How to Use a Short Path Distillation Assembly: A Step-by-Step Guide for Botanical Processing

Short path distillation separates the compounds in a botanical extract by boiling point. Under deep vacuum those boiling points drop sharply, so delicate compounds can be vaporised at far lower temperatures and condensed just a few centimetres away, which keeps heat damage to a minimum.

This guide walks you through a full run on a 2L or 5L short path distillation kit, such as the HLO 2L Short Path Distillation Kit or the Helios Short Path Distillation Kit With Digital Heating Mantle, from preparing your material to shutting down and cleaning. Follow the order below closely: in short path work, the sequence of vacuum, heat and cooling matters as much as the temperatures themselves.

What you'll need

Everything below connects through standard 24/40 ground glass joints, so components can be swapped or upgraded later.

Before you start: prepare the material

The cleaner your feed material, the cleaner and safer the run. Before it goes into the still flask it should be:

• Winterised, so fats, waxes and lipids have been removed. These otherwise carry over and cloud the distillate.
• Fully stripped of solvent, ideally on a rotary evaporator. Even small amounts of leftover solvent or water boil violently under vacuum and can throw material straight up into the head.
• Filtered, so no particulate ends up scorching on the flask wall.

If you're unsure how much solvent remains, plan for a longer degassing stage (step 5).

Step by step

1. Inspect the glassware. Check every piece for chips, scratches and star cracks, especially around joints and the flask base. Glass under vacuum and heat is under real stress, and a flawed piece can implode. Everything should be clean and completely dry.
2. Assemble and seal. Clamp the still flask over the mantle on a lab jack, with the stir bar inside. Fit the short path head, thermometer, cow receiver and receiving flasks, then the cold trap and vacuum line to the pump.
   • Apply a thin band of high-vacuum grease to the upper part of each 24/40 joint and twist to seat it. The joint should turn clear with no streaks.
   • Secure every joint with a keck clip (metal or plastic) and support the glass with clamps, not the joints.
   • Position the thermometer bulb just below the head's side arm so it reads the vapour, not the flask.
   • Fit the insulated jackets to the head and flask if you're using them.
3. Set the condenser. Start the chiller circulating. With viscous botanical oils, run the condenser warm enough for the distillate to keep flowing; too cold and it thickens or solidifies in the head and blocks the path. Charge the cold trap.
4. Load the flask. Add your prepared material, keeping it below half the flask's volume to leave room for foaming. Start the stirrer at a steady, moderate speed.
5. Pull vacuum first, then degas gently. With the heater still off or on a low setting, open the system to the pump and watch the vacuum gauge. Any remaining solvent, water and dissolved gas will bubble off. Hold at low heat until bubbling settles and the vacuum level stabilises. If the vacuum won't come down, find the leak now (see Troubleshooting) rather than mid-run.
6. Ramp the heat in stages. Raise the mantle temperature gradually, letting the system settle at each stage. Watch for vapour rising and condensing in the head. Never heat faster than the system can keep up with, and stay within the limits of your glassware and mantle.
7. Collect your fractions. Lighter, more volatile compounds come over first, then the main fraction, while heavier residues stay in the flask.
   • Rotate the cow receiver to a fresh flask whenever the vapour temperature shifts or the colour or flow of the distillate changes.
   • Log mantle temperature, vapour temperature, vacuum level and time at each change so you can repeat a good run.
8. Shut down in the right order. Turn off the heat and lower the mantle on the jack. Let the flask cool under vacuum; venting hot material to air oxidises it and puts thermal shock on the glass. Once cool, vent slowly (with nitrogen if you have it), then stop the pump and chiller.
9. Clean and maintain. Disassemble once everything is at room temperature. Wipe the grease from the joints, clean the glassware with a suitable solvent such as ethanol, and dry it fully. Empty the cold trap and check the pump oil, changing it if it's discoloured.

Safety

• Wear safety glasses or a face shield and heat-resistant gloves throughout. Glass under vacuum can implode, and hot oil causes serious burns.
• Never leave a run unattended, and keep the area clear of anything flammable.
• Work in a well-ventilated space and vent the pump exhaust away from your working area.
• Use only an electric heating mantle; never an open flame.
• Keep the lab jack under the mantle so you can drop the heat away from the flask instantly if something goes wrong.
• Follow the operating limits in the manuals for your mantle, chiller and pump.

Troubleshooting

Shop short path kits

Every kit we stock uses borosilicate glass and standard 24/40 joints, so you can start small and expand later:

• HLO 2L Short Path Distillation Kit: glassware only or with a digital heating mantle, a flexible starting point for smaller batches
• Helios Short Path Distillation Kit With Helios Digital Heating Mantle: 2L and 5L options for higher throughput
• Helios Short Path Turn Key Kit: a complete setup for labs that want everything in one order
• Short Paths & Parts: heads, flasks, cows, cold traps and spares for building or maintaining your own system

Final tips

• Do a dry run first: assemble, pull vacuum and leak-check before you ever load material.
• Let the system reach thermal equilibrium at each stage before pushing further.
• Keep a run log. Recording temperatures, vacuum levels and fraction changes is the quickest route to consistent results.
• Maintain your cold trap and pump oil; most vacuum problems start there.

Need help choosing a size or the right supporting kit? Get in touch with the BHO Hardware team or call 0114 229 1807.