Multistage Batch Distillation

Multistage batch distillation of liquid mixtures is of great importance; it is used extensively in laboratories and in small production units. A batch distillation column is in essence a multi-purpose unit. The calculation of multistage batch distillation of binary mixtures is based on the Rayleigh equation for single stage batch distillation. For infinite number of stages in the column, the minimum energy requirement can be analytically calculated for ideal mixtures with constant relative volatility. Less energy is required for the operation at constant distillate concentration. The basis of Pontryagin’s maximum principle is a system of differential equations that describes the time dependence of the state variables of the process. Batch distillation of ternary mixtures is preferentially performed with constant reflux ratio. A more complex situation arises in azeotropic mixtures due to the existence of distillation boundaries. Multicomponent batch distillation is governed by the Rayleigh equation.