Sciencemadness Discussion Board

12 V vacuum pumps for filtration/distillation

Keras - 4-5-2019 at 06:48

First off, I'd like to apologise since it seems the subject has been raised many times along the ages, but I wanted to be certain that the cheap vacuum pumps like this one are really fit for vacuum filtration/distillation (my distillation apparatus is made of Rodaviss elements, so I expect the air leaks to be pretty low). I suppose the -75 kPa figure means the pump can suck around .75 bar, right?

Thanks, and sorry again for bringing up such a tired subject.


[Edited on 4-5-2019 by Keras]

Sulaiman - 4-5-2019 at 07:36

I think that pump is more than adequate for filtration,
both in terms of pressure and flow.
I use a similar (cheaper) pump and I can not praise it enough - for filtrations

For distillation I'd expect water to boil around 50oC, az.H2SO4 at about 260 - 270 etc.
and for simple distillations only (no Hempel column etc.)

It would help to reduce b.p. somewhat,
but I have only used my little vacuum pump for distillation only twice,
so others here may have better advice.
Overall I think it is less than ideal for distillations.

P.S. I suggest that you consider two pumps, one for filtrations and one for distillations.
The pump pointed to looks ideal fror filtrations,
distillation also requires a cow, pig, or Perkin Triangle etc.
and usually fine control over heating, cooling, variable take-off head etc. ... $Xy
So buy this pump (or similar) now for filtrations,
and if/when you budget for a full vacuum distillation kit
you will probably choose a rotary vane pump.
Vacuum distillations are uncommon in hobby chemistry.

Regarding actual pressure;
(Absolute Pressure) = (Atmospheric Pressure) - (Pressure difference produced by Pump) ... simple

Unfortunately
. Atmospheric Pressure - varies with Lattitude, Altitude and local weather
. Pressure difference produced by Pump - varies with atmospheric pressure, temperature, wear, maintenance and cleanliness of the Pump

So don't get too technical - or get really techinical.

I guess that if you have pressurised water available then a water aspirator vacuum pump would be most suitable for your combined needs,
- judging by reports of members - as I don't have an aspirator vacuum pump myself.

[Edited on 4-5-2019 by Sulaiman]

Keras - 4-5-2019 at 07:58

Quote: Originally posted by Sulaiman  

I think that pump is more than adequate for filtration, both in terms of pressure and flow.
I use a similar (cheaper) pump and I can not praise it enough - for filtrations

For distillation I'd expect water to boil around 50oC, az.H2SO4 at about 260 - 270 etc.
and for simple distillations only (no Hempel column etc.)

distillation also requires a cow, pig, or Perkin Triangle etc.
and usually fine control over heating, cooling, variable take-off head etc. ... $Xy
So buy this pump (or similar) now for filtrations, and when you've budgeted for a full vacuum distillation kit you will probably choose a rotary vane pump.
Vacuum distillations are not common in hobby chemistry.

[Edited on 4-5-2019 by Sulaiman]


Thanks!

Well, I have a distillation apparatus such as the one you see depicted on the attached image + a heating mantle that goes from 0 to ca. 450 °C. In fact, I'd thought about vacuum distilling hydrogen peroxide to increase its concentration from 12 to, say, 30%. I’m not sure the small pump I plan to buy can lower the pressure sufficiently to be able to carry this out around, as you mention, 50 °C or so.

Screenshot 2019-05-04 at 17.52.17.png - 93kB

Sulaiman - 4-5-2019 at 08:13

hydrogen peroxide can be concentrated at ambient pressure so I guess any pump would help

I believe that fractionating colums do not work well with varying pressure;
a small pressure change can move equilibriium zones in a column by several theoretical plates,
upsetting thermal stability and reducing fractionating power significantly.

In this specific case,
I do not know how effective your column with the proposed pump would be with H2O2 :(

P.S. I really think that you should check the recent threads on aspirators,
the more I think about it the more an aspirator seems more suitable for your needs,
- IF you have water at reasonable pressure and flow rate available.

[Edited on 4-5-2019 by Sulaiman]

Keras - 4-5-2019 at 08:36

Quote:
Quote: Originally posted by Sulaiman  
hydrogen peroxide can be concentrated at ambient pressure so I guess any pump would help.

In this specific case, I do not know how effective your column with the proposed pump would be with H2O2 :(


I thought it was impossible to concentrate hydrogen peroxide by distillation at ambient pressure because at 100°C the rate of decomposition of the peroxide is too high.

Also it seems concentrated hydrogen peroxide can be made by dissolving sodium percarbonate in diethyl ether. Anyways.

The idea here is of course to boil off the water. I’m not sure where your reservations come from! :)

P.S.: And no, I have no water source available. I operate inside an old shed, and I use a pail as a source of water that I cycle through the condenser.

[Edited on 4-5-2019 by Keras]

morganbw - 4-5-2019 at 13:54

I have intentions on having a pump similar to what you presented.
I plan to use it for vacuum filtrations only.

CobaltChloride - 4-5-2019 at 15:30

I have bought a similar looking 12V vacuum pump from ebay, although mine was just around 12USD and it works perfectly fine for vacuum filtration, although I have yet to test it for vacuum distillation.

draculic acid69 - 4-5-2019 at 19:12

Buy a $80 harbor freight oil pump for distillations or build your self a recirculating aspirator setup.dont spend $35 on a pump that's only good for filtration as the $12 ones work just fine for that.neither the 12 or 35 $ pumps Will be good for distillation.spend $80 on a vacuum pump or $10 on a aspirator and $30 on a water pump ,tubing and tub like nurdrage did in one of his videos.dont waste time money and effort on trying to make something inadequate work.ive done that in the past and it was a learning curve.just my advice.do with it as you will.

[Edited on 5-5-2019 by draculic acid69]

Keras - 5-5-2019 at 00:08

Quote: Originally posted by draculic acid69  
Buy a $80 harbor freight oil pump for distillations or build your self a recirculating aspirator setup.
[Edited on 5-5-2019 by draculic acid69]


Okay, I already own a water pump since I feed fresh water into my condenser from a bucket and back into it. So that makes sense – I could kill two birds with a stone: use the pump to make vacuum and feed the output of the aspirator to the condenser. Alright, the temperature of the water will increase as the distillation progresses so the vacuum will not be stable, but I guess that’s a consistent setup nevertheless.

I found this aspirator at around 35 bucks. Seems to be high-quality German stuff, made of PP with lot of seals, so I guess I will plump for it. Any comments?

Thanks!





Aspirator.png - 125kB

monolithic - 5-5-2019 at 05:57

Quote: Originally posted by Keras  
Quote: Originally posted by draculic acid69  
Buy a $80 harbor freight oil pump for distillations or build your self a recirculating aspirator setup.
[Edited on 5-5-2019 by draculic acid69]


Okay, I already own a water pump since I feed fresh water into my condenser from a bucket and back into it. So that makes sense – I could kill two birds with a stone: use the pump to make vacuum and feed the output of the aspirator to the condenser. Alright, the temperature of the water will increase as the distillation progresses so the vacuum will not be stable, but I guess that’s a consistent setup nevertheless.

I found this aspirator at around 35 bucks. Seems to be high-quality German stuff, made of PP with lot of seals, so I guess I will plump for it. Any comments?

Thanks!







You'll probably need something more powerful than an aquarium pump. Look at the specs of the aspirator you purchased - most of them will list minimum requirements for pressure at a specified flow rate to generate its rated maximum vacuum. And remember that a pump delivering 30 psi or 2 gpm is a lot different than 30 psi at 2 gpm. I think RV diaphragm pumps are have been used with some success. NurdRage has a video on YouTube about his DIY recirculating aspirator.

Keras - 5-5-2019 at 08:05

Quote: Originally posted by monolithic  

You'll probably need something more powerful than an aquarium pump. Look at the specs of the aspirator you purchased - most of them will list minimum requirements for pressure at a specified flow rate to generate its rated maximum vacuum. And remember that a pump delivering 30 psi or 2 gpm is a lot different than 30 psi at 2 gpm. I think RV diaphragm pumps are have been used with some success. NurdRage has a video on YouTube about his DIY recirculating aspirator.


The pump I was thinking of is given for 3000 L/h or 50L/mn (> 10 gpm). Since the value of the pressure differential is tied to the flow, I suppose the greater the flow, the highest the vacuum. Now, I don’t really know how to correlate the pump's output pressure to the flow except by the Bernoulli equation, but that doesn’t apply. If you have any equation which does that, please go ahead.

monolithic - 5-5-2019 at 08:26

Quote: Originally posted by Keras  
Quote: Originally posted by monolithic  

You'll probably need something more powerful than an aquarium pump. Look at the specs of the aspirator you purchased - most of them will list minimum requirements for pressure at a specified flow rate to generate its rated maximum vacuum. And remember that a pump delivering 30 psi or 2 gpm is a lot different than 30 psi at 2 gpm. I think RV diaphragm pumps are have been used with some success. NurdRage has a video on YouTube about his DIY recirculating aspirator.


The pump I was thinking of is given for 3000 L/h or 50L/mn (> 10 gpm). Since the value of the pressure differential is tied to the flow, I suppose the greater the flow, the highest the vacuum. Now, I don’t really know how to correlate the pump's output pressure to the flow except by the Bernoulli equation, but that doesn’t apply. If you have any equation which does that, please go ahead.



I'm not sure about equations. Many pumps have spec sheets with a flow/pressure graph. I imagine it has to be empirical, since impeller design would have such a large impact on pressure and flow characteristics?

[Edited on 5-5-2019 by monolithic]

Sulaiman - 5-5-2019 at 08:49

For fairly low pressures I have tried peristaltic pumps - very low flow rate but
the needle on my cheap gauge appears to be the same as for my rotary vane pump.
==============================================
I bought the pumps for condenser water circulation to control condensation rate by coolant flow rate,
I've abandoned this for high flow rate temperature controlled coolant.
I may use one to maintain a low pressure atmosphere for a different project,
but I would not use them for filtrations as I'm not that patient.
=====================================
If just for filtrations, or distillations at low pressure,
have you considered a hand operated vacuum pump ?
e.g. https://www.ebay.co.uk/itm/Hand-Held-Brake-Bleeder-Tester-Se...

and cheap HVAC vacuum pumps are getting even cheaper https://www.ebay.co.uk/itm/Vacuum-Pump-3CFM-1-Stage-1-4-HP-H...

Keras - 5-5-2019 at 09:24

Quote: Originally posted by monolithic  

I'm not sure about equations. Many pumps have spec sheets with a flow/pressure graph. I imagine it has to be empirical, since impeller design would have such a large impact on pressure and flow characteristics?


BTW, I just found that the water should be between 3 and 6 bar for the water aspirator to work correctly. I am not sure how that translate in terms of the pump I wanted to buy. On the other hand, some comments say the water from the pump can rise up to 2.5 m. I’m wondering if I can make anything out of this.

EDIT: The pump is supposed to push 50 L/min through a ø 10 mm hose. That gives an output velocity of 10 m/s roughly. Applying the Bernoulli equation (.5 ρv² + ρgz + P = constant), if the "jet" stops at 2.5 m, this gives an output pressure of 75 kPa or 0.75 bar. Not that much :(
Quote: Originally posted by Sulaiman  

If just for filtrations, or distillations at low pressure, have you considered a hand operated vacuum pump ?
e.g. https://www.ebay.co.uk/itm/Hand-Held-Brake-Bleeder-Tester-Se...

and cheap HVAC vacuum pumps are getting even cheaper https://www.ebay.co.uk/itm/Vacuum-Pump-3CFM-1-Stage-1-4-HP-H...


Is a hand operated vacuum pump suitable for low pressure distillation? I wonder. Besides, the one I’m familiar with is given for 100 mbar max. I think a water pump can achieve 30 mbar. As for the HVAC vacuum pump, I’m a bit weary. It seems cheap, is not applicable to filtration unless bleeded, which apparently makes it overheat and smoke, and for distillation water or other liquids would condense in the mechanism, no?

[Edited on 5-5-2019 by Keras]

karlos³ - 5-5-2019 at 11:45

I use such a thing for vacuum filtration, works like a charm, nice item and cheap too.
It is a bit loud but I can filter a liter of yeast broth in less than a minute to a clean liquid, fine for extraction.

DrScrabs - 5-5-2019 at 11:57

I don´t know if I can add anything of value but I´ve used my 12V 3L/min membrane pump with great results in vac dist. It only archieves a max of 400 mbar abs and I normally use a salt/ice cooled trap and the system does a good job stripping solvents (bp>60 deg C). I had to attach a passive heat sink because it got quite warm and for advanced applications I got a rotary pump now :D

Keras - 6-5-2019 at 01:04

Quote: Originally posted by DrScrabs  
I don´t know if I can add anything of value but I´ve used my 12V 3L/min membrane pump with great results in vac dist. It only archieves a max of 400 mbar abs and I normally use a salt/ice cooled trap and the system does a good job stripping solvents (bp>60 deg C). I had to attach a passive heat sink because it got quite warm and for advanced applications I got a rotary pump now :D


I was planning to get a submersible 220 V pump. I don’t want the hassle of using a 12 V power supply. I’ll see if I can get something a bit more powerful than 3L/min, but thanks for the input!