Rotary Evaporators

MEMED said:

cheers guys. Hey gholla, are u and squattingbull partners? Just curious. Im surprised yall dont already have this on lock with your situation and all. Its maaaad important to know whats up when your at the level your playing on gholla. Get a clue, or get swallowed up! Word from the wise, no offence.

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MEMED,

Yeah squattingbull is my roommate and our team biologist/chemistry guru. I do the mechanical stuff. We were both pretty sure about the answer, and had assumed the correct thing, but wanted to know for sure. And you're totally right, which is why we asked before we dropped any cash on a rotovap

We're learning all the time!

GH

gholladay said:

MEMED,

Yeah squattingbull is my roommate and our team biologist/chemistry guru. I do the mechanical stuff. We were both pretty sure about the answer, and had assumed the correct thing, but wanted to know for sure. And you're totally right, which is why we asked before we dropped any cash on a rotovap

We're learning all the time!

GH

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^^What he said. We stay on the grind in hopes of expanding our knowledge and experience base every day. Thanks for the help and the advice. Our knowledge has pretty much always outstripped our build timeline but we are trying to catch up as best we can! Best to think twice and purchase once.

whatevs, like I said, no disrespect, just curious. I can appreciate your perspectives. For me its always been buy first learn later. Im a hands on learner. Ive got a huge stockpile of carp tho...lol.... Awesome guys, good luck.

I'm posting this up here also as I'm just about certain it should work, and if so, is actually better than a rotovap in that it's not using delicate expensive glassware, it has no rotating vacuum connections, an expensive heavy duty motor isn't required, there's no water bath hassle, you don't need a lifting mechanism, and on and on as it's just so simple.

Here's my idea,

Your going to place your solvent/oil solution directly into a suspended heated stock pot vacuum chamber, and 'swing it' so the bottom tilts as it goes about it's arc. You'll also need a separate cold trap and solvent rated pump, like a Welch.

Just too easy huh?

My underground chemist design,

You'd start with a standard commercial stock pot vacuum chamber with a silicone heater with PID controller on the bottom, like this,
http://www.amazon.com/HeatVac-Kettl...8176870&sr=8-1&keywords=vacuum+chamber+heater

Best Value Vacs also sells silicone heaters with PID controllers like the above.

That may work alone as a test, but the way to do this properly is to also use a silicone heater with it's own PID controller wrapped around the lower area of the stock pot. You are creating a high quality heating mantle around the bottom of the pot so it would be worth the time and expense to order a custom band heater, just contact Keenovo at eBay.

You can suspend it by the handles, a cord coming up from each side of the handles with the four of them connected to a common suspension cord. The vacuum hose should keep the pot from rotating.

To swing it, place a record player under it. A short upright rod (bolt sticking up? lol) is mounted to the platter, how far out from the center of the platter it's located is going to be a major variable in dialing in performance, so it's location should be adjustable. The upright rod connects/floats in a small inverted 'cup' mounted to the center bottom of the heater. The 'cup' can be any small goomatchie with a hole in it that's easily attached to the bottom of the mat. Most old record players have multiple speeds, if you get a really old one without a speed lock motor you can further adjust the speed with a Variac.

I picked up my five gallon chamber and imitated the tilting swish, and I can't imagine this not working.

If anyone with the talent and skills could provide a sketch, I'd love it!

I definitely like the idea of eliminating the glassware especially from the perspective of using something that doesn't have a narrow neck or has a way to get it out other than trying to pour it through the tiny opening on a standard rotovape. We kicked around the idea for a while to try and find a lampworker who could make one where the top of the flask could come off and you could actually take the oil down to almost zero solvent and still get it out and then scrape whats left. But as you said back to the expensive and very breakable glassware.

Are you trying to have the basic pivot around a central point or more of an occilatory back and forth? Just trying to get an image of what you have in mind. My lab partner gholladay is an CAD machine if you get it to the point you want some drawings made he may be able to help you out. I like the idea in general though. The rotovape is a great tool clearly, but it would be nice to have something more industry specific that was easier to work with oil in that final more viscous state. Good thoughts and thanks for sharing.

SquattingBull said:

I definitely like the idea of eliminating the glassware especially from the perspective of using something that doesn't have a narrow neck or has a way to get it out other than trying to pour it through the tiny opening on a standard rotovape. We kicked around the idea for a while to try and find a lampworker who could make one where the top of the flask could come off and you could actually take the oil down to almost zero solvent and still get it out and then scrape whats left. But as you said back to the expensive and very breakable glassware.

Are you trying to have the basic pivot around a central point or more of an occilatory back and forth? Just trying to get an image of what you have in mind. My lab partner gholladay is an CAD machine if you get it to the point you want some drawings made he may be able to help you out. I like the idea in general though. The rotovape is a great tool clearly, but it would be nice to have something more industry specific that was easier to work with oil in that final more viscous state. Good thoughts and thanks for sharing.

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I wrote and rewrote the wording, that's a working description, the center of the bottom of stock pot is moved around in a circle by the post sticking up from the old phonograph turntable. If the support cords meet up, and are attached at a single point to whatever's going to be supporting everything up near the top of the pot (within a foot or so,) as the pot goes around the tilt will be enough to slosh the solvent/oil solution far up the walls if you choose to run it at slow speed.

This shouldn't take much design evolution, you should get a working model first try even if it's jerry rigged.

Best, thanks!

SquattingBull said:

Is it possible to run a rotovape at a low enough temperature to make dabable absolutes or is the temperature so low it wouldn't allow for evaporation to occur in the first place?

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If you use vacuum you can pull off the solvent at relatively low temperatures.

I definitely like the idea of eliminating the glassware especially from the perspective of using something that doesn't have a narrow neck or has a way to get it out other than trying to pour it through the tiny opening on a standard rotovape. We kicked around the idea for a while to try and find a lampworker who could make one where the top of the flask could come off and you could actually take the oil down to almost zero solvent and still get it out and then scrape whats left. But as you said back to the expensive and very breakable glassware.

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Why bother? At 120F the oil is still very liquid and the residual in the flask is minimal. Unless you are running very small batches the losses are tiny. For that matter, if you need to recover every drop, after puring the oil out add a ml. or two of alcohol to the flask and let it rotate in the bath for a few. Pour that out onto a separate dish and let the alcohol boil off to atmosphere with a bit of heat.

The added expense of custom flasks won't be worth it. You also don't want something with a clamp on the joint that's going to fling water from the bath EVERYWHERE...

Just to add my two cents about buying quality. One of the rotovaps I have is a thirty year old Buchi unit. Brand new condensers and glassware still fit and I'll be able to get seals and glass to fit for another decade at least. Used Buchi stuff is plentiful as well.

Two other points:
-Concentricity of the vapor tube. Any runout will cause the seal to leak and vacuum operation will be almost impossible.
-Tapered joints: Accuracy and the type of ground finish are critical to getting flasks off easily. The accuracy of those joints is also critical to a good vacuum seal.

Peace, RB

SquattingBull said:

I definitely like the idea of eliminating the glassware especially from the perspective of using something that doesn't have a narrow neck or has a way to get it out other than trying to pour it through the tiny opening on a standard rotovape. We kicked around the idea for a while to try and find a lampworker who could make one where the top of the flask could come off and you could actually take the oil down to almost zero solvent and still get it out and then scrape whats left. But as you said back to the expensive and very breakable glassware.

Are you trying to have the basic pivot around a central point or more of an occilatory back and forth? Just trying to get an image of what you have in mind. My lab partner gholladay is an CAD machine if you get it to the point you want some drawings made he may be able to help you out. I like the idea in general though. The rotovape is a great tool clearly, but it would be nice to have something more industry specific that was easier to work with oil in that final more viscous state. Good thoughts and thanks for sharing.

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The rotary evaporator works by drawing the liquid into a thin film up the side wall as it rotates, exposing greater surface area to the heat and vacuum.

Evaporating solvents like ethanol can result in heavy bumping, so attention needs to be given to controlling the bumping or shielding the vacuum intake.

On a drum style evaporator, the outer wrapper is what would need to be heated, as opposed to the bottom.

Siskiyou Sam and I got our vacuum unions from Deublin, but not sure where he picked up his electrical slip ring. I gave him connections for a combined rotary vacuum union and slip ring, but neither of us ever got an answer from the German firm.

http://www.deublin.com/products/rotating-unions/

You will note at http://skunkpharmresearch.com/rotary-evaporator-from-siskiyou-sam/, that SS dumped his by folding down the front drum roller support, which allow the drum to tilt downward and drain.

Rickys bong said:

If you use vacuum you can pull off the solvent at relatively low temperatures.



Why bother? At 120F the oil is still very liquid and the residual in the flask is minimal. Unless you are running very small batches the losses are tiny. For that matter, if you need to recover every drop, after puring the oil out add a ml. or two of alcohol to the flask and let it rotate in the bath for a few. Pour that out onto a separate dish and let the alcohol boil off to atmosphere with a bit of heat.

The added expense of custom flasks won't be worth it. You also don't want something with a clamp on the joint that's going to fling water from the bath EVERYWHERE...

Just to add my two cents about buying quality. One of the rotovaps I have is a thirty year old Buchi unit. Brand new condensers and glassware still fit and I'll be able to get seals and glass to fit for another decade at least. Used Buchi stuff is plentiful as well.

Two other points:
-Concentricity of the vapor tube. Any runout will cause the seal to leak and vacuum operation will be almost impossible.
-Tapered joints: Accuracy and the type of ground finish are critical to getting flasks off easily. The accuracy of those joints is also critical to a good vacuum seal.

Peace, RB

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Thank for the input and to be frank I agree with you on every front which is why we are already getting rotovapes but I think Sky has some good points and I am always open to expanding the way I think about it. The reason we never looked into custom flasks is exactly what you just described. Also, the Buchi experience you described is exactly why that is one of the two companies we have been shopping with for our new equipment as I have heard many great things about being able to replace parts even on much older machines that still work great. I appreciate your input though it just reaffirms our next purchase thank you brother.

Gray Wolf said:

The rotary evaporator works by drawing the liquid into a thin film up the side wall as it rotates, exposing greater surface area to the heat and vacuum.

Evaporating solvents like ethanol can result in heavy bumping, so attention needs to be given to controlling the bumping or shielding the vacuum intake.

On a drum style evaporator, the outer wrapper is what would need to be heated, as opposed to the bottom.

Siskiyou Sam and I got our vacuum unions from Deublin, but not sure where he picked up his electrical slip ring. I gave him connections for a combined rotary vacuum union and slip ring, but neither of us ever got an answer from the German firm.

http://www.deublin.com/products/rotating-unions/

You will note at http://skunkpharmresearch.com/rotary-evaporator-from-siskiyou-sam/, that SS dumped his by folding down the front drum roller support, which allow the drum to tilt downward and drain.

Click to expand...

I didn't think about the bumping aspect GW that is very valid. As much as I would love to build something that I felt like could do as well if not better than a roto it is factors like that that make me feel like the juice may not be worth the squeeze. I still like the idea of a drum evaporator like the DIY build yall posted on SPR and that may be a project we decide to undertake in the future but given the relatively short timeline we are working with for needing at least one or two almost immediately we are probably going to have to go with a tried and true to get us started in that realm. Thanks as always for your guidance.

Gray Wolf said:

The rotary evaporator works by drawing the liquid into a thin film up the side wall as it rotates, exposing greater surface area to the heat and vacuum.

And my so would mine, the stock pot tilts, and the tilt point moves around three hundred and sixty degrees, creating a constantly refreshed thin film along the inner wall of the chamber.

Evaporating solvents like ethanol can result in heavy bumping, so attention needs to be given to controlling the bumping or shielding the vacuum intake.

There's not much room in a one or two liter flask so you have little room in a rotovap if the solution foams up, but in a five gallon stock pot with the vac port way up at the top, there's several times the amount of room for expansion.

On a drum style evaporator, the outer wrapper is what would need to be heated, as opposed to the bottom.

If your referring to the design I offered, I said to use a silicone heater on the bottom, and a wrap around silicone heater on the lower wall.

Siskiyou Sam and I got our vacuum unions from Deublin, but not sure where he picked up his electrical slip ring. I gave him connections for a combined rotary vacuum union and slip ring, but neither of us ever got an answer from the German firm.

http://www.deublin.com/products/rotating-unions/

You will note at http://skunkpharmresearch.com/rotary-evaporator-from-siskiyou-sam/, that SS dumped his by folding down the front drum roller support, which allow the drum to tilt downward and drain.

With my idea you'd just come off vac, remove the polycarbonate lid, detach from the supporting cords or chains, and pour out.

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Further, you could put a spigot at the bottom, and a feed port in the lid, and run it continuously under vacuum, try doing that with a Buchi or Heidolph.

Further, you could put a spigot at the bottom, and a feed port in the lid, and run it continuously under vacuum, try doing that with a Buchi or Heidolph.

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The buchi I have used had a feed port for continuous operation without removing the flask. How does a spigot at the bottom work under vacuum, wouldn't you be sucking in atmosphere when it was opened?

flatslabs said:

The buchi I have used had a feed port for continuous operation without removing the flask. How does a spigot at the bottom work under vacuum, wouldn't you be sucking in atmosphere when it was opened?

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Vacuum line on the otherwise sealed receiving container. Slightly back off the vacuum in the chamber during transfer.

I've already tried a manual test of the action, try it for yourself with some liquid in broad bottom pot.

https://laboregon.wordpress.com/2014/08/29/rotovap-maximus/
Slip Ring for the the Rotovape Maximus was from Keyo Electric Co LTD in China.

Siskiyou Sam said:

https://laboregon.wordpress.com/2014/08/29/rotovap-maximus/
Slip Ring for the the Rotovape Maximus was from Keyo Electric Co LTD in China.

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Welcome to the party Sam Didn't know you had a blog ... anyways, how well does it work?

Siskiyou Sam said:

https://laboregon.wordpress.com/2014/08/29/rotovap-maximus/
Slip Ring for the the Rotovape Maximus was from Keyo Electric Co LTD in China.

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Ive wondered the same question about its efficiency compared to a stock roto. Regardless I have seen that build before and was impressed every time. Nice work regardless.

I totally agree Sam's device is kicker, just way too much work if there's a simpler way.

SkyHighLer said:

I wrote and rewrote the wording, that's a working description, the center of the bottom of stock pot is moved around in a circle by the post sticking up from the old phonograph turntable. If the support cords meet up, and are attached at a single point to whatever's going to be supporting everything up near the top of the pot (within a foot or so,) as the pot goes around the tilt will be enough to slosh the solvent/oil solution far up the walls if you choose to run it at slow speed.

This shouldn't take much design evolution, you should get a working model first try even if it's jerry rigged.

Best, thanks!

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Pictures of the test I just did to test my own hypothesis of the action. One liter of water was used. To make it climb the walls I had to do a tight high speed swish. A nice and slow (15-60rpm) wide arc (12" center to center) keeps most of the volume of liquid to one side as it moves around. Might be interesting to try just the bottom heater first with slow wide action.

SkyHighLer said:

Further, you could put a spigot at the bottom, and a feed port in the lid, and run it continuously under vacuum, try doing that with a Buchi or Heidolph.

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Meyers spins a disc to create a thin film.

Eden Labs makes a system that uses a 3/4" magnetic stir bar in a large round bottom glass chamber, to create the thin film. They originally offered it for ethanol reclaim, but are now using it as a molecular still.

Other alternatives to spinning the pot vertically or rotating it on its side.?

Siskiyou Sam said:

https://laboregon.wordpress.com/2014/08/29/rotovap-maximus/
Slip Ring for the the Rotovape Maximus was from Keyo Electric Co LTD in China.

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Thanks for joining the party SS!