Unformatted text preview: = exp 21.0192 − T, oC Ps of A, torr 78.41
78.50
78.60
78.70
78.80
78.90
79.00
79.10
79.20
79.30
79.40
79.50
79.60
79.70
79.80
79.90
80.00
80.10
80.11 721.3
723.3
725.5
727.8
730.0
732.3
734.6
736.8
739.1
741.4
743.7
746.0
748.3
750.6
752.9
755.2
757.5
759.9
760.0 Ps of B, torr KA KB xA yA 760.0
762.8
765.9
769.1
772.2
775.4
778.6
781.7
784.9
788.1
791.4
794.6
797.8
801.1
804.3
807.6
810.9
814.2
814.4 0.9491
0.9517
0.9547
0.9576
0.9606
0.9636
0.9665
0.9695
0.9725
0.9755
0.9785
0.9816
0.9846
0.9876
0.9907
0.9937
0.9968
0.9998
1.0000 1.0000
1.0037
1.0078
1.0119
1.0161
1.0202
1.0244
1.0286
1.0328
1.0370
1.0413
1.0455
1.0498
1.0541
1.0584
1.0627
1.0670
1.0713
1.0716 0.000
0.071
0.147
0.220
0.290
0.357
0.422
0.484
0.544
0.602
0.658
0.712
0.764
0.814
0.862
0.909
0.954
0.997
1.000 0.000
0.067
0.140
0.210
0.278
0.344
0.408
0.469
0.529
0.587
0.644
0.699
0.752
0.804
0.854
0.903
0.951
0.997
1.000 The Txy plot is shown on the next page. It is drastically different from the one based on
experimental data. Thus, Raoult's law Kvalues for the benzeneethyl benzene system are greatly
in error. Consequently, no calculations are made for parts (a) to (f). They would predict only
very small differences between yA and xA over a very small temperature range. Exercise 4.6 (continued)
Raoult’s law prediction of Txy curves for
BenzeneEthyl alcohol at 1 atm Exercise 4.6 (continued) Exercise 4.7
Subject: Steam (B) distillation of stearic acid (A).
Given: T = 200oC. Vapor pressure of pure stearic acid at 200oC = 0.40 kPa.
Assumptions: Partial pressure of stearic acid in vapor = 70% of the pure vapor pressure.
Find: Kilograms of acid distilled per kilogram of steam added as a function of total pressure
from 3.3 kPa to 101.3 kPa.
Analysis: pA = 0.7(0.4) = 0.28 kPa pB = P − pA = P − 0.28 (1) yi = pi / P (2) M A = 284.5 , M B = 18.02 Using Eqs. (1) and (2),
kg A yA M A pA M A
0.28(284.5)
4.42
=
=
=
=
kg B yB M B pB M B (P0.28)(18.02) P − 0.28 (3) Solving Eq. (3) for values of P from 3.3 to 101.3 kPa gives the following results: P, kPa
101.3
75
50
25
15
10
5
3.3 kg A/kg B
0.0438
0.0592
0.0890
0.1790
0.3006
0.4553
0.9376
1.4650 Exercise 4.7 (continued) Exercise 4.8
Subject: Vaporliquid equilibrium for benzene (A)  toluene (B) system at 1 atm
Given: Average relative volatility = 2.5. Vapor pressure data.
Assumptions: Raoult's and Dalton's laws.
Find: xy diagram for αA,B = 2.5.
xy diagram for Raoult's law using vapor pressure data.
(a) Temperature for 25 mol% vaporization of a 70 mol% A/30 mol% B mixture.
Composition of condensed vapor and liquid residue.
(b) Plot of Raoult's law Kvalues as a function of temperature. Analysis: For a constant relative volatility, Eq. (48) applies. For αA,B = 2.5,
yA = α A,B xA
1 + xA α A,B − 1 = 2.5xA
1 + 15xA
. Solving this equation for values of xA = 0 to 1.0 gives the following:
xA
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 yA
0.0000
0.2174
0.3846
0.5172
0.6250
0.7143
0.7895
0.8536
0.9091
0.9574
1.0000 Exercise 4.8 (con...
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 Spring '11
 Levicky
 The Land

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