I'm a home-scale experimenter/dabbler in the arts of distilling liqueurs/spirits and essential oils, and right now I'm trying to see what vacuum
distillation(at very low temperatures) can add to the finished product as far as taste, aroma, and color go. For my initial experiments, I've been
using a simple glass set-up with a 1000ml boiling flask in a sand bath with a liebig condenser. I've been using an automotive vacuum(for brake lines,
etc.) attached to the vacuum take-off valve. I've just been trying to bring ethyl alcohol(everclear) over as an experiment, but I've been having some
trouble.
I'm hoping this thread can be used to troubleshoot some of the problems I've been having and/or correct some of the goofy non-chemist methods i may
have been using from the start.
Right now my biggest problem is that I seem to be losing vacuum. This may be through one of the clamped connections between where the glass fits
together, or it may be from the tubing connected to the vacuum take-off. Is there a good method to check for leaks or a fool-proof method for sealing
connections so they can't possibly leak in the first place?
I have been using vacuum grease with ground glass joints(+keck clamps) that fit well together, so I'm doubting that I'm losing vacuum through the
actual glass connections in the set-up, although I'm still entertaining that possibility.
My thought is that I'm losing it through the tubing I've attached to the vacuum take-off. I used a flour-based paste to seal it over, but maybe that
isn't the best idea? Maybe the tubing itself is too porous and I need to get higher quality tubing? Any idea as to resources to find this?
Also, if anyone wants to throw any critiques out there about the set-up I'm using(after viewing the pics), I'm all ears. I'm really new to vacuum
distillation and I'm sure I'm making some mistakes that I'm unaware of.
Thanks! Pyro - 12-1-2014 at 13:16
are you using enough vacuum grease?
if so (if not, most likely) it will be that vacuum takeoff system, maybe the valve
PS: you ain't operating no moonshine still, you are using precision ground glass equipment, get some real grease (corning is good)
[Edited on 12-1-2014 by Pyro]BromicAcid - 12-1-2014 at 13:55
From the pictures it looks like you are using the right amount of vacuum grease, the pictures where I see your joints they look clear. As long as
they are clear with no bubbles they are plenty good, when they start to fail you will see bubbles or occlusions where the joints have started to come
apart or where solvent is beginning to escape.
What are you using the paste for on your vacuum takeoff? You should be able to slide the tubing over whatever sort of nipple is there and have a
tight fit. The tubing looks like actual vacuum tubing so I doubt that it is too porous. I give you the same advice I gave someone else recently:
Empty out your setup, dry the setup and re-assemble it. Then try to pull vacuum on the setup. Vacuum check your setup, can your setup be pulled to
the same pressure as your pump will put on itself without anything else connected? If so you're sealed up pretty good.
As with the same recent question I answered on the subject my thought would be that you are not condensing your vapors. How cold is the fluid going
through your condenser? Are you keeping your receiver cold (much colder than the boiling point of your spirits) and do you have a trap in line that
is cooled after your setup? Every bit of vapor that does not condense is detrimental to your vacuum and makes your vacuum pump fight that much harder
to maintain the status quo. What sorts of pressures are you going to? And why do you think vacuum will help you? My thought would be that without a
good condenser you are going to lose volatile components to your pump and affect the subtle flavors you might be trying to cultivate. Also note that
azeotropes are affected by pressure so distilling azeotropic ethanol under reduced pressure might not give the pressure and temperature parameters you
might expect to produce boiling.S.C. Wack - 12-1-2014 at 15:00
1000ml boiling flask in a sand bath with a liebig condenser. I've been using an automotive vacuum(for brake lines, etc.) attached to
the vacuum take-off valve.
If there is leakage at tapered joints or one needs clips it's because the vacuum is too small. Even parts from different makers should mate well and
be difficult to pull apart while distilling with only the lightest smear of a smear of grease.Panache - 15-1-2014 at 15:53
With that pump on such a tiny setup your problem is not ingress through ground glass joints or lack of grease.
So I understand your problem, you turn on your vacuum, get a particular pressure then over time that pressure increases significantly.
If that's the case then its a very odd problem as why do you initially get a good vacuum then it dies off.
My only guess at this is that you are not condensing your ethanol vapour entirely (condenser not cold enough or receiver not cooled, and the ethanol
vapour is diluting your vacuum pump oil, thereby reducing the maximum obtainable vacuum.
Ideally your setup should include a t-piece somewhere close to the receiver, with the branch of the t-piece going to a needle valve then to
atmosphere. When you turn on your pump have the needle valve fully open, then close it slowly, increasing the vacuum slowly, this gives you finer
control over the vacuum, albeit in a crude way. it works well because your pump is over specced.
hope this helps.
