Here is our procedure:
PROCEDURE
In this experiment, the rotary evaporator is being used to distill ethanol out of winterized, filtered butane hash oil (BHO).
1. Add 500 ml of BHO/ethanol mixture to the evaporating flask. Note that greater volumes may be appropriate in situations where a larger flask is used but care should be taken as to avoid filling the flask over half full.
2. Lock the flask into place on the rotary valve and lower the unit into the warming bath.
3. Set the temperature of the bath to 25ºC.
4. Set the rotation of the flask at 160 rpm. Note that faster speeds may be achievable in a larger flask but operators noticed that higher rotational speeds in the 1 L flask resulted in excessive bumping.
5. Set the initial vacuum level to 80 mbar to begin the process. Increase the vacuum over the course of the distillation as follows.
a. 0-1 min: Pull down for atmospheric pressure to 80 mbar.
b. 1-5 min: Hold at 80 mbar.
c. 5-10 min: Reduce pressure to 60 mbar, hold. At 10 min, about 50 ml of ethanol should have been reclaimed.
d. 10-15 min: Reduce pressure 40 mbar, hold. At 15 min, about 100 ml of ethanol should have been reclaimed.
e. 15-45 min. Reduce pressure to 20 mbar, hold. Vacuum does not exceed 20 mbar but will remain on constantly at this point. At 45 min, about 450 ml of ethanol should have been reclaimed. Note that it is important to leave some ethanol behind so as to be able to easily remove the remaining material from the evaporation flask.
f. The material is collected, spread on PTFE sheets, and placed in the vacuum oven to complete final purge.
RESULTS
Once a pressure of 20 mbar has been achieved, ethanol is recovered at a rate of 11.6 ml/min. This can vary slightly due to the density of the product ie. Ratio of BHO to ethanol. Faster distillation rates are achievable at higher temperatures but more supervision is required to minimize bumping. Furthermore, qualitative evaluations suggest that higher operational temperatures resulted in a somewhat degraded final product. Cold temperature distillations are possible as well but result in increased distillation time and no noticeable improvement in final product.
The unit is easy to clean and dismantle but it can be difficult to remove all of the material once distillation is complete. This is an issue that all rotary evaporators have however and it should not be held against this piece of equipment in particular. As a result, it is up to the operator to make sure that the consistency of the final product is appropriate for their final purpose.
Manually refilling the collection task is easy but somewhat time consuming as the operator has to take care to bring the vacuum down slowly when starting a new batch. Continuous operation is possible with additional equipment and is most likely the missing piece in terms of integrating this equipment into a production setting.
What are your thoughts on lower vacuum levels as it pertains to the bulk removal of ethanol? Does it provide more stability (equilibrium?) within the apparatus or just lower the boiling point even further? I ask because I typically use a cheap HVAC vacuum pump instead of my Varian with the following setup:
2L heating/stirring mantle -> 2L 24/40 2-neck boiling flask (-> all glass thermowell) -> 200mm vigreux column -> 3-way 75 degree head (-> glass stopper) -> 200mm Dimroth condenser -> Friedrichs condenser -> Straight vacuum take-off adapter (-> cold trap -> vacuum pump) -> 2L boiling flask (in insulated sleeve with dry ice)
When I keep the boiling flask filled between 50-25% (and monitor heat and stir settings), I am able to achieve .8L-1L per hour removal with thermocouple readings in the 50F-60F range.