I am using the rotary evaporator to evaporate n-hexane, I used 250ml of hexane and I am evaporating it at 40-45°C. How long will it approximately take?
Marah,
You will require a few more details to do the calculation - the surface area, initial mass of n-hexane and air velocity. You can calculate the convective mass transfer coefficient using the appropriate Sherwood number correlation. Based on this, the convective mass transfer rate and the time of vaporization can be found. This approach involves a few simplifying assumptions and hence the answer will be approximate.
Dear Marah Al Taher just in case that this question is still of interest to you: The boiling point of n-hexane at normal pressure is 69 °C. Thus evaporation using a rotary evaporator at 40-45 °C under vacuum will be rather rapid. I would have estimated 15-20 minutes for evaporating 250 ml. What was your experience? For such a process there is no need to make lengthy calculations. Much better is to just try it out experimentally. For future work you can also try n-pentane instead of n-hexane. It has an even lower boiling point (36 °C at normal pressure) and is less toxic than n-hexane.
Good luck with your research and best wishes!
with a bath temperature of 45 °C and a vacuum of about 200 mbar, you can distill hexane with a rate of about 6 liter/hour on a benchtop rotary evaporator (e.g from Buchi). So your 250 ml will be distilled in about 5 minutes. factors that influence the performance are mainly flask size and rotation speed. larger flask and higher speed will increase the performance.
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