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Water treatment by pitch-based activated carbon fiber
Desalination, 98 (1994) X5-160 Elsevier Science B.V. Amsterdam -
155 Printed in The Netherlands
Water treatment by pitch-based activated carbon fiber Norifumi Shindol, Yoshitada Otani2, Gennosuke Inoue3 and Kunitaro Kawazoe4 IOsaka Gas Co. Ltd., 4-I-2 Hironomachi, Chuo-ku, Osaka 541, 2Unitika Co. Ltd., 4-68 Kitakutarocho, Osaka, jWater Re-use Promotion Center, 2-3-4 Akasaka, Tokyo 107, 4University of Tokyo, Tokyo 113 (Japan)
SUMMARY
Recently lakes, swamps and suburban rivers of cities have become growingly polluted according to various kinds of waste water drainage. For domestic and industrial waters much call has been made on advanced water treatment techniques to where more adsorption operation is employed by granular and powdered activated carbon for removal of organic substances, color, odor, etc. We already succeeded in a promising result from two experiments at Kashiwai Water Works of Chiba Prefecture and Murano of Osaka Prefecture using a pitch-based activated carbon fiber (ACF). This paper deals with the further development that the pitch-based ACF has been reformed and the development of higher performance ACF ventured on.
REFORMING
ACF
With a view to commercialization of ACF by improving removal performance of dissolved organic substances and trihalomethane formation, experiments on conventional pitch-based ACF were carried out by enlarging pore size based on this ACF.
OOll-9164/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDlOOll-9164(94)00140-5
156
Micropore distribution of reformed carbon$ber The reformed carbon fiber used in this experiment has been reactivated after applying special treatment to the conventional pitch-based ACF. The microporous distribution was measured by the low temperature nitrogen adsorption method. From the examples in Table I and Fig, 1 it can be seen that while maintaining micropore size, mesopore size has increased selectively. Especially in the reformed carbon fiber of the C series, it can be seen that pores of about 198, grow. t!icropore
pore radius
ilesopore pore radius
-101 IO-2508
A-10
BJH Kethcd
WPKethod desorption
side
Fig. 1. Pore distribution.
dV/dr YS r
Plot
desorption
BJH Nethod desorption
side
side
dY/dr vs r
dV/dr vs r
Plot
Plot
157 TABLE I
Pore distribution of Reformed Activated Carbon Fiber (ACF) Conventional ACF
Granular activated
Reformed ACF
carbon
Reduction rate against A-10, %
-
Specific surface area, m2/g 1076 Total pore volume, ml/g 0.566 Specific micropore surface area, m2/g 1082 Micropore pore volume, ml/g 0.545 Specific mesopore surface area, m2/g Mesopore pore volume, ml/g
20
27
50
1141
1156
1640
0.680 1110
14.6 0.021
0.558 59.7 0.122
0.734 1105 0.555 79.5 0.179
0.930 1612 0.823 72.5 0.107
886 0.589 808 0.406 97.3 0.183
Sulface observation by the Scanning Electron Microscope (SEM)
Electron microscopic photos taken at pre- and post-performance are shown in Figs. 2 and 3, respectively. While there was a very smooth surface before reforming, mesopores are found after reforming. However not many were generated so that there was no change in the radius of the fiber, and therefore no problem arose in its utilization for water treatment. Adsorption by model materials
Adsorption performance was measured by using such model materials as vitamin Br2, DES (dodecyl benzene sulfonic acid sodium), PTS @aletoluene sulfonic acid sodium), BS (benzene sulfonic acid sodium). Fig. 4 shows the results of adsorption performance of large molecular vitamin Bl2. Improved performance was found compared with conventional ACF (A-10:1000 m2/g). Especially, the performance of he most advanced reformed sample (E-l) exceeds that of granular activated carbon.
Fig. 2. A-10.
Fig. 3. E-l.
DBS, PTS and BS are different in the alkyl group linked to the benzene ring, and the order of adsorption performance to respective activated carbon varied so much that it was impossible to explain merely by formation of mesopores like vitamin B 12.
159
Fig. 4.
Vitamin B12 adsorption test.
However, the adsorption performance of the reformed carbon fiber was equal or more for each of the materials. In other words, it has been found that the adsorption performance will never be degraded by reforming and the performance of larger molecular material has been improved. The remarkable improvement of reformed carbon fiber in its adsorption performance has been confirmed also with TOC and TOXP.
WATER TREATMENT TEST BY REFORMED CARBON
A model test of water treatment was conducted using reformed carbon fiber. Industrial water was filtered by Whatman paper, and the effect of adsorption treatment was measured by the amount of trihalomethane formation potential after adsorption and by the amount of dissolved organic substances. The typical condition of water flow is shown in Table II and the removal effect in Table III.
160 TABLE II
Water flow condition
Column
Adsorbent
1
Reformed carbon fiber F-400
2
Weight of adsorbent (g)
Height of packed bed of adsorbent (mm)
Mean flow rate in packed bed (l/h)
Flow rate per unit weight of adsorbent (flow-rate load) (l/g/h)
9.0
110
0.89
0.099
7.9
60.00
122
0.96
0.016
7.6
TABLE III
Removal rate of treated water Column
Adsorbent
1
Reformed GAC F-400
2
SV (l/hr)
carbon fiber
Average removal at 50 l/ACF-g and at 8 l/GAG-g (%) THM potential VX. E260
7.9
77
56
83
7.6
79
57
83
CONCLUSION
From advanced water treatment tests using reformed ACF, the following was found: Required degree of activation of reformed carbonfiber An activation almost equal to that of reformed carbon fiber (Table I) is required in order to reach the target level of removal, a THM potential >80% and TOC >SO%, and it is believed that advanced treatment performance either equal to or greater than granulated activated carbon will be attained if reformed carbon fiber around this level is used. Water flow conditions Subject to the degree of activation of reformed carbon fiber, the conditions required would be about 5V = 8/h and water flow ratio = 50 m3/ACF kg. Regeneration Regeneration by alkali is possible with any of the reformed carbon fibers, the same as with raw material carbon fiber.
155 Printed in The Netherlands
Water treatment by pitch-based activated carbon fiber Norifumi Shindol, Yoshitada Otani2, Gennosuke Inoue3 and Kunitaro Kawazoe4 IOsaka Gas Co. Ltd., 4-I-2 Hironomachi, Chuo-ku, Osaka 541, 2Unitika Co. Ltd., 4-68 Kitakutarocho, Osaka, jWater Re-use Promotion Center, 2-3-4 Akasaka, Tokyo 107, 4University of Tokyo, Tokyo 113 (Japan)
SUMMARY
Recently lakes, swamps and suburban rivers of cities have become growingly polluted according to various kinds of waste water drainage. For domestic and industrial waters much call has been made on advanced water treatment techniques to where more adsorption operation is employed by granular and powdered activated carbon for removal of organic substances, color, odor, etc. We already succeeded in a promising result from two experiments at Kashiwai Water Works of Chiba Prefecture and Murano of Osaka Prefecture using a pitch-based activated carbon fiber (ACF). This paper deals with the further development that the pitch-based ACF has been reformed and the development of higher performance ACF ventured on.
REFORMING
ACF
With a view to commercialization of ACF by improving removal performance of dissolved organic substances and trihalomethane formation, experiments on conventional pitch-based ACF were carried out by enlarging pore size based on this ACF.
OOll-9164/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved. SSDlOOll-9164(94)00140-5
156
Micropore distribution of reformed carbon$ber The reformed carbon fiber used in this experiment has been reactivated after applying special treatment to the conventional pitch-based ACF. The microporous distribution was measured by the low temperature nitrogen adsorption method. From the examples in Table I and Fig, 1 it can be seen that while maintaining micropore size, mesopore size has increased selectively. Especially in the reformed carbon fiber of the C series, it can be seen that pores of about 198, grow. t!icropore
pore radius
ilesopore pore radius
-101 IO-2508
A-10
BJH Kethcd
WPKethod desorption
side
Fig. 1. Pore distribution.
dV/dr YS r
Plot
desorption
BJH Nethod desorption
side
side
dY/dr vs r
dV/dr vs r
Plot
Plot
157 TABLE I
Pore distribution of Reformed Activated Carbon Fiber (ACF) Conventional ACF
Granular activated
Reformed ACF
carbon
Reduction rate against A-10, %
-
Specific surface area, m2/g 1076 Total pore volume, ml/g 0.566 Specific micropore surface area, m2/g 1082 Micropore pore volume, ml/g 0.545 Specific mesopore surface area, m2/g Mesopore pore volume, ml/g
20
27
50
1141
1156
1640
0.680 1110
14.6 0.021
0.558 59.7 0.122
0.734 1105 0.555 79.5 0.179
0.930 1612 0.823 72.5 0.107
886 0.589 808 0.406 97.3 0.183
Sulface observation by the Scanning Electron Microscope (SEM)
Electron microscopic photos taken at pre- and post-performance are shown in Figs. 2 and 3, respectively. While there was a very smooth surface before reforming, mesopores are found after reforming. However not many were generated so that there was no change in the radius of the fiber, and therefore no problem arose in its utilization for water treatment. Adsorption by model materials
Adsorption performance was measured by using such model materials as vitamin Br2, DES (dodecyl benzene sulfonic acid sodium), PTS @aletoluene sulfonic acid sodium), BS (benzene sulfonic acid sodium). Fig. 4 shows the results of adsorption performance of large molecular vitamin Bl2. Improved performance was found compared with conventional ACF (A-10:1000 m2/g). Especially, the performance of he most advanced reformed sample (E-l) exceeds that of granular activated carbon.
Fig. 2. A-10.
Fig. 3. E-l.
DBS, PTS and BS are different in the alkyl group linked to the benzene ring, and the order of adsorption performance to respective activated carbon varied so much that it was impossible to explain merely by formation of mesopores like vitamin B 12.
159
Fig. 4.
Vitamin B12 adsorption test.
However, the adsorption performance of the reformed carbon fiber was equal or more for each of the materials. In other words, it has been found that the adsorption performance will never be degraded by reforming and the performance of larger molecular material has been improved. The remarkable improvement of reformed carbon fiber in its adsorption performance has been confirmed also with TOC and TOXP.
WATER TREATMENT TEST BY REFORMED CARBON
A model test of water treatment was conducted using reformed carbon fiber. Industrial water was filtered by Whatman paper, and the effect of adsorption treatment was measured by the amount of trihalomethane formation potential after adsorption and by the amount of dissolved organic substances. The typical condition of water flow is shown in Table II and the removal effect in Table III.
160 TABLE II
Water flow condition
Column
Adsorbent
1
Reformed carbon fiber F-400
2
Weight of adsorbent (g)
Height of packed bed of adsorbent (mm)
Mean flow rate in packed bed (l/h)
Flow rate per unit weight of adsorbent (flow-rate load) (l/g/h)
9.0
110
0.89
0.099
7.9
60.00
122
0.96
0.016
7.6
TABLE III
Removal rate of treated water Column
Adsorbent
1
Reformed GAC F-400
2
SV (l/hr)
carbon fiber
Average removal at 50 l/ACF-g and at 8 l/GAG-g (%) THM potential VX. E260
7.9
77
56
83
7.6
79
57
83
CONCLUSION
From advanced water treatment tests using reformed ACF, the following was found: Required degree of activation of reformed carbonfiber An activation almost equal to that of reformed carbon fiber (Table I) is required in order to reach the target level of removal, a THM potential >80% and TOC >SO%, and it is believed that advanced treatment performance either equal to or greater than granulated activated carbon will be attained if reformed carbon fiber around this level is used. Water flow conditions Subject to the degree of activation of reformed carbon fiber, the conditions required would be about 5V = 8/h and water flow ratio = 50 m3/ACF kg. Regeneration Regeneration by alkali is possible with any of the reformed carbon fibers, the same as with raw material carbon fiber.