Mark L. Stone

Testing of polymer membranes for the selective permeability of hydrogen

Selective gas barriers are of prime importance in thin polymer membranes. The focus of this work was to find a polymer membrane that allows the transport of H2 and acts as a barrier to CO2 and chlorinated organics. Membrane screening has included the following testing: single gas permeability measurements, mixed gas separations, and polymer physical characterization. Single gas permeability measurements were made using the time-lag method for five gases (H2, O2, N2, CO2, and CH4). Permeability coefficients and selectivities for the gas pair H2/CO2 are presented. Mixed gas separations were performed to measure actual separation factors for H2/CCl4 and to determine the effects on hydrogen permeability caused by exposing polymers to chlorinated hydrocarbons. The results of basic polymer characterization, such as polymer density and glass transitions, are addressed. #The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE-AC07-99ID13727. Accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

Chemical Separations Using Shell and Tube Composite Polyphosphazene Membranes

Abstract Several applications of modular shell and tube polyphosphazene coated membrane units are reported in this paper. These modules were used to measure the mixed-gas separation properties of poly[bis(phenoxy)phosphazene] based polymers on a larger scale. Transport behavior was determined using the variable volume technique. The test gas mixture was SO2/N2 at temperatures between 80[ddot]C and 270[ddot]C. Transport of these gases was found to be a sorption controlled process. Several organic-aqueous and organic-organic separations have been performed using the polyphosphazene coated shell and tube modules. The separations include: methylene chloride/water, acetic acid/water, isopropyl alcohol/water, glycerol/water, and hexane/soy oil. The membranes were prepared using slip casting techniques. The results of these studies show that polyphosphazene membranes can effectively be used to separate acid gases and organic chemicals from various waste streams in harsh, chemically aggressive environments.

Preparation and characterization of membranes with adjustable separation performance using polyphosphazene membranes

Abstract Preparation of polymeric membranes with dynamically adjustable separation properties is a new area of research. The approach described herein involves adjusting the permeate pressure of a swollen polymeric membrane to alter its separation properties. For example, during the separation of methylene blue from isopropyl alcohol, pressure on the permeate side was increased such that both methylene blue and alcohol were passed, resulting in no separation. The permeate pressure then was decreased and only colorless isopropyl alcohol passed through the membrane. A subsequent increase in the pressure on the permeate side results in no separation once again demonstrating that the effects were fully reversible. In a mixed dye experiment in isopropyl alcohol, methylene blue and rose bengal were separated with the lower-molecular-weight methylene blue permeating with isopropyl alcohol while the rose bengal was retained in the feed. The new membranes are distinguished by improved control of separation paramet...

Gas Permeation Testing Results from the Mixed Waste Focus Area Improved Hydrogen Getter Program

Abstract: The gas permeabilities of more than 20 polymers were measured using pure and mixed gas techniques. The motivation was to determine potential materials that could be used to protect hydrogen getter particles from poisons while permitting sufficient hydrogen rates to enable the getters use in TRUPACT types of containers. A rate of five barrers or larger is needed. Of the materials screened in the pure gas tests, more than 15 qualified. Nine materials qualified in the mixed gas tests, but of the nine only three had high CCI4 rejection rates and four others would greatly reduce the transport of the CCl4.

Characterization of two polyphosphazene materials as membranes in membrane induction mass spectrometry

Membrane introduction mass spectrometry (MIMS) has made large strides in capability improvement since its introduction. The main progress has been in systematic design changes that has allowed this technique to measure analytes in the parts-per-trillion range, samples that have had no special handling or pre-treatment. In spite of these improvements, however, the most important component of MIMS—the membrane—has not been optimized. In this paper, the results of testing two polyphosphazene polymers is reported and compared with those of silicone rubber. The results show that the rich chemical diversity possible with the phosphazene materials and their tailorability, make them good candidates for MIMS applications.

Chlorocarbon Permeabilities Of Several Polymeric Membranes Determined By Membrane Introduction Mass Spectrometry (Mims)

Membrane introduction mass spectrometry uses a semipermeable membrane to enhance the response of a mass spectrometer. The chemical composition of the membrane determines its permeation rates to various species. Careful selection of the membrane may make it possible to characterize more definitively close members of a chemical family. This article gives the results of an initial survey of the permeabilities, as determined by MIMS, of a variety of polymers to a family of chlorocarbons that are often the major components of subsurface remediation concerns. #The submitted manuscript has been authored by a contractor of the U.S. Government under contract No. DE-AC07-99ID13727. Accordingly, the U.S. Government retains a non-exclusive, royalty-free license to publish or reproduce the published form of this contribution, or allow others to do so, for U.S. Government purposes.

PURE GAS PERMEABILITIES OF A SERIES OF SUBSTITUTED BISPHENOXY PHOSPHAZENE POLYMERS

Polyphosphazenes are a class of inorganic polymers characterized by the phosphorus nitrogen repeating unit that forms the backbone. The phosphorus is pentavalent and the backbone has alternating single and double bonds. This leaves two coordination sites on the phosphorus free for substituted with a variety of nucleophilic groups. Several hundred polyphosphazene formulations have been reported in the literature. The ease of controlling the type and number of substituents provides a unique opportunity to develop special series of polymers to investigate structure property relationships. In this paper the pure gas permeabilities of a series of substituted bisphenoxyphosphazene polymers is reported. The polymers were exposed to ten different gases and the resulting permeabilities were analyzed using the time lag method. The time lag method enables the permeability to be broken down into its solubility and diffusivity components. Careful examination of the results makes it possible to determine what types of substituent-gas interactions are responsible for the overall permeabilities in the polymers. Some of the polymers showed low permeabilities for all of the test gases, while others showed very large differences among the different gases tested. Especially interesting differences were observed for the series of alkanes tested. The results permit the prediction of what types of mixed gas separations might be worth pursuing.

Water Transport Polymers – Structure/Property Relationships of a Series of Phosphazene Polymers

A study was undertaken to explore the water passing properties of a series of phosphazene polymers versus the attached pendant group structure. Pendant groups containing different numbers of ethyleneoxy groups were synthetically attached to the backbone of phosphazene polymers. Phosphazene polymers facilitate these types of studies because, during their synthesis, the polymer backbone is formed first and then the desired pendant groups are attached through nucleophilic substitution. For these studies, four polymer series were synthesized and tested for their water passing properties. The polymers contained different amounts of ethyleneoxy units. Two different polymer families were synthesized and compared in this work. The critical difference in the two polymer series is that one contained pendant groups with aromatic rings, in addition to the oligioethyleneoxy moieties, while the other has no aromatic rings in its structure. Polymers with phenyl group-containing pendant groups exhibited poor water permeability if they possessed fewer than six ethyleneoxy units. Polymers with more than six ethyleneoxy units inserted between the phenyl ring (tail) and the polymeric backbone exhibited reasonable water permeability. Two additional series of polymers with mixed pendant groups were synthesized and the water passing properties of the phosphazenes varied in proportion to the hydrophilic to hydrophobic balance induced by each individual pendant group. A final study of polymers with shorter pendant groups demonstrated the effect of pendant group on water permeability. These studies suggest that the polyphosphazenes may be tailored for specific water passing applications.