On Mon, 09 Sep 2013 21:33:58 -0400, Joe Gwinn
wrote:

In article , Ed Huntress
wrote:

On Mon, 09 Sep 2013 08:53:53 -0400, Joe Gwinn
wrote:

In article ,
Scromlette wrote:

It's got some minor metal work involved, but unfortunately no guns or
politics.....

I use quite a bit of methylated spirits to clean electronic PCBs as part
of a cottage business I run. The solvent becomes laden with dissolved
rosin flux & has to be discarded so I've been thinking about distilling
it for reuse. It's costing me 3 or 4 dollars per litre.


I was toying with the idea of electrically heating an old pressure
cooker vented through either a copper coil or an old refrigerator heat
exchanger. I'm not sure if draping wet cloth on the heat exchanger would
be sufficient cooling.

This can work, but be aware the some of the vapor will escape, and is
*very* flammable. I would do this outside, well away from away
buildings.

A long enough bit of copper tubing will work as a condenser, so long as
there is adequate airflow.

The alcohol may destroy the seal rubber. Some pressure cookers will
accept large viton O-rings. Maybe some makers use viton.


I think the BP of the methylated spirits is ~ 82 Celsius (180F).

That sounds about right.

It's not a good idea to get the pot too hot. I'd set it up in a double
boiler arrangement, unless you implement an automatic controller.
Regulating temperature by hand without a double boiler is likely to
cause trouble.


Has anyone any experience doing this sort of thing (moonshine perhaps?)

Lots of folk, but they are in the woods, and tend to shoot revenuers
and other nosey people.


Will it be worth the effort?

Depends on volume of alcohol to be processed.


Joe Gwinn

If you cool the condenser, vapor doesn't have to escape. In fact, you
can seal the outlet with a cork or rubber stopper and put a simple
gooseneck (a manometer) in the same stopper, and you can maintain
*negative* pressure.

Yes, I've done it, with a fancy laboratory reflux still made of 100%
glass, distilling ethyl alcohol (you blow off the fusel oil and light
aromatics, waiting for the temperature to indicate ethanol, before
turning on the cooling water). It works as well with copper, and it
doesn't have to be reflux.

True enough. But I'm assuming a homebrew still, far from lab grade.
I'd start outside for sure.


If this is methanol, check for a potential reaction between the
alcohol and copper. Ethyl alcohol is no problem, obviously, but I
don't know about methyl.

Hmm. Never heard of this, but maybe. Perhaps one of our resident
chemists will chime in.


I've seen copper-coil condensers run through a bucket of water that
will cool and condense the outlet to negative pressure. You just have
to pour in cold water from time to time, and let the excess flow over
the side of the bucket. That's what the gooseneck is for -- to tell
you when you're getting positive pressure and you need to pour cold
water around the condenser.

Why do you want negative pressure, given that ethanol won't decompose
from the heat at atmospheric pressure?

Joe Gwinn

Just to avoid explosive vapors.

The reason I think you should check the corrosive effects on copper is
that methanol has been a problem with copper and brass parts in race
cars, where it's used as a fuel.

--
Ed Huntress