vaccum reflux

[rangaz]

I'm yet to see a proper reflux vacuum still so I'm just wondering how they have been constructed by others. If using an inline still, it would just be as simple as reducing the pressure within the column? If so it could easily be done by sealing the collection vessel with a cork and connecting an evacuator airtight just above the cooling coil. I can't see this as being much harder to add into the construction. The only problems I can think is the need to have colder coolant. How low would the pressure have to be before higher percentages could be achieved?

[markx]

It depends of course on the percentages desired, but I believe that reducing the pressure by half an atmosphere would already have a significant effect. If one can trick the percentage past the azeotropical point the result can go up to 100% purity. Vaccuum is just one way of doing that, another way is to bind the water by some additional component in the disitllation mixture. For example saline solutions have been known to be introduced into the column during distillation to bind water and up the percentage at normal pressures.

Or one can add a significant quantity of soluble nonvolatile matter into the boiler (e.g. some salt NaCl, NaNO3, KNO3, KCl etc.) that will lower the partial vapour pressure of water at a given temperature (by interacting with water molecules in the liquid phase) and therefore up the % of alcohol in the initial vapour mixture in the boiler.

p/p1=1-X

Where

p is the vapour pressure of pure solvent
p1 is the vapour pressure of the solution (salt+ solvent)
X is the molar fraction of the salt in the solution


That would not increase the final % of product but due to the altered vapour composition can increase the purity of the final distillate.

[schnell]

they don't look any different from a normal still except for the output line. you need a vacuum adaptor placed there.

i've used a laboratory rotary evaporator (fancy vacuum still) with an anti-splash adaptor to make a highly effective vacuum reflux column. if you're an organic chemist you probably have one around, other folks wouldn't use them much.

in the CRC you can look up the azeotropes. with a small simple vacuum pump it is easy to hit the 99.5% mark. this will of course rehydrate if you leave it in an open topped container in a humid environment. but then you'd probably want to add some water to it anyways...

[Dog Meat]

Is it possible to get some more background? drawings pics etc of the vacuum connection when put on an existing unit? Any follow up reading?

[schnell]

here's photos of a basic kit for organic chemistry on this site

http://organicglassware.com/" onclick="window.open(this.href);return false;" rel="nofollow

in the first picture of the basic kit the vacuum adaptor is the thing at the bottom of the second column next to the three necked flask.

the vacuum adaptor is usually used between the reciever and the leibig condensor and is then connected by a hose to an aspirator or vacuum pump.

[junkyard dawg]

Now that looks like a fun set of glassware! I'd love to have that to play with. the homedistiller version of the 'erector' set...

[nanosleep]

....sealing the collection vessel with a cork....

I think you'll want to provide an air return line from the collection vessel to the cold side of the condenser. The collection vessel may not fill if you don't have this 'burp' line. This is especially the case if the output line from head to collection vessel is small (1/4 copper tube or similar).
Basically you connect together everything that was open to the atmosphere (cold side of the condenser, collection vessel) and apply a vacuum to fake a low 'atmosphere pressure'.

[droxemin]

Is it possible to get some more background? drawings pics etc of the vacuum connection when put on an existing unit? Any follow up reading?

Here are pics of my homemade vacume distill apparatus,i use it every day for my exelent non tax paying brew .
Damn how do i put these image´s in here?????[/img]http://i226.photobucket.com/albums/dd22 ... ynd117.jpg

[CoopsOz]

You need to create an account at somewhere like http://www.photobucket.com and put the image tag in your post. There is a site that doesn't require creating an account but the name slips me. I guess I've had to many DWWG's.

[jake]

the organic chem lab survival manual
James W Zubrick author ISBN# 0-471-38732-0
interesting read for those of us not into grades
my wife bought it for my 11 year old who quickly out grew his chem set.