Short path distillation
How does short path distillation work?
Short path distillation systems have many names, such as modular distillation, fractional distillation, and obviously short path. Do not confuse this step with extraction processes, this is technically the final stage of refinement. The short path distillation equipment consists of glassware assembled to make up the unit along with some recirculating water heaters and a vacuum pump.
They key to this process is understanding the boiling points of the compound you are trying to collect. A short path distillation system works by adding your solution into a boiling flask and heating it up to reach the boiling point of your target compound. The size of your boiling flask will determine how much material you can process at a time. Luckily this technique does not take up much lab space so they can be installed in a small section of the lab and operation is not very intensive.
When the solution is heated, vapor will evaporate out of the main flask and be cooled along your condenser. These components create an advantage by having the vapor only travel a short distance before they are re condensed into the end products. Certain compounds stay in vapor form and travel over your final product into a cold trap for waste products, while your desired compounds re condense into a liquid form and collect as your end product.
As temperatures are raised, undesirables like residual solvents are removed and you are finally left with pure distillate. The compounds you target, specifically thc, will create fully decarbed end products that achieve high purity due to the level of separation. Cannabis distillation in a vacuum system is considerably lower cost from other distillation units and offer many benefits due to their ease of modifications. Short path distillation process works for any number of compounds that can be collected as long as you account for their boiling point and what temperature they re condense at to slightly adjust your operation.
Step by Step Guide
Completely assemble your short path distillation kit. Grease all joints and make sure everything is vacuum tight. Connect pump, turn on, and allow to reach full vacuum. After 5-10 mins the gauge should read <50 millitorr (micron). If it does not you may have a leak somewhere and will need to identify the leak before continuing.
Connect the heater/chiller to the condenser part of the distillation head and jacketed receiver and begin to circulate at the minimum set value. Note: the fluid must enter at the bottom and exit out of the top of any condenser or jacket. Not all kits may include a jacketed receiver.
Connect a small chiller or cooling system to the condenser and jacketed bottle between the cold trap and the jacketed receiver. Any temperature between 0 to 25°C is enough to cool and colder is better but do not allow to ice (i.e. do not go below 0°C).
Add dry ice to your vacuum trap then add alcohol. Keep adding either dry ice or alcohol until the trap is filled and the liquid has become roughly as viscous as oil or syrup.
Start the mantle temperature at 45-60°C and apply vacuum (do not apply heat to a sealed vessel without first applying some vacuum or opening to atmosphere). The vacuum will need to be throttled to prevent over boiling or stacking (aka muffin). Continue to both slowly open the valve to the vacuum and raise the temperature of the mantle. Try and prevent the vacuum gauge from reaching above 500 millitorr during this process. Continue until your fraction begins to thicken (approx. mantle temp 140°C).
Adjust the circulation temperature in the head to 140-180°C (actual value based on preference) NOTE: Temperatures above 120°C is going to require a special heat transfer fluid called Syltherm. The tubing for this section, the hose barbs, and any other materials that meet the fluid must be made of viton, PTFE, PFA, or other materials capable of withstanding prolonged use with temperatures up to 200°C. Do not use silicone tubing. If you do not have the appropriate equipment do not exceed 120°C. Do not use silicon tubing with silicone heat transfer fluids such as Syltherm.
Warning: High temperature fluids can scald and burn. If the system leaks it will melt, burn, or smoke materials it meets and will be very difficult to stop the leak. Proceed with caution.
Continue to raise the temperature on the mantle until the condensed material is free of any coloration or streaks of impurities.
When you are confident your collected fraction is free from impurities you can begin collecting the main body.
With your jacketed receiver first close the valve to the collection flask. Next release vacuum on the collection flask by turning the glass stopcock valve. Note: Rotating one way will pull vacuum, the opposite direction will release vacuum. If you connect the valve to an inert gas supply, it will blanket your collection flask and prevent oxidation of your collected fractions.
Once the vacuum is release remove the collection flask and replace with a new clean flask. Slowly rotate the glass stopcock 180°. This will vacuum the flask and when completed (typically ~30 seconds) you can open the valve to the collection flask.
Continue to collect your main body until the color is too red or the distillation slows to a crawl. You can adjust your distillation speed with your temperature (hotter will go faster), but the distillation head has a speed limit. You want stuff flowing up and down at the same time in the column. If there is a floor created by the upward flow the column is flooded and separating poorly. If this happens lower the temp, allow the column to settle, and begin adjusting the temperature up again, but more slowly this time. You can continue up to 220°C, but do not exceed this temp. If the distillation slows you may be ending the fraction.
Collect tails fraction of re-distillation at another time.
When completed you should have 2-3 fractions of distillate that has been separated. Your second or main fraction will contain the compound you have targeted, in this case thc. If done properly you will achieve a very pure thc distillate with a decent production capacity based on the size of your short path.