Sciencemadness Discussion Board - Practical Vacuum Distillation

Practical Vacuum Distillation

taniya.pinkpower1986 - 30-1-2009 at 17:54

I have practical experiance in working with Liebig,Vigreux and many other Condensers.But when it comes to Vacuum Distillation its a diffrent story I only have some theoritical knowledge about Vacuum Distillation but no practical experiance.IF ANY MEMBER HERE HAVE SOME PRACTICAL KNOWLEDGE ON VACUUM DISTILLATION PLEASE SHARE IT.It would be of great help if some one tells,how to set up apparatures to perform Vacuum Distillation?

Practical Vacuum Distillation

taniya.pinkpower1986 - 30-1-2009 at 18:04

Aspirator%20Bottles.jpg - 4kB

taniya.pinkpower1986 - 30-1-2009 at 18:07

Above pic is that of an Aspirator that I am going to use

tentacles - 30-1-2009 at 19:36

That would appear to be a carboy, not an aspirator. I use a vacuum distillation rig to distill acids (HNO3, acetic). It's just a cheap plastic aspirator, some PE tubing from the hardware store, and a repurposed ammonia distilling rig. I am too cheap to own a heating mantle so I float the RBF in a pot of water on a hotplate/stirrer. I assemble the joints with teflon tape and the merest smear of silicone grease to get a solid seal.. I don't even use clamps, the vacuum does a fair job of holding things together when the apparatus are setup right. I DO cover the top of the RBF and wrap the glass tubing to the top of the condenser to keep efficiency up. There's no need to reflux if you're just distilling nitric from H2SO4 and a nitrate salt.

edit: I should note, the plastic aspirator that I purchased had no nozzle, so in stock configuration it sucked badly. I machined a bit of UHMW on my lathe with a 1.6mm hole and crammed that in the top of the aspirator. I tried also with a 2mm hole and got harder vacuum, and more flow but the water consumption was about 2x that of the slightly smaller aperture. I still get about 24-26" of vacuum with mere city water pressure.

another edit: What are you planning on vacuum distilling, anyways? That would be helpful to indicate what kind of stuff you need to do the job safely and properly.

[Edited on 30-1-2009 by tentacles]

Practical Vacuum Distillation

taniya.pinkpower1986 - 30-1-2009 at 22:55

Well for me cost is the biggest issue I will probably use a plastic aspirator like u have used.Any ways IT WOULD BE NICE IF PICTURE OF A VACUUM DISTILLATION SET UP IS POSTED.Seeing into it probably I can set up my own

Attachment: Aspirators with stopcock Catalouge.pdf (321kB)
This file has been downloaded 1357 times

taniya.pinkpower1986 - 30-1-2009 at 22:57

Ohhhhhh sorry! By the way above I have posted catalouge of a company which makes Aspirators for lab use(in PDF)

Saerynide - 30-1-2009 at 23:00

Theres not much to it that differs from normal distillation. Just hook the setup to the trap and aspirator and distill away as you would normally. Make sure you release the vacuum before you shut off the water, or water will be sucked in.

Saerynide - 30-1-2009 at 23:01

http://orgchem.colorado.edu/hndbksupport/dist/distsetup/vacd... << pictures of set up like you mentioned

Sauron - 31-1-2009 at 01:23

There's simple vacuum distillation such as stripping solvent using a rotavap and aspirator pump, and there's fractional vacuum distillation which involves a somewhat more complex glassware setup than does fractionation at ordinary pressure.

I reccomend

Elements of Fractional Distillation
Vogel's Practical Organic Chemistry
Synthetic Organic Chemist's Laboratory Survival Manual
The Chemist's Companion

Browsing the catalogs of Ace, Kimble/Kontes, Corning/Pyrex, LabGlass, ChemGlass, and Aldrrich will teach you a lot.

You need to:

match pot size and heat source to column and condenser capacities
Select column type (and packing if independent)
BTW a Vigreaux is a column not a condenser
Select still head (to control variable reflux ratio)
Select Takeoff system, fraction cutter, and vacuum isolation system
Select vacuum control system
Select vacuum gauge
Select vacuum pump
Select manifold if any, cold traps, check valves, suckback protection etc etc.

You also need to be concerned about possible foaming and bumping in the pot.

How are you going to cool your condensers (because you will probably have at least two condensers, one in still head and one main condenser for downward delivery). A recirculating thermostated chiller is a great convenience especially if your main supply is not very cool.

chemrox - 31-1-2009 at 17:19

I don't think she's up to vacuum pumps, traps, reflux ratio's, etc. yet.. just be sure to open the vacuum relief BEFORE shutting the aspirator off! It is a very common mistake to turn the aspirator off and ruin the experiment with water backflow. I've done it.

Ozone - 31-1-2009 at 20:54

A drawing, mostly for a reason to play with the clips in ChemBioDraw.

I prefer to put a "T" in the vacuum line after the trap (not shown) for manual regulation...If it starts to get too frisky I let some air in with my thumb. This works very well and really allows you to drive it (a pump works best, but an aspirator is OK).

A capillary (a Pasteur pipette with the end drawn in a flame) with a bit of tubing and a clamp can also be used to control the vacuum in the rig.

Cheers,

O3

vac distillation rig_small.jpg - 66kB

chemrox - 1-2-2009 at 00:48

Hey Oz, thanks- we'd better talk about the bleeder. In order to prevent bumping you might need to have a capillary tube entering the liquid to release a slow stream of bubbles.

Sauron - 1-2-2009 at 01:05

That's the simplest possible setup for a vacuum distillation with no provision for fractionation.

Suitable for distilling a liquid from a solid, or seperating two liquids with a difference of >100 C in bp with reasonable efficiency.

But as soon as you want to separate two volatile liquids with a bp difference of ,100 C, things get a lot more complicated both in theory and in terms of setup and control.

taniya.pinkpower1986 - 1-2-2009 at 03:29

Thanks every one,for your suggestions.I REALLY LIKE THIS FORUM FOR ALL THESE NICE MEMBERS.

. Anyways can you guys give me some more ideas about the Aspirators? like how they work,how to opreate them etc?Well I am thinking of making my Vacuum Distillation set up as Cheap and Simple as I can.Do any of you have a picture or catalouge of such aspirators?Then please post it.

Practical Vacuum Distillation

taniya.pinkpower1986 - 1-2-2009 at 04:01

11020.jpg - 33kB

taniya.pinkpower1986 - 1-2-2009 at 04:03

Above I have posted a pic of what appears to be an Aspirator.Can anyone confirm it?What type of Aspirator is it?How to operate this?

not_important - 1-2-2009 at 04:18

This type is for pulling a slow stream of gas, usually air, through a system. The bottle is filled with water, the exhaust point of whatever system is to have the gas pulled through it attached to a stopper in the top of tthe bottle, and the tap opened enough to draw the gas/air through the system at the desired rate.

Obviously when the bottle nears being empty the action will slow and cease. It also generates only a slight vacuum, equal to the height of the water in the bottle ( mm or cm of water). It has almost no use for distillation, one rare one being drawing CO2 through an otherwise closed distillation system being used to distill sulfur; the slow flow of CO2 helps sweep out any gases trapped in the sulfur.

------

Per Sauron's comment below, nowadays 'aspirator' means the class of device he showed, an eductor-jet pump. In older texts these were often refered to as filter pumps or just pumps, as in "...filtered off at the pump".

The aspirator bottle is now mostly used to supply a liquid, the tap near the bottom being useful for that, or collect the fluid from aspiration - most in a medical context.

Quote:

aspirator (n):
an apparatus for producing suction or moving or collecting materials by suction ;

[Edited on 1-2-2009 by not_important]

Sauron - 1-2-2009 at 04:23

Nope.

An aspirator (vacuum) pump is a metal or more usually plastic, inverted L-shaped device that attaches to a water faucet over a drain or sink, the side arm has a tublation for vacuum tubing . With cold water running it can develop about 20-30 torr and that is adequate for a lot of routine work. See Nalgene website for pics of a typical plastic aspirator. The colder your tap water the better the cacuum.

Photo below is a nice Chapman aspirator pump from Aldrich site.

[Edited on 1-2-2009 by Sauron]

g007631.jpg - 48kB

Ozone - 1-2-2009 at 09:51

Yep, that will do it. I was putting fourth the simplest case (fractionation is another topic). A vigreux (or packed column) between the pot and head will be the simplest fractionating rig.

To make the operation go more smoothly, under vacuum, a "cow" at the end of the condenser and several receivers works best for me. By rotating the "cow" (because of the resemblence to a cow's udder) you can collect multiple fractions without breaking the vacuum.

Cheers,

O3

Cow adapter_crop_small.jpg - 281kB

superman1451 - 1-2-2009 at 12:27

Quote:

Originally posted by Sauron
Nope.

An aspirator (vacuum) pump is a metal or more usually plastic, inverted L-shaped device that attaches to a water faucet over a drain or sink, the side arm has a tublation for vacuum tubing . With cold water running it can develop about 20-30 torr and that is adequate for a lot of routine work. See Nalgene website for pics of a typical plastic aspirator. The colder your tap water the better the cacuum.

Photo below is a nice Chapman aspirator pump from Aldrich site.

[Edited on 1-2-2009 by Sauron]

I have one of these and for some reason it would not work. I had a water hose attached to it and turned it on full but no vaccum was pulled. Does it matter which way the aspirator is pointed? and any suggestions for getting it to work would be very appreciated

Ozone - 1-2-2009 at 19:45

The threaded end goes to the faucet, the side arm to your apparatus and the bottom to the drain. Frequently these become clogged with scale from the water. This occurs most commonly at the interface with the side arm. If you have water flowing though the thing (and it should be jetting out) and there is no vacuum, then the side arm must be plugged up. Usually. a quick rinse with 1:1 HCl will do the trick.

See also Venturi jet or effect. That's how it works.

Cheers,

O3

watson.fawkes - 2-2-2009 at 10:09

Quote:

Originally posted by Ozone
To make the operation go more smoothly, under vacuum, a "cow" at the end of the condenser and several receivers works best for me. By rotating the "cow" (because of the resemblence to a cow's udder) you can collect multiple fractions without breaking the vacuum.

I'm missing something, I'm sure. Where are the valves? I don't see how you replace the flasks during the run. Or alternately, do you simply plan the collection strategy completely in advance? In that case, I assume that you use different size flasks. How easy is it to turn the ground glass joint under vacuum?

Saerynide - 2-2-2009 at 20:40

Quote:

Originally posted by superman1451
I have one of these and for some reason it would not work. I had a water hose attached to it and turned it on full but no vaccum was pulled. Does it matter which way the aspirator is pointed? and any suggestions for getting it to work would be very appreciated

It seems to work better if you put a plastic tube over it that goes into the drain (so put the end of the aspirator into a long tube). Having just the end of the aspirator spraying water into the air doesnt do a very good job, I dunno why. Even my chem professors agree, but they werent able to explain why lol.

superman1451 - 2-2-2009 at 21:02

Quote:

Originally posted by Saerynide
It seems to work better if you put a plastic tube over it that goes into the drain (so put the end of the aspirator into a long tube). Having just the end of the aspirator spraying water into the air doesnt do a very good job, I dunno why. Even my chem professors agree, but they werent able to explain why lol.

Perhaps it creates greater pressure? A member at APC suggested machining a nozzle that narrowed the outlet hole, but I don't have access to any way of machining anything.

pantone159 - 2-2-2009 at 21:43

Quote:

Originally posted by watson.fawkes
I'm missing something, I'm sure. How easy is it to turn the ground glass joint under vacuum?

I don't understood this either - do you just rotate the ground glass joint to select the different udders? It isn't a problem to do this under vacuum? BTW - I like that there is a bovine-derived chem in your pic of the "cow".

chemrox - 3-2-2009 at 00:13

@Ozone: please post the whole apparatus (or I can tomorrow)

Ozone - 3-2-2009 at 19:31

OK, let's see.

I usually plan the fractionation ahead. The usual, 1 forerun, 1 fraction; two are left for either other fractions or to catch the remainder that comes over. The header joint is well greased which enables it to be turned easily. You can use collection flasks of various size as you see fit. The spiky bits on the side of each teat are for the connection of springs which should serve to keep the collector from falling off. I just use Keck clamps.

To the best of my knowledge, the rubber tubing on the bottom of the aspirator serves to "muffle" the water jet coming out of the bottom. This prevents it from spattering all over the place (from the side *and* when it strikes the bottom of the sink) and making a mess. I've not noticed a difference in vacuum either way.

OK, I was at a conference all day so I'll put together a sample apparatus for photography tomorrow. [Actually, tomorrow I have day-two of conference and I am judging science fair thursday. this would have to be done on Friday, then.]

I thought the BSA was a nice touch

.

Moooo,

O3

[Edited on 3-2-2009 by Ozone]

[Edited on 3-2-2009 by Ozone]

chemrox - 3-2-2009 at 22:20

You have to grease the shit out of the joint or put a teflon sleave on it. NB there's an inner part not shown that direct condensate to the lowest "udder." I intended to post the whole apparatus but my camera ran low on batteries. I will post the pic tomorrow to make this very useful piece of equipment clear to all. BTW this isn't the only kind of glassware that turns on an ST joined under vacuum. McLeod Gauges are often set up that way.

crazyboy - 3-2-2009 at 22:41

I have seen these before although it was three pronged. I believe that the "cow" is attached at the end where one would normally put a receiving flask and at each udder is a small receiving flask. Distill under vacuum and the fraction you distill falls into the receiving flask pointing down. When another fraction begins to distill over you turn the cow and the fraction is collected in a separate flask.

the whole cow setup

chemrox - 4-2-2009 at 11:43

cow-pics 006.JPG - 81kB

superman1451 - 4-2-2009 at 19:35

holy cow!

How is that placed on the apparatus?

Ozone - 4-2-2009 at 20:36

I'll post a photograph of a whole assembled apparatus tomorrow evening.

That's a big-ass cow, Chemrox! My setup is a little different. Both of my cows, 24/40 125mL and a 14/20 25mL, are male at the header so I have to use a "gender-bender". I also do not have the drip tube. While nice, and I want one, mine works pretty well just by gravity (it's not as big, though).

Cheers,

O3

Sedit - 4-2-2009 at 21:04

Thats a pretty cool setup.

Iv seen little pig adaptors but Iv never seen a cow.

Do you ever have problems with different fractions ending up mixing trace amounts in each other from the sides of the receiver?

Ozone - 5-2-2009 at 18:16

Okay, here's the whole thing. I might put up a picture of a rig with a vertical condenser tomorrow.

You are going to get trace amounts anyway (this technique is not perfect). It is still MUCH easier to purify a fraction than the whole mix (even with the tube, "heart cutting" is difficult).

Cheers,

O3

[Edited on 5-2-2009 by Ozone]

Fractionator_01_small.jpg - 412kB

Ozone - 5-2-2009 at 18:21

A closeup of the vacuum adapter, gender bender and outfitted cow.

If you look closely at the vacuum adapter, you will see where the tube used to be. The 'bender was a tight fit and eventually, the tube broke off

. Bummer.

O3

cow closeup_01_small.jpg - 284kB

Practical Vacuum Distillation

taniya.pinkpower1986 - 10-2-2009 at 02:33

Thanks everyone for such nice pics and good infos........................Now it may sound a little stupid.Can I use a hand vacuum pump like this one in pic

Hand%20Vacuum%20Pump.jpg - 22kB

crazyboy - 10-2-2009 at 17:45

Those are for vacuum filtration not distillation. This thread is about practical vacuum distillation. It's simply not practical to stand a set up pumping away for hours only to pull a slight vacuum, get carpral tunnel and then have the thing break on you.

Get an aspirator or a vacuum pump.

I have an aspirator but no sink in my workspace so I need to totally rearrange my garage before installing a sink and finally vacuum distilling my nitric acid that has been in my freezer for the past three months.

chemrox - 10-2-2009 at 18:05

get an aspirator or for a little more money an aspirator pump. Both have their uses. An apsirator pump has a water reservoir and a mechanical pump that pumps water through internal aspirators. No need to run up the water bill but the e bill suffers a bit.
@O3- ours aren't all that different. I went 250 on the flask for the cow and my receivers are 75 ml with 14/20 joints. I forgot to have him put spring holders on them so I need some 14/20 Klecks. I like having the flow director with the larger volume cow but at 125 you might not need it. I like having the white board right there where you work!! I have written on the cabinets and windows and parts of the floor...
I noticed you're using a vigeraux. I saw a dramatic improvement when I started using a Snyder column. The distillation I have planned is for something that boils around 168/0.3 mm so for that I'm using a short path with a 1" built-in vigeraux. I could show the vacuum station but I don't want her to despair.

[Edited on 10-2-2009 by chemrox]

Ozone - 10-2-2009 at 21:15

Yeah, mine's 24/40. I have ~ 1m worth of Snyder ball columns which are very nice to use--but I only really use them for solvent recovery. I find that it helps to drop some of the solvent into the top of the column (wet the column) prior to use. I suppose I could add a pic of some Snyders tomorrow.

I also have straight wall columns which I pack with steel wool, glass balls, etc. which perform better than the vigreaux. The vigreaux, however...is easy..and usually works very well. It's a great place to start.

Maybe we should address vacuum manifolds...later.

Nothing like the sound of chattering Snyder columns in the morning!

O3

chemrox - 11-2-2009 at 19:47

"Nothing like the sound of chattering Snyder columns in the morning!"

hehehe .. yeah that's the best!

I got a three cock manifold made for $45. I can't understand how Ace and Kontes even, charge so bloody much for those things...even with the high vac cocks. It probably took the glassblower about 10 minutes. I benefit from the guy (my glassblower) being really busy. When it doesn't make it impossible to get repairs on short notice that is. Like now. I'm working with a new guy I got through the U. We'll see how he does.

[Edited on 11-2-2009 by chemrox]

Engager - 21-3-2009 at 17:36

I use vacuum setup based on rotary oil vacuum pump, it can provide vacuum up to 0.1 mm. Hg. However setups you shown in this topic look somekind unusual for me.

1. As far as i can see in provided setups nobody uses manometer or other pressure control. Use of pressure control is absolutely essential because pressure greatly affects boiling points, if pressure in system will be too low, even high boiling liquid can destill off just about room temperature and there will be great difficulty to condense it even in long condenser cooled by cold water stream. Before preforming vacuum destilation you must at first select work pressure range such that lower border pressure will provide high enough boiling point of reaction mixture to condense distillate efficently and high border pressure that allows to destill your mixture with selected heat source (e.g water or oil bath) at acceptable rate while not allowing destilled substances to undergo thermal decomposition (for example HNO3 is thermaly unstable). Apropriate pressure range can be selected from vapor pressure / temperature graph for distilled substance.

2. I don't see boiling capilary in your setups, and this is very strange, because it's absence makes vacuum destillation unstable and even dangerous. Under reduced pressure gasses that are dissolved in reaction mixture quickly escape from reaction mixture and seed gas bubbles esential for stable boiling no longer form - liquid can easily become overheated. This is absolutely inacceptable because overheated liquid mixture sooner or later will boil up with great violence, it can jump over to condenser outlet and in some cases even explosive boil up is possible (heat explosion). To solve this problem a boiling capilary is used in vacuum setups, this is thin glass tubbing with very small hole in the end that is passed almost to the bottom of distilation flask, then system is evacuated it passes stream of small air bubbles from atmosphere witch aid phase chance and allow liquid to have stable boiling. This additional air inlet is also used to fine tune pressure by means of gas valve connected to the top of the inlet capilary.

3. I don't see any trap devices between vacuum outlet and vacuum pump. If you are using water stream vacuum pump if pressure in water system will suddenly change water from the pump can easily jump into distillate flask and cause some nasty chemical reactions (especialy if destilled substances react violently with water). If you are using oil vacuum pump some uncondensed fumes can reach pump oil and dissolve in it to lower maximum vacuum, or if fumes are aggressive they can react with oil or corrode parts of vacuum pump. In usual setups there are trap flasks between vacuum outlet and vacuum pump. In case of water stream pump trap serve as emergency drain in case of water stream pressure fluctuations, and in case of oil pumps this trap flask is usualy strongly cooled (for example with solid CO2) to freeze any vapours not condensed by condenser and not allow them to enter pump oil or leave evacuated system.

[Edited on 22-3-2009 by Engager]

Gruson - 25-3-2009 at 01:48

Since I intend vacuum distilling and use of a rotary evaporator with an oil pump as well (<1mbar), I was wondering if I could replace the dry ice/acetone cold trap with an 60 cm graham condensor. (water on the outside) This would be cooled with an refrigerated circulator bath, this one http://www.capovani.com/dp/cat/107/63160/iinfo.cfm?LCl=986&a... to be more precise. It would be running with water/EG at -5 till -8 degrees celcius. Is this sufficient to prevent solvent from reaching the pump oil? The rotavap/liebig cooler would also be cooled with this temperature.

Lambda-Eyde - 25-3-2009 at 02:54

That all depends on what you intend to distill. Look up a graph on the BP of the solvent with pressure plotted in, and cross-check that with the temperature of the condensing water and the efficiency of your condenser.

Panache - 3-4-2009 at 22:30

Quote: Originally posted by Gruson

Since I intend vacuum distilling and use of a rotary evaporator with an oil pump as well (<1mbar), I was wondering if I could replace the dry ice/acetone cold trap with an 60 cm graham condensor. (water on the outside) This would be cooled with an refrigerated circulator bath, this one http://www.capovani.com/dp/cat/107/63160/iinfo.cfm?LCl=986&a... to be more precise. It would be running with water/EG at -5 till -8 degrees celcius. Is this sufficient to prevent solvent from reaching the pump oil? The rotavap/liebig cooler would also be cooled with this temperature.

Remember that although something may be well below its boiling point for a given pressure it still may have some, even significant, vapour pressure and as such will eventually end up in your pump.
For most common solvents this is not really problematic as your can bleed them from your oil easily enough (assuming a vane pump here). Especially if using a fully synthetic vac pump oil. However for distillations of more reactive substances you really want to avoid any contamination into your pump and -8 ain't gonna cut it even for moderate vacuums. That is why the dry ice cold finger is standard good practise, however its annoying for the home experimenter because you must have the dry ice around and it has this silly habit of subliming away and warming up the earth.

I posted recently in relation to small domestic benchtop ice cream makers being an excellent alternative to the dry ice cold finger. They run continuously (i leave mine on all week), sit at around -38 and negate the need for the consumable dry ice. I just fill mine with ethanol and immerse the trap into it.

Gruson - 6-4-2009 at 00:11

That is an excellent idea. I presume you have the icemaker with built-in compressor? Which type exactly? (I believe you have a "Nemox"?) I can get my hands on dry ice, but that would be a 70 km drive. Okay for one particular synthesis, but I was looking for a solution on the long term. Does ethanol has the heat capacity needed for efficiently cooling the cold trap?

Panache - 6-4-2009 at 00:55

Quote: Originally posted by Gruson

That is an excellent idea. I presume you have the icemaker with built-in compressor? Which type exactly? (I believe you have a "Nemox"?) I can get my hands on dry ice, but that would be a 70 km drive. Okay for one particular synthesis, but I was looking for a solution on the long term. Does ethanol has the heat capacity needed for efficiently cooling the cold trap?

The reason i leave it on all week is it has about a 20min warm-up time (ha funny to describe it as this) before it is at it lowest temperature. This solution is not as good as dry ice obviously, but many more times convenient and permanent. I use ethanol because i have it and didn't want to use any solvents potentially aggressive to the polymers of the unit, whatever they may be. If your unit is fully cooled it works fine.

Globey - 6-4-2009 at 18:36

A great OTC method I've adapted uses a Reynolds Handi-Vac, hand held vacuum pump, and have had decent results. Not the same as my carbon vane, but it seems to be able to deal with the organic vapors so far, and is handy and easy to grab real quick. Maybe not for critical sensitive work, but surely to speed things along which otherwise are slow, but not necessarily all that heat sensitive without it.

marksev1 - 7-4-2009 at 08:20

What about the crushed ice with calcium chloride hexahydrate in ratio 2:3, i read that it achieves temp. about -40 degrees celsius...would that be sufficient (for example for DCM)? And also calcium chloride is quite cheap.

[Edited on 7-4-2009 by marksev1]

Shingoshi - 19-7-2009 at 20:26

Would this be the right thread to ask questions about boiling butane (or ammonia) from water using Mazzei Injectors? I can start a new thread if I need to. I want to know if such aspirators are capable of the task?

Here's the information on these injectors:
http://www.mazzei.net/products/injector_info.htm

Shingoshi

not_important - 19-7-2009 at 22:09

Is your goal to purify the water, or to recover the butane/ammonia?

For simply removing the gas, bubbling air through the water might do the job, use a packed column with counterflow of air and water.

A different purpose...

Shingoshi - 19-7-2009 at 22:57

Quote: Originally posted by not_important

Is your goal to purify the water, or to recover the butane/ammonia?

For simply removing the gas, bubbling air through the water might do the job, use a packed column with counterflow of air and water.

The system is a completely closed-loop. I'm looking for a way to drop the temperature of the liquid by causing it, or a gas in solution with it, to boil. I want to know can I use a venturi to produce the vacuum to make a mixture vaporize, instead of using heat as is commonly done in absorption refrigeration systems.

Shingoshi

not_important - 19-7-2009 at 23:55

Vacuum coiling of water is used industrially, high pressure steam driven venturi devices can freeze water by removing heat through vapour. Check the vapour pressure vs temperature tables for water.

I think you need to run the maths on the concept, I have doubts it could be run as a closed system, recovering the 2nd substance from the exhaust water stream is also going to be a problem.

Shingoshi - 20-7-2009 at 00:14

Absorptive Refrigerators are closed systems. So why would it be a problem here, when it's not for the refrigerator? I'm trying to remove the need for a heat source, and replace it with the injector for creating the vacuum. Why doesn't that make sense?

Shingoshi

not_important - 20-7-2009 at 00:31

Add heat adds no matter to the system, the low boiler is removed in a relatively pure state; it can be cooled and either condensed or absorbed back into the higher boiling fluid. Using an injector mixes the low boiler with the injector working fluid, there's no simple method of recovering it from the vapour or injector working fluid. Plus what is the ratio of cooled water to injector exhaust stream?

Shingoshi - 20-7-2009 at 08:59

not_important,
Here's the link to the project in question. I guess anyone else can look at it now too!
http://www.xtremesystems.org/forums/showthread.php?t=229936

What would stop me from stacking two venturis in series? How many venturis would I need to get and maintain the vacuum I need?

Shingoshi

not_important - 20-7-2009 at 12:11

First, are you sure the case you picked will stand the negative pressure? Firgure out how much force will be on it under vacuum.

Second, yes you can stack Venturis in series with the 'downstream' one being larger than the upstream one as it has to handle the full flow of the upstream.

Beffore going any further, you should analyse the requirements. Don't think about the liquid you will use, you will calculate what it's properties need to be.

How much heat is being generate, and what is the target temperature. How do you plan to dump the heat; remember that pumps will add heat to the system, and dry heat exchanges can not cool below ambient temperature.

So you end up with a heat source of X watts that you want to keep at temperature Y while rejecting that heat into a sink of temperature Y. This lets you calculate the thermal impedance, and the size of the heat sink if you are rejecting heat into the ambient air - heat sink vendors should show you how to calculate that.

Venturis using liquids will give you no lower vacuum than the vapour pressure of the liquid at its working temperature.

Moving this topic to the correct location...

Shingoshi - 20-7-2009 at 17:44

Quote: Originally posted by not_important

First, are you sure the case you picked will stand the negative pressure? Firgure out how much force will be on it under vacuum.

This case is nothing more than a miniature clean-room, in which the components will operate. The coolant-loop is completely closed. If there were any leaks into the cavity of the case, the process would stop. And, if the vacuum system isn't strong enough to boil water, how would it have enough power to impact the structure of the case?

Second, yes you can stack Venturis in series with the 'downstream' one being larger than the upstream one as it has to handle the full flow of the upstream.

I almost didn't understand you here. But now I realize by upstream, you mean the pump. And by downstream, you mean the outlet of the injector. This is precisely how the design is configured

Before going any further, you should analyse the requirements. Don't think about the liquid you will use, you will calculate what it's properties need to be.

How much heat is being generate, and what is the target temperature. How do you plan to dump the heat; remember that pumps will add heat to the system, and dry heat exchanges can not cool below ambient temperature.

This system will have a maximum cpu count of 12 in the present configuration. Given 75 Watts per processor, the load will greater than 900 Watts when the cooling system is included. The cooling system will produce some heat. Though I'm not sure yet how much. I intend to simply provide the largest cooling system to handle any possible load.

So you end up with a heat source of X watts that you want to keep at temperature Y while rejecting that heat into a sink of temperature Y. This lets you calculate the thermal impedance, and the size of the heat sink if you are rejecting heat into the ambient air - heat sink vendors should show you how to calculate that.

Venturis using liquids will give you no lower vacuum than the vapour pressure of the liquid at its working temperature.

I will copy this post to the main thread for this project, as this will end up being off-topic (if not already). I would encourage you or anyone else to join in the discussion there:
http://www.xtremesystems.org/forums/showthread.php?p=3917399...

Shingoshi

[Edited on 2009.7.21 by Shingoshi]

aspirator

darel - 21-7-2009 at 12:46

I have been using a vacuum pump with an absorbtion train to catch as much of the corrosive fumes from entering pump with some success. But I would like to use an aspirator because I have to change the oil after 2 disillations of HNO3. I am looking to reuse the water to save money. I have heard of using bilge pumps. I don't think these will work because there is not a lot of pressure behind them. I am thinking of using an electric pressure washer and rigging it up in a way so as to have it in a five gallon pail circulating.

I also found this on ebay

http://cgi.ebay.com/Buchi-B-169-Aspirator-Pump_W0QQitemZ3801...

would this be worth investing in?

entropy51 - 21-7-2009 at 13:08

darel, $195 will buy an awful lot of H2O where I live, and H2O is not cheap here either.

IMO the pump on ebay might be worth it if (1) it was in excellent condition, and it probably isn't and (2) you do one heckuva lot of vacuum distillations, or maybe use well water and have to pay for pumping it.

I think the trick with aspirators is to get a good one. Some use much less H2O than others. I have found the more pricey glass aspirators to be much better than the cheap plastic ones. I don't have to run my glass aspirator with a full open tap to get an excellent vacuum, if the system is leak-free.

DIY aspirator pumps work very well, but the pump head and flow characteristics have to be matched to those of the aspirator which can require some trial and error.

I don't know if this actually applies or not...

Shingoshi - 21-7-2009 at 15:03

Quote: Originally posted by darel

I have been using a vacuum pump with an absorbtion train to catch as much of the corrosive fumes from entering pump with some success. But I would like to use an aspirator because I have to change the oil after 2 disillations of HNO3. I am looking to reuse the water to save money. I have heard of using bilge pumps. I don't think these will work because there is not a lot of pressure behind them. I am thinking of using an electric pressure washer and rigging it up in a way so as to have it in a five gallon pail circulating.

I also found this on ebay

http://cgi.ebay.com/Buchi-B-169-Aspirator-Pump_W0QQitemZ3801...

would this be worth investing in?

I found this link while searching for something else. Here's the link (Read the part about the collection of oil):
http://www.wondermagnet.com/diamagh2o.html

At least, it should be interesting or intriguing.

Shingoshi

[Edited on 2009.7.21 by Shingoshi]

darel - 21-7-2009 at 21:54

I do have a well that I pump from. Does anyone have any plans for a DIY Aspirator pump.

uchiacon - 16-8-2009 at 23:57

Hey guys, I plan on constructing an aspirator with a water pump I got from a $1 reserve auction for $100, normally sold for $274.

Its a jet waterpump, 460W, 30PSI and able to suck water from 7M down. It pumps 46L/min and has a max head of 35M. Also says its suitable for use in pools etc.

So I'm just wondering if this will work for an aspirator, is it just right? I'm guessing it should provide quite a crazy vacuum right?

Because there is such a lack of any real instructions on this on the internets, I'm kinda fumbling round in the dark here.
Heres the article I'm going off.

designer-drugs.com/pte/12.162.180.114/dcd/chemistry/equipment/aspirator.html

Can somebody please post any useful information on making an aspirator, I've got no idea of what the smaller pipe ratio should be to the large to make the vacuum etc.

Cheers.

JohnWW - 17-8-2009 at 00:29

I bought a similar pump at a local auction here for $50 earlier this year. It also has a pressure chamber on its top. I bought it partly for irrigation purposes, and partly to add extra delivery pressure to a fire-fighting hose.

uchiacon - 17-8-2009 at 00:58

MM so is it too powerful then? I want as much vacuum as water can offer. Planning on distilling nitric.

The one I love...

Shingoshi - 17-8-2009 at 01:18

I found this pump a while ago. I was impressed with it's construction. It's made by a company called Shertech.

I've wanted to use it to drive this injector by Mazzei. The 1585X

Shingoshi

[Edited on 2009.8.17 by Shingoshi]

darel - 17-8-2009 at 09:36

I am looking for an electric pressure washer. I was going to take the motor out of that. yea it's a huge overkill. I haven't found plans but it seems pretty straight forward.

We think alike!

Shingoshi - 17-8-2009 at 09:59

Quote: Originally posted by darel

I am looking for an electric pressure washer. I was going to take the motor out of that. yea it's a huge overkill. I haven't found plans but it seems pretty straight forward.

Harbor Freight Tools has some pretty cheap pressure washers. And I thought why not do the same thing as you've suggested here. I may still do that. Because in my case, I really do need the high pressure.

Shingoshi

[Edited on 2009.8.17 by Shingoshi]

uchiacon - 18-8-2009 at 01:46

Could you post those plans? Any info on making aspirators or anything would be great.

uchiacon - 19-8-2009 at 04:19

I've just been looking through the aspirator threads on the forum, and if anything, it's just made me even more confused. I don't like the idea of those cheap looking plastic aspirators(I have no idea how they can get away with selling them for $30US), and they probably wouldn't be able to handle the pressure and flow rate of my pump.

So could anybody just post some pics of their OTC constructed aspirator or something? Don't have the necessary tools(lathe etc) to make it properly, and I'm pretty sure one could be constructed from OTC brass fittings from a plumbing store. Normally I don't have any trouble making things, but for the lack of tutorials(and frogfot's site being removed) I'm left high and dry.

I really want to make my white nitric before I'm 15(and various nitrations) and the only thing standing in my way is the obstacle of constructing a hydroaspirator... :mad:

Any help will be appreciated.
Cheers

watson.fawkes - 19-8-2009 at 05:46

Quote: Originally posted by uchiacon

So I'm just wondering if this will work for an aspirator, is it just right? I'm guessing it should provide quite a crazy vacuum right?

"Crazy vacuum"?-no. Regular water aspirators are limited by vapor pressure. There are higher pressure ejector pumps that run on steam that get down lower than the vapor pressure of their working fluid, but they use very fast exit streams to do it. What you might get is higher gas pumping rates than an ordinary faucet-tap aspirator. If you want even higher suction rates, build two aspirators and gang them in sequence, with a common manifold feeding both nozzles.

The only two parts of an aspirator that aren't off the shelf are the penetration of the water pipe into the air flow and the nozzle. You should be able to build the bulk of the device out of PVC pipe. Drill a hole in an end cap and glue in a pipe section to get your penetration. As for a nozzle, use a brass end cap and drill a hole in the end. You'll need to use a drill press for that, if you don't want to be breaking drill bits. You'll find the whole system easier to assemble if you break the air pipe into two sections with a union. Locate the union in a place were the water nozzle sticks out.

uchiacon - 19-8-2009 at 14:33

Could I look at some pictures of your home made aspirator? I'm a bit unfamiliar with some of the terms you are using.

watson.fawkes - 19-8-2009 at 16:55

Quote: Originally posted by uchiacon

Could I look at some pictures of your home made aspirator? I'm a bit unfamiliar with some of the terms you are using.

I don't have a PVC one myself. Perhaps I should make one as a demo.

If you have questions about vocabulary, just ask.

uchiacon - 19-8-2009 at 21:11

One of these aspirators should definately be able to pump out enough air for vacuum nitric distillation right?

People have been saying the vacuum provided by one of these aspirators should be able to create a 20-30torr vacuum so that the nitric boils below decomp point.

Seems like a lot of threads here go on huge tangents, or only briefly cover some parts of a process... i.e the nitric acid thread only having about 4-5 posts on the vacuum aspects...

watson.fawkes - 20-8-2009 at 06:04

Quote: Originally posted by uchiacon

One of these aspirators should definately be able to pump out enough air for vacuum nitric distillation right?

How big is the distillation and how big is the pump?

Quote:

People have been saying the vacuum provided by one of these aspirators should be able to create a 20-30torr vacuum so that the nitric boils below decomp point.

Go look up the vapor pressure of water at two ordinary operating temperatures: 40° C for room temperature, 5° C for ice water. This is the lower limit of pressure for a regular water aspirator.

uchiacon - 22-8-2009 at 03:40

I've got a 1L boiling flask, a 500ml boiling flask as a receiver, a condenser with a 20cm long jacket... and the attachments to make it all fit.

If you have a larger aspirator it's going to suck more air than a smaller one correct? Down to the vapour pressure of water I'd presume?

I'm struggling to see what I'd need to build this aspirator, and I can always get my dad to pay for one off the internet, but if I chose to build one I would have to do it with my own money. However, My pump is a 46L/min job with 30 PSI, and I'm quite certain the bought aspirator could not take that much pressure. And the pump might fail too. Without a pressure tank, it is harder to get a higher pressure correct?

Will you have a problem of bumping between 20-30torr? So if you concentrating your nitric will you have to get a magnetic stirrer with your hotplate?

Also... I found this with a google images search for metallic aspirators...
designer-drug.com/pte/12.162.180.114/dcd/chemistry/meth.louisfreeh.html#7.2

Thats got some interesting stuff in it, including a guide to making 70% nitric and some information on an aspirator pump.
Least those meth makers have helped me in some way!

[Edited on 04-07-09 by uchiacon]

[Edited on 04-07-09 by uchiacon]

watson.fawkes - 22-8-2009 at 05:42

Quote: Originally posted by uchiacon

If you have a larger aspirator it's going to suck more air than a smaller one correct? Down to the vapour pressure of water I'd presume?

The rate of an ejector pump is proportional to the surface area of contact between the working fluid and the gas being pumped. The pumping mechanism is momentum transfer between the working fluid and the gas, so it's the total contact area between these two that matters. So yes, a larger pump will pump faster, where you measure size by this surface area, not by the bulk size of the pump.

The vapor pressure of the working fluid is a lower limit. Depending on operator parameters, it may not be achievable.

Quote:

However, My pump is a 46L/min job with 30 PSI, and I'm quite certain the bought aspirator could not take that much pressure. And the pump might fail too. Without a pressure tank, it is harder to get a higher pressure correct?

I fail to see what a pressure tank has to do with this system. And 30 psi is a rather low pressure for most materials.

uchiacon - 24-8-2009 at 01:09

Yeah, but the pipe diameters are 1", and 1/2ing that diameters is sure to increase pressure. I think I'll just buy a aspirator attachment, I can't be screwed making one. Its too complex, and I don't have the money or the time to do so.

I'm mainly concerned about the 46L/min, 760ml/s... isnt that a lot?

[Edited on 04-07-09 by uchiacon]

watson.fawkes - 24-8-2009 at 03:49

Quote: Originally posted by uchiacon

Yeah, but the pipe diameters are 1", and 1/2ing that diameters is sure to increase pressure.

No. I don't know what fundamental misunderstanding you have about pressure in fluid dynamics, but you've got one. Do some reading. Start with the Wikipedia article on fluid dynamics.

Quote:

I'm mainly concerned about the 46L/min, 760ml/s... isnt that a lot?

The pump you've got is way overspecified for a small aspirator.

uchiacon - 27-8-2009 at 01:18

ffffffffff....

So unless I could have part of that water being pumped through another tube leading off, the pump is kinda useless to me. Am I correct here? Maybe if I could divert part of the water flow before the aspirator fitting then I wouldn't have to worry about too many L/s.

I just read this guide here
designer-drugs.com/pte/12.162.180.114/dcd/chemistry/equipment/aspirator.html and ran with that, considering these is absolutely fucking nothing on this subject on the internets...

In which case, should I just try and resell this pump? I got it for $100 with normal retail 270. Should I flog it and try to get something smaller with a more powerful PSI? Any reccommendations?

Oh, and theres also this vacuum pump going on trademe for $28... goes down to 10torr. If I set up a vapour trap then it would be ultimate for nitric distillation right? Its really cheap, but it might go up to about $50-60... worth it? And for the vapour trap, possible to use a low volatility solvent to catch the HNO3 vapours?

[Edited on 04-07-09 by uchiacon]

[Edited on 04-07-09 by uchiacon]

watson.fawkes - 27-8-2009 at 08:35

Quote: Originally posted by uchiacon

Maybe if I could divert part of the water flow before the aspirator fitting then I wouldn't have to worry about too many L/s.

At some point you're going to have to try something without knowing in advance whether it will work. Why don't you do that sooner than later? Learning the emotional skill of taking risks is a far more useful skill to develop than any particular skill with vacuum systems.

Using diversion valves seems like a perfectly reasonable solution to experimenting with a too-big pump. Use two, one on the aspirator line and one on the dump line. (Or find a three-way valve, which is a little harder.) You can run your dump line back into an input tank, even if you're not making a completely closed system.

What I would heartily recommend is using pressure and vacuum gauges. Put a pressure gauge on your pump supply, if only to make sure that you're not overpressurizing your pipe. Put a simple vacuum gauge on a test chamber, to see how well your aspirator pumps down. Gauges are cheaper than you might think, even if you have to mail-order them.

uchiacon - 27-8-2009 at 21:10

Thing is, I'm two years too young to get a job and I dont have the money to spend on experimentation.

Theres that pump on trademe, I'll see if I can get that. 10 torr is better than an aspirator can do. The nitric would boil at 30-40 C at that vacuum wouldnt it?

watson.fawkes - 28-8-2009 at 06:22

Quote: Originally posted by uchiacon

Thing is, I'm two years too young to get a job and I dont have the money to spend on experimentation.

There are two kinds of risk here, and you're addressing them piecemeal. One is the risk of destroying equipment; the other is the risk of your experiment not working. You express worry about the first risk by stating you don't have money, but you're not asking questions about how to avoid frying your pump. You're asking questions about how to ensure that your distillation works the first time, but you're not acknowledging your fears. Now I can offer some assistance about equipment, but my willingness to do so is limited by what you're willing to do for yourself.

The great replacement for money is time. So spend some time. You've repeatedly asked about boiling point under reduced pressure, but to my sight you haven't been looking for a vapor pressure table for the solutions of interest. You have questions about pumps, but I haven't seen you trying to understand the differences between differences in pump designs, what they do when overloaded, what a pressure/flow curve is, etc.

uchiacon - 31-8-2009 at 22:45

I'm not asking for sympathy, I'm simply asking a few straight questions, easily answered in a sentence or so. You're making out that I cant be screwed doing any research. No, thats complete bullshit. I didn't construct my own ball mill, interpret other schematics and research for weeks on chlorate cells to be told that.

I'm stating my circumstances, I'm not asking to be constantly spoonfed. I have some questions here that I just need simple answers to to steer me in the right direction. I realise that I should have done a bit more research regarding fluid dynamics and such, and thank-you for steering me in that direction. I am fourteen, not forty. What were you doing when you were 14?

And no, time is fucking NOT a substitute for money. Thats bullshit. Time? Can time buy me the necessary bits for my aspirator? Yeah, maybe if I had a job. Sure, in few cases time can be a substitute for money, but not in mine.

Am I asking "ok, find me some designs, I can't be screwed pouring over the couple of topics here and what little information on this topic that there is on the internet"? No, I am not a k3wl, I just have almost not idea where to start on this apart from 'fumbling around in the dark', as it is.

I wouldn't be asking these questions if they had been asked before in another thread. Now please, stop treating me like a fucking k3wl (christ, at this age I should be encouraged) and either point out where I should read or give me the brief answer to the question.

"..but I haven't seen you trying to understand the differences between differences in pump designs, what they do when overloaded, what a pressure/flow curve is, etc."
Ok, so imagine you're fourteen and somebody tells you that.
I'm no pump engineer, and no doubt it would take quite a few manuals to learn those things. If I had some information you needed, I wouldn't act like you're acting to me, so why don't you pay me the same courtesy?

[Edited on 04-07-09 by uchiacon]

hosko - 23-10-2011 at 01:49

Removed cross-post. Multiple posts won't help you getting better answers or getting answers in less time. Please continue the discussion over here:

http://www.sciencemadness.org/talk/viewthread.php?tid=15104

[Edited on 23-10-11 by woelen]