CAT 2 CHP 372 2024-2025
It is necessary to separate by distillation 100 kmol/h of a process stream containing 60 mol% benzene and 40 mol% ethylbenzene, with the objective of obtaining a high purity (99.5 mol%) benzene product and an ethylbenzene product. Two schemes are to be considered:
Scheme I: An initial flash separation prior to distillation, and then distill the resulting benzene rich product to remove the ethylbenzene. This process is shown schematically in Figure 1 below. The feed to the flash separator is at its boiling point, with 60% vapour. The vapour stream is then fed to a distillation column having a reflux ratio of 1.
Scheme II: A direct distillation of the process stream (at its boiling point); reflux ratio of 1.
Determine:
a) The concentration of the vapor and liquid streams from the flash operation;
b) The number of stages necessary to produce a bottoms product of 99% ethylbenzene for scheme I;
c) The number of stages for the distillation column of scheme II to produce the two products of the same composition as in scheme I
Equilibrium X-Y plots are included for your use.
$$F, X_F$$
$$V, Y_D$$
$$L, X_B$$
Figure 1 Distillation column
MOLE FRACTION BENZENE IN VAPOUR
MOLE FRACTION BENZENE IN LIQUID
$$y = -1.7343x^4 + 5.4308x^3 - 6.5511x^2 + 3.853x$$
