Question:
Part 1
A mixture of Benzene, Toluene, and Xylene is to be separated in a two-stage distillation plant. 500 kmol of the mixture is heated up and fed to the first distillation column at 200 °C. 98% of the Xylene in the feed is recovered in the bottom product (P1) and 95% of Toluene in the feed leaves in the top product of first column (F2). The reflux ratio (R1/F2) for the first column is set to 2.2. Other information can be found in Figure 1 and Table 2. Determine the unknown flowrates and compositions and fill Table 2.
Part 2
The product of the first column (F2) is fed to the second column. 99% of Benzene in the stream is recovered in the top product (P3) and 98% of Toluene leaves in the bottom stream. Reflux Ratio for this column (R2/P3) is set to 4. Use the known flowrates and compositions from Table 2 and fill out the rest of the table.
Part 3
a) Calculate the heat duty (in kW) of the heat exchanger and all the condensers and reboilers in this process.
b) The reboilers and the heat exchanger in his process are designed to use superheated steam at 15 bar and 450 °C for heating and discharge it as superheated steam at 15 bar and 300 °C. How much steam (in kg/h) is required for the entire process?
c) All the condensers are designed to use cooling water at 25 °C and discharge it at 70 °C. How much cooling water (in m3 /day) is required for the entire process?
Table 1 Enthalpy of the pure components in / .
TEMPERATURE
BENZENE
BENZENE
TOLUENE
TOLUENE
XYLENE
XYLENE
(°C)
(LIQUID)
(VAPOUR)
(LIQUID)
(VAPOUR)
(LIQUID)
(VAPOUR)
25
86.5
33912.8
112.5
38112.8
136.3
43621.3
50
3548.5
35998.2
4127.6
40872.7
4927.7
47145.7
75
7160.8
38206.6
8332.4
43747.3
9930.2
50815.3
100
10935.2
40507.3
12736.8
46733.5
15153.2
54629.7
125
14878.1
42863.8
17349.0
49822.5
20604.2
58584.1
150
18996.6
45235.4
22179.0
53001.4
26292.5
62671.9
175
23308.2
47578.2
27238.5
56249.2
32229.0
66882.6
200
27830.8
49819.1
32536.4
59526.7
38424.9
71198.2
225
34716.5
53953.3
38067.3
62750.7
44889.6
75586.0
250
42050.2
57730.8
44902.4
66854.2
51623.0
79980.7
275
51398.9
61602.4
53219.9
71720.3
58582.4
84231.3
300
60603.5
65573.9
63257.1
76670.7
67370.3
89732.7
Table 2 Composition of the streams
Name
Phase
Temperature
Flowrate
Benzene
Toluene
Xylene
[?]
[ / ]
%
%
%
B1
Liquid
285
465
2.5
7.96
89.54
B2
Liquid
240
697.24
1.83
97.47
0.7
C1
Liquid
225
C2
Liquid
205
F0
Liquid
60
500
45.6
33
21.4
F1
Liquid
200
F2
Liquid
225
385
P1
Liquid
285
115
P2
Liquid
240
157.08
P3
Liquid
205
227.92
R1
Liquid
225
R2
Liquid
205
U1
Vapour
285
U2
Vapour
240
V1
Vapour
225
V2
Vapour
205
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