7
$\begingroup$

I want to assemble a "hobbyist-level" vacuum distillation apparatus for extracting small volumes of "typical" solvents (e.g., water, alcohols, ketones, diols).

I already have standard lab glassware with 24/40 joints, 10mm barbed inlets.

How do I select a suitable pump?

  1. I would want a pump that can run for extended periods to perform vacuum desiccation.
  2. So far my research suggests that I should be looking at diaphragm pumps, but:
  3. I don't know if there are other features or specifications available in a low-three-figure pump that will make life easier.
  4. What kind of tubing do I want? I know that larger inner diameter is better, but I don't know if something special is used instead of regular tubing to support the vacuum, or what the standard adapters and sizes are to come off the 10mm glass fittings.

What elements need to be part of such an apparatus, and how should they be configured? E.g., I have seen mention of:

  1. Filters: What are used, and when are they necessary?
  2. Traps: Does this only refer to "cold traps," which I understand to simply be another condenser in front of the pump? If so, is it correct that this would only help if I can cool the "trap" significantly below the temperature I'm using for the primary distillate condenser?
  3. Manometers
  4. Capillary bubblers: I can't even find anything on these, other than what's mentioned here.

Also, how do these answers change if I'm doing vacuum desiccation of the named solvents (i.e., where the only difference is I don't care to capture the evaporate)? E.g., can I just let the system exhaust through the pump?

$\endgroup$
6
$\begingroup$

Don't bother with a powered pump: Get a water aspirator (I recommend the $20 Humboldt H-12020, which uses 10mm or 3/8" inner diameter tubing just like your glass), connect to faucet, and using utility water (1-2 gallons/minute) it can pull over 500 torr, which should be adequate for your applications. Sure, you're flushing away a lot of water, but you don't have to bother with traps or filters.

(Actually, the H-12020 does have a check valve, but to ensure you don't get even a little water sucked into the apparatus when you shut off the aspirator you might want to add a separate valve or simple trap, but that's easy compared to a cold trap.)

You should buy "thick-walled vacuum tubing" for all connections if you want to run full vacuum.

Finally, for safety you do need some bump countermeasure. A "capillary bubbler" is just a tube that lets a tiny stream of bubbles into the boiling flask. Yes, that is reducing the vacuum, but a proper capillary tube admits a trivial amount of gas into the system. When possible, however, I prefer stirring. Running a magnetic stirrer in the boiling flask also prevents bumping, and is better than a bubbler because it doesn't introduce potentially contaminating gases into the mix (or require the supply of a neutral gas).

A decent reference for practical distillation is Zubrick's Chapter 20 ("Distillation for Dummies") available online here.

$\endgroup$

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.