Fractional vs Simple Distillation
Distillation is a physical separation method, which is used to separate compounds from a mixture. It is based on the boiling points of the components in the mixture. When a mixture has different component with different boiling points, they evaporate at different times when heating. This principle is used in the distillation technique. Assume there are two substances A and B in a mixture, and A has the higher boiling point. In that case, when boiling, A will evaporate slower than B; therefore, the vapor will have a higher amount of B than A. So the proportion of A and B in the vapor phase is different from the proportion in the liquid mixture. The conclusion is that, the most volatile substances will be separated from the original mixture, whereas less volatile substances will be remained in the original mixture.
In a laboratory, a simple distillation can be carried out. When preparing an apparatus, a round bottom flask should be connected to a column. End of the column is connected to a condenser and cold water should be circulated in the condenser so that when vapor travels through the condenser it gets cooled. Water should travel in the opposite direction of the vapor, and which allows maximum efficiency. The end opening of the condenser is connected to a flask. The entire equipment should be air sealed so that the vapor won’t escape during the process. A heater can be used to supply the heat to the round bottom flask, which contains the mixture to be separated. When heating, the vapor moves up the column and goes into the condenser. When it travels inside the condenser, it becomes cool and liquefies. This liquid is collected in the flask kept at the end of the condenser.
A simple distillation is a distillation method as described above. In this method, the vapor produced directly goes into the condenser without traveling through a tall column. Therefore, the condensation happens very fast. However, this method may have the disadvantage of producing a distillate with less purity. Since all the volatile compounds tend to evaporate when the heat is supplied, the vapor will contain a mixture of volatile compounds. The ratio of compounds in the mixture can be determined according to their ratio in the original mixture. According to the Raoult’s law, mixture’s composition will be identical to the composition of the vapors at the given temperature and pressure.
If we want to get a good separation in the simple distillation method, it is beneficial to use a mixture that has largely varied boiling points. Else, the components in the mixture should be non-volatile (solid) except the one we need to separate. In this case, only the intended component will evaporate and separate out purely.
When the components in the mixture have closer boiling points, we can use fractional distillation method to separate them out. A fractional column is used in this method. At each level of the fractionating column, the temperature will be different, so the components related to that temperature will remain in that section as vapor while other are condensed back to the round bottom flask.
What is the difference between Simple Distillation and Fractional Distillation?
• In the fractional distillation method, a fractionating column is used in contrast to simple distillation.
• When the components in the mixture have closer boiling points, fractional distillation method is used. When they have a large difference in their boiling points, simple distillation can be used.
• Raoult’s law can be neglected in the simple distillation but, in fractional distillation, it is taken into consideration.