Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which several fractions of the compound will evaporate. It is a special type of distillation. Generally the component parts boil at less than 25 Â°C from each other under a pressure of one atmosphere (atm). If the difference in boiling points is greater than 25 Â°C, a simple distillation is used.