Minimum Reflux: One of the important information about a column could be the value of minimum reflux. Knowing its value we can get an idea of the operating reflux and an estimate of the number of stages. The easiest method is to draw the equilibrium curve and locate the intersection of the q-line and the equilibrium curve. Draw a line originating from (x_D, x_D) and passing through this intersection point. Extend this line to y-axis. The steps involved in finding the minimum reflux ratio are:

(1) Draw point (1) having coordinates (x_F/q, 0).

(2) Draw point (2) having coordinates (x_F, x_F).

(3) Join points (1) and (2) and extend the line (1-2) to intersect the equilibrium curve and obtain point (3).

(4) Draw point (4) having coordinates (x_D, x_D).

(5) Now join point (4) with (3) and extend the line (4-3) to intersect at y-axis at point (5). Point (5) has the coordinates (0, x_D/(R_m+1)).

(6) Calculate R_m given by

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Module for Calculation of Minimum Reflux:

x_F		feed composition, mole fraction
x_D		distillate composition, mole fraction
q		feed quality
x3		intersection of q-line with equilibrium curve, x3
y3		intersection of q-line with equilibrium curve, y3
Point 5		intercept, x_D/(R_m+1)
α		relative volatility)