Medical Cannabis and Falling Liquid Film
🔍 CED Perspective Lens: Medical Cannabis and Falling Liquid Film
Dr. Benjamin Caplan, MD
A falling film evaporator concentrates a liquid extract by letting it run as a thin film down a heated surface, so the solvent boils off quickly at a gentle temperature. In cannabis processing it is the step that removes ethanol or another solvent after extraction, leaving a concentrated extract and recovering the solvent as vapor for reuse.
Falling Film Evaporation Process: From Feed Inlet to Concentrated Extract
This diagram illustrates a falling film evaporation process, highlighting the key components and flow directions. It starts with the “Feed Inlet” where the initial liquid feed is introduced. As this feed travels downward under gravity, it forms a thin “Falling Film” on the heated surface of the evaporator. At the same time, a “Heating Jacket” supplies controlled heat to the falling film, initiating evaporation.
Two outlets are featured in the diagram: one for “Concentrated Extract” and another for “Vapor Outlet.” The concentrated extract is the liquid that remains after evaporation, collected for further use or processing. The vapor outlet is the exit point for the evaporated component, typically recovered or treated for other applications.
Falling film evaporation is used in industries ranging from food and beverage to pharmaceuticals and petrochemicals. Its efficiency in concentrating solutions and separating volatile from non-volatile components makes it valuable for producing high quality extracts and for resource recovery.
The Five Parts of the Diagram
Feed inlet
The dilute extract enters at the top. In a cannabis lab this feed is usually the solution that comes out of an ethanol wash of plant material: a large volume of solvent carrying a small amount of dissolved cannabinoids, terpenes, and other plant compounds.
Heating jacket
A jacket around the evaporator surface supplies heat, most often as hot water or steam. Because the film is thin, the heat only has to travel a short distance, so the liquid reaches boiling quickly without being held at high temperature for long.
Falling film
Gravity draws the feed down the heated surface as a thin, even film. The large surface area relative to the volume of liquid is what makes this design fast, and the short residence time is what protects heat sensitive compounds.
Concentrated extract outlet
The liquid that reaches the bottom has lost most of its solvent. It leaves as the concentrated extract, which then moves on to further steps such as winterization, decarboxylation, or distillation.
Vapor outlet
The solvent leaves as vapor, is condensed back to liquid, and is stored for reuse. Recovering the solvent lowers cost and reduces the amount of ethanol a facility has to buy and dispose of.
Where This Fits in Cannabis Extract Processing
Solvent based extraction produces a dilute solution, and every solvent method needs a way to remove that solvent before the extract can be used. A narrative review of medicinal cannabis processing describes solvent removal by evaporation as a routine post-extraction step, and notes that the choice of extraction and post-processing method shapes which compounds survive into the final product (Lazarjani 2021). Falling film evaporation is one of the higher throughput ways to do that removal, which is why it appears in larger ethanol based operations.
What This Does and Does Not Show
The diagram is a schematic. It does not show operating temperature, vacuum level, throughput, or the condenser and solvent tank that sit downstream of the vapor outlet, and it does not describe any specific piece of equipment. It is meant to make the direction of flow and the purpose of each part visible.
References
This page is a reconstruction of the original CaplanCannabis.com diagram page. The book that grew out of that series, The Doctor-Approved Cannabis Handbook, is available here.
Frequently Asked Questions
What is a falling film evaporator?
A device that concentrates a liquid by letting it run as a thin film down a heated surface. The thin film boils quickly at a gentle temperature, the solvent leaves as vapor, and the concentrated liquid is collected at the bottom.
Why is falling film evaporation used in cannabis processing?
Solvent based extraction, especially with ethanol, produces a dilute solution. The solvent has to be removed before the extract can be used, and falling film evaporation removes it quickly while recovering the solvent for reuse.
What happens at the vapor outlet?
The evaporated solvent leaves as vapor, is condensed back to liquid, and is stored for reuse. Recovering it lowers cost and reduces solvent purchase and disposal.
Why does a thin film matter?
A thin film has a large surface area relative to its volume, so heat reaches the liquid quickly and the liquid spends only a short time at temperature. That speed protects heat sensitive compounds.
What comes after the concentrated extract outlet?
The concentrated extract typically moves on to further steps such as winterization, decarboxylation, or distillation, depending on the product being made.
