First and foremost, many thanks to Heidolph Instruments for providing a demo model of their Hei-VAP Precision ML G3 for evaluation.
Rotary evaporators are used to separate solvents from laboratory samples under reduced pressure. All rotary evaporators, at a minimum, consist of a motor driven evaporation flask that spins in a heated bath. As the flask spins, a thin film of the sample is spread over the surface area of the entire flask due to the centrifugal and frictional forces. Reducing the pressure by incorporating a vacuum system allows for low temperature distillate to travel out of the evaporation flask through a vapor duck into the condensing column where the solvent is collected. The complete system can be seen in Figure 1.
Figure 1. Hei-VAP Precision ML G3 experimental configuration.
The objective of this report is to provide an overview of the various components, an evaluation of the system as a whole, and to provide a general outline of operations and findings as they may pertain to the cannabis world.
The heart of the system is the human machine interface (HMI) pictured in Figure 2.
Figure 2. Hei-VAP HMI.
All system parameters are adjusted by use of the HMI. Buttons to turn the warming bath and rotation on are found in the lower right hand portion of the controller. The up and down arrow buttons in the lower left hand corner are used to raise or lower the evaporation flask through the means of a mechanical lift. That is actually what the “ML” stands for in the product code. Heidolph also offers a, “HL”, hand lift model.
Menu tabs, seen at the top of the display, can be selected with the clickable white dial. “SETpressure” mode is visible in the image above and allows the user to manually select vacuum level, rotation speed, and bath temperature. Both actual value and set point are displayed.
The warming bath, pictured in Figure 3., is capable of receiving up to a 5L evaporation flask. The flask pictured is 1L. The warming bath is capable of achieving temperatures up to 210ºC and has nice overshoot protection that engages when the temperature is over by 5ºC or if the bath runs dry.
Figure 3. Warming bath with 1L evaporation flask.
The pressure in the system is controlled by the vacuum control box seen in Figure 4.
Figure 4. Vacuum control box.
Pressure is measured using a pressure transducer mounted near the top of the condensing column and regulated using the vacuum switch that is mounted on the base of the unit. The pressure transducer and vacuum switch can be seen in Figure 5.
Figure 5. Vacuum switch is on the left and pressure transducer is on the right.
Heidolph offers a wide range of glass options with their equipment but the set included with the sample unit was the G3 glass set. The G3 vertical condenser has the smallest space requirements and fits easily on a laboratory benchtop. The vacuum line and pressure transducer line are installed at the top of the condensing column. At the top of the column there is also a spare port that optionally can be used to measure the vapor temperature. The collection flask clips onto the bottom of the condensing column and can be removed quickly and easily.
Figure 6. Condensing column is on the left; Recovery flask connected to condensing column on the right.
Temperature in the condensing column is maintained by the Heidolph RotaChill Chiller that is manufactured by Fisher Scientific and offers temperature ranges between -20ºC and +40ºC with a cooling capacity of 1290 W (4401 BTU/h) at +20ºC. A picture of the chiller can be seen in Figure 7.
Figure 7. RotaChill chiller manufactured by Fisher Scientific.
In this experiment, the rotary evaporator is being used to distil 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.
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.
Figure 8. Winterized and fully purged shatter.
In conclusion, the Hei-VAP precision from Heidolph Instruments is a valuable addition to any laboratory or production facility that is interested in processing high quality hassle free winterized products. An example can be seen in Figure 8.
The only problems experienced with the machine were related to the chiller. Two demo chillers were tested initially and both proved to be defective. The first chiller had a leak in the refrigerant tank that allowed air to enter the system and caused the pump to cavitate and shut off. It should be noted however that the flow sensor installed in the chiller shut the pump down before further damage could be done. The second chiller seemed to have a sensor issue that resulted in a low fluid level error.
As these were demo units that had been shipped repeatedly around the country it is most likely that the damage had been done during shipping and handling or by previous users. Customer service handled the claims with curtesy and replacement units were delivered quickly.