Batch Distillation An Example of a Cumulative Balance

Illustration 2.5 Batch Distillation An Example of a Cumulative Balance Batch distillation is practiced with considerable frequency both on a laboratory and an industrial scale for the purpose of separating and purifying liquid mixtures. 

As is usual in systems of some complexity, a number of different balances can be made depending on the choice of balance space. We may choose, for example, to make an unsteady integral balance about the still, or to make a similar balance about the receiver. They can be instantaneous or cumulative in time and can involve total or component mass balances. 

The balance considered here is the cumulative balance up to some point in time t. We apply the scheme previously given in Equation 2.7 and write  

Mass initially present = Mass left in still + Mass in receiver 

Cumulative balances such as the two simple expressions (Equations 2.15a and Equation 2.15b) are often overlooked in modeling, or else written out without much thought to their origin. It is important to note that they are quite independent of the unsteady integral balances mentioned previously and consequently serve as additional tools that can be used to supplement the model equations. Typically, they are used as adjuncts to instantaneous balances in batch distillation. We can, for example, solve for either still or distillate composition and obtain 

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Illustration 2.6 Batch Distillation An Example of a Cumulative Balance... 

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