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Polyamide thin-film composite membranes prepared by interfacial polymerization for pervaporation separation
Desalination 200 (2006) 387–389
Polyamide thin-film composite membranes prepared by interfacial polymerization for pervaporation separation Shu-Hsien Huanga, Chi-Lan Lib, Chien-Chieh Hua, H.A. Tsaic, Kueir-Rarn Leea*, Juin-Yih Laia a
R&D Center for Membrane Technology and Department of Chemical Engineering, Chung Yuan University, Chung-Li 32023, Taiwan email: [email protected] b Department of Chemical Engineering, Nanya Institute of Technology, Chung Li, 32034, Taiwan c Department of Textile Science, Nanya Institute of Technology, Chung Li, 32034, Taiwan Received 19 October 2005; accepted 6 March 2006
1. Introduction Pervaporation is an important membrane process in chemical industries in which valuables are isolated from the liquid mixture. Dehydration of alcohols and other organic solvents is a wellknown example for pervaporation process. Polyamides have been studied as one of suitable membrane materials because of their high thermal stability, excellent mechanical strength and high resistance to organic solvents. Polyamides show high selectivity in dehydration of alcohol at wide range of water concentrations. However, it shows low permeation flux because of the lower free volume and low solubility of water. In order to improve the permeation flux of polyamide membranes without sacrificing the selectivity, the membrane morphology must be converted from a dense thick symmetric membrane to an asymmetric or composite type morphology. The development of composite membranes is one of the key *Corresponding author.
factors for successful application of polyamide membranes in many areas. The composite membrane with the polyamide thin layer can be prepared by interfacial polymerization. Many researchers have focused their attention on the reverse osmosis [1] and nanofiltration separation processes [2] by using the thin-film composite membranes. However, there are few reports on investigating the pervaporation of polyamide thin-film composite membranes [3]. In addition, the interfacial polymerization technique is an adequate method for the preparation method of the composite membrane with ultrathin and dense polyamide skin layer. Maybe it can improve the permeation rate and maintain the selectivity. Therefore, in this study, the polyamide thin-film composite membranes were prepared by the interfacial polymerization of triethylenetetramine (TETA) and trimesoyl chloride (TMC) onto the surface of asymmetric polyacrylonitrile (PAN) membranes to be utilized in the pervaporation of the aqueous alcohol mixtures. It was expected to have
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2006.03.386
S.-H. Huang et al. / Desalination 200 (2006) 387–389
2. Results and discussion Fig. 1 exhibits the surface morphology of the modified PAN membrane and the polyamide thin-film composite membranes using the modified PAN membranes as supports prepared by the various immersion time of the aqueous solution. In Fig. 1(a), the modified PAN membrane appears as an even surface. Obviously, the surface morphologies of the polyamide thin-film composite membranes using the modified PAN membranes as supports can be affected by the immersion time of the aqueous solution. The surface morphology of the polyamide thin-film composite membranes can be changed from dense, finely dispersed nodular structures to packed tightly by the spherical globules as increasing the immersion time of the aqueous solution from 1 to 30 min, as shown in Fig. 1(b)–(e). Fig. 2 exhibits the effect of the immersion time of the aqueous solution on the pervaporation
(a)
(b)
(d)
(e)
(c)
Fig. 1. SEM photographs of the surfaces of the modified PAN membrane and the polyamide thin-film composite membranes using the modified PAN membranes as supports at 5000´ : (a) the modified PAN membrane; the polyamide thin-film composite membranes using the modified PAN membranes as supports prepared by the various immersion time of the aqueous solution (2 wt.% TETA/water); (b) 1 min; (c) 5 min; (d) 10 min; (e) 30 min (immersion time of organic solution: 3 min).
Permeation rate (g/m2 h)
good performances for the dehydration of the aqueous alcohol mixtures.
500
100
450
90
400
80
350
70
300
60
250
50
200
40
150
30
100
20
50
10
0
Water conc. in permeate (wt.%)
388
0 0
5
10 15 20 25 30 Immersion time of aqueous solution (min)
35
Fig. 2. Effect of the immersion time of the aqueous solution on the pervaporation performances of 90 wt.% aqueous IPA solution through the polyamide thin-film composite membranes using the modified PAN membranes as supports.
separation performance of 90 wt.% aqueous IPA solution for the polyamide thin-film composite membranes using the modified PAN membranes as supports. As shown in Fig. 2, the water concentration in permeate keeps in the range of 90–95 wt.% as increasing the immersion time of the aqueous solution. This is because that the crosslinking network was formed by the interfacial polymerization of TETA containing two primary amines and two secondary amines with TMC having three acid chlorides on the surfaces of the modified PAN support. The permeation rate almost keeps constant for the immersion time of the aqueous solution below 10 min. Above this time, the permeation rate increased with increasing the immersion time of the aqueous solution. The permeation rate was 370 g/m2 h for 30 min immersed. The reason is probably that the primary amines and secondary amines on the TETA and the acid chlorides on the TMC were not all to be used to crosslink. Such as some acid chlorides are changed to the carboxyl acids by hydrolysis and cannot participate in the interfacial
S.-H. Huang et al. / Desalination 200 (2006) 387–389
polymerization. Therefore, the unreacted amines and carboxyl acids formed from the hydrolysis of the acid chlorides maybe can improve the permeation rate.
composite membrane could be the candidate for the pervaporation process. References [1]
3. Conclusions The polyamide thin film composite membranes were prepared successfully by using the interfacial polymerization of TETA and TMC on the surfaces of modified porous PAN membranes. From the analyses of SEM, it was found that the polyamide active skin layers of the composite membranes are dense, rough, and finely dispersed nodular structures, packed tightly by the spherical globules. From the pervaporation performance, it was considered that the polyamide
389
[2]
[3]
I.J. Roh, S.Y. Park, J.J. Kim and C.K. Kim, Effects of the polyamide molecular structure on the performance of reverse osmosis membranes, J. Polym. Sci. Part B: Polym. Phys., 36 (1998) 1821–1830. I.-C. Kim, J. Jegal and K.-H. Lee, Effect of aqueous and organic solutions on the performance of polyamide thin-film composite nanofiltration membranes, J. Polym. Sci. Part B: Polym. Phys., 40 (2002) 2151–2163. J.-H. Kim, K.-H. Lee and S.Y. Kim, Pervaporation separation of water from ethanol through polyimide composite membranes, J. Membr. Sci., 169 (2000) 81–93.
Polyamide thin-film composite membranes prepared by interfacial polymerization for pervaporation separation Shu-Hsien Huanga, Chi-Lan Lib, Chien-Chieh Hua, H.A. Tsaic, Kueir-Rarn Leea*, Juin-Yih Laia a
R&D Center for Membrane Technology and Department of Chemical Engineering, Chung Yuan University, Chung-Li 32023, Taiwan email: [email protected] b Department of Chemical Engineering, Nanya Institute of Technology, Chung Li, 32034, Taiwan c Department of Textile Science, Nanya Institute of Technology, Chung Li, 32034, Taiwan Received 19 October 2005; accepted 6 March 2006
1. Introduction Pervaporation is an important membrane process in chemical industries in which valuables are isolated from the liquid mixture. Dehydration of alcohols and other organic solvents is a wellknown example for pervaporation process. Polyamides have been studied as one of suitable membrane materials because of their high thermal stability, excellent mechanical strength and high resistance to organic solvents. Polyamides show high selectivity in dehydration of alcohol at wide range of water concentrations. However, it shows low permeation flux because of the lower free volume and low solubility of water. In order to improve the permeation flux of polyamide membranes without sacrificing the selectivity, the membrane morphology must be converted from a dense thick symmetric membrane to an asymmetric or composite type morphology. The development of composite membranes is one of the key *Corresponding author.
factors for successful application of polyamide membranes in many areas. The composite membrane with the polyamide thin layer can be prepared by interfacial polymerization. Many researchers have focused their attention on the reverse osmosis [1] and nanofiltration separation processes [2] by using the thin-film composite membranes. However, there are few reports on investigating the pervaporation of polyamide thin-film composite membranes [3]. In addition, the interfacial polymerization technique is an adequate method for the preparation method of the composite membrane with ultrathin and dense polyamide skin layer. Maybe it can improve the permeation rate and maintain the selectivity. Therefore, in this study, the polyamide thin-film composite membranes were prepared by the interfacial polymerization of triethylenetetramine (TETA) and trimesoyl chloride (TMC) onto the surface of asymmetric polyacrylonitrile (PAN) membranes to be utilized in the pervaporation of the aqueous alcohol mixtures. It was expected to have
Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.desal.2006.03.386
S.-H. Huang et al. / Desalination 200 (2006) 387–389
2. Results and discussion Fig. 1 exhibits the surface morphology of the modified PAN membrane and the polyamide thin-film composite membranes using the modified PAN membranes as supports prepared by the various immersion time of the aqueous solution. In Fig. 1(a), the modified PAN membrane appears as an even surface. Obviously, the surface morphologies of the polyamide thin-film composite membranes using the modified PAN membranes as supports can be affected by the immersion time of the aqueous solution. The surface morphology of the polyamide thin-film composite membranes can be changed from dense, finely dispersed nodular structures to packed tightly by the spherical globules as increasing the immersion time of the aqueous solution from 1 to 30 min, as shown in Fig. 1(b)–(e). Fig. 2 exhibits the effect of the immersion time of the aqueous solution on the pervaporation
(a)
(b)
(d)
(e)
(c)
Fig. 1. SEM photographs of the surfaces of the modified PAN membrane and the polyamide thin-film composite membranes using the modified PAN membranes as supports at 5000´ : (a) the modified PAN membrane; the polyamide thin-film composite membranes using the modified PAN membranes as supports prepared by the various immersion time of the aqueous solution (2 wt.% TETA/water); (b) 1 min; (c) 5 min; (d) 10 min; (e) 30 min (immersion time of organic solution: 3 min).
Permeation rate (g/m2 h)
good performances for the dehydration of the aqueous alcohol mixtures.
500
100
450
90
400
80
350
70
300
60
250
50
200
40
150
30
100
20
50
10
0
Water conc. in permeate (wt.%)
388
0 0
5
10 15 20 25 30 Immersion time of aqueous solution (min)
35
Fig. 2. Effect of the immersion time of the aqueous solution on the pervaporation performances of 90 wt.% aqueous IPA solution through the polyamide thin-film composite membranes using the modified PAN membranes as supports.
separation performance of 90 wt.% aqueous IPA solution for the polyamide thin-film composite membranes using the modified PAN membranes as supports. As shown in Fig. 2, the water concentration in permeate keeps in the range of 90–95 wt.% as increasing the immersion time of the aqueous solution. This is because that the crosslinking network was formed by the interfacial polymerization of TETA containing two primary amines and two secondary amines with TMC having three acid chlorides on the surfaces of the modified PAN support. The permeation rate almost keeps constant for the immersion time of the aqueous solution below 10 min. Above this time, the permeation rate increased with increasing the immersion time of the aqueous solution. The permeation rate was 370 g/m2 h for 30 min immersed. The reason is probably that the primary amines and secondary amines on the TETA and the acid chlorides on the TMC were not all to be used to crosslink. Such as some acid chlorides are changed to the carboxyl acids by hydrolysis and cannot participate in the interfacial
S.-H. Huang et al. / Desalination 200 (2006) 387–389
polymerization. Therefore, the unreacted amines and carboxyl acids formed from the hydrolysis of the acid chlorides maybe can improve the permeation rate.
composite membrane could be the candidate for the pervaporation process. References [1]
3. Conclusions The polyamide thin film composite membranes were prepared successfully by using the interfacial polymerization of TETA and TMC on the surfaces of modified porous PAN membranes. From the analyses of SEM, it was found that the polyamide active skin layers of the composite membranes are dense, rough, and finely dispersed nodular structures, packed tightly by the spherical globules. From the pervaporation performance, it was considered that the polyamide
389
[2]
[3]
I.J. Roh, S.Y. Park, J.J. Kim and C.K. Kim, Effects of the polyamide molecular structure on the performance of reverse osmosis membranes, J. Polym. Sci. Part B: Polym. Phys., 36 (1998) 1821–1830. I.-C. Kim, J. Jegal and K.-H. Lee, Effect of aqueous and organic solutions on the performance of polyamide thin-film composite nanofiltration membranes, J. Polym. Sci. Part B: Polym. Phys., 40 (2002) 2151–2163. J.-H. Kim, K.-H. Lee and S.Y. Kim, Pervaporation separation of water from ethanol through polyimide composite membranes, J. Membr. Sci., 169 (2000) 81–93.