Rotary evaporation and Short-path distillation are both common types of equipment used to extract THC and CBD from hemp plants. This simple guide will help you understand the processes and applications of both forms of extraction equipment.
Rotary Evaporation
Since their invention in 1950, rotary evaporators have served as universal pieces of equipment for gently and effectively removing solvents from organic, inorganic, and polymeric materials. According to Chemistry LibreTexts, “Rotary evaporation is the process of reducing the volume of a solvent by distributing it as a thin film across the interior of a vessel at elevated temperature and reduced pressure.” Rotary evaporators are one of the most popular tools for solvent removal due to their ability to quickly process large quantities of solvents with low boiling points. Rotary evaporation works by the mechanical rotation of a flask to increase the surface area of the solvent, which quickens the rate of evaporation and improves efficiency. This rotation is done under a vacuum, which reduces the solvent’s boiling point and helps remove the solvent from less-volatile samples.
Short-Path Distillation
According to the Royal Society of Chemistry, short-path distillation is “A method of separating mixtures based on differences in their volatilities in a boiling liquid mixture under reduced pressure.” Because it uses a lower boiling temperature, short-path distillation equipment is especially useful for separating compounds that are unstable at higher temperatures. It’s also beneficial for purifying small quantities of compound.
Short-path distillation involves using a heated flask to gradually increase the temperature of the extraction material that’s fed into it. As the mixture heats up, its vapors rise into a fractioning tubing with the aid of a vacuum. The vapors travel a short distance—often only a few centimeters—into the tubing before being condensed, which is where the term “short-path” comes from. Because the vapors only travel a short distance, minimal quantities of the compound are wasted on the sides of the equipment. After passing through the fractioning tubing, the vapors enter the condensing tube. Here, they are cooled by water in a recirculating chiller, which allows for their condensation. Depending on the weight of each fraction, they will be separated throughout the condensing tube into different receiving flasks.
Difference between a rotary evaporator and a short path distillation
- Distillation process: Rotary evaporation is a simple distillation process that involves heating a liquid mixture in a flask and evaporating the more volatile compound, which is then condensed in a separate flask using a cooling system. Short path distillation, on the other hand, is a more complex distillation process that involves heating the liquid mixture under high vacuum conditions to reduce the boiling point of the compounds and minimize thermal degradation. The distillation process is carried out in a fractionating column, which helps to separate the compounds based on their boiling points.
- Equipment: A rotary evaporator typically consists of a heating bath, a sample flask, a condenser, and a collection flask. Short path distillation, on the other hand, involves a more complex distillation system that includes a heating mantle, a fractionating column, a condenser, a vacuum pump, and a collection flask. The equipment used in short path distillation is more expensive and requires more maintenance than a rotary evaporator.
- Yield and purity: While both techniques are effective at separating compounds, short path distillation is generally considered to be more efficient and capable of achieving higher levels of purity and yield than rotary evaporation. This is because short path distillation operates under high vacuum conditions, which allows for lower boiling points and reduced thermal degradation of the compounds. Short path distillation is typically used for compounds with higher boiling points or that are more sensitive to heat, while rotary evaporation is better suited for compounds with lower boiling points.
- Cost: Rotary evaporators are generally less expensive than short path distillation equipment, and can be a more cost-effective option for small-scale distillation. Short path distillation equipment is more expensive and requires more maintenance, but can be a better option for large-scale distillation or for compounds that require higher levels of purity and yield.
Overall, both rotary evaporation and short path distillation are effective techniques for separating and purifying compounds, but the choice of technique will depend on the specific requirements of the application. Rotary evaporation is a simpler and less expensive option for compounds with lower boiling points, while short path distillation is a more complex and expensive option for compounds with higher boiling points or that are more sensitive to heat.
