Analysis of Simple Distillation using Phase Diagram

The changes in the mole fractions in vapour and liquid on the phase diagram are shown in the Figure below:

From our understanding of the phase diagram, we noted that:

the initial vapour condensed is rich in A, but as distillation proceeds, the distillate will become leaner (i.e. less of A).

the process is an unsteady-state process, whereby the concentration of more volatile component in the distillate and residual decreases gradually with the passage of time.

on the other hand, the quantity of distillate collected increases and the liquid remaining in the still decreases.

there is a trade-off between quantity and concentration: the larger the quantity of the distillate, the poorer is the concentration of the more volatile component (A).

This is the same changes as observed in the analysis of VLE.

The Table below shows the trade-off between mole fraction MVC in the distillate against quantity of distillate collected, using a binary mixture example.

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