Question

Q1. A mixture of toluene and benzene is to be separated continuously in a distillation column with the equilibria data provided in the table below. The required top product composition contains 95 mol% of benzene, and the bottom product composition contains 10 mol% of benzene. A feed consisting of 40 mol% benzene and 60 mol% toluene at its boiling point is fed to the column.

Thermodynamic data: VLE data for Benzene & Toluene

x	0	0.058	0.155	0.256	0.376	0.508	0.659	0.823	1	x
y	0	0.128	0.304	0.453	0.596	0.72	0.83	0.922	1	y

Sketch a diagram of the column, labelling it with your knowns and unknowns. List any assumptions you require for calculations.                                                                               [3 Marks]

Draw the x-y diagram.                                                                                                                   [3 Marks]

Determine the minimum reflux ratio for the column.                                                    [2 Marks]

If you are operating with a reflux ratio twice that of the minimum reflux ratio. Determine how many theoretical stages are required in the rectification section and stripping section of the column.                                                                                                                                               [5 Marks]

What plate would you introduce the feed on?                                                                  [2 Marks]

What is the definition of the term q with respect to the q-line. How is q-line affected by the condition of the feed? What are the implications of this on the dynamics of the distillation column                                                                                                                                                [6 Marks]

Explain the effect of increasing and decreasing the reflux ratio on the ease and cost of the separation.                                                                                                                                                 [3 Marks]

Answer 1