Page 280 - Separation process engineering

Figure 7-2. Distillation column

At the pinch point, where compositions are constant,

(7-21)

The equilibrium expression can be written in terms of K values as

(7-22)

Combining Eqs. (7-20) to (7-22) we obtain a simplified balance valid in the region of constant
compositions.

(7-23)
Defining the relative volatility α = K/K and combining terms in Eq. (7-23),
ref
i
i

(7-24)
Solving for the component vapor flow rate, V Min i,j+1 , and rearranging
y

(7-25)