Solving Glass-Cleaning Challenges in Short-Path Distillation of Cannabis Oils

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As the trend toward legalizing cannabis increases in the U.S. and elsewhere, so, too, do the number of organizations manufacturing cannabis distillates and concentrates to satisfy demand for products in their various forms. The distillation process is considered a high-maintenance activity by most commercial suppliers of cannabis concentrates. Glass used in short-path distillation is particularly susceptible to becoming soiled by baked-on and polymerized contaminants, because the process involves crude concentrates that are boiled until the desired components are distilled out, leaving behind unwanted residues. This necessitates frequent replacement of distillation and other processing glassware, having additional equipment on site to minimize production down time, and removing tenacious contaminants before equipment can be reused.

Cognizant of the costs involved in purchasing glassware to create cannabis concentrates, many producers have turned to a somewhat risky equipment cleaning process involving baths containing caustic chemicals. This is viewed by producers as a necessary inconvenience to ensure clean glassware is available to continue production. There are three downsides to this practice:

1. When caustic chemicals are used, the residence time for glass can be lengthy in order to break through layers of plasticization, thus delaying return to service.
2. Regulations may stipulate that adjustments be made to internal operating procedures in the event caustic chemicals create hazardous working conditions.
3. The chemicals are dangerous to handle at high concentrations and need to be disposed of safely and correctly. This generally involves contracting with a chemical disposal service, and may involve storing chemicals on site in containers such as 55-gallon drums.

Another alternative is scrubbing by hand using abrasive mixtures—a practice that does not bode well for hands or glassware.

A way to overcome these challenges is to use ultrasonic cleaners, a more efficient and environmentally friendly alternative.

Ultrasonic cleaning

Ultrasound is generally described as sound above the range of human hearing, typically greater than 20,000 cycles per second (20 kHz). Ultrasonic cleaners are fitted with transducers attached to the bottom and/or sides of a tank filled with a cleaning solution. When activated by generators, transducers cause the tank bottom to serve as a vibrating membrane at frequencies measured in thousands of cycles per second (kilohertz), sending sound waves pulsing through the cleaning solution.

These waves produce millions of tiny vacuum-filled bubbles that shoot out a powerful jet of liquid—on the order of 10,000 psi—when imploding. The force of the implosions, called cavitation, lifts and carries away contaminants from objects being cleaned. The implosion of these microscopic bubbles has been calculated to create temperatures in excess of 10,000 °F. Yet, this occurs so quickly that the cleaning process is robust enough for engine parts but gentle enough for electronics and surgical instruments, and, as will be shown, for glassware and other equipment used in short-path distillation.

Selecting an ultrasonic cleaner

Cleaning is accomplished in tanks, and ultrasonic cleaners are offered in a wide range of tank capacities. Measure the dimensions of the largest pieces of cannabis production equipment to be cleaned and make sure to select a tank that will accommodate them. Consider that cleaning is accomplished in parts baskets, the dimensions of which are slightly less than tank dimensions.

In addition, you need to know the working depth of the cleaning fluid as it relates to what you are cleaning. The working depth is the distance from the inside bottom surface of the basket to the surface of the liquid in a filled tank. This is important because parts being cleaned must be fully immersed in the liquid. An ultrasonic cleaner control panel is shown in Figure 1.

Figure 1 – Control panel of an ultrasonic cleaner.

Cleaning flasks and short-path distillation glassware

A benefit of ultrasonic cleaning technology is that the cavitation that blasts away contaminants can occur inside round-bottom multinecked flasks (Figure 2) and similar containers immersed in and filled with the cleaning solution formulation. This is because the sound waves pass through the glass to act on the cleaning solution inside.

Ultrasonic cleaners are available in a wide range of prices. Some basic units feature a simple “on-off” control, while others can offer a variety of features, some of which, in addition to tank size, are important for cleaning short-path distillation glassware.

Figure 2 – Cannabis flask before cleaning.

Ultrasonic frequency

Most ultrasonic cleaners operate between 35 and 45 kHz. This frequency range is well suited to the vast majority of cleaning tasks. A lower frequency, such as 35 kHz, produces larger cavitation bubbles. When these bubbles implode, they release a stronger cleaning energy. Stubborn deposits on glassware can be effectively removed at lower frequencies.

A higher frequency produces smaller cavitation bubbles. These cover fine-featured complex surfaces more thoroughly and are gentler than low frequencies. Frequencies of 80 kHz or higher can more effectively penetrate narrow apertures such as in tubing.

Because short-path distillation can create a variety of cleaning challenges, dual-frequency ultrasonic cleaners may prove more cost-effective in the long run. Examples include operating at user-selected 37/80 kHz or 35/130 kHz.

Other useful features for cleaning short-path distillation equipment

1. Sweep is a small but automatic ± variation in ultrasonic frequency. What it does is provide uniform distribution of cavitation action, thereby avoiding areas of no or intense cleaning plus what is called harmonic vibration.
2. Degas speeds the removal of cavitation-inhibiting trapped air in fresh cleaning solutions. While this can be accomplished by running the equipment with no cleaning load, it is faster, especially when using large cleaning tanks.
3. Pulse provides a boost of ultrasonic energy and is activated to remove particularly tenacious contaminants.
4. Variable power (together with ultrasonic frequency options) allows users to develop optimum cleaning programs based on what is being cleaned and the nature of the contaminants.
5. Timers allow operators to “set and forget” cleaning cycle duration, freeing them to perform other tasks.
6. Heaters bring the cleaning solution formulation to the temperature recommended by the manufacturer. While ultrasonic action in itself heats the solution, heaters do it faster.

All of these options played a role in the pilot studies undertaken at The Clear (San Francisco, CA) with the assistance of Tovatech (South Orange, NJ) and in the selection of equipment and cleaning solution formulations currently in use.

Cleaning solution formulations for short-path distillation equipment

As noted above, caustic cleaning solutions and manual scrubbing with abrasives are not viable options for glassware and other equipment used in short-path distillation. Two biodegradable cleaning solution concentrates that can be diluted with water were evaluated, both of which proved highly satisfactory:

• Cleaning solution CLN-RS 75 (iUltrasonic, South Orange, NJ) with a pH of 3.5 can be used at full strength or diluted to 50% with water in an ultrasonic cleaner.
• Elma tec clean S2 (Singen, Germany) with a pH <1 in concentrate form is diluted to 1 to 5% with water. A representative cleaning cycle is 2–5 minutes, depending on the extent of contamination.

Both formulations are characterized as biodegradable, but local health department regulations should be followed regarding disposal of spent cleaning solutions.

Figure 3 – Flask filled with cleaning solution and positioned in the ultrasonic cleaner.

Figure 4 – Flask after ultrasonic cleaning but before rinsing for reuse.

Cleaning internal flask surfaces

As noted above, cavitation can safely remove contaminants that deposit inside containers such as round-bottom multinecked flasks. As persistent contaminants are not likely to be present on outside flask surfaces, it is not necessary to fill the entire cleaning tank with a cleaning solution formulation.

A suggested procedure is as follows:

• Add water and a wetting agent such as dishwashing detergent to the ultrasonic cleaner tank fill line.
• Fill flasks with enough cleaning solution to fully cover the contaminants.
• Place the base of the flasks in the water (Figure 3)—full immersion is not necessary. Trays and clamps are available to support flasks during the cleaning cycle.
• Activate the ultrasound. Cavitation passes through flask walls and acts on the contaminants (Figure 4).

Conclusion

Ultrasonic cleaning can replace potentially dangerous caustic or solvent baths and the associated disposal challenges. It reduces the need to stock backup/replacement glass components; helps lower production down time; and utilizes an environmentally friendly, biodegradable cleaning formulation.

Robert Sandor, Ph.D., is director, Tovatech LLC, 11 Harrison Ct., South Orange, NJ 07079, U.S.A.; tel.: 973-913-9735; e-mail: [email protected]; www.tovatech.com. Brian Maltais is co-founder, The Clear, San Francisco, CA, U.S.A.