A solution is a homogeneous mixture that is well-mixed to form a single layer, separation of this mixture components is not easy through filtration and a separating funnel. Instead, we use fractional and simple distillation.
“Simple distillation separates a mixture based on the difference in boiling points between two components. It is effective when the boiling points of the components are significantly different. Fractional distillation is used when the boiling points of the components are close. It employs a fractionating column to separate the mixture based on their different boiling points. It provides better separation efficiency by allowing multiple distillations within the column.”
The general process of both distillations is the same and is based on the difference in the boiling points of the mixture components. It involves heating the solution in a round-bottom flask to allow the component with a lower boiling point to vaporize first. Then this pure vapor will pass into the condenser, where it cools and condenses to form the distillate.
The separation process is divided into three main steps:
- Vaporization
- Condensation
- Collection
Generally, the component with a low boiling point will evaporate and separate before the component with a higher boiling point will retain for a longer time in the flask.
Simple distillation vs. Fractional Distillation
| Simple Distillation | Fractional Distillation |
| It separates a mixture of components with large gaps between boiling points (usually >70 °C) | It separates mixtures with components having relatively closer boiling points |
| It consists of a simple apparatus with two flasks and a container | It consists of complex apparatus with a fractionating column |
| There is no long column, but a smaller temperature difference is still there between top and bottom corners | The fractionating column is long and the heat does not distribute evenly. It is hotter below and colder on the top |
| Usually, simple distillation is used to separate solvents from solutions and to remove mineral impurities | It cannot separate solvents from solutes |
| It is commonly done once | Usually, it is a repetitive process |
| For example, Used to purify seawater | For example, Applied to separate crude oil into fuel components |
Simple distillation
- Simple distillation is used to separate substances in mixtures with widely disparate boiling points (the difference in boiling points between the compounds is greater than 70 °C).
- The experimental setup is simple having two flasks and a condenser.
- The process is useful for purifying relatively pure liquids, getting rid of volatile organic solvents, or separating the liquid from polymerization products and mineral impurities.
Fractional distillation
- Fractional distillation is used when the boiling points of the compounds to be separated are very close to each other in a way that simple distillation can’t be employed. The separated components are collected in different fractions, whose identity is usually then confirmed via spectroscopy or TLC (thin layer chromatography).
- In fractional distillation, the experimental setup consists of complex apparatus and a fractionating column.
The fractionating column is long and the heat does not distribute evenly. It is hotter below and colder on top.
The vapor condenses if the temperature is below its boiling point. But when the temperature is matching its boiling point the vapor will remain in its vapor state. Therefore, the first distillate will be liquid with a lower boiling point. Its boiling point can be reached more easily at the very top of the column, allowing it to distill over first. The liquid with a high boiling point distills later, as the second fraction.
- Fractional distillation is used in several industries: like oil refineries, the production of high-purity silicon from chlorosilanes, and the separation of water and ethanol.
Concepts Berg
What is the principle of fractional distillation?
The basic principle of fractional distillation is that different liquids boil and evaporate at different temperatures. Thus when heating a mixture containing a different substance the one with a lower boiling point starts to boil first and convert into vapors.
What are the steps involved in Fractional distillation?
The separation process is divided into three main steps:
- Vaporization: the transformation of liquid to vapors
- Condensation: the transformation of vapors back to liquid
- Collection of the condensed vapors.
What are the advantages of fractional distillation over simple distillation?
Simple distillation cannot be used to separate two liquids with a small difference in boiling points, in such cases, fractional distillation is used. Also, fractional distillation is more efficient than the process of simple distillation because the glass beads in the fractionating column provide better condensation of the liquid.
Why are ethanol and water separated by fractional distillation?
Ethanol is more volatile than water. Ethanol has a lower boiling point (78°C) which is smaller than water (100 °C) and thus a mixture of ethanol and water can be separated by the method of fractional distillation.
