G98

Composition of liquid on first plate.

The temperature of distillation is fixed by safety considerations at 410 K and, from a knowledge of the vapour pressures of the three components, the pressure in the still is found to be about 6 kN/m2. The composition of the vapour in the still is found from the relation yso = aoxso/Xaxs. The liquid composition on the first plate is then found from equation (i) and for ortho:

and:

The values of the compositions as found in this way are shown in the following table. The liquid on plate 7 has a composition with the ratio of the concentrations of ortho and para about that in the feed, and the feed will therefore be introduced on this plate. Above this plate the same method is used but the operating equations are equation (ii). The vapour from the sixteenth plate has the required concentration of the ortho isomer, and the values the meta and para are sufficiently near to take this as showing that sixteen ideal plates will be required.

Using the relation vmo = aoxmo/Xax„

Plate compositions below the feed plate

Component

xs

ffXj

ys

Xl

ax1

y1

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