Author Topic: Appropriate Length of Vigreux Column  (Read 2262 times)

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scarmani

  • Guest
Appropriate Length of Vigreux Column
« on: September 26, 2003, 08:49:00 PM »
After reading posts

Post 308445 (missing)

(greeter: "column length q.", Newbee Forum)
and

Post 308448 (missing)

(Osmium: "Yes, that is probably too long.", Newbee Forum)
, Swim was wondering what an appropriate length for a Vigreux column would be, under the following constraints:

The column would be used for vacuum fractionation of liquid volumes between 25 mL and 200 mL.  The boiling points of the desired fractions would range from 65°C to 130°C.  The distillation flask size would range from 100 mL to 500 mL.

Swim's current thinking is a 15 or 20 cm Vigreux column would be best.

Swim also wonders about the practice of wrapping insulation around the Vigreux.  Does this adversely affect the separating efficiency of the column?  If not, what is the best way of wrapping insulation around the column, and is there any particular insulating material that is recommended?


hest

  • Guest
*lol*
« Reply #1 on: September 27, 2003, 02:51:00 AM »
The length and the seperation follows, a looong collum is good to seperate complex mixture a short one is good to seperate not so complex mixtures. a 30cm is usual good enough but the wacumjaced is much more effective. Insulate with cotton and Al-foil

Osmium

  • Guest
> a 30cm is usual good enough Well, for...
« Reply #2 on: September 27, 2003, 08:23:00 AM »
> a 30cm is usual good enough

Well, for 50ml or less I'd never use a 30cm column.


terbium

  • Guest
Distilling columns.
« Reply #3 on: September 27, 2003, 10:15:00 AM »
A Vigereux column is not very effecient anyway. It may add only one more plate to your fractionation. So just use a not very long Vigereux. If you need a better fractionation then you need a packed, vacuum jacketed column with variable reflux head.

Insulation - With a fancier distillation rig you want very good insulation on the column, the necessary temperature gradient in the column being established by the return of condensed distillate down the column from the reflux head.
With a Vigereux and things boiling at 65°C+ I don't think you are liable to over insulate so just go ahead and wrap the column in glass wool; you are only going to get one additional plate from the Vigereux column in any event.


technology

  • Guest
200mm seems to be
« Reply #4 on: September 27, 2003, 09:07:00 PM »
200mm Vigurex column seems to be the one, once again it depends on what you are doing... of course i can take a guess, so i would go with a 200mm column..

the rest is up to you.

Osmium

  • Guest
It all depends on so many factors that this...
« Reply #5 on: September 28, 2003, 03:42:00 AM »
It all depends on so many factors that this question cannot be answered without you specifying a lot more details.


scarmani

  • Guest
more details
« Reply #6 on: September 29, 2003, 09:41:00 PM »
swim is grateful for the responses and apologizes for his tardy reply.

swim's use for this is part of a vacuum distillation setup as per the thread

Post 454619

(scarmani: "Synthesis of 2,5-dimethoxy-1-ethylbenzene", Newbee Forum)
(especially No 458275). irrespective of such use, the column was broken recently due to mishandling. in its place was ordered 2 vigreux columns, of lengths 150mm and 200mm (24/40 joints).

there are 2 vacuum fractionations for which this column is required:

1) 65°C @ .7mmHg; this is a modification of a fractionation that is "supposed" to occur (see earlier cited thread) from 120-140°C at the water pump (assume ~15mmHg). the boiling point goes right down to 65°C when extrapolated using the Clausius-Clayperton equation for this setup, and this is the first fraction that comes out of the sample.

2) 110-135°C @ .7mmHg; this is modified from 90-110°C @ .2mmHg, see appropriate religious text for elucidation:

"The organic phase was stripped under vacuum yielding 10.8 g of a dark viscous oil. This was distilled at 90-110 °C at 0.2 mm/Hg to yield a colorless oil that, on cooling, set to white crystals."

distillation 2 has yet to occur in the lab (column accident occurred immediately  prior to attempt), see referenced thread for setups. the setup will change slightly with a 2-way adapter at the bottom of the vigreux column to accomodate having the vacuum bleed into the reaction flask. this is an attempt to control bumping, which was severe during fractionation 1.


Osmium

  • Guest
> 110-135°C @ .7mmHg; this is modified from
« Reply #7 on: September 30, 2003, 01:44:00 AM »
> 110-135°C @ .7mmHg; this is modified from 90-110°C @ .2mmHg,

You cannot use a capillary to control bumping, you will never reach a suitable vacuum when there is an intentional leak in the system. This boiling point is way too high for this to work.

I don't think that using columns is necessary in this case, they might cause more trouble than it's worth.


L_jamf

  • Guest
Thanks For Advice
« Reply #8 on: September 30, 2003, 08:42:00 AM »
Swim is greatful for the pointers.  As an aside, Swim is wondering, IS there is an effective way to control bumping of high-boiling, viscous liquids during vacuum distillation?

Swim knows this topic has been covered ad nauseaum, since Swim has looked at Vogel and UTSFE.  (for example, in the recent thread: 

Post 460684

(ShaiGuy: "Vaccum distilation/Fine Hair Capillary", Chemicals & Equipment)
)

But after having tried shredded teflon tape, vigorous magnetic stirring, and capilary bleed, often, bumping  persists.  Swim has not tried glass wool, but it seems like it could cause loss of product due to adsorption onto its large surface area (?)

Swim concludes that as long as the bumping does not eject distilling liquid into the recieving flask, it is acceptable & par for the course.


Osmium

  • Guest
Small flask, big stir bar, fast stirring ...
« Reply #9 on: September 30, 2003, 09:11:00 AM »
Small flask, big stir bar, fast stirring speed. You should be able to see the bottom of the flask when the stirrer is spinning, so don't try to distill too much.
Alternatively you could use a Kugelrohr apparatus.


L_jamf

  • Guest
threshold for vigreux?
« Reply #10 on: October 01, 2003, 11:13:00 AM »
Os, swim sends thanks for the vacuum distillation tips, they will be implemented immediately.

is there a particular threshold amount of fluid which would warrant usage of a vigreux column? for the time being, that's all that's available, as swim doesn't possess the ~$2k for a Kugelrohr apparatus (although that would be great to have).

another piece of glassware that is of particular interest would be a distilling head (one w/ a short condenser), particularly a vacuum jacketed one (to insulate the thing and speed distillation along). is the ~$250 one would pay for such a distilling head worth it?

until funds can be raised, any suggestions for an intermediate piece (prior to a Kugelrohr) of equipment that would ease working with volumes of 25-250mL for these vacuum distillations would be great. the distillation head is just an idea along that line, and swim would like to keep price to the ~$300 zone.


hest

  • Guest
destilation
« Reply #11 on: October 01, 2003, 12:31:00 PM »
Usual, iff your product is ok, an clasien is enough. just heath gentel (1-2 drops/sek) and it will bee nice. No need for vacuumjacet hi.tec.