Separations analysis fundamentals - Principles of Chemical Separations with Environmental Applications - page 42

y

T

x

0

x , y

1

Figure 3.8 T - x - y graphical representation of a VLE system.

T

T

(a) (b)

x , y x , y

Figure 3.9 (a) Maximum boiling-point azeotrope; (b) minimum boiling-point
azeotrope.

line at that value, and read the corresponding values of x A and y A from the respective
curves.
Two types of azeotrope, maximum boiling point (Figure 3.9(a)) and minimum boiling
point (Figure 3.9(b)), can be represented on this type of diagram.
If the VLE data can be represented by a linear relationship, y

= Kx , a graph of K vs

total pressure can be one method to represent the data.

3.4.2 Calculation methods

K-values

A K -value K i , can be defined for each component ( i ) in the vapor or liquid phase:

y i
x i .

K i ≡

(3.3)

This allows for easy use in calculations of separation processes where phase equilibrium
data are needed. Historically, this approach was used prior to the advent of personal
computers when calculations involving linear terms were much simpler to implement.