Author Topic: Proper length/ type of condensor/column  (Read 596 times)

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moco

  • Guest
Proper length/ type of condensor/column
« on: November 30, 2002, 03:51:00 AM »
Used tfse nothing answered my question. Nothing in Zubricks.
What's best for App. and proper length?
*Simple/vacuum distill: West,Leibig? what length?
*Fractional:Vigereux,column packed? What length?
*Reflux: West,Leibig,Graham/coiled? What length?
 It would seem flask size/reaction mixture volume would be relative to condensor/column length.  Many options! Your expertise will be effusively apppreciated.

Stranger?I go back to TS1 days.Just Read and learn. 

Rhodium

  • Guest
For reflux and distillation, the condenser should
« Reply #1 on: November 30, 2002, 04:44:00 AM »
For reflux and distillation, the condenser should be long enough so that the ring of condensing liquid is no further than 1/2 (or at most 2/3) of its length. This will vary with the boiling point of the solvent, the boiling rate, flask size, and the temperature/flow rate of the cooling water.

A West condenser is made out of thinner glass, and is thus more fragile, but it gives better cooling.

A packed column of the same length as a Vigreaux will give better separation, but more holdup.

You cannot reflux using Graham condenser, it is used for downward distillation. When refluxing, a coil condenser is infinitely better than a Liebig or West, but it is more expensive.

All choices have different advantages and disadvantages, so there is no simple rule. You have to choose the equipment that suits your intended usage the most. Ideally, you need at least one of each type of condenser in your kit, and preferably also for every standard taper size.

Myself, I have one kit being 14/20, one 19/22 and one 29/40. The 14/20 size I use for what I classify as microscale reactions and distillation of 1-50g of substance, using 10-100ml RB flasks. The 19/22 kit is the "standard size" in Europe (what 24/40 is in the US), and is used for all regular-size reactions and distillation of 50-250g of substance, using 100-500ml RB flasks. Finally, the 29/42 kit is for reflux and distillation of 250-2000g of substance (such as solvent recovery), using 500-3000ml flasks. I have never needed anything larger than that, and never anything smaller (I do have an "antique" 10/18 quickfit kit, but it is so small it is more cumbersome to use than its worth), you can easily distill 1-2g using a 10ml RB boiling flask, a short-path distillation apparatus (those which include distillation head, condenser and vacuum adapter in a single 2x3" size unit) and 5ml pear flasks as recievers.

It is important to never use too small glassware (as the smallest bumping will then flush your solution right through the condenser), and neither too big (as you easily overheat your solution, and lose a lot of product when trying to distill, as the product will just coat the inside of your flask instead of distilling over). A good rule of thumb is that boiling flasks should always be between 1/4 and 1/2 full for optimum performance, and never more than 2/3 full for safety reasons. There are no danger involved in using flasks to only 10% of its capacity, but it is wasteful and lowers your yield.

moco

  • Guest
Thank R, Well I just read a long distill thread ...
« Reply #2 on: November 30, 2002, 05:22:00 AM »
Thank R, Well I just read a long distill thread from 01' by labtop. He suggests the vigereux about 200-400mm for fractional of oil.

moco

  • Guest
So, shall it be WEST or Leibig for simple/vacuum ...
« Reply #3 on: November 30, 2002, 05:41:00 AM »
So, shall it be WEST or Leibig for simple/vacuum  applications found here. How fragile is the WEST? Many photos are inconclusive as the two are very similar except the water surface area surrounding inner tube of condenser. It doesn't make sense to me that more water surrounds the inner tube of the Leibig than the West, yet you say the west cools better. Hell, I'll take your word on though that's for sure.

cthulhujr

  • Guest
Swim has a West
« Reply #4 on: November 30, 2002, 06:50:00 AM »
The thinner glass must be on the interior tube, with the outer tube being of normal thickness. It seems no more fragile than other types when handled. Swim simply chose it thinking it would be easier to clean the smooth interior surface.

Iä-R'lyeh! Cthulhu fhtagn! Iä Iä!