Vapor distillation and azeotropic distillation

Vapor distillation: A distillation method in which water vapor is introduced directly into a liquid mixture that is immiscible with water; it is often used to lower the operating temperature in order to evaporate substances with high boiling points or those that are sensitive to heat from the feed mixture. In the process of steam distillation, water vapor serves as a heat carrier and to lower the boiling point. Azeotropic distillation: A third substance (azeotrope) is added to the system; this azotrope has the property of being able to form a minimum azeotrope with one or several of the substances in the system that are to be separated.

Vapor distillation is similar to stripping, using steam to increase the partial pressure of other components in the gas phase. Azeotropic distillation involves adding a entrainer to enable another component and the azeotrope to be distilled off from the top of the column in the form of an azeotrope.

Substances soluble in water can also be subjected to steam distillation by introducing water vapor, such as in the distillation of glycerin.

Vapor distillation: Since water and the components are immiscible, it differs from Raoult’s law in the case of miscible substances. Therefore, their gas phases are also independent, with each partial pressure being the saturated vapor pressure of its pure component. According to Dalton’s law of partial pressures, the total vapor pressure is the sum of the vapor pressures of the components that are immiscible with each other. Boiling occurs when the vapor pressure reaches the pressure of the surrounding environment. As the temperature rises, the total vapor pressure increases; boiling occurs when it exceeds the pressure of the surrounding environment, and this temperature is known as the boiling point. Since the vapor pressure of a single component at this temperature is lower than the total vapor pressure, the pure component will not boil! Therefore, steam distillation lowers the boiling point (bubble point) of the mixed components!

Azeotropic distillation: Simply put, it involves two components with similar volatility; ordinary distillation is not sufficient to separate them. A third component – an azeotrope-forming agent – must be added to react with one of these components, forming an azeotrope. The boiling point of this azeotrope is generally lower. During distillation, an azeotrope is obtained at the top of the tower. The other component is at the bottom of the tower.

This post was last edited by xw5447 on 2010-5-1 21:46. 1# nzy1983 Steam distillation is a method used to separate and purify liquid or solid organic substances. Based on the law of partial pressures, steam is introduced into the mixture to be separated or purified to cause it to boil; as a result, the organic substances are distilled out along with the steam at a temperature much lower than their boiling point, i.e., below 100°C. The substance to be separated or purified must meet the following conditions: ① It is insoluble or poorly soluble in water; ② It does not undergo any chemical reaction with water at its boiling point; ③ It must have a certain vapor pressure at 100°C in order to determine the approximate content of organic substances in the distillate. Azeotropic distillation is often used to separate mixtures that have very similar boiling points at atmospheric pressure. In a binary system such as that separating ethanol and water, since ethanol and water can form an azeotrope and the azeotrope temperature at atmospheric pressure is very close to the boiling point of ethanol, conventional distillation methods can only yield a mixture of ethanol and water, without allowing the production of anhydrous ethanol. To this end, a third substance is added to the ethanol-water system; this substance is known as an azeotrope-forming agent. An azeotrope-forming agent has the property of being able to form azeotropes with one or several substances in the system to be separated. During the distillation process, the boiling agent will evaporate from the top of the tower in the form of an azeotrope, while anhydrous ethanol is obtained at the bottom of the tower. This is azeotropic distillation.

Find an organic chemistry lab book that provides detailed explanations.

I’ll mention a few applications: for the atmospheric distillation of crude oil, steam distillation is used, while for the catalytic distillation of MTBE, azeotropic distillation is employed

Just find a textbook on principles of chemical engineering and take a look, and you’ll understand

I’m also looking for information on this topic