What Is an Azeotrope?

An azeotrope means that when two or more homogeneous solutions of different components are mixed in a specific ratio, they have only one boiling point under a fixed pressure. At this time, this mixture is called an azeotrope. When the azeotrope reaches its azeotropic point, because the component proportion of the gas part and the liquid part produced by its boiling are exactly the same, the solution components cannot be separated by distillation. In other words, the two components of the azeotrope cannot be separated by simple distillation or fractional distillation.

An azeotrope means that when two or more homogeneous solutions of different components are mixed in a specific ratio, there is only one at a fixed pressure.

Use of azeotrope:

Like some

In the past, when CFC-113 was used to clean the residual rosin flux on printed electronic circuit boards, in order to improve the removal effect of polar dirt, an azeotrope cleaning agent composed of CFC-113 and ethanol was used. It is composed of about 90% CFC-113 and 10% ethanol. It has a minimum azeotropic point of 46.5 ° C (the boiling point of CFC-113 is 47.6 ° C and the boiling point of ethanol is 78.3 ° C). This azeotropic cleaning agent also Used in gas phase steam cleaning and dehydration drying. It can be seen that even solvents with good cleaning performance such as CFC-113 are sometimes formulated into azeotropic mixtures in actual use.

Because the cleaning effect of various ODS replacement cleaning agents is often inferior to CFC-113, they are often formulated as mixed solvents during use, and some can also be formulated as azeotropic mixtures. For example, HCFC-225 with a boiling point of 54 ° C and ethanol with a boiling point of 78.3 ° C and an azeotrope AK225AE with the lowest azeotropic point and a boiling point of 52 ° C are used to clean the rosin flux remaining on the printed electronic circuit board. As well as dehydration and drying. HCFC-141b can also be mixed with methanol to form an azeotropic mixture to achieve better cleaning results. The new ODS replacement cleaning agent perfluorocycloalkane, because of its low cleaning power, also needs to be mixed with solvents such as cyclopentanone to be used as a mixed solvent. Some of them are formulated as azeotrope. In recent years, n-PB, which has been prosperous, is often used as a mixed solvent with azeotropic point. ^[2]

The synthesis of the azeotropic mixture separation process can be mainly divided into geometric inference methods based on residual curves and algebraic methods based on mathematical planning.

Earlier researchers mostly used residual curves to analyze and study the separation process of azeotrope. Because the rectified product is confined to the rectification zone where its feed is located, certain methods must be used to cross the rectification boundary and reach other rectification zones in order to recover nearly pure components. The method most widely used in industry to cross the rectification boundary is to introduce a mass separation agent ^[3] .

(1) Research progress abroad

Stichlmair et al. Developed a method for separating agent selection for any given system. Subsequently, Stickhlmairand Herguijuela proposed and developed the concept of tendency to separation, which can be used to deal with systems containing multiple azeotropes and complex distillation boundary structures. Doherty and Caldarola proposed a systematic azeotropic column sequence synthesis method for homogeneous systems. Later, PhamandDoherty extended the previous method to heterogeneous systems. Wahnschafft et al. Introduced the concept of "operating leaves" to judge the feasibility of separation and design the separation process. Safritand Westerberg has studied the synthesis of batch azeotropic distillation processes. For these comprehensive methods of geometric inference based on the ternary residual curve, FienandLiu, WidagdoandSeider conducted an extremely detailed review. In recent years, Thong et al. Have developed a systematic method for the synthesis of multicomponent homogeneous azeotropic separation processes. This method is mainly based on their previous work and a series of stream reuse rules. It is worth mentioning that the method of Thong et al. Can not only obtain the separation process, but also obtain more detailed equipment parameters.
(2) domestic research progress

Domestic scholars have done little research on the synthesis of azeotropic mixtures. Xing Cheng and Liu Guilian of Xi'an Jiaotong University have studied the feasibility of separation across the boundary of the distillation unit, and proposed a method to analyze the composition changes in the rectification section and the stripping section by using the volatility of each component to determine its feasibility. Based on the work of Feng et al., Zhang Zhong of Tianjin University has established a new method to determine all possible operating units, and improved the superstructure (largest structure) synthesis method. Dalian University of Technology Jinshan et al. Used PetriNet to model the azeotropic mixture separation process and systematically improved the work of Adi et al.