Novel Nanostructured Polymer-Inorganic Hybrid Membranes for Vapor

Chapter 15

Novel Nanostructured Polymer-Inorganic Hybrid Membranes for Vapor-Gas Separation Downloaded by PENNSYLVANIA STATE UNIV on September 12, 2012 | http://pubs.acs.org Publication Date: April 20, 2004 | doi: 10.1021/bk-2004-0876.ch015

Zhenjie He, Ingo Pinnau, and Atsushi Morisato Membrane Technology and Research, Inc., 1360 Willow Road, Suite 103, Menlo Park C A 94025

N o v e l polymer/inorganic hybrid membranes exhibit extraordinary gas separation properties for vapor/gas separation applications. In contrast to conventional polymer/filler systems, the incorporation of nano-sized, nonporous inorganic fillers in rigid, high-free-volume, glassy polymers simultaneously increased vapor permeability and vapor/gas selectivity significantly. For example, a hybrid membrane of poly(4methyl-2-pentyne) [PMP] containing 22 vol% TS-530 fumed silica had a mixed-gas n-butane permeability of 25,000 Barrer, four times higher than that of pure P M P . In addition, the nbutane/methane selectivity increased from 13forpure P M P to 21 for the silica-filled P M P membrane. The enhanced gas separation properties of polymer/filler hybrid membranes result from an increase of the free volume in the polymer matrix due to disruption of polymer chain packing induced by the filler. The general applicability of this approach was demonstrated with other nano-sized inorganic filler/polymer hybrid systems, such as PMP/carbon black and Teflon A F 2400/fumed silica.

218

© 2004 American Chemical Society

In Advanced Materials for Membrane Separations; Pinnau, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2004.

219 During the past 20 years, most membrane-based gas separation applications have involved the separation of permanent gases, such as nitrogen from air; carbon dioxide from methane; and hydrogen from nitrogen, argon, or methane. However, a significant potential market lies in separating mixtures containing condensable gases. The separation of organic monomers from nitrogen, C hydrocarbons from methane, and C hydrocarbons from hydrogen are all processes of considerable industrial importance. For example, approximately 1% of the 30 billion lb/year of monomer used in polyethylene and polypropylene production is lost in the nitrogen vent streams from resin purge operations (/). Recovery of these monomers would save U . S. producers about $ 100 million/year. Similarly, in the production of natural gas, raw gas must often be treated to separate propane and higher hydrocarbons from the methane to bring the heating value and dew point to pipeline specification, and to recover the valuable higher hydrocarbons as chemical feedstock. Finally, most refineries produce off-gas streams that contain 20-30% hydrogen and 70-80% hydrocarbons. Currently, these streams are used as fuel or simply flared. It has been estimated that about 800 MMscfd of hydrogen in off-gas streams, with a potential value of $300 million, are lost annually in refineries in the United States (2). Poly(l-trimethylsilyl-1-propyne) [PTMSP], a glassy, high-free-volume acetylene-based polymer, exhibits both the highest C hydrocarbon/methane and C + hydrocarbon/hydrogen selectivity and the highest C hydrocarbon permeability of any known polymer (3,4). However, a major disadvantage of P T M S P as a membrane material for organic-vapor/permanent-gas separation applications is its very limited solvent resistance. PTMSP is soluble in essentially all liquid hydrocarbons, which prohibits its use in most industrial applications. A n alternative acetylene-based polymer, poly(4-methyl-2-pentyne) [PMP] is stable against condensed hydrocarbon vapors, but its organic-vapor/permanent-gas selectivities and permeabilities are lower than those of PTMSP (5,6). In this study, the gas permeation properties of P M P films containing nonporous, nano-sized, fumed silica fillers were evaluated. Incorporation of these ultrafine, dense fillers in the glassy polymer matrix leads to an unexpected increase in permeability as well as vapor/gas selectivity (7,8). 2 +

Downloaded by PENNSYLVANIA STATE UNIV on September 12, 2012 | http://pubs.acs.org Publication Date: April 20, 2004 | doi: 10.1021/bk-2004-0876.ch015

2 +

2+

2

2 +

Background Gas and vapor permeation through nonporous polymer membranes is usually rationalized by the solution/diffusion model. This model assumes that the gas phases on either side of the membrane are in thermodynamic equilibrium with their respective interfaces, and that the interfacial sorption process is rapid compared with the rate of diffusion through the membrane. Thus, the rate-limiting step is diffusion through the polymer membrane, which is governed by Fick's law of diffusion. In simple cases, Fick's law leads to the equation: a)


220 3

2

where J is the volumetric gas flux (cm (STP)/cm s), D is the diffusion coefficient of the gas or vapor in the membrane (cm /s), / is the membrane thickness (cm), S is the solubility coefficient (cm (STP)/cm cmHg), and Ap is the pressure difference across the membrane (cmHg). The gas permeability, P, is usually expressed in Barrers (1 Barrer = 1 x 10" cm (STP)cm/cm scmHg), and is given by: 2

3

3

10

3

2


P= DxS

(2)

For a given membrane material and two gases, A and B , the ideal selectivity, a is defined as the ratio of the permeability coefficients of the gases:

A/B

The membrane selectivity is the product o f two terms, the ratio of the permeant diffusion coefficients and the ratio of die permeant solubility coefficients. The ratio of diffusion coefficients (D /D ) is referred to as the diffusivity selectivity, reflects the ability of the polymer to differentiate molecules of different sizes. The solubility selectivity, (S/S ), is the ratio of the solubility coefficients of the gases, reflecting the relative condensibilities of the gases. Solubility coefficients typically increase with molecular size, because large molecules are normally more condensable, and hence more soluble in polymers than small molecules. The balance between the diffusivity selectivity and the solubility selectivity determines whether a membrane material is permanent-gas-selective or organic-vaporselective. For conventional glassy polymers, a tradeoff relationship exists between the gas selectivity and permeability, that is, die higher the selectivity, the lower the gas permeability and vice versa (9). Conventional glassy polymers are permanentgas/organic-vapor selective, because the diffusivity selectivity is much larger than the solubility selectivity. On the other hand, rubbery materials, such as polydimethylsiloxane [PDMS], and rigid, high-free-volume, glassy P T M S P and P M P are more permeable to large organic vapors. In the separation of organic vapors from permanent gases, this permeability/selectivity tradeoff relationship does not exist (/ 0). A n example of this behavior, the relationship between n-butane permeability and w-butane/methane selectivity for several polyacetylenes and P D M S , is shown in Figure 1. In this case, polymers having higher n-butane permeability also exhibit higher n-butane/methane selectivity. This behavior is typically for any membrane process that involves the separation of large, organic vapors from small, permanent gases in which the larger penetrant is the more permeable mixture component. Because the diffusion coefficient of the large molecule will always be lower than that of the smaller penetrant, the diffusivity selectivity, D /D will always be less than one. Therefore, advanced polymers with improved selectivity for organic-vapor/permanent-gas separation should have A

B

B

vapo

gasf



221 a diffusivity selectivity as close to one as possible. For rubbery polymers this can be achieved by increasing the chain mobility, whereas glassy polymers must have high free volume coupled with large inter- and intrachain spacing. PTMSP, a highfree-volume, glassy polymer exhibits the highest gas permeability and highest nbutane/methane and w-butane/hydrogen selectivities of any known polymer. These properties derive directly from its high free volume, interconnectivity of free volume elements, and large interchain spacing. However, PTMSP has very limited solvent resistance in hydrocarbon environments. A n alternative, high-free-volume, glassy polymer, P M P , has much better solvent resistance than PTMSP, but its organic-vapor/permanent-gas selectivity and organic vapor permeability are lower than those of PTMSP. In this work, we investigated the possibility of enhancing the gas separation performance of high-free-volume P M P and Teflon AF2400 (Du Pont, Wilmington, DE) by incorporating nano-sized filler particles, such as fumed silica or carbon black, into the polymer matrix.

100

PTMSP *

1 0

5 £ O

PTPSDPA

r

•>

PMJ>J *DMS

1

0> w

e

: *P-2H

0.1 10

100

n-C H 4

1,000 1 0

10,000

100,000

permeability (Barrer)

Figure 1.Mixed-gas n-butane/methane selectivity as a function of n-butane permeability. PMP: poly(4-methyl-2-pentyne); PTMSP: poly (1-trimethylsilyl-1propyne); PDMS: polydimethylsiloxane; PTPSDPA: polyfl-phenyl-2-[ptriisopropylsilyl)phenyl]acetylene); P-2H: poly(2-hexyne).Feed: 2 vol% nC H /98 vol% CH ;feedpressure: 150 psig; permeate pressure: 0 psig; temperature: 25°C 4

J(

4


222 Experimental Polymer Synthesis Poly(4-methyl-2-pentyne) [PMP] was synthesized following the procedure of Pinnau and Morisato ( i i ) . The monomer, 4-methyl-2-pentyne, was purchased from Lancaster (Windham, NH). The monomer was dried over calcium hydride for 24 hours. The catalysts, niobium pentachloride (NbCl ) and triphenyl bismuth (Ph Bi) were purchased from Aldrich Chemicals and used without further purification. A solution of 1.32 g of N b C l and 2.14 g P h B i in 188 ml cydohexane was stirred at 80°C for 10 minutes under dry nitrogen. Thereafter, a monomer solution of 20 g 4-methyl-2-pentyne in 28 ml cydohexane was added dropwise to the catalyst solution, and the mixture was reacted for 4 hours at 80°C. The viscosity of the solution increased very rapidly. The highly viscous polymer solution was poured into a large amount of methanol, filtered to recover the polymer, and dried under vacuum. The polymer was dissolved in cydohexane and reprecipitated twice from methanol to remove excess monomer, oligomers, and catalysts. The yield was 87%. s


3

5

3

Polymer F i l m Preparation Isotropic, dense films of P M P were prepared by casting from a cydohexane solution (2 wt% polymer) onto a glass plate. The films were dried at ambient conditions for 24 hours and then under vacuum at 80°C for three days. To ensure that the films were completely solvent-free, the films were removed from the oven and periodically weighed on an analytical balance. The thicknesses of the films were determined with a precision micrometer. Film samples with thicknesses of 20 to 50 pm were used for die permeation measurements. Several different silica types (CAB-O-SIL, Cabot Corp., Tuscola, IL) were used in this study; the properties of these materials are listed in Table I. The L-90, M-5 and EH-5 Aimed silica which have an - O H surface group, are hydrophilic. The TS-530 type fumed silica is modified with a - S i ( C H ) surface group and is hydrophobic. A s well as differences in the surface group chemistry, the various fumed silica types have different particle diameters. The size of the silica particles is an important parameter in the functionality of polymer/filler hybrid membranes, as shown later. Silica-filled P M P films were made by dispersing 10-45 wt% (based on polymer) ultrafine fumed silica particles in the P M P solution. The dispersion was mixed in a high-speed blender for 10 minutes and then cast immediately onto a glass plate. The silica-filled P M P membranes were dried as described above. The film thicknesses of the silica-filled P M P membranes were about 50 to 200 pm. 3

3


223


Carbon black-filled P M P films were made by die same method as the silica-filled P M P films. Another high-free-volume glassy polymer Teflon A F 2400, a copolymer containing 87 mol% 2,2-bistrifluoromethyl-4,5-difluoro-l,3-dioxole and 13 mol% tetrafluoroethylene, obtained from D u Pont (Wilmington, DE), was also blended with fumed silica to form nanostructured hybrid membranes. Table I. Physical properties of filler types used to prepare nanostructured P M P and Teflon A F 2400 membranes _ _ _ _ _ _ _ Particle Size Filler Type Surface Area Surface Groups (nm) (m /g) L-90 30 90 -OH 14 M-5 -OH 200 7 EH-5 -OH 380 TS-530 13 -Si(CH ) 210 12 Carbon black 1500 2

3

3

Pure-Gas Permeation Measurements The pure-gas permeation properties of the blend membranes were measured at 25°C with nitrogen, oxygen, methane, hydrogen, and carbon dioxide at a feed pressure of 50 psig and atmospheric permeate pressure (0 psig). The experiments were performed using the constant pressure/variable volume method. For comparison, a pure, unfilled P M P film was tested under the same conditions.

Mixed-Gas Permeation Measurements The mixed-gas permeation properties of pure polymer and polymer/filler hybrid films were determined with a gas mixture comprising 2 vol% w-butane/98 vol% methane. The experiments were also performed with the constant pressure/variable volume method. The feed pressure in all experiments was 150 psig; the permeate pressure was atmospheric (0 psig). The compositions of feed, residue, and permeate were determined with a gas chromatograph equipped with a thermal conductivity detector. The stage-cut, that is, the permeate to feed flow rate was always less than 1%. Under these conditions, the residue composition was essentially equal to the feed composition, and concentration polarization effects were negligible. P M P and silica-filled P M P films were also tested with a 50 vol% propane/50 vol% hydrogen mixture.


224

Results and Discussion


Effect of Filler on Pure-Gas Permeation Properties of PMP/Silica Hybrid Membranes Nonporous fillers usually function as barriers to gas transport in polymers. The obstructive behavior of nonporous fillers to gas transport in polymers has been used to increase the barrier properties of polymers in packaging applications (12,13). Adding impermeable fillers to conventional polymers leads to a reduction in gas permeability by reducing the fraction of the membrane through which diffusion can occur and by increasing the average diffusion path length required for a gas to permeate the membrane (14-16). The reduction in gas permeability by addition of nonporous, impermeable fillers can be predicted by the well-known Maxwell model (14). This model predicts that for membranes containing dispersed, impermeable, spherical fillers, the permeability of the membrane, P , can be expressed as: b

f

2-2f

2+ + J

(4)

where P is the permeability of the pure polymer and 4> is the volume fraction of the filler. The Maxwell model predicts that the permeability of the polymer/filler hybrid membrane decreases by increasing the filler content. Filled P M P membranes were prepared using a surface-modified, hydrophobic silica type, TS-530, with silica contents of 5.7,10,19,22, and 25 vol%. Figure 2 shows die pure-gas nitrogen permeability of P M P and TS-530 filled P M P as a function of the filler content. The prediction by the Maxwell model for the permeability of the hybrid system is also shown for comparison. The data in Figure 2 show surprisingly that the nitrogen permeability of the silica-filled P M P film increases significantly as the filler content increases. The nitrogen permeability of P M P with 25 v o l % TS-530 is three times that of pure P M P . Contrary to this unexpected increase, the calculated permeability of 25 v o l % TS530 filled P M P , using equation 4, is only 67% of that of pure P M P . This unusual increase in gas permeability is in singular contrast to the behavior of conventional polymer/filler hybrid membranes (14-16). The permeabilities of silica-filled P M P for oxygen, methane, hydrogen, and carbon dioxide as a function of filler content are shown in Figure 3. The data show the same trend for all gases tested, that is, the gas permeabilities increase dramatically by increasing the filler content in the hybrid P M P membranes. The decrease in gas permeability in conventional polymer/nonporous filler systems is due to a decrease in the fraction of membrane through which permeation c


225


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10

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30

Silica in Poly(4-methyl-2-pentyne) (vol%) Figure 2. Pure-gas nitrogen permeability offilled PMP films as a function of nano-sizedfiller content. Feed pressure: 50 psig; permeate pressure: 0 psig; temperature: 25°C. 15,000 i i i i i | i i i i | i i i i | i i i i | i i i i

0

5

10 15 Filler content (vol%)

20

25

Figure 3. Pure-gas permeability offilled PMP films as a function offiller content. Feed pressure: 50 psig; permeate pressure: 0 psig; temperature: 25°C.



226 can occur and an increase in the tortuous diffusion path around the filler particles. Flexible rubbery materials, such as polydimethylsiloxane or natural rubber, can pack efficiently around the filler particles, which provide an impermeable barrier to gas transport. On the other hand, P M P is an extremely rigid, high-free-volume glassy polymer, in which the polymer chains pack very inefficiently. The nanosized silica filler particles inhibit the ability of the rigid P M P polymer chains to pack in their equilibrium state. A s a result, the addition of nano-sized fumed silica to P M P resulted in a disruption of polymer chain packing, leading to an increase in free volume and permeability in die hybrid system. This hypothesis is illustrated schematically in Figure 4.

The permeability increase in PMP/silica hybrid membranes is coupled with a decrease in gas selectivity. Figure 5 shows the pure-gas oxygen/nitrogen and carbon dioxide/methane selectivities of P M P and PMP/TS-530 silica membranes as a function of the filler content. A s the filler content in P M P increases, the oxygen/nitrogen and carbon dioxide/methane selectivities of the membranes decrease. The addition of impermeable, nano-sized fumed silica to P M P increases the free volume in the polymer matrix, which leads to increased gas diffusion coefficients. However, the diffusion coefficients for large molecules, such as nitrogen and methane, increase more relative to those of small molecules, such as oxygen and carbon dioxide. Consequently, oxygen/nitrogen and carbon dioxide/methane selectivities decrease with increased filler content. The decrease in selectivity seems to imply the existence of macroscopic defects in the hybrid membrane. However, the results of our mixed-gas experiments show that the selectivity decrease is not a result of gross defects and/or contribution of Knudsen diffusion, as discussed below.


227


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Filler content (vol%)

Figure 5. Pure-gas selectivity offilled PMP films as a function of silica filler content (TS-530). Feed pressure: 50 psig; permeate pressure: 0 psig; temperature: 25°C.

Effect of Filler Type on Mixed-gas Permeation Properties of PMP/Silica H y b r i d Membranes Mixed-gas permeation experiments provide a simple, efficient method to prove that incorporation of nano-sized filler particles to rigid, high-free-volume, glassy polymers can lead to molecular disruption of polymer chain packing. The mixedgas permeation properties of silica-filled (13 vol%) P M P films are compared to those of a pure P M P film for a 2 v o l % n-butane/98 v o l % methane mixture in Figure 6. The n-butane/methane selectivity of pure P M P was 13 coupled with a nbutane permeability of about 6,000 Barrer. The addition of hydrophilic (L-90, M - 5 , and EH-5) fillers to P M P increased both the n-butane/methane selectivity and nbutane permeability significantly. The type and fractional loading of filler particles in the polymer matrix affect the membrane permeability and selectivity. For example, at equivalent filler loading, the n-butane permeability and n-butane/methane selectivities increase significantly as the average filler particle size decreases. Results illustrating this effect are shown in Figure 6 for P M P films containing silica particles of different sizes. A t the same filler loading, the number of particles present is inversely proportional to the cube of the particle diameter. Consequently, a large number of small particles disrupt polymer chain packing more efficiently than a few large particles. The largest increases in n-butane permeability and n-butane/methane


228


selectivity were observed for the P M P film containing 7 nm EH-5 filler. The nbutane/methane selectivity for a P M P film containing 13 v o l % hydrophilic silica EH-5 was 26 coupled with a n-butane permeability of 19,000 Barrer. Thus, the nbutane/methane selectivity of the EH-5 filled P M P film increased two-fold and the n-butane permeability increased more than three-fold over that of a pure P M P membrane. The PMP/silica hybrid membranes clearly show a significantly better performance for n-butane/methane separation than the pure P M P membrane.

30

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n-C H 4

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I

12,000 1 0

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16,000

20,000


Figure 6. Mixed-gas permeation properties of PMP and PMP/silica (13 vol%) hybridfilms determined with a 2 vol% n-butane/98 vol% methane mixture. Feed pressure: 150 psig; permeate pressure: 0 psig; temperature: 25°C.

In additional mixed-gas permeation experiments, the properties of P M P and silica-filled P M P films were evaluated with a 50 v o l % propane/50 v o l % hydrogen mixture. Figure 7 compares the mixed-gas propane/hydrogen selectivity and propane permeability of 13 v o l % silica-filled P M P with those of pure P M P and rubbery P D M S . Again, with the addition of filler, propane/hydrogen selectivity as well as propane permeability of silica-filled P M P increase significantly. The largest increases in propane/hydrogen selectivity and propane permeability occurred with


229 15

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6,000 g

1 1

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8,000

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10,000


Figure 7. Mixed-gas permeation properties of PMP and PMP/silica (13 vol%) hybridfilms determined with a 50 vol% propane/50 vol% hydrogen mixture. Feed pressure: 100 psig; permeate pressure: 0 psig; temperature: 25°C.

the hydrophobic filler TS-530. The PMP/TS-530 hybrid membrane showed a two fold increase in selectivity and permeability over that of a pure P M P film.

Effect of Filler Content on Mixed-Gas Permeation Properties of PMP/Silica Hybrid Membranes. The effect of silica content on the permeation properties of filled P M P films was determined at 25°C with a 2 vol% n-butane/98 vol% methane gas mixture. The filler content was varied between 6 and 22 vol%, using a hydrophobic fumed silica type (TS-530). The effect of increasing the silica filler content in the P M P film on the permeation properties is shown in Figure 8. The data show that the w-butane permeability increased four-fold, from about 6,000 Barrer for the pure P M P film to about 25,000 Barrer for a P M P film containing 22 vol% filmed silica TS-530. More importantly, the mixed-gas nbutane/methane selectivity increased from 13 for a pure P M P film to 21 for the filled P M P film.


230

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6 vol /. T S 530 0

•

•PMP 10 5,000

10,000

15,000

n-C H 4

1 0

20,000

25,000

30,000


Figure 8. Mixed-gas permeation properties of PMP and PMP/silica hybrid films as a function of filler content. Feed composition: 2 vol% n-butane/98 vol% methane; feed pressure: 150 psig; permeate pressure: 0 psig; temperature: 25°C.

To investigate the mechanism and demonstrate the general applicability of nano-sized filler/polymer hybrid membranes, we evaluated the permeation properties of different polymer/filler types. Additional blend membranes were made from (i) P M P and carbon black (individual particle size of 12 nm) and (ii) Teflon A F 2400 (a rigid, high-free-volume, perfluorinated glassy polymer) and fumed silica (TS-530). Both types of nanostructured hybrid membranes were tested with a 2 vol% «-butane/98 vol% methane mixture under the same test conditions as described above. The effect of various filler types on different, high-free-volume glassy polymers, illustrated as the ratio of permeability and selectivity of filled membranes to the permeation properties of the pure polymer membranes, is shown in Figure 9. The data in Figure 9 show clearly that for different high-free-volume, glassy polymer/nano-sized filler hybrid membranes, the effect of fillers on the gas


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11

10 n-C H 4

1 0

100

P e r m e a b i l i t y ratio

filled/unfilled

Figure 9. Mixed-gas n-butane/methane selectivity ratio as a function of the nbutane permeability ratio offilled/unfilled membrane for different polymer/filler hybrid membranes. Feed composition: 2 vol% n-butane/98 vol% methane; feed pressure: 150 psig; permeate pressure: 0 psig; temperature: 25°C.

permeation properties follows the same trend. A s the filler content in the hybrid membranes increases, the n-butane permeability increases and is accompanied by a dramatic increase in n-butane/methane selectivity. It is noteworthy that a pure Teflon A F 2400 membrane is methane/n-butane selective. However, the addition of fumed silica reverses the selectivity of Teflon A F 2400, that is, the hybrid membrane becomes n-butane/methane selective. The n-butane/methane selectivity of a Teflon A F 2400/35 vol% TS-530 membrane is 4.5 times higher than that of the pure Teflon A F 2400 membrane. More dramatically, the n-butane permeability of the filled Teflon membrane increases 30-fold. Our results indicate that any nanosized, nonporous, inorganic filler incorporated into high-free-volume, glassy polymers can function as a spacer material that disrupts polymer chain packing. To achieve enhanced vapor permeability and increased organic-vapor/permanent-gas selectivity, the size of the filler particles should be similar or smaller than the chain dimensions of the polymer ( 10 >

r

PTPSDPA

PDMS

»electi


:

•

1 : *P-2H

ft 4 10

100

n-C H 4

1,000 1 0

10,000

100,000


Figure 10. Mixed-gas n-butane/methane selectivity as a function of n-butane permeability for various polymers and TS-530-filled PMP. (•) 6, 11, 19, 22 vol% TS-530 filled PMP.

Conclusions In previous studies, addition of nonporous, inorganic fillers to rubbery or lowfree-volume, glassy polymers resulted in a decrease in the permeability of the hybrid membrane (14-16). B y choosing rigid, high-free-volume, glassy polymers, we observed completely opposite behavior. In our study, incorporation of nonporous, nano-sized fillers to the matrix of a high-free-volume glassy polymer, such as P M P , resulted in unexpected increases in the organic-vapor/permanent-gas selectivity and organic-vapor permeability. It is suggested that the permeability increase is due to an increase of the free volume in the polymer matrix by disruption of the polymer chain packing. The general applicability of this approach was demonstrated using different polymer and filler types. Our study shows that the organic vapor/permanent-gas separation properties of rigid, high-free-volume, glassy polymers can be improved significantly by molecular manipulation of polymer chain packing by incorporation of nano-sized fillers.


233

Acknowledgement This work was kindly supported by the National Science Foundation under contract number DMI-9760767.

References


1.

2.

3. 4. 5. 6.

7. 8. 9. 10. 11. 12.

13.

14. 15. 16.

E P A Guideline Series, "Control of Volatile Compounds from Manufacture of High Density Polyethylene, Polypropylene, and Polystyrene Resins," P B 84 134600 (November 1984). Anand, M . "Novel Selective Surface Flow Membranes," Proceedings of the Industrial Waste Program, Department of Energy, Albuquerque, N M , May 17-19, 1994. Pinnau, I; Toy, L . G . J. Membrane Sci. 1996, 116, 199. Pinnau, I.; Casillas, C.G.; Morisato, A.; Freeman, B.D. J. Polym. Sci. Part B: Polym. Phys. 1996, 34, 2613. Morisato, A.; Pinnau, I. J. Membrane Sci. 1996, 121, 243. Morisato, A.; He, Z.; Pinnau, I. in Polymer Membranes for Gas and Vapor Separation; Chemistry and Materials Science; Freeman, B . D . ; Pinnau, I., Eds.; A C S Symposium Series 733; American Chemical Society: Washington, D C , 1999; pp 56-67. Pinnau, I; He, Z. U.S. Patent 6,316,684, 2001. Merkel, T. C.; Freeman, B. D.; Spontak, R. J.; He, Z.; Pinnau, I.; Meakin, P.; Hill, A . J. Science, 2002, 296, 519. Robeson, L . M . J. Membrane Sci. 1991, 62, 165. Freeman, B . D.; Pinnau, I. TRIP, 1997, 5, 167. Pinnau, I.; Morisato, A . U.S. Patent 5,707,423, 1998. Koros, W. J. Barrier Polymers and Structures; Koros, W . J., Eds.; A C S Symposium Series 423; American Chemical Society: Washington, D C , 1990; p p l . Bissot, T. C. Barrier Polymers and Structures; Koros, W . J., Eds; A C S Symposium Series 423; American Chemical Society: Washington, D C , 1990; pp 225. Barrer, R . M . in Diffusion of Polymers, Crank, J; Park, G.S. (Eds.), Academic Press, New York, 1968, pp 165-217. Van Amerongen, G.J., Rubber Chem. Tech., 1964, 37, pp 1065-1152. Barrer, R. M.; Barrie, J. A.; Raman, N . K . Polymer, 1962, 3, 605.


Novel Nanostructured Polymer-Inorganic Hybrid Membranes for Vapor

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