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Effect of water on the facilitated transport of olefins through solid polymer electrolyte membranes
Journal of Membrane Science 181 (2001) 289–293
Short communication
Effect of water on the facilitated transport of olefins through solid polymer electrolyte membranes Seong Uk Hong, Jung Yong Kim, Yong Soo Kang∗ Center for Facilitated Transport Membranes, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, South Korea Received 24 February 2000; received in revised form 25 September 2000; accepted 27 October 2000
Abstract Polymer electrolyte membranes composed of poly(2-ethyl-2-oxazoline) (POZ) and AgBF4 are prepared for olefin/paraffin separations. The stability and effect of relative humidity on permeance and selectivity are investigated using propylene/propane mixed gases. The selectivity of propylene over propane remains high on the long time operation with a dry feed gas, indicating that membranes are effective for propylene/propane separation in the absence of water. As humidity of the feed gas increases, both propylene and propane permeances increase, which resulting in the slight decrease of selectivity. © 2001 Published by Elsevier Science B.V. Keywords: Facilitated transport; Relative humidity; Solid polymer electrolyte; Olefin/paraffin separation
1. Introduction Olefin/paraffin separation is one of the most important processes in petrochemical industries and is currently carried out by the energy intensive cryogenic distillation process. According to the recent report by DOE, 0.12 Quads of energy (1 Quad = 1015 BTU) is used yearly for olefin/paraffin distillation [1]. This large energy and capital investment requirement provides the incentive for olefin/paraffin separation research. The membrane process using the concept of facilitated transport has been considered to be an energy-saving process. In the facilitated transport ∗ Corresponding author. Tel.: +82-2-958-5362; fax: +82-2-958-6869. E-mail address: [email protected] (Y.S. Kang).
(FT) membranes, carrier-mediated transport occurs, in addition to a normal Fickian transport, due to the reversible reaction of carrier with a specific solute, and separation efficiency can be improved remarkably. Therefore, a substantial body of studies has been performed to separate olefin/paraffin mixtures using the concept of facilitated transport in liquid [2–9] as well as solid membranes containing silver [10–14] or copper cation [15]. Because evaporation of liquid media in liquid membranes gives a serious drawback and problems for practical applications, the development of solid FT membranes is demanding. Recently, we have reported solid FT membranes containing AgBF4 or AgCF3 SO3 dissolved either in poly(2-ethyl-2-oxazoline) or poly(N-vinylpyrrolidone) for the separation of olefin/paraffin mixtures [12,13]. Although these membranes did not contain any kind of plasticizers, both olefin permeance and its selecti-
0376-7388/01/$ – see front matter © 2001 Published by Elsevier Science B.V. PII: S 0 3 7 6 - 7 3 8 8 ( 0 0 ) 0 0 6 2 8 - 1
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vity over paraffin were very high on the operation with a dry feed stream. In polymer electrolyte membranes, silver salts are dissolved in polymer solvents to make solid solution and consequently to produce free silver cations, which are a carrier for olefin [10,12,16]. This implies that polymer solvents in polymer electrolyte membranes can act as a replacement of water in liquid membranes. Therefore, olefin facilitation occurs without water in the polymer electrolyte membranes. However, polymer electrolyte membranes are extremely hygroscopic and their properties may be affected by water content. Therefore, in this study, the effect of water on the facilitated transport of olefin is investigated to verify that these membranes are effective even in the absence of water.
2. Experimental 2.1. Sample preparation Poly(2-ethyl-2-oxazoline) (POZ) (molecular weight = 500, 000 kg/mole), and silver tetrafluoroborate (AgBF4 ) (98%) were purchased from Aldrich Chemical Co. (Milwaukee, WI) and used without further purification. An appropriate amount of the silver salt was dissolved in the 20 wt.% POZ solution in water and stirred for several hours at room temperature. The mole ratio of a carbonyl oxygen to a silver ion in the solution was 1:1. The solution was then coated onto a microporous membrane support (from SAEHAN Industries, Korea) to make composite membranes using a RK Control Coater® . The membranes were first dried overnight at 40◦ C in a light-protected convection oven under nitrogen environment and subsequently in a vacuum oven at room temperature for 72 h. The thickness of the polymer electrolyte top layer was about 1 m. 2.2. Gas permeation experiments The permeation properties of the composite membranes were investigated at 23◦ C with a propylene/propane (50/50 by volume) mixed gas. The feed pressures for stability test and humidity experiment were 276 and 138 kPa (gauge pressure), respectively, while a permeate pressure was atmospheric. Volumetric gas flow rates were measured with a soap-bubble
Fig. 1. A schematic diagram of gas permeation apparatus.
flowmeter. The compositions of permeates were analyzed by using a HP 6890 gas chromatography (Wilmington, DE) equipped with a thermal conductivity detector (TCD). A schematic diagram of gas permeation apparatus is shown in Fig. 1. By changing the ratio of flow rates of dry feed gas (1) and water-saturated feed gas (2), relative humidity (RH) of the feed gas was controlled. The total feed flow rate was fixed to 8.5 cm3 /min. Relative humidity was measured with a digital thermohygrometer (HM 141 indicator and HMP 46 probe from VAISALA, Finland).
3. Results and discussion A stability test was first carried out using the dry feed gas, for the POZ/AgBF4 membrane with [OZ]:[Ag] = 1:1 mole ratio, at 23◦ C and 1p = 276 kPa. The membrane was mounted in a permeation cell shortly after taken out from the vacuum oven. A plot of total permeance versus time is shown in Fig. 2. As shown in Fig. 2, about 12–15 h have passed before reaching a steady state and the total permeance of mixed gas at the steady state was 11.3 GPU (1 GPU = 1 × 10−6 cm3 (STP)/cm2 s cmHg). The stage cut, the ratio of permeate to feed flow rates, was 0.05. The permeance of each component Qi , was also calculated using the following equation: Qi =
yi J pf xi − pp yi
(1)
S.U. Hong et al. / Journal of Membrane Science 181 (2001) 289–293
291
Fig. 2. Total permeance of propylene/propane mixed gases as a function of permeation time for the POZ/AgBF4 system with [OZ]:[Ag] = 1:1 mole ratio at 23◦ C and 1p = 272 kPa. A solid line was drawn to guide the eye.
where xi and yi are the mole fractions of component i in the feed and permeate streams, respectively, J the total permeate flux (cm3 /cm2 /s), and pf and pp the pressures (cmHg) on the feed and the permeate sides of the membrane, respectively. The calculated permeance values were 34.18 and 0.34 GPU for propylene and propane, respectively, and the ideal separation factor α ij (=Qi /Qj ) was 100.52. Recently, Yamaguchi et al. [7] made a Nafion/AgBF4 blend membrane containing 1 wt.% glycerin as a plasticizer and also performed the stability test using dry feed and permeate streams. The membrane showed initially olefin selectivity over paraffin, but the olefin permeance dramatically decreased with time and reached the same order as the paraffin permeance after 100 min. The membrane recovered the facilitation effect for olefin after adding some amount of water to the feed compartment. To stabilize the olefin flux, the feed stream had to have at least 20% relative humidity. The results implied that the membrane lost liquid media with time due to evaporation and hydration played an important role in olefin transport. They proposed that olefin–carrier reaction in their membrane was more likely a gas–liquid reaction rather than a gas–solid reaction. On the contrary, although the membrane prepared in this study did not contain any kind of plasticizer,
it still showed very high olefin selectivity over paraffin on the operation with a dry feed gas even at long time and remained stable. The results may imply that the membrane prepared in this study is effective on the separation of propylene/propane mixture without the aid of water. To see the effect of water on the separation of propylene/paraffin mixtures more clearly, by changing the relative humidity (RH) of the feed gas from 0 to 40%, the permeation experiments were carried out. Fig. 3 shows selectivity and permeance of each component as a function of relative humidity (RH) at 23◦ C and 1p = 138 kPa. The stage cut was 0.03. For the point at RH = 0%, a value was obtained after reaching the steady state using only dry feed gas. Then, by changing the ratio of flow rates of dry feed gas (1) to water-saturated feed gas (2) in Fig. 1, the RH value was controlled. About four hours have passed before getting the steady state at each step. Up to RH = 5%, permeances are approximately constant at 87 and 0.3 GPU for propylene and propane, respectively. When RH is greater than 10%, however, the permeances of both components increase gradually, which resulting from the overall increase of both the facilitated transport of propylene and the Fickian diffusion of propylene and propane owing to the plasticization of the membrane by water. As a result, the permeances reach 252 and 1 GPU for propylene and
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Fig. 3. Selectivity of propylene over propane and permeances of propylene and propane as a function of relative humidity for the POZ/AgBF4 system with [OZ]:[Ag] = 1:1 mole ratio at 23◦ C and 1p = 138 kPa.
propane, respectively, at RH = 40%. However, the selectivity decreases from 290 to 252. This phenomenon may be from the increased portion of the Fickian diffusion with increasing water content of the membrane. A water sorption experimental result indicated that the water content in the POZ/AgBF4 (1:1) membrane at 25◦ C and RH = 25% was about 9.5 wt.%. Ho and Dalrymple [8] performed a similar experiment using a poly(vinyl alcohol) membrane containing silver nitrate (AgNO3 ). A dry membrane was first installed in the permeation cell. The feed and sweep nitrogen gas streams were saturated with water vapor before entering the permeation cell. Upon exposure to the water-saturated gas streams, olefin permeance increased very rapidly initially with time, then the degree of increase was lessened and reached the steady state finally. In other words, the olefin permeance increased by increasing the water content in the membrane until it was equilibrated with the water vapor, i.e. saturated with water. The saturated water content in the swollen membrane was about 38 wt.%. Our finding is different from their results which showed no facilitation effect of olefin in the absence of water.
4. Conclusions The results indicate that the membrane prepared in this study shows facilitation effect of olefin without
the aid of water and is insensitive to the humidity of the feed stream at low RH values. When the relative humidity (RH) is higher than 10%, the permeances of both propylene and propane increase gradually owing to the plasticization of the membrane by water, which resulting in the slight decrease of propylene selectivity over propane.
Acknowledgements The authors gratefully acknowledge financial support from the Ministry of Science and Technology of Korea through the Creative Research Initiatives Program. References [1] R.B. Eldridge, Olefin/paraffin separation technology: a review, Ind. Eng. Chem. Res. 32 (1993) 2208. [2] O.H. LeBlanc, W.J. Ward, S.L. Matson, S.G. Kimura, Facilitated transport in ion-exchange membranes, J. Membr. Sci. 6 (1980) 339. [3] M. Teramoto, H. Matsuyama, T. Yamashiro, Y. Katayama, Separation of ethylene from ethane by supported liquid membranes containing silver nitrate as a carrier, J. Chem. Eng. Jpn. 19 (1986) 419. [4] M. Teramoto, H. Matsuyama, T. Yamashiro, S. Okamoto, Separation of ethylene from ethane by a flowing liquid membrane using silver nitrate as a carrier, J. Membr. Sci. 45 (1989) 115.
S.U. Hong et al. / Journal of Membrane Science 181 (2001) 289–293 [5] C.A. Koval, T. Spontelli, Condensed phase facilitated transport of olefins through an ion-exchange membrane, J. Am. Chem. Soc. 110 (1988) 293. [6] O.I. Eriksen, E. Aksnes, I.M. Dahl, Facilitated transport of ethene through nafion membranes. Part I. Water swollen membranes, J. Membr. Sci. 85 (1993) 89. [7] T. Yamaguchi, C. Baertsch, C.A. Koval, R.D. Noble, C.N. Bowman, Olefin separation using silver impregnated ionexchange membranes and silver/polymer blend membranes, J. Membr. Sci. 117 (1996) 151. [8] W.S. Ho, D.C. Dalrymple, Facilitated transport of olefins in Ag+ -containing polymer membranes, J. Membr. Sci. 91 (1994) 13. [9] A.J. van Zyl, J.A. Kerres, W. Cui, M. Junginger, Application of new sulfonated ionomer membranes in the separation of pentene and pentane by facilitated transport, J. Membr. Sci. 137 (1997) 173. [10] S. Sunderrajan, B.D. Freeman, I. Pinnau, Sorption and spectroscopic analysis of silver–olefin interaction in polymer electrolytes, Polym. Mater. Sci. Eng. 77 (2) (1997) 267.
293
[11] I. Pinnau, L.G. Toy, S. Sunderrajan, B.D. Freeman, Solid electrolyte membranes for olefin/paraffin separation, Polym. Mater. Sci. Eng. 77 (2) (1997) 269. [12] S.U. Hong, J.H. Jin, J. Won, Y.S. Kang, Solid polymer electrolytes containing silver ions and their application to facilitated transport membranes, Adv. Mater. 12 (2000) 968. [13] Y.S. Yoon, J. Won, Y.S. Kang, Polymer electrolyte membranes containing silver ion for facilitated olefin transport, Macromolecules 33 (2000) 3185. [14] H.S. Kim, J.H. Ryu, H. Kim, B.S. Ahn, Y.S. Kang, Reversible olefin complexation by silver ions in dry poly(vinylmethylketone) membrane and its application to olefin/paraffin separations, Chem. Commun. (2000) 1261. [15] Y.H. Kim, J.H. Ryu, J.Y. Bae, Y.S. Kang, H.S. Kim, Reactive polymer membranes containing cuprous complexes in olefin/paraffin separation, Chem. Commun. (2000) 195. [16] J. Jin, S.U. Hong, J. Won, Y.S. Kang, Spectroscopic studies for molecular structure and complexation of silver polymer electrolytes, Macromolecules 33 (2000) 4932.
Short communication
Effect of water on the facilitated transport of olefins through solid polymer electrolyte membranes Seong Uk Hong, Jung Yong Kim, Yong Soo Kang∗ Center for Facilitated Transport Membranes, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, South Korea Received 24 February 2000; received in revised form 25 September 2000; accepted 27 October 2000
Abstract Polymer electrolyte membranes composed of poly(2-ethyl-2-oxazoline) (POZ) and AgBF4 are prepared for olefin/paraffin separations. The stability and effect of relative humidity on permeance and selectivity are investigated using propylene/propane mixed gases. The selectivity of propylene over propane remains high on the long time operation with a dry feed gas, indicating that membranes are effective for propylene/propane separation in the absence of water. As humidity of the feed gas increases, both propylene and propane permeances increase, which resulting in the slight decrease of selectivity. © 2001 Published by Elsevier Science B.V. Keywords: Facilitated transport; Relative humidity; Solid polymer electrolyte; Olefin/paraffin separation
1. Introduction Olefin/paraffin separation is one of the most important processes in petrochemical industries and is currently carried out by the energy intensive cryogenic distillation process. According to the recent report by DOE, 0.12 Quads of energy (1 Quad = 1015 BTU) is used yearly for olefin/paraffin distillation [1]. This large energy and capital investment requirement provides the incentive for olefin/paraffin separation research. The membrane process using the concept of facilitated transport has been considered to be an energy-saving process. In the facilitated transport ∗ Corresponding author. Tel.: +82-2-958-5362; fax: +82-2-958-6869. E-mail address: [email protected] (Y.S. Kang).
(FT) membranes, carrier-mediated transport occurs, in addition to a normal Fickian transport, due to the reversible reaction of carrier with a specific solute, and separation efficiency can be improved remarkably. Therefore, a substantial body of studies has been performed to separate olefin/paraffin mixtures using the concept of facilitated transport in liquid [2–9] as well as solid membranes containing silver [10–14] or copper cation [15]. Because evaporation of liquid media in liquid membranes gives a serious drawback and problems for practical applications, the development of solid FT membranes is demanding. Recently, we have reported solid FT membranes containing AgBF4 or AgCF3 SO3 dissolved either in poly(2-ethyl-2-oxazoline) or poly(N-vinylpyrrolidone) for the separation of olefin/paraffin mixtures [12,13]. Although these membranes did not contain any kind of plasticizers, both olefin permeance and its selecti-
0376-7388/01/$ – see front matter © 2001 Published by Elsevier Science B.V. PII: S 0 3 7 6 - 7 3 8 8 ( 0 0 ) 0 0 6 2 8 - 1
290
S.U. Hong et al. / Journal of Membrane Science 181 (2001) 289–293
vity over paraffin were very high on the operation with a dry feed stream. In polymer electrolyte membranes, silver salts are dissolved in polymer solvents to make solid solution and consequently to produce free silver cations, which are a carrier for olefin [10,12,16]. This implies that polymer solvents in polymer electrolyte membranes can act as a replacement of water in liquid membranes. Therefore, olefin facilitation occurs without water in the polymer electrolyte membranes. However, polymer electrolyte membranes are extremely hygroscopic and their properties may be affected by water content. Therefore, in this study, the effect of water on the facilitated transport of olefin is investigated to verify that these membranes are effective even in the absence of water.
2. Experimental 2.1. Sample preparation Poly(2-ethyl-2-oxazoline) (POZ) (molecular weight = 500, 000 kg/mole), and silver tetrafluoroborate (AgBF4 ) (98%) were purchased from Aldrich Chemical Co. (Milwaukee, WI) and used without further purification. An appropriate amount of the silver salt was dissolved in the 20 wt.% POZ solution in water and stirred for several hours at room temperature. The mole ratio of a carbonyl oxygen to a silver ion in the solution was 1:1. The solution was then coated onto a microporous membrane support (from SAEHAN Industries, Korea) to make composite membranes using a RK Control Coater® . The membranes were first dried overnight at 40◦ C in a light-protected convection oven under nitrogen environment and subsequently in a vacuum oven at room temperature for 72 h. The thickness of the polymer electrolyte top layer was about 1 m. 2.2. Gas permeation experiments The permeation properties of the composite membranes were investigated at 23◦ C with a propylene/propane (50/50 by volume) mixed gas. The feed pressures for stability test and humidity experiment were 276 and 138 kPa (gauge pressure), respectively, while a permeate pressure was atmospheric. Volumetric gas flow rates were measured with a soap-bubble
Fig. 1. A schematic diagram of gas permeation apparatus.
flowmeter. The compositions of permeates were analyzed by using a HP 6890 gas chromatography (Wilmington, DE) equipped with a thermal conductivity detector (TCD). A schematic diagram of gas permeation apparatus is shown in Fig. 1. By changing the ratio of flow rates of dry feed gas (1) and water-saturated feed gas (2), relative humidity (RH) of the feed gas was controlled. The total feed flow rate was fixed to 8.5 cm3 /min. Relative humidity was measured with a digital thermohygrometer (HM 141 indicator and HMP 46 probe from VAISALA, Finland).
3. Results and discussion A stability test was first carried out using the dry feed gas, for the POZ/AgBF4 membrane with [OZ]:[Ag] = 1:1 mole ratio, at 23◦ C and 1p = 276 kPa. The membrane was mounted in a permeation cell shortly after taken out from the vacuum oven. A plot of total permeance versus time is shown in Fig. 2. As shown in Fig. 2, about 12–15 h have passed before reaching a steady state and the total permeance of mixed gas at the steady state was 11.3 GPU (1 GPU = 1 × 10−6 cm3 (STP)/cm2 s cmHg). The stage cut, the ratio of permeate to feed flow rates, was 0.05. The permeance of each component Qi , was also calculated using the following equation: Qi =
yi J pf xi − pp yi
(1)
S.U. Hong et al. / Journal of Membrane Science 181 (2001) 289–293
291
Fig. 2. Total permeance of propylene/propane mixed gases as a function of permeation time for the POZ/AgBF4 system with [OZ]:[Ag] = 1:1 mole ratio at 23◦ C and 1p = 272 kPa. A solid line was drawn to guide the eye.
where xi and yi are the mole fractions of component i in the feed and permeate streams, respectively, J the total permeate flux (cm3 /cm2 /s), and pf and pp the pressures (cmHg) on the feed and the permeate sides of the membrane, respectively. The calculated permeance values were 34.18 and 0.34 GPU for propylene and propane, respectively, and the ideal separation factor α ij (=Qi /Qj ) was 100.52. Recently, Yamaguchi et al. [7] made a Nafion/AgBF4 blend membrane containing 1 wt.% glycerin as a plasticizer and also performed the stability test using dry feed and permeate streams. The membrane showed initially olefin selectivity over paraffin, but the olefin permeance dramatically decreased with time and reached the same order as the paraffin permeance after 100 min. The membrane recovered the facilitation effect for olefin after adding some amount of water to the feed compartment. To stabilize the olefin flux, the feed stream had to have at least 20% relative humidity. The results implied that the membrane lost liquid media with time due to evaporation and hydration played an important role in olefin transport. They proposed that olefin–carrier reaction in their membrane was more likely a gas–liquid reaction rather than a gas–solid reaction. On the contrary, although the membrane prepared in this study did not contain any kind of plasticizer,
it still showed very high olefin selectivity over paraffin on the operation with a dry feed gas even at long time and remained stable. The results may imply that the membrane prepared in this study is effective on the separation of propylene/propane mixture without the aid of water. To see the effect of water on the separation of propylene/paraffin mixtures more clearly, by changing the relative humidity (RH) of the feed gas from 0 to 40%, the permeation experiments were carried out. Fig. 3 shows selectivity and permeance of each component as a function of relative humidity (RH) at 23◦ C and 1p = 138 kPa. The stage cut was 0.03. For the point at RH = 0%, a value was obtained after reaching the steady state using only dry feed gas. Then, by changing the ratio of flow rates of dry feed gas (1) to water-saturated feed gas (2) in Fig. 1, the RH value was controlled. About four hours have passed before getting the steady state at each step. Up to RH = 5%, permeances are approximately constant at 87 and 0.3 GPU for propylene and propane, respectively. When RH is greater than 10%, however, the permeances of both components increase gradually, which resulting from the overall increase of both the facilitated transport of propylene and the Fickian diffusion of propylene and propane owing to the plasticization of the membrane by water. As a result, the permeances reach 252 and 1 GPU for propylene and
292
S.U. Hong et al. / Journal of Membrane Science 181 (2001) 289–293
Fig. 3. Selectivity of propylene over propane and permeances of propylene and propane as a function of relative humidity for the POZ/AgBF4 system with [OZ]:[Ag] = 1:1 mole ratio at 23◦ C and 1p = 138 kPa.
propane, respectively, at RH = 40%. However, the selectivity decreases from 290 to 252. This phenomenon may be from the increased portion of the Fickian diffusion with increasing water content of the membrane. A water sorption experimental result indicated that the water content in the POZ/AgBF4 (1:1) membrane at 25◦ C and RH = 25% was about 9.5 wt.%. Ho and Dalrymple [8] performed a similar experiment using a poly(vinyl alcohol) membrane containing silver nitrate (AgNO3 ). A dry membrane was first installed in the permeation cell. The feed and sweep nitrogen gas streams were saturated with water vapor before entering the permeation cell. Upon exposure to the water-saturated gas streams, olefin permeance increased very rapidly initially with time, then the degree of increase was lessened and reached the steady state finally. In other words, the olefin permeance increased by increasing the water content in the membrane until it was equilibrated with the water vapor, i.e. saturated with water. The saturated water content in the swollen membrane was about 38 wt.%. Our finding is different from their results which showed no facilitation effect of olefin in the absence of water.
4. Conclusions The results indicate that the membrane prepared in this study shows facilitation effect of olefin without
the aid of water and is insensitive to the humidity of the feed stream at low RH values. When the relative humidity (RH) is higher than 10%, the permeances of both propylene and propane increase gradually owing to the plasticization of the membrane by water, which resulting in the slight decrease of propylene selectivity over propane.
Acknowledgements The authors gratefully acknowledge financial support from the Ministry of Science and Technology of Korea through the Creative Research Initiatives Program. References [1] R.B. Eldridge, Olefin/paraffin separation technology: a review, Ind. Eng. Chem. Res. 32 (1993) 2208. [2] O.H. LeBlanc, W.J. Ward, S.L. Matson, S.G. Kimura, Facilitated transport in ion-exchange membranes, J. Membr. Sci. 6 (1980) 339. [3] M. Teramoto, H. Matsuyama, T. Yamashiro, Y. Katayama, Separation of ethylene from ethane by supported liquid membranes containing silver nitrate as a carrier, J. Chem. Eng. Jpn. 19 (1986) 419. [4] M. Teramoto, H. Matsuyama, T. Yamashiro, S. Okamoto, Separation of ethylene from ethane by a flowing liquid membrane using silver nitrate as a carrier, J. Membr. Sci. 45 (1989) 115.
S.U. Hong et al. / Journal of Membrane Science 181 (2001) 289–293 [5] C.A. Koval, T. Spontelli, Condensed phase facilitated transport of olefins through an ion-exchange membrane, J. Am. Chem. Soc. 110 (1988) 293. [6] O.I. Eriksen, E. Aksnes, I.M. Dahl, Facilitated transport of ethene through nafion membranes. Part I. Water swollen membranes, J. Membr. Sci. 85 (1993) 89. [7] T. Yamaguchi, C. Baertsch, C.A. Koval, R.D. Noble, C.N. Bowman, Olefin separation using silver impregnated ionexchange membranes and silver/polymer blend membranes, J. Membr. Sci. 117 (1996) 151. [8] W.S. Ho, D.C. Dalrymple, Facilitated transport of olefins in Ag+ -containing polymer membranes, J. Membr. Sci. 91 (1994) 13. [9] A.J. van Zyl, J.A. Kerres, W. Cui, M. Junginger, Application of new sulfonated ionomer membranes in the separation of pentene and pentane by facilitated transport, J. Membr. Sci. 137 (1997) 173. [10] S. Sunderrajan, B.D. Freeman, I. Pinnau, Sorption and spectroscopic analysis of silver–olefin interaction in polymer electrolytes, Polym. Mater. Sci. Eng. 77 (2) (1997) 267.
293
[11] I. Pinnau, L.G. Toy, S. Sunderrajan, B.D. Freeman, Solid electrolyte membranes for olefin/paraffin separation, Polym. Mater. Sci. Eng. 77 (2) (1997) 269. [12] S.U. Hong, J.H. Jin, J. Won, Y.S. Kang, Solid polymer electrolytes containing silver ions and their application to facilitated transport membranes, Adv. Mater. 12 (2000) 968. [13] Y.S. Yoon, J. Won, Y.S. Kang, Polymer electrolyte membranes containing silver ion for facilitated olefin transport, Macromolecules 33 (2000) 3185. [14] H.S. Kim, J.H. Ryu, H. Kim, B.S. Ahn, Y.S. Kang, Reversible olefin complexation by silver ions in dry poly(vinylmethylketone) membrane and its application to olefin/paraffin separations, Chem. Commun. (2000) 1261. [15] Y.H. Kim, J.H. Ryu, J.Y. Bae, Y.S. Kang, H.S. Kim, Reactive polymer membranes containing cuprous complexes in olefin/paraffin separation, Chem. Commun. (2000) 195. [16] J. Jin, S.U. Hong, J. Won, Y.S. Kang, Spectroscopic studies for molecular structure and complexation of silver polymer electrolytes, Macromolecules 33 (2000) 4932.