Sciencemadness Discussion Board - Need help with vacuum distillation setup...

Need help with vacuum distillation setup...

evil_lurker - 17-7-2006 at 03:33

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]

solo - 17-7-2006 at 03:58

Off the top, a vacuum adjustable gauge...................solo

Rosco Bodine - 17-7-2006 at 04:17

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 .

evil_lurker - 17-7-2006 at 05:57

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]

Magpie - 17-7-2006 at 08:18

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]

evil_lurker - 17-7-2006 at 09:25

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...

leu - 17-7-2006 at 19:08

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

Rosco Bodine - 17-7-2006 at 21:48

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 .

chromium - 18-7-2006 at 03:18

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.

1281371269 - 30-9-2009 at 10:50

Would a hand held vacuum pump suffice for vacuum distillation and filtering? This would be a lot easier than setting up an aspirator.

hissingnoise - 30-9-2009 at 11:49

Hand pumps are good for filtering---for vacuum distilling you'll need an aspirator. . .

entropy51 - 30-9-2009 at 11:51

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]

1281371269 - 30-9-2009 at 12:03

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?

entropy51 - 30-9-2009 at 12:56

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.

1281371269 - 2-10-2009 at 08:01

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.

chemrox - 2-10-2009 at 08:05

manometer-trap-manostat-ballast-acid/moisture absorbent colmn ... not in the above order

entropy51 - 2-10-2009 at 08:10

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.

UnintentionalChaos - 2-10-2009 at 09:30

You'll need a somewhat beefy pump at that too. Matching sink pressure is a tall order.

1281371269 - 2-10-2009 at 09:42

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?

entropy51 - 2-10-2009 at 10:20

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.

Contrabasso - 2-10-2009 at 12:04

If you intend to distil corrosives then a metal body pump needs protection and will die quickly anyway.

zed - 2-10-2009 at 14:19

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.

JohnWW - 3-10-2009 at 00:50

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

entropy51 - 3-10-2009 at 08:23

Mossydie was asking about using that plastic jug as a water reservoir, not a "vacuum reservoir".

[Edited on 3-10-2009 by entropy51]

Contrabasso - 3-10-2009 at 13:34

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.

gsd - 4-10-2009 at 07:08

Since this thread was reopened by mossydie, throughout the posts nobody has talked about what vacuum is required? is it 100 torr, 30 torr or 1 torr?

If we are discussing anything below 30 torr then even a very properly designed water jet ejector (the so called "aspirator") will not do the job as at that pressure, the tap water at normal temperature will start boiling.

The only practical alternative - however messy - remains is oil ring vacuum pump.

gsd

[Edited on 4-10-2009 by gsd]

entropy51 - 4-10-2009 at 08:42

Quote: Originally posted by gsd

If we are discussing anything below 30 torr then even a very properly designed water jet ejector (the so called "aspirator") will not do the job as at that pressure, the tap water at normal temperature will start boiling.

Bullshit. The vapor pressure of H2O isn't 30 torr until 29 C, which is a lot warmer than my tap water ever gets.

My aspirator easily reaches 15 torr in the summer when the tap water is relatively warm. It reaches 10 torr in the winter when the water is quite cold.

See vapor pressure table

http://intro.chem.okstate.edu/1515SP01/Database/VPWater.html

I knew you were blowing smoke out your arse about being a distillation expert.

gsd - 4-10-2009 at 09:12

Quote: Originally posted by entropy51

Bullshit. The vapor pressure of H2O isn't 30 torr until 29 C, which is a lot warmer than my tap water ever gets.

Thats what I said. In my part of the world tap water temperature almost round the year is between 30 to 35 Deg. C. So pulling vacuum below 30 torr with that is not possible on sustainable basis.

I of course had no way to know where you live. In tundra or in tropics.

Quote: Originally posted by entropy51

My aspirator easily reaches 15 torr in the summer when the tap water is relatively warm. It reaches 10 torr in the winter when the water is quite cold.

Yes sure. in Alaska you can get 5 torr most of the time. But everybody can't go there just to do distillation.

Quote: Originally posted by entropy51

I knew you were blowing smoke out your arse about being a distillation expert.

LOL. looks like still smarting over the loss of face in the last encounter'

Well mover over smart "arse" It is you who is farting around by discussing topic in air without giving any specifics.

gsd

PS. Vapour pressure of water in mmHg can be calculated by using the Antoine's Equation:

Log Ps = 7.96681 - (1668.2/(228 +T))

Where Log is to the base 10
Ps is vapour pressure in mmHg (or torr)
and T is in Deg C.

gsd

entropy51 - 4-10-2009 at 09:57

Quote:

Thats what I said. In my part of the world tap water temperature almost round the year is between 30 to 35 Deg. C

Sounds like you're drinking urine to me. More BS.

gsd - 4-10-2009 at 10:34

Quote: Originally posted by entropy51

Quote:

Thats what I said. In my part of the world tap water temperature almost round the year is between 30 to 35 Deg. C

Sounds like you're drinking urine to me. More BS.

ROFLOL

What a specimen!
Is prepared to go to any length to have a last word!
It takes all sorts to make this wonderful virtual world of sciencemadness

gsd

entropy51 - 4-10-2009 at 10:43

You may have the last word. Please don't take my jibes seriously.

gsd - 4-10-2009 at 11:47

Quote: Originally posted by entropy51

Please don't take my jibes seriously.

Taking your jibes seriously?

In case you have not noticed, I was 'Rolling On Floor Laughing Out Loudly" after reading your childish rejoinder.

gsd

1281371269 - 5-10-2009 at 14:11

Sorry to have caused an argument

I can get something like this:
http://cgi.ebay.co.uk/Lotus-Diamond-600-Pond-Pump_W0QQitemZ1...

with perhaps a little more power if necessary, or a central heating pump, for much cheaper than a vacuum pump and grease. Of course I'd also need to work out connectors, a reservoir (would a bucket do or should it be a bit more high tech?) and buy an aspirator, but it would still work out quite a bit cheaper. Will the above link have enough power? If not, what sort of pumps should I look for or should I get the vacuum pump linked to before?

Sorry for all these questions, I haven't been able to find much information on this anywhere...

UnintentionalChaos - 5-10-2009 at 14:35

Quote: Originally posted by Mossydie

Sorry to have caused an argument

That's a very low powered pump, unfortunately. "Maximum head height" is as high as the pump can move a column of water with it's current output hose (0 flow rate, simply fighting gravity).

Aspirators are meant to run at sink pressures, which are usually between 20 and 40psig, IIRC (1.4~2.7bar). Using the maximum head to represent the most pressure the pump can put out, and simple barometer equations, we find that the maximum output pressue of that pump (assuming no friction losses and without raising the tubing at all at the original output diameter) is 0.0784bar.

If I'm not mistaken, scaling down the output hose diameter will net you a significant boost in pressure, since P=Fa. There will be losses from friction, however. You'll need to match the diameter of the threading on your aspirator.

I'm used to using the nalgene aspirators in lab, and they claim to be effective down to 8psig, though I can't imagine their performance is stunning at those kinds of pressures.

There may be some faulty logic in there. Feel free to correct me. Maybe the output pressure will change relative to hose volume instead....I'm not too sure.

[Edited on 10-5-09 by UnintentionalChaos]

grndpndr - 6-10-2009 at 02:41

I have some interest in a vacum distillation setup using the inexpensive
water aspirator.Does water temp have an effect on vacum one could expect from the water aspirator.Our well water leaves the well head at over 130f and depending on where you live in town the tap water can exceed115f.In fact most houses dont need thier water heaters even in summer thier used instead for cool water reserviors.

[Edited on 6-10-2009 by grndpndr]

gsd - 6-10-2009 at 06:48

@grndpndr

Let us say your house receives water at 115 Deg F = 46.1 Deg. C. As per Antoine's Equation given upthread, this corresponds to vapour pressure of water = 76 mmHg or 76 Torr.

This is the maximum THEORATICAL vacuum you can pull. Even with the best of hardware and very carefully made leak proof system, you can expect to go up to about 80 to 85 torr. Make generous allowances for your Inexpensive setup.

gsd

1281371269 - 6-10-2009 at 11:46

http://cgi.ebay.co.uk/Stuart-Turner-Monsoon-3-bar-twin-showe...

Something like that seems the way to go.

1281371269 - 6-10-2009 at 14:15

Phillip Harris have just delightfully informed me that they have discontinued the vacuum adaptor (did they tell me this when I placed the order? Of course not. I had to email them asking why it hadn't arrived to be informed :mad:

) and I can't find any others.

There's only one thing I can forsee needing a vacuum for which is white fuming HNO3, and I don't need any of that, so I'm going to put this whole thing on hold until I'm better armed with knowledge, necessity and finance to tackle it.

Thanks so much to those who have answered my questions on the topic, I'm sure the information will be of use in the future.

[Edited on 6-10-2009 by Mossydie]