Rectification of Binary Mixtures

The separation of two liquids from each other by fractional distillation may be accomplished in two general ways (1) the batch, or intermittent, method and (2) the continuous method. In the former, the composition and temperature at any point in the system are changing continually in the latter, conditions at any point are constant. 

SorePs Method. Sorel (Ref. 17) developed and applied the mathematical theory of the rectifying column for binary mixtures. He calculated the enrichment, the change in. composition from plate to plate, by makin 3Sergy and material balances around each plate and assunie that equilibrium was attained between the vapor and liquid leaving the plate. He proceeded stepwise through the column T)y applying this rhethod successively from one plate to the next. 

Owing to the steady-state condition involved in continuous distillation, its analysis is simpler than batch operation and so will be considered first. 

The equations for SorePs method will be derived for the case illustrated in Fig. 7-1. The column is assumed to be operating continu-oudy on a binary mixture with the feed entering on a plate between the top and bottom. The column is provided with heat for reboiling by conduction such as steam coils in the kettle the case of the use of live or open steam will be considered later. A simple total condenser 

Consider the region bounded by the dotted line in Fig. 7-1., The only material entering this section is the vapor from the nth plate Vn) while leaving the section is the distillate D and the overflow from the (n + l)th plate On+i. 

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Lewis, W. K., Rectification of Binary Mixtures. Plate Efficiency of Bubble Cap Columns, Ind. Eng. Chem., 28, 399-402 (1936). 

Batch Rectification of Binary Mixture. Assume that the equimolal mixture already considered, page 376, is to be distilled in this manner, and it is desired to evaluate the effect of the column holdup. 

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