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evil_lurker
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Need help with vacuum distillation setup...
Sometime in the next couple days the UPS man should stop by the house and shit out a nice 2 stage 3CFM vacuum pump.
I understand the mechanics of the process all but one... how do you maintain a steady vacuum level when using a mechanical pump?
[Edited on 17-7-2006 by evil_lurker]
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solo
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Off the top, a vacuum adjustable gauge...................solo
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Rosco Bodine
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A nice automatic vacuum regulator will cost quite a lot .
The alternative and what should be used anyway is
a large volume vacuum trap which will act as a
vacuum reservoir and a ballast volume which will
prevent sudden pressure fluctuations , used in combination with an air bleed needle valve which
can be opened up allow a controlled leak of air into the intake of the pump to limit the ultimate vacuum
which can be produced .
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evil_lurker
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| Quote: | Originally posted by Rosco Bodine
A nice automatic vacuum regulator will cost quite a lot .
The alternative and what should be used anyway is
a large volume vacuum trap which will act as a
vacuum reservoir and a ballast volume which will
prevent sudden pressure fluctuations , used in combination with an air bleed needle valve which
can be opened up allow a controlled leak of air into the intake of the pump to limit the ultimate vacuum
which can be produced . |
That's kinda what I was thinking...
But most of the hardware store variety needle valves seem to not be fine enough to get the job done. Welch appears to have a nice pump mounted vacuum
regulator, except they want like $230 for it!
What if I were to build a large capacity resevoir system and used that as the sole source of vacuum?
That would eliminate the need for a dry ice trap and provide a steady source of vacuum, provided of course there were no leaks.
[Edited on 17-7-2006 by evil_lurker]
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Magpie
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I think Rosco's suggestion is good.
I wouldn't count on your system being tight enough that your reservoir alone would do the job. Also, you will be offgassing some vapors, I presume.
I bought an excellent stainless steel needle valve from my local industrial supplier for ~ $50. I'd be surprised if you couldn't find something
equivalent in brass for much less.
When it comes right down to it you could probably use just a pinch clamp and a piece of rubber hose.
[Edited on 17-7-2006 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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evil_lurker
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Well the UPS man has shitteth.
I played with the pump some, hooked up the cheap vacuum gauge from cymar to it on a short piece of regular clear hardware tubing and plugged the end.
It pegged it out in less than a second... and it sorta collapsed the hose so I'm thinking that the gauge might be off...
But then again, what do I know? This is the first time I've actually used any of this stuff...
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leu
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A capillary tube with a rubber tube closed by a pinchcock clamp works quite well 
If the distilland is air sensitive, connect a ballon inflated with an inert gas, or use a magnetic stirrer 
Chemistry is our Covalent Bond
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Rosco Bodine
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A plastic aquarium airflow valve in plastic or brass
would probably work fine as an air bleed control ,
and an empty 5 gallon propane bottle would make a
good vacuum reservoir and trap . Actually the main shutoff supply valve on a 5 gallon propane tank would
probably work as an air bleed valve or a flow limiter
depending on how you hook everything up . Also to protect your pump from acid vapors you will need some sort of bubbler airstone immersed in
limewater as a scrubber , followed up by a pleated or wound yarn water cartridge filter or something similar to filter out any liquid
spray mist that may come off the scrubber . You will need a check valve or two in the system also .
Here's a cheap brass needle valve . It looks pretty
much like the icemaker line sort of valve which any hardware store would carry and would probably also work .
http://www.surpluscenter.com/item.asp?UID=2006071800180356&a...
As a last resort you could use an old empty
automotive freon recharge can and the filler valve ,
which is a needle valve which actually punctures the
seal on the top of the can creating its own matching seat .
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chromium
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| Quote: | Originally posted by evil_lurker
What if I were to build a large capacity resevoir system and used that as the sole source of vacuum?
That would eliminate the need for a dry ice trap and provide a steady source of vacuum, provided of course there were no leaks.
[Edited on 17-7-2006 by evil_lurker] |
This can be used if you need rather low vacuum - something like 200 or 100 mm Hg. Higher vacuum is very sensitive to minor leaks and is highly
affected by amount of substances that have vaporised at particular time. Reservoir must be really huge to compensate for this.
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1281371269
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Would a hand held vacuum pump suffice for vacuum distillation and filtering? This would be a lot easier than setting up an aspirator.
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hissingnoise
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Hand pumps are good for filtering---for vacuum distilling you'll need an aspirator. . .
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entropy51
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A hand pump is OK for small filtration jobs, but for distillations I don't think the vacuum will be steady enough and eventually your hand will fall
off from exhaustion.
There's nothing easier than setting up an aspirator if you have a source of running water.
I use one of these little pumps for filtering (not flammable solvents) to save on the water bill. It might work for not too demanding
distillations, but I've never tried it.
http://scientificsonline.com/product.asp?pn=3082650&bhcd...
[Edited on 30-9-2009 by entropy51]
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1281371269
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Ah I didn't realise that I would have to keep pumping it.
I was planning to get an aspirator barrel and have the water running from this into another container via the aspirator, so that it could be reused.
How do I know when I have achieved a vacuum and can turn off the water?
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entropy51
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It sounds like you're talking about an aspirator that drains water out of a container, thus pulling air in at the top. That's no good for either
filtration or distillation. You need an aspirator that attaches to a sink faucet (or is supplied with water from a resorvoir using a pump - they are
described in other threads here).
I have a Hg manometer attached to my vacuum line so that I know when the system is pumped down (usually to less than 15 Torr) and that there are no
leaks. You can also use some type of vacuum gauge, even a simple Bourdon gauge which has a clock face and a moving needle to read the vacuum (usually
in inches of Hg below atmospheric pressure).
I've never seen anyone turn off the water (if you do it will suck water into the system). The standard way is to leave the aspirator running for the
duration of the distillation.
Check out some of the organic lab manuals in the forum library for details.
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1281371269
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I was talking about something like this:
http://www.philipharris.co.uk/webapp/wcs/stores/servlet/Prod...
It's advertised as an aspirator barrel, so surely I could attach an aspirator to it and have the water run into another barrel?
As I don't have running water, it might be easier just to save up for an electric vacuum pump.
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chemrox
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manometer-trap-manostat-ballast-acid/moisture absorbent colmn ... not in the above order
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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entropy51
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No, that won't drive an aspirator.
Is there an outside hose connection that you could attach an aspirator to? You could then run your vacuum hose into your lab. Not ideal, but can be
made to work. One lab I worked in had an aspirator pump in another room and the vacuum hoses ran probably 100 feet to the hoods. It worked fine.
But a pump might be the best option under the circumstances.
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UnintentionalChaos
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You'll need a somewhat beefy pump at that too. Matching sink pressure is a tall order.
Department of Redundancy Department - Now with paperwork!
'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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1281371269
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Got my eye on this:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=230...
So if those barrels labelled as aspirators can't drive a vacuum, what purpose exactly do they serve?
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entropy51
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See if you can find out how badly the pump on ebay has been abused. I can testify that if cared for pumps can last 40 years, but usually people pump
acid fumes through them and never change the oil. If you get it, I'd change the oil, run it a while, then change it again to clean it out. Use
vacuum pump oil.
Those barrels are probably best for dispensing distilled water. I've seen them used for pulling gas through a system at low flowrates, but that's an
ancient technique.
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Contrabasso
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If you intend to distil corrosives then a metal body pump needs protection and will die quickly anyway.
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zed
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If you wish to create a vacuum reservoir, I don't recommend barrels. Even a 5 gallon propane tank concerns me. Such containers may be susceptible
to collapse.
Too much surface area, too thin walls.
50 gallon steels drums, even heavy gauge drums, crumple and cave-in like paper cups, when subjected to high vacuum.
At 15PSIx 12inches x 12 inches...... One square foot of external barrel surface, is subjected to approximately 2000 lbs of pressure.
Steel pipe makes a much better storage vessel. Thicker walls, in relation to less surface area.
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JohnWW
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Regarding the design or specification of vessels for use as vacuum reservoirs, see my post on this page:
http://www.sciencemadness.org/talk/viewthread.php?tid=12686
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entropy51
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Mossydie was asking about using that plastic jug as a water reservoir, not a "vacuum reservoir".
[Edited on 3-10-2009 by entropy51]
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Contrabasso
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From what I understand aspirator pumps work with a typical water pressure of 2 - 4 bar to get much vacuum or rate of evacuation. If you are going to
carry water upstairs to create this pressure think 30ft/10m per bar or Atm so for 4 bar you need a lab in a tower block 120ft high!
It has been done to get a pump in a bucket of water and use that to pump through the aspirator pump -it needs to be a worthy pump but it's cheaper to
replace the water than to replace vac pump oil every few weeks.
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