The Batch Analogy

The composition changes in the CS from the bottom toward the distillate product, Xad the top as the stages progress upward. The change in composition is described by a modified version of the DPE for a rectifying CS 

FIGURE 4.1 A typical continuous rectifying CS in a simple column, producing a distillate Xad- 

FIGURE 4.2 A simple batch distillation configuration with a constant feed stream addition 

X and y are the liquid and vapor molar fractions, respectively, in the vector form. 

The unsteady-state mass balance over the liquid in the still results in 

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