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simulator with ideal Kvalues. The results are as follows:
Case
Vapor, kmol
Liquid, kmol
Vapor mol frac:
Benzene
Toluene
oXylene
Liquid mol frac:
Benzene
Toluene
oXylene (a) 100oC,
1 atm
67.64
32.36 (b) 100oC,
2 atm.
0
100 0.395
0.305
0.300 (d) 150oC,
1 atm
100
0 0.60
0.25
0.15 0.698
0.224
0.078 (c)105oC,
0.1 atm.
100
0 0.60
0.25
0.15 0.60
0.25
0.15 Only in the Case (a), are two phases formed. At 1 atm, the bubble point is 91.3oC and the dew
point is 107.5oC. Exercise 4.30
Subject: Prove that, at equilibrium, vapor is at its dew point and liquid is at its bubble point.
Analysis: After equilibrium is achieved, separate the vapor from the liquid and analyze the
separate phases.
zi
xi =
(1)
For the liquid: Apply Eq. (5), Table 4.4,
1 + Ψ Ki − 1
At the bubble point, Ψ = V/F = 0 and, therefore, from Eq. (1), xi = zi . Also, then, Ki xi = Ki zi = yi and, therefore, C
i =1 Ki xi = C
i =1 Ki zi = C
i =1 For the vapor: Apply Eq. (6), Table 4.4, yi = 1, which is the bubblepoint equation, Eq. (412). yi = Ki zi
1 + Ψ Ki − 1 (2) At the dew point, Ψ = V/F = 1 and, therefore, from Eq. (2), yi = zi . Also, then, xi = yi /Ki = zi /Ki
C
C
yi C zi
and, therefore,
=
=
xi = 1 , which is the bubblepoint equation, Eq. (412).
i =1 Ki
i =1 Ki
i =1 Exercise 4.31
Subject: Bubblepoint temperature of feed to a distillation column.
Given:
2.8.
Find: Feed at 1.72 MPa (250 psia) with a composition in kmol/h below. Kvalues in Fig.
Bubblepoint temperature. Analysis: Iterate on temperature until the bubblepoint equation, Eq. (412), is satisfied,
C i =1 Ki zi = 1 (1) For the first guess, take the temperature that gives the Kvalue for nC4 = 1.0, that is 225oF. This
result and one for 200oF is as follows:
T = 225oF
T = 200oF
Component fi , kmol/h
zi
Ki
K i zi
Ki
K i zi
C2
1.5
0.03
4.8
0.144
4.3
0.129
C3
10.0
0.20
2.1
0.420
1.9
0.380
nC4
18.5
0.36
1.0
0.360 0.81 0.292
nC5
17.5
0.34 0.44 0.150 0.34 0.116
nC6
3.5
0.07 0.21 0.015 0.15 0.011
Sum:
51.0
1.00
1.089
0.928
o
By linear interpolation, T = 211 F for Eq. (1) to be satisfied. Exercise 4.32
Subject: Bubble and dew point pressures of binary mixture at constant temperature.
Given: Mixture of 50 mol% benzene (A) and 50 mol% toluene (B) at 90oC (194oF). Vapor
pressures from Fig. 2.4 (19.5 psia for A and 7.9 psia for B).
Assumptions: Raoult's law for Kvalues.
Find: Bubble and dew point pressures.
Analysis: Substitution of Raoult's law, Eq. (3) in Table 2.3, into Eqs. (412) and (413) for the
bubble and dew points, respectively, gives,
Bubble point: C
i =1 Dew point: C
i =1 Ki zi = C
i =1 Pi s zi
= 10 or
.
P C
zi
zi P
=
= 10 or
.
Ki i =1 Pi s C Pi s zi = P (1) i =1
C
i =1 Eq. (1) gives 13.70 psia for the bubble point. zi
1
=
s
Pi
P (2) Eq. (2) gives 15.8 psia for the dew point. Exercise 4.33
Subject: Bubble point, dew point, and flash of a water (W)  acetic acid (A) mixture.
Given: Equimolar mixture of W and A at 1 atm. Correlations of liquidphase activity
coefficients for W and A as a function of liquidphase mole fractions and temperature:
Assu...
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This document was uploaded on 02/24/2014 for the course CBE 2124 at NYU Poly.
 Spring '11
 Levicky
 The Land

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