Calculating K Values (VLE Coefficients)

In summary, the person is doing a multicomponent distillation with exotic chemicals and needs the vapour-liquid-equilibrium coefficients, also known as K-values, at feed conditions. They plan to use the Antoine equation to calculate the K-values, but are unsure if the pressure value obtained from the equation will be the saturated vapour pressure of component i. Raoult's law states that the partial pressure of each species in the vapor phase is equal to its mole fraction in the liquid phase times its pure-component vapor pressure, which can be calculated using the Antoine equation at a given temperature. The person is grateful for having their question clarified.
  • #1
_Greg_
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Right so basically, I'm doing a multicomponent distillation with some exotic chemicals.
My feed comes in at 13kPa and 60*C, so it's under vaccum. This will be a two phase mixture.
What I need is the vapour-liquid-equilibrium coefficients, 'K- values' at feed conditions.
I'm basing this on an ideal system to start with then I'll do it as non-ideal (fugacity coefficients etc)

So for now, I'm planning on using the Antoine Equation ln P = A - ( B /( T + C) ) (from coulson & richardson vol 6)
Now the K values can be calulated with Raoults law Ki = Pi(sat)/Pt
My question is, will the pressure value I get from the Antoine equation be the saturated vapour pressure of component i? (Pi(sat))

Sorry this probably sounds terrible, but it's been a while
 
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  • #2
From google:

Mathematically, Raoult’s law is expressed as

y(i)P = x(i)P(i)sat for all species (i= 1, 2,...,N)

where xi is the liquid phase mole fraction, yi is the vapor phase mole fraction, P(i)sat is the vapor pressure of pure component i, and P is the total pressure. In words, Raoult’s law says that the partial pressure of each species in the vapor phase is equal to its mole fraction in the liquid phase times its pure-component vapor pressure.

And P(i)sat you can calculate with the Antoine equation at a given temperature, so you're right
 
  • #3
Thanks Vulgar
Just wasn't sure because there's different forms of the antoine equation, some say Psat, other just say P. Could have done this like 2 years ago, now in my final year I struggle with some of the basics lol.
Cheers for clearing that up ;)
 

What is the purpose of calculating K values in VLE?

The purpose of calculating K values, also known as vapor-liquid equilibrium coefficients, is to determine the composition of the vapor and liquid phases in a multi-component system at equilibrium. This information is important in various industrial processes such as distillation, absorption, and extraction.

How are K values calculated?

K values can be calculated using various methods such as the Raoult's law, Antoine equation, and Wilson equation. These methods use different parameters such as temperature, pressure, and component properties to estimate the vapor-liquid equilibrium ratios.

What factors affect the accuracy of K value calculations?

The accuracy of K value calculations depends on factors such as the complexity of the system, the accuracy of the thermodynamic models used, and the quality of the experimental data used to validate the calculations. Other factors include the presence of non-ideal behavior, phase changes, and the number of components in the system.

Can K values change under different conditions?

Yes, K values can change under different conditions such as temperature, pressure, and composition. As these conditions change, the equilibrium between the vapor and liquid phases may shift, resulting in different K values. Therefore, it is important to consider the specific conditions when calculating and using K values.

What are the limitations of using K values in VLE calculations?

One limitation of using K values is that they are only applicable for systems at equilibrium. This means that they cannot accurately predict the behavior of non-equilibrium systems. Additionally, K values are based on thermodynamic models and may not account for other factors such as intermolecular interactions and phase changes, which can affect the accuracy of the calculations.

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