Vacuum Pumps for Vacuum Distillation

[rootbeers]

I am in the market for a Vacuum Pump. My current situation is I am using an aspirator that affixes to the mains water, has to be run at full pressure to draw a semi decent vacuum for what I need, but it can't keep pace with expansion of the alcohol vapours when heat is applied to the flask.

So I really need a Vacuum pump... Anyone here use vacuum pumps and have any recommends?

I have seen the Ebay and Amazon offerings as well as the scientific supplies sites. Nearest one I have found is an educational supplier but they want £399 for one that looks no different than the £195 ebay jobs.

Suggestions, ideas on where to look, who to see, wine and dine... I have at present exhausted all avenues I can think of, someone here may have an idea or three.

[jonnys_spirit]

I use an allinonewinepump and a sterlitech rocker 300 for vacuum transfers. Have not done vacuum distillation yet but sterlitech also makes similar with ptfe chemical resistant components which might be recommended if you’re pulling a vacuum in an etoh environment and don’t want the rubber parts to melt.

Cheers!
-jonny

[OtisT]

Hi Rootbeers. I bought my vacuum pump at the auto supply store.

I’m sure you know that this is dangerous stuff. Be careful.

I’m no expert though I have a little experience. I have learned the hard way that you can’t vacuum while the heat is on! The boiler will outpace any vacuum system. And you need a very big second condenser unless you want to sent hot alcohol vapor through your vacuum pump and make a mess, or worse. I learned that one the hard way and got lucky I only needed to change the oil in my pump.

I think the trick is to have a completely sealed system so you only need to vacuum once per batch. Check out some of the threads by Manu de hanoi. Some good info there.

Good luck. Otis

[rootbeers]

Hi Rootbeers. I bought my vacuum pump at the auto supply store.

I’m sure you know that this is dangerous stuff. Be careful.

Yep, I am, I have enough lab experience to know how dangerous steam is...

I’m no expert though I have a little experience. I have learned the hard way that you can’t vacuum while the heat is on! The boiler will outpace any vacuum system.

Your temperature is too high if your outpacing your pump.

Vacuum distillation is used in the distilling industry because it saves a lot of energy and your input of heat is literally halved so instead of the 79 degrees Celsius, you use a temperature like 38 degrees Celsius. I am currently distilling with a low vacuum of about 21mmHg at my elevation which is about 20mbar lower than sea level.

And you need a very big second condenser unless you want to sent hot alcohol vapour through your vacuum pump and make a mess, or worse. I learned that one the hard way and got lucky I only needed to change the oil in my pump.

With the lower temperature, its more about surface area as the vapour condensates along the whole tube, its pretty strange to actually see the process.

I plan on making a short video with my better quality camera to show this process as I find it really interesting.

I am still experimenting with a gain alcohol of a known strength to ensure that the process is going as planned.

I think the trick is to have a completely sealed system so you only need to vacuum once per batch. Check out some of the threads by Manu de hanoi. Some good info there.

The main issue as you rightly point out is the seals, my glass wear is 24/29 or 24/40 joints that are supposed to be ground standard taper joints.

Whilst all the quality glass I bought from an educational supplier here in the UK was top notch and very nice, the same can't be said for the glass that comes from China, of the pieces from china, I have about 6 pieces left as it breaks easily. The British stuff, I had a flash with some glycerol in it, a 500ml conical 24/29 joint with stopper as a 3.3 boro glass and it bounced off the floor, didn't break.

You get what you pay for... which is why this investment in a pump requires some research.

Thanks for the input.

[rootbeers]

I do think that I might have an answer to my question, one that is cheapest option, simplest option and currently fits my pocket until I can afford a decent pump.
Instead of the full pump, how about the main working part for it???

12 Volts, 42 Watts, 3.5Amp, 120kPa Vacuum.

Says its for gas and lab work, so should be chemically safe.

It might help someone needing a cheap option.



Spec:
DC Mini Vacuum Pump, 12V 5L/min 120kpa Mini Vacuum Low Noise Pump No Maintenance No Oil Negative Pressure Suction Pumping for Gas Analysis Sampling Instrument

Brand: Vikye
Micro-pump is powered by miniature DC motor drive, drive internal mechanical eccentric motion, driven by an eccentric movement inside the diaphragm reciprocates

Small size, stable and reliable, high efficiency, suction capacity is up to 5L/ min
Low noise, low power consumption. Especially suitable for high negative environmental requirements
No maintenance, no oil, no pollution delivery medium
Micro-pump is mainly used in medicine, gas analysis sampling, instrument and other fields

[jonnys_spirit]

I like to use an intermediate large glass overflow container (carboy) between the pump and the target vacuum system. You could fashion something like that as a water filter to protect the pump seals from etoh vapor. Sorta like a thumper.

That pump is worth a try for the pricing. A vacuum meter or guage would be nice to plumb in.

Cheers!
-j

[OtisT]

I don’t think a carboy is a good thing to have in your vacuum system. It’s thin glass and not designed for that kind of pressure. Very dangerous at the pressure you need to have a significant impact on evaporation temps. Boom.

What is the benefit of the extra space? If it’s part of the overall volume of your vacuumed system it’s just more volume to vacate. It won’t really stop a rush of vapor w/o a condenser in there. I could see a potential use for a tank in that position if you have a valve between it and the rest of the system. With that you could vacate the extra tank well below the pressure in your primary system, stop your pump and close that off, then open the middle valve to normalize pressure between the two sides which would lower pressure on the boiler side and will not send vapor into your pump.

Otis

[Windy City]

The great thing about this site is that with a little searching you can find a lot of answers.
Check out these threads on building a vacuum still

https://homedistiller.org/forum/viewtop ... 50&t=50242

https://homedistiller.org/forum/viewtop ... 50&t=44081

Hope it helps

[Bushman]

Not sure I am ready to jump into vacuum distillation but I do use a vacuum in my vacuum filtration system and am wondering if I can use the same pump for both. Will have to do some research.

[boomstick]

Vacuum distillation is used in the distilling industry because it saves a lot of energy and your input of heat is literally halved so instead of the 79 degrees Celsius, you use a temperature like 38 degrees Celsius. I am currently distilling with a low vacuum of about 21mmHg at my elevation which is about 20mbar lower than sea level.

I was pondering this too the other week but is it really true? You still have to put in the energy to transfer your liquid to vapour which requires a lot more energy than the heating energy. Also at lower pressures i believe that vaporization energy cost increases.
I think in the end your energy saving would be a very small.

[OtisT]

Hi Rootbeers. I bought my vacuum pump at the auto supply store.

I’m sure you know that this is dangerous stuff. Be careful.

Yep, I am, I have enough lab experience to know how dangerous steam is...

I’m no expert though I have a little experience. I have learned the hard way that you can’t vacuum while the heat is on! The boiler will outpace any vacuum system.

Your temperature is too high if your outpacing your pump.

Vacuum distillation is used in the distilling industry because it saves a lot of energy and your input of heat is literally halved so instead of the 79 degrees Celsius, you use a temperature like 38 degrees Celsius. I am currently distilling with a low vacuum of about 21mmHg at my elevation which is about 20mbar lower than sea level.

Beyond steam you also need to be careful of the pump you end up buying to replace your Venturi. That was the main cause of my warning to you when I read you were vacuum pumping while distilling. The wrong pump could become an ignition point if you pump flammable vapor through it.

It’s not just Heat input that will prevent a vacuum pump from keeping up with the vapor being created. Even with the heat off, I could not get a good sized vacuum pump to keep up with the vapor produced just from lowering pressure on a warm liquid. Even without applying heat input just lowering pressure will cause your primary charge to boil, so the greater the vacuum the more vapor that is produced. Maybe on a small scale like with your lab equipment it’s doable with just a better pump? The process I landed on when pressure became too high while distilling was to turn off the heat, allow the boiler charge to significantly drop in temp to the point where it would not boil at my target pressure, I would vacate the system to my target pressure and close off the pump, then I could turn the heat back up and start distilling again at my desired boil temp.

I’m not saying it can’t be done and would be happy to see and learn how someone solve this problem. I’ll keep following to see how this turns out for ya. Good luck. Otis

[rootbeers]

I made a short video showing a few bits of the setup and a sped up part of the process that shoes that at even low temperatures, the amount of energy in compared to the boiling point is significant.

I use an aspirator, which is the type of suction pump that uses water pressure to pull the vacuum, the downside is that the vacuum is low compared to that of pumps, the plus side is that the gas output will saturate any flammable elements in water as the water jet and vacuum air are created in a chamber together, so any vapours will end up in water being sent down the drain.

A continual vacuum needs to be pulled in any setup because the boiling off gasses at the different temperature changes that happen will decrease the vacuum pressure.



I plan when my new kitchen is installed, to do a full length video (sped up of course!) showing the start to finish of a distillation run.

In the video, the temperature of the media is 49°c when boiling point is normally 79°c, with a good full vacuum, the temperature that boil off begins is 38°c.I am still experimenting with this current set up, when I get a better pump and a better digital manometer, thats when I will be able to properly record results and take some data readings. Get some real data.

I want to try to find the best temperature and the lowest vacuum needed and possibly design a vacuum pump that can do that and control any heaters in the heating stage.

I have also seen that peristaltic pumps can be used to pump a vacuum, no idea how much or if it can keep pace, but interesting to know as that is one option that can be investigated.

Thanks for the reply.

[rootbeers]

I bought a stop gap option, the 120kPa vacuum pump, problem now is the manometer range is not enough.

So I bought an ETI 9275, expecting it to turn up in 3 to 5 days, get a phone call to say that the shipment is delayed until August as they are waiting on parts deliveries... Suez popped to mind there....

So now my experiments and continuation of working on this side of the art, is now on hold until the ETI turns up so I can measure the effectiveness of the pump.

[manu de hanoi]

A continual vacuum needs to be pulled in any setup because the boiling off gasses at the different temperature changes that happen will decrease the vacuum pressure.

you arent supposed to run an oil vane pump continuously unless you have a super strong condenser and a cold trap (weak condenser but very low temp).
If you do run without that, the oil will get contaminated with water and turn into mayo and you'll have to change the oil. Liquid ring pumps dont have this drawback (they run on water like aspirators) but are costly (especially the dental small ones) and the vacuum can't go below the boiling point of the water.
There are videos on youtube for making your own jet aspirator pumps using 20 USD membrane pumps. There are really fun and might be enough for your glass setup, but again vac not lower than water boiling point.

A peristaltic would be cool but i'm afraid there's a risk the flex tube would collapse under vacuum