Operation pressure

Operation pressure
A / atmospheric distillation It is a distillation process is performed under normal atmospheric pressure, such as distillation of crude oil in refinery.
B / vacuum distillation Distillation process is carried out using vacuum pressure (pressure less than atmospheric pressure),the reduce in pressure cause to reduce in boiling point of components therefore the vacuum distillation is used to separate the heavy components such as atmospheric distillation residues (RC) to avoid decomposed their molecules , the vacuum pressure is generate by using ejector or vacuum pumps.
4 - The type and nature of the mixture:
A / distillation of a real mixture: The mixture is called real mixture when have initial and final boiling point, this mixture is distilled by normal distillation.
B / distillation of azeotropic mixture Some liquid mixture cannot be separated by distillation because the volatility of components are approaches ( relative volatility of mixture normal is equal to one) . This type of mixture is called azeotropic mixture like, ethyl alcohol and water form an azeotrope of 95.6% at 78.1 °C. So to distillate this type we change the rate of volatilization of the mixture by adding benzene C6H6 to make mixture rate volatility is greater than one compared to alcohol.
Immiscible liquids, such as water and benzene, easily form azeotropes. Commonly, these azeotropes are referred to as a low boiling azeotrope because the boiling point of the azeotrope is lower than the boiling point of either pure component (ethyl alcohol). The new azeotropes (water and benzene ) is separated from the top of the tower either alcohol will be withdrawn from the bottom of the tower.