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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.

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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.

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  • $\begingroup$ 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
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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.

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