Ask the Experts: 5 Questions on Wiped Film Distillation

Wiped film distillation is often carried out using strict set of methods and parameters from internal Standard Operating Procedures, but incoming extract material composition is not fixed; it changes depending on various factors, so do product goals. Dean Segal, vice president of sales and marketing for Pope Scientific, shares distillation approaches and strategies for adapting to such changes for optimization of product quality, yield and profit.

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.

Pope Turnkey, 3-Stage, PLC Controlled, Pharmaceutical-grade, Cannabinoid Distillation System

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 re-distilled 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 re-distilled to obtain product upwards of 90% 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 re-distilling the residue (increasing yield) or else re-distilling the distillate (increasing purity). Alternatively, the first stage could be used for stripping out excessive (>3%) 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 Cannabis Distillation stills.

Originally published in Cannabis Business Times

Pope On Stage at CannaTech Tel Aviv 2019

Dean Segal Presenting at Canntech

Ask the Experts on Distillation: 5 Questions with Dean Segal

For further refinement of your extracted cannabis material, it’s important to understand the options available on the market, as well as how to make your distillation process as efficient and seamless as possible. Here, Dean Segal of Pope Scientific shares some things you need to know about wiped film stills, how to improve wiped film still operation results and more.

1. What are some advantages of a wiped film still (WFS)?
A WFS is a high-efficiency molecular short path distillation system utilizing high vacuum, dynamic wall wiping, brief heating and a condensing surface a short distance from the evaporation surface. This, plus the continuous mode operation of the WFS cuts the heating residence time to seconds, versus hours. That’s important, because the longer the material boils, the more it will degrade—resulting in lower purity, yield, clarity and ultimately, profit. WFS will perform the same in larger size and throughput versions, as it will enlarge proportionally, leaving ample room for proper evaporation. “Short path” units, because they are spherical in make-up, do not have this scalability advantage. In fact, when they are made larger, the ratio of volume to available evaporation area (boundary where liquid interfaces with vapor) declines substantially, and relative throughput decreases.

2. Will wiped film molecular distillation work well after different types of extraction and other process steps?
Yes. You can count on improved purity and clarity whether hydrocarbon, ethanol, supercritical or other extraction methods were utilized. Winterizing (removing wax) is not required, but without it, you’ll need to clean and maintain the still more often. The still will also work well whether or not decarboxylation has been performed.

3. Should a wiped film still be procured large enough for estimated production rates a year or two down the road?
No, there are operational problems that arise when the equipment is much larger than needed for the near term. Start with a still matching actual production rate needs for the first six months, then revisit multiple unit needs later after operation has been running steadily. And because the WFS is scalable, when much greater quantities of material need to be processed, larger versions of equipment can be successfully utilized.

4. What is the most common problem typically encountered in operating wiped film stills?
By far, the most frequent issues we see have to do with insufficient prior removal of light components such as ethanol, water, lighter terpenes, gases, etc. These should have been decreased to lower values earlier via more aggressive rotovaping, decarboxylating and feed flask degassing. This allows greater vacuum, less flashing, better color, throughput, purity and yield. An early indication of a problem is when the first pass is running at more than a few torr and/or more than 1 percent of feed collecting in the cold trap.

5. What things are helpful to improve wiped film still operation results?
Proper maintenance of vacuum pumps and leak checking is more important than massive capacity rotary vane and booster pumps. If better than 0.02-torr in a clean, dry still is not obtainable, check for leaks and pump health and learn how to use your gas ballast valve! Know the inter-relationship of feed rate, vacuum level and temperature. Strategize your operation based on extract composition and product goals, and tweak parameters to optimize each run. Adapt for variations in starting material.

Originally published in Cannabis Business Times | Ask the experts: Distillation