In rotary evaporation, as in a lot of other things happening in your lab, time is of the essence. Maybe you need those APIs purified ASAP, or maybe your clients needed that ethanol removed from the cannabis they sent you yesterday. Bottom line is a rotary evaporator can only spin so fast, but we got your back. In today’s blog post we’ll give you a few tips and tricks to speed up your rotary evaporation process.
Increase your Vessel Size
It might sound counterintuitive to use a vessel that is considerably larger than your sample size. However, increasing your vessel size is the way to go if you’re aiming for a more efficient process. A larger vessel means an increased surface area, which means that a bigger portion of your flask will be in contact with the water in the water bath, which paves the way for a quicker and more even heating process. At the same time, using a large vessel also means that the sample inside of the flask is exposed to more air, making evaporation more efficient!
Increase your Vacuum Level
As discussed in one of our previous blog posts, using a controllable vacuum source gives you the luxury of adjusting the pressure with surgical pressure, thus providing you with your desired evaporation rate. Variating the pressure (increasing it to be more specific), will decrease the pressure, and thus make your process faster. And while this is generally true, you need to avoid a few pitfalls, like bumping and foaming. A sharp decrease in pressure can also lead to a hasty evaporation, not allowing the solvent to evaporate properly. The uncondensed vapor might end up inside of the vacuum pump, which is undesirable to say the least. Oh, and did we mention that sharp drops of pressure in your flask might make it implode?
Increase your Bath Temperature
This one’s pretty straightforward: a higher bath temperature means a higher rate of evaporation, and a more efficient process. Just make sure that your sample can handle an increased temperature without any side reactions occurring, do your best to avoid bumping, and follow the rule of 20 to avoid too much solvent vapor formation.
Increase your Rotation Speed
Last but not least, increasing the rotation speed of your evaporation flask. To better understand how this works, we need to take a closer look at the two main functions achieved by rotating the flask: It improves the heat transfer from the water bath to the solvent and the flask, and it increases the evaporation rate by increasing the surface area of the liquid inside of the flask. However, reaching too high of a speed can lead to the sample being pressed against the sides of the flask, thus greatly reducing the efficiency of the process. You want to aim for 250-280 rpm to reach optimal turbulence.