Rotovap questions

bunbun · Oct 2, 2017

Hi all,
New to extracts and have questions about rotovapping. Using a 5L rotovap with 29mm Hg of vacuum, which I thought should be plenty capable to extract ethanol at lower temps, like 40C or less, but it doesn’t seem to pull off ethanol as expected, or takes hours for small batches. Experimenting with higher temps, like 55-65C, and mixture will boil, but still seems little ethanol condenses off, and don’t want to degrade product. It does thicken, but even when it appears finished and nothing else comes off, I swear it still has the smell of ethanol. Even after hours of leaving it. Can rotovaps make final product or does there need to be a final finishing step?

blastfrompast · Oct 2, 2017

I believe most people just use the rotovap to recover the pricey ethanol then finish the purge in a vac oven...

fyi u will need to bump ur temps up a bit with ethanl vs butane when it comes to the finishing step...well at least imho.

BigJohnny · Oct 2, 2017

Set the vac regulator to 60 Torr, temp on the bath to 113F, start rotation to 100rpm and let the bath warm the flask while the vac pulls down.

Onc vac is achieved open the injection port and inject approx. 500ml of solution into the load flask. Once it starts condensing open the injection valve just enough to match the condensation rate. let it run and it should recover at a decent rate.

When it comes to the speed, I tend to try and have it at a speed that's enough to keep the puddle "chasing" the bottom of the flask, so essentially is always running down but never makes it to the bottom.

Gray Wolf · Oct 3, 2017

Here is our test of the Heidolph, which shows parameters:

https://skunkpharmresearch.com/evaluation-of-heidolph-instruments-hei-vap-precision-ml-g3/

Phineas Freak · Oct 3, 2017

How do you get the final product out of the flask? Is it runny enough to just pour. Do you heat? Do you scrape it out?

Just observing.

Gray Wolf · Oct 3, 2017

Phineas Freak said:
How do you get the final product out of the flask? Is it runny enough to just pour. Do you heat? Do you scrape it out?

Just observing.

We either pour early and use the vacuum oven to finish it off, or chase it out of the boiling flask with a heat gun, leaving behind a thin film.

We use alcohol to remove that film and process that once we collect enough for a batch.

Old Gold · Oct 3, 2017

How are you guys dealing with pouring out of 20L and 50L flasks? Seems a little sketchy to pour from unless you have some kind of lab jack that grips the flask and has rotational degrees-of-freedom.

My plan for the 20L I'll be working on soon is to grab some PFA tubing, and literally suck the hot oil out of the flask and into the short path apparatus, using vacuum suction.

For our smaller 2L or 5L loads we are more able to just pour it out hot (100-120C) and dissolve that final film like GW mentioned above.

easystephen · Oct 3, 2017

Old Gold said:
How are you guys dealing with pouring out of 20L and 50L flasks? Seems a little sketchy to pour from unless you have some kind of lab jack that grips the flask and has rotational degrees-of-freedom.

My plan for the 20L I'll be working on soon is to grab some PFA tubing, and literally suck the hot oil out of the flask and into the short path apparatus, using vacuum suction.

For our smaller 2L or 5L loads we are more able to just pour it out hot (100-120C) and dissolve that final film like GW mentioned above.

I built a flask handling cart for pouring out of our 50L evaporating flask. It works quite well and we typically pour off 15kg of crude from the flask into a bucket in one shot. There's a frame on wheels and a square flat surface on top with a hole cut out into which the flask sits. There is a channel cut out to the from the circle to the front so the neck of the flask can fit through when rotating the flask for pouring.

bunbun · Oct 3, 2017

Gray Wolf said:
Here is our test of the Heidolph, which shows parameters:

https://skunkpharmresearch.com/evaluation-of-heidolph-instruments-hei-vap-precision-ml-g3/

Thank you for the link. For some reason the figures and images don't appear, but the write-up was nice.

bunbun · Oct 3, 2017

BigJohnny said:
Set the vac regulator to 60 Torr, temp on the bath to 113F, start rotation to 100rpm and let the bath warm the flask while the vac pulls down.

Onc vac is achieved open the injection port and inject approx. 500ml of solution into the load flask. Once it starts condensing open the injection valve just enough to match the condensation rate. let it run and it should recover at a decent rate.

Will try, thank you. From other comments seems like there will still be residuals that need vac oven or other way to fully purge.

whatthe215 · Oct 4, 2017

Old Gold said:
How are you guys dealing with pouring out of 20L and 50L flasks? Seems a little sketchy to pour from unless you have some kind of lab jack that grips the flask and has rotational degrees-of-freedom.

My plan for the 20L I'll be working on soon is to grab some PFA tubing, and literally suck the hot oil out of the flask and into the short path apparatus, using vacuum suction.

For our smaller 2L or 5L loads we are more able to just pour it out hot (100-120C) and dissolve that final film like GW mentioned above.

I've been removing 50L flasks by hand with 10-20kg of oil a few times per day for a year now. Whoever is steadier and stronger grabs the flask with ov-gloves (grippy heat insulating gloves) and the other person unscrews the seal AND guides the neck back away from the rotovap to ensure it doesn't kick back and crack anything.

Across International has a stand thing that can go into the bath and hold the flask while you unscrew, but now that I'm thinking about it, I think the team and I are more comfortable just doing it by hand.

After sucking the first few kg of oil through your tubing contraption you'll likely switch, I've tried it and it isn't worth it.

In general, and especially if you're using Chinese rotos, keep extra evap flasks on hand just incase. Inspect for hairline or star cracks before putting the flask on every time.

BigJohnny · Oct 4, 2017

bunbun said:
Will try, thank you. From other comments seems like there will still be residuals that need vac oven or other way to fully purge.

I've had stuff come out smelling like it as still full of alcohol, but I've been letting the flask rotate for a while after shutting off the injection valve to let it purge the remaining.

Much of the stuff I pull out now doesnt have that smell and I put it right into the distiller

Old Gold · Oct 4, 2017

whatthe215 said:
After sucking the first few kg of oil through your tubing contraption you'll likely switch, I've tried it and it isn't worth it.

Too messy or too slow?

whatthe215 · Oct 9, 2017

Old Gold said:
Too messy or too slow?

Both. My recommendation for flasks with a large enough opening (China 20L and 50L flasks) is this:

- Buy arm gloves, the kind for inseminating cows and some rubber bands to hold it at shoulder. Have silicone spatulas.

a) Finish rotovaping @ ~60c, kill vac, stop rotation, insert stopping key (so it doesn't rotate when you unscrew,) then let sit for 10-15min so oil can collect from walls and get to temperature 60c.

b) Remove evap flask and pour out as much oil as you can. Let sit upside down for 5-10min dripping into collection container. Use heat gun carefully if desired.

c) Turn evap flask so that you can reach in with arm glove and spatula and scrape out as much as you can. After the first time you'll probably dial in the method. I scrape the top first so I can see inside. Scrape upwards and then pull the oil covered spatula out and deposit into collection container.

** You'll dial in time to wait before starting spatula scraping depending on oil consistency/type. Too early = too hot for your arm and oil will fall right off spatula, too late = very difficult to scrape, more left behind. There's a perfect 5 or 10 min window. **

d) Use minimum amount of ethanol/solvent required to dissolve left over oil in flask. Save it for rainy day, put it in your ultrasonic solvent bath, whatever. Rotovap once you've got enough and need the solvent back. Squirt bottles help. Using arm gloved hand to swish solvent around and rub sides helps tremendously.

Done properly and with fresh arm gloves, I can't imagine a cGMP inspector or whatever having much of an issue with this method, although it may seem a bit ghetto.

Alternatively, throw away the rotovap and get an industrial solvent recycling machine.

Old Gold · Oct 10, 2017

I own grilling gloves (I could buy similar sleeves too), and a pair of PVC gloves that work pretty well for shorter periods of handling. I will probably build a stand on a rectangular furniture dolly to pour from. It seems most logical. I typically pour out at 100C-120C right now, and then use a tiny bit more ethanol to get the last bit out. I'll try the spatula method too, probably much colder like you mentioned.

I've been wanting to R&D some nitrogen-assisted or steam-assisted evaporation. A lot of people seem to finally be building out proper falling film evaporators. That's definitely a better route for big industry.

Thanks for the tips!

SkyHighLer · Oct 10, 2017

whatthe215 said:
Both. My recommendation for flasks with a large enough opening (China 20L and 50L flasks) is this:

- Buy arm gloves, the kind for inseminating cows and some rubber bands to hold it at shoulder. Have silicone spatulas.

a) Finish rotovaping @ ~60c, kill vac, stop rotation, insert stopping key (so it doesn't rotate when you unscrew,) then let sit for 10-15min so oil can collect from walls and get to temperature 60c.

b) Remove evap flask and pour out as much oil as you can. Let sit upside down for 5-10min dripping into collection container. Use heat gun carefully if desired.

c) Turn evap flask so that you can reach in with arm glove and spatula and scrape out as much as you can. After the first time you'll probably dial in the method. I scrape the top first so I can see inside. Scrape upwards and then pull the oil covered spatula out and deposit into collection container.

** You'll dial in time to wait before starting spatula scraping depending on oil consistency/type. Too early = too hot for your arm and oil will fall right off spatula, too late = very difficult to scrape, more left behind. There's a perfect 5 or 10 min window. **

d) Use minimum amount of ethanol/solvent required to dissolve left over oil in flask. Save it for rainy day, put it in your ultrasonic solvent bath, whatever. Rotovap once you've got enough and need the solvent back. Squirt bottles help. Using arm gloved hand to swish solvent around and rub sides helps tremendously.

Done properly and with fresh arm gloves, I can't imagine a cGMP inspector or whatever having much of an issue with this method, although it may seem a bit ghetto.

Alternatively, throw away the rotovap and get an industrial solvent recycling machine.

"Alternatively, throw away the rotovap and get an industrial solvent recycling machine."

There is no reason to use a rotovac to rip solvent when the oil is going to be fractionated.

Rotovacs are extremely dangerous, and extremely expensive, and are invaluable in the lab, where they belong, these are not generally meant for production situations when viable alternatives exist.

Rather than step all the way up to industrial solvent recovery systems, there is a line of common commercial solvent recovery systems that should do nicely, they are referred to as solvent recyclers.

The smallest, 3-5 gallon units are used for such things as automobile paint shop in-house solvent recovery, machine shops, etc.

Much larger sizes, and various options, including vacuum/feed/removal are available.

The smaller units use nylon or Teflon bags, remove the bag, cut a corner, and let it drain, squeegee all but the very the last out.

These units have advanced controls to allow the use of solvents with various boiling points. (The new controllers with both power and temperature control would be better yet, recently I've proven to myself that floating the temperature at the boiling point, and adjusting the boiling level by regulating the power available to the heater is far smoother than trying to control the boiling with PID temperature control alone. This goes for your Buchi and Heidolph rotovapes too, lol.)

BECCA SS17.5 (17.5 Gal) Solvent Distillation Recycler - Features

https://www.youtube.com/watch?v=m8jgVCHO-Gw

BECCA HC (6 Gal) & SC (3 Gal) Solvent Distillation Recycler - Features

https://www.youtube.com/watch?v=_NDX8GghGrk

Sidewinder Model M2 Presentation

https://youtu.be/q-bM74dCZ4k?t=33s

Digital Man · Oct 11, 2017

Just imagine how nice it's gonna be in the near future to go straight from extraction to fractioning ........ and skipping the BS process of winterization entirely.

Goldleaflabs · Oct 12, 2017

A lot of people have been using our reactors for your final solvent purge and degassing. You can use the stirrer to agitate and when it's all done you can drain it out of the bottom.

GNYC · Oct 12, 2017

whatthe215 said:
Both. My recommendation for flasks with a large enough opening (China 20L and 50L flasks) is this:

- Buy arm gloves, the kind for inseminating cows and some rubber bands to hold it at shoulder. Have silicone spatulas.

a) Finish rotovaping @ ~60c, kill vac, stop rotation, insert stopping key (so it doesn't rotate when you unscrew,) then let sit for 10-15min so oil can collect from walls and get to temperature 60c.

b) Remove evap flask and pour out as much oil as you can. Let sit upside down for 5-10min dripping into collection container. Use heat gun carefully if desired.

c) Turn evap flask so that you can reach in with arm glove and spatula and scrape out as much as you can. After the first time you'll probably dial in the method. I scrape the top first so I can see inside. Scrape upwards and then pull the oil covered spatula out and deposit into collection container.

** You'll dial in time to wait before starting spatula scraping depending on oil consistency/type. Too early = too hot for your arm and oil will fall right off spatula, too late = very difficult to scrape, more left behind. There's a perfect 5 or 10 min window. **

d) Use minimum amount of ethanol/solvent required to dissolve left over oil in flask. Save it for rainy day, put it in your ultrasonic solvent bath, whatever. Rotovap once you've got enough and need the solvent back. Squirt bottles help. Using arm gloved hand to swish solvent around and rub sides helps tremendously.

Done properly and with fresh arm gloves, I can't imagine a cGMP inspector or whatever having much of an issue with this method, although it may seem a bit ghetto.

Alternatively, throw away the rotovap and get an industrial solvent recycling machine.

lol with such a large amount we've always just hooked a hose from the fractional to the injection port for the roto and put an extra long injection tube on first inside the ball. then turned on the vac on the fractional and pulled as much as we could via the hose and then rehooked everything back up and went about our jobs. we wouldn't get it all out of the roto and wouldn't worry about it unless we switched strains or parameters of something. then we would do exactly as you listed above.

BlackestofOps · Oct 12, 2017

SkyHighLer said:
"Alternatively, throw away the rotovap and get an industrial solvent recycling machine."

There is no reason to use a rotovac to rip solvent when the oil is going to be fractionated.

Rotovacs are extremely dangerous, and extremely expensive, and are invaluable in the lab, where they belong, these are not generally meant for production situations when viable alternatives exist.

Rather than step all the way up to industrial solvent recovery systems, there is a line of common commercial solvent recovery systems that should do nicely, they are referred to as solvent recyclers.

The smallest, 3-5 gallon units are used for such things as automobile paint shop in-house solvent recovery, machine shops, etc.

Much larger sizes, and various options, including vacuum/feed/removal are available.

The smaller units use nylon or Teflon bags, remove the bag, cut a corner, and let it drain, squeegee all but the very the last out.

These units have advanced controls to allow the use of solvents with various boiling points. (The new controllers with both power and temperature control would be better yet, recently I've proven to myself that floating the temperature at the boiling point, and adjusting the boiling level by regulating the power available to the heater is far smoother than trying to control the boiling with PID temperature control alone. This goes for your Buchi and Heidolph rotovapes too, lol.)

BECCA SS17.5 (17.5 Gal) Solvent Distillation Recycler - Features

https://www.youtube.com/watch?v=m8jgVCHO-Gw

BECCA HC (6 Gal) & SC (3 Gal) Solvent Distillation Recycler - Features

https://www.youtube.com/watch?v=_NDX8GghGrk

Sidewinder Model M2 Presentation

https://youtu.be/q-bM74dCZ4k?t=33s

Has anyone used one of these solvent recyclers? I am worried that without rotation or agitation with vacuum, that oil could become over-decarboxylated.

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