[d_block]

My work has recently acquired a 50 L rotovap and I had a few questions regarding its operation. Since it is such a large rotovap the vacuum pump we got to run it is pretty powerful. This also means its pretty expensive to continually have turned on. My boss wants to get the system to a pressure deemed suitable and then close the system and turn off the pump. I think this is a bad idea and goes against everything I learned as an undergrad. We both understand that doing his idea will increase the pressure and could possibly lead to explosion, but he thinks that since the system had already been evacuated and is rather large this might not be a problem.

So, I guess ultimately I am asking if a rotovap can be operated this way safely and effectively or is it just a reality that the vacuum pump must be running if the rotovap is in operation?

[wildfyr]

It won't hurt anything, it just wont work. Unless the system is sealed supremely well within a few minutes or hours it will be back at 1 atmosphere.

I don't see where there is an explosion risk?

[d_block]

I guess I was just told to never heat a closed system because it could lead to explosion. Since the system is really large it does seem unlikely to happen though.

Ya, ok that makes sense. Thank you for your response

[wildfyr]

Oh, well heating it with something in it would certainly be bad. And if air is leaking in while youre heating... well that is heating "something."

[Corribus]

As wildfyr mentioned, maintaining vacuum without the pump on will be your biggest problem. Rotovaps have lots of leaky joints and are designed to be run with the vacuum source left continually on. Even with the pump running it's hard to maintain a really low vacuum on a rotovap. Even a less leaky vacuum distillation system is typically run open to the pump.

I don't see much of an explosion hazard. You're not going to be taking anything to real temperature extremes and the leakiness again will save you. At worst, you'll cause a joint to fail (flask popping off - mess but no shrapnel). Chemical glassware is designed to withstand reasonable changes in pressure. Nevertheless: you are right, heating a closed system is best avoided as a general rule unless you absolutely need to do it and are using glassware specifically designed for it (e.g., air sensitive reactions done under nitrogen).