Molecular distillation is a form of distillation carried out under high vaccum, known as molecular, where a light fraction is separated from a heavy fraction using a wiped film evaporator. Product contact time with the heating wall is very short, avoiding heat degradation.This distillation is described as «short-path» because the evaporated light fraction condenses immediately on a condenser placed at the core of the evaporator. Molecular distillation methods have been utilized for processing vitamins, epoxy resins, highly concentrated pure fatty acids, including essential oils having similar characteristics to cannabis oil.
Molecular Distillation allows the distillation of high boiling point products at moderate temperatures through the application of high vacuum; and the short exposure period to evaporative temperatures minimizes the potential for thermal degradation or isomerization. More recently, these separation methods have been widely employed in the processing of hemp oil for medicinal and recreational uses to facilitate the separation of high value hemp oil fractions, such as THC and CBD.
There are a number of different types of molecular distillation units but most popular systems are the wiped film and the short path still, they have been proven to be the most versatile system. While wiped-film molecular stills are recognized as the premier machines in the marijuana industry for cannabis distillation, including hemp oil distillation.This paper will focus primarily on the wiped film distillation unit.
The Wiped Film distillation system distinguishes itself from other styles in that the potential vacuum capability is greater than other styles of thin film evaporators, and is generally considered capable of vacuum (expressed as absolute pressure) as low as 0.001 mm Hg. This capability is very important in those fields of chemistry where excess temperatures may damage the molecule being distilled.
Before we discuss the distillation of hemp, we need to know how hemp is processed. Moving upstream in the process, the crude hemp oil processed in distillation units is typically derived from three popular extraction methods: supercritical co2 extraction, hydrocarbon extraction, ethanol extraction. All of the methods are capable of producing a good quality of crude extract for subsequent distillation.
However, we shold know that the quality of the extract will have an impact on the distillation, impurities such as water, ethanol, wax, may preclude obtaining the high vacuum levels and result in low separation efficiency. In order to improve the separation efficiency, some post-extraction treatments, such as winterization, deepth filtration,decarboxylation and degassing should be performed before the distillation.
Most people know that they will need do the winterization and filtration before do the molecular distillation, but they may have some questions about the decarboxylation and degassing. Decarboxylation is a process and chemical reaction that removes a carboxyl group from a molecule and releases carbon dioxide. Before cannabis is decarboxylated, there isn’t naturally occurring CBD or THC present in the plant.
Instead, these phytocannabinoids are found in an acidic state, better known as cannabidiolic acid (CBDA) and tetrahydrocannabinolic acid (THCA). Decarboxylation converts the acidic cannabinoids to their non-acidic forms, THC and CBD. Decarbing is achieved by applying just the right amount of heat and time to result in extracting these highly desirable cannabinoids.With wiped film, decarbing must be done as a separate process before distillation. If decarbing happens during distillation, spattering will occur contaminating the oil with raw extract.
Regarding degassing, check the article here: Why degassing is necessary before your perform short path distillation? Fortunately, the wiped film distillation equipment is versatile and it is possible to remove the undesirable lower boiling point contaminants by conducting an initial distillation at moderate vacuum where the distillate will be composed of, for example, water, ethanol and perhaps some terpenes. Typically, the quantity of distillate is small (e.g., % Distillate < 5%) and the de-gassed product is collected at the residue receiver. After the low boiling point compounds are removed, redistilling the residue product can usually be accomplished at a higher vacuum level (having removed the low boilers) where the target THC and/or CBD compounds are separated as distillate.
Some equipments has a degasser, which could do the degassing before the molecular distillation, for some multi-stage wiped film distillation units, normally the first stage will be a degassing system(usually a thin film evaporator), after degassing, the residue will be pumped into the second stage wiped film distillation system. Multiple stage systems are quite common in the specialty chemical sector, and it is expected that production demand and price (not to mention Federal and State regulations) will dictate if multiple stage units will gain popularity in the hemp oil market.