1. Do wiped film molecular stills operate similarly to boiling flask “short path” stills?
No, boiling flask stills are batch-mode apparatuses where compositions change incrementally the entire run. Wiped film molecular distillation is a continuous mode operation, thus the feed, distillate and residue compositions remain constant for the entire run. Feed material, kept flowing at a fixed feed rate, enters a high vacuum heated boiling zone for a short residence time, where some portion of it is evaporated away and condensed. Thus, the feed is split into two streams, distillate and residue, both being collected and/or pumped away. Three principal operating parameters— feed rate, temperature and vacuum level— determine how much is collected as distillate and how much is collected as residue, sometimes referred to as the “split” or “mass balance” (MB).
2. Should molecular stills be run the same way each time?
Incoming feed material changes in quality and composition, plus product goals can change as well. Thus, for optimal results, it’s better to modify parameters rather than keep them fixed for every run. A rule of thumb is to shoot for splitting the feed into something close to the total cannabinoid percentage. For example, if a new extract lot comes in at 60-percent total cannabinoid, aim for a MB of roughly 60:40, not 85:15.
3. How is distillation optimized to accommodate product goals?
One approach, (A), is quality over yield; the other, (B), is yield over quality. In approach A, one may adjust the temperature to a MB to correspond to a bit under the percent of cannabinoid, resulting in a clear yellow distillate of good quality. There may be a nominal amount of cannabinoid remaining in the residue that can be combined later with other residues from similar runs, and later, this material can be redistilled to recover a “second squeeze” of cannabinoid for less critical product use. In approach B, a “deeper” cut is made, with MB somewhat greater than the percent cannabinoid to ensure most of the available cannabinoid is removed. If the goal includes having at least some premium-grade product, the distillate, instead of residue, may be redistilled to obtain product upwards of 90-percent cannabinoid, and the residue, depending on its analysis, may be utilized in a secondary product line, particularly when clarity and lightness is not essential, e.g., chocolate edibles.
4. Can different strategies be incorporated into the design of a production system?
Yes, this is accomplished by having more than two stages in the system. If there are three stages, the third can be used either for redistilling the residue (increasing yield) or else redistilling the distillate (increasing purity). Alternatively, the first stage could be used for stripping out excessive (> 3 percent) solvents, the second for collection of any remaining solvent and heavier terpenes, and the third for cannabinoid distillation. Having four stages makes it possible to run two, two-stage distillations in parallel, doubling the throughput of the still system. Great flexibility is possible with such multistage systems.
5. Are terpenes lost in a molecular distillation system?
Often, most terpenes are lost prior to the distillation step. If they are still present and in usable condition, they can be captured for reuse such as adding back to final distillate product via incorporation of an external condenser—a component, which is one of the features of Pope stills.