Chapter 11 Transport Process and Unit Operations C.J. Geankoplis

 11.7-3 Vaporization of Multicomponent Alcohol Mixture

The vapor-pressure data are given below.

T (˚C)	Vapor Pressure (mmHg)
	Methanol	Ethanol	n-Propanol	n-Butanol
50	415	220.0	88.9	33.7
60	629	351.5	148.9	59.2
65	767	438	190.1	77.7
70	929	542	240.6	99.6
75	1119	665	301.9	131.3
80	1339	812	376.0	165.0
85	1593	984	465	206.1
90	1884	1185	571	225.9
100	2598	1706	843	387.6

Following is the composition of a liquid alcohol mixture to be fed to a distillation tower at 101.32 kPa: methyl alcohol (x_A = 0.30), ethyl alcohol x_B = 0.20), n-propyl alcohol (x_C = 0.15), and n-butyl alcohol (x_D = 0.35). Calculate the following assuming that the mixture follow Raoult;s law.

(a)    Boiling point and composition of vapor in equilibrium.

(b)    Dew point and composition of liquid in equilibrium.

(c)    The temperature and composition of both phases when 40% of the feed is vaporized in a flash distillation.

Solving:

(a)

Using trial and error method

Trial	T (°C)	P^0_A	P^0_B	P^0_C	P^0_D	Sigma XiP^0_i
1	80	1339	812	376.0	165.0	678.25
2	85	1593	984	465	206.1	816.585
3	83	1481.4	915.2	429.4	189.66	761.251

Value for T= 83°C determined by using interpolation. Data 1 use at T = 80°C and data 2 use at T = 85°C.

The closest value is T = 83°C, and it becoming the boiling point.

(b)

Using trial and error method

Trial	T (°C)	P^0_A	P^0_B	P^0_C	P^0_D	Sigma Xi/P^0_i
1	90	1884	1185	571	225.9	0.00214
2	100	2598	1706	843	387.6	0.001314

The closest value is T = 100°C, and it becoming the dew point.

(c)

Trial	T (°C)	P^0_A	P^0_B	P^0_C	P^0_D	Sigma
1	85	1593	984	465	206.1	0.148
2	90	1884	1185	571	225.9	0.013

The closest value is T = 90°C. Then the temperature is 90°C.

That's answer for Question 11.7-3