About Essential oil Distillation FAQs

1. What is the purpose of molecular distillation equipment?

Extraction can only go so far in purifying cannabinoids such as THC and CBD. Therefore, a different technique is needed for increasing purity. A thermal separation technique works well at this point because cannabinoids have a different boiling point range than other materials in the extraction mixture. Molecular (short-path) distillation is the best thermal separation method for this heat-sensitive material because it is the gentlest type, causing the least amount of thermal degradation of product.

2. Is molecular distillation similar to extraction?

No, they are quite different operations. With extraction, solids, (or sometimes liquids) are brought into contact with a solvent. In cannabinoid work, the solvent is typically ethanol, or butane/propane, or supercritical pressurized CO2, or others. Certain compounds such as cannabinoids, terpenes, chlorophyll are dissolved into the solvent, after which the solvent is evaporated away. The separation is accomplished via an affinity of the target compounds to be transferred by dissolution into the solvent. With distillation, the separation is carried out not by solvent affinity, but by differences in the volatility (boiling points), between the various compounds. More volatile materials are more easily distilled and condensed as distillate while the heavier materials remain as liquid collected as residue. Distillation is performed after extraction to further concentrate and purify the desired compounds.

3. What level of purity is expected with the Pope molecular stills?

It depends on the quality and composition of the feed material, factors going back to the original plant strains plus all subsequent handling and processing prior to distillation. Often, extracted material prior to distillation is in a range of 55-70% cannabinoid, and it is typical to distill this up to a range from 85-90+%, with beyond 97% being reported. In addition to increased percentage purity, the product is significantly lighter yellow in color, with high clarity.

4. Does molecular distillation require addition of solvents?

No, additional solvents or other compounds do not need to be added to the feed material. This question often arises because potential users know that concentrate from extraction can be quite thick and viscous. But rather than using “thinning agents” such as solvents, the high viscosity or melting point of cannabinoids is handled by keeping materials warm enough to flow throughout the entire set of distillation components. Equipment needed for these heating functions is provided in the Pope still systems configured for cannabinoid applications – there is nothing else needed to buy.

5. What is the difference between Pope’s wiped film molecular still (WFMS) and a short-path still or a fractional still?

There seems to be a lot of confusion and misuse of terminology in this type of equipment. So, below are some points to keep in mind:

A. Molecular distillation is the same thing as short-path distillation. These both imply use of high vacuum and a condensing surface in close proximity to a heated evaporation surface. For many applications such as cannabinoids and other compounds with even greater molecular weight and boiling points, if this distance is not close, the equipment will not work well, if at all.

B. Some people associate the term “short-path” only with a basic glassware setup involving a basic boiling flask with a neck leading to a condenser and a receiver flask(s), or else a similar variation called a KIugelrohr. These are also referred to as pot stills, (in the vessel, not marijuana sense), and are all considered batch mode apparatus. But these are only one type (and the simplest) of short-path or molecular still – there are other forms, including Pope’s continuous mode WFMS.

C. Molecular stills are not fractional stills. Fractional still equipment implies the utilization of a vertical packed column providing multiple equilibrium stages or “theoretical plates”, requiring the condenser to be further away from the boiling flask and reached only after the sometimes quite long obstacle of the packed column, a problem for heat-sensitive materials such as cannabinoids. The single theoretical plate of molecular stills is sufficient for most cannabinoid work and offers the least product degradation (Pope does offer fractional distillation equipment of several different types and size ranges for other applications).

6. So what is the advantage of a Pope WFMS over a basic boiling flask type molecular short-path still?

There are several, including:

A. The WFMS is a continuous mode, rather than a batch mode still. This means that with larger or special flasks, or with liquid pumps, they can operate for extended periods of time with any quantity of feed material and with the same consistent product composition over time. The WFMS is also scalable, such that when much larger quantities of material need to be processed, larger versions of the same type of equipment can be utilized to accommodate the greater throughputs required. Batch mode stills such as the BFMS are very limited in scalability.

B. The WFMS offers much less thermal degradation and greater product purity and yield because of: i) a very short residence exposure time to a heated surface – only a matter of seconds, compared to many hours in a BFMS, and ii) a highly efficient dynamic rotating wiped film action providing turbulent moving thin-film mixing compared to the limited, less dynamic liquid/vapor interface of simple boiling flask apparatus.

7. How is the distillation carried out?

There are normally two (or more) passes made through the Pope still. The first is to remove whatever amount of remaining air, gas, water, solvents and terpenes remain in the extract. The second carried out at greater vacuum and temperature, is normally for distillation of the cannabinoids away from the heavier residue including chlorophyll, heavier waxes, sugars, salts, pesticides, dark-colored components, and other undesired matter. Without the first devolatilization pass, the cannabinoid distillation will be slower and not be as successful because the vacuum obtained will be weaker and micro flashing of gasses and volatiles will physically carry some undesired compounds and colors over to your cannabis distillate, THC distillate or CBD distillate product.  The overall process will run better, with significantly greater quality, yield, and throughput if prior to the first pass, all volatiles lighter than terpenes, such as ethanol have already been thoroughly removed. There are also additional distillation strategies which are covered in training at Pope.

8. Why does removing volatiles before the first distillation pass matter so much?

The goal of the first distillation pass is to remove as many of the terpenes as possible. If these are removed well in pass 1, it will allow for a higher performance during pass 2, with less flashing and greater vacuum, throughput, purity, yield and clarity. However, if the feed to pass 1 also contains leftover solvent—typically ethanol—it weakens the overall operating vacuum, (no matter what type of, or how large the vacuum pumps are), leading to less terpene removal. This has a spillover effect because pass 2 is burdened with more terpenes in the feed, diminishing the above-mentioned performance and results of this pass. It’s best to have much less than 0.5% solvent in the pass 1 feed.

9. Is extreme vacuum level and capacity required?

No, in fact, very high vacuum level in the evaporator body is not even attainable because of the vapor pressure/temperature properties of cannabinoids.  For the cannabinoid pass,  the typical body temperature range of 130 – 180°C, the vacuum range observed is normally roughly around 0.06  to 0.3 torr, no matter what kind of vacuum pump is utilized. Pope mounts the vacuum sensors on the vacuum arms of still bodies, as close to the process as possible, where more meaningful, useful, and accurate readings are obtained. Some people have mentioned to us that their experience has been that much greater vacuum levels had been observed and required with various competitors’ equipment they have used. However, in those situations, the sensors have typically been mounted directly near the inlet to vacuum pumps where an optimistic reading is observed. By that point, vapors will have been collapsed and condensed on internal and/or external condensers plus a very low-temperature cold trap, resulting in magnitudes less numbers of molecules per volume at the sensor – the factor that actually defines vacuum level!. Pope’s molecular stills are capable of true body vacuum levels of better than 0.001 torr – but only when the materials being processed possess very low vapor pressure and much greater boiling points and molecular weights than cannabinoids. Sometimes, clients prefer to have optional diffusion or other type high vacuum booster vacuum pumps in addition to rotary vane type that  Pope provides as standard, with the reasoning being greater vacuum and better product result.  We have found, however, that in most cases, this is unwittingly done to compensate for not having removed the volatiles prior to distillation as covered above or other vacuum weakening causes such as poor cleaning methods, leaks, or poor maintenance of the primary vacuum pump.

10. Does the operator need to be highly educated and experienced to operate the Pope still?

Not necessarily, but this is not a “set it and forget it” operation such as in the case of a rotary evaporator or other simple batch devices. Being that this is normally the final processing step prior to packaging, that the feed material can have varying composition and quality, that the final product specification goals of various batches may vary depending on management, marketing, and retailer preferences, and that the Pope still operation can be adjusted to accommodate these variations, there is some thought that goes into proper operation. With good analytical information on the distillation feed material, well laid out product goals, and an operator who is interested and strives to learn and to accomplish these goals, there will be much greater success than where some of these factors are missing.

11. Does this equipment work well for distillation after different types of extraction methods and other processing steps?

Yes. Whether the extraction method used is butane/propane, supercritical CO2, ethanol or other means, distillation with the Pope stills will perform excellently and will significantly increase product purity. And whether or not the material has been winterized, (dewaxed), or whether or not it has been decarboxylated, the distillation will work well. However, with greater wax content, there will be more cleaning and maintenance required because the wax tends to often leave hard to remove deposits and plaque on process surfaces. In addition, the product will never be as optically clear or pure compared to the wax-free starting material. Also, non-discarded material can be tricky, sometimes undergoing partial decarbing while being distilled leading to weaker vacuum levels and foaming. Of course, the final product purity, yield, and appearance are also affected by initial plant strain and quality, the type and quality of the extraction process, and the subsequent steps carried out prior to distillation.

12. Why are wipers used instead of rollers?

Pope’s diagonally slotted wipers are designed to provide optimized thin film turbulence and to not only propel the material in a circular path around the inner cylindrical heater surface but also downwards, resulting in shorter and controllable residence time. Rollers utilized by other manufacturers rely on gravity for the downward motion, are not as efficient, and may also fling residue material to the internal condenser.

13. What is the difference between hemp and marijuana and how does this affect distillation results?

Both hemp and marijuana are varieties of Cannabis Sativa [Genus: Cannabis/Species: Sativa]. The big difference is that hemp contains greater amounts of CBD and lesser amounts of THC than typical marijuana, with the best-selected strains being developed that contain very low to undetectable percentages of THC. This is very important because when distilling CBD for greater concentration, whatever THC is present will co-distill and become greater in percentage in the distillate as well. Thus plant material with < 0.3% THC can become concentrated to even >10% in some cases.

14. Are Pope’s Wiped Film Molecular Stills used any differently in the processing of hemp than they are in the processing of cannabis?

Not really. In both cases, we are removing remaining light materials, solvents, and gases first, then distilling cannabinoids (THC, CBD, etc.) away from heavier botanical materials including chlorophyll, lipids, salts, sugars, and possibly heavy metals and pesticides. As always, parameters should be set for optimization based on variances in natural starting composition and product goals. Something to keep in mind with CBD production: Oftentimes, hemp harvesting is crude and can include not just buds and trim, but whole plants—stems and all. Wax content in extractions of this nature will be much greater than in typical cannabis THC processing. If winterization is not performed, distillation equipment can get clogged more readily, requiring significantly greater maintenance and cleaning.

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