Azeotrope separation

It depends on the method you use for separation. If distillation is employed, it’s definitely necessary; generally, this involves adding a third component or changing the operating conditions

It is definitely necessary to disrupt the boiling point. Either a third substance is added to form another azeotrope, or extraction is carried out.

Teacher Huayuan told us that there are generally two methods for separating azeotropes by distillation: azeotropic distillation and extractive distillation.

If distillation is to be used for separation, it is necessary to break the azeotrope; otherwise other separation methods must be employed. Your question is too general – for example, isopentanol and water can form an azeotrope, but they are immiscible, so they separate simply by allowing them to stand and layer

This post was last edited by jintchinssen on 2011-1-20 09:31. The methods for separating azeotropes include azeotropic distillation, extractive distillation, and membrane separation. Azeotropic distillation refers to a distillation process in which a third component (known as an entrainer) is added to a two-component azeotrope; this component forms new azeotropes with one or both of the components in the feed mixture, thereby enabling the feed mixture to be separated using conventional distillation methods. Azeotropic distillation can separate solutions with the lowest azeotopic point, solutions with the highest azeotropic point, as well as systems with similar volatilities. The process of azeotropic distillation depends on the properties of the azeotrope formed between the entrainer and the original components. In azeotropic distillation, an appropriate entrainer must be selected. The requirements for the entrainer are as follows: (1) The entrainer should be able to form a new azeotrope with the component to be separated, and the boiling point of this azeotrope should be lower than that of the pure components; generally, the difference in their boiling points should be at least 10℃ ； (2) The lower the amount of entrainer contained in the new azeotrope, the better, in order to reduce the amount of entrainer needed as well as the energy required for vaporization and recovery ； (3) The new azeotrope is preferably a heterogeneous mixture to facilitate separation by layering ； (4) Non-toxic, non-corrosive, and good thermal stability ； (5) It is easy to obtain and inexpensive. Extractive distillation is similar to azeotropic distillation; it also involves adding a third component (known as an extractant or solvent) to the feed mixture in order to alter the relative volatility of the existing components and achieve separation. The difference is that the boiling point of the extractant is required to be much higher than that of the components in the feed solution, and it should not form an azeotrope with those components. Extractive distillation is commonly used to separate solutions in which the boiling points (volatilities) of the various components differ very little. When selecting an extractant, the following should be primarily considered: (1) The extractant should cause a significant change in the relative volatility among the original components ； (2) The extractant should have low volatility; that is, its boiling point should be higher than that of the pure component, and it should not form an azeotrope with the original component ； (3) Non-toxic, non-corrosive, and good thermal stability ； (4) Easy to obtain and inexpensive. The characteristics of extractive distillation and azeotropic distillation are compared as follows: (1) The extractant is easier to select than the entrainer ； (2) The extractant hardly vaporizes during the distillation process; therefore, the energy consumption of extractive distillation is lower than that of azeotropic distillation ； (3) In extractive distillation, the amount of extractant used can vary over a wide range, whereas in azeotropic distillation, the appropriate amount of entrainer is generally fixed; therefore, extractive distillation is more flexible and easier to control ； (4) Extractive distillation is not suitable for batch operation, whereas azeotropic distillation can be carried out in batch mode ； (5) The operating temperature for azeotropic distillation is lower than that for extractive distillation; therefore, azeotropic distillation is more suitable for separating thermosensitive solutions. Membrane separation is a method designed based on the principle of selective permeability of biological membranes to substances, used for separating mixed samples containing different components. The membranes used in separation are polymer materials designed and synthesized as needed, and the mixed sample to be separated can be either a liquid or a gas. From the above, it can be seen that separating azeotropes does not necessarily require breaking the azeotrope temperature.