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Rotary Evaporation Techniques For Higher-Quality Cannabis Products

Cannabis Rotary Evaporation, Part III:

New Uses For An Established Technique

With the cannabis market raking in $6.7 billion in 2016 in the U.S. and Canada and the market expected to hit $20.2 billion by 2021, processors are looking for the best ways to increase their product quality and grow profit margins.

With a predicted compound growth rate of 25%, the market is expected to be bigger than even the dotcom boom, according to Forbes.com.

To produce the highest-quality products, processors are looking to more traditional methods of extraction and isolation. Using techniques long established in the botanical, chemical and distilled spirits industries, cannabis processors have several options to improve their manufacturing techniques.

We’ve already looked at solvents and ethanol extraction in earlier blogs. Here’s a look at how processors can use rotary evaporation to better isolate the extracts and components:

Applying Rotary Evaporation To Cannabis Processing

A fixture in many labs, the rotary evaporator is a common tool for solvent removal. The process allows the solvent to be removed in a controlled manner under vacuum.

It’s also easily scalable, ranging from smaller bench top flasks up to 5 liters to pilot scale, using flasks of 20 liters and more. This flexibility makes it very adaptable when processing cannabis.

How The Process Works

As the pressure is reduced using a vacuum pump in the rotary evaporator, the boiling point of the solvent, ethanol in this case, is lowered.
Typically, the distilling flask (A) is filled to 50% volume. The water bath (B) is heated to 30-40°C. The condenser temperature (F), controlled by a recirculating chiller, is set to -10°C to 0°C. Once the water bath and condenser have reached the set points, the distillation flask is rotated from 150-200 rpm. This creates a thin film on the upper surface of the glass cylinder, which increases the solution surface area and enhances the solvent evaporation rate. Applying an appropriate vacuum to the system (H) lowers the boiling point.

To achieve a recommended target, set the vacuum to achieve an ethanol vapor temperature of 15-20°C. As the ethanol evaporates, it will condense and collect into the distillate flask (G). Optimization of the parameters allows for easy reproducibility.

Things To Watch For When Using Rotary Evaporators

While it may be tempting to try to tweak the process by increasing the evaporation rate by lowering the vacuum and/or increasing the water bath temperature, this will cause capacity overload on the condenser. Doing this actually causes the evaporation rate to exceed the condensation capacity of the recirculating chiller.

This causes ethanol vapor to pass through the condenser and into the vacuum pump. Cannabis extracts require lower water bath temperatures to minimize thermal decomposition. So the condenser temperature of -10°C to 0°C will require a chiller with adequate cooling capacity at those low temperatures.

There are other ways to increase throughput while still maintaining quality. There are a variety of options for automatic vacuum control and refilling accessories, both manual and automated, that can be added to rotary evaporators.

To learn more about improving your cannabis processing, read our whitepaper, “The Cannabis Workflow and the Importance of Temperature Control.”

Download Your Cannabis Whitepaper Now!

6 thoughts on “Rotary Evaporation Techniques For Higher-Quality Cannabis Products

  1. Hello
    I am extracting cbd etc from Hemp Plants .My currant method is producing crude first run oil
    I am going to purchase a rotary evaporator and chiller . Is this the best system for cleaning the multiple kilos of crude oil i have?
    I have hundreds of pounds to soak and extract. I realize winterization is a better option but until i can afford to scale up to a different extraction system i will stay with my process
    Regards
    Clint

    1. What is the extraction method from the hemp plants? If the extraction method is ethanol it would be advisable to extract cold which eliminates the need for winterization. Scope out Capna. Then it’s just a matter of removing the ethanol. The decision to utilize a rotary evaporator for this will depend upon the total amount of ethanol. A rotary evaporator will not remove lipids, fats, etc. from an extract that hasn’t been winterized.

  2. Hi, I am using isopropyl usp and want to make good quality RSO, so I have a question regarding the vacuum level inside the rotovap. To prevent condenser-overload while evaporation/condensation of the solvent, what is the correct level for the pump, in units of megapascal (MPa)?

    1. Using the 10/30/50 rule; meaning condenser set to 10 ⁰C; rotary evaporator water bath set to 50 ⁰C adjust the vacuum pump to 78 mbar (0.0078 MPa) to yield an IPA vapor temperature of 30 ⁰C. Having a DT of 20 ⁰C for the vapor and condenser will maximize efficiency.

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