Mr.Spice
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Vacuum Distillation anyone?
I'm trying to get a vacuum distillation going and am having trouble understanding the basics of a vacuum pump and how to set it up with a distillation
apparatus. I understand that there needs to be some sort of water trap, and that there needs to be a vacuum adapter at the end of the receiving flask.
But the aspirator just dumps the water out? and in all diagrams I come across there are supposed to be 2 hoses for water out and in. where do they
attach to? I am really confused and stuck. any and all help is greatly appreciated!
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bfesser
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Thread Moved
20-2-2014 at 14:25 |
ZIGZIGLAR
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I can't see the video, but I assume it illustrates the following: The top of the Venturi aspirator is the water INLET, the bottom is the OUTLET and
the side arm is where the vacuum is created.
A normal set up would involve connecting the top of the aspirator to a water source/faucet and having the bottom running freely into the sink/drain OR
diverting this water flow through the water condenser you are using in your distillation aparatus (if applicable), THEN being ran to the drain.
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Mr.Spice
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ZIGZIGLAR: so the hose on the water inlet is attached through tubing to the water aspirator, and the bottom end can either run into the sink through
the water condenser. You kind of lost me there, I'm trying to make sense of it but am having some trouble. and what does the water outlet attach to?
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ZIGZIGLAR
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Quote: Originally posted by Mr.Spice  | | ZIGZIGLAR: so the hose on the water inlet is attached through tubing to the water aspirator, and the bottom end can either run into the sink through
the water condenser. You kind of lost me there, I'm trying to make sense of it but am having some trouble. and what does the water outlet attach to?
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Aspirators do vary in design ... most of the ones I've seen have a threaded inlet, which is designed to screw into a typical household faucet. Some
are different and have a hose barb for all 3 connections and it is up to you to figure out the best way to connect this to your water source.
The water outlet can just be left to flow freely down the drain. It is the flow of the water through the internals of the aspirator that generates
suction at the side arm. If you are using a condenser in your set up, it is less wasteful to run the aspirator water through the condenser before
being sent down the drain.
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Nickdul
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ZIGZIGLAR,
Running an aspirator output to a condenser, unless it allows for considerable unrestricted flow, you will be decreasing the efficiency of the
aspirator. I suppose this is to conserve water, and in that case the water can be run from the tap/faucet to the condenser and then to the aspirator
but unless your glass can handle high pressures and flow, I wouldn't recommend either (plus, you'd want water running through the venturi to be as
cold as possible).
Mr. Spice,
refer to the wikipedia page on aspirators (http://en.wikipedia.org/wiki/Aspirator_%28pump%29), I believe the image and text will explain fully what an aspirator is and how it is operated
and by what principle. There is also an illustration that you will find useful at http://en.wikipedia.org/wiki/File:Simple_distillation_appara... vaccum "ïnput" is at 9, at the vacuum adapter.
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ZIGZIGLAR
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I don't disagree. You can add a bleed valve to the aspirator output to reduce flow to the condenser without impacting on flow output from the
aspirator. It is wasteful, but much less so.
I would personally prefer to recirculate water to the condenser from an ice slurry with a submersible pump. However, to an absolute beginner lacking
in a lot of basic equipment, it's handy to be able to repurpose a single device to serve that of two.
I've never used an aspirator in an environment where the drain water is not recycled, because I can't justify being so wasteful. If I absolutely
needed to use an aspirator at home or something, I'd probably have the waste water diverted to water the garden or something 
But I have a vacuum pump capable of going to 10 microns and a regulator to control the suction pretty tightly.
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Mr.Spice
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Nickdul: I see the vacuum adapter on the side of the distillation flask, and I realize that it should be connected to a vacuum pump, I guess where I'm
getting lost is how to connect the water supply to the vacuum (do you need to do that?) and what to do with the hoses that attach to the water inlet
and outlet? what do they connect to?
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Mr.Spice
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Nickdul: I see the vacuum adapter on the side of the distillation flask, and I realize that it should be connected to a vacuum pump, I guess where I'm
getting lost is how to connect the water supply to the vacuum (do you need to do that?) and what to do with the hoses that attach to the water inlet
and outlet? what do they connect to?
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Mr.Spice
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ZIGZIGLAR: do you have any designs I cloud look at for vacuum pumps that recirculate water?
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ZIGZIGLAR
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Mr.Spice: What kind of flask are we talking about? There's only two major flasks I can think of that have vacuum adaptors built in. Schlenk flasks,
designed to accept a backflow of inert gas to perform reactions that are sensitive to air and a Filter flask, which is generally a conical shape with
flat bottom - these are designed to be connected to a vacuum, but as a form of suction for pulling a lquid through a filter, not for distillation in a
closed chain aparatus.
Proceeding with a vacuum distillation using a filter flask is probably not advisable as it is generally considered unsafe to reduce the pressure in
flasks that have angular surfaces. Implosion may not occur with the ultimate vacuum possible from an aspirator, but I wouldn't be risking that when
you can go ahead and buy a round bottom flask for $20.
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ZIGZIGLAR
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Vacuum pumps that internally recirculate water start at around $300+, I think. For less than this price you can just get a basic rotary vane vacuum
pump that could preduce a stronger vacuum.
I have a feeling that we aren't talking the same language ...
What are you actually trying to do?
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Nickdul
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That is the way to go!
There are high-flow, high-pressure water pumps available in garden and DIY stores. It is a neat project to combine an aspirator with one of these and
a reserve water container. These have been made and a search on the forum will bring up some valuable threads.
That said, a trip to the junkyard, scoring an old refrigerator pump, adding a filter to the output and inlet, and you've got a pretty decent vacuum
pump. Short life and inconvenient, your mileage may vary.
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TheAlchemistPirate
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Hey I am planning on doing vacuum distillation and have almost no knowledge about how to set up a vacuum apparatus or how to use it. Could someone
give me a link to a site that explains what apparatus I need and how to use it? I cant find a guide anywhere on the internet. I thought that vacuum
distillation setups cost thousands of dollars, but apparently not. I only know that people use vacuum distillation to lower the temperature of what
theyre distilling to hinder decomposition from heat, and that you have to set up a pump and gauge of some kind to a normal high quality distillation
setup.
"Is this even science anymore?!"
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Mailinmypocket
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There are some good books availble for free here:
http://library.sciencemadness.org/library/index.html
If you look in the first one or two chapters lots of the organic chemistry books describe how to do vacuum distillations. Also, Googling "vacuum
distillation lab guide" will give some good results.
You only need a distillation set up with a special end for your condenser called a vacuum take off adapter. This has a barbed connection when your
vacuum line goes.
Check out the forum library and if you have more detailed questions after then let us know. "Experimental organic chemistry" by Norris is a good book
as well as "systematic experiments in organic chemistry" by Cummings.
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TheAlchemistPirate
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| Quote: Originally posted by Mailinmypocket | There are some good books availble for free here:
http://library.sciencemadness.org/library/index.html
If you look in the first one or two chapters lots of the organic chemistry books describe how to do vacuum distillations. Also, Googling "vacuum
distillation lab guide" will give some good results.
You only need a distillation set up with a special end for your condenser called a vacuum take off adapter. This has a barbed connection when your
vacuum line goes.
Check out the forum library and if you have more detailed questions after then let us know. "Experimental organic chemistry" by Norris is a good book
as well as "systematic experiments in organic chemistry" by Cummings. |
Ok thanks
"Is this even science anymore?!"
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Chemosynthesis
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I also recommend this. The pumps can even be made cheaply with an aquarium pump, some brass fittings, and vinyl tubing. I have one a friend put
together around here somewhere. They heat up, though, so if you want to circulate cold water, definitely do what ZIG says and make ice beforehand.
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mayko
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| Quote: Originally posted by Mailinmypocket |
If you look in the first one or two chapters lots of the organic chemistry books describe how to do vacuum distillations. Also, Googling "vacuum
distillation lab guide" will give some good results.
You only need a distillation set up with a special end for your condenser called a vacuum take off adapter. This has a barbed connection when your
vacuum line goes.
Check out the forum library and if you have more detailed questions after then let us know. "Experimental organic chemistry" by Norris is a good book
as well as "systematic experiments in organic chemistry" by Cummings. |
These are good resources for a schematic overview of vacuum distillation, but actual teaching procedures for it seem to be pretty sparse. Here's the
best one I've seen thusfar:
http://ocw.mit.edu/courses/chemistry/5-301-chemistry-laborat... (see p. 35)
Does this seem like a good candidate for the home lab? Vacuum distillation didn't make it into my education somehow, grumblegrumble...
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Magpie
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A vacuum distillation is just a normal distillation done at a low pressure. Normally P=0-60 mmHg, depending on the vacuum source available. The
exact pressure used/attained is usually not that important.
There are some new requirements and characteristics:
1. You need a vacuum source, usually a water driven aspirator or a vacuum pump.
2.You need a vacuum hose (heavy walled, non-collapsible) to run from the pump to the hose barb on the vacuum adapter. This adapter links the
condenser to the receiver flask.
3. The whole system must be vacuum tight (or nearly so). Silicone greased glass taper fittings are the usual.
4. An ebulliator tube quite possibly will be required to prevent dangerous bumping.
5. A vacuum gauge is desirable. This is teed into the vacuum line.
6. There is a safety hazard, ie, a risk of a dangerous glassware implosion. Personal protection must be provided with eye protection being the
minimum.
Establish vacuum before heating the pot. Break vacuum slowly. You have to understand and think things through more carefully than with atmospheric
distillations. Gaining experience will help greatly.
The single most important condition for a successful synthesis is good mixing - Nicodem
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greenlight
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I want to start vacuum distilling my red fuming nitric acid to get a more concentrated cleaner acid and I was wondering how important it is to place a
cold water trap for the fumes between the apparatus and the vacuum pump? Will my diaphragm vacuum pump become corroded and damaged fast if I do not
use one?
Should I just go out and buy a trap before I vacuum distill the Nitric acid?
[Edited on 19-11-2014 by greenlight]
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macckone
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Nitric fumes will eat a diaphragm quickly.
Use an aspirator and sodium hydroxide trap.
If you reciruclate add sodium carbonate and
Use a pump rated for waste or salt water.
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