3
$\begingroup$

I notice that Graham condensers tend to come in three main sizes: 200mm, 300mm and 400mm. What are the relative merits of each size?

My typical application is vacuum distillation of organic solvents like ethanol and acetone with the goal of a single pass distillation.

|improve this question
$\endgroup$
2
$\begingroup$

A longer condenser presents a greater surface area and longer path length that vapors must get past in order to escape into the atmosphere. A short condenser will work fine if you are refluxing or distilling a high-boiling liquid, or if you are not concerned about losing some of the material as vapor. A longer condenser is preferable for a more volatile liquid. Vacuum distillation of an already low boiling liquid like ethanol or acetone (why use vacuum?) would likely require a long condenser.

You can get better efficiency from any condenser if you use a colder circulating liquid in the jacket (such as ethylene glycol with a circulating chiller). Alternatively, consider using a cold-finger condenser with a dry ice-acetone mix as the coolant.

|improve this answer
$\endgroup$
  • $\begingroup$ If you do not use vacuum, separating ethanol from water takes multiple distillations. Using vacuum allows the separation in a single distillation. $\endgroup$ – Shaka Boom Jul 13 '16 at 14:46
  • $\begingroup$ The "multiple distillations" can all be accomplished at the same time by using an efficient distillation column. However, you will not be able to get any higher than 95% ethanol as it is an azeotrope. $\endgroup$ – iad22agp Jul 13 '16 at 16:10
  • $\begingroup$ @iad22agp What about with pressure-swing distillation? $\endgroup$ – f'' Jul 17 '16 at 23:47
0
$\begingroup$

Vacuum distillation of ethanol/acetone isn't wise. Setup time is longer, changing flasks is more difficult, the apparatus is bulkier and a lot of ethanol will go to the pump. Try normal pressure distillation with an efficient distillation column.

Longer condenser means: less material will fly through, but more material will sit on condenser. For large scale distillation use larger condensers. For small scale - use shorter one.

Vacuum distillation makes sense for liquids like DMSO with boiling point much higher than 100C.

|improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.