The rotary evaporator (rotovap) rarely appears outside of well-provisioned chemistry labs. That means that despite being a fundamentally simple device, their cost generally puts them out of reach for amateur chemists. Nevertheless, they make it much more convenient to remove a solvent from a solution, so [Markus Bindhammer] designed and built his own.
Rotary evaporators have two flasks, one containing the solution to be evaporated, and one that collects the condensed solvent vapors. A rotary joint holds the evaporating flask partially immersed in a heated oil bath and connects the flask’s neck to a fixed vapor duct. Solvent vapors leave the first flask, travel through the duct, condense in a condenser, and collect in the second flask. A motor rotates the first flask, which spreads a thin layer of the solution across the flask walls, increasing the surface area and causing the liquid to evaporate more quickly.
Possibly the trickiest part of the apparatus is the rotary joint, which in [Markus]’s implementation is made of a ground-glass joint adapter surrounded by a 3D-printed gear adapter and two ball bearings. A Teflon stopper fits into one end of the adapter, the evaporation flask clips onto the other end, and a glass tube runs through the stopper. The ball bearings allow the adapter to rotate within a frame, the gear enables a motor to drive it, the Teflon stopper serves as a lubricated seal, and the non-rotating glass tube directs the solvent vapors into the condenser.
The flasks, condenser, and adapters were relatively inexpensive commercial glassware, and the frame that held them in place was primarily made of aluminium extrusion, with a few other pieces of miscellaneous hardware. In [Markus]’s test, the rotovap had no trouble evaporating isopropyl alcohol from one flask to the other.
This isn’t [Markus]’s first time turning a complex piece of scientific equipment into an amateur-accessible project, or, for that matter, making simpler equipment. He’s also taken on several major industrial chemistry processes.
Since a lot of the complexity is in the rotary seal would it not be possible to simplify the apparatus by connecting the vessel to a flexible tube that is wound in the manner of a clockspring. The motor could then repeatedly turn the vessel 720 degrees (for instance) clockwise and then 720 degree couter clockwise whilst maintaining a completely airtight seal.
The vessel is rotated to cover its inside with the liquid. If you dont want rotary joint, why not make the liquid rotate instead?
By swirling the bottom vessel like a wisky glass?
This may generate a wave in the heater bath but dampers in the heat bath may keep it under control.
That could work. But swirling the glass to spread the liquid would require more rapid motion than a typical rotovap. Shaking the glassware like that is an invitation for loosening seals. (or bashing into something if it isn’t positioned right at the start. I can imagine doing that myself.)
This is how the commercial device that I have used worked. There is a pool of heated water with a spinning agitator at the bottom. The vessel that holds to liquid to be distilled is stationary. and the the various glassware was assembled above the stationary vessel.
This is much simpler in my opinion but I honestly don’t know enough about rotatory evaporation to say if the two processes would produce the same result. I think it should but I am not an expert in this.
Maybe. But usually vacuum tubes are rather stiff. But in this case it is not a very high vacuum,it should work.
They don’t have to be stiff, honestly. Most vacuum equipment is overbuilt. I’ve pulled a vacuum on soft rubber tubing before and it was fine.
The rate of evaporation/distillation depends on temperature, surface area, vapor path distance and cross section, temperature of cold distillate container, and vacuum pressure. Anything you can do to favor molecular transfer will speed up the process.