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ceramic nanocomposite membranes in gas sweetening
Desalination 250 (2010) 1140–1143
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Fabrication of PEBA/ceramic nanocomposite membranes in gas sweetening☆ M. Akhfash Ardestani a,c, A.A. Babaluo b,c,d,⁎, M. Peyravi a,c, M.K. Razavi Aghjeh b,c,d, E. Jannatdoost a,c,e a
Chemical Engineering Department, Sahand University of Technology, P.O. Box 51335/1996, Tabriz, I. R. Iran Polymer Engineering Department, Sahand University of Technology, P.O. Box 51335/1996, Tabriz, I.R. Iran c Nanostructure Material Research Center (NMRC), Sahand University of Technology, P.O. Box 51335/1996, Tabriz, I.R. Iran d Institute of polymeric materials, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Islamic Republic of Iran e Chemical Engineering Department, Urmia University of Technology, Urmia, I.R. Iran b
a r t i c l e
i n f o
Available online 14 November 2009 Keywords: Organic–inorganic hybrid membrane Poly (ether-block-amide) Gas sweetening Nanocomposite
a b s t r a c t Poly (ether-block-amide) (PEBA)/ceramic nanocomposite hybrid membranes were fabricated by dip-coating of ceramic nanocomposite porous support in PEBA solution and their performance in gas separation (CO2 and N2) was examined. Tubular supports were used as substrates for hybrid membranes and Poly (etherblock-amide) was applied as a selective layer. PEBA based on N6 and PEO was synthesized via a two step process. The formation of new ester bond between N6 and PEO in the synthesized copolymer was proved by FT-IR spectroscopy. AFM micrographs indicated that the morphology is the dispersion of high stiffness nanostructured PA domains in the amorphous region of PEO matrix. Experimental results showed that at high concentration of coating solution, a uniform PEBA layer was formed on the porous ceramic support with higher performance for the separation of CO2/N2 binary gas mixture. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Poly (ether-block-amide) (PEBA) is a thermoplastic elastomer comprising of hard and soft segments of polyamide (PA) and polyether (PE) respectively. The polymer structure consists of a linear chain of polyamide segments interspaced with polyether segments, having the following general chemical formula:
In this segmented block copolymer, there are two microphaseseparated domains: the polyamide crystalline domains provide mechanical strength and the polyether amorphous domains offer high permeability due to the high chain mobility of the ether linkage [1]. Different grades of PEBA polymers are commercially available, and they generally have excellent mechanical strength and good chemical resistance [2]. Membranes made from certain grades of PEBA polymers exhibited good performance for the separation of polar (or quadrupolar)/non-polar gas pairs (CO2/N2, SO2/N2 or CO2/H2) [3,4].
Asymmetric composite membranes consisting of a thin separation layer and a nanoporous support are used in almost all industrially important gas separation processes. The dense layer was responsible for the separation, while the porous sub-layer provided mechanical strength to the selective layer with minimum resistance to the permeation of components [5,6]. Organic–organic hybrid membranes that composed of a dense polymeric selective layer on a porous polymeric support are one of the most common types of asymmetric composite membranes. The major drawbacks of this membranes are low permeability, low mechanical, chemical and thermal stability [7]. Therefore, high performance hybrid membranes could be only obtained by using asymmetric multilayer porous ceramic supports. This kind of membrane is called organic–inorganic hybrid membrane [5]. In this work, a new PEBA copolymer based on nylon6 and poly (ethylene oxide) is synthesized with multi-block structure. Multilayer porous ceramic supports are prepared with controllable microstructures using nanocomposites technology. Then PEBA/ceramic nanocomposite membranes are fabricated by dip-coating of ceramic nanoporous support in PEBA solution. Membranes were examined by pure gases (CO2 and N2) permeation tests. 2. Experimental 2.1. Nanocomposite ceramic support preparation
☆ Presented at the 12th Aachener Membrane Kolloquium, Aachen, Germany, 29-30 October, 2008. ⁎ Corresponding author. E-mail address: [email protected] (A.A. Babaluo). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.09.127
Tubular nanostructured supports were used as substrates for hybrid membranes. Tubular alumina supports (15 mm diameter, 3 mm thickness and 75 mm length) were prepared by gel-casting as a novel forming
M.A. Ardestani et al. / Desalination 250 (2010) 1140–1143
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method [8,9]. Nanostructured support intermediate layer was composed of two concentric layers with a decreasing pore size which were made-up of in-house synthesized submicron and nanoalumina powders (submicron powder: 240 nm [10] and nanopowder: 60 nm [11]). Using nanocomposite technology, nanostructured support top-layer was fabricated by bidispersed colloidal suspensions of nanoalumina and nanozirconia powders (nanozirconia powder: 45 nm [12]). Dip-coating method was utilized for preparing the interlayers and top-layer. 2.2. Synthesis of poly (ether-block-amide) (PEBA) Segmented block copolymer based on nylon6 (N6) and polyethylene oxide (PEO) (both purchased from Sigma-Aldrich Co) with stoichiometric ratio was synthesized in a two step process. The first step was the prepolymerization of N6 in the presence of adipic acid (AA) (purchased from Merck) for carboxy terminating of N6 at 250 °C and the second one was polycondensation of the first step product with PEO in the presence of Ti(OBu)4 (purchased from Merck) as a catalyst (1.5–3 mmol kg− 1 based on the amount of reactant) and Irganox 1010 (purchased from Ciba Geigy Co) as a thermostabilizer (0.05 to 0.1 wt.% based on the total amount of reagents) at the same temperature to a high molecular weight. The synthesized copolymer was dried in high vacuum (0.6 bar) at 50 °C overnight. 2.3. PEBA/ceramic nanocomposite membrane preparation PEBA/ceramic nanocomposite membranes were fabricated by dipcoating of ceramic nanocomposite porous support in PEBA solution. Coating solutions were prepared by dissolving PEBA in acid formic/1propanol (3:2 v/v) (both purchased from Merck) at 80 °C under vigorous mixing and reflux conditions. The PEBA concentration in the coating solution ranged from 3 to 30 wt.%. Membranes were dried in an oven overnight to remove any residual solvent. 2.4. Copolymer and membrane characterization FTIR analysis was carried out in a UNICAM Matson 1000, in the wavenumber range of 400–4000 cm− 1. The composition of the copolymer was determined using a 200 MHz, BRÜKER H NMR spectrometer. Differential thermal analyses were carried out for copolymer and homopolymers by a Perkin Elmer Pyris Diamond TG/DTA analyzer. The XRD patterns were determined on a TW3710 Philips X'Pert diffractometer. Atomic force microscopy (AFM, Dual Scope Tm C-21 scanning probe microscope) was utilized to study the morphology of the copolymer samples. Morphology and surface topology of the nanostructure supports and manufactured PEBA/ceramic nanocomposite membranes were investigated by scanning electron microscopy (SEM, CamScan MV2300). 2.5. Gas permeation experiments Single gas permeation measurement was carried out in ambient conditions to evaluate the performance of manufactured PEBA/ ceramic nanocomposite membranes in gas separation. Measurements of CO2 and N2 permeation were made at pressure differences up to 6 bars. Permeance was measured using the stainless steel permeator with a permeation area of 22.608 cm2.
Fig. 1. SEM images of surface (a) and cross view (b) of nanostructure support.
Also, no penetration of intermediate layers in the support could be observed. With regard of the SEM images, the fabricated nanostructure ceramic supports promote a high performance in membrane separation processes due to its defect-free surface and its multilayer structure with no penetration.
3.2. Copoly (ether-block-amide) (PEBA) In general structure of copolymer, the hard and soft blocks are linked together by ester groups. In order to check the presence of ester groups, FT-IR spectroscopic measurements were carried out proving in this way the formation of block copolymer rather than a polymer blend. In Fig. 2 the FT-IR spectrum of PEO-N6 copolymer shows characteristic peaks of hydrogen-bonded amide groups at 3300, 1646, 1542 and 1284 cm− 1 (Fig. 2, A,B,C,D). Also, the broad band centered around 1100 cm− 1 can be attributed to the ether C–O–C asymmetric stretch (E). In addition, a band at 1730 cm− 1 was attributed to the C O stretching of ester group which confirms the formation of the ester linkage in the copolymer. The chemical structure of the synthesized copolymer was investigated by H NMR spectrum. From the results of H NMR, the chemical structure of
3. Results and discussion 3.1. Nanocomposite ceramic support The SEM images micrographs of surface and cross view of nanostructured ceramic supports are shown in Fig. 1. As can be seen, by applying the mentioned modification procedure, an even surface with reduced pore size was achieved and cracks of surface were disappeared significantly.
Fig. 2. FT-IR spectrum of PEO–N6 copolymer.
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M.A. Ardestani et al. / Desalination 250 (2010) 1140–1143
the copolymer from the mole fraction of copolymer constituents is derived as follows:
–½ðCH2 –CH2 –OÞp1:0 –½ðCðOÞ–ðCH2 Þ5 –NHÞq1:2 – H NMR results suggest that the chemical structure of copolymer could be a multi-block type. Thermal properties and phase separation behavior of the synthesized copolymer in comparison with homopolymers were investigated using DTA and the obtained results were shown in Fig. 3(a). The results of the conducted characterization suggest that the obtained PEBA consists of two distinct crystalline phases: a rich crystalline phase of N6 and a crystalline phase of PEO which can be dispersed in amorphous phase of PEO as well some amount of noncrystallized hard segment. The depression of the melting temperature of the crystalline phase in the final product relative to homopolymers, confirms the formation of copolymer structure which is in good agreement with FT-IR results. In other words, DTA results confirmed the synthesis of copolymer with high degree of micro-phase separation. Surface morphology and micro-phase separation of the synthesized copolymer were investigated by AFM. AFM phase images of this sample (Fig. 3(b)) show monodispersed morphology of high stiffness PA phase into a soft rubbery PEO matrix phase. The obtained morphology for the synthesized copolymer reveals micro-phase separation of PA (hard segments) and PEO (soft segments) phases which is in good agreement with DTA results. AFM micrographs with high magnification reveal that the high stiffness PA domains have nanometric structures which can be desirable in manufacturing of polymeric membranes with high performance in separation processes. More detailed studies on performance of this membrane are under investigation.
Fig. 3. (a): XRD pattern of the PEO–N6 copolymer (b): DTA thermograms of the PEO, N6 and copolymer.
3.3. PEBA/ceramic nanocomposite membranes and gas permeation results PEBA/ceramic nanocomposite membranes were fabricated by dipcoating of ceramic nanocomposite porous support in copolymer (PEBA) solution. Microscopic images of the prepared PEBA/ceramic nanocomposite membranes showed that after double coating with 3 wt.% PEBA solution, the membrane surface was not uniform, also no good results were obtained in CO2/N2 binary gas mixture separation. So the polymer concentration in coating solution was increased to 10 wt.%; although after four dip-coating steps, the surface was smoother but still a perfect uniform surface was not achieved. It will be expected that, at high
Fig. 4. SEM images of surface (a) and cross section (b) of the fabricated hybrid membranes and permeance (c) of CO2 and N2 through these membranes.
M.A. Ardestani et al. / Desalination 250 (2010) 1140–1143
concentration of coating solution, a uniform PEBA layer is formed on the porous ceramic support with higher thickness, so the polymer concentration was increased to 30 wt.%. SEM images of the fabricated hybrid membrane surface and cross view are shown in Fig. 4(a) and (b). As can be seen, after four dip-coating steps, a uniform PEBA layer was formed on the porous ceramic support with high thickness (~140 µm) and then these membranes can be suitable for the separation of polar/ non-polar gas pairs. Permeation of CO2 and N2 through this hybrid membranes at different operating pressures is shown in Fig. 4(c). As can be seen, the permeation of CO2 is in agreement with literature but no N2 was permeated. Therefore the ideal selectivity of these membranes for CO2/N2 binary mixture can be predicted very high (infinite). These membranes show a suitable permeability for CO2 as a polar gas and no permeation for N2 as a nonpolar gas molecule. Apparently, with varying the operating condition this membrane performance could be optimized in CO2/N2 binary gas mixture separation and this object is under investigation in our future work. 4. Conclusion PEBA copolymer was successfully synthesized based on N6 and PEO. Several methods were applied to characterize the synthesized copolymer. The obtained results confirmed uniform dispersion of nanostructured
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crystalline phase in the amorphous matrix which is very important in their performance for membrane processes. Also PEBA/ceramic nanocomposite membranes were fabricated and their performance in gas separation was examined. It was found that at high concentration of coating solution, a uniform PEBA layer was formed on the porous ceramic support and consequently membranes show a high performance for the separation of CO2/N2 binary mixture. References [1] R. Joseph, J.R. Flesher, PEBA® High Performance Polymers: Their Origin and Development, Elsevier, 1986. [2] PEBAX®—Basis of Performance, Polyether Block Amide, Elf Atochem Technical Document. [3] V.I. Bondar, B.D. Freeman, Journal of Polymer Science. Polymer Physics 37 (1990) 2463. [4] V.I. Bondar, B.D. Freeman, Journal of Polymer Science. Polymer Physics 38 (2000) 2051. [5] A. Tabe-Mohammadi, Journal of Separation Science Technology 34 (1999) 2095. [6] Final report by membrane technology and research, low-quality natural gas sulfur removal/recovery, 1998. [7] T.V. Gestel, C. Vandecasteele, Journal of Membrane Science 207 (2002) 73. [8] A.A. Babaluo, M. Kokabi, M. Manteghian, Journal of European Ceramic Society 24 (2004) 3779. [9] B. Bayati, AA. Babaluo, 11th National Iranian Chemical Engineering Congress, Tarbiat Modares University, Tehran, Iran, November 28–30, 2006. [10] P. Ahmadian, A.A. Babaluo, IChEC 2008, January 2–5, 2008, Kish Island, Iran. [11] M. Tahmasebpour, A.A. Babaluo, Powder Technology 191 (2009) 91. [12] M. Tahmasebpour, A.A. Babaluo, M.K. Razavi Aghjeh, Journal of the European Ceramic Society 28 (2008) 773.
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Fabrication of PEBA/ceramic nanocomposite membranes in gas sweetening☆ M. Akhfash Ardestani a,c, A.A. Babaluo b,c,d,⁎, M. Peyravi a,c, M.K. Razavi Aghjeh b,c,d, E. Jannatdoost a,c,e a
Chemical Engineering Department, Sahand University of Technology, P.O. Box 51335/1996, Tabriz, I. R. Iran Polymer Engineering Department, Sahand University of Technology, P.O. Box 51335/1996, Tabriz, I.R. Iran c Nanostructure Material Research Center (NMRC), Sahand University of Technology, P.O. Box 51335/1996, Tabriz, I.R. Iran d Institute of polymeric materials, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Islamic Republic of Iran e Chemical Engineering Department, Urmia University of Technology, Urmia, I.R. Iran b
a r t i c l e
i n f o
Available online 14 November 2009 Keywords: Organic–inorganic hybrid membrane Poly (ether-block-amide) Gas sweetening Nanocomposite
a b s t r a c t Poly (ether-block-amide) (PEBA)/ceramic nanocomposite hybrid membranes were fabricated by dip-coating of ceramic nanocomposite porous support in PEBA solution and their performance in gas separation (CO2 and N2) was examined. Tubular supports were used as substrates for hybrid membranes and Poly (etherblock-amide) was applied as a selective layer. PEBA based on N6 and PEO was synthesized via a two step process. The formation of new ester bond between N6 and PEO in the synthesized copolymer was proved by FT-IR spectroscopy. AFM micrographs indicated that the morphology is the dispersion of high stiffness nanostructured PA domains in the amorphous region of PEO matrix. Experimental results showed that at high concentration of coating solution, a uniform PEBA layer was formed on the porous ceramic support with higher performance for the separation of CO2/N2 binary gas mixture. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Poly (ether-block-amide) (PEBA) is a thermoplastic elastomer comprising of hard and soft segments of polyamide (PA) and polyether (PE) respectively. The polymer structure consists of a linear chain of polyamide segments interspaced with polyether segments, having the following general chemical formula:
In this segmented block copolymer, there are two microphaseseparated domains: the polyamide crystalline domains provide mechanical strength and the polyether amorphous domains offer high permeability due to the high chain mobility of the ether linkage [1]. Different grades of PEBA polymers are commercially available, and they generally have excellent mechanical strength and good chemical resistance [2]. Membranes made from certain grades of PEBA polymers exhibited good performance for the separation of polar (or quadrupolar)/non-polar gas pairs (CO2/N2, SO2/N2 or CO2/H2) [3,4].
Asymmetric composite membranes consisting of a thin separation layer and a nanoporous support are used in almost all industrially important gas separation processes. The dense layer was responsible for the separation, while the porous sub-layer provided mechanical strength to the selective layer with minimum resistance to the permeation of components [5,6]. Organic–organic hybrid membranes that composed of a dense polymeric selective layer on a porous polymeric support are one of the most common types of asymmetric composite membranes. The major drawbacks of this membranes are low permeability, low mechanical, chemical and thermal stability [7]. Therefore, high performance hybrid membranes could be only obtained by using asymmetric multilayer porous ceramic supports. This kind of membrane is called organic–inorganic hybrid membrane [5]. In this work, a new PEBA copolymer based on nylon6 and poly (ethylene oxide) is synthesized with multi-block structure. Multilayer porous ceramic supports are prepared with controllable microstructures using nanocomposites technology. Then PEBA/ceramic nanocomposite membranes are fabricated by dip-coating of ceramic nanoporous support in PEBA solution. Membranes were examined by pure gases (CO2 and N2) permeation tests. 2. Experimental 2.1. Nanocomposite ceramic support preparation
☆ Presented at the 12th Aachener Membrane Kolloquium, Aachen, Germany, 29-30 October, 2008. ⁎ Corresponding author. E-mail address: [email protected] (A.A. Babaluo). 0011-9164/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2009.09.127
Tubular nanostructured supports were used as substrates for hybrid membranes. Tubular alumina supports (15 mm diameter, 3 mm thickness and 75 mm length) were prepared by gel-casting as a novel forming
M.A. Ardestani et al. / Desalination 250 (2010) 1140–1143
1141
method [8,9]. Nanostructured support intermediate layer was composed of two concentric layers with a decreasing pore size which were made-up of in-house synthesized submicron and nanoalumina powders (submicron powder: 240 nm [10] and nanopowder: 60 nm [11]). Using nanocomposite technology, nanostructured support top-layer was fabricated by bidispersed colloidal suspensions of nanoalumina and nanozirconia powders (nanozirconia powder: 45 nm [12]). Dip-coating method was utilized for preparing the interlayers and top-layer. 2.2. Synthesis of poly (ether-block-amide) (PEBA) Segmented block copolymer based on nylon6 (N6) and polyethylene oxide (PEO) (both purchased from Sigma-Aldrich Co) with stoichiometric ratio was synthesized in a two step process. The first step was the prepolymerization of N6 in the presence of adipic acid (AA) (purchased from Merck) for carboxy terminating of N6 at 250 °C and the second one was polycondensation of the first step product with PEO in the presence of Ti(OBu)4 (purchased from Merck) as a catalyst (1.5–3 mmol kg− 1 based on the amount of reactant) and Irganox 1010 (purchased from Ciba Geigy Co) as a thermostabilizer (0.05 to 0.1 wt.% based on the total amount of reagents) at the same temperature to a high molecular weight. The synthesized copolymer was dried in high vacuum (0.6 bar) at 50 °C overnight. 2.3. PEBA/ceramic nanocomposite membrane preparation PEBA/ceramic nanocomposite membranes were fabricated by dipcoating of ceramic nanocomposite porous support in PEBA solution. Coating solutions were prepared by dissolving PEBA in acid formic/1propanol (3:2 v/v) (both purchased from Merck) at 80 °C under vigorous mixing and reflux conditions. The PEBA concentration in the coating solution ranged from 3 to 30 wt.%. Membranes were dried in an oven overnight to remove any residual solvent. 2.4. Copolymer and membrane characterization FTIR analysis was carried out in a UNICAM Matson 1000, in the wavenumber range of 400–4000 cm− 1. The composition of the copolymer was determined using a 200 MHz, BRÜKER H NMR spectrometer. Differential thermal analyses were carried out for copolymer and homopolymers by a Perkin Elmer Pyris Diamond TG/DTA analyzer. The XRD patterns were determined on a TW3710 Philips X'Pert diffractometer. Atomic force microscopy (AFM, Dual Scope Tm C-21 scanning probe microscope) was utilized to study the morphology of the copolymer samples. Morphology and surface topology of the nanostructure supports and manufactured PEBA/ceramic nanocomposite membranes were investigated by scanning electron microscopy (SEM, CamScan MV2300). 2.5. Gas permeation experiments Single gas permeation measurement was carried out in ambient conditions to evaluate the performance of manufactured PEBA/ ceramic nanocomposite membranes in gas separation. Measurements of CO2 and N2 permeation were made at pressure differences up to 6 bars. Permeance was measured using the stainless steel permeator with a permeation area of 22.608 cm2.
Fig. 1. SEM images of surface (a) and cross view (b) of nanostructure support.
Also, no penetration of intermediate layers in the support could be observed. With regard of the SEM images, the fabricated nanostructure ceramic supports promote a high performance in membrane separation processes due to its defect-free surface and its multilayer structure with no penetration.
3.2. Copoly (ether-block-amide) (PEBA) In general structure of copolymer, the hard and soft blocks are linked together by ester groups. In order to check the presence of ester groups, FT-IR spectroscopic measurements were carried out proving in this way the formation of block copolymer rather than a polymer blend. In Fig. 2 the FT-IR spectrum of PEO-N6 copolymer shows characteristic peaks of hydrogen-bonded amide groups at 3300, 1646, 1542 and 1284 cm− 1 (Fig. 2, A,B,C,D). Also, the broad band centered around 1100 cm− 1 can be attributed to the ether C–O–C asymmetric stretch (E). In addition, a band at 1730 cm− 1 was attributed to the C O stretching of ester group which confirms the formation of the ester linkage in the copolymer. The chemical structure of the synthesized copolymer was investigated by H NMR spectrum. From the results of H NMR, the chemical structure of
3. Results and discussion 3.1. Nanocomposite ceramic support The SEM images micrographs of surface and cross view of nanostructured ceramic supports are shown in Fig. 1. As can be seen, by applying the mentioned modification procedure, an even surface with reduced pore size was achieved and cracks of surface were disappeared significantly.
Fig. 2. FT-IR spectrum of PEO–N6 copolymer.
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M.A. Ardestani et al. / Desalination 250 (2010) 1140–1143
the copolymer from the mole fraction of copolymer constituents is derived as follows:
–½ðCH2 –CH2 –OÞp1:0 –½ðCðOÞ–ðCH2 Þ5 –NHÞq1:2 – H NMR results suggest that the chemical structure of copolymer could be a multi-block type. Thermal properties and phase separation behavior of the synthesized copolymer in comparison with homopolymers were investigated using DTA and the obtained results were shown in Fig. 3(a). The results of the conducted characterization suggest that the obtained PEBA consists of two distinct crystalline phases: a rich crystalline phase of N6 and a crystalline phase of PEO which can be dispersed in amorphous phase of PEO as well some amount of noncrystallized hard segment. The depression of the melting temperature of the crystalline phase in the final product relative to homopolymers, confirms the formation of copolymer structure which is in good agreement with FT-IR results. In other words, DTA results confirmed the synthesis of copolymer with high degree of micro-phase separation. Surface morphology and micro-phase separation of the synthesized copolymer were investigated by AFM. AFM phase images of this sample (Fig. 3(b)) show monodispersed morphology of high stiffness PA phase into a soft rubbery PEO matrix phase. The obtained morphology for the synthesized copolymer reveals micro-phase separation of PA (hard segments) and PEO (soft segments) phases which is in good agreement with DTA results. AFM micrographs with high magnification reveal that the high stiffness PA domains have nanometric structures which can be desirable in manufacturing of polymeric membranes with high performance in separation processes. More detailed studies on performance of this membrane are under investigation.
Fig. 3. (a): XRD pattern of the PEO–N6 copolymer (b): DTA thermograms of the PEO, N6 and copolymer.
3.3. PEBA/ceramic nanocomposite membranes and gas permeation results PEBA/ceramic nanocomposite membranes were fabricated by dipcoating of ceramic nanocomposite porous support in copolymer (PEBA) solution. Microscopic images of the prepared PEBA/ceramic nanocomposite membranes showed that after double coating with 3 wt.% PEBA solution, the membrane surface was not uniform, also no good results were obtained in CO2/N2 binary gas mixture separation. So the polymer concentration in coating solution was increased to 10 wt.%; although after four dip-coating steps, the surface was smoother but still a perfect uniform surface was not achieved. It will be expected that, at high
Fig. 4. SEM images of surface (a) and cross section (b) of the fabricated hybrid membranes and permeance (c) of CO2 and N2 through these membranes.
M.A. Ardestani et al. / Desalination 250 (2010) 1140–1143
concentration of coating solution, a uniform PEBA layer is formed on the porous ceramic support with higher thickness, so the polymer concentration was increased to 30 wt.%. SEM images of the fabricated hybrid membrane surface and cross view are shown in Fig. 4(a) and (b). As can be seen, after four dip-coating steps, a uniform PEBA layer was formed on the porous ceramic support with high thickness (~140 µm) and then these membranes can be suitable for the separation of polar/ non-polar gas pairs. Permeation of CO2 and N2 through this hybrid membranes at different operating pressures is shown in Fig. 4(c). As can be seen, the permeation of CO2 is in agreement with literature but no N2 was permeated. Therefore the ideal selectivity of these membranes for CO2/N2 binary mixture can be predicted very high (infinite). These membranes show a suitable permeability for CO2 as a polar gas and no permeation for N2 as a nonpolar gas molecule. Apparently, with varying the operating condition this membrane performance could be optimized in CO2/N2 binary gas mixture separation and this object is under investigation in our future work. 4. Conclusion PEBA copolymer was successfully synthesized based on N6 and PEO. Several methods were applied to characterize the synthesized copolymer. The obtained results confirmed uniform dispersion of nanostructured
1143
crystalline phase in the amorphous matrix which is very important in their performance for membrane processes. Also PEBA/ceramic nanocomposite membranes were fabricated and their performance in gas separation was examined. It was found that at high concentration of coating solution, a uniform PEBA layer was formed on the porous ceramic support and consequently membranes show a high performance for the separation of CO2/N2 binary mixture. References [1] R. Joseph, J.R. Flesher, PEBA® High Performance Polymers: Their Origin and Development, Elsevier, 1986. [2] PEBAX®—Basis of Performance, Polyether Block Amide, Elf Atochem Technical Document. [3] V.I. Bondar, B.D. Freeman, Journal of Polymer Science. Polymer Physics 37 (1990) 2463. [4] V.I. Bondar, B.D. Freeman, Journal of Polymer Science. Polymer Physics 38 (2000) 2051. [5] A. Tabe-Mohammadi, Journal of Separation Science Technology 34 (1999) 2095. [6] Final report by membrane technology and research, low-quality natural gas sulfur removal/recovery, 1998. [7] T.V. Gestel, C. Vandecasteele, Journal of Membrane Science 207 (2002) 73. [8] A.A. Babaluo, M. Kokabi, M. Manteghian, Journal of European Ceramic Society 24 (2004) 3779. [9] B. Bayati, AA. Babaluo, 11th National Iranian Chemical Engineering Congress, Tarbiat Modares University, Tehran, Iran, November 28–30, 2006. [10] P. Ahmadian, A.A. Babaluo, IChEC 2008, January 2–5, 2008, Kish Island, Iran. [11] M. Tahmasebpour, A.A. Babaluo, Powder Technology 191 (2009) 91. [12] M. Tahmasebpour, A.A. Babaluo, M.K. Razavi Aghjeh, Journal of the European Ceramic Society 28 (2008) 773.