Understanding the Principles Behind Distillation

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Distillation is one of the most common separation techniques used in laboratories or industries where liquid chemicals are separated based on their volatilities. Distillation is usually done by vaporizing the liquid mixture in one vessel and condensing the vapors into another. The liquid mixture being distilled is called distilland and the resulting liquid is called distillate. In laboratories, there are several types of distillation used according to the needs such as simple distillation which involves only one vaporization-condensation cycle or vacuum distillation where the process is carried out under reduced pressure. Distillation makes use of the apparent physical property of the liquids: the boiling point. This method will produce an excellent result if the boiling points of the liquids distilled differ significantly from one another.

We need to understand the reason why boiling phenomena occurs. A pure liquid in an open container will boil when its vapor pressure (the pressure of a vapor in its equilibrium with its non-vapor phases) is the same as the ambient pressure. To attain the above condition, a liquid must be heated until it reaches a certain temperature in which the molecules of the liquid have sufficient energy to overcome the attractive forces between them. This specific temperature is called a boiling point/saturation temperature and importantly, it is varied for many different liquids. Moreover, boiling point depends on pressure. Normal boiling point of liquids occurs at one atm or the standard sea level pressure; for example, water’s normal boiling point is 100 °C. Boiling point will decrease at higher elevations due to the decrease in atmospheric pressure. Likewise, as the surrounding pressure increases, boiling point will continue to increase and stop at a critical point in which liquid and gas properties become identical; boiling point decreases as the ambient pressure decreases until reaching the triple point (specific temperature and...
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