Unformatted text preview: = KA x A
KA − KB
If the given vapor pressure data are fitted to Antoine equations, we obtain:
xA = PAs = exp 16.6541 − 4088.12
T + 203.924 (7) PBs = exp 23.0155 − 9336.97
T + 321434
. (8) Where vapor pressure is in torr and temperature is in oC. Solving, Eqs. (1) to (8),
In solving the equations, P = 13.3 kPa or 99.8 torr. The results are tabulated on the next page.
Below the table is a McCabeThiele plot of yA versus xA for determining the minimum reflux for
xD = 0.995 and a horizontal qline at y = 0.90, which intersects the equilibrium curve at
x = 0.572. Therefore, the slope of the rectifying section operating line at minimum reflux is
(L/V)min = (0.995  0.90)/(0.995  0.572) = 0.225. From a rearrangement of Eq. (77),
Rmin = (L/V)min/[1  (L/V)min] = 0.225/(10.225) = 0.290. Therefore, the reflux ratio for operation
= 1.6Rmin = 1.6(0.290) = 0.464. Analysis: (continued) Exercise 7.21 (continued) T, oC Ps of A, torr Ps of B, torr
135.3
99.8
13.1
136.5
104.1
13.8
137.8
108.9
14.6
140.3
118.8
16.3
142.8
129.5
18.2
145.3
140.9
20.3
147.8
153.1
22.6
166.2
25.1
150.3
152.8
180.2
27.9
211.1
34.2
157.8
160.3
228.1
37.8
162.8
246.3
41.8
165.3
265.6
46.2
167.8
286.1
50.9
307.9
56.1
170.3
172.8
331.1
61.8
175.3
355.6
68.0
177.8
381.6
74.7
180.3
409.2
81.9
438.3
89.9
182.8
185.3
469.1
98.5
185.7
474.2
99.9 KA
1.000
1.043
1.092
1.191
1.297
1.411
1.534
1.665
1.805
2.115
2.286
2.468
2.661
2.867
3.085
3.317
3.563
3.824
4.100
4.392
4.701
4.751 KB
0.131
0.138
0.147
0.164
0.183
0.203
0.226
0.251
0.279
0.343
0.379
0.419
0.463
0.510
0.562
0.619
0.681
0.748
0.821
0.901
0.987
1.001 xA
1.000
0.953
0.903
0.814
0.733
0.659
0.592
0.530
0.472
0.371
0.326
0.284
0.244
0.208
0.173
0.141
0.111
0.082
0.055
0.028
0.004
0.000 yA
1.000
0.993
0.986
0.970
0.951
0.931
0.908
0.882
0.853
0.784
0.744
0.700
0.650
0.596
0.535
0.468
0.395
0.313
0.224
0.125
0.017
0.000 Analysis: (continued) Exercise 7.21 (continued) Exercise 7.21 (continued)
Analysis: (continued)
Now determine the tray requirements for actual operation. Using Eq. (77), with the
operating reflux ratio of 0.464, L/V = R/(1 + R) = 0.464/(1 + 0.464) = 0.317. Because such high
purity distillate and bottoms products are to obtained, use 3 McCabeThiele diagrams. The first
diagram is for the high purity region of component A from y and x = 0.9 to 1.0. The operating
line for the rectifying section begins at {0.995, 0.995} and, with a slope of 0.317, intersects the
vertical axis for x = 0.90 at y = 0.965. The entire region is covered in the second diagram, the
feed stage is located optimally. The low concentration region is covered in the third diagram.
From these three diagrams, it is seen that 8 theoretical plates plus a partial reboiler are needed.
The feed is sent to plate 4 from the top. Analysis: (continued) Exercise 7.21 (continued) Analysis: (continued) Exercise 7.21 (continued) Exercise 7.22
Subject:
Distillation of a mixture of A and B based on boilup, rather than reflux,
requirements.
Given: A bubblepoint feed...
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 Spring '11
 Levicky
 The Land

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