[How To] Build a Recirculating Botanical Oil Extraction System
Modular, scalable equipment designed for simple, affordable, and efficient separation of high-value medicinal herbal compounds from plant fibers & bitters using recycled solvating hydrocarbons.
Follow the process flow diagram above to make sense of the steps outlined below.
1. Extraction Vessel
This is where the action happens. The vessel is loaded from the top with a permeable bag of plant material, usually a food-grade nylon filter bag which has been pre-filled via a pouring cone with lightly hammer-mill pulverized flowers or trim. A void consisting of about 20% of the vessel’s volume is left at the top to allow vapors to collect while the plant material remains submerged in the sustainable solvating fluid. This fluid dissolves oleoresin target compounds within the botanical matrix and carries them to the next step.
2. Primary Transfer Hose
A hose or pipe carries dissolved concentrate in the fluid to the oil collection vessel. The upper entry point to the hose is a dome-shaped concentric reducer that prevents oil from accumulating in the extraction vessel. The hose is braided stainless steel on the outside to resist corrosion and provide durability, while the inside is PTFE (Teflon) to provide a smooth path that also prevents excessive early oil deposition. The hose is removable for cleaning.
3. Oil Collection Vessel
The botanical oil and fluid deposit into this slightly slanted tank which is lined with a removable sheet of PTFE and jacketed with an insulated circulating water jacket. A portable propane-fueled heater connected to a small energy-efficient water utility pump is used to heat the oil collection vessel. Heat vaporizes the solvating fluid, sending it through a connection on the upper cap into the recovery system. When all liquid has been vaporized and vacuumed out by the pump, the sticky, waxy oil residue is left over. The raw extract can be removed with the liner while a fresh, clean liner is inserted for the next batch.
4. Rotary Vane Pump
A durable dual-phase pump moves gas vapor, liquid, or both depending on which valves are opened. One pump can be used in an alternating operation mode to first pump liquid solvating fluid into the extraction vessel and then pull off the vapor, or two pumps can be used simultaneously, one for vapor and one for liquid, to reduce batch time. Proper inline filtration and controlled operating conditions ensure that no botanical oil ever passes through the pump.
5. Vapor Condenser
In my case, the vapor condenser is simply a stainless steel brewing coil in a 5-gal bucket of chilled water kept cool by the water chiller. A larger vapor cooler with greater efficiency and simple maintenance would consist of two heat exchangers: 1) a shell-and-tube heat exchanger that transfers heat from the condensing vapor to the oil collection vessel’s heating water, and 2) an air-cooled finned heat exchanger resembling a cleaner version of a car’s radiator with a large fan that brings the solvating fluid back to ambient temperature, further condensing the remaining vapor into liquid.
6. Solvent Reservoir
This is as simple as a repurposed 100-lb gas cylinder rated for 300 psi or more with a dip tube that allows for liquid or vapor takeoff and deposition. It could also be more complicated if you want a larger reservoir.
7. Water Chiller
An aquarium water chiller is used to keep the water at or below ambient temperature within the basic water-cooled version of the vapor condenser.
After refining the extract with ethanol to remove residual solvating fluid, either separately in the open or within the oil collection vessel during a refining step, the crude waxy oil from this process can be added to coconut oil or chocolate for easy consumption and enjoyment.
Design Notes
Properly-rated tri-clamp fittings are used for a seamless connection interface on vessels. They do not accumulate residue and can be opened quickly. Nylon and Buna-N chemical-resistant O-rings can be used depending on what solvating fluid is chosen.
The solvating fluid, which is recycled and recirculated through the process, may be a blend of widely available isomers and short-chain aliphatic compounds that are inherently safe due to their low toxicity, moderate operating pressures, natural presence in the environment, and low concentration at atmospheric pressure especially in the presence of a helper such as ethanol. Flammability is a concern but is regularly controlled in the oil & gas industry.
The rotary vane pump could be replaced with two separate pumps designed specifically for liquid and vapor-liquid mixtures, respectively, if process conditions are precisely controlled.
Use conveyor belts on a larger version to carry plant material into and out of the extraction vessel.
A larger version can also be mounted on a durable steel I-beam skid that can be transported on a semi-trailer truck bed.
Stainless steel is used for all vessels that contact or could contact the extracted oil.
Flexible rubber hoses and rigid stainless steel tubing are used in combination throughout the process to direct flow.
Pressure, temperature, and weight sensors work fine as basic analog instruments for a small system. On a faster, larger system, digital gauges could be plugged into a small computer to monitor operating parameters and alarms. Programmable logic controllers (PLCs) are typically used, but they are overly complicated and outdated considering how far digital technology has come since the 1960s.
You can also read my article, Why I Gave Up on Cannabis for a While, to see how I put this design to use in real life. My bachelor’s degree is in chemical & biomolecular engineering from NC State University, an ABET-accredited school ranked 10th among U.S. universities by the Shanghai Ranking Consultancy. I have also managed a pilot water treatment system at one of North America’s largest power plants, located in Georgia, and started up an oil refining operation at a plastic-to-oil recycling facility in the Sweetwater area west of Atlanta.
I hope you found this design to be practical and interesting. Illustration components are sourced from Vectors Market, Vitaly Gorbachev, Nikita Golubev, smalllikeart, and Freepik via FlatIcon.