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Seperation of Meta-Dichlorobenzene by Adsorption
A Process for Separating Meta - Dichlorobenzene under Vapor Phase by Adsorption
 
SUN Yao - jun, GUO Guo-qing, WANG Li-ping, WU Tai-liu, LONG Ying-cai
 
(Department of Chemistry ,Fudan University ,Shanghai 200433 ,China)
 
[Abstract] Detailed studies were performed on the conditions of the process for separating meta-dichlorobenzene from a mixture of dichlorobenzenes on the hydrophobic adsorbent S-I under vapor phase ,where steam was employed as desorbent. Optimal conditions for the process are: temperature (193 ±1)℃, GHSV 1.8 h-1,desorption time 5 min. At a desorption temperature of (193 ±1) ℃,GHSV 1.6 h-1, with a first stage desorption time of 3 min, and a second stage desorption time of 27 min, the yield of meta-dichlorobenzene is over 30 %.
 
[Keywords] meta-dichlorobenzene; vapor phase; adsorption separation; desorption; MFI zeolite; adsorbent
 
[Brief introduction]
Effect of adsorption temperature and gas hourly space velocity
Figure 1 Relationship between yields of m-dichlorobenzene and GHSV at 187℃.
Figure 2 Relationship between yields of m-dichlorobenzene and adsorption temperatures at different GHSV.
 
 
Screening test of desorption conditions
Table 1 Relationship between desorption GHSV and time
Desorption GHSV/h-1
Desorption time/min
Weight percents of p – DICB /%
0.87
0~45
46.3
 
45~280
9.07
1.57
0~30
46.91
 
30~45
4.13
2.57
0~30
47.45
 
30~45
3.50
3.12
0~30
48.21
 
30~45
3.17
 
Table 2 Life-time test of adsorbent
Cycles of adsorption and desroption process /time
Weight percents of p-DICB in liquid after adsorption /%
Yields of m-DICB /%
1
0.09
35
10
0.07
34
50
0.12
36
130
0.09
34
 
Table 3 Influence of initial desorption time to yields of m-DICB
Initial desorption time /s
Initial desorption yield of m-DICB /%
Weight percents of p-DICB /%
45
28.2
21.1
60
30.6
22.7
75
32.4
27.3
120
39.1
26.8
180
42.0
30.6
Table 4 Results of 10-time continuous tests
Cycles / time
1
2
3
4
5
6
7
8
9
10
Average
One-way yields of m-DICB /%
 
34.2
32.9
37.8
27.2
34.4
32.9
30.1
36.6
30.7
32.9
33.0
Weight percents of p-DICB in liquid after adsorption /%
0.18
0.22
0.19
0.09
0.21
0.16
0.12
0.13
0.14
0.25
0.17
 
Table 5 Material balance of 5-time continuous tests (unit /%)
Cycles /time
1
2
3
4
5
Average
m-DICB
99.9
97.6
96.0
99.6
96.2
97.8
p-DICB
98.7
99.2
100.0
99.8
97.0
98.9
o-DICB
96.6
97.5
98.8
99.0
94.6
97.3
Liquid efficency
100.0
97.4
96.3
99.0
95.0
97.5
 
 
Conclusion
The optimal conditions of the process for separation meta-dichlorobenzene from dichlorobenzene mixtures on the hydrophobic adsorbent S-I under vapor phase with steam as desorbent as follow:
1.       Adsorption condition: temperature (193±1℃), GHSV (1.8 h-1), time (5 min), yield of m-DICB (≥30%);
2.       Desorption condition: temperature (193±1℃), GHSV (1.57 h-1), initial time (3 min), secondary time (27 min);
3.       Based on above conditions, 7-tower continuous process is recommended.
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