Post-extraction and pre-distillation processes

The three key cannabis processing steps are extraction, distillation and isolation. Today, we are going to focus on the post-extraction process, mainly distillation. A standardized process is very important for the consistency and the quality assurance and control of the final products. A few steps must be taken before doing distillation to improve the through put and the efficiency and to get high quality distillate.

Winterization and filtration

Following extraction, the classic cannabis processing step is “winterization”. It is the most popular dewaxing method for cannabis oil. The common practice is to add the crude oil into a polar solvent (mostly ethanol) at 5-10 times the volume of crude oil, mix them thoroughly, and keep it at low temperature (around -40 ᵒC) for about 24-48 hrs. This promotes the precipitation of the waxes and lipids from the solution and it is usually done in a jacketed reactor. After winterization, the mixed solution should go through a filtration system, to get rid of the waxes and the lipids. Although some people suggest that the winterization process can be avoided if the ethanol extraction was done at -40 ᵒC or below, there is no solid evident to prove that the waxes and lipids are within a certain limit.

Solvent recovery

After winterization and filtration, the solution at this stage is crude oil suspended in 5-10 volume of ethanol. The solvent recovery process is to separate the ethanol from the crude oil and recover the ethanol for reuse. The process involves heating the mixer in a container at a relatively low temperature, so that only the ethanol evaporates and condenses. The classic example of this is a rotary evaporator, where large round bottom flasks are held in warm baths under vacuum to evaporate and condense ethanol. The size of the flask has restricted the efficiency of this process. Therefore, for industrial scale, other types of evaporators such as falling film evaporator or thin/wiped film evaporator play an important role. The ethanol recovery rate can reach to few hundreds or thousand liters per hour by these methods.

Decarboxylation

This process is a bit controversial. Theoretically decarboxylation means to release the carboxylic acid (COOH) moieties from the cannabinoid molecules. For example, to change the CBDA or THCA to CBD or THC. During this process, the crude oil releases the CO2 and other volatiles, which reduce the releasing of gases in the distillation process. There are a few ways to do decarboxylation, most common way is to heat the crude oil in a container at around 130-140 ᵒC for 1-2 hrs. This can be done in a jacketed reactor, heated flask, rotary evaporator or a vacuum oven.

Distillation

The distillation process is to further refine the crude oil and separate cannabinoids from the residues. It is a separation of molecules based on boiling point and molecular weight. Since different molecules evaporate at different temperatures, different components can be separated by controlling the evaporation and condensation temperatures. The two widely applied methods are short path distillation and wiped film (or so-called thin film) distillation. After this process, the distillate making process is completed. There are lots of parameters to consider in this process to make high quality distillate, which we will discuss next time.


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