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Author: Subject: vacuum distillation Schmiddy
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posted on 7-11- at 08:51 vacuum distillation


Hi

brand new to the forum although I've been reading for several years.

I am the proud owner of some ground joint glassware(24/29) and have used it for several years now for some basic distillation but would like to take my distillations to the next level.

I must confess I didn't do much schooling so what I know I come by honestly so if I make any basic mistakes forgive me


Now my first question is relating to recirculating systems.

I use a 6 gallon bucket and good sized pump for cooling my condensor
works very well and with a 40cm condensor and a steady supply of ice I've managed to distill diethyl ether(from starter fluid) chloroform(from bleach) and I just finished a run of petroleum ether/hexane from gasoline/petrol.

now I want to do some vacuum distillations but my aspirator can currently only attach to my sink faucet and I want a recirculating system for the aspirator water like I have for my cooling water as using the sink is wasteful and rather loud.

I'm thinking something like this will work
https://www.ebay.ca/itm/130PSI-DC-12V-6L-Min-Water-High-Pres...

now my aspirator is a humboldt metal aspirator modified with garden house threaded fitting on it, it has no numbers on it and was obtained from a now defunct hobby science supplier out of Utah.

is there a minimum size I should be shooting for in my resevoir size for the aspirator?

I plan to use it with ice to obtain a better vacuum so I'm thinking a chest cooler larger than 30L preferably bigger than 50L will dome good.

I'm also planning to build some traps as well as acid fumes have already caused some corrosion of my aspirator and with a recirculating system any nasty fumes don't get flushed down the drain.

any one having any experience with vacuum distillations on a hobby level and running those distillations in a home lab please chime in.




greenlight
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posted on 7-11- at 12:01

I have never used a water aspirator but I suggest buying an actual laboratory vacuum pump from ebay if you can afford one and will use it often.
I use mine all the time especially for filtering precipitates rapidly.

I have done quite a few vacuum distillations with it too. Just inspect your glassware for cracks before applying any vacuum and don't use flat bottom flasks.
If distilling nasty substances you can put a dreschel gas washing bottle or two between the vacuum takeoff adapter and the pump filled with the appropriate neureslizing reagent. I usually use washing bottles, one with sodium hydroxide and one with bicarbonate solution when distilling 99% white nitric acid and the pump still runs beautifully years on.

If you want to roughly calculate how much of a vacuum you can obtain with your chosen setup, place some hot water in the apparatus, and pull a full vacuum. The water will boil because the vapor pressure of the water will be greater than the external pressure in the setup. As soon as the water stops boiling, take its temperature quickly as possible. You can find tables of the boiling point of water at different reduced pressures on google and match the temp it was last boiling at to the pressure to get a decent idea of the vacuum you can achieve.



[Edited on 7-11- by greenlight]



Ubya
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posted on 7-11- at 12:33

i haven't done a vacuum distillation yet as i haven't needed to do one and generally i don't trust my chinese distillation glassware to survive negative pressures, buit i built a recirculating aspirator vacuum pump for general filtration and vacuum application.
i used a 60W 100psi diaphragm water pump, similiar to the one you said you want to use, and a metal aspirator pump from deschem (ebay). i tried 2 styles to arrange vacuum aspirator and water pump, this is what i'm using right now.


it is pretty loud, the pump should be suspended or padded, the vibrations get amplified from the container and then by my fumehood, not nice to hear for multiple hours.
the water volume is pretty low, maybe 2 liters, it heats up quickly (10°C in 10 minutes maybe), i'm working to actively cool it (and the condenser water recirculator).
the bubbles created by the pump output would be suckes back in the input tube, ruining the vacuum, so i just put a cleaning sponge as a filter between the input and output tubes (i don't have a picture with me right now)




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posted on 7-11- at 16:29 Schmiddy
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posted on 7-11- at 16:40

Quote: Originally posted by Ubya  i haven't done a vacuum distillation yet as i haven't needed to do one and generally i don't trust my chinese distillation glassware to survive negative pressures, buit i built a recirculating aspirator vacuum pump for general filtration and vacuum application.
i used a 60W 100psi diaphragm water pump, similiar to the one you said you want to use, and a metal aspirator pump from deschem (ebay). i tried 2 styles to arrange vacuum aspirator and water pump, this is what i'm using right now.


it is pretty loud, the pump should be suspended or padded, the vibrations get amplified from the container and then by my fumehood, not nice to hear for multiple hours.
the water volume is pretty low, maybe 2 liters, it heats up quickly (10°C in 10 minutes maybe), i'm working to actively cool it (and the condenser water recirculator).
the bubbles created by the pump output would be suckes back in the input tube, ruining the vacuum, so i just put a cleaning sponge as a filter between the input and output tubes (I don't have a picture with me right now)


that's a slick little setup but I wouldn't try that with less than five gallons
and moving up to a larger resevoir and one with an easy to open lid(to add ice and remove water) will solve most of the issues you have now.

for distillations I would want something that stays evenly cool or cold to pull an even and strong vacuum.

I'm thinking for the size of the pump it could be placed in a styrofoam box or have an acoustic cover of some kind.

does the pump itself get quite hot? Ubya
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posted on 7-11- at 17:35

it gets hot, but not dangerously hot.
mu pump system is small because i'm trying to make everything as small as possible as vacuum pump, condenser water recirculator, cooling system etc must fit under my fumehood, i can't afford a 20L bucket for everything




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posted on 7-11- at 17:52

is there a particular reason why your cooling resevoirs must fit in the fume hood?

I can't think of any reason why your cooling water resevoir needs to be in there.

is this designed to be a mini or portable lab? S.C. Wack
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posted on 7-11- at 17:58

You can refuse to consider mixing in a water chiller now that I've mentioned it.



"You're going to be all right, kid...Everything's under control." Yossarian, to Snowden Schmiddy
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posted on 7-11- at 18:35

Quote: Originally posted by S.C. Wack  You can refuse to consider mixing in a water chiller now that I've mentioned it.

I keep my lab well stocked with abundance of frozen 1 litre water bottles and full ice cube trays at the ready.'

I prefer to run my aspirator on the coldest water possible for best vacuum
as well as my condensor.

since I am building a heat exchanger for another project the 3/8" copper tubing I have may come in handy for building a chiller as well. Ubya
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posted on 8-11- at 08:18

Quote: Originally posted by Schmiddy  is there a particular reason why your cooling resevoirs must fit in the fume hood?

I can't think of any reason why your cooling water resevoir needs to be in there.

is this designed to be a mini or portable lab?
I don't have a dedicated space for my lab, I don't have a room for it, the best I could do is build a fume hood just outside the door of my apartment (I live on the last floor so it doesn't bother my neighbours), but the space is not much at all, so I have to cram everything I need in maybe a 1x1m area (under the fume hood or on the sides)




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posted on 8-11- at 10:00