Despite what many people believe, distillation does not actually produce
anything. Distillation is simply a process wherein the different boiling
temperatures of constituents in a base product are used as a method of
separating them, collecting only those that are desired, while discarding
the remainder. Distillation is simply a very effective method of purification.
There are two primary methods of distillation- Traditional (also known as
Pot Distillation) and Reflux. Depending on the product that you intend to
distill, you will need to select the most appropriate method of distillation
in order to achieve your desired result.
Traditional distillation is used when you do not have several constituents
with varying boiling points, or a goal of collecting one component in specific. Although Traditional Distillation does not offer the high degree of separation and purity associated with Reflux Distillation, it is extremely well suited to certain products. Generally, if you intend to distill essential oils, that is, the oils from an organic substance, you will choose the Traditional Distillation method.
This is because you will use a solvent, such as water, glycerine, or alcohol, to dissolve the oils from the organic material and to carry them on the vapor to the condenser, and ultimately to your collection container. Traditional Distillation is also widely used in alcohol distillation for products such as whisky. This is because certain characteristics with varying boiling points are desired. In this case, reflux distillation would separate these components out in the distillation column, and they would not be collected.
Reflux Distillation, in contrast, offers a very high degree of purity. This is because a longer column is used, where many of the components will not reach the top of the column. As vapor rises in the distillation column, the temperature gradually decreases. This causes components with higher
boiling points to reach a certain level in the column where they fall below their vaporization temperature, condense back into liquid, and descend in the column. This separates these components from the vapor with a lower
boiling point as it continues to rise in the column. Each component separates from the rising vapor in this manner until, at the top of the column, you have a single remaining product.
To enhance this separation, we use what is called reflux. In simple terms, refluxing is causing the liquid to condense and re-evaporate in the column prior to finally exiting via the condenser. The number of times that you cause the vapor to ‘reflux’ before exiting the column is called the reflux ratio. Careful control of the reflux ratio through control of the heat input and the speed of your cooling water allows you control over the purity of your distillate. It is important to remember that a slower distillation by increasing your reflux ratio will result in a more pure finished product.
As stated, refluxing causes the components from the kettle to separate based on boiling temperature. Imagine that the illustration to the left is your distillation column (please note that during distillation the temperature breakdown will not be as evenly spaced as shown in the diagram). You will
see that the temperature drops as you ascend in the column. At the bottom, all constituents with a boiling point of 100oC or lower are boiling (in vapor form). But as you rise in the column the temperature drops below 100oC (the boiling point of water), thus water vapor will turn back into liquid form, and be separated from the mixture.
As you rise in the column further, the constituent with the next highest boiling point will fall below its vaporization point, and be separated from the mixture. As it turns back into liquid, it will also fall back down the column until its temperature rises to its boiling point again, where it turns back into vapor, and begins to rise through the column again. This
continues to happen as you rise in the column, with each constituent being separated from the mixture based on its boiling point until you reach the top of your column.
At the top of the column, all components with a boiling point equal to or less than the temperature at that point will be present. This means that by careful control of the temperature at the top of your column you are able to produce extremely pure product. The temperature is controlled by a combination of the heat input and the speed and temperature of your cooling water through the amount of reflux created. You will notice during use that by reducing the flow of your cooling water slightly, the temperature may not change however the speed at which you remove the distillate will increase. The result is a less pure distillate.
Because all of these different boiling points take up some space in the length of your column, it is much more difficult, or even impossible, to use a short column and truly obtain proper reflux and separation. This results in lowered purity of your distillate. For this reason it is very important that your column be of sufficient length in order to produce a pure product. The still Pot Still Head is not of sufficient length for use as a reflux unit.