- Email: [email protected]
Preparation, characterization, and application of activated carbon membrane with carbon whiskers
Desalination 202 (2007) 247–252
Preparation, characterization, and application of activated carbon membrane with carbon whiskers S.D. Baea*, C.W. Leeb, L.S. Kangb, A. Sakodac a
Department of Environmental Engineering, Silla University San 1-1, Gwaebop-dong, Sasang-gu, Busan 617-736, South Korea Tel. +82-51-999-6270; Fax +82-51-304-3200; email: [email protected] b Department of Environmental Engineering, Pukyong National University 559-1 Daeyeon-dong, Nam-gu, Busan 608-737, South Korea c Institute of Industrial Science, University of Tokyo 4-6-1, Komaba, Meguro-ku, Tokyo, 153-8505, Japan Received 31 July 2005; accepted 23 December 2005
Abstract A novel activated carbon membrane with carbon whiskers (W-ACM) for wastewater and drinking water treatments was designed and prepared. This membrane has carbon whiskers on its surface for preventing the deposition and accumulation of particles and has activated carbon layer below its carbon whiskers for the adsorption of dissolved organics. Adsorption capacity of the membrane was compared with a granular activated carbon and an activated carbon fiber by using phenol. Prevention of the particle deposition on the membrane surface was elucidated by the filtration of water containing polymethyl methacrylate (PMMA). In this filtration, the carbon whiskers on the activated carbon membrane significantly extended the membrane lifetime, because of preventing the particle deposition on/within the membrane pores. From these results, this novel membrane can be a promising tool for the hybrid processes for wastewater and water treatment with long lifetime. Keywords: Activated carbon membrane; Carbon whisker; Adsorption; Fouling
1. Introduction Wastewater reuse has extensively been considered because recent industrialization and urbanization have accelerated pollution in water
*Corresponding author.
environment, making it a limited resource for water supply [1]. Treatment processes for wastewater reuse usually have adopted water treatment process such as biological treatment, coagulation, sand filtration, membrane filtration and activated carbon adsorption. Recently, membrane filtration such as microfiltration and ultrafiltration, which
Presented at the conference on Wastewater Reclamation and Reuse for Sustainability (WWRS2005), November 8–11, 2005, Jeju, Korea. Organized by the International Water Association (IWA) and the Gwangju Institute of Science and Technology (GIST). 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2005.12.061
248
S.D. Bae et al. / Desalination 202 (2007) 247–252
are increasingly used in the field of wastewater reuse, has shown good result for removing BOD or COD, turbidity, color, odor, bacteria and viruses. However, despite of the membrane filtration for the effective removal of these contaminants, it has limitation because it cannot remove contaminants which are smaller than the membrane pore size [2]. Because of such limitation of the membrane, a combination with proper treatment processes is required for successful application of the membrane process on wastewater reclamation. Since raw waters and wastewater usually contain particles ranging from nanometer to micrometer in size, as well as dissolved contaminants, it is not easy for any single unit operation to remove all contaminants at one time. Recently, removal of particulate and dissolved matters was achieved when filtration and adsorption processes are successfully combined in surface water treatment [3]. Activated carbon membrane (ACM) was found to be a promising tool for hybrid water treatments in terms of filtration and adsorption capacity for low molecular weight dissolved organics [4]. However, during the membrane filtration operation, deposition and accumulation of fine particles usually occur on and within the membrane. In this work, a new method for preparing the activated carbon membrane with carbon whiskers (Fig. 1) was proposed to solve the problem.
2. Materials and methods 2.1. Materials A ceramic pipe (inner diameter = 9 mm, outer diameter = 13 mm, pore size = 2.3 mm) (Kubota Co. Ltd., Japan) was used as membrane support. Microspheres with various compositions of poly(vinylidenechloride) (PVdC) and poly(vinylchloride) (PVC) of 0.10–0.15 mm in diameter (Asahi Kasei Co. Ltd., Japan) were used as a precursor of the activated carbon layer in the membranes. Reagent grade of ferric sulfate (Wako Pure Chemical, Japan) was used as catalysts for carbon whiskers formation. All of other chemicals used in this study were in reagent grades [5]. 2.2. Procedure A ceramic pipe plugged one end by a polymer paste was slowly dipped into a certain ratio of PVdC/PVC polymer latex microspheres and taken out with rotating at 600 rpm, and dried in atmosphere for 1 h. By repeating this procedure two times, the aggregate of polymer microspheres was formed on and within the ceramic support. For W-ACMs, the treated pipe was immersed in ferric sulfate solution (0.5 M) and dried in atmosphere for 3 h. This procedure was repeated two times. For ACMs, this ferric sulfate immersing
Feed
Carbon whisker layer Activated carbon layer Ceramics support Permeate Permeate
Fig. 1. A conception figure of activated carbon membrane with carbon whiskers.
S.D. Bae et al. / Desalination 202 (2007) 247–252
was not performed. The polymer latex was carbonized as follows. First, the sample was put in a quartz tube placed in an electric oven and the temperature was risen from the room temperature to 300°C at 10°C/min and kept at 300°C for 30 min, since the major thermal decomposition was expected to occur at this temperature range. For ACMs, the temperature was risen again to 1100°C at 10°C/min, kept at 1100°C for 48 min to complete the carbonization, and cooled down naturally to the room temperature. For W-ACMs, the temperature was rise again to 1100°C at 10°C/min, kept at 1100°C for 30 min. Then, 19.3% methane with nitrogen gas was fed into the furnace and kept at 1100°C for 18 min for CVD. The furnace was also cooled down naturally to the room temperature. Fig. 2 shows the summary of membrane preparation.
249
600 rpm
Support ceramic pipe OD = 13 mm ID = 9 mm Pore dia. = 2.3 mm
Polymer latex PVdC + PVC Particle dia. = 0.10 ~ 0.15 mm
Formation of particle aggregate layer
Room temperature, 1 h Drying
For ACM with whiskers (Repeating two times)
600 rpm
Ferric sulfate solution 0.5 M
2.3. Characterization Coating with ferric sulfate
The morphology of the surface of membranes prepared in this study was observed with a scanning electron microscope (SEM) (Topcom, SM-300, Japan). The phenol adsorption capacity was estimated with a batch adsorption experiment. A precisely weighed 10–50 mg sample was added to a 120 mL vial containing 100 mL of phenol solution (6–100 mg L–1). A stirring bar was also added to the vial. Afterwards, the vial was immediately sealed with a cap. The sealed vial was placed in a constant temperature water bath kept at 25°C and the mixture in the vial was well stirred by a magnetic stirrer for 24 h. The concentration of phenol was then measured with the absorbance of a 269 nm wavelength by a spectrophotometer (Shimadzu, UV-1600, Japan). Two commercial activated carbons, i.e. a granular activated carbon, Filtrasorb 400 (Calgon, USA), and activated carbon fiber, A-15 (Unitika, Japan), were also used for comparison.
Repeating two times
For ACM without whiskers (without coating ferric sulfate)
Room temp. 3h
Drying
10ºC/min 300ºC, 30 min 10ºC/min 1100ºC, 48 min
ACM
CVD with methane, 18 min
ACM-W
Fig. 2. Membrane preparation.
The filtration property of the W-ACM45 (derived from PVdC/PVC= 45/55 (wt.%/wt.%)), W-ACM70 (PVdC/PVC = 70/30) and W-ACM90 (PVdC/PVC=90/10) mentioned above was compared with the ACM45 (PVdC/PVC = 45/55).
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W-ACM45
W-ACM70
W-ACM90
Fig. 3. SEM pictures of carbon whiskers on the surface and evaluated for W-ACMs prepared with different PVC/PVdC ratio.
2.4. PMMA filtration PMMA filtration experiment using thus prepared membranes was performed using a dead-end apparatus made from a commercial screw-necked glass bottle (2 L in volume capacity). A hole was made at lower side of the bottle, and the membrane module was inserted into the bottle through this hole. The interspace was filled with a silicone rubber plug. The inside of the bottle was pressurized with nitrogen gas. The solution was agitated with a magnetic stirrer during experiment. The penetrated water was collected at drainage side of the membrane module with time elapsed, and weighed with an electrical balance. 3. Results and discussion 3.1. Characterization of prepared membranes Fig. 3 shows the SEM pictures of W-ACM45, W-ACM70 and W-ACM90. The carbon whiskers with a diameter of approximately 0.2–0.6 mm were observed by scanning electron microscope (SEM). The phenol adsorption isotherms of three W-ACMs are shown in Fig. 4. The adsorption capacity of the W-ACM was increased with
increasing the PVdC/PVC ratio. This outcome could be understood by the consideration that the micropores were formed by the release of chloride from PVdC. However the extent of decrease of micropore with the decrease of PVdC/PVC ratio was far from expected. The reason is not clear yet, but some possibilities are considered. One is that the micropores might be blocked by methane CVD. The other is that the release of chloride from PVdC might be restricted by coexisting PVC. Further investigations are needed on these points.
1000
Amount adsorbed, q [mgC/gC]
Poly(methyl methacrylate) (PMMA) with 0.8, 5 and 10 mm in diameter (Soken Chemical and Engineering, Japan; density = 1.19 g cm–3) was used as a model particle.
100 F-400 ACM90 A-15
10
W-ACM90 W-ACM70 W-ACM45
1
0.1
1
10
Equilibrium concentration, C
100
[mgC/L]
Fig. 4. Adsorption isotherm of phenol various carbon materials (25°C).
S.D. Bae et al. / Desalination 202 (2007) 247–252
Fig. 5 shows the change in of permeate flux through W-ACM45 and ACM when 0.8 mm PMMA particle suspensions of various concentrations were fed. Note that the X-axis of this graph is the number of filtrated particles. In all concentration cases, the fluxes of W-ACM45 were higher than those of ACM, meaning that the carbon whiskers prevented the flux lowering due to the particulate accumulation on the membrane surface. Especially, when 10 ppm PMMA suspension was filtrated (top in Fig. 5), the extremely quick reduction of flux was observed at the initial stage of the filtration. This quick lowering would be due to the occurring of the membrane pore blocking by PMMA particles. While, this flux lowering was not obvious in W-ACM45, meaning that the carbon whisker prevented the particle blocking of the
1.2 W-ACM(10 W-ACM (10ppm) ppm) ACM(10 ACM (10ppm) ppm)
1.0 0.8
251
membrane pores, taking place at the initial stage of the filtration. This quick lowering was diminished with increasing the suspension concentration. It was thought that when the concentration of particles was high, many collisions of particles happened and the possibility of particle penetration into the membrane pore was reduced. As mentioned below, the blocking mechanism is thus changed according to the suspension concentration. Fig. 6 shows the change in flux in ACM and W-ACM45 when 5 mm PMMA particle suspensions of various concentrations were fed. Same as the results of 0.8 mm PMMA particles, the fluxes across W-ACM45 were higher than that of ACM. Thus, the carbon whisker also prevented the flux lowering due to the accumulation of 5 mm PMMA particles on the membrane. The flux variation when 10 mm PMMA was fed is shown in Fig. 7. The fluxes across W-ACM45 were also higher than that of ACM, when various concentration of 10 mm PMMA solution was fed.
0.6 0.4 1.2
0.0 1.2
1.0
W-ACM(100 W-ACM (100ppm) ppm) ACM(100 ACM (100ppm) ppm)
1.0
0.8
0.8
0.6
0.6
Relative flux, J/J0[-]
Relative flux, J/J0[-]
0.2
0.4 0.2 0.0 1.2 1.0
Number of filtrated particles, M [/m2]
0.8
0.4 W-ACM (10 ppm) ACM (10 ppm)
0.2 0.0 1.2 1.0
Number of filtrated particles, M [/m2] 0.8 0.6
0.6 0.4
0.4
W-ACM (1000ppm) ppm) W-ACM(1000 ACM (1000ppm) ppm) ACM(1000
0.2 0.0 0
5
W-ACM (100 ppm) ACM (100 ppm)
0.2
10
Number of filtrated particles, M [×10
15 13
–2
m ]
Fig. 5. Change in relative flux across the membranes as a function of the number of particles accumulated on the membranes (PMMA: 0.8 mm).
0.0
0
1
2
3
4
5
6
Number of filtrated particles, M [×1011 m–2]
Fig. 6. Change in relative flux across the membranes as a function of the number of particles accumulated on the membranes (PMMA: 5 mm).
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Therefore, it was concluded that the carbon whiskers were effective to filtrate various sizes of suspended particles. On the other hand, in ACM filtration, the flux lowering at the initial stage was decreased in 5 and 10 mm PMMA filtration cases as compared with a 0.8 mm PMMA filtration case. As mentioned above, this lowering is due to the particle blocking. These results indicated that the particles larger than 5 mm are difficult to block the pores of ACM. Thus, it can be said that the prevention mechanism of the carbon whiskers for the particle blocking is different with particle size. 4. Conclusions We have developed a novel activated carbon membrane with carbon whiskers (W-ACM) and also characterize it by phenol adsorption and PMMA filtration for activated carbon layer and carbon whiskers, respectively. As a result, it is possible to utilize the W-ACM as a hybrid processes for wastewater treatment with long 1.2 W-ACM (10 ppm) ACM (10 ppm)
1.0
Relative flux, J/J0[-]
lifetime. The W-ACM was successfully prepared by the pyrolysis of PVdC/PVC composite microspheres as a precursors of the activated carbon adhered on the ceramic support followed by the methane CVD, and the diameter of the carbon whiskers and pore size of the membrane could be controlled by changing PVdC/PVC ratio of the microspheres. Moreover, the newly developed carbon whisker layer successfully prevented PMMA particles from sticking to the external surface of the membranes. The carbon whiskers prevented the blockage of water passing holes in the membrane by small particles (0.8 mm) accumulation. When larger particles (5–10 mm) as compared to the carbon whisker size were filtrated, the carbon whiskers contributed to prevent the dense packing of the cake layer. Also, the newly developed activated carbon layer had the adsorption capacity of phenol comparable to the commercial activated carbons. It can be concluded that the novel composite membrane developed in this work can be utilized widely in the practical and commercial water treatments.
0.8
References
0.6
[1]
0.4 0.2 0.0 1.2 1.0
[2]
Number of filtrated particles, M [/m2]
0.8 0.6
[3] 0.4 W-ACM (100 ppm) ACM (100 ppm)
0.2 0.0 0
1
2
3
4
5
6
[4]
Number of filtrated particles, M [×1010 m–2]
Fig. 7. Change in relative flux across the membranes as a function of the number of particles accumulated on the membranes (PMMA: 10 mm).
[5]
K.H. Ahn and K.G. Song, Application of microfiltration with a novel fouling control method for reuse of wastewater from a large-scale complex, Desalination, 129 (2000) 207–216. G.T. Seo, Y. Suzuki and S. Ohgaki, Biological powdered activated carbon (BPAC) microfiltration for wastewater reclamation and reuse, Desalination, 106 (1996) 39–45. S. Mozia and M. Tomaszewska, Treatment of surface water using hybrid processes-adsorption on PAC and ultrafiltration, Desalination, 162 (2004) 23–31. A. Sakoda, T. Nomura and M. Suzuki, Activated carbon membrane for water treatment, Adsorption, 3 (1996) 93–98. S.D. Bae, M. Sagehashi and A. Sakoda, Activated carbon membrane with filamentous carbon for water treatment, Carbon, 41 (2003) 2973–2979.
Preparation, characterization, and application of activated carbon membrane with carbon whiskers S.D. Baea*, C.W. Leeb, L.S. Kangb, A. Sakodac a
Department of Environmental Engineering, Silla University San 1-1, Gwaebop-dong, Sasang-gu, Busan 617-736, South Korea Tel. +82-51-999-6270; Fax +82-51-304-3200; email: [email protected] b Department of Environmental Engineering, Pukyong National University 559-1 Daeyeon-dong, Nam-gu, Busan 608-737, South Korea c Institute of Industrial Science, University of Tokyo 4-6-1, Komaba, Meguro-ku, Tokyo, 153-8505, Japan Received 31 July 2005; accepted 23 December 2005
Abstract A novel activated carbon membrane with carbon whiskers (W-ACM) for wastewater and drinking water treatments was designed and prepared. This membrane has carbon whiskers on its surface for preventing the deposition and accumulation of particles and has activated carbon layer below its carbon whiskers for the adsorption of dissolved organics. Adsorption capacity of the membrane was compared with a granular activated carbon and an activated carbon fiber by using phenol. Prevention of the particle deposition on the membrane surface was elucidated by the filtration of water containing polymethyl methacrylate (PMMA). In this filtration, the carbon whiskers on the activated carbon membrane significantly extended the membrane lifetime, because of preventing the particle deposition on/within the membrane pores. From these results, this novel membrane can be a promising tool for the hybrid processes for wastewater and water treatment with long lifetime. Keywords: Activated carbon membrane; Carbon whisker; Adsorption; Fouling
1. Introduction Wastewater reuse has extensively been considered because recent industrialization and urbanization have accelerated pollution in water
*Corresponding author.
environment, making it a limited resource for water supply [1]. Treatment processes for wastewater reuse usually have adopted water treatment process such as biological treatment, coagulation, sand filtration, membrane filtration and activated carbon adsorption. Recently, membrane filtration such as microfiltration and ultrafiltration, which
Presented at the conference on Wastewater Reclamation and Reuse for Sustainability (WWRS2005), November 8–11, 2005, Jeju, Korea. Organized by the International Water Association (IWA) and the Gwangju Institute of Science and Technology (GIST). 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2005.12.061
248
S.D. Bae et al. / Desalination 202 (2007) 247–252
are increasingly used in the field of wastewater reuse, has shown good result for removing BOD or COD, turbidity, color, odor, bacteria and viruses. However, despite of the membrane filtration for the effective removal of these contaminants, it has limitation because it cannot remove contaminants which are smaller than the membrane pore size [2]. Because of such limitation of the membrane, a combination with proper treatment processes is required for successful application of the membrane process on wastewater reclamation. Since raw waters and wastewater usually contain particles ranging from nanometer to micrometer in size, as well as dissolved contaminants, it is not easy for any single unit operation to remove all contaminants at one time. Recently, removal of particulate and dissolved matters was achieved when filtration and adsorption processes are successfully combined in surface water treatment [3]. Activated carbon membrane (ACM) was found to be a promising tool for hybrid water treatments in terms of filtration and adsorption capacity for low molecular weight dissolved organics [4]. However, during the membrane filtration operation, deposition and accumulation of fine particles usually occur on and within the membrane. In this work, a new method for preparing the activated carbon membrane with carbon whiskers (Fig. 1) was proposed to solve the problem.
2. Materials and methods 2.1. Materials A ceramic pipe (inner diameter = 9 mm, outer diameter = 13 mm, pore size = 2.3 mm) (Kubota Co. Ltd., Japan) was used as membrane support. Microspheres with various compositions of poly(vinylidenechloride) (PVdC) and poly(vinylchloride) (PVC) of 0.10–0.15 mm in diameter (Asahi Kasei Co. Ltd., Japan) were used as a precursor of the activated carbon layer in the membranes. Reagent grade of ferric sulfate (Wako Pure Chemical, Japan) was used as catalysts for carbon whiskers formation. All of other chemicals used in this study were in reagent grades [5]. 2.2. Procedure A ceramic pipe plugged one end by a polymer paste was slowly dipped into a certain ratio of PVdC/PVC polymer latex microspheres and taken out with rotating at 600 rpm, and dried in atmosphere for 1 h. By repeating this procedure two times, the aggregate of polymer microspheres was formed on and within the ceramic support. For W-ACMs, the treated pipe was immersed in ferric sulfate solution (0.5 M) and dried in atmosphere for 3 h. This procedure was repeated two times. For ACMs, this ferric sulfate immersing
Feed
Carbon whisker layer Activated carbon layer Ceramics support Permeate Permeate
Fig. 1. A conception figure of activated carbon membrane with carbon whiskers.
S.D. Bae et al. / Desalination 202 (2007) 247–252
was not performed. The polymer latex was carbonized as follows. First, the sample was put in a quartz tube placed in an electric oven and the temperature was risen from the room temperature to 300°C at 10°C/min and kept at 300°C for 30 min, since the major thermal decomposition was expected to occur at this temperature range. For ACMs, the temperature was risen again to 1100°C at 10°C/min, kept at 1100°C for 48 min to complete the carbonization, and cooled down naturally to the room temperature. For W-ACMs, the temperature was rise again to 1100°C at 10°C/min, kept at 1100°C for 30 min. Then, 19.3% methane with nitrogen gas was fed into the furnace and kept at 1100°C for 18 min for CVD. The furnace was also cooled down naturally to the room temperature. Fig. 2 shows the summary of membrane preparation.
249
600 rpm
Support ceramic pipe OD = 13 mm ID = 9 mm Pore dia. = 2.3 mm
Polymer latex PVdC + PVC Particle dia. = 0.10 ~ 0.15 mm
Formation of particle aggregate layer
Room temperature, 1 h Drying
For ACM with whiskers (Repeating two times)
600 rpm
Ferric sulfate solution 0.5 M
2.3. Characterization Coating with ferric sulfate
The morphology of the surface of membranes prepared in this study was observed with a scanning electron microscope (SEM) (Topcom, SM-300, Japan). The phenol adsorption capacity was estimated with a batch adsorption experiment. A precisely weighed 10–50 mg sample was added to a 120 mL vial containing 100 mL of phenol solution (6–100 mg L–1). A stirring bar was also added to the vial. Afterwards, the vial was immediately sealed with a cap. The sealed vial was placed in a constant temperature water bath kept at 25°C and the mixture in the vial was well stirred by a magnetic stirrer for 24 h. The concentration of phenol was then measured with the absorbance of a 269 nm wavelength by a spectrophotometer (Shimadzu, UV-1600, Japan). Two commercial activated carbons, i.e. a granular activated carbon, Filtrasorb 400 (Calgon, USA), and activated carbon fiber, A-15 (Unitika, Japan), were also used for comparison.
Repeating two times
For ACM without whiskers (without coating ferric sulfate)
Room temp. 3h
Drying
10ºC/min 300ºC, 30 min 10ºC/min 1100ºC, 48 min
ACM
CVD with methane, 18 min
ACM-W
Fig. 2. Membrane preparation.
The filtration property of the W-ACM45 (derived from PVdC/PVC= 45/55 (wt.%/wt.%)), W-ACM70 (PVdC/PVC = 70/30) and W-ACM90 (PVdC/PVC=90/10) mentioned above was compared with the ACM45 (PVdC/PVC = 45/55).
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S.D. Bae et al. / Desalination 202 (2007) 247–252
W-ACM45
W-ACM70
W-ACM90
Fig. 3. SEM pictures of carbon whiskers on the surface and evaluated for W-ACMs prepared with different PVC/PVdC ratio.
2.4. PMMA filtration PMMA filtration experiment using thus prepared membranes was performed using a dead-end apparatus made from a commercial screw-necked glass bottle (2 L in volume capacity). A hole was made at lower side of the bottle, and the membrane module was inserted into the bottle through this hole. The interspace was filled with a silicone rubber plug. The inside of the bottle was pressurized with nitrogen gas. The solution was agitated with a magnetic stirrer during experiment. The penetrated water was collected at drainage side of the membrane module with time elapsed, and weighed with an electrical balance. 3. Results and discussion 3.1. Characterization of prepared membranes Fig. 3 shows the SEM pictures of W-ACM45, W-ACM70 and W-ACM90. The carbon whiskers with a diameter of approximately 0.2–0.6 mm were observed by scanning electron microscope (SEM). The phenol adsorption isotherms of three W-ACMs are shown in Fig. 4. The adsorption capacity of the W-ACM was increased with
increasing the PVdC/PVC ratio. This outcome could be understood by the consideration that the micropores were formed by the release of chloride from PVdC. However the extent of decrease of micropore with the decrease of PVdC/PVC ratio was far from expected. The reason is not clear yet, but some possibilities are considered. One is that the micropores might be blocked by methane CVD. The other is that the release of chloride from PVdC might be restricted by coexisting PVC. Further investigations are needed on these points.
1000
Amount adsorbed, q [mgC/gC]
Poly(methyl methacrylate) (PMMA) with 0.8, 5 and 10 mm in diameter (Soken Chemical and Engineering, Japan; density = 1.19 g cm–3) was used as a model particle.
100 F-400 ACM90 A-15
10
W-ACM90 W-ACM70 W-ACM45
1
0.1
1
10
Equilibrium concentration, C
100
[mgC/L]
Fig. 4. Adsorption isotherm of phenol various carbon materials (25°C).
S.D. Bae et al. / Desalination 202 (2007) 247–252
Fig. 5 shows the change in of permeate flux through W-ACM45 and ACM when 0.8 mm PMMA particle suspensions of various concentrations were fed. Note that the X-axis of this graph is the number of filtrated particles. In all concentration cases, the fluxes of W-ACM45 were higher than those of ACM, meaning that the carbon whiskers prevented the flux lowering due to the particulate accumulation on the membrane surface. Especially, when 10 ppm PMMA suspension was filtrated (top in Fig. 5), the extremely quick reduction of flux was observed at the initial stage of the filtration. This quick lowering would be due to the occurring of the membrane pore blocking by PMMA particles. While, this flux lowering was not obvious in W-ACM45, meaning that the carbon whisker prevented the particle blocking of the
1.2 W-ACM(10 W-ACM (10ppm) ppm) ACM(10 ACM (10ppm) ppm)
1.0 0.8
251
membrane pores, taking place at the initial stage of the filtration. This quick lowering was diminished with increasing the suspension concentration. It was thought that when the concentration of particles was high, many collisions of particles happened and the possibility of particle penetration into the membrane pore was reduced. As mentioned below, the blocking mechanism is thus changed according to the suspension concentration. Fig. 6 shows the change in flux in ACM and W-ACM45 when 5 mm PMMA particle suspensions of various concentrations were fed. Same as the results of 0.8 mm PMMA particles, the fluxes across W-ACM45 were higher than that of ACM. Thus, the carbon whisker also prevented the flux lowering due to the accumulation of 5 mm PMMA particles on the membrane. The flux variation when 10 mm PMMA was fed is shown in Fig. 7. The fluxes across W-ACM45 were also higher than that of ACM, when various concentration of 10 mm PMMA solution was fed.
0.6 0.4 1.2
0.0 1.2
1.0
W-ACM(100 W-ACM (100ppm) ppm) ACM(100 ACM (100ppm) ppm)
1.0
0.8
0.8
0.6
0.6
Relative flux, J/J0[-]
Relative flux, J/J0[-]
0.2
0.4 0.2 0.0 1.2 1.0
Number of filtrated particles, M [/m2]
0.8
0.4 W-ACM (10 ppm) ACM (10 ppm)
0.2 0.0 1.2 1.0
Number of filtrated particles, M [/m2] 0.8 0.6
0.6 0.4
0.4
W-ACM (1000ppm) ppm) W-ACM(1000 ACM (1000ppm) ppm) ACM(1000
0.2 0.0 0
5
W-ACM (100 ppm) ACM (100 ppm)
0.2
10
Number of filtrated particles, M [×10
15 13
–2
m ]
Fig. 5. Change in relative flux across the membranes as a function of the number of particles accumulated on the membranes (PMMA: 0.8 mm).
0.0
0
1
2
3
4
5
6
Number of filtrated particles, M [×1011 m–2]
Fig. 6. Change in relative flux across the membranes as a function of the number of particles accumulated on the membranes (PMMA: 5 mm).
252
S.D. Bae et al. / Desalination 202 (2007) 247–252
Therefore, it was concluded that the carbon whiskers were effective to filtrate various sizes of suspended particles. On the other hand, in ACM filtration, the flux lowering at the initial stage was decreased in 5 and 10 mm PMMA filtration cases as compared with a 0.8 mm PMMA filtration case. As mentioned above, this lowering is due to the particle blocking. These results indicated that the particles larger than 5 mm are difficult to block the pores of ACM. Thus, it can be said that the prevention mechanism of the carbon whiskers for the particle blocking is different with particle size. 4. Conclusions We have developed a novel activated carbon membrane with carbon whiskers (W-ACM) and also characterize it by phenol adsorption and PMMA filtration for activated carbon layer and carbon whiskers, respectively. As a result, it is possible to utilize the W-ACM as a hybrid processes for wastewater treatment with long 1.2 W-ACM (10 ppm) ACM (10 ppm)
1.0
Relative flux, J/J0[-]
lifetime. The W-ACM was successfully prepared by the pyrolysis of PVdC/PVC composite microspheres as a precursors of the activated carbon adhered on the ceramic support followed by the methane CVD, and the diameter of the carbon whiskers and pore size of the membrane could be controlled by changing PVdC/PVC ratio of the microspheres. Moreover, the newly developed carbon whisker layer successfully prevented PMMA particles from sticking to the external surface of the membranes. The carbon whiskers prevented the blockage of water passing holes in the membrane by small particles (0.8 mm) accumulation. When larger particles (5–10 mm) as compared to the carbon whisker size were filtrated, the carbon whiskers contributed to prevent the dense packing of the cake layer. Also, the newly developed activated carbon layer had the adsorption capacity of phenol comparable to the commercial activated carbons. It can be concluded that the novel composite membrane developed in this work can be utilized widely in the practical and commercial water treatments.
0.8
References
0.6
[1]
0.4 0.2 0.0 1.2 1.0
[2]
Number of filtrated particles, M [/m2]
0.8 0.6
[3] 0.4 W-ACM (100 ppm) ACM (100 ppm)
0.2 0.0 0
1
2
3
4
5
6
[4]
Number of filtrated particles, M [×1010 m–2]
Fig. 7. Change in relative flux across the membranes as a function of the number of particles accumulated on the membranes (PMMA: 10 mm).
[5]
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