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Author: Subject: Short Path Distillation Experience Needed
tiger1
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[*] posted on 15-4-2008 at 13:48
Short Path Distillation Experience Needed


Being a newbie I fretted over whether to start this in the Technochemistry section. It really isn't all that technical although certainly not as simple as your basic distillation.

I just procurred an ACE #9317-42 short path distillation unit that has 14/20 joints with a 10/18 thermometer joint and vacuum jacketed 'column'. My question is mainly in regard to appropriate volumes/appropriate scale. I'm distilling at 118-20 at 0.1mm a rather viscous material and I have concerns about clogging the condensor portion which is a straight shot roughly 4" X 5mm id condensor portion with only 1.5" jacketed for water cooling. The 'column' portion is 2" long and will be filled with the thermometer as column packing.
Enough description, here are the points I will incorporate. If anyone has any substantially different points please share them so I can get this right the first time.

1 - I plan to fill the cooling jacket with ciculating water at about 70oC (substance MP is 59-60). Warmer water or air cool?
2 - I'll use the thermometer as column packing with the bulb placed at the bottom of the column right where the column attaches to the distilling flask joint. Pull it back some?
3 - I expect to get about 30ml product from 40ml crude oily residue, any more will be bonus. I'll use a 100ml rb magnetically stirred and heated with a Thermowell mantle as distilling flask and a 100 ml pear shaped receiving flask. Is this too great a volume to try to run all at once or should I break it down into smaller runs?
4 - I'm leaning toward not using a bleed tube and going with magnetic stirring as I have a strong stirrer which has no problem stirring through the mantle I'll use.

Any suggestions would be greatly appreciated and please forgive any newbie ignorance or at least flame me lightly if needed.

I've found plenty of general info on short path distillation but very little specific to this type of unit. Thanks for any help that can be offered.
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mono
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[*] posted on 15-4-2008 at 18:42


MP must be BP I assume?

[Edited on 15-4-2008 by mono]




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Sauron
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[*] posted on 15-4-2008 at 19:41


My advice would be to reduce your pot size (presently I take it to be 100 ml in a 200 ml flask?) and boil up rate.

You want the minimum boilup rate that will allow vapor to reach top of column. That is only way you will get a decent separation.

If material solidifies in condenser, drain coolant. The vacuum pump will keep product moving and if it does not liquify in condenser it will certainly do so in your cold trap!

You ARE using a cold trap?




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tiger1
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[*] posted on 15-4-2008 at 20:48


To clarify, MP = MP, BP, as I stated is 118-120 at 0.1mm. I want to run the 'coolant' at a temp above the MP to avoid the product solidifying in the condensor, correct?

Again, I'm distilling 40ml of oily residue from a 100ml rb. You think I should use a 200ml rb for 40ml of crude product? And yes, I'm using a cold trap, even at $25 a gallon, pump oil is costly, not to mention pump rebuild kits.

Thanks for the tips folks. Any others?
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tiger1
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[*] posted on 15-4-2008 at 21:14


Sauron, my mistake, you said use a smaller, not larger pot. So, is 40ml in a 100ml flask reasonable?
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Sauron
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[*] posted on 15-4-2008 at 21:36


Up to 50% of nominal pot capacity is fine.

You might conside 25 ml in a 50 ml flask; recognizing this may mean doing 4 runs.

I thought you were distilling 100 ml at one time, which is probably too much for one of these lil ole short-paths. But 40 ml is OK, I think.

A Kugelrohr would be ideal.
I was rooting around on Ace's site for something else and found this.



[Edited on 16-4-2008 by Sauron]

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tiger1
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[*] posted on 15-4-2008 at 23:35


Many thanks Sauron. I've had a Kugelrohr fantasy for some time, kind of like a wet dream ya' know. Hopefully someday I'll come across one. Thanks.
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Sauron
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[*] posted on 16-4-2008 at 01:21


I am actualizing my kugelrohr fantasy, presently. I just bought a current model Kugelrohr (air bath/oven and motor set) and two of the older larger air ovens. The current model handles flasks to 2 L (working capacity 650 ml) and the older model twice that (4 L, working cap.1300 ml). Another member is supposed to take one of the older ones off my hands but he is presently mum so if he stays that way, it may become available, if you want it. It is $350. No glassware. Just the air oven and an air motor.



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