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Effect of impregnation on the pore structure of a tubular carbon membrane
NEW CARBON MATERIALS Volume 25, Issue 6, Dec 2010 Online English edition of the Chinese language journal Cite this article as: New Carbon Materials, 2010, 25(6):475–478.
NOTES
Effect of impregnation on the pore structure of a tubular carbon membrane ZHANG Yong-gang*, LU Ming-chao State Key Laboratory of Hollow Fiber Membrane Materials and Processes, School of Environmental and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300160, China
Abstract: To adjust and control the porous structure in the inner face of a tubular carbon membrane (TCM), impregnation methods were used, and the effects of impregnation on the pore size distribution were analyzed by adjusting impregnant concentrations and impregnation times. SEM images show that the impregnation treatment can repair the pore defects on the TCM surface. Data on the micropore size distribution indicate that the pore size of the TCM becomes smaller and its distribution becomes narrower with increasing impregnant concentrations and impregnation times, which indicates that impregnation conditions can be used to adjust the pore size and structure of the TCM. Key Words: Tube carbon membranes; Impregnation; Pore size; Pore distribution
1
Introduction
Carbon membranes have good resistance to chemical erosion and are electrically conductive, which can be used at high temperature[1-3]. It is believed as an effective method to solve environmental pollution problems, such as wastewater treatment, erosion liquid separation, and gas recycle and utility [4-10]. Pore size and their structure are not only the key parameter membrane but also technically difficult to control at industrial scale. To obtain tubular carbon membrane (TCM) with satisfactory micropore size, impregnation technique was used to adjust and control the porous structure in inner face of TCM, and the effects of impregnation on pore structure of TCM were analyzed.
2 2.1
Experimental Preparation of TCM
Mesocarbon microbeads (MCMBs), which has more regular spherical shape, narrower particulate size distribution, and higher carbon content than macromolecule polymer, was used as raw material[11-12] to prepare TCM[6,13-16]. The MCMB supplied by Tianjin Tiecheng Battery Material Co Ltd. had an average particle size of 15µm and density of 1.5 g/cm3. First, the MCMB was mixed with appropriate amount of carboxymethyl cellulose as binder. Then the obtained mixture was blended with appropriate amount of water to form soft mud. Finally, the mud was extrusion molded and carbonized under nitrogen flow to obtain TCM.
2.2
Impregnation of TCM
Impregnant was prepared by dissolving phenolic resin in absolute alcohol. Then, the TCM was soaked in the impregnant at room temperature for 5 min. The soaked TCM was dried at room temperature and carbonized at 700 °C in N2 protection. 2.3
Characterization of TCM
SEM images of inner face and cross section of TCM were obtained using a QUANTA200 scanning electron microscopy at 15.0 kV. The micropore size of TCM was measured by bubble-point methods[17] at 20 °C, in which nitrogen was used as permeance gas and isopropyl alcohol as wetting agent.
3 3.1
Results and discussion Effect of impregnation on morphology of TCM
Fig.1 shows the inner face morphologies of the TCM before and after impregnation (that is, the changes of membrane pore structure) with 15% alcohol solution of phenolic resin by mass fraction. Fig.1 (b) shows the enlarged image of the inner face of TCM before impregnation: the TCM has many big pores, whose size is too large to have a separation action. So the big pores are modified by impregnation with phenolic resin. Fig.1 (c) shows the inner face of TCM after impregnation. The inner face of TCM was covered by thick phenolic resin. After carbonization, the phenolic resin on the inner face
Received date: 10 April 2010; Revised date: 7 December 2010 *Corresponding author. E-mail: [email protected] Copyright©2010, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved. DOI: 10.1016/S1872-5805(09)60046-9
ZHANG Yong-gang et al. / New Carbon Materials, 2010, 25(6): 475–478
Fig.1 Inner face morphologies of the tube carbon membrane before and after impregnating treatment. (a) cross section of the tube carbon membrane; (b) before impregnating; (c) after impregnating; (d) carbonization of carbon membrane after impregnating with 15% alcohol solution of carboxy methylcellulose
Fig.2 Inner face morphologies of the tube carbon membrane with different concentration alcohol solution of carboxy methylcellulose. (e) 3%；(f) 30%
of TCM was decomposed into carbonaceous material. Therefore, the impregnation can repair obviously the pore defects. Fig.1(d), Fig.2(e) and Fig.2(f) are SEM images of TCM, which were obtained by the same impregnation and heat treatment at 1 073K in N2 protection, but the impregnant concentrations were 15, 3, and 30% by mass fraction, respectively. From the three images, it can be found that the impregnation can repair the pore defects on surface of TCM, and the repairing effect was improved with increasing impregnant concentration.
Fig.3(g) and (h) shows the cross-sectional SEM images of TCM before and after impregnation with 15% impregnant by mass fraction. It was found that the pore structure in cross section has no changes, which means that impregnation treatment to TCM could only adjust the pore structure on the membrane surface and could not penetrate into the membrane body. 3.2 Effect of impregnant concentration on pore size distribution of TCM Fig.4 gives the measurable pore size changes of TCM
ZHANG Yong-gang et al. / New Carbon Materials, 2010, 25(6): 475–478
Fig.3 Cross section morphologies of the tube carbon membrane before and after impregnating treatment (g) before impregnating; (h) after impregnating
could convert the phenolic resin coated around large pores into carbonaceous materials, which decreased the pore size of large pores that are considered defects for separation and also the pore distribution becomes narrow with the impregnation. 3.3 Effect of impregnation times on pore size distribution of TCM
Fig.4 Effect of impregnating solution concentration on pore size
Fig.5 shows the pore size distributions of TCM impregnated with the same impregnant mass fraction of 10% for one, two, and three times. Fig.5 shows that the pore size of TCM became small with increasing of the impregnating times. It was found that increasing the impregnation times makes more carbonaceous materials deposited from phenolic resin, which decreases pore size.
distribution of carbon membrane
4
Conclusions
Impregnation could not only decrease pore size of the TCM but also make the pore distribution narrow in the inner face, which indicates that the impregnation modification could be beneficial to improve the separation performance of TCM. Acknowledgments The authors gratefully acknowledge Tianjin Key Technologies R & D Program (05YFGDGX10000-3) for their financial supports. The authors also appreciate Professor C.Y.Wang for offering the raw material-mesocarbon microbead. Fig.5 Effects of impregnation times on pore size distribution of carbon membrane
impregnated with 0%, 15% and 30% alcohol solution of phenolic resin by mass fraction. The TCM pore size become small and pore distribution become narrow with increasing impregnant concentration. The membrane pore size of the untreated TCM was centered approximately 0.230 µm, while the membrane pore size of TCM treated with mass fraction 15 and 30% impregnant was centered approximately 0.210 and 0.180 µm, respectively. The carbonization of the impregnated samples
References [1] QIU Hai-peng, LIU Lang. Carbon separation membrane[J]. New Carbon Materials, 2003, 18(1): 80. [2] Ismal1 A F, David L. A review on the latest development of carbon membranes for gas separation[J]. Journal of Membrane Science, 2001, 193: 1-l8. [3] Wei Wei，Hu Haoquan，You Longbo，et a1．Preparation of carbon molecular sieve membrane from phenol-formalde-hyde novolac resin[J]．Carbon，2002，40(3)：465-467. [4] Damle A S, Gangwal S K, Venkataraman V K. Carbon mem-
ZHANG Yong-gang et al. / New Carbon Materials, 2010, 25(6): 475–478
brane for gas separation: Developmental studies[J]. Gas Separa-
from synthetic naphthalene isotropic pitch[J]. Carbon，1999, 37:
tion and Puritication. 1994, 8(3): 137.
1285-1297.
[5] Rao M B, Sircars S. Gas separation by absorbent membranes: US,5104425[P].
[12] ZHANG Yong-gang, WANG Cheng-yang, YAN Pei. Mesocarbon microbeads heat-treated at low temperature in presence of
1999.
[6] WEI We, LIU Su-qin, WANG Tong-hua, et al. Preparation of carbon membrane[J]. Chemical Industry and Engineering Progress. 2000, 19(3): 18-21.
CoCl2 as the anode material of a Li-ion battery[J]. New Carbon Materials, 2007, 22(1): 35-39. [13] Centeno T A, Fuertes A B. Influence of separation temperature
[7] WANG Tong-hua, WEI Wei, LIU Shu-qin, et al. The study on tubular porous carbon membrane[J]. New Carbon Materials. 2000, 15(1): 6-11.
on the performance of adsorption-selective carbon membranes[J]. Carbon, 2003, 41(10): 2016-2019. [14] QIN Guo-tong, WANG Chun, WEI Wei. Preparation of a
[8] Fuertes A B. Adsorption-selective carbon membrane for gas separation[J]. Journal of Membrane Science, 2000, 177(1-2) : 9-16.
mesoporous carbon membrane from resorcinol and formaldehyde[J]. Carbon, 2010, 48(14): 4206-4208. [15] Yoshimune M, Yamamoto T, Nakaiwa M, et al.. Preparation of
[9] Centeno T A , Vilas J L, Fuertes A B. Effects of phenolic resin
highly mesoporous carbon membranes via a sol–gel process us-
pyrolysis conditions on carbon membrane performance for gas
ing resorcinol and formaldehyde [J], Carbon, 2008, 46(7):
separation[J]. Journal of Membrane Science, 2004, 228(1): 45-54.
1031-1036. [16] Katsaros F K, Steriotis T A, Romanos G E, et al.. Preparation
[10] DONG Yong-Rong, Nakao M, Nishiyama N, et al. Gas permea-
and characterisation of gas selective microporous carbon mem-
tion and pervaporation of water/alcohols through the micropor-
branes[J]. Microporous and Mesoporous Materials, 2007,
ous
carbon
membranes
prepared
from
resorci-
nol/formaldehyde/quaternary ammonium compounds[J]. Separation and Purification Technology, 2010, 73(1): 2-7. [11] Young-Chul Chang, Hun-Joon Sohn, Cha-Hun Ku, et al. Anodic performances of mesocarbon microbeads (MCMB) prepared
99(1-2): 181-189. [17] DING Xiang-jin, ZHANG Ji-zhou; BAO Zhi-qin, et al. Improved calculating way for the micro-pore-size distribution measured by bubble-point methods[J]. Journal of Inorganic Materials. 2000, 15(3): 493-498.
NOTES
Effect of impregnation on the pore structure of a tubular carbon membrane ZHANG Yong-gang*, LU Ming-chao State Key Laboratory of Hollow Fiber Membrane Materials and Processes, School of Environmental and Chemical Engineering, Tianjin Polytechnic University, Tianjin 300160, China
Abstract: To adjust and control the porous structure in the inner face of a tubular carbon membrane (TCM), impregnation methods were used, and the effects of impregnation on the pore size distribution were analyzed by adjusting impregnant concentrations and impregnation times. SEM images show that the impregnation treatment can repair the pore defects on the TCM surface. Data on the micropore size distribution indicate that the pore size of the TCM becomes smaller and its distribution becomes narrower with increasing impregnant concentrations and impregnation times, which indicates that impregnation conditions can be used to adjust the pore size and structure of the TCM. Key Words: Tube carbon membranes; Impregnation; Pore size; Pore distribution
1
Introduction
Carbon membranes have good resistance to chemical erosion and are electrically conductive, which can be used at high temperature[1-3]. It is believed as an effective method to solve environmental pollution problems, such as wastewater treatment, erosion liquid separation, and gas recycle and utility [4-10]. Pore size and their structure are not only the key parameter membrane but also technically difficult to control at industrial scale. To obtain tubular carbon membrane (TCM) with satisfactory micropore size, impregnation technique was used to adjust and control the porous structure in inner face of TCM, and the effects of impregnation on pore structure of TCM were analyzed.
2 2.1
Experimental Preparation of TCM
Mesocarbon microbeads (MCMBs), which has more regular spherical shape, narrower particulate size distribution, and higher carbon content than macromolecule polymer, was used as raw material[11-12] to prepare TCM[6,13-16]. The MCMB supplied by Tianjin Tiecheng Battery Material Co Ltd. had an average particle size of 15µm and density of 1.5 g/cm3. First, the MCMB was mixed with appropriate amount of carboxymethyl cellulose as binder. Then the obtained mixture was blended with appropriate amount of water to form soft mud. Finally, the mud was extrusion molded and carbonized under nitrogen flow to obtain TCM.
2.2
Impregnation of TCM
Impregnant was prepared by dissolving phenolic resin in absolute alcohol. Then, the TCM was soaked in the impregnant at room temperature for 5 min. The soaked TCM was dried at room temperature and carbonized at 700 °C in N2 protection. 2.3
Characterization of TCM
SEM images of inner face and cross section of TCM were obtained using a QUANTA200 scanning electron microscopy at 15.0 kV. The micropore size of TCM was measured by bubble-point methods[17] at 20 °C, in which nitrogen was used as permeance gas and isopropyl alcohol as wetting agent.
3 3.1
Results and discussion Effect of impregnation on morphology of TCM
Fig.1 shows the inner face morphologies of the TCM before and after impregnation (that is, the changes of membrane pore structure) with 15% alcohol solution of phenolic resin by mass fraction. Fig.1 (b) shows the enlarged image of the inner face of TCM before impregnation: the TCM has many big pores, whose size is too large to have a separation action. So the big pores are modified by impregnation with phenolic resin. Fig.1 (c) shows the inner face of TCM after impregnation. The inner face of TCM was covered by thick phenolic resin. After carbonization, the phenolic resin on the inner face
Received date: 10 April 2010; Revised date: 7 December 2010 *Corresponding author. E-mail: [email protected] Copyright©2010, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved. DOI: 10.1016/S1872-5805(09)60046-9
ZHANG Yong-gang et al. / New Carbon Materials, 2010, 25(6): 475–478
Fig.1 Inner face morphologies of the tube carbon membrane before and after impregnating treatment. (a) cross section of the tube carbon membrane; (b) before impregnating; (c) after impregnating; (d) carbonization of carbon membrane after impregnating with 15% alcohol solution of carboxy methylcellulose
Fig.2 Inner face morphologies of the tube carbon membrane with different concentration alcohol solution of carboxy methylcellulose. (e) 3%；(f) 30%
of TCM was decomposed into carbonaceous material. Therefore, the impregnation can repair obviously the pore defects. Fig.1(d), Fig.2(e) and Fig.2(f) are SEM images of TCM, which were obtained by the same impregnation and heat treatment at 1 073K in N2 protection, but the impregnant concentrations were 15, 3, and 30% by mass fraction, respectively. From the three images, it can be found that the impregnation can repair the pore defects on surface of TCM, and the repairing effect was improved with increasing impregnant concentration.
Fig.3(g) and (h) shows the cross-sectional SEM images of TCM before and after impregnation with 15% impregnant by mass fraction. It was found that the pore structure in cross section has no changes, which means that impregnation treatment to TCM could only adjust the pore structure on the membrane surface and could not penetrate into the membrane body. 3.2 Effect of impregnant concentration on pore size distribution of TCM Fig.4 gives the measurable pore size changes of TCM
ZHANG Yong-gang et al. / New Carbon Materials, 2010, 25(6): 475–478
Fig.3 Cross section morphologies of the tube carbon membrane before and after impregnating treatment (g) before impregnating; (h) after impregnating
could convert the phenolic resin coated around large pores into carbonaceous materials, which decreased the pore size of large pores that are considered defects for separation and also the pore distribution becomes narrow with the impregnation. 3.3 Effect of impregnation times on pore size distribution of TCM
Fig.4 Effect of impregnating solution concentration on pore size
Fig.5 shows the pore size distributions of TCM impregnated with the same impregnant mass fraction of 10% for one, two, and three times. Fig.5 shows that the pore size of TCM became small with increasing of the impregnating times. It was found that increasing the impregnation times makes more carbonaceous materials deposited from phenolic resin, which decreases pore size.
distribution of carbon membrane
4
Conclusions
Impregnation could not only decrease pore size of the TCM but also make the pore distribution narrow in the inner face, which indicates that the impregnation modification could be beneficial to improve the separation performance of TCM. Acknowledgments The authors gratefully acknowledge Tianjin Key Technologies R & D Program (05YFGDGX10000-3) for their financial supports. The authors also appreciate Professor C.Y.Wang for offering the raw material-mesocarbon microbead. Fig.5 Effects of impregnation times on pore size distribution of carbon membrane
impregnated with 0%, 15% and 30% alcohol solution of phenolic resin by mass fraction. The TCM pore size become small and pore distribution become narrow with increasing impregnant concentration. The membrane pore size of the untreated TCM was centered approximately 0.230 µm, while the membrane pore size of TCM treated with mass fraction 15 and 30% impregnant was centered approximately 0.210 and 0.180 µm, respectively. The carbonization of the impregnated samples
References [1] QIU Hai-peng, LIU Lang. Carbon separation membrane[J]. New Carbon Materials, 2003, 18(1): 80. [2] Ismal1 A F, David L. A review on the latest development of carbon membranes for gas separation[J]. Journal of Membrane Science, 2001, 193: 1-l8. [3] Wei Wei，Hu Haoquan，You Longbo，et a1．Preparation of carbon molecular sieve membrane from phenol-formalde-hyde novolac resin[J]．Carbon，2002，40(3)：465-467. [4] Damle A S, Gangwal S K, Venkataraman V K. Carbon mem-
ZHANG Yong-gang et al. / New Carbon Materials, 2010, 25(6): 475–478
brane for gas separation: Developmental studies[J]. Gas Separa-
from synthetic naphthalene isotropic pitch[J]. Carbon，1999, 37:
tion and Puritication. 1994, 8(3): 137.
1285-1297.
[5] Rao M B, Sircars S. Gas separation by absorbent membranes: US,5104425[P].
[12] ZHANG Yong-gang, WANG Cheng-yang, YAN Pei. Mesocarbon microbeads heat-treated at low temperature in presence of
1999.
[6] WEI We, LIU Su-qin, WANG Tong-hua, et al. Preparation of carbon membrane[J]. Chemical Industry and Engineering Progress. 2000, 19(3): 18-21.
CoCl2 as the anode material of a Li-ion battery[J]. New Carbon Materials, 2007, 22(1): 35-39. [13] Centeno T A, Fuertes A B. Influence of separation temperature
[7] WANG Tong-hua, WEI Wei, LIU Shu-qin, et al. The study on tubular porous carbon membrane[J]. New Carbon Materials. 2000, 15(1): 6-11.
on the performance of adsorption-selective carbon membranes[J]. Carbon, 2003, 41(10): 2016-2019. [14] QIN Guo-tong, WANG Chun, WEI Wei. Preparation of a
[8] Fuertes A B. Adsorption-selective carbon membrane for gas separation[J]. Journal of Membrane Science, 2000, 177(1-2) : 9-16.
mesoporous carbon membrane from resorcinol and formaldehyde[J]. Carbon, 2010, 48(14): 4206-4208. [15] Yoshimune M, Yamamoto T, Nakaiwa M, et al.. Preparation of
[9] Centeno T A , Vilas J L, Fuertes A B. Effects of phenolic resin
highly mesoporous carbon membranes via a sol–gel process us-
pyrolysis conditions on carbon membrane performance for gas
ing resorcinol and formaldehyde [J], Carbon, 2008, 46(7):
separation[J]. Journal of Membrane Science, 2004, 228(1): 45-54.
1031-1036. [16] Katsaros F K, Steriotis T A, Romanos G E, et al.. Preparation
[10] DONG Yong-Rong, Nakao M, Nishiyama N, et al. Gas permea-
and characterisation of gas selective microporous carbon mem-
tion and pervaporation of water/alcohols through the micropor-
branes[J]. Microporous and Mesoporous Materials, 2007,
ous
carbon
membranes
prepared
from
resorci-
nol/formaldehyde/quaternary ammonium compounds[J]. Separation and Purification Technology, 2010, 73(1): 2-7. [11] Young-Chul Chang, Hun-Joon Sohn, Cha-Hun Ku, et al. Anodic performances of mesocarbon microbeads (MCMB) prepared
99(1-2): 181-189. [17] DING Xiang-jin, ZHANG Ji-zhou; BAO Zhi-qin, et al. Improved calculating way for the micro-pore-size distribution measured by bubble-point methods[J]. Journal of Inorganic Materials. 2000, 15(3): 493-498.