Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: zsinger on April 12, 2014, 11:13:33 PM
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All,
As I disseminated to all a few months ago, my rotary pump gave out. I am having a few problems fractionally distilling, and would really like this option, as I absolutely refuse to waste water with a water aspirator (Green Chemistry my butt!). As I already have sufficient access to a rotovap anytime in my lab, this will be the absolute most expensive purchase of my young chemical career. Vacuum just makes everything easier! (especially with azeotropes using swing distillation-->GREAT new trick I learned)
More to the point: Any particular thumbs up for one particular pump (links appreciated). Also, any thumbs down. I want a 2 stage rotary vane pump. Not buying used again.
-Zack
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Just curious, what's the connection between Green Chem. & a water aspirator?
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Water aspirators are usually NOT green, as they frequently use a faucet and need a source of positive pressure to keep the vacuum. Therefore, cannot reuse water unless you have some sort of recirculation tank. Therefore, wasted water. Therefore, not green. Most fish tank pumps only suffice for condensing and refluxing….not aspiration for a vacuum.
-Zack
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There is NO such thing as green chemistry!!!
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;D ;D ;D ;D ;D Like the "Hydrogen Car"………Well genius Ford engineer……How did you obtain that H2(g.). Well, I ran a current through water and………oh wait, I had to use electricity to run that current……..I grew the electricity on my money tree in the backyard!!!!!!!!
Sorry Disco….Couldnt resist! :) All in good fun.
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Additionally,
MUST I buy the chemical resistant ones if I have a scrub bottle between the takeoff and the actual vacuum? I can literally buy 5 non-chem resistant that are far more powerful for the price of one resistant and weak science pump. I think I would rather chance it, and save the 5 grand on the chemical resistant ones.
-Zack
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You can build a water aspirator that recycles the water. You just have to change it. No faucet.
Just a thought.
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Additionally,
MUST I buy the chemical resistant ones if I have a scrub bottle between the takeoff and the actual vacuum? I can literally buy 5 non-chem resistant that are far more powerful for the price of one resistant and weak science pump. I think I would rather chance it, and save the 5 grand on the chemical resistant ones.
-Zack
This depends on what you are scrubbing out and what with.
Our high vacuum had a liquid N2 trap and anyone putting volatile corrosives near the high vac were banned from using it for a day or two because they ruin it very quickly.
What corrosives are you working with and what are you using as a scrubber?
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Scrubber will be a regular erlenmeyer with slightly alkaline NaOH solution, and really only gaseous acids, in my case, need to be neutralized.
-Z
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You're going to pull water into the pump every time you use it. Will emulsify with the oil and shorten it's life dramatically.
Put it this way, if you put a drop of water in your car engine oil every day it will ruin it, same applies to a rotary pump.
It's your pump but a scrubber is bad news if you don't have a cold trap.
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Just don't think I can spend 5k for a chemical resistant one………What exactly do you mean by a "cold" trap? As in the scrub solution is ice cold?
-Z
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What are you distilling that prohibits removal of corrosive material first anyway?
How much acid (approx) is present in the crude material?
There are cheaper, better alternatives to your proposed set up depending on the application.
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I think changing the oil every third or fourth distillation would probably solve the oil mess?
-Z
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I think changing the oil every third or fourth distillation would probably solve the oil mess?
-Z
Your solvent reaching the pump at all is the problem, hence why there's a market for chemical resistant ones, that and you'd go through a tonne of oil not to mention hassle. Organic solvents eat through parts very quickly.
What archer is suggesting is having a cold finger connected along the vacuum line before the pump. The cold finger then is kept immersed in liquid N2 meaning any solvent vapour gets condensed before it gets pulled into the pump.
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What archer is suggesting is having a cold finger connected along the vacuum line before the pump. The cold finger then is kept immersed in liquid N2 meaning any solvent vapour gets condensed before it gets pulled into the pump.
Do you have regular access to liq. N2?
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What archer is suggesting is having a cold finger connected along the vacuum line before the pump. The cold finger then is kept immersed in liquid N2 meaning any solvent vapour gets condensed before it gets pulled into the pump.
Do you have regular access to liq. N2?
Indeed I do. Depending on the strength of the pump, ice/salt mix won't be cold enough to condense the vapour before the pump can pull it in so liquid nitrogen is used. You could experiment with mixes of dry ice and organic solvents though to keep things cold.
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What archer is suggesting is having a cold finger connected along the vacuum line before the pump. The cold finger then is kept immersed in liquid N2 meaning any solvent vapour gets condensed before it gets pulled into the pump.
Do you have regular access to liq. N2?
Indeed I do. Depending on the strength of the pump, ice/salt mix won't be cold enough to condense the vapour before the pump can pull it in so liquid nitrogen is used. You could experiment with mixes of dry ice and organic solvents though to keep things cold.
Sorry, not you, I was wondering if the OP had access.
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I've always just used dry ice baths with acetone or ethanol to cool down my trap. As long as you clean it out regularly (and aren't being careless) it is sufficiently cold for most applications I have come across.
OP: If you have a NaOH solution scrubber in line with a high-vac you will just succeed in pulling water into your pump or plugging your cold trap.
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I do have access to liquid nitrogen, but this sounds like more of a PITA than just biting the bullet now. Im just going with a science one and am going to create an aspirator which recirculates for now. DARN those science pumps are expensive!!!!!!!!!!!!!!!!!
-Zack