Holdup rectification

For preliminary studies of batch rectification of multicomponent mixtures, shortcut methods that assume constant molal overflow and negligible vapor and liquid holdup are useful. The method of Diwekar and Madhaven [Ind. Eng. Chem. Res., 30, 713 (1991)] can be used for constant reflux or constant overhead rate. The method of Sundaram and Evans [Ind. Eng. Chem. Res., 32, 511 (1993)] applies only to the case of constant remix, but is easy to apply. Both methods employ the Fenske-Uuderwood-GiUilaud (FUG) shortcut procedure at successive time steps. Thus, batch rectification is treated as a sequence of continuous, steady-state rectifications. 

The time t required for batch rectification at constant reflux ratio and negligible holdup in the trap can be computed by a total material balance based on a constant boilup rate V, as shown by Block. ... 

The batch distillation of binary mixtures will be considered fpr the cases of (1) no rectification, (2) rectification without liquid holdup in the column, and (3) rectification with holdup. 

Rectification without Liquid Holdup in Column Finite Reflux Ratio In this case, it is assumed that the distillation is carried out with a fractionating column, that the holjluii f liquid in the column is neg igi-... 

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. 

Rectification without Liquid Holdup in Column. Total Reflux, For the case of no liquid holdup, Eq. (14-1) applies to each of the components, but the difficulty involves the evaluation of Xd as a function of Xl. 

Batch Rectification of Multicomponent Mixture at Total Reflux. As an example, consider the fractionation of an equimolal mixture of A, B, C, and D at total reflux with relative volatility ab = 2.0, ao = 4.0, and ad — 8.0. The column is equivalent to three theoretical plates and holdup of liquid will be neglected. 

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