Vacuum Distillation

richard

I considering starting to dabble a bit on vacuum distillation.

I would like to first start on my lab still set up which is as shown.

Does any one have any pictures showing the recommended set up. For the vacuum, I have a vacuum pump that I use for gassing when evacuating my fridge plant.

From what I have read / seen so far ......... You need to allow for a very small needle (or sorts ??) for air ingress direct into the product within the bottom bowl. You connect the vacuum after the PC at point of exit from the assembly.

Comments / recommendations ??

grim

I wouldn't pull a vacuum on the glassware shown, those bulbs look huge, and the glass shrapnel would probably hurt.

The simplest approach is to keep the whole system under vacuum, including the product collection tank, and everything needs to be designed for the stresses of vacuum.

Obviously, vacuum take-off needs to be after the product condenser, otherwise you risk drawing off vapor. Also, be sure that under no circumstances can you draw liquid through the vacuum take-off, you'll kill your pump.

You are probably wondering how you make cuts on a vacuum system. Yeah, that's the problem. With lab glass, you need to use something called a Cow, and you make the cuts blind.

Otherwise you need to design a very fancy system that uses a peristaltic pump to draw off distillate without losing vacuum.

richard

Thanks.

That sounds quite easy to build from SS. But what has me concerned is that if I have a product collection tank under vacuum, then surely I am running the risk of the collected alcohol starting to boil again as it is under vacuum. ??

grim

That depends on your distillate temperature. You'll need to run your condensers colder than you would need to at ambient. Depending on your level of vacuum and ambient, you may need to cool your collection vessel as well.

grim

Just one caveat, not that you are boiling the distillate without heat - but if the condensers aren't cooling well and you are pulling off hot distillate in a hot ambient, you may be losing volatiles to vapor, which would be pulled off through the vacuum pump. If you are doing this to be able to capture some very delicate botanical aromas, you don't want to blow off those volatiles and pump them out.

I tried this twice, I gave up on it. I figure it's easier to just try to make enough money to afford a large Buchi Rotovap with vacuum pump.

Fiji_Spirits

@richard said: That sounds quite easy to build from SS. But what has me concerned is that if I have a product collection tank under vacuum, then surely I am running the risk of the collected alcohol starting to boil again as it is under vacuum. ??

I don't think you will want to pull that much vacuum. IIRC you need something like a 40f temperature gradient to get condensation so your product won't boil.

Besides adding a little heat gives more control points for operation of the still.

Ryan

I designed and had fabricated a vacuum distillation system with the goal to achieve as close to 100% ABV as possible. Here is what I discovered:

1. Designing the kettle and collection pot is not difficult math if you are somewhat familiar with ASME boiler code. You'll have to perform shell and reinforcement sizing calcs for your kettle and collection vessel size.
2. The smallest diameter site glass I used under full vacuum was 2" borosilicate...I would not go larger for stress reasons...do your calcs. for your glass.
3. I charged the boiler with 95% ABV.
4. My column was 4" diameter 8' tall packed with ceramic raschig rings.
5. I made my own cooling system out of an A/C window unit, and ice-chest and a pump pumping polypropylene glycol through the condensing systems. I achieved 7 degree C on front end and return was 15 degrees C. That was more than cold enough. Be sure to have a condenser on the suction side of your vacuum pump to knock down any ethanol vapors prior to entering your vacuum pump. Theoretically once a vacuum is achieved you shouldn't have to kick your pump back on...however in real life I was losing about 1 in of Hg every 15 minutes and had to re-achieve the 30 in of Hg I was going for. I kept the system between 25-30 in of Hg.
6. My kettle (50 L) was heated with a barrel heater.
7. Once under vacuum I achieved distillation at 110 degrees F. The boil was quite unstable. I did not have a way to keep the solution mixing. I think a mixer would have given better boiling results.
8. I only achieved 97% ABV.

I don't consider the project a complete failure because my future plans are to vacuum distill gin and a variety of other infusions at lower ABVs (~55%). I anticipate different flavor profiles from distilling these infusions at lower than normal temperatures.

jacksonbrown

Cool experiment but Az is over 97% ABV (by volume) at ambient pressure, did you mean ABW? An 8' column should handle that no worries without the vacuum.
Is there a type of vacuum pump that can handle all the product going through it? It would simplify the design a lot.
Mount the pump on top of the reflux condenser and hook up the product condenser to the outlet of the pump for ambient collection.
Best of both worlds

Ryan

@jacksonbrown said: Cool experiment but Az is over 97% ABV (by volume) at ambient pressure, did you mean ABW?

Well that's sad. Maybe my results were worse that I thought. I thought Az at atm was 96.2%?

I don't quite understand your question concerning the product going though the vacuum pump. Once you establish a vacuum theoretically (if your system is "air tight" and has no leaks) you shouldn't have to turn your vacuum pump back on. Anyway you really don't want your product going thought the vacuum pump. You would not only pick up pump oil in your product but you'd probably ruin your pump pretty quickly.

I'll keep playing around with my system when time allows. It's a rather time consuming experiment. I think my theory is sound just not my execution. I know a lot of areas where I can make improvements. For example, I thinking of getting a used freezer and installing my product condenser, vacuum pump condenser and product container inside the freezer with a container of prop-glycol in the freezer circulating though the condensers.

Ryan

This is what my vacuum system looks like.

jacksonbrown

@Ryan said: Well that's sad. Maybe my results were worse that I thought. I thought Az at atm was 96.2%?

Depends if its ABV or ABW. My data shows 97.184%-ABV which is 95.58%-ABW. Wiki says 95.63% by weight.
We all work on ABV but the chem eng books all quote ABW or even molar.

@Ryan said: You would not only pick up pump oil in your product but you'd probably ruin your pump pretty quickly.

Exactly but if the pump could handle it... everything downstream of the pump could be atms. Cuts are easy again, no chilling of condensate and it would practically condense itself when returning to pressure. You just need the right pump.

Kind of like a vapour recompression system that pulls instead of pushes.
You might even be able to do it with air. Those venturi vacuum jiggers could work like a cold TVR.
I'm just thinking out aloud, I've not tried any of it.

grim

You guys would laugh like hell at my vacuum rig.

It's basically 2" pipe and triclamp pieces in an upside down U.

The left side was few pipe segments joined together to make about a 3 foot pipe, with the SD element guard kit at the bottom. The top was 2 90' elbows going back down to a 2" PC. Under the PC was a tee with another pipe section at the bottom as the collection vessel. Vac was connected at the tee. I used a HVAC vac pump.

I figured it would be damn near impossible to implode pipe segments, and I had them all laying around anyway. It started with a ... "Huh, I wonder." And before I knew it, it was basically all together.

I even improvised a botanical basket with a 2" TC gasket screen and a little botanical satchel above it.

Ryan

@jacksonbrown said: Exactly but if the pump could handle it... everything down steam of the pump could be atms. Cuts are easy again, no chilling of condensate and it would practically condense itself when returning to pressure. You just need the right pump.

That is interesting. If you can provide a link to a pump like that I would be very interested in seeing it.

I have to imagine that type of pump is not cheap. I did my entire project for less than $3,000. The vacuum pump was less than $200.

I tried the venturi vacuum system with a water pump and and a plastic venturi and achieved 22 in of Hg. Not quite a true vacuum however it's a very cheap method of achieving some level of vacuum.

I think the bottom line is, a vacuum system is very sensitive and very unforgiving. I will need a lot more time and thinking to tune my system in. However as I mentioned in my previous post I am not disappointed that I cannot achieve almost 100% ABV, I'm more excited about the prospect of cold distilling various infusions.

grim

Problem is that the vapor is going to condense IN the pump, and aren't most of these lubricated with prodigious amounts of oil?

You would essentially need a pump that could self-lubricate (seal really, not lubricate) with distillate.

grim

I believe @Telluride confirmed that you can use a peristaltic to extract distillate from the collection vessel of a continuous still without collapsing the tubing or breaking vacuum.

Your condenser can drip right into a reducer and then into a hose-barb and peristaltic. With variable speed you could match the pump speed to take off rate.

Too bad you couldn't pull the requisite vacuum with the peristaltic - then you'd have the magic bullet.

jacksonbrown

@grim said: Problem is that the vapor is going to condense IN the pump

So use that to your advantage. A jacketed, liquid ring pump with a teflon mech seal would probably work.
I've not looked into it at all so I'm clearly talking out my arse but that's the path I would investigate.

Ryan

@grim said: Problem is that the vapor is going to condense IN the pump, and aren't most of these lubricated with prodigious amounts of oil?

Yeah, I made the same concern @jacksonbrown in a previous post.

My solution to the problem of keeping ethanol vapors out of the vacuum pump was to connect the vacuum pump on the product container side and pull the vapors though a condenser prior to the pump suction. It worked well for me. You can see the vacuum pump condenser on top of product tank on the right side of my 3D rendering. It's a simple spiral SS tube that is housed in a cold glycol counter flow. The vapor travels though the SS tube and any vapor that is condensed drips back down into the product condenser prior to reaching the vacuum suction pump tubing.

grim

We invent the craziest shit here

Ryan

Lol.

Ryan

@jacksonbrown said: So use that to your advantage. A jacketed, liquid ring pump with a teflon mech seal would probably work. I've not looked into it at all so I'm clearly talking out my arse but that's the path I would investigate.

At least this give me something to go on.

jacksonbrown

Let us know if you find anything interesting :)>-
The problem is, the price of a product is directly proportional to how bespoke it is.
That pump may solve a heap of other problems and save some money elsewhere but it will cost a shitload extra too.

grim

So are we back to just buying a rotovap?

I think they go as big as 5l.

Single botanical extractions - you could still make a good amount of gin a day.

grim

Or upsize my simple vacu-U design with a 4" boiler and a larger collection tank.

Sightglass would be nice too.

That's predicated on triclamp spool sections being as strong as a purposely designed pressure vessel. And running only neutral spirit for gin distillation.

jacksonbrown

@Ryan said: Once you establish a vacuum theoretically (if your system is "air tight" and has no leaks) you shouldn't have to turn your vacuum pump back on.

That could be where the issue was actually?? Where were you measuring the pressure? Downstream of the condenser?
Could it be that the boiler boiling was producing enough pressure that the az was still there?
If the vapour speed in the column was super high there could be some back pressure so the boiler wasn't actually at vacuum. Was the bp of the boiler where it should have been? Just a thought

richard

Have a look at this YouTube clip:

https://www.youtube.com/watch?v=Vio9M0gkT5w

grim

Yeah don't do that.

grim

Hate you guys, now I've gone and spent a ton of cash on parts for a new vacuum still.

Unsensibel

:))

grim

Screaming deal on the low-temp chiller though, 1/3rd hp and a working temp of -25f.

Vac pump is dry type for solvent extraction- does 7.5 torr max.

Going for room-temperature distillation of azeo.

Fiji_Spirits

Gosh. That's ambitious. Seems like order of magnitudes more robust equipment is needed the cooler you get. I'm forced to wonder the point of diminishing returns.

My gut tells me that point is something like about 120-140f.

Are you gonna be able to use modular triclamp stuff at that vacuum?

Fiji_Spirits

Oh. As a side note. Using the words "authentic" and "bespoke" as primary descriptors with the intention of adding gravity to ones statement of worth, makes my eyes roll back and blood come out my ears and forever brands the speaker as a hipster doofus.