Author Topic: Dry trap for vacuum pump  (Read 546 times)

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wolfx

  • Guest
Dry trap for vacuum pump
« on: December 06, 2003, 03:04:00 PM »
I have found a site that sells vacuum pumps and supplies in the Web. I have a question on one item. This one is a low priced dry trap, that consists essentially of a container with zeolite ( is is the same as molecular sieve, BTW ? ) in series with the vacuum pump.

I would like to know if this setup would be effective in avoiding solvents, water and the like from degrading the vacuum. Right now, I have to change my pump oil everytime I distill ketone or the like. Typically the vacuum starts at 0.80 mmHg, at the end of the distillation it is at least 2.0 mmHg, sometimes degrades to about 10 mmHg. After flushing the pump and changing the oil, back to 0.80 mmHg.
BTW, I am starting with the aspirator, then switching to the pump, but still see the vacuum degrading more than I would like it to.

If it is OK, how many times could I use the pump before having to reload the zeolite ?

Also, how much the vacuum would be lowered by the extra hardware in series with the pump ?

n00dle

  • Guest
coldtrap
« Reply #1 on: December 06, 2003, 05:49:00 PM »
drytraps are okay, but the zeolite gets wet almost immediately so you have to hope that you aren't going to have more solvent pass thru the pump than zeolite/drying agent. depending on the boiling point of the solvents, it is probably better to make a cold trap, ie, a condensor attached to the end of the pump that condenses all the solvent back to liquid before it reaches the pump. using salt+ice+water seems sufficient for some reactions, but dry ice is another cheap possibility..

Osmium

  • Guest
Try removing most of the solvents from your...
« Reply #2 on: December 07, 2003, 05:51:00 AM »
Try removing most of the solvents from your ketone under aspirator vacuum before using the oil pump vacuum for distillations.
Always use the gas ballast on your pump, and once you're finished with the distillation keep that pump running for a while longer so it can get rid of the volatiles dissolved in the oil.

> Typically the vacuum starts at 0.80 mmHg, at the end of the distillation it is
> at least 2.0 mmHg, sometimes degrades to about 10 mmHg.

Oh boy. How can you tell which fraction is coming over with such a wild variation of the vacuum?


wolfx

  • Guest
To Osmium : The vacuum usually degrades ...
« Reply #3 on: December 07, 2003, 02:17:00 PM »
To Osmium :

The vacuum usually degrades gently, that is, what I see is the ketone being difficult to come out, the temperature incresases, etc, finnaly it starts to distill. I have had no problem in separating the first boiling fraction ( sometimes I have a bit colorless fraction, which I assume is MDP1P, before the ketone, more commonly just the ketone ).

There seems to be a big difference in density between these two. I allways measure the ketone density, I usually get 1.2-1.15, I don't think I ever got 1.1 or less.

I will try working more with the aspirator and also running the pump with the ballast open.

THX, W.