Sciencemadness Discussion Board - Hand vacuum pump vs mechanical

Hand vacuum pump vs mechanical

Bestbmc - 30-8-2021 at 10:01

Hi everyone,

I am looking to use vacuum filtration and I was browsing deschem and saw that they offered a flask, funnel and hand vacuum pump for 40-50 dollars.

I also want to vacuum distill some chemicals in the future and I wanted to know if it is worth it to purchase a hand vacuum pump now if it works well, or just buy a cheap vacuum pump for $60 that could also be used for vacuum distillation.

Does anyone have recommendations with the hand pumps or the cheap $60-70 vacuum pumps you can find on Amazon? The reviews seem to be quite mixed.

Fyndium - 30-8-2021 at 10:30

Unless you seal the system hermetically, it will leak and require constant pumping, so vacuum distillation cannot be done without mechanical pump. Likely you'll need a huge reservoir, in order of 10's of m3's to keep the vapor pressure low enough during distillation, as it constantly generates more vapor, or you'd have to remove energy from the system at huge rates not achievable my ordinary labware.

I use small 4$ membrane pumps for vacuum filtration. They generate 100-300mbar vacuum or something like that, never measured it, but works well in vacuum filtrations. Single phase rotary vane pumps on eBay for 50$ work well for vacuum distillations, given you use good condensers, a coldfinger with CaCl2 trap at -30C, and change the oil often. I use paraffin oil in my pumps with good success.

Dr.Bob - 30-8-2021 at 10:39

I second that, a mechanical vacuum pump will barely work for an easy filtration, but not for a distillation. Imagine trying to run a manual refrigerator or vacuum cleaner, you can only generate a small flow for a short time. Its worth it to find a small cheap vacuum pump.

Bestbmc - 30-8-2021 at 12:55

Thanks,

I was going to buy a hand pump and then a motorized vacuum pump later on, but if there are good motorized pumps for $50 on eBay, it makes more economical sense to skip the hand pump and buy a single motorized pump.

karlos³ - 30-8-2021 at 13:48

Its a nice exercise though

Fyndium - 30-8-2021 at 14:37

I just ordered my - ahem - third rotary vane pump.

The issue with these reefer evacuation pumps is that they do not like too much about solvent vapors and seem to lose their ultimate vacuum eventually. I was able to distill BzH at 45-50C first, but later it went to 140C for 240C bp liquids, and further on. Now I use my most corroded pump for filtrations, it still generates much over 90% vac and some solvent carryover is not an issue anymore. I also do a first strip with these by evaporating any remaining volatiles off, change receiver flask and add coldfinger and do the actual run with the new pump. Frequent oil change(I change it every time I use the pump basically) keeps the pumps pretty decent. Paraffin oil generate full vacuum but costs 10 times less than actual vacuum oil and is otc.

Btw, I used fuel primer pumps for filtrations initially, thanks for Cody's Lab for kidea. It worked, but I admit it was PITA.

[Edited on 30-8-2021 by Fyndium]

Sulaiman - 31-8-2021 at 05:50

Quote: Originally posted by Bestbmc

Thanks,

I was going to buy a hand pump and then a motorized vacuum pump later on, but if there are good motorized pumps for $50 on eBay, it makes more economical sense to skip the hand pump and buy a single motorized pump.

I bought a dual stage rotary vacuum pump (Cheap Chinese HVAC type) to use for vacuum distillations and filtration.
Using the pump for filtration is pointless as it evaporates many solvents at RT, and causes the filtrate to foam.
I've not mastered using the pump for vacuum distillations, in fact I've given up for a while.
Very low pressure distillations commonly need a very cold condenser (plus valves, gauge, traps..) and I'm not ready for that yet.
So, I suggest that you buy a cheap vacuum pump for filtration
(eg almost any of the 12v vacuum pumps available via eBay, Amazon etc. will work.)
Buy a more expensive pump when you know exactly what you need.
I dont have a manual/hand vacuum pump but YT videos of users (some SM members also) have used them successfully,
so your initial consideration of the kit is a viable option.
(more effort, less complications and noise)
Once you evacuate a filter flask, surprisingly little pumping is required.

[Edited on 31-8-2021 by Sulaiman]

Fyndium - 31-8-2021 at 07:08

https://www.ebay.com/itm/224200363652

For example. These are what I use for filtrations, for the most place. They generate perhaps 0.9-0.7bar vacuum, while rotary will go to down to 1mbar. When I really want to suction cake to dryness, I apply rotary pump.

Fuel hand primer pumps are el cheapo option for 5 bucks. I actually used then with good success for long time before emerging to diaphragms, because I got lazy doing grip exercises all day long.

For the rotary vane pumps, I consume these. The smallest one does the job, at least up to 5L reactor volume with zero issues.

https://www.ebay.com/itm/254455748012

For the ultimate pump, one might look into KNF 2 stage diaphragms. They are designed for lab applications, and they generate very high and consistent vacuum. Price tag? For used unit, might get under $1k. The cheaper ones only produce a very mediocre 90mbar vacuum, which does not help at all, even when distilling the easier stuff. For example, LABOPORT N 820 G might do the job. It offers 6mbar absolute vacuum, which is decent for most general applications. A 240C stuff boils at 100C. New unit cost 1700€ incl VAT, for the Dysropeans.

For the price, one shall get 34 units of rotary vane pumps. I have consumed two so far (as to not produce a high vacuum anymore) and just ordered the third one, so I'm still pretty far away.

[Edited on 31-8-2021 by Fyndium]

Vacuum gear

MadHatter - 31-8-2021 at 21:58

http://www.sciencemadness.org/talk/viewthread.php?tid=1649#p...

This is an older link to my vacuum gear. It's the 4th post down. In the picture
the hydroaspirator in the middle was always my favorite because of its low
cost. These things are great for vacuum distillation provided the water running
through the device is very cold. I would NEVER use the rotary vane pump to
distill corrosive materials.

macckone - 31-8-2021 at 22:14

I use a modified aquarium pump for vacuum filtration.
I have both an aspirator set up and a single stage rotary vane.
If you use a rotary vane pump, you really have to use a cold trap and filter and change the oil regularly.

I sometimes use the aquarium pump for distillation when I want containment and not real vacuum.
Again with a cold trap and filter arrangement.

metalresearcher - 31-8-2021 at 22:41

Quote: Originally posted by Fyndium

https://www.ebay.com/itm/224200363652

For example. These are what I use for filtrations, for the most place. They generate perhaps 0.9-0.7bar vacuum, while rotary will go to down to 1mbar. When I really want to suction cake to dryness, I apply rotary pump.

Fuel hand primer pumps are el cheapo option for 5 bucks. I actually used then with good success for long time before emerging to diaphragms, because I got lazy doing grip exercises all day long.

Weird. I got a $130 vacuum pump from Amazon which evacuates to at most 6mbar. I boiled ice water from 0 C which is 6mbar and afterwards all remaining water froze so it was below triple point pressure and temperature.
For filtering I use a hand squeezer to lower the pressure under the filter which works fine.

Bestbmc - 1-9-2021 at 05:43

I after reading this more, I think it’s best if I buy a low cost 12v one for filtrations and small distillations and buy a larger one in the future once I have more practice and the proper setup for a cold trap.

Fyndium - 1-9-2021 at 07:30

For cold trap, I have found CaCl2 solution at -35C a suitable alternative for other than very volatile stuff. When distilling higher bp stuff, the trap had only very little condensate, in order of a single drop at the bottom, but more volatile solvents will pass, and the issue is, even when the trap stops them, it fills up quickly and renders it ineffective. Solution here is to first strip and evaporate more volatile stuff with lower vac pump, aspirator or a sacrificial, secondary rotary pump like I do, which is already damaged such that it does not produce nowhere full vacuum but is very suitable for such stuff.

Using dry ice acetone bath is the classic method, but commonly dry ice is so expensive that it will render most reactions far from worthy.

Bestbmc - 1-9-2021 at 17:40

One last question, it might fit better on another thread but since this one is active, would it be safe to pull a vacuum with one of the 12v vacuum pumps on a flat bottom flask?
Another older thread “Vacuum glass implosion?” Noted that it is not good practice to pull a vacuum on flat bottomed flasks, but I only have flat bottomed flasks currently. Would it be worth it to buy one or two round bottom flasks for distillation (I don’t have a heating mantle, so I would have to use a sand bath), or is the pump just too weak to pull a strong enough vacuum to get close to its breaking point?

karlos³ - 1-9-2021 at 20:59

Quote: Originally posted by Bestbmc

One last question, it might fit better on another thread but since this one is active, would it be safe to pull a vacuum with one of the 12v vacuum pumps on a flat bottom flask?
Another older thread “Vacuum glass implosion?” Noted that it is not good practice to pull a vacuum on flat bottomed flasks, but I only have flat bottomed flasks currently. Would it be worth it to buy one or two round bottom flasks for distillation (I don’t have a heating mantle, so I would have to use a sand bath), or is the pump just too weak to pull a strong enough vacuum to get close to its breaking point?

Those little pumps, I got one too, are not suitable for distillations.
Very suitable for filtrations, but really, not at all for distillations.

FBF's can stand a little bit of vacuum, once in a while, its not overly dramatic.
You should still avoid it, but they are not going to pop in an instant.

Fyndium - 2-9-2021 at 00:32

I have used small pumps with erleys all the time, 1L, 2L, 5L. They generate so little vacuum that it does not matter.

But for actual vacuum pumping, always use round vessels in all cases.

You won't benefit from using small pumps for vacuum. You need to reach 95%+ vacuum for it to be effective at all for distillations, much higher if you desire to distill higher bp stuff. Small pumps only generate 10-30% vacuum, which you barely notice a difference on bp.

macckone - 4-9-2021 at 10:43

Yes. Small pumps are more for containment than BP reduction.

Mateo_swe - 7-9-2021 at 10:40

The very cheap small 12V electric pumps is great for most filtrations and when they break put a new one in.
The hand pump is only useful for fast easy filtrations and will have short lifespan.
If you want to dry a filtrated compound on the funnel you would need to hand pump continuously for a while, thats not doable.

But an aspirator connected to a waterpump is also good for filtrations and it doesnt care if its corrosive stuff.
Well maybe it does take damage after a while but they are cheap to replace and works good.
The corrosive gases end up in the pumpwater, something to remember if its some toxic stuff.

For vacuum distillations you need a better pump.
If chemistry is a hobby you know you will continue with then a diafragm vacuumpump for lab use it best but they cost more.
Used quality lab diaphragm pumps like KNF, vaccubrand is offered on ebay, sometimes good deals can be made.

earpain - 11-9-2021 at 20:34

Forgive me friends but I will now be the voice of dissent! =P
Almost every poster here has mentioned that a downside of strong motorized vacuum pumps is, in one sense or another, that they pull TOO much vacuum.

And then start suggesting multiple vacuum pumps to strip different solvents in the mixture?
I'd like you meet my friend. His(her?) name is Needle Valve.
People say to attach as air bleed IN via a T adapter, however I'm preeeety sure this releases much filtrate in its' vapor phase when using for filtration.

In fact, I have a HVAC pump that I eventually removed the needle valve for, because i realized that the "Blank Off Valve" as they call it, which is a big tough ball valve with a big handle, right under the inlet connection(s).....is...easy to 'feather', as in, it has a nice wide range between fully closed and fully open, and that range is wonderfully linear with 760torr -> zero-ish.

I almost never use a trap! Seriously. If something is so volatile that it requires a trap, than it's actually not only easier but FASTER to distill atmospherically.

If it's an acid i use my aspirator.

Occam's Razor, I embrace thee.

S.C. Wack - 11-9-2021 at 22:11

No need for valves for filtrations that last a minute or so...turn on the pump, hold the hose in your hand, attach your hand to the flask...very precise control.