Extractors use cold temperatures of -20º C and below to reduce the solubility of polar compounds (e.g., chlorophyll) and target desired compounds (e.g., cannabinoids). When plant waxes and chlorophyll are extracted, they must be removed with post-processing steps such as winterization. Temperatures between -20º C and -80º C are used for winterization, making a colder initial extraction the more efficient single-step process.
This technique is generally used with ethanol given its high polarity relative to other solvents of choice. Ethanol is also commonly used for winterization. Hydrocarbon solvents are also utilized at cold temperatures due to low boiling points (e.g., butane at -0.5º C and propane at -42º C). These solvents are non-polar and inherently more selective. Even so, dewaxing may be integrated into a closed-loop hydrocarbon system to remove fats and lipids with chilled, sub-zero hydrocarbon solvent.
In general, lower temperature reduces extraction efficiency. For this reason, manufacturer Delta Separations recommends that cold ethanol extraction be performed in the range of -30º C to -40º C. The company notes that “…a lower temperature would result in massive electrical costs and reduced overall efficiency. It would lengthen extraction times and reduce overall yield due to the ethanol’s reduction in solvency.”
Capna Systems is another manufacturer with sub-zero chilling for ethanol. They offer several systems that operate between -50º C and -80º C.
Temperatures lower than -80º C are popularly considered cryogenic for winterization as well as extraction. During winterization, the purpose of such low temperatures is to speed up the separation of unwanted compounds. Cryogenic liquids such as nitrogen, helium, and argon with boiling points below -150º C can be used for cooling.
EthoEx developed ethanol systems capable of extracting cannabis at -90º C. The company points out that extraction at -40º C creates crude oil that may yet require purification. To make up for less efficient extraction, the EthoEx system recirculates and flushes solvent into biomass continuously. Electricity and liquid nitrogen are used to achieve such low temperatures.
Temperature is undoubtedly a critical variable across extraction systems. Cold temperatures are generally used for cannabis and other botanicals when non-polar target compounds must be targeted/separated from polar compounds and/or waxes.