Pope Wiped-Film Molecular Stills (WFMS) are a special type of short-path, molecular distillation equipment. These are continuous mode systems, as opposed to batch vessel distillation apparatus. The diagram below of the cannabinoid purification distillation process illustrates the means of this technology and shows the flow of the feed material and the separation of component fractions within the equipment.

Feed material is delivered from a feed flask into a cylindrical evaporation section, having heating, on the outside, (either electric resistance or circulating hot fluid jacket type), and a diagonally slotted wiper mechanism forcing liquid around and downward in a thin film on the inside. In the center of the body is a closely positioned internal condenser, providing a short path for vapor molecules traveling from the heated surface to the condenser surface. For cannabinoids, the internal condenser fluid must be kept elevated (~70°C) to prevent high viscosity or freeze up of THC, CBD and related components. During the journey downward, lighter (lower boiling point) fractions of the liquid begin to vaporize, move to the internal condenser and condense, falling down as a liquid into a well that captures and separates the distilled liquid (cannabinoid) which flows into a receiver flask. Heavier residue material (Chlorophyll, salts, sugars, heavy wax fractions) does not evaporate and instead travels the length of the still body and flows into a different receiver flask. Because of the optimized Pope design, this all happens within a number of seconds, and under vacuum-lowered temperatures, thus minimizing any possibility of product degradation.

While Cannabinoids are caught and collected by the internal condenser, a different, external condenser, maintained at a chilled temperature, can capture terpenes (which are lighter than cannabinoids). The isolated terpenes are then collected in another, separate receiver flask. Depending on the composition of the feed material and the goals of the operator, some quantities of different terpenes are obtainable which can be very useful for various product formulations. Any remaining vapors which escape both the internal and external condensers and which may contain small amounts of solvents, water or lighter terpene components, are collected in a cold trap maintained at an ultra-low temperature. The trap serves the purpose of maintaining lowered vacuum levels in the still system and protecting the vacuum pump from contamination from the light vapors.

It is important to maintain a steady feed rate, body temperature and vacuum level. In the standard glass molecular still systems, feed rate and vacuum are maintained manually. Pope also offers positive displacement feed pumps, automatic flow rate controllers, automatic vacuum controllers and other advanced features including product discharge pumps, multiple in-series staged still unit skid mounted systems and computer/PLC control. As clients’ product production requirements increase, Pope can assist with technology consistent throughout the product line, allowing straightforward process equipment scale up. Equipment for processing 24/7 at more than 200 kg/hr is offered, well more than sufficient for any cannabinoid application!

The Molecular Background

Basic evaporation and condensation

Wiped-Film still technology takes advantage of the fact that each chemical substance has a characteristic vapor pressure. It is this relative difference in vapor pressures which dictates how easily a complex compound can be separated into its constituent components.

Since the molecules of all matter are in constant motion in varying degrees, depending upon the chemical composition of that matter and the temperature and pressure applied to it, molecules near the surface have a tendency to escape into the surrounding atmosphere. As temperature increases and pressure decreases, this escaping tendency usually increases and the substance is said to vaporize.

The force generated by these escaping molecules is referred to as the vapor pressure of that material at a particular temperature and pressure. It is the relative difference in vapor pressure of substances which dictates how easily a complex compound can be separated into its constituent compounds.