Optimizing your RotoVap


The problem with fully removing solvent in a 20L+ rotovap is getting it out all out of the boiling flask in a timely manner.

One solution that works is replacing the glass boiling flask for a 12 inch stainless steel spool, reducer and custom flange allowing for the removal of the bottom cap but this requires custom fabrication and will put more stress on your rotovap’s motor and you can no longer see the flask bump, however if you know what your doing and have good vacuum it speeds things up considerably


better heat transfer too. :thinking: if only there was a way to see in there

although if the bump is that high you’re probably in trouble anyway.


I like the durability and my staff can live without seeing the reaction, if it bumps its too late BUT sadly the limiting factor is of course the condenser temp and surface area. Add’s up to about an hour saved on a run using a China 50L roto (toption)

I would imagine most folks batches that are going to SPD will be pulled out of the roto at about 80-90% reduced solvent and then finish purge in their SPD boiling flask before VOC & Head fractions ?


Depending on which roto you have, you can reprogram the interface to allow the heating elements to exceed the 100°C cap (I set all mine to 200°C). Then simply replace the water with some clear silicone oil ( @beakerandwrench sell the good stuff hit up @Lilibel )
An important tidbit if you go through with this - slow down your RPM’s to 40-60 when your temps are in excess of 100°C or you will have hot fucking oil everywhere, not fun :joy::tired_face: - or if you have an Across 20L they apparently sell the poly domes for them now but proceed with caution regardless. I was setting my bath temp to 200°C and although the elements struggled along, temps eventually hit 140°C and I adjusted the PID accordingly. The vac pump was able to get the system down to about 13 torr with zero bubbles in the flask when stationary… so we were pretty confident the decarb was a success.
Oh and also, it’s a good idea to invest in that rotating flask holder, and some durable heat resistant gloves… And keep some aquaphor around :grimacing:

Edit: we had such a blast with this mod, bought a few more 20L rotating flasks and we started doing carbon scrubs and enzyme incubation in the rotos as well. The absence of oxygen during these procedures does wonders for anti-degradation while under heat.


Thanks for the shoutout; yes we sell good heating fluid in the shop.
Definitely reduce the RPMs if you’re going this route or get the splash guard!!!
I always wanted to experiment with this; I used a kugelrohr in the past and it got me thinking about a hot bath for rotovap…


What do you run your vac at


I remove crude with no remaining solvent from 6x 50L rotovaps every day or two depending on production. If you’re fully removing the evaporation flask to empty you’re causing a lot of unnecessary work for yourself and (IMO) risking breakage on an expensive piece of glass that can shut down your production. And if you have to let it cool down enough to make it safe for a human to handle, your crude is no longer going to be at an optimal temp to flow very well.

If you’re going to fab something out of stainless, make yourself a slurp tank with a flexible hose to pull your crude out at 65+*C.


I’ve been decarbing in the roto for years it’s rhe only way to do it, the moment I see the squiggles comin into my etho I dump it to keep them anything after that I just use to clean glass I don’t want to keep compounding terps in my etho. That usually is around 75-85c as soon as that happens I turn my temp to 145c and by the time it reaches that temp it’s done decarbing and you strip a lot of volitales as a bonus.


im guessing you’re using silicone oil or some liquid that goes past 100c? Boiling water does not raise the temperature beyond 100c until all the water has vaporized. I am about to switch over to dimethicone 1000 cst to get the bath past 100c the stuff is 55 bucks per gallon https://www.ebay.com/itm/100-Pure-Silicone-Oil-Dimethicone-Liquid-Fluid-1000-cst-1oz-64oz-ounce/232381726298


I use duratherm s it’s a silicone oil same same transfer fluid I use in the wipes film. I’ll check that stuff out, duratherm’s prices have gone way up but I’ve been using the same 5 gallons for years. There’s no degradation at those high temps like a lot of the heat transfer fluids


im not sure how much duratherm costs but the dimethicone above is not lab grade i dont think. i dont really care though. i cant afford the good stuff lol.


It use to be about 50 a gallon and they would sell to you even if you weren’t a company, it’s the same stuff beaker and wrench sell for 300 a gallon. Check out dynalene, and like I said the duratherm lasts for years so depending on how much you need just a get a gallon or 2


ok the 1000 cst stuff is far to viscous. you want the 5-20 cst silicone oil for heating bath. the 5cst stuff has a flash point of 135c the 20cst stuff is 232c



How are you removing the crude from the 50L flasks?


I built a slurp cart out of a modified cone bottom brewing tank, vacuum pump and a harbor freight furniture moving dolly. Use a piece of 3/8" ID 1/2" OD poly tubing to go down into the evaporation flask once the crude has cooled to around 65-75*C. I added sight glasses so I can see how full it is and legs to lift up the brewing tank so I can stick a 5 gal bucket underneath it for when I’m emptying it.


Is the crude fairly viscous at this temperature? Are you able to get the majority of the material out?


At 70+*C I’d estimate that decarbed, winterized crude flows similarly to 30wt motor oil at room temp. I’ve never bothered to weight it but I estimate that I leave behind 2-3 grams at the bottom of the evaporation flask but I don’t consider that a big deal when I’m pulling multiple liters of crude out of every roto, after the first run the amount that is left behind is equal to the amount that is in the flask when I start doing solvent recovery on the next batch.


Think I might try this and compare it to running the dry ice condenser


Do you have a chiller option to run cold fluid through there?

If not.

Get ahold of one of those pumps I’ve mentioned. Eco 633. They are magnetic driven pumps and temps and cold alcohol won’t phase it.

Get a large rectangle cooler and a really tall spaghetti pot. Put the pump in the pot connect line to bottom port, top going back to the spaghetti pot. Cut holes so the lid can go back on. I used a plastic home depot lid. Fill the pot and let it run to fill the coil and bury the pump a few inches.

In the large cooler with the pot in it. Make a dry ice slurry and keep mashing it in and topping it off. It can get beyond - 50. But since you are doing recovery it’ll keep fighting back and you’ll have to keep on the cooler. But, that’d work if you are in a pinch. Don’t let dry ice get into the spaghetti pot and create a boil. The chunk and bubbles will mess the pump up. So will ice if it got in there.


I’ve was planning on just using well water or a 5g bucket, making some 1L ice molds to throw in to keep the temp below 40f or using my cryocool immersion chiller. I think this Aldrich super condenser although small will recover more etoh then the Dewar setup. But who knows.