Solvent Recovery Systems

Solvent Recovery Systems

April 23, 2019

Rotary Evaporation or Rotovap

Rotovap systems work by putting your solvent in a large round flask. The bottom of the flask rests in a water bath that can be heated to prevent the solvent from freezing during the evaporation process. The neck of the flask is attached to a motor and a vacuum. The motor will continuously spin the flask so that the solvent is continuously agitated and spread out along the interior walls of the flask, promoting evaporation. The vacuum removes the solvent vapors into a condenser where it is collected for reuse.  Rotovaps are a tried and true method of solvent recovery but having to reload each batch can be slow and labor intensive compared to falling film evaporation methods. There are continuous feed rotovap methods where material is pulled in and pumped out of the flask via tube inserts but the processing time is still much slower than falling or wiped film evaporation methods. One frequent misunderstanding that occurs when reading the load capacity of a Rotovap is that the size of the evaporating flask does not determine how much material can be processed per batch. The load capacity of the evaporating flask runs between 20-60% the size of the flask because surface area is needed for evaporation to take place. Thus a 10 litre evaporating flask can only run between 2-6 litres at a time.


Falling Film Evaporators

A falling film evaporator works by running a film of solvent mixture (we call it Red Liquor) down a heated surface. The solvent quickly evaporates off this surface and immediately condenses on a cooler adjacent surface. Alternatively, if the film of solvent is running down the interior surface of a cylinder, the vapor is piped off to an external condenser. The large surface area to volume ratio of a falling film evaporator makes for a very effective heat transfer and evaporation cycle. Keeping the pressure low while the evaporated solvent recondenses will preserve more terpenes in the resulting product.  For production processes targeting higher cannabinoid extraction and forgoing the capture of terpenes, higher evaporation pressures can be used to reduce energy costs. Falling film evaporators, depending on how they’re designed, can process upwards of 60 liters per hour whereas most rotovaps can usually only remove 5-10 liters of solvent per hour. Falling film evaporators are used in both batch and continuous processes which render them are highly scalable.


Wiped or Thin Film Evaporators

Wiped film or thin film Evaporators work by feeding the recovered oil continuously down a cylinder. This film of oil is continuously thinned out by a wiper running along the heated surface to increase the evaporation rate. A typical wiped film evaporator will have a heated cylinder with the solvent running down the interior walls with a ‘wiper’ continuously thinning the film of solvent running down the heated walls. Oil vapors will then condense on a cold surface at the center of the cylinder. Wiped film evaporators are great for more viscous solvents or solvents sensitive to heat. Like falling film evaporators, wiped film distillation systems can also operate at high processing speeds with a continuous feed.   


Conventional Stills

High tech methods of catching every terpene and polyphenol molecule are incredible but they can also be incredibly expensive. If your mission is high yield of cannabinoids at fast processing speeds with moderately priced equipment, then a simple still might be your best bet. From essential oil makers to moonshiners, this tried and true method consists of heating your solvent in a ‘kettle’ and allowing the solvent vapor to condense inside a coil. As the solvent is collected in the condenser coil, it drips down and is recaptured in a separate container. To heat the kettle, a water filled tube is usually run into a firebox where the water is boiled and turned into steam. This steam is then run into the kettle through a coiled tube where it heats up the solvent before exiting the kettle and into a condenser. The condenser converts the steam back into water that is then eventually pumped back into the firebox to complete the cycle. The higher temperatures used in this solvent recovery method precludes the capture of more delicate terpenes and polyphenols but is incredibly efficient at extracting cannabinoids. Commercial producers using conventional stills often add terpenes such as myrcene, pinene, and limonene back into their honey oil to make up for their loss in this process.

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