Figure 1; My dirty old Chinese Short Path.
This is a basic introduction to short path distillation of cannabinoids. We will be going over preparation of crude, compiling parts lists, how-to assemble, and safe operating procedures of your Short Path Distillation (SPD) apparatus. I’m not an expert on the subject, but I have completed over 100 2L(liter) and 5L SPD runs and I have distilled CBD, D9-THC, D8-THC, and CBG.
The general premise of fractional distillation is to separate compounds by incrementally increasing your heat and as compounds reach their boiling point one by one and the vapor of these compounds will condense and the operator can collect the individual fractions.
This is typically done in a vacuum because at reduced pressure the boiling point of the liquid is lower than at atmosphere. Short path distillation is a method used to purify relatively small volumes because the shorter the distance they need to travel the less material is lost on the walls of the apparatus.
Much like alcohol distillation, we will have our heads, which are the most volatile fraction with the lowest boiling points. Followed by the main body which is where we will be collecting our purified cannabis fraction (distillate) and finally the tails which is pretty much everything left behind.
Definitions & Acronyms
Short Path Distillation:SPD
Boiling point: BP
Distillation: The action of purifying a liquid by a process of heating and cooling (Oxford)
Vacuum: A space or container from which the air has been completely or partly removed (Oxford)
Boiling Flask: The largest flask, it holds the crude and it is the flask that is heated.
(Heating) Mantle: A piece of equipment used to heat our boiling flask, in this case it is bowl shaped and heated by electric wires embedded in glass fiber.
SPD Head: The piece of glass condenses vapors from the boiling flask
Fraction: Each of the portions into which a mixture may be separated by a process in which the individual components behave differently according to their physical properties. (Oxford)
Heads: The first fraction to boil off, the lightest and most volatile molecules.
Main Body: The target compound
Tails: What is left after collecting the main body, the molecules with the highest boiling points.
Winterization is the process of removing lipids and waxes from your solution using secondary solvents, cold temperatures, and filtration. This step is important to perform prior to distillation because the wax’s BP(boiling point) is close enough to your cannabinoid fraction that it will co-distill and your end product will be cloudy
Decarboxylation is the process of using heat to remove the carboxylic acid group from your cannabinoid. This will result in the release of CO2 and can be a very volatile reaction, especially under vacuum and in a closed system. For this reason, we will want to perform this step in a large stainless bucket, in an oven if possibl. Cascade makes ovens specifically for decarboxylation. A heater-stirrer plate works as well. This step can be completed in your SPD but is not recommended because it’s a very volatile reaction and a good way to make a mess. The Molecular Short Path Guild of America’s Instagram page has lots of pictures with examples of what can happen if you’re not careful.
Figure 2; A SPD with its insides completely coated in crude because someone pulled a vacuum on material that was not fully decarboxylated.
Photo credit: wkuconsulting
Even if your concentrate appears to be fully decarboxylated it is wise to slowly ramp up your vacuum when starting your run as any remaining acidic cannabinoids can decarboxylate rapidly and cause a mess if you’re not paying attention.
The type of pump most commonly used for short path distillation is dual-stage rotary vane. Some examples of commonly used pumps are the Edwards E2M28 and the Leybold D25B.
An inexpensive pump used on a 2L system with good results is the KozyVacu which I picked up on Amazon for under $200 and got down to 17microns connected directly to the pump.
The general rule with vacs for SPD is 3-4 CFM (Cubic feet per minute) per liter of capacity in your BF(Boiling Flask), so a 2L SPD needs a 6CFM-8CFM pump to keep your microns down where you want them
Figure 3; Digital vac gauge that is displaying the system’s micron level
It is very important to have a gauge on your system to measure vacuum. You can use an analog gauge to get a general idea of where you’re at and check for large leaks however you will have a much easier time with a digital gauge such as the Bullseye. The reason for this is that we are going down double-digit microns and when you’re using a micron as a measurement the numbers go up exponentially compared to using an inhg (inches mercury) gauge. For example, 28.35INHG is 94.8% and the equivalent to 40,000 microns, whereas 29.4inhg is equivalent to 97.4% vacuum or 20,000 microns. 99.90% vacuum is 750 micron or 29.89inhg. We are trying to get down close to a 99.99% vacuum (100 microns or 29.916) when operating and all the way down to 99.999% when the gauge is attached directly to the pump, which is the equivalent to 10 microns or 29.9196inhg.
Your boiling points will be directly affected by your vacuum depth, the lower you can get your microns the lower temperatures you will need to distill.
This Nomograph from Sigma Aldrich is a tool you can use to see a compounds BP at a set vacuum.
It is very important to have a manifold in between your vacuum pump and your apparatus so that you can control and release vacuum or pressure. Most pumps have two modes, on and off, so when you’re starting your run you will start with your valve all the way open and the pump running and then slowly close the valve while observing your boiling flask, if violent foaming occurs you are not fully decarboxylated and you need to open your valve back up to avoid filling your head and collection, and sometimes even your cold trap with hot liquid crude. Another example where a manifold comes in handy is at the end of your run when you remove vacuum, a balloon full of nitrogen or another inert gas can be placed over the intake of the manifold and your system will be filled with nitrogen rather than air which can cause oxidation and darken your end product.
In between your vacuum pump and your SPD we employ what is called a cold trap. It is exactly what it sounds like, a chilled vessel that condenses vapor that would otherwise get in our vacuum pump which can damage it and cause some nasty smells. There are multiple options for coldtraps including dry ice slurries and mechanical traps that are powered by chillers. These will collect terpenes and other volatile compounds however they will not typically be usable and will smell like hard boiled egg farts.
Figure 4; Vapors condensing in cold trap
You will want to grease all your joints before pulling a vacuum on your system. Glassware that is ungreased can get stuck together which makes it difficult to disassemble your system which is required in between runs to collect your distillate and clean out your cold trap. Trying to pull two dry pieces of glass apart is very frustrating and can end with expensive pieces of glass being broken, even worse if it’s a piece required to operate the system and you don’t have a spare!
High-temperature grease such as Apiezon high-temperature vacuum grease is required on joints that get very hot such as where the boiling flask connects to your head. This grease is very expensive, about $200 for a small 100-gram tube. You don’t need much and a tube should last for 100+ runs. Other joints still need to be greased but don’t require the expensive high temp grease. Dow Corning is a popular choice of lubricant for SPD operators.
You need to make sure your heating mantle is also a magnetic stirrer, they don’t all have that feature and I’ve accidentally purchased one that wasn’t able to stir after not thoroughly reading the spec sheet.
Another nice feature to spring for is digital vs analog, when you’re ramping up slowly it’s nice to have that precision and it’s nice to have a digital readout of your set temp AND actual temp.
Your heating mantle should be the same size as your boiling flask, meaning that you should not use a flask that is too small. If your flask is a little too small you can line the mantle with foil and fill any remaining gaps with sand. Many companies make thermal wraps that cover the mantle to keep in heat and some even have heating capabilities. You can use aluminum foil if you’re on a budget.
Heaters and Chillers
We use recirculating chillers/heaters to keep our head and sometimes cold trap at the correct temperature. You want the temperature in your head to be cool enough to condense vapors but warm enough for distillate to flow, somewhere between 40c-60c. Some operators use higher temps in their head for part of their run AKA “hot condenser tek” which can help reject some impurities that co-distill with the cannabinoid fraction.
Cleaning your apparatus
A good way to clean your SPD after a run is to put some solvent of choice in your boiling flask and run the system at atmosphere. Make sure you have proper ventilation for this.
|Production Line Steps||Equipment Name|
|Material preparation||□ Oven□ Stainless Steel Pot□ Hot Gloves□ Glass Funnel□ Scale|
|Short Path Glassware||□ 2 Liter 2-neck boiling flask□ Thermometer coupling□ Distillation ‘head’□ Mono-cow or tri-cow□ 3 x 250 ml receiving flasks□ 1 x 1L receiving flask□ Cold trap|
|Other||□ 2 Liter Heating Mantle□ Vacuum grease□ Kek clips□ Thermometer□ Bar Magnet (rare earth, AlNiCo)□ Aluminium Foil□ Vacuum pump□Vacuum hose, w/ valve□ 5 x Cork rings□ 2 lab jacks□ 2 retort stands with clamps and support rings□ Flash light□Internet access□ Digitial Vac gauge|
|Disposables||□ Dry ice□ Alcohol for slurry□ Vacuum pump oil□ Snacks|
To start you need a clean and well lit workspace, a clean spacious work bench, and a comfortable chair.
I like to set everything up from left to right, but you don’t have to. This is an imaginary off the shelf 2 liter SPD set up but by no means the only way to assemble a functional system and every manufacturer is a little different. For instance all the hoses on this example set up will be GL fittings, vacuum hose, and hose clamps and a more expensive set up might be “full bore” with kf25 connections which have their pros and cons.
- Place your heating mantle on the table, and place your boiling flask in the mantle.
- Place your support stands on the table behind the mantle with the clamps and rings facing you. One directly behind the mantle and the other about 18” to the right. The stand closest to the mantle will hold the neck of your head and the stand to the right will support your cold trap.
- After you’ve added your crude to the boiling flask you’re ready to put the head on to your boiling flask (BF). First wipe off any crude from the center of your BF and apply a high-temperature vacuum grease. This joint does not get a kek clip, it will melt! The second joint on your BF is off centered and will house a thermometer coupling for your temp probe. This will also receive high temp grease and no kek clip.
- Moving right we will attach either a monocow or tricow to the other end of our head with grease and a kek clip. (Tricows are useful because you don’t have to break vacuum and switch receiving flasks. If you do switch flasks in the middle if if a run you have to cool down before you break vacuum and then slowly ramp back up, which takes time.)
- The cow will have one to three flasks attached to the bottom and in most cases a GL fitting on the top for a hose that leads to the bottom port of the cold trap. You will need a lab jack and cork ring to support the receiving flask, if it is a tricow one flask will rest on the cork and the others will suspend in the air.
Tip- Use PTFE tape with GL fittings.
- The top port of the cold trap connects to the vacuum pump.
- Once the system is put in place and stable you can hook up the lines to the condenser, there should be 3 ports; thermal fluid in, out, and one port for your vacuum gauge. All of those will be GL fittings in this scenario, the fluid ports will be part of an outer jacket and the vacuum gauge port will be the 3rd port. Some systems have an outlet for a gauge elsewhere on the system.
- Put stoppers in any empty holes you might have in your system, and don’t forget to grease them and remember to use high temperature grease if it’s on the BF.
- Tighten all your hose clamps and test for leaks.
Figure 5- The pieces:
PPE: The following should be worn for Short Path Distillation:
- Closed toed shoes
- Splash goggle
- Lab coat
- Leather gloves
Potential Hazards and Risks; Glassware under vacuum can implode
|Stainless Pot containing winterized crude is place in oven for decarboxylation140c for 2 hours or until foaming/bubbling has subsided.|
|Using glass funnel pour your decarboxylated oil into your boiling flask. Pour slowly as foaming can occur. Fill BF to 60%-70% full. iv. Grease all joints, use grease rated for high heat on BF joints. Apply Kek clips on joints that don’t risk high heat. v. Turn Heating mantle on, ramp up temperatures slowly (10 degree increments) as too large of an increase of temperature at one time can result in over shooting your target temperature. Turn on stir bar. Set the heater/chiller connected to your condenser to 50c-60c. Place dry ice and alcohol in your cold trap or turn on the recirculating chiller if using. vi. At or before 80c pull vacuum on your SPD. Do this very slowly while keeping a close eye on your BF and condenser to avoid refluxing (bumping) into your receiving flask. Make sure your cold trap is chilled at this point. You will start to recover any residual solvents and remaining terpenes. vii. On your mono or tri cow, set a 250ml receiving flask to catch any solvents or terpenes that we see as you slowly ramp temps up to 200c in 10-20 degree increments. Some of your heads will end up in the receiving flask and some will condense in your cold trap.. viii. Keep an eye on the drips coming into your cow/flask. If it looks like liquid it’s not ready. if it looks green or blue it’s not ready. if it’s opaque, it’s not ready. If it’s golden, translucent, and stretches before the distillate drops into your flask it’s ready. If it starts to coil you;ve gone too far. ix. (If using a single cow) Kill the heat on your mantle. As heat reaches 180c backfill your system with nitrogen via the vacuum release valve. Switch to your 1 liter receiving flask. If using a tri cow just rotate to a larger receiving flask. x. Pull vac on your system. Keep an eye on vac gauge for leaks. slowly ramp temps up to 180c or until you start to distill again. xi. Ramp up temps 2-5 degrees at a time until your start to notice a color change in your distillate. Then repeat steps ix and x. This usually happens around 225c-230c. Most main body collection will happen around 205-217 Mantle temp, 170c-190c vapor temp. xii. After collecting all your fractions, kill temp. Release vacuum/back fill the system with nitrogen after you reach temps below 180c. Clean flask while hot. Add solvent and run solvent through system into flask or jar. xiii. Turn off all equipment and clean station|
Figure 6; Crude boiling in the heating mantle. The glass did not fit snuggly in the mantle so it was lined with tin foil and the gaps were filled with sand (play sand). The foil also protects the mantle from any crude spills.
Figure 7; Action in the vigreux, these are the first vapors trying to make their way up the neck and into the head for condensation. Ideally you want to keep all your visible ‘action’ in this area to avoid ‘bumping’
Figure 8; First couple drips of head fraction making their way out the head. There’s most likely some residual distillate from the last run mixed in here based off the color. If you run some clean solvent through your system after a run you wont have this issue your next run. This was not a production run and we had limited time so we skipped a few steps that we would normally do.
Figure 9 and 9.1; 250ml flask with the ‘heads’ fraction we collected, mostly sesquiterpenes
Figure 10; Swapping the 250ml flask off the monocow for a 1L flask to collect the main body
Figure 11; Steady stream of distillate cow into the collection flask
Figure 12; Cannabinoid fraction/main body
BreakingDabs (BrokenDabs.com) is a website with a paywall committed to educating operators on advanced distillation techniques.
Summit SPD (Summit-research.tech is a website that designs and sells SPD systems and ancillary products. They’re usually on the cutting edge but it comes with a hefty price tag. They also have educational resources for distillation in their treasure chest. You might need to use the wayback machine to find an older archive of the treasure chest for some things because it seems like they put up paywalls since i’ve last visited.
Right here on Gray Wolfs Lair you can learn about things like winterization, decarboxylation, and all sorts of other things that play into making high quality distillate.
Future4200.com a community driven forum filled with great information. Just make sure you use the search bar and do some reading before asking any basic questions. I promise any question you have has been thoroughly discussed there.
Rocco Glassware- American made scientific glass