The processing of raw cannabis plants to extract cannabinoids and other compounds can be carried out using a variety of methods. Some of the most popular methods are extraction using CO2, a hydrocarbon (usually butane), or ethanol. Which one is used depends on a variety of factors, including the amount of raw material to be processed, and the final application of the product, for example what form it will take and whether it’s for recreational or medicinal use.

Cannabis Extraction Methods

The cannabis market uses three main extraction techniques. In all processes, the plant material is subjected to a solvent to remove active compounds from the plant matter and filtered to yield a solution of the solvent with plant extracts.All processes rely on standard techniques that have been used for years in the botanical, chemical and petrochemical, and distilled spirits industries.

Super CriticalCarbon Dioxide

Usecarbon dioxide (CO2) pressurize the CO2 to its subcritical orsupercritical state.The CO2 stream passes through a chamber containing cannabis material. The distillate can be isolated easily by reducing the pressure which evaporates theCO2, leaving a cannabis extract with no solvent. Working ontemperature and pressure affords CO2 systems the ability to yield extracts with a complete terpene profile.

Liquefied Hydrocarbons

Pressurize butane, propane or other low molecular weight hydrocarbons to a liquid state. The liquid hydrocarbon passes through a bed of cannabis material and filter, yielding an extract solution of hydrocarbon and plant extract. Like the CO2method, a reduction in pressure evaporates the hydrocarbon liquid, yielding a solvent-free plant extract.This method requires great attention to safety due to the flammability of the hydrocarbon used.

Ethanol Extraction

Use food grade or USP grade ethanol as a solvent to extract plant material. This method varies from vessels to reactors, filter reactors, spinning vessels to barrels. A popular process has the ethanol chilled to <-20°C (-4°F) either in a cold room or freezer and then pumped into a container of cannabis.After a soak period, the ethanol solution is either filtered or the plant material removed in a ‘tea bag’ fashion. The resultant mother liquor of ethanol and extract is then concentrated by removing the ethanol. Typical distillation apparatus used to remove the ethanol include rotary evaporators, falling film evaporators or a batch vacuum distillation system

In this article, we’ll focus on the method of ethanol extraction. Ethanol extraction can be carried out by a number of methods including cold, warm, or room-temperature processing. Some ethanol extraction processes involve the use of a rotary evaporator setup to remove the ethanol from the extract solution.

Here, we take a closer look at ethanol extraction for cannabis applications, with a particular focus on ethanol removal using a rotary evaporator. We’ll include information about the steps involved in ethanol extraction, optimal conditions for removing ethanol, and misconceptions about the ethanol removal process.

Ethanol Extraction Methods for Cannabis Applications

Here’s a bit more information about the main methods of ethanol extraction:

  • Room temperature process: This involves raw cannabis being soaked in ethanol to pull soluble compounds from the plant matter into the solvent. The cannabis is then removed and the solvent is evaporated.
  • Cold process: The cannabis plant is soaked in ethanol that has been chilled. This prevents undesirable compounds such as waxes and pigments from solubilizing, but it also means extraction of desired compounds is slower.
  • Hot process: This involves using hot ethanol to solubilize compounds. The Soxhlet technique is a popular example of hot ethanol extraction. This uses a specialized piece of equipment called a Soxhlet extractor. However, this is difficult to scale up and results in undesirable compounds, such as bitter-tasting chlorophyll ending up in the solvent.

Ethanol extraction is popular for various reasons. It can be used to extract a full spectrum of compounds from cannabis plants, or the process can be tweaked to prevent certain compounds from solubilizing. Equipment costs for ethanol extraction are generally lower than for other extraction methods. Another plus is that the ethanol can be recovered and recycled, allowing for cost savings.

In addition, ethanol extraction can be scaled, so it’s suitable for processing large volumes of cannabis. In some ethanol extraction procedures, you’re simply soaking the plant matter in a vat, so the major limitation is the size of the vessel. Depending on regional or industry regulations, you’re also limited by the acceptable volume of ethanol that can be safely used and stored at a given time.

Which instruments are needed for the Ethanol Extraction Method?

Rotary Evaporator, Water Chiller, Vacuum Pump

The rotary evaporator enables the removal of solvent in a controlled manner under vacuum. Sizes range from bench top (to 3L flasks) to pilot scale (20 L and up). Reducing the pressure in the rotary evaporator by a vacuum pump lowers the boiling point of the solvent to be removed. In this caseethanol has to be removed.Typically, the distilling flask is filled to 50% volume. The water bath is heated to 30-40°C. The condenser temperature, controlled by a recirculating chiller, is set to -5°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 the2upper surface of the round glass flask, which increases the solution surface area and enhances the solvent evaporation rate. Applying an appropriate vacuum to the system 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.

Pay attention:Increasing the evaporation rate by lowering the vacuum and/or increasing the water bath temperature can lead to capacity overload on the condenser. The evaporation rate can exceed the condensation capacity of the recirculating chiller. In this case, ethanol vapor will pass through the condenser and into the vacuum pump. Cannabis extracts require lower water bath temperatures to minimize thermal decomposition.

As a consequence,the condenser temperature of -5°C to 0°C will require a good quality chiller with adequate cooling capacity at those low temperatures.Temperature control plays a vital role in the cannabis extraction workflowtherefore it is paramount to use good and reliable instruments. Attention to detail and optimization of the processing conditions from extraction to component isolation remain critical to maximization of yield and purit.

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