heaviest component appearing in the distillate and is called the heavy key component. The main purpose of the fractionation is the separation of B from C.

11.7.4. The calculation of the number of plates required for a given separation

One of the most successful methods for calculating the number of plates necessary for a given separation is due to Lewis and Matheson(38). This is based on the Lewis-Sorel method, described previously for binary mixtures. If the composition of the liquid on any plate is known, then the composition of the vapour in equilibrium is calculated from a knowledge of the vapour pressures or relative volatilities of the individual components. The composition of the liquid on the plate above is then found by using an operating equation, as for binary mixtures, although in this case there will be a separate equation for each component.

If a mixture of components A, B, C, D, and so on has mole fractions xA, xB, xc, xD, and so on in the liquid and yA, yB, yC, yD, and so on in the vapour, then:


yB yB yB yB yB

Xa Xb Xr Xd , a ab--1- &bb--1- &cb--1- &db--1" '

Xb Xb Xb Xb

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