Fractional Distillation versus Simple Distillation

Simple distillation

Simple distillation is a single stage distillation where a liquid mixture is boiled and the resulting vapor condensed. Wiped film and short path distillation are examples of single stage distillation. Simple distillation can provide a moderate improvement in purity. It is useful in situations where you are attempting to separate compounds with very different boiling points. Think of distilling water to remove salt.

Short Path Distillation – Simple Distillation
single stage distillationThe vapor has a higher purity than the boiling liquid. The increase in purity is equivalent to one stage of evaporation and condensation.

 

Short path and wiped film are both single stage distillations (simple distillation).

Vapor liquid diagram simple distillation
The condensed distillate has the same purity as the vapor above the boiling liquid.  The total increase in purity is only a single stage.

 

Fractional Distillation

Fractional distillation starts out the same as simple distillation. Crude extract is boiled. This single stage produces vapor with moderately higher purity than the starting liquid (crude extract). So far it’s the same as short path or wiped film.

Once the vapor enters the fractional distillation column such as a spinning band column, the magic begins. The spinning band distillation column creates additional stages of separation inside it by increasing vapor/liquid contact. In the case of spinning band distillation, the rotating band dynamically forces the vapor and liquid together. The spinning band pumps the higher boiling components back into the boiling flask and allows the lightest components to pass through.

These additional stages of separation is what drives the ability to produce such high levels of purification.

Fractional distillation, and especially spinning band, is capable of making difficult separations. Some terpenes have boiling points that are close to that of THC and CBD. Spinning band has the ability to remove these terpenes which cause odor, bad taste, and color.

Spinning Band Distillation – Fractional Distillation
 

single stage distillationOne stage of separation occurs in the boiling flask. The vapor has a higher purity than the liquid.

fractional distillation

 

 

 5-10 more stages of separation take place in the Spinning Band Distillation column.

Each stage of separation increases the purity of the vapor.

multiple stages of separation

 

 

 

 

What Does This Mean For Your Distillations?

It is important to note that this is not the true vapor-liquid diagram for the distillation of cannabis oil. These diagrams come in all shapes and sizes, and the shape and size tell you how a given separation will go. Also, these graphs are best used when only considering two components. Anything more than a “binary” mixture gets more complicated.

However, the bottom line is that more stages equals a better separation. The reason wiped film and short path require multiple (2-3) passes is they offer only one stage at a time. Our spinning band systems can offer upwards of 10 of these stages. This is the real reason why spinning band is capable of a single pass.

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