As mentioned earlier, if we want to dive deep into the concept of equilibrium. We will learn about how to predict the VLE of systems. It is one of the most important topics to understand to excel in the field of Chemical Engineering for GATE exams.

## What is VLE?

The meaning of VLE is Vapour- Liquid Equilibrium. Now if we are to understand this in simple terms, we can say that it is the distribution of a species in its chemical form into the liquid state and the vapor state. There have been several path-breaking discoveries in the field of VLE in the form of laws such as Raoult’s Law, Henry’s Law, and Dalton’s Law.

### Understanding some terms for predicting the VLE of a system

To understand deeply the ways of predicting the VLE of a system, we will have to understand many terms that will come frequently. Some of those terms are partial pressure, vapor pressure, and vapor phase. We need to have a thorough understanding of these terms in advance. It is always assumed that the system will take up the whole volume of the container.

Now in simple and understandable terms, partial pressure is the total pressure that is exerted by the gas. It is simply the addition of the pressure exerted by every particle in the solution individually. The partial pressure is independent of all the factors concerning the particles like the type of particle and the size.

## Ways to predict the VLE of a system

There are many ways to predict the VLE of a system. But in this article, we will be going through only some of them regarding how to predict.

- Soave Redlich Kwong Equation of State So, the first method is the SRK equation of the state also known as the SRK EOS. It involves many terms such as interaction parameters, infinite dilution relative volatility, Henry’s constant, and infinite dilution activity coefficients.

Apart from these terms involved, this method helps to predict the VLE of the system by generating the pressure data in regions of the whole concentration. This method is one of the most precise and accurate methods and is also widely used. The value of the constant can easily be determined by using the pressure charts.

- NRTL Equation – This is one of the recently developed methods for predicting the VLE of a particular system. For this method to work adequately, we should have the hydrocarbon water and a graph having negative deviation from Raoult’s Law. The compounds required here should be polar in nature and extensive knowledge of binary mixtures is a prerequisite.

The mixtures or the systems for which this way works the best include the ones having a negative deviation from Raoult’s Law, having amines in water, and both polar and nonpolar mixtures. Now, this method involves knowing the coordination number of the resultant system and the compounds involved. It also involves the ratio of the molar volume of the components.

## Application of the VLE Data

The main purpose of having the VLE data is to obtain the number of compounds that are required to be separated by the process of distillation. The data that is required by the Vapour Liquid Equilibrium data can also be used to determine at what temperature precisely, the process of condensation will start for a particular mixture. Another important use of the VLE data is how all the components in a particular mixture are separated. Hence, it is evident that this process has a variety of uses in different types of industries.

The data that is predicted by VLE is also comparatively cost-efficient and in comparison, to the other processes, it is very easy to perform also as generally the data can simply be obtained by the processes of distillation and condensation itself, and no costly processes are required.

## Importance of Equilibrium in VLE Data

The importance of equilibrium increases when we need to maintain the fact that the temperature required for the mixture has to remain a certain constant and not change over time. If the temperature keeps changing then the calculation would become much more difficult and many other factors such as air pressure will also come into play.

## Vapor-Liquid Equilibrium Diagram

This diagram is used by scientists around the world who are working on different ways to predict the VLE system. As mentioned above in the article, the graph should be of a system that indicates the negative deviation towards Raoult’s Law. These types of mixtures include the ones like the addition of methylamine in water and other such amines. The importance of such diagrams increases when we have to observe a particular thing over a long period.

### Conclusion

Though not many ways have been discovered yet to determine the data predicted by VLE it is still said to be one of the most promising research areas in the field of chemistry as many things are yet to be figured out properly, especially for the GATE aspirants.