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. |