Rotary Vacuum Solvent Recovery Problem

[soxthefox]

Hey, I'm having a problem isolating a plant extract out of methanol. The solution is about 15% extract by mass. My institute has a rotary vacuum evaporator, however, I have been attempting to use this to no avail and no one here is especially experienced with the apparatus. I really don't know what the problem could be - here's my trouble shooting thus far:

 

• vacuum pressure on the system is 10inhg;
• none or very minimal leaks;
• water bath temp first attempted at 60C won't even evaporate off at 90C;
• tried different speeds of rotations;
• condensor is running.

 

Yesterday it started working for a small period of time, but then I realized that the rotating flask was loose. Once I firmly reattached the methanol stopped evaporating into the condensor. Please help I've tried several other recovery techniques all of which have burned or ruined my extract.

 

 

[Maximilian]

Are you sure you added methanol? Try evaporating a pure methanol solution and see what happens.

[soxthefox]

Hey still looking for any help on this final step in my extraction procedure. I've been carrying out the other steps and now just have a lot of methanolic and ethanolic extract waiting to be isolated.

 

2 interesting things I've noticed that might be of help.

 

1) when I increase pressure to above 20inHg the solvent starts to appear in the condensor. this may be a solution to my problem, but the vacuum that I am using is very finicky at this pressure and oscilates between extremely high negative pressure or reverts back to around 10inHg. Is 20inHg an acceptable pressure for a system such as this or am I forcing something that shouldn't be forced?

 

2)when I disconnect the flask with containing the extract forcing a leak between the condensor and the flask the solvent will start evaporating. I don't really know why this is.

 

(and yes I made sure it was methanol and ethanol by weighing the solvents before adding them. Good thought though I wouldn't put it past me.)