Question

1. Use the data given in the table below to construct a temperature-composition diagram for cyclohexane toluene mixture (see p. 134 in the textbook for an example of such plot). Based on your plot, what is the composition of the distillate obtained by simple distillation of 20 mole percent cyclohexane and 80 mole percent toluene? Show your work on the plot (submit your plot).

T ⁰C	Mol % Cyclohexane Liquid	Mol % Cyclohexane Vapor
110.7	0	0
108.3	4.1	10.2
105.5	9.1	21.2
103.9.	11.8	26.4
101.8	16.4	34.8
99.5	21.7	42.2
97.4	27.3	49.2
95.5	32.3	54.7
93.8	37.9	59.9
91.9	45.2	66.2
89.8	53.3	72.4
88	59.9	77.4
86.6	67.2	81.1
84.8	76.3	86.4

2. Refer to the plot you constructed in Q#1 to answer this question. Estimate the composition of the distillate of the same mixture (20 mole % cyclohexane) if the distillation column had three theoretical plates. (Show your work on the plot)

3. What would be the minimum number of theoretical plates required to achieve 100% purification so that the distillate contains 100 mole % cyclohexane. (Show your work on the plot)

4. The number of theoretical plates is crucial for a good separation inn fractional distillation, but is not the only factor that would effect the results of the degree of separation. Give one other factor that can contribute to the success of fractional distillation? Explain.

Answer 1

The temperature composition graph of this data is attached

The liquid has a composition of 20 mole percent cyclohexane and 80 mole percent toluene so it will boil at about 100.2 ^oC.

So the vapours obtained will have a composition of 40 mol% cyclohenaxe and 60 mol% toluene

see figure

If a fractionalting column has a theoretical plate of 3 it means the vapour phase will reboil 2 more times. SO from this we can see that a column having 3 theoretical plate will give a distillate with composition 79mol% cyclohexane and 21 mol% toluene

see attached

To calculate the number of theoretical plates required to get 100% purification to cyclohexane I will add another point to the temperature-composition diagram which is the boiling point of cyclohexane at 80.7 ^oC. From this the numbre of theoretical plates to get 100% purification to cyclohexane is found to be 7.

See attached