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Short Path Distillation Basics

by BVV |

 Table of Contents

What Is Short Path Distillation?

Short-path distillation is a form of fractional distillation used to separate an oleoresin into its active compounds: essential oils, resin, and more. It creates a "distillate," or pure compound in the form of a clear-golden liquid with little to no taste or color.

During the short-path and pre-processes, the crude oleoresin is stripped down to less than a quarter of its total active compounds. It loses all terpenes (smell and flavor) to achieve an extremely potent final product. This can be used as a precursor for isolation and crystallization. Short-path distillation provides a cleaner separation of compounds but sacrifices throughput when compared to other techniques such as wiped film.

How Does Short Path Fractional Distillation Work?

Oleoresin is heated within a boiling flask where temperature and vacuum pressure force the active compounds to evaporate. That vapor is then pulled into the condenser by the vacuum pump to re-condense into a solid form. This is so it can be collected in the individual flasks attached to the receiving cow. This process operates similarly to a rotovap. 

Short Path Setup Components

​​Investing in a short-path distillation turnkey setup for your business is a great way to better control your operations, streamline your processes, and increase your output. Before you shop BVV, you can get a comprehensive understanding of each of its parts below.

Chiller

The term "chiller" can be misleading when talking about short-path. That’s because vapor can be recondensed at any temperature that’s at least 20 degrees colder than what it was originally boiled off at. For example, a 380°F temp is colder than the 400°F that the compound boiled off at, but this is by no means cold.

When doing short path distillation, the temp range will be about 100°C to 250°C (212°F to 482°F) on the heating mantle. The short path condenser should sit between 40°C and 60°C, but we prefer 50°C (122°F). This temperature keeps the short-path apparatus from clogging and is "cold" enough to easily recondense any vapors that travel toward the condenser.

Vacuum Pump

Short-path distillation can be very chemically abrasive to your vacuum pump, so it’s imperative to own a chemically resistant vacuum pump to achieve extreme depth. The pump should reach at least 50 microns—but the deeper the better. The preferred type of pump for distillation is a rotary vane (oil) pump to help with this. For this reason, it’s recommended you change your oil before every distillation. This allows for the best depth and keeps your vacuum pump at peak performance.

Cold Trap

The cold trap plays an important role in catching any vapors that pass through the condenser. This protects and prolongs the lifespan of your vacuum system.

Short Path

The short path itself is made up of a heating mantle and four major glass components: the boiling flask, the short path head, the receiving cow, and the receiving flasks. The heating mantle is similar to the heat bath on a rotovap. This is how you’ll heat the mixture inside the boiling flask.

The head is the key to distillation. Inside the head are small indentations called "Vigreux." These create contact points for the vapors to bump as they travel up into the head. They serve as the "theoretical plates" needed for distillation so that the vapors are purified before entering the condenser path. The head also encompasses the part of the condenser where the vapors are re-condensed into a beautiful clear-golden color. The three receiving flasks correspond to the three main fractions: heads, main body, and tails.

How to Operate a Standard Short Path Distillation Setup

New to short-path fractional distillation? Use this operating procedure as a basic starting point. Once mastered, you can adjust the parameters to suit your specific needs. Temperatures and procedures will vary slightly according to the operator or material used.

Note: Before attempting distillation, a full winterization and decarboxylation procedure should be done. This removes any residual solvents and inactive compounds from the extracted oil.

  1. Place the PTFE stir bar in the boiling flask and—using the supplied glass funnel—begin loading material into it.

  2. Once material is loaded, assemble all glassware and adjust stands to secure glassware.

    1. Place a small amount of grease on each male joint.

    2. To spread grease, turn the glass in a circular motion. You should see the grease spread completely around the joint.

    3. Place keck clips on respective joints. If you’re using a 3-neck, it should be oriented so that the first fraction goes into the first receiving flask—not the middle receiving flask.

  3. Unit setup begins by attaching the heater/chiller to the inlet and outlet ports on the short path. Once connected, set the temperature to 50°C.
  4. Connect your vacuum pump to one of the 4 ports on the supplied vacuum manifold. The manifold allows you to isolate each component of the short path with one extra to relieve air pressure.

  5. Connect the cold trap to the receiving cow. Then, connect the other cold trap port to the manifold and fill the cold trap with dry ice.

    1. To keep the trap contents from vacuum boiling: place the cold trap receiving flask in a dish with dry ice.

  6. Connect the supplied gauge to the manifold. Make sure all valves on the manifold are in the open position before beginning.

  7. Insert thermometer probe into the thermometer adapter on the head. Secure the thermometer slightly below the condenser opening
.
    1. Do this by tightening down the plastic cap so that the gasket is compressed from within.

  8. Insert the thermal probe into the boiling flask adapter and repeat the same process as above to create a vacuum seal. You want to secure the probe as deep as possible without disturbing the PTFE stir bar.

  9. Ensure all connections are secure and all components are in working order. At this point, you’re ready to begin operation.

    1. If you have insulation rope:

      1. Wrap the boiling flask and the bottom quarter of the head.
      2. Leave Vigreux visible to observe the reaction.

  10. Close the valve on the manifold that’s open for airflow. As your vacuum pump begins to pump down, examine the gauge to ensure there are no leaks.

  11. Begin heat and stirring. Turn on heat and set to 60°C. Turn on stirring and set to approximately 200 RPM.
    1. If using an analog heating mantle:

      1. Set the heating knob to the middle position

      2. Leave it at this temp if using an analog mantle for the duration of the distillation.

      3. If you see little to no reaction, bump the knob up slightly past the halfway position until a reaction begins.

  12. Once the temperature reaches 50°C, increase the mantle temp to 140°C. Allow the mantle to heat up to about 10 degrees less than your set point. This gradual increase prevents overshooting. Any of the following activities are normal at this time:

    1. Some reaction in the head

    2. A dripping cold trap
    3. Rapidly changing tempers on the head thermometer

  13. Once the mantle reaches 130°C, set the temp to 220°C, with some variability for different materials. Avoid going above 250°C.

  14. You should start to see a reaction in the distillation head around 180°-190°C. This is your first "heads" fraction. The first fraction will be all unwanteds. Great care should be taken to isolate this fraction from others. You will notice this fraction is dark with reds, oranges, and possibly blues.

  15. You’ll know this fraction is over when you see a slight color change towards golden in the head. This reaction increases to be your "main body" fraction. Allow this fraction to self-clean the head for a minute or two. Then, rotate the cow to the middle receiving flask. Reaction in the head may vary but should never stop. Increase stirring speed to 400-800 RPM as fluid level decreases in the flask. 

    1. If no reaction is present: temperature increases should be no higher than 10 degrees at a time.

    2. If minimal reaction occurs, then you are still on the initial "heads" fraction. Avoid turning the cow too early so the clean receiving flask for the main body isn’t ruined.

  16. The final "tails" fraction is a mixture of the second and third fractions. When you see an obvious color change, this means the tails fraction has hit.

    1. This is your signal to turn the receiving cow to the final flask.
    2. However, it’s optimal to try and turn the receiving cow right before this fraction hits. This will keep your main body as pure as possible.

    3. Save this for re-distillation at a later time.

  17. As the fluid level decreases further, set stirring to 900-1000+ RPM. You may need to compensate with a bit more heat as well. Increase the temp an additional 10 degrees if the reaction has subsided.

  18. Once the reaction stops, and the distillate has stopped flowing, the process is complete.

    1. Stop the heat

    2. Stop the stir

    3. Stop the vacuum pump

    4. Open the valve to let the atmosphere into the system.
 

FAQs About Short Path Distillation 

Why Did My Distillate Turn Darker?

Distillate will oxidize after exposure to atmosphere and light. Keep distillate in a cool dark place to minimize exposure and reduce chances of oxidation.

Can I Leave Ethanol in My Mixture to Use as a Transfer Medium When Pouring Into the Boiling Flask?

You can, but it should be avoided. You’ll end up with a large amount of alcohol in the cold trap which will be prone to vacuum boil-off. This gets trapped in your pump and ruins it very quickly. This also causes violent foaming and bubbling inside the boiling flask.

What Kind of Tubing Should I Use?

We recommend gum rubber for vacuum tubing and silicone for chiller tubing.

How Much Material Do I Need for Proper Distillation?

We recommend 1 gram of material per 2mL of capacity. You should fill the boiling flask approximately halfway. This would result in a 2 L system needing about 1000 grams of material for proper distillation.