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ACS Conference, Philadelphia, PA. 22 – 26 August 2004

ACS 2004 Conference
Philadelphia, Pa, 22 – 26th August
Abstracts of Attendees

Haiqing Lin’s Abstract

Reverse-selective, highly branched polymers for purification of hydrogen and other light gases

H. Lin, University of Texas at Austin
B. Freeman, University of Texas at Austin
L. Toy, Research Triangle Institute
V. Bondar, Research Triangle Institute
R. Gupta, Research Triangle Institute
S. Pas, CSIRO Manufacturing Science and Technology
A. Hill, CSIRO Manufacturing Science and Technology

Polymeric membranes are used in many applications, including gas separations, due to inherently low energy requirements for molecular scale separations. Hydrogen, a potential future energy source, is usually produced by steam reforming of hydrocarbons and requires removal of byproducts such as CO2 and H2S. Highly efficient membrane materials will be more permeable to large impurity molecules (e.g., CO2) than to H2 to produce purified H2 at high pressure; such behavior of reverse selectivity is opposite to that exhibited by the vast majority of polymers. Here, polar, rubbery, branched hydrogels photopolymerized from poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) methyl ether acrylate (PEGMEA) are shown to have outstanding performance for acid/polar gas removal from H2. Surprisingly, introduction of methyl ether chain ends (i.e., PEGMEA) markedly improves CO2/H2 selectivity from 19 to 40 and CO2 permeability from 6.6 to 52 Barrers at -20oC; these materials exhibit the best separation performance reported to date for solid non-facilitated transport membranes.

Gordon Research Conference, New London, NH. 1-6 August 2004

Gordon Research Conference 2004
New London, NH, 1 – 6th August 2004
Abstracts of Attendees

Conor Braman’s Abstract

Water transport and fouling properties of crosslinked poly(ethylene glycol)

C. Braman, University of Texas at Austin
B. Freeman, University of Texas at Austin

All current ultrafiltration membranes are finely porous and are, therefore, subject to fouling by particulates, organics, and other wastewater components, resulting in a dramatic decline in the water flux (Ho 1999). Our approach to enhancing the severely limited fouling resistance of conventional ultrafiltration membranes is based on coating them with highly water permeable, nonporous, fouling resistant polymers. Crosslinked poly(ethylene glycol) (PEG) is used as the base material for the coatings because it is highly hydrophilic and has shown resistance to protein attachment (Ostuni 2001).

UV-induced radical polymerization of PEG diacrylate (PEGDA), which contains 13 PEO units, and PEG acrylate (PEGA), which contains 7 PEO units, was used to prepare crosslinked PEG films. The composition of the initial polymerization mixture used was between 20/80 and 100/0 for (PEGDA +PEGA)/water, with the focus being on those samples prepared with higher initial water concentration.

For the freestanding films, data on water flux and fouling resistant properties will be presented. Polymerization induced phase separation (PIPS) and its relevance to polymer transport properties will be discussed as well.

To characterize the properties of PEG films in crossflow experiments, a composite crosslinked PEG membrane was prepared. This composite membrane consists of a porous membrane support and ideally a thin, approximately one micron, dense coating of crosslinked PEGDA. An interfacial polymerization strategy was used to prepare a thin, uniform film at the membrane surface. This strategy is still in the development stage, and the challenges therein will be discussed. Preliminary water transport and fouling properties of these composites have been characterized and will be described. The utility of these composites is shown by comparing their performance with that of uncoated porous ultrafiltration membranes.

Emanuele Ostuni, R. G. C., R. Erik Holmlin, Shuichi Takayama, and and G. M. Whitesides (2001). “A Survey of Structure-Property Relationships of Surfaces that Resist the Adsorption of Protein.” Langmuir (17): 5605-5620.

Ho, C.-C. Z., A. L. (1999). “Effect of membrane morphology on the initial rate of protein fouling during microfiltration.” Journal of Membrane Science (155): 261-275.

Hao Ju’s Abstract

Membrane Performance Modification via Mechanical Stretching

B. McCloskey, University of Texas at Austin
H. Ju, University of Texas at Austin
B. Freeman, University of Texas at Austin
D. Lloyd, University of Texas at Austin
D. Lawler, University of Texas at Austin
L. Worrel, University of Texas at Austin
J. Moorhouse, University of Texas at Austin
Y. Wu, University of Texas at Austin

One of the primary concerns in the application of microfiltration and ultrafiltration membranes is membrane fouling. There are numerous membrane properties (and foulant properties) that have an affect on fouling mechanisms and subsequently membrane performance. The literature has suggested that a membrane’s pore aspect ratio (defined as the ratio between the pore’s major and minor axis) has an affect on certain bacteria attachment to poly(ether sulfone) (PES) membranes. Therefore, by physically controlling the aspect ratio of membrane pores (i.e. through a membrane stretching process), the fouling characteristics of the membrane can be modified. The purpose of the research presented here is to look at the effect that membrane pore geometry has on membrane performance (most notably flux and rejection) when filtering solutions containing various foulants.

In this study, ~0.2 mm mean pore diameter phase inversion PES membranes were used to purify three solutions in dead-end and crossflow filtration. One can see from the data that uniaxially stretching these membranes to 150% of their original length increases pure water flux. Stretching also increases flux and reduces flux decline, but has little effect on rejection for feed solutions containing 1g/L BSA. Stretching has little effect on flux, flux decline, and rejection for feed solutions containing oil-water emulsions at 1500 ppm. After small amounts of time, stretching reduces flux and rejection for the microsphere solution, but the flux and rejection for stretched and unstretched samples converge to a single value for longer operating times.

Bryan McCloskey’s Abstract

Membrane Performance Modification via Mechanical Stretching

B. McCloskey, University of Texas at Austin
H. Ju, University of Texas at Austin
B. Freeman, University of Texas at Austin
D. Lloyd, University of Texas at Austin
D. Lawler, University of Texas at Austin
L. Worrel, University of Texas at Austin
J. Moorhouse, University of Texas at Austin
Y. Wu, University of Texas at Austin

One of the primary concerns in the application of microfiltration and ultrafiltration membranes is membrane fouling. There are numerous membrane properties (and foulant properties) that have an affect on fouling mechanisms and subsequently membrane performance. The literature has suggested that a membrane’s pore aspect ratio (defined as the ratio between the pore’s major and minor axis) has an affect on certain bacteria attachment to poly(ether sulfone) (PES) membranes. Therefore, by physically controlling the aspect ratio of membrane pores (i.e. through a membrane stretching process), the fouling characteristics of the membrane can be modified. The purpose of the research presented here is to look at the effect that membrane pore geometry has on membrane performance (most notably flux and rejection) when filtering solutions containing various foulants.

In this study, ~0.2 mm mean pore diameter phase inversion PES membranes were used to purify three solutions in dead-end and crossflow filtration. One can see from the data that uniaxially stretching these membranes to 150% of their original length increases pure water flux. Stretching also increases flux and reduces flux decline, but has little effect on rejection for feed solutions containing 1g/L BSA. Stretching has little effect on flux, flux decline, and rejection for feed solutions containing oil-water emulsions at 1500 ppm. After small amounts of time, stretching reduces flux and rejection for the microsphere solution, but the flux and rejection for stretched and unstretched samples converge to a single value for longer operating times.

Rajeev Prabhakar’s Abstract

Not Available

Alyson Sagle’s Abstract

Characterization of Commercial Reverse Osmosis Membranes

A. Sagle, University of Texas at Austin
B. Freeman, University of Texas at Austin

Reverse osmosis (RO) membranes have been used for several decades to purify water. Most commercial RO membranes today are thin film composites of crosslinked polyamides on a polysulfone support. The membranes used in this work, GE Osmonics AG and AK RO membranes, are thin film composites of this nature. Work was done to characterize the performance of these materials. As a starting point, water flux measurements in dead-end cells were done with phosphate buffered water of pH 7.4. Fouling by oil was also investigated in dead-end cells by measuring the flux and rejection from an oil/water emulsion. It was found that the surfactant used to create the emulsion was also contributing to membrane fouling. Further oil/water fouling studies will be conducted with a different surfactant. Protein fouling and rejection was also tested in both dead-end and crossflow configurations. The RO membranes showed excellent rejection of protein with a nominal decrease in flux in a crossflow configuration.

In addition to fouling studies, chemical stability of the membranes was also tested. Polyamide membranes have shown that exposure to even small levels of chlorine greatly reduces their performance. Chlorine is often used in water treatment processes as a disinfectant or for membrane cleaning. Studies were done to examine the chemistry behind the degradation and the effects of the amount of chlorine exposure on the membrane performance. FTIR analysis showed that the polyamide underwent ring chlorination as the literature suggests. This basic work characterizing commercial membranes lays a foundation for future research into the modification of membranes to reduce fouling. Possibilities being considered for modification include grafting molecular branches onto the membrane surface. A second method could be applying a hydrophilic thin coating to the surface. This can be done via several methods (i.e. hydrogen abstraction, interfacial reactions, or redox reactions). A wide range of materials are available for use in modifying membrane surfaces, however factors such as mechanical strength, hydrophilicity, and functionality all must be considered.

Yuan-Hsuan Wu’s Abstract

Membrane Performance Modification via Mechanical Stretching

B. McCloskey, University of Texas at Austin
H. Ju, University of Texas at Austin
B. Freeman, University of Texas at Austin
D. Lloyd, University of Texas at Austin
D. Lawler, University of Texas at Austin
L. Worrel, University of Texas at Austin
J. Moorhouse, University of Texas at Austin
Y. Wu, University of Texas at Austin

One of the primary concerns in the application of microfiltration and ultrafiltration membranes is membrane fouling. There are numerous membrane properties (and foulant properties) that have an affect on fouling mechanisms and subsequently membrane performance. The literature has suggested that a membrane’s pore aspect ratio (defined as the ratio between the pore’s major and minor axis) has an affect on certain bacteria attachment to poly(ether sulfone) (PES) membranes. Therefore, by physically controlling the aspect ratio of membrane pores (i.e. through a membrane stretching process), the fouling characteristics of the membrane can be modified. The purpose of the research presented here is to look at the effect that membrane pore geometry has on membrane performance (most notably flux and rejection) when filtering solutions containing various foulants.

In this study, ~0.2 mm mean pore diameter phase inversion PES membranes were used to purify three solutions in dead-end and crossflow filtration. One can see from the data that uniaxially stretching these membranes to 150% of their original length increases pure water flux. Stretching also increases flux and reduces flux decline, but has little effect on rejection for feed solutions containing 1g/L BSA. Stretching has little effect on flux, flux decline, and rejection for feed solutions containing oil-water emulsions at 1500 ppm. After small amounts of time, stretching reduces flux and rejection for the microsphere solution, but the flux and rejection for stretched and unstretched samples converge to a single value for longer operating times.

NAMS Conference, Honolulu, HI. 26 – 30 June 2004

NAMS 2004 Conference
Honolulu, Hawaii 26 – 30th June
Abstracts of Attendees

Conor Braman’s Abstract

Water transport and fouling properties of crosslinked poly(ethylene glycol)

C. Braman, University of Texas at Austin
B. Freeman, University of Texas at Austin

All current ultrafiltration membranes are finely porous and are, therefore, subject to fouling by particulates, organics, and other wastewater components, resulting in a dramatic decline in the water flux (Ho 1999). Our approach to enhancing the severely limited fouling resistance of conventional ultrafiltration membranes is based on coating them with highly water permeable, nonporous, fouling resistant polymers. Crosslinked poly(ethylene glycol) (PEG) is used as the base material for the coatings because it is highly hydrophilic and has shown resistance to protein attachment (Ostuni 2001).

UV-induced radical polymerization of PEG diacrylate (PEGDA), which contains 13 PEO units, and PEG acrylate (PEGA), which contains 7 PEO units, was used to prepare crosslinked PEG films. The composition of the initial polymerization mixture used was between 20/80 and 100/0 for (PEGDA +PEGA)/water, with the focus being on those samples prepared with higher initial water concentration.

Dense, free-standing films of crosslinked PEGDA appear to show a non-linear relationship between transmembrane pressure difference and flux, and the theoretical basis for this result will be discussed. To characterize the properties of PEG films in crossflow experiments, a composite crosslinked PEG membrane was prepared. This composite membrane consists of a porous membrane support and a thin, approximately one micron, dense coating of crosslinked PEGDA. An interfacial polymerization strategy was used to prepare a thin, uniform film at the membrane surface. Water transport and fouling properties of these composites have been characterized and will be described. The utility of these composites is shown by comparing their performance with that of uncoated porous ultrafiltration membranes.

Emanuele Ostuni, R. G. C., R. Erik Holmlin, Shuichi Takayama, and and G. M. Whitesides (2001). “A Survey of Structure-Property Relationships of Surfaces that Resist the Adsorption of Protein.” Langmuir (17): 5605-5620. Ho, C.-C. Z., A. L. (1999). “Effect of membrane morphology on the initial rate of protein fouling during microfiltration.” Journal of Membrane Science (155): 261-275.

Scott Kelman’s Abstract

Effect of Crosslinking on Gas Transport Properties of High Free Volume Gas Separation Materials

S. Kelman, University of Texas at Austin
B. Freeman, University of Texas at Austin

High free volume polymer membranes are often very weakly size-sieving and, consequently, can remove large gas or vapor molecules from a gas mixture with smaller molecules. This capability finds application in reverse-selective gas separations such as VOC removal from permanent gas streams and monomer recovery from the exhaust of polymerization reactors. Poly(1-trimethysilyl-1-propyne) (PTMSP) is a stiff chain, high free volume glassy polymer well known for its very high gas permeability [1]. PTMSP also has outstanding vapor/gas selectivity. For example, the n-C4H10/CH4 mixed gas selectivity is 30, which is the highest value ever reported for this gas pair effects [2]. This makes PTMSP an interesting material for vapor/gas separations.

However, gas permeabilities in PTMSP are sensitive to processing history and time [1]. PTMSP undergoes significant physical aging, which is the gradual relaxation of nonequilibrium excess free volume in glassy polymers [3]. PTMSP is also soluble in many organic compounds leading to potential dissolution of the membrane in the process streams where separation properties are of greatest interest. These processes compromise the practical utility of PTMSP. Studies have been performed to slow the aging process in PTMSP. For example, Jia et al. [4] crosslinked PTMSP with bis azides in an effort to stabilize the large excess free volume elements. They found that physical stability of crosslinked PTMSP was achieved at the expense of reduced O2 and N2 permeability.

The effect of crosslinking PTMSP on aging behavior and transport properties of large organic molecules are presented. Crosslinking is successful in maintaining the permeability and vapor/gas selectivity of PTMSP over time. N2, O2, CH4 permeability values were constant over 100 days, while n-butane permeability increased for a crosslinked PTMSP membrane. The chemical resistance of PTMSP is strongly enhanced by crosslinking. For example crosslinked PTMSP is insoluble in common PTMSP solvents such as toluene and cyclohexane. The reaction between the bis azide crosslinker and PTMSP was observed using FTIR and XPS analysis. Crosslinking reduced the FFV of the polymer and therefore permeability decreased. Initial nitrogen permeability in crosslinked PTMSP was a factor of 4 less than pure PTMSP. Nanoparticles such as fumed silica and POSS particles were added to the crosslinked polymer to counteract the decrease in permeability.

[1] K. Nagai, T. Masuda, T. Nakagawa, B. D. Freeman and I. Pinnau, Poly(1-Trimethylsilyl-1-Propyne) and Related Polymers: Synthesis, Properties and Functions, Progress in Polymer Science, 26 (2001) 721-798.
[2] I. Pinnau and L. G. Toy, Transport of Organic Vapors through Poly(1-Trimethylsilyl-1-Propyne), J. Membrane Sci., 116 (1996) 199-209.
[3] L. C. E. Struik, Physical Aging in Amorphous Polymers and Other Materials, Elsevier, Amsterdam, 1978, pp. 7-9.
[4] J. Jia, PhD Thesis, Michigan State University, 1997.

Haiqing Lin’s Abstract

Reverse-selective, highly branched polymers for purification of hydrogen and other light gases

H. Lin, University of Texas at Austin
B. Freeman, University of Texas at Austin
L. Toy, Research Triangle Institute
V. Bondar, Research Triangle Institute
R. Gupta, Research Triangle Institute
S. Pas, CSIRO Manufacturing Science and Technology
A. Hill, CSIRO Manufacturing Science and Technology
D. Dworak, The University of Akron
M. Soucek, The University of Akron

Polymer membranes are used in many applications, including gas separations, due to their inherently low energy requirements for molecular scale separations. Hydrogen, a potential energy source for fuel cells, is produced by steam reforming of hydrocarbons and requires removal of byproducts such as CO2 and H2S. Highly efficient membrane materials will be more permeable to large impurity molecules (e.g., CO2) than to H2 to produce purified H2 at high pressure; such behavior is opposite to that exhibited by most polymers, which sieve penetrants mainly based on relative molecular size, and are, therefore, more permeable to H2 than to CO2. We present results of studies aimed at separating molecules based on the relative affinity of the penetrants for the membrane. Based on an extensive survey of interactions between polar moieties in polymers and CO2, the polar ether units in ethylene oxide are promising candidates for preparing materials with high acid gas permeability and high selectivity for larger CO2 and H2S over smaller H2.

We have prepared and characterized a systematic series of polar, rubbery, branched hydrogels based on poly (ethylene glycol diacrylate) (PEGDA, which is a crosslinker) and the monomers poly(ethylene glycol methyl ether acrylate) (PEGMEA, which has a methyl ether end group) and poly (ethylene glycol acrylate) (PEGA, which has a hydroxyl end group). Crystallization of poly(ethylene oxide) can be completely suppressed by the choice of branch length (i.e., monomer molecular weight) and composition. Introducing PEGMEA into PEGDA improves CO2 permeability by 400% (from 110 to 570 Barrers) and CO2/H2 selectivity by 65% (from 7 to 12) at infinite dilution and 35C, as PEGMEA content increases from zero to 99 wt.%. However, copolymers of PEGDA and PEGA do not show any improvement in permeation properties relative to those of PEGDA alone. A copolymer containing 91 wt.% PEGMEA and the balance of PEGDA exhibits a mixed gas H2S permeability of 2,500 Barrers and H2S/H2 selectivity of 50 at 22C. Temperature could be manipulated to achieve better separation properties. For example, a copolymer containing 70 wt.% PEGMEA and the balance of PEGDA exhibits CO2 permeability of 52 Barrers and CO2/H2 selectivity of 40 at -20C, based on pure gas measurements at an upstream pressure of 4.4 atm. These materials exhibit the best CO2/H2 separation performance reported to date for solid non- facilitated transport membranes. Examples of the separation properties of these materials for CO2/CH4 and CO2/N2 separations will also be shown. The results are interpreted in terms of the effects of polymer chemical structure on free volume, as probed by density and positron annihilation lifetime spectroscopy (PALS), and glass transition temperature.

Scott Matteucci’s Abstract

Interactions of basic nanoparticles with polyacetylenes and their influence upon gas transport and aging properties

S. Matteucci, The University of Texas at Austin
R. Raharjo, The University of Texas at Austin
S. Kelman, The University of Texas at Austin
B. Freeman, University of Texas at Austin

Due to increasing use of H2 in refining and as an expected fuel for fuel cells, there is growing interest in finding economically and industrially feasible methods of producing and purifying H2. Currently H2 is produced from steam reforming of hydrocarbons, which produces byproducts such as CO2, H2O, and CO.

Relative to current separation technologies for purifying H2, membranes offer advantages of compact size, modularity, low capital costs, and low environmental impact [1]. However most membranes separate gases based on molecular size, which causes smaller gases (e.g. H2) to permeate preferentially into the low pressure stream. Since H2 is the major component of the feed stream and since H2 is typically required at or above the feed pressures which would be available for membrane separators, there is significant interest in membranes that could remove the minor components (e.g. CO2) and maintain H2 at high pressure. High free volume glassy polymers such as poly(1-trimethylsilyl-1-propyne) [PTMSP] can selectively remove larger, more condensable gases from mixtures with smaller, less condensable species. Additionally the permeability of high free volume glassy polymers can be greatly increased by dispersing nanosized inorganic nonporous particles, such as fumed silicia [FS], in the polymer matrix [2].

Our goal has been to use nanoparticles to selectively improve the solubility of CO2 in nanocomposite membranes, thereby increasing the CO2 / H2 selectivity. We have found that PTMSP membranes containing 0 to 25 % by volume of basic nanoparticles (3-100 nm diameter) exhibit higher permeabilities for CO2 (up to 106,000 Barrers at 35oC) and permanent gases relative to the previously reported pure polymer or PTMSP/FS composites [2]. However, the nanocomposite selectivity is similar to that of the pure polymer. Physical aging properties are also reported for nanocomposites. While nanocomposite samples do age, their long-term permeation properties are substantially above those of PTMSP alone. Both polymer-particle and gas-particle interactions are believed to contribute to the altered transport properties. These interactions have been observed using FTIR, XPS, and AFM and will be discussed herein. These results will also be extended to other high free volume glassy polymers to study the generality of the observed changes in permeation and aging properties.

[1] A. Kohl and R. Nielsen, Gas Purification, 5th ed., Gulf Publishing Company, Houston, 1997, pp. 1238-1295.
[2] T. C. Merkel, B. D. Freeman, R. J. Spontak, Z. He, I. Pinnau, P. Meakin and A. J. Hill, Ultrapermeable, Reverse-Selective Nanocomposite Membranes, Science, 296 (2002) 519-522.

Rajeev Prabhakar’s Abstract

Plasticization-resistant membranes for CO2 removal from natural gas

R. Prabhakar, University of Texas at Austin
B. Freeman, University of Texas at Austin
I. Roman, MEDAL L. P. / Air Liquide /P>

Polymer membrane-based separation of CO2 from natural gas is gaining attention due to the compact size, low energy requirement, ease of use and scale-up, and potential for offshore installation of membrane systems. Current membranes, however, suffer losses in separation performance under field conditions due to plasticization of the polymer. This is caused mainly by sorption of CO2 and higher hydrocarbons into the polymer membrane in amounts sufficient to increase polymer chain mobility and reduce its ‘size-sieving’ ability. The result is a loss of the product, methane, from the feed stream into the low pressure permeate stream. This requires either a second membrane module to recover the lost product and recompress it to pipeline specifications, or to simply accept the loss – both of these can be expensive options.

Efforts have been made to suppress plasticization of current polymer membranes by blending with other polymers, thermal treatment of membranes and crosslinking of polymer chains.1-6 While some success has been achieved in delaying the onset of plasticization to higher partial pressures of the plasticizing penetrants, these approaches essentially “treat the symptom” rather than the fundamental cause. An alternate approach is to address the core issue of high solubility of higher hydrocarbon compounds by considering polymeric materials with inherently low solubility for these compounds. Completely fluorinated polymers can exhibit low solubility for higher hydrocarbons. In this presentation, the experimentally-determined pure and mixed gas transport properties of these materials will be presented. Also, their potential as plasticization-resistant membranes will be discussed based on CO2-CH4 mixed-gas permeation results up to industrially-significant CO2 partial pressures. For example, Hyflon AD 80, which is a copolymer containing 80 mole% 2,2,4-trifluoro-5-trifluoromethoxy-1,3- dioxole (TTD) and 20 mole% tetrafluoroethylene (TFE), exhibits very high CO2 permeability (of the order of 200 Barrers) and reasonable CO2/CH4 selectivity (in the range of 9 to 12) for feed streams up to 800 psia containing 20% CO2.

(1) Bos, A.; Punt, I.; Strathmann, H.; Wessling, M. AIChE J. 2001, 47, 1088- 1093. (2) Bos, A.; Punt, I. G. M.; Wessling, M.; Strathmann, H. J. Polym. Sci. Part B. Polym. Phys. 1998, 36, 1547-1556. (3) Bos, A.; Punt, I. G. M.; Wessling, M.; Strathmann, H. Separation and Purification Technology 1998, 14, 27- 39. (4) Staudt-Bickel, C.; Koros, W. J. J. Membrane Sci. 1999, 155, 145-154. (5) Wind, J. D.; Staudt-Bickel, C.; Paul, D. R.; Koros, W. J. Industrial and Engineering Chemistry Research 2002, 41, 6139-6148. (6) Wind, J. D.; Staudt-Bickel, C.; Paul, D. R.; Koros, W. J. Macromolecules 2003, 36, 1882-1888.

Roy Raharjo’s Abstract

The Effect of Substituent Size and Shape on Gas Transport Properties in Substituted Polyacetylenes

R. Raharjo, University of Texas at Austin
H. Lee, University of Texas at Austin
B. Freeman, University of Texas at Austin
T. Sakaguchi, Kyoto University
T. Masuda, Kyoto University

Poly[1-phenyl-2-[p-(trimethylsilyl) phenyl]acetylene] (PTMSDPA) is a highly permeable, glassy, substituted acetylene polymer. Like poly(1- trimethylsilyl-1-propyne) (PTMSP), this polymer is more permeable to larger, more condensable hydrocarbons than to smaller, less condensable permanent gases. Therefore, it may be useful for separations such as the removal of higher hydrocarbons from natural gas or hydrogen streams. Although PTMSDPA has outstanding properties for such separations, PTMSDPA is soluble in common hydrocarbons and, therefore, would not be suitable for use as a commercial membrane in such applications. However, desilylation of this polymer renders it completely insoluble, thereby strongly improving its chemical resistance. The resulting polymer, poly(diphenylacetylene) (PDPA), has a fractional free volume (FFV) of 0.23, slightly lower than that in PTMSDPA (0.26). The pure gas permeation properties of various light gases and hydrocarbons in PTMSDPA and PDPA at 35oC are reported and compared to those in other substituted polyacetylenes. A significant decrease in gas permeability values, most likely due to the decrease in the FFV, is observed after desilylation. For example, the permeability of nitrogen is reduced by almost 50%, from 640 to 280 Barrers. The permeability of n- butane is reduced even more, from 16000 to 2400 Barrers. The permeability measurement was done at 35oC with an upstream pressure of 50 psig (4.46 bar) for all permanent gases, methane, ethane, and propane and 8 psig (1.56 bar) for n-butane. The downstream pressure was maintained at atmospheric.

2002 Cooperative Research Award in Polymer Science and Engineering

Sponsored by the Eastman Kokak Company

Prof. Benny Freeman
Prof. Benny Freeman
Dr. Ingo Pinnau
Dr. Ingo Pinnau

Professor Benny Freeman of the Chemical Engineering Department at University of Texas at Austin and Dr. Ingo Pinnau of Membrane Technology and Research (MTR) are winners of the 2002 Award for Cooperative Research in Polymer Science and Engineering presented by the American Chemical Society’s (ACS) Division of Polymeric Materials: Science and Engineering (PMSE). Dr. Brian Benecewicz, Chairman of the PMSE Cooperative Research Award Committee, announced the award, which has been presented annually since 1992, when it was endowed by a gift from the Eastman Kodak Company to PMSE.

Dr. Freeman, Professor of Chemical Engineering at the University of Texas at Austin, and Dr. Pinnau, Principal Scientist at MTR, won the 2002 award based on sustained, significant contributions in the areas of gas, vapor, and liquid separations using polymer and polymer-based membranes. Their pioneering research has identified fundamental limitations of existing membranes and led to new materials that elegantly circumvent these limitations. For example, they identified new polymers and polymer-based nanocomposites that, in contrast to conventional polymer membranes, are much more permeable to larger, more soluble molecules (e.g., n-butane) than to smaller molecules (e.g., methane). Membranes prepared from such polymers enable selective separation of volatile or toxic organic vapors from air gases and removal of condensable hydrocarbons from natural gas for dewpoint and heating value control. They have recently conceived of and reduced to practice the concept of applying thin (<1 µm), nonporous coatings of self-assembled block copolymers to the surface of conventional porous membranes for water treatment. These coatings reduce membrane fouling by more than 90% in some applications, such as purification of oily wastewater. Advanced membranes for drinking water production may also benefit from this approach.

Since 1994, their cooperative research has resulted in more than 25 joint publications, two ACS Symposium Series books, many jointly led conferences and symposia, more than 4 million dollars of Federal research support for cooperative research projects between Professor Freeman and Dr. Pinnau, more than 20 joint oral presentations, and significant advancement of the field of novel separations using polymer membranes. Evaluators of the nomination were impressed by the quality of the scientific contributions and by the breadth of joint activities. Professor Freeman is a recognized leader in the science of small molecule transport in polymers. Fundamental research in his laboratory bears directly upon membranes for liquid, gas, and vapor separations; controlled drug delivery devices and techniques; barrier plastics for food and specialty packaging; monomer and solvent removal from formed polymers; and physical aging of glassy polymeric materials and membranes. The National Science Foundation, National Academy of Engineering, the ALCOA Foundation, and the Japan Society for the Promotion of Science (JSPS) have recognized his research. Dr. Pinnau is an authority on polymer-based membranes for separations applications. He directs the materials and membrane production group at MTR, and he has developed a variety of polymeric, solid polymer electrolyte, metal, and nanocomposite membranes for next-generation separation applications in the chemical, petrochemical, and allied industries. He holds 22 U.S. patents and has been honored three times by his selection to receive a prestigious JSPS Fellowship.

The awards, which each include a $1500 prize, will be presented at PMSE's awards luncheon at the Spring 2002 American Chemical Society meeting in Orlando, Florida.

For more information, contact Brian Benicewicz, Rensselaer Chairman, PMSE Cooperative Research Award Committee

C&EN: Science & Technology: Waterworks

SCIENCE & TECHNOLOGY
April 9, 2001
Volume 79, Number15
CENEAR 79 15 pp.32-38
ISSN 0010-2347

WATERWORKS
Research accelerates on advanced water-treatment technologies as their use in purification grows

MAIRIN B. BRENNAN, C&EN WASHINGTON

Conventional water purification is a tried-and-true process that hasn’t changed much in decades: Coagulation and flocculation, sedimentation, sand or gravel filtration, and chlorine disinfection are the customary steps. Wresting fresh water from seawater is also a long-standing technique, especially in oil-rich, water-starved countries where the cost of the energy-intensive process is not an issue.

Read more

CNN Sci-Tech: New plastics may keep soft drinks from falling flat

February 6, 1997
From Correspondent David George

RALEIGH, North Carolina (CNN) — Ever wonder why soft drinks sometimes go flat even before you’ve opened the bottle? Ever wonder when somebody’s going to do something about it?

Wonder no more. Researchers at North Carolina State University (NCSU) are experimenting with liquid crystal polymers they say could be used to make plastic soda bottles and other plastic packaging virtually impervious to gas leakage, thus greatly increasing the “shelf life” of hundreds of products.

Leakage is a universal problem in plastic packaging. Every plastic soda bottle that rolls off a production line, every food product packed in plastic, and every plastic container of any kind on any store shelf anywhere will leak to some degree.

It may not be apparent to the casual observer, but slow, invisible leaks can affect the quality of products.

“Anything we have is vulnerable to some degree to air, the oxygen in the air, loss of flavor, gain of outside odors,” said packaging consultant Aaron Brody.

The problem, NCSU researchers say, is that oxygen and other gasses dissolve into the walls of polymer-based plastic containers much like sugar dissolves in coffee.


Dr. Freeman
Dr. Freeman

“The molecules of water actually dissolve into the body of the polymeric film, and then move through the polymeric film itself,” says Dr. Benny Freeman, one of the researchers trying to solve the problem.
Dr. Freeman speaking about this issue.

Freeman and others are conducting experiments to compare the ability of various liquid crystal polymers to form gas-tight barriers.


Chris McDowell
Chris McDowell

The test involves suspending polymer samples from springs inside gas-filled chambers. The more gas a material absorbs, the heavier it gets, says doctoral candidate Chris McDowell.


Freeman compares the molecules in polymers to logs lined up together to form an oxygen barrier 100 times better than that of today’s soda bottles.

Depending on the outcome of the experiments, the airtight polymers may have other uses. Freeman says the electrical industry is already considering using a sleeve made of liquid crystal polymers to extend the life of underground power cables.

And Brody, co-author of an authoritative book on packaging, says the day may soon come when the public will find even beer packaged in plastic, just like soft drinks.

“We’re converting just about everything else into plastic,” he says, “Why not beer?”

Tomorrow Today examines a new weapon against termites — one that drastically reduces the amount of toxic chemicals needed to control the pests.

Pulse Planet: Barrier Plastics

ambience: soda pouring, fizzing

Anyone who’s ever opened a bottle of soda knows that sound. But why is it that even unopened plastic soda bottles lose their fizz over time? I’m Jim Metzner, and this is the Pulse of the Planet.

“The carbon dioxide that gives soda what people normally associate with as fizz is soluble and will dissolve into the wall of the plastic and be transported through the plastic and escape. In much the same way that air in your tires will eventually escape and the tire pressure goes down with time.”

Benny Freeman is an Associate Professor of chemical engineering at North Carolina State University. He’s been studying the effectiveness of plastic packaging.

“Any plastic will permit leakage of small molecules through the plastic. The current packaging materials for things like soda bottles have leak rates that are acceptable for large sizes, but become unacceptable for smaller size bottles or for applications like beer packaging which are more sensitive to things like oxygen coming in from the outside of the package.”

And that’s why you don’t currently see beer packaged in plastic containers.

“For an application like beer where beer is very very sensitive to even small amounts of oxygen, the major factor limiting the use of plastic packaging for beer is that oxygen from the surrounding atmosphere gets into the package and causes the beer to get stale or taste flat.”

But Professor Freeman and his colleagues are on the track of using new kinds of plastic which form more effective barriers. We’ll hear more in future programs.

Pulse of the Planet is presented by DuPont, makers of better things for better living.

To really hold that fizz

SCIENCE NEWS ONLINE
Food for Thought
August 24, 1996

If it sits on the shelf long enough, even an unopened 2-liter bottle of Coca-Cola or Diet Sprite will lose its zesty effervescence. What happens is the pent up carbon dioxide slowly leaks through microscopic holes in the molecular structure of the container’s plastic. Fortunately, not all plastics are as permeable as the inexpensive polyethylene terephthalate (PET) used to make large soft-drink bottles. One novel class of more rigid polyesters appears to offer particular promise for bottled drinks. It develops extraordinary barrier properties after it’s been transformed into a liquid crystal, for example, by heating.
Benny D. Freeman of North Carolina State University began working with these experimental materials 5 years ago under a grant issued jointly by the National Science Foundation and Electric Power Research Institute (EPRI). Initially, his mission was one of basic research: to understand how heat alters the structure and barrier properties of these polyesters.

At room temperature, they’re frozen glasses. On a molecular level, they resemble microscopic pick-up sticks that had been dropped onto a flat surface — splaying into a disordered pile with ends sticking every which way. Between individual sticks are big gaps, ones large enough for a soft drink’s carbonation to slowly sneak through.

Under heating, Freeman has found, this polyester begins to align and order itself into tightly packed rows of parallel sticks — like boxed toothpicks. This structure possesses far smaller holes for carbon dioxide or any other molecules to slip through. In fact, heat treating can improve the barrier properties of the starting polyester 10 to 100 fold (depending on what’s trying to escape). That increase is substantial, Freeman notes, since the plastic had started out about as leaky as the PET used in today’s soft drink bottles.

Prototype underground cable using the novel plastic as a moisture barrier. The plastic is that thick grey-white cylinder surrounding the inner cable wires. Credit: Raloff
Prototype underground cable using the novel plastic as a moisture barrier. The plastic is that thick grey-white cylinder surrounding the inner cable wires. Credit: Raloff

Based on Freeman’s findings and EPRI’s financing, a small company in Waltham, Mass., is already developing one such experimental liquid crystal polymer into a superior moisture guard for underground electric cables (above, right). Though these designer plastics are expensive — typically about $10 to $15 per pound, so little is needed that they’re expected to add no more than perhaps a penny per foot to the cost of cable that now runs about $1.25 per foot.

If the new cable sheathing becomes commercially successful, Freeman says, “that single application would double the worldwide market for liquid crystal polymers to about 20 million pounds per year.” Such a dramatic increase in demand for this plastic should also bring down its cost, making it more attractive to bottlers of carbonated beverages, including many who eschew plastics today.

For instance, commercial plastics are so permeable to oxygen, which can destroy the taste of beer, that brewers have generally stuck to glass and metal. Liquid-crystal polyester bottles should preserve the flavor of your ale or lager far longer — though still not as long as glass.

Or consider juice purveyors. Limonene and many other trace flavorants in fruit juices and soft drinks can migrate into PET and other conventional packaging plastics. Not only can this change a drink’s taste, but if the plastic were later reused for some other application, it could shed those trace contaminants into other foods or materials where they might not be appreciated. Liquid crystal polymers appear to make such good barriers, Freeman says, that they could seal in or out any possible adulterants far better than today’s commercial plastics — though, again, not quite as well as glass.

In fact, where bottlers want to sterilize and reuse containers, these experimental polyesters might well stand in for glass, offering the convenience of no breakage and lighter weight.

Heat-transformed plastic, now a liquid crystal, as viewed through an optical microscope. Crossed polarizing filters bring out the colors and patterns in this plastic. Credit: Freeman, N.C. State Univ.
Heat-transformed plastic, now a liquid crystal, as viewed through an optical microscope. Crossed polarizing filters bring out the colors and patterns in this plastic. Credit: Freeman, N.C. State Univ.

While it might be fun to imagine these bottles changing colors, like mood rings of yore (photos, above), bottlers will probably opt for a more prosaic clear or milky opaque form. Indeed, Freeman points out, the liquid crystalline materials in watch faces and some toys change their hue only after they have been sandwiched between two sheets of polarized film and then subjected to a force that temporarily imposes order onto their normally amorphous rod-like structure.

References:

McDowell, C.C., H.C. Shen, and B.D. Freeman. 1966. Thermal transitions and structure evolution in PICT, a soluble nematic LCP exhibiting a kinetically trapped, disordered structure. American Chemical Society annual meeting (polymer division), New Orleans.

Benny D. Freeman, Department of Chemical Engineering, North Carolina State University, Raleigh, NC 27695-7905.

This week’s Food for Thought is prepared by Janet Raloff, senior editor of Science News.

Experimental Plastic Could Keep Soda Fizz From Fizzling

ELIZABETH TENNYSON
Associated Press Writer

Raleigh (AP) – Does your soda go flat? Is the gas tank on your car corroding? Are your wine bottles to heavy?

If so, researchers at North Carolina State University may have the solution to your problems.

Chemical engineers at the school are working on a strain of liquid crystalline polymer plastic that could seal in flavor and carbonation while keeping out air. The plastic could also be used to stop corrosion of fuel tanks and underground power lines.

“The main science behind it is these polymer molecules pack very well,” said Chris McDowell, a doctoral student working on the project. “The molecules are long and stiff like a pen. That allows them pack together so there is no room for small molecules like oxygen to pass through.”

Beer and wine are extremely sensitive to oxygen and quickly lose their flavor if air gets into the packaging. But the new variety of plastic, known as PICT, could keep enough oxygen out to make plastic beer and wine containers practical.

The plastic also could be used to extend the shelf life of bottled soda, which now keeps for six to eight weeks, and to make smaller, 12-ounce, soda bottles. Existing plastic bottles, which are made from another kind of plastic called PET, can be used to hold only 16 or more ounces of soda.

“Due to how fast these small molecules migrate through PET polymers, you cannot have small packages, ” McDowell explained. “It has to do with the amount of surface area in the smaller packages.”

Dr. Benny Freeman, associate professor of chemical engineering, presented the team’s findings Monday at the American Chemical Society’s annual meeting in New Orleans.

Researchers are uncertain how long commercial development of their plastics might take, but estimate the new food bottles could appear on store shelves within the next decade. The process is expensive now, but Freeman believes his group’s work will pave the way for cost-effective production of food containers and specially coated underground cables.

“Underground electric power cables with a thin coating of these plastics would have substantially longer lifetimes than non-coated cables because of the prevention of moisture ingress and subsequent corrosion,” Freeman said. “Yet adding the coating only adds about one cent per foot to the total production cost.”

Freeman also hopes the plastic will be used to make lightweight, corrosion resistant fuel tanks for cars running on reformulated gasoline.

The project is currently funded by the National Science Foundation and the chemical company Hoechst Celanese.