Purification by Altering Solubility (Winterization)

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  • By Goldleaf Scientific
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The process of removing waxes, fats, and lipids in general is often called winterization or dewaxing. When a solvent has several compounds with differing solubility you can remove the least soluble compounds by decreasing the solubility of the whole system. Altering the temperature, differences in polarity and agitation are ways to manipulate solubility and each has its own benefits and faults. The main idea is to force the solvent to hold too much of a solute or solutes and then shift the solubility to make some of the solute held by the solvent drop out. Increasing the temperature of the solvent increases solubility and lowering the temperature of the solvent reduces solubility. Changing the temperature is the most common method for altering solubility. When the temperature of the alcohol/oil solution is sufficiently reduced the least soluble compounds will precipitate out of solution.

Alcohols are ideally suited for this task as they are polar solvents while waxes are very non-polar, yet dissolve the waxes well. This difference in polarity aids the separation but is not mandatory. Any solvent can be used, even the solvents used to perform the initial extraction like butane. Simply reducing the temperature sufficiently is enough for the waxes to fall out of solution but because the butane is also non-polar the waxes will want to stay dissolved. In order to create an effective separation a larger temperature swing is needed and this usually takes more cannabinoids with it. The waxes left after filtration would have a significant portion of cannabinoids.

The size of the molecule also has an effect. In general solvents with longer hydrocarbon chains will be capable of dissolving more of a solute. So, heptane which has seven carbons in its chain will be able to dissolve more of a compound than butane which has four. The size, weight, and hydrocarbon chain length on the solute also play a role. Molecules which are lighter and smaller are generally capable of being dissolved in greater degree than heavier and larger molecules. So, if you were to do an extraction the lightest smallest molecules will be dissolved first and the heaviest largest molecules would be last.

Alcohols are very sensitive to the water content and increasing the ratio of water to alcohol will drastically affect the solubility of the alcohol. 95% ethanol is the most suitable in that it will retain almost all your cannabinoids while excluding almost all the waxes. If the amount of water is too little the alcohol will be too aggressive and will dissolve unwanted compounds. If there is too much water you will reduce the solubility and the unwanted compounds that are dissolved, but will also lose more cannabinoids (some will be left behind in the waxes). The process of dissolving into a solvent, cooling, filtering, and distilling can quickly become a bottleneck in the production process.

This is where a rotary evaporator becomes useful because it speeds up the distillation process. ​You don’t have to use ethanol to winterize. The process explained above works for any solvent. The reason why ethanol is almost always used is because it gets out the most waxes with losing much cannabinoids, but you may determine that productivity is more important than a small loss in cannabinoids and use a single solvent dewaxing (winterization) technique. 


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