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labrat00

creating vacuum for distillation

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other than using an aspirator or some expensive vacuum equipment, are there any ways to create a vacuum strong enough but not too strong to complete the distillation?

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Your best option is a compressor from a discarded refrigerator or airconditioner. Usually free, it really sucks :rolleyes: ! -As much as you need, and available in many powers-

Miguel

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The traditional aproach is a water jet type aspirator. Cheap, easy and almost impossible to kill.

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If you are in a three storey building.

Fill a narrow hose with water and attach one end to the apparatus and a tap to the other.

Dangle the other end out of a window, walk downstairs and open the tap letting the water drain out carefully so that air cannot get in. If the hose drops more than 35m the last bit of water should be held in the hose by the vacuum above it (If the drop is less than 35m you can turn off the tap before the water is drained out and achieve a partial vacuum)

 

The more vertical the hose, the better and a narrowing of the end with the tap to get a fast outflow as there is less chance of air getting into the hose as the water drains.

 

Another classic way of whipping up a 'quick and dirty' vacuum is to heat a vessel with a little water in the base so the steam displaces most of the air. The vessel is then sealed (or attached to apparatus) and allowed to cool. As the steam condenses it makes a decent partial vacuum which is maintained for some time as, if the pressure increases more of the steam condenses.

 

You need a strong vessel, though,

 

And finally, A really dirty method I used for degassing small quantities of buffers (very effectively, I might add). If you are in a bio lab you probably have access to 60mL plastic syringes with luer fittings (from Beckton Dickinson etc). If you can arrange apparatus such that the syringe is connected to the apparatus with no air in the system you can draw back the syringe and create a pocket of vacuum inside the barrel (It takes some strength. Shove AA batteries or similar between end of plunger and rim of barrel to hold it). Once you have applied the correct temperature to your distillant for a while you will have a syringe full of distillate to condense as you like.

These syringes can hold >15 bar of pressure and seem to hold a vacuum for at least several minutes and the luer fittings are held on all the more tightly with the low pressure (At high pressures they tended to burst off at inopportune moments)

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how fast does the gas need to come out? as far as i know, distillation is going to produce quite a bit of gas.

also what are you distilling?

 

the syringe can be taken a little further... dirtier too

 

i built a vacuum pump out of a jam jar, 10ml syringe, a large bead and two check valves off a fish tank.

it was put together with hot glue and the only problems i've had was water flash boiling in the syringe only to condense when it repressurised and the lid sealing too tight. (i did eventually fudge a relief valve)

it's not the fastest to evacuate the chamber but mine gets to about 10Kpa from total vacuum.

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