Distillation is a chemistry laboratory technique designed for purifying or separating liquids, and has been in practice for hundreds of years. The distillation apparatus has evolved into many different types of stills and each has a particular form and function. Most distillation occurs in chemical refineries or alcoholic beverage distilleries. It involves boiling a mixture so that a portion of its vapours can be collected separately.
This is the most rudimentary form of distillation. A liquid mixture is heated and the vapours are channelled through a condenser which cools the vapour back to a liquid. This liquid is collected in a receiving reservoir. This technique is best for separating chemicals that have very different boiling points.
Fractional distillation is relatively similar to simple distillation, except for the addition of a fractionating column. As the vapours are liberated from solution, they pass through a column that has a large, non-reactive surface area. This surface area allows for condensation and re-evaporation before the chemical reaches the final condenser and collection receptacle.
This process takes an initially static amount of liquid and distils a portion into the receiving vessel, as opposed to continuous distillation.
With continuous distillation, a small amount of liquid to be distilled is constantly fed into the still pot where it is heated and evaporates some of its contents. The contents are then continuously collected in a receiving vessel.
Some compounds cannot be heated directly because of their propensity to decompose. Steam distillation is one answer for this. Steam is bubbled through a mixture whereupon some molecules from the mixture evaporate into the steam. The steam is then collected and condensed, generally yielding a dual layer solution of polar and non-polar compounds.
This method of distillation allows compounds with high boiling points to be distilled. The boiling point of chemicals changes depending on the air pressure they are exposed to. Lowering the pressure lowers the boiling point. A vacuum source added to the distillation apparatus serves just this purpose. It allows compounds to be distilled that might otherwise break down if heated too vigorously.
Industrial distillation generally involves large setups of one or more types of distillation. Quite frequently there are large fractionating columns under vacuum for this purpose. Additionally, as in the distillation of crude oil for petroleum, the fractionating column will have numerous collection ports, in order to collect compounds that have different boiling points.