web.  I imagine that several people out there have pictures they could post, but they probably wouldn't be as good as what you would find on a college chemistry website.  all of SWIM's got deleted when he decided it was necessary to bury a lot of equipment and various other items.


If pacman influenced us, we'd glide around dark rooms eating pills and listen to repetitive music.

Chromic

  • Guest
Re: Fractional Distillation Review
« Reply #3 on: July 13, 2001, 03:46:00 AM »
GJ, I just remembered your pics... well, let's go thru one of yours (not to pick on you!!!)...



That shows a simple distillation under vacuum (not a fractional distillation).

Note:
- the clamps should have been placed on the neck of the distillation flask and on the condenser (or the neck of the receiving flask)
- Leibig (straight) condenser should have been used, the one pictured is for reflux
- An aluminum pot with oil in it works better than the pyrex measuring cup. Measuring cups should not be directly heated.
- Vacuum lines are usually a material like an air compresser hose (I'm sure the one you had was suitable for vacuum, but vinyl certainly isn't).
- Rubber stoppers shouldn't be used with ground glass, and where you've got one, normally a thermometer adapter and mercury thermometer are used
- An insulated fractionating column can be placed between the distillation flask and the three-way adapter to setup for a fractional distillation.

But that gives a great idea on how to set up for a fractional distillation. I should take some pics of my setup one of these days so you guys can pick me apart.

goiterjoe

  • Guest
Re: Fractional Distillation Review
« Reply #4 on: July 13, 2001, 10:27:00 PM »
that picture was taken at a time unrelated to the topic of the website it was on(and the only picture unrelated to that webpage; SWIM just added it in to start the page off with a pictureabout distillation.)  This rig was set up for distilling water from sulfuric acid followed by distilling the acid, which didn't require a column.  and normally SWIM would have a candy thermometer in the top of the distillation rig(albeit still stuck through a #4 rubber stopper), but since acid was being distilled and the thermometer has a metal probe, it was omitted for this instance.  the vacuum tubing being used here has held up better for SWIM than the red tubing you refer to.  it has a strong metal/nylon webbing in it that prevents it from buckling under vacuum.  the clamps were arranged in a downright stupid manner in this instance.  normally the clamps are attached at the neck of the distilling flask and the neck of the receiving flask so that you can easily raise and lower the distilling flask out of the oil bath(or raise/lower the receiving flask out of an ice or dry ice bath).  Somehow the fastening bolt for one of the clamps became bent and prevented the clamp from tightening up around the neck of the distilling flask, but it would close enough to go around the outside of the condensor.  the alcohol somehow convinced SWIM that instead of at least putting the one good joint around the neck of the distilling flask and ghetto rigging the receiving flask up, he would be fine to just clamp both brackets to the condensor and let the vacuum hold it together later on.  this worked, although it could have been a mess, and the bolt was replaced later on.  as far as the allihn condensor being used, what can he say?   SWIM's a cheap son of a bitch;  it seemed like it would work well enough, and it has so far. no need to buy extra glass if he can get away without it.

the only thing I will try to defendfor SWIM is him using the pyrex measuring cup for an oil bath.  sure, aluminum definitely won't crack under heat, but you cant grab the handle of an aluminum pot that's been on a maxed out heating mantle for a few hours with your bare hands either.  this can easily be done with pyrex though since it dissipates heat so well.  and SWIM has heated a couple of pyrex measuring cups in this manner repeatedly with no problems, although it might be a major problem if it does mess up.  that is why SWIM has switched to using a homemade heating mantle now.


If pacman influenced us, we'd glide around dark rooms eating pills and listen to repetitive music.

weasil

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Re: Fractional Distillation Review
« Reply #5 on: July 14, 2001, 06:22:00 AM »
Yeah 40mm allihn is a nice piece of glass for the home.
Just a quick Q for ya:
I have a reciever that has no vent to the atmosphere.
I was wondering if this piece can be used to distil volatile solvents such as DCM that I would rather not breath?

Chromic

  • Guest
Re: Fractional Distillation Review
« Reply #6 on: July 14, 2001, 11:36:00 AM »
You need to vent... or pressure could build up in the distillation apparatus.

KrZ

  • Guest
Re: Fractional Distillation Review
« Reply #7 on: July 14, 2001, 10:08:00 PM »
Vacuum fractional distillation is quite tricky.  You need a large column diameter to be able to do it, otherwise you will get total reflux.  That is to say, a 12.5 mm column will be totally insufficient for working with high-temperature BPs at the 300ml level. Of course, a silvered oldershaw plate column will give the best separations, but they are quite expensive.  I used to find it effective to use a 12.5mm vacuum-jacketed column without any packing when doing vacuum fractionation, it definitely aids the separations well, you get good 2-4C spreads and a big (noticeable) temperature drop in between fractions.

goiterjoe

  • Guest
Re: Fractional Distillation Review
« Reply #8 on: July 15, 2001, 03:11:00 AM »
the homemade heating mantle is pretty ghetto, but it works.  SWIM picked up a buffet burner for Xmart, a square yard of asbestos-type material from a fireplace specialty store, and a bag of sand.  the flame retardant material was stiched into a semispherical shape.  the buffet burner was taken apart from the plastic holder so that it was just a coil and a regulator switch.  The coil was pushed in in the center to make a spherical shape to match the curve of a 500ml flask.  the coil was inserted into the flame retardant fabric, filled with sand to keep the burner off of the fabric and to make it full, and the fabric was stitched up completely(with picture hanger wire used to stitch throughout.)  it doesn't work as well as an oil bath for precise heating levels, but there is no worry of a flask inploding since the majority of the flask is covered with a sand blanket and an implosion under vacuum won't cause the oil bath to be sucked into the vacuum pump.


If pacman influenced us, we'd glide around dark rooms eating pills and listen to repetitive music.