The Vespiary

The Hive => Methods Discourse => Topic started by: Bubbleplate on May 16, 2002, 01:13:00 PM

Title: Vacuum Pump Survey
Post by: Bubbleplate on May 16, 2002, 01:13:00 PM
I was dreaming about buying a Vacuum Pump. There's so many types out there, its a hard choice. Whats a decent brand that will be able to pull 25-29 Hg and will last a bit? Has to be able to handle solvents. I see the Gast Diaphragm types; then there's the Oil based ones like Edwards, Welch, Leybold, etc.
Any suggestions/experiences?
Title: teflon
Post by: tao on May 16, 2002, 02:47:00 PM
I remember hearing about knf teflon oiless pumps. For a nice one you have to pay but it's very resistant to solvents and doesn't require a lot of maintenance.
Title: unit's
Post by: hest on May 16, 2002, 06:25:00 PM
USE A PROPER WACUM UNIT
torr mmHg and (best) mbar will work.
I guess that 25-29 Hg means 25-29 inch of Hg, that is less than a lousy watherpump. For destilation you need 1-7mbar.
(twostag oilpump's from Edwards like 2E2 is a greath pump)
Title: get the
Post by: wyndowlicker on May 16, 2002, 11:36:00 PM
get the ritchie yellowjacket 1.5cfm or 3 cfm bad ass pump its even got the shape of a bee.gets you where you want to go. :P
I will choke untill I swallow!Who are you to judge or strike me down!Miss you Kerra!
Title: Distillation question
Post by: sYnThOmAtIc on May 24, 2002, 07:31:00 AM
Is it possible to lose goods during a vac distillation? Say one is using a 3cfm vacuum pump boils water at about 10c give or take a lil. Will the vapors of the boiling substance be evacuated in to the pump line?
Title: Yes, that is a real possibility. E.g.
Post by: Osmium on May 24, 2002, 10:44:00 AM
Yes, that is a real possibility. E.g. when you distill sassy oil at a temp of 70°C quite a bit will end up in your pump. That's one reason why your distillation temperature shouldn't be too low and your cooling water as cold as possible.
I'm not fat just horizontally disproportionate.
Title: cold trap?
Post by: ClearLight on May 24, 2002, 06:09:00 PM

  sounds like a calcium chloride/water cold trap is needed... btw what are the tradeoffs between the diaphram based pumps and the oil based???

   Ever since I heard about the guy who got busted when they gc/ms his pump oil, I got reaaall leary about oil pumps..

Infinite Radiant Light - THKRA
Title: Oil pumps usually reach a lower vacuum, but of ...
Post by: Osmium on May 24, 2002, 06:53:00 PM
Oil pumps usually reach a lower vacuum, but of course are more prone to corrosion than full-teflon diaphragm pumps.

> Ever since I heard about the guy who got busted when they
> gc/ms his pump oil, I got reaaall leary about oil pumps..

They will find the same residues in a diaphragm pump too.

I'm not fat just horizontally disproportionate.
Title: sweet ass
Post by: chem_123 on May 24, 2002, 07:14:00 PM
keep the info. comin' boys, SWIM's gonna aquire a pump soon, and SWIM needs to know what to look for in a pump...keep talking about the difference between the different types, and what separates the men from the boys.
Dreaming of the sweet honey  :)
Title: If your just startin out, a good pump to get is ...
Post by: pickler on May 25, 2002, 01:31:00 AM
If your just startin out, a good pump to get is the yellowjacket one. They are good and you can get one at a pawn shop for about 100 bucks. Even if it only works for one synth, you can make enough to buy 50 pumps.
We'll soon find out if I'm a chemist or not!
Title: air conditioning vacuum? you mean compressor
Post by: chem_123 on May 25, 2002, 09:44:00 AM
what is the air conditioner vacuum?
Dreaming of the sweet honey  :)
Title: same difference
Post by: Rhodium on May 25, 2002, 10:57:00 AM
Fridge pumps, AC units - all are air pumps. Depending if you utilize the "suck-in" or "blow-out" connection you can call them either vacuum pumps or air compressors.
Title: Os, what would be your pet, money-no-object ...
Post by: placebo on May 25, 2002, 03:41:00 PM
Os, what would be your pet, money-no-object (within reason, say US$3k) pump of choice? Least upkeep, hassles, noise, vibration, best reliability, vacuum, all-rounder?
Please supply a url.
Bored...
Title: Depends what you need it for!
Post by: Osmium on May 26, 2002, 01:27:00 AM
Depends what you need it for!
Ideally you should have both, a diaphragm and an oil pump (KNF or Vacuubrand for the diaphragm pump).
I'm not fat just horizontally disproportionate.
Title: fuck
Post by: foxy2 on May 26, 2002, 04:22:00 AM
I could have had a NEW, approximately $3000 knf diaphram pump for like $550.  But i waited just a bit to long....

Wonder if a bee lucky bee got it, hope so.  You Euros would have loved it cause it was wired for you, I think thats why it was so cheap. :(
Those who give up essential liberties for temporary safety deserve neither liberty nor safety
Title: Well SWIM has a pump that Os already said was too ...
Post by: placebo on May 26, 2002, 12:10:00 PM
Well SWIM has a pump that Os already said was too big (cfm) and doesn't go as low as one would like. Although it is very nice for vac filtering etc. So in a never-ending struggle to please Os. SWIM would like a pump more befitting of his manliness. Something for vac distillation of our beloved ketone and freebase amine in glass of not insignificant size, say.. 5L RBFs. Quiet, reliable, as little upkeep as possible, not waiting an hour for ultimate vacuum.

Would something like a vaccubrand MD 4C with the PC201 (

http://www.vacuubrand.net/chemistry_systems/default.htm (http://www.vacuubrand.net/chemistry_systems/default.htm)

) be acceptable?

placebo... on a never-ending journey to please Os.
Bored...
Title: These pumps are very well suited for rotovaps, ...
Post by: Osmium on May 27, 2002, 10:59:00 AM
These pumps are very well suited for rotovaps, filtrations, distillations etc. The usual in use vacuum for the smaller one is about 12-15mbar, I have used that pump often for sassy distillation, rotovapping, vacuum isomerisation etc.

For ketone and product distillation I preferred an oil pump (with really old smelly oil which I never changed, another way to limit your vacuum  ;) ). The one rated for 2mbar should work well for that purpose too.

I once witnessed a distillation attempt of sassy using a 6L flask and a MZ2C, and it was not pretty. Lots of bumping. But that wasn't the pump's fault, you either need to use a capillary extending to the bottom of the flask for good mixing or overhead stirring. Magnetic stirring didn't work. The reason is that the oil overheated at the bottom of the flask, and when it reached the surface it vigorously boiled causing the horrible bumping.

Let's say you have 15mbar of vacuum in the vapor phase above the liquid and 20cm (8 inches)of oil in the flask. Then the pressure on the flask's bottom will be much higher, meaning the oil will overheat. Using the above numbers and assuming the oil has a density of 1.0 the pressure on the bottom of the flask will be about 35mbar (because of the liquid column's weight has to be added)! Without efficient stirring this hot overheated oil, when it eventually rises to the surface will explosively evaporate. Using a capillary will make sure that the vacuum is the same everywhere, and the introduced gas bubbles will sort of catalyse the evaporation/boiling.
Same happens during the vacuum isomerisation BTW, that's why I never did it big scale. A 2L flask worked well with magnetic stirring, bigger ones were bumping horribly.
I'm not fat just horizontally disproportionate.
Title: Why stuff bumps under vacuum
Post by: Rhodium on May 28, 2002, 12:06:00 AM
Oh, so that's why stuff bumps much easier with high vacuum! I've never read that ANYWHERE - of course physical chemistry theory will make you able to predict that, but the tough part is to make the connection in the first place!

I'd like you to write a 250+ page book called "Tips & Tricks in the organic chemistry laboratory", you always seem to have so good explanations for every little practical thing one hasn't thought about before!
Title: Thanks all for your comments and suggestions
Post by: Bubbleplate on May 29, 2002, 02:18:00 AM
They'll be helpful when shopping. BTW, I seemed to have run across what looks to be a great deal:

http://www.XXXXXXXXXXXXXXXXXXXXXXXx (http://www.XXXXXXXXXXXXXXXXXXXXXXXx)


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Check it out.