Question 2 [30 marks]

A tray distillation column fractionates a mixture of n-hexane, n-heptane, and n-octane. The

liquid leaving the last tray (lowermost tray) is introduced to a reboiler which operates at 413

K and 3.07 bara. The composition of the liquid entering the reboiler is shown in Table 2.

Table 2. Composition of liquid entering reboiler.

Composition (mol basis)

Component

n-hexane

n-heptane

n-octane

0.12

0.78

0.1

a. Calculate the boil-up ratio of this operation.

[10 marks]

b. Determine the composition of the vapor entering the last tray (lowermost tray) of the

column.

[10 marks]

2

c. There is a suggestion from a newly joined process engineer to increase the reboiler

temperature to 420 K while maintaining the pressure and feed composition the same.

Evaluate the feasibility of this suggestion. You need to support your evaluation with

detailed calculations.

[10 marks]