Short Path Distillation – A Definition

Short Path Distillation – A Definition

First, what is Distillation?

Distillation is very common process in chemistry, industry, food science, and in our case, cannabis and hemp and the major cannabinoids CBD and THC. From botanical essential oils to alcoholic beverages like whiskey, to the oil in your vape pen, the products of distillation are spread throughout our lives.

In its essence, distillation is used to separate and to “distil” compounds. The process works via differences in the conditions (heat, pressure) required to change the phase of components of the mixture.

Most commonly, distillation is used to separate a mixture of liquids, with the liquid being heated to force the separation of components (which have differing boiling points) into the gas phase.

The gas is then condensed back down into liquid form and collected in a vessel. Although distillation is most applied to liquids, the reverse process is used to separate gases by liquefying components using changes in pressure and/or temperature.

History of Distillation

Distillation is an ages-old technique that dates as far back as ancient Babylon and has seen widespread use in all manner of applications over the millennia. In fact, the earliest known evidence of distillation was found in a terracotta distillation device from 3,000 BC in the Indus valley of Pakistan.

Distillation was used by the Babylonians of Mesopotamia to have been used to make perfumes. Distillation of alcoholic beverages occurred much later when the Arab chemist Al-Kindi distilled alcohol in Iraq in the 9th century. The distillation of alcoholic beverages was commonplace in the 12th century in China and Italy.

What is Fractional Distillation?

Fractional distillation is the process of manipulating the physical and thermodynamic properties of a mixture for the purpose of separating its components or fractions. Chemical compounds are separated by heating them to a temperature at which one or more fractions of the mixture will vaporize.

With a base knowledge of the molecular weights and boiling/condensing points of the substance to be separated, a series of heating and cooling elements can be used to evaporate and re-condense a purified distillate from the original mixture. A large difference in the boiling points of each individual component makes the separation process all the easier.

With a base knowledge of the molecular weights and boiling/condensing points of the substance to be separated, a series of heating and cooling elements can be used to evaporate and re-condense a purified distillate from the original mixture. A large difference in the boiling points of each individual component makes the separation process all the easier.

Generally, for fractional distillation, the component parts have boiling points that differ by less than 25 °C (45 °F) from each other under a pressure of one atmosphere. If the difference in boiling points is greater than 25 °C, a simple distillation is typically used.

However, the risk of thermal degradation of one or both components in a mixture increases linearly with the introduction of the heat that drives the evaporation of the derivatives. To mitigate this, the boiling point of materials to be distilled can be lowered with the same linear relationship by introducing a vacuum which allows for greater evaporation efficiency, lower boiling temperatures, and shorter residence times (time the solution is exposed to heat). 

How does Short Path Distillation Work?

The short version of how short path distillation works, especially with regards to the refinement of crude cannabis or hemp oil is by separating out multiple desirable and undesirable compounds (THC, CBD, terpenes, etc.). The distillation of various compounds occurs at various boiling points and specific compounds can be collected in intervals.

As the sought-after cannabinoid reaches its boiling point it is vaporized, condensed, and collected in a vessel. The final product being beautifully pure distillate which is used in a wide variety of end-products, everything from vape pens, topicals, edibles, gel caps, sublinguals, and more.

Typically, the distilled product has no taste or smell because it has had the terpenes separated out. These may then be added back in depending on the end-product that you’re trying to produce.

How to Make THC or CBD Distillate using Short Path Distillation?

Short path distillation individually isolates and concentrates the major and minor cannabinoids such as CBD, THC, CBG, etc. and of course, terpenes. If we perform distillation correctly, the result will be distillates of around 99% pure. Short path distillation delivers clean and clear distillates by separating out and concentrating cannabis and hemp oil into three distinct categories:

  1. Cannabinoids – by controlling temperature and pressure points specific desired cannabinoids are extracted individually.
  2. Terpenoids and Flavonoids – each with their unique boiling points are collected or “pulled” individually. These may then be reintroduced or “recombined” to the final product, these are known as “recombined derivatives” and typically used in vape pens to create unique flavor combinations.
  3. Contaminants – removal of undesirable by-products like residual solvents, moulds, and pesticides.

Terpenes, Flavonoids, and Short Path Distillation

Terpenes are known for being quite fragile and may be destroyed during the distillation process if we’re not paying attention. Terpenes boil at different temperatures than cannabinoids so terpenes extra care is needed to preserve them and pull them at the right point in the process.

Short path distillation does allow for the pulling of terpenes using vacuum pressure with the intention of saving them for later in the process or adding to other end-products.

Regarding the distillation of Cannabis oils in a lab setting, a workflow involving multiple cuts to remove several fractions of terpenes from decarboxylated crude oil ensures the absolute deepest vacuum possible during the cannabinoid pass. These terpenes must be removed as their highly volatile nature creates vapor pressure, which in turn increases the volume of gas that must be displaced by the pump to achieve a desirable distillation pressure for the desired oils.

After this step, preliminary fractions often referred to as the, “tails” will be distilled. This fraction is usually of lower quality and is separated from the main fraction known as the, “heart” fraction of the distillation which will yield the more pristinely colored and pure distillate. The end portions of the distillation will also present with subpar quality oil that is separated and is also referred to as, “tails” fractions.

The resulting lower-quality products are often used as the base for edible or topical products as opposed to the highest quality distillates that will be found in vape pens.

What Equipment do I need for my Short Path Distillation Setup?

Deciding on which short path distillation equipment you need or which fractional distillation apparatus to utilize varies depending on the technology used but generally the basics are the same in a typical short path distillation setup:

  • Condensers
  • Chilling units
  • Heating equipment for evaporation
  • Vacuum pump and gauge – for sucking and trapping air
  • Receiving vessel – for collecting of fractional distillates

What Equipment do I need for my Short Path Distillation Setup?

Common to many labs, a traditional short path distillation apparatus consists of a large boiling flask typically made of a Borosilicate glass. This material is resistant to the immense amount of heat it is meant to endure during a distillation.

Along the vapor path a condensing coil will be connected through which chilled water or an analogous fluid will be run for the purpose of condensing distillates.

One or more receiving flasks are situated just under the tip of the condensing surface for the collection of the purified fractions of the distillation.

Occasionally, multiple stages of condensers are used to isolate components that have boiling points that are far enough apart that the vapours from each can be selectively captured by the condenser chilled to condensing temperature of each substance, respectively. This technique is known as fractional distillation.

A magnetic stirring element is typically used for agitation in order to keep the base mixture homogenized and free of the thermal degradation that occurs from prolonged exposure to the heating element.

To protect the vacuum pump, a cold trap is incorporated just upstream to condense any highly volatile terpenes from coating the inner components and compromising the lifespan of the pump.

What is Wiped Film Distillation?

As the industry evolved, however, there stood another piece of technology that would be applied to cannabis distillation just as the short path distillation array had before it. Wiped film distillation has been used for many years in the refinement of petroleum oils. With a small shift in parameters, it was clear that an automated molecular distillation solution was the destiny of cannabis purification. Wiped films went on to become the standard for production scale distillate production for a myriad of reasons. With jackets through which heat regulated transfer fluid is pumped to heat the inner surfaces of the distillation array, a more sophisticated molecular distillation machine was engineered.

A wiped film distillation apparatus uses wipers to apply a thin film of oil onto the inside of a heated cylindrical surface from which the desired cannabinoids will evaporate in real time as the crude falls down the column. At the center of the wipers is situated a condensing coil that is chilled to condense the distillate as would be done on a short path coil.

This methodology ensures the absolute minimum residence time for the sensitive cannabinoids on the heated surface. At the base of the evaporator cage, the evaporative and condensing surface areas are separated and reduced to two arms from which the end products are dispensed.

With the use of gear motors for the delivery of the oil onto the column from the heat jacketed holding tank as well as the dispensing arms, the need to break vacuum to change vessels is eliminated. This feature is particularly noteworthy as the oxygen from the atmosphere in contact with the sensitive and hot cannabinoids will allow the oil to burn on itself and show as a dark striation in the finished product.

Also numbering among the improvements to a traditional short path distillation apparatus is the incorporation of a more robust turbo molecular pump that can be used to achieve vacuum in excess of 1*10^-4mbar. The combination of the low pressures as well as the maximized surface area make for a yield that is considerably greater than conventional distillation arrays.

These units can even be plumbed together using a heat jacketed transfer hose and set to distil terpenes one array through to cannabinoids on the second column. Any operator would see the operation of a wiped film distillation array as a massive improvement when being able to move away from the need to rely on the replacement of flasks or a batch system for manufacturing scale production of distillate. Cleaning the surfaces of each piece of glass used during short path distillation is a chore that is all but eliminated by a sophisticated wiped film distillation array.

What is Rolled Film Distillation?

When we developed our own Rolled Film Short Path Distillation equipment, the RFD-27, we chose to incorporate rollers in lieu of wipers. This differing approach takes advantage of the additional evaporative surface area that is created while the rollers are not in contact with the evaporator cage to increase efficiency and throughput.

Additionally, a liquid nitrogen cold trap has been incorporated into the RFD-27 to provide extensive protection to the delicate rotors of the turbo molecular pump from any terpenes that may have escaped the terpene strip.

Finally, the use of stainless steel as the base material for the machine infrastructure avoids incidences of breakage due to negligence or wear and tear. Glass construction is useful for learning purposes, but accounting for the price of redundant glassware can be cumbersome.

For an affordable price, the RFD-27 provides a consistent, high-quality distillate at a feed rate of 4-5L/hr. With a service team that’s ready and able, our platform is designed with the operator and the business owner in mind. 

The Future of Short Path Distillation Equipment

As the need for more refined molecular distillation equipment progresses, so does the sophistication of the ancillary technology used on the associated machinery. Dosing pumps, for example, are the simplest and most straightforward way to allow for the continuous operation of a rolled film distillation array.

Without these pumps, the outlets of the distillation arms would feed into flasks that would need to be replaced once filled. This presents a problem in a production setting, as during the removal of these flasks there is a brief instance in which the interior of the evaporator is exposed to atmospheric oxygen that risks burning sensitive cannabinoids.

In addition, the cleaning of these flasks for multiple uses can prove quite cumbersome. The incorporation of these pumps into the main body of the machine will make for an altogether better user experience.

Another innovation on the horizon is the use of multiple stages of evaporator bodies allowing for cuts on different components of the crude mixture.

In standard operation, the terpene fraction of the oil is removed first, followed by hard and light cuts done on the same system. With a multistage distillation array, these cuts can be done continuously within the same machine. Aside from the obvious labor, transfer loss, and work time that is avoided during the movement of the oil from one stage to another, a multistage distillation minimizes exposure of delicate cannabinoids to oxygen and light that degrades them and reduces quality of the end-product.

The addition of another column can even be used to squeeze the last drops of viable cannabinoid product out of what most would consider unworkable waste residue while it is still hot and malleable.

Need more information about our Short Path Distillation equipment?

Click through to our RFD-27 Rolled Film Short Path Distillation page or contact us at +1(800) 837-1333 or email