Impact of H+ ion irradiation on Matrimid®. I. Evolution in chemical structure

Ion beam irradiation can be used to modify the structure and gas transport properties of glassy polymers. This is the first of two studies that focus on the impact of H⁺ ion irradiation on the structure and permeation properties of the polyimide Matrimid®. Specifically, the evolution in chemical structure after H⁺ irradiation over a range of fluences was analyzed using FTIR spectroscopy and dissolution studies. Although H⁺ ion irradiation at very low ion fluences induced little modification in the chemical structure, irradiation at relatively high ion fluences resulted in crosslinking of the irradiated films. The branched structure of the aliphatic methyl (CH₃) was the most sensitive to the H⁺ ion irradiation. The para‐disubstituted aromatic ring showed the strongest resistance toward ion irradiation and required fairly high doses to induce degradation. Two potential crosslinking mechanisms related to the degradation of the aliphatic methyl and the benzophenone carbonyl were presented. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2010–2019, 2003     

Effect of H+ and N+ Irradiation on Structure and Permeability of the Polyimide Matrimid®

Abstract

This paper presents a comparison of the impact of H⁺ and N⁺ ion irradiation on the chemical structure, microstructure, and gas permeation properites of the polyimide, Matrimid®. While irradiation with both ions resulted in evolution of chemical structure with loss of functional groups and crosslink formation, there was greater modification of polyimide structure following N⁺ irradiation at similar total deposited energy. Irradiation with N⁺ resulted in simultaneous large increases in permeance and permselectivity at comparatively low ion fluences or irradiation time. For example, irradiation at 4 × 10¹⁴ N⁺/cm² resulted in a 2.5 fold increase in He permeance with a selectivity of He/CH₄ of 340. Much higher H⁺ fluences were required to achieve similar total deposited energy and combined increases in permeance and permselectivity. The larger modification in chemical structure and gas permeation properties following N⁺ irradiation was attributed to the relatively large energy loss and damage from the nuclear energy relative to electronic energy loss.     

Advanced Gas Separation Membrane Materials: Rigid Aromatic Polyimides

Abstract

Permeabilities, solubilities, diffusivities, and selectivities for He/CH₄ and CO₂/CH₄ gas pairs are reported for four aromatic polyimides having systematic variations in intersegrnental packing and intrasegmental mobility. As intersegmental packing is disrupted by bulky substituents, gas diffusivities are generally increased, but diffusivity selectivities of He/CH₄ and CO₂/CH₄ are correspondingly decreased. Simultaneous suppression of intrasegmental mobility and intersegmental packing, however, yields significant increases in both diffusivity and diffusivity selectivity, and consequently in permeability and permselectivity. For example, packing-disrupted and mobility-restricted 6FDA-DAF polyimide provides significantly higher permeabilities and permselectivities than commercially available polymers currently being used as membrane materials.     

Carbon molecular sieve membranes derived from Matrimid® polyimide for nitrogen/methane separation

A commercial polyimide, Matrimid® 5218, was pyrolyzed under an inert argon atmosphere to produce carbon molecular sieve (CMS) dense film membranes for nitrogen/methane separation. The resulting CMS dense film separation performance was evaluated using both pure and mixed N₂/CH₄ permeation tests. The effects of final pyrolysis temperature on N₂/CH₄ separation are reported. The separation performance of all CMS dense films significantly exceeds the polymer precursor dense film. The CMS dense film pyrolyzed at 800 °C shows very attractive separation performance that surpasses the polymer membrane upper bound line, with N₂ permeability of 6.8 Barrers and N₂/CH₄ permselectivity of 7.7 from pure gas permeation, and N₂ permeability of 5.2 Barrers and N₂/CH₄ permselectivity of 6.0 from mixed gas permeation. The temperature dependences of permeabilities, sorption coefficients, and diffusion coefficients of the membrane were studied, and the activation energy for permeation and diffusion, as well as the apparent heats of sorption are reported. The high permselectivity of this dense film is shown to arise from a significant entropic contribution in the diffusion selectivity. The study shows that the rigid ‘slit-shaped’ CMS pore structure can enable a strong molecular sieving effect to effectively distinguish the size and shape difference between N₂ and CH₄.     

Gas permeation in miscible homopolymer-copolymer blends: II. Tetramethyl bisphenol-A polycarbonate and a styrene/acrylonitrile copolymer

Gas sorption and transport properties for He, H₂, O₂, N₂, Ar, CH₄, and CO₂ at 35°C near atmospheric pressure have been obtained for miscible blends of tetramethyl bisphenol-A polycarbonate (TMPC) and a random copolymer of styrene with acrylonitrile (SAN) containing 9.5% by weight of acrylonitrile. All gas permeability, diffusion, and solubility coefficients obtained are lower than that calculated from the semilogarithmic additivity rule. These results are qualitatively interpreted by ternary solution theory and activated state theory which have been proposed to describe gas sorption and diffusion in miscible blends. The negative deviation of gas permeabilities for the blends from this rule can be explained semiquantitatively by free volume theory which takes volume contraction on mixing into account. The negative deviation increases with gas molecular size which results in larger ideal gas separation factors than that calculated from the additivity rule. For He/CH₄ and H₂/CH₄ pairs, the permselectivities for the blends are higher than that for either pure TMPC or SAN. The deviation from additivity for gas transport properties of TMPC/SAN blends is the opposite of that observed in the first paper of this series for PMMA/SAN blends. This can be attributed to the stronger interactions in TMPC/SAN blends than in PMMA/SAN blends.     

Effect of ultraviolet light irradiation on gas permeability in polyimide membranes. II. Irradiation of membranes with high-pressure mercury lamp

A photocrosslinkable polyimide membrane was prepared and investigated with regard to the effect of ultraviolet light irradiation (UV-irradiation) using a high-pressure mercury lamp on their gas permeabilities and permselectivities. Permeability and diffusion coefficients for O₂, N₂, H₂, and CO₂ were determined using the vacuum-pressure and time-lag methods. Sorption properties for carbon dioxide were determined to evaluate the changes in the free volume in the membranes by the irradiation. The apparent gas permeabilities decreased and permselectivity, particularly for H₂ over N₂, increased with increasing UV-irradiation time without a significant decrease in the flux of H₂. They depended on the membrane thickness, suggesting asymmetrical changes in the membrane due to UV-irradiation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 49–60, 1998     

Gas permeation in miscible blends of poly(methyl methacrylate) with bisphenol chloral polycarbonate

The miscibility of poly(methyl methacrylate) (PMMA) with bisphenol chloral polycarbonate (BCPC) has been studied using differential scanning calorimetry (DSC), optical indication of phase separation on heating (i.e., lower critical solution temperature (LCST) behavior), density measurement, and gas permeation. All evidence indicates that PMMA is miscible with BCPC over the whole blend composition range. Single composition-dependent glass transition temperature and LCST behavior have been observed for each blend. The specific volumes of the blends follow closely the simple additivity rule indicating the interaction between PMMA and BCPC is weak. Gas permeability coefficients for He, H₂, O₂, Ar, N₂, CH₄, and CO₂ measured at 35°C under 1 to 2 atm upstream pressure are lower than those calculated from the semilogarithmic additivity rule. The difference between this calculated permeability and the measured one increases with gas molecular size. As a result, the ideal gas separation factors for He/CH₄, CO₂/CH₄, and O₂/N₂ gas pairs estimated from the ratio of pure gas permeabilities are higher than predicted from the semilogarithmic additivity rule. These permeation results were interpreted in terms of the free volume theory and the activated state theory, which have been proposed to describe gas transport behavior in polymer mixtures.     

Carbon molecular sieve membranes for natural gas purification: Role of surface flow

Carbon molecular sieve membranes (CMSM) were prepared from the pyrolysis of polyimide films within a temperature range of 600°C-800°C under nitrogen stream. The membrane samples were characterized and tested for the permeation of He, CH₄, CO₂, and N₂ at different pressures and temperatures, respectively. The CMSM700 membrane (pyrolyzed at 700°C) showed an ideal selectivity of ~ 11 for N₂/CH₄ with a permeability of 2.18 × 10⁻¹⁵ mol · m/m² · s · Pa for N₂. The separation mechanism for the N₂/CH₄ pair was shown to be largely molecular sieving rather than surface flow. The membrane showed an ideal selectivity of ~ 500 for the CO₂/CH₄ pair with a CO₂ permeability of 9.72 × 10⁻¹⁴ mol · m/m² · s · Pa. The permeability of He was lower than that of CO₂, suggesting that the surface flow played a significant role in the CO₂ permeation. The updated permeability-selectivity tradeoff curves show that this CMSM membrane compared favourably with other membrane materials reported in the literature for the removal of N₂ and CO₂ from CH₄ for natural gas upgrading.     

Modified polysulfones 5: synthesis and characterization of tetramethyl polysulfones containing trimethylsilyl groups and their gas transport properties

Polysulfones with rigid backbone structures and silyl-containing substituents were prepared as membrane materials with potentially enhanced gas transport properties. Tetramethylbisphenol-A polysulfone (TMPSf) and tetramethylbiphenol polysulfone (TMPPSf) were made by polycondensation then post-modified to introduce trimethylsilyl (TMS) groups by bromination and lithiation methodology. Substitution of high levels of TMS groups at the ortho-sulfone sites was achieved using direct lithiation followed by addition of a trimethylsilane electrophile. In an approach to increase the overall TMS substitution level as well as introduce these groups on the bisphenol segment, both TMPSf and TMPPSf were cleanly brominated to a degree of substitution (DS) of 2.0 for bromine. While the subsequent lithium-halogen exchange and reaction with TMS electrophile did not give high regioselectivity because of steric hindrance, the overall DS of TMS in the polymers was increased when excess n-butyllithium was used to activate both brominated and ortho-sulfone sites. The polymer structures were characterized by NMR spectroscopy. Their thermal properties as well as O₂, N₂, CO₂ and CH₄ gas transport properties were measured. Polymers with a high DS of TMS had very high CO₂ and O₂ permeabilities and good permselectivities from N₂. The permselectivities of CO₂/N₂ were at or close to the Robeson upper-bound performance line [J. Membr. Sci. 62 (1991) 165].     

Effect of nano‐silica on gas permeation properties of polyether‐based polyurethane membrane in the presence of esterified canola oil diol as a nucleation agent for hard segments

In this research esterified canola oil diol (COD) was used to synthesize a green thermoplastic polyurethane. The mixture of synthesized COD as a polyester and polytetramethylene‐glycol as a polyether with different molar ratios were used to synthesize a thermoplastic polyurethane. Membranes were prepared by solution casting technique and nano‐silica particles were used to improve their gas separation performance. The effects of COD segments on phase separation and thermal properties of blocky segments of polyurethanes were evaluated using Fourier transform infrared spectroscopy and thermal gravimetric analysis. Results showed that phase separation behavior of the synthesized polyurethane was significantly increased with COD content. The COD segments showed high tendency to interact with hard segments of polyurethane in a way that new domains with higher thermal stability is created. Permeability of pure CO₂, CH₄, N₂, and He gases were taken using constant pressure method at different pressures. Nano‐silica particles showed high inclination to interact with COD segments and significantly influenced the phase separation as well as gas permeation properties of polyurethane. Interactions of nano‐silica particles with the soft segments of polyurethane increased the glassy behavior of polymer and improved the CO₂/CH₄, CO₂/N₂, and CO₂/He ideal selectivities (permselectivities). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45979.     

Incorporation of carbon nanofibers into a Matrimid polymer matrix: Effects on the gas permeability and selectivity properties

Composite membranes containing carbon nanofibers (CNFs) and Matrimid were prepared by a solution‐casting method. Prepared Matrimid–CNF composite membranes were characterized with X‐ray diffraction, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and mechanical testing techniques. The mechanical properties of the composite membranes increased over that of the pristine polymeric membranes. To develop a broad fundamental understanding of the connection between the composite architecture and gas‐transport properties, both the gas‐permeability and gas‐separation characteristics were evaluated. The gas‐transport properties of the Matrimid–CNF composite membrane was measured with a single gas‐permeation setup (He, H₂, N₂, CH₄ and CO₂) at ambient temperature with the variable‐volume method. The incorporation of CNFs (0.5–10 wt %) into the Matrimid matrix resulted in approximately a 22% reduction in the gas permeation of various gases, (H₂, He, CO₂, N₂, and CH₄). Moreover, an improvement of 1.5 times in the gas selectivity was observed for CO₂/CH₄, H₂/CH₄, He/CH₄, and H₂/N₂ compared to pristine polymeric membrane. Hence, such polymer–CNF composite membranes could be suitable for gas‐separation applications with high purity requirements. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46019.     

Reducing the crystallinity of high molecular weight poly (ethylene oxide) using ultraviolet cross-linking for preparation of gas separation membranes

CO₂-selective cross-linked poly (ethylene oxide) (PEO) membranes were prepared by the UV irradiation of high molecular weight PEO in the presence of benzophenone as photo-initiator, which act as a hydrogen-abstracting agent. The main goal was to study the effects of the cross-linking process on the structural properties of hydrogel films intended for the gas separation applications. It was found that the gel fraction, and cross-link density enhanced, and the crystallinity, and the size of spherulites decreased by the cross-linking process. Moreover, the permeation performances for N₂, O₂, CH₄, and CO₂ and the relationship between the gas permeation performances and physical properties were investigated. The results indicated that the degree of cross-linking and crystallinity could be controlled by changing the initiator concentration, as by increasing the initiator content, the crystallinity percent and gas permeability of the membranes decreased, and the gas pair ideal selectivity of CO₂/N₂, CO₂/CH₄, CH₄/N₂, and O₂/N₂ increased.     

Sorption and interactions of gases in polyaniline powders of different doping levels

Sorption of different gases (N₂, O₂, CH₄, and CO₂) were performed on as-synthesized polyemeraldine base, on HCl 4M doped, on NH₄OH 1M undoped, and on HCl 10^?2M redoped powders. In the pressure range examined (100–700 torr), linear sorption isotherms were observed for N₂ and correspond to an ordinary dissolution in Henry's law state. Concerning O₂, CH₄, and CO₂, nonlinear isotherms were evidenced and could be described by the dualmode sorption mechanism proposed for glassy polymers, which consists of the combination of a Henry's type dissolution with a Langmuir sorption in unrelaxed gaps between macromolecular chains. Specific interactions between polyaniline (PANi) and O₂, CH₄, and CO₂, were studied. Gas permeation experiments were performed by using different upstream pressures, P₁, and have confirmed the dissolution of Henry's type for N₂ and the dualmode mechanism for O₂ and CO₂. From the fits of the sorption isotherms, gas solubilities of N₂, O₂, CH₄, and CO₂ were calculated for three different gas pressures and analyzed in terms of gas separation for permeation experiments. © 1995 John Wiley & Sons, Inc.     

Transport properties of gases through integrally skinned asymmetric composite membranes prepared from date pit powder and polysulfone

Studies were conducted on transport properties and separation performance of date pit/polysulfone composite membranes for CO₂, CH₄, N₂, He, and H₂ gases. Date seeds were obtained and processed into powder. Asymmetric flat sheet membrane was prepared by solvent casting method with 2–10 wt % date pit powder. Membrane characterization was done using high pressure gas permeation, X‐ray diffraction, thermogravimetric, and scanning electron microscope analyses. The separation performance and the plasticization resistance property were evaluated in terms of gas permeability, selectivity, and plasticization pressure, respectively. Time dependent performance properties were evaluated up to a pressure of 40 bar for 75 days. Results obtained showed the highest selectivity values of 1.54 (He/H₂), 3.637 (He/N₂), 2.538 (He/CO₂), 2.779 (He/CH₄), 3.179 (H₂/N₂), 3.907 (H₂/CO₂), 1.519 (CH₄/N₂), 1.650 (CO₂/N₂), and 1.261 (CO₂/CH₄) at 10 bar and 35 °C feed pressure and temperature, respectively. The resulting composite membrane showed about 39.50 and 66.94% increase in the selectivity of He/N₂ and CO₂/CH₄, respectively, as compared to the pure polysulfone membrane. Thus, the membrane composites possess some potentials in membrane gas separation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43606.     

Ion beam irradiation effect on gas permeation properties of polyimide films

This study deals with the ion beam irradiation effect on gas permeation properties of polyimide films. 2 MeV α, 500 keV, and 170 keV N⁺ ions were used for modifying the membranes. It was found that there are two different effects according to the implantation dose. In the case of small-dose irradiation, ion implantation causes a raise of permeability both for CH₄ and H₂. When the implantation dose reaches a more important level, the implanted membranes have at the same time high permselectivity for H₂/CH₄ and high permeability for H₂. The relationships between the permeation properties and microstructure of the films are also discussed. © 1995 John Wiley & Sons, Inc.     

The permeation resistance of interface and the directional dependence of permeation in plasma-grafted composite membranes

Composite membranes were prepared by grafting plasma-polymerized films onto the surface of nonporous poly (dimethylsiloxane) films. Gas permeabilities of the composite membranes were measured at 35°C, 1 atm for N₂, 0₂, CO₂ and CH₄. The permeation properties of the composite membrane was analyzed using the series resistance model. There was a great interfacial resistance to CH₄ permeation through the composite membrane. The interfacial resistance was negligible for the other gases. The interfacial resistance seems to be a result of an interfacial layer caused by the interaction between the bulk two layers. For CH₄ gas, the permeation rate through the composite membrane was affected by the direction of flow. The directional dependence was negligible for the other gases.     

Effects of uniaxial drawing and heat-treatment on gas sorption and transport in PVC

Sorption and transport measurements for various gases in rigid poly(vinyl chloride) were made following uniaxial drawing and heat treatment. The permeabilities of He, Ar, N₂, and CH₄ were found to be essentially independent of pressure in PVC while CO₂ showed a complex pressure dependence which varied with prior exposure and degassing history. Sorption isotherms were analyzed by the dual mode sorption model, and the parameters obtained were correlated with the Lennard–Jones potential-well depth of the gas. The Henry's law coefficient for CO₂ was found to be significantly larger than expected which is believed to be the result of a specific interaction with PVC. Uniaxial drawing of PVC above its glass transition caused significant reductions in gas permeabilities, of which roughly one-third is attributable to the accompanying heat treatment rather than molecular orientation per se. The physical state of the polymer was characterized by density, birefringence, and calorimetry. Changes in gas sorption and permeation behavior are discussed in terms of these results.     

Enhanced gas separation properties by using nanostructured PES‐Zeolite 4A mixed matrix membranes

The polymer–zeolite mixed matrix membranes were fabricated by incorporating nanosized or microsized zeolite 4A into polyethersulfone. A comparison of zeolite 4A nanocrystals and microcrystals was made by using SEM, XRD, N₂ adsorption–desorption measurements. Zeolite particles were well‐distributed in the polymer phase, as reflected by the SEM images. The effects of the zeolite 4A particle size on the gas permeation performance were studied. Experimental results demonstrate that mixed matrix membranes exhibit decreased gas permeabilities due to the barrier effect of zeolite particles. The obtained permselectivity is greatly enhanced for He/N₂, H₂/N₂, He/CO₂, and H₂/CO₂ gas pairs, especially for nanosized zeolite 4A mixed matrix membranes. The gas permeation performance difference is observed between the nanostructured and microstructured membranes, which is attributed to a combined effect of different zeolite composition and different particle size. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3800–3805, 2006     

Application of poly (amide-<Emphasis Type="Italic">b</Emphasis>-ethylene oxide)/zeolitic imidazolate framework nanocomposite membrane in gas separation

Mixed matrix membranes (MMMs) are gaining increasing interest in academic and industrial research due to their combined, desirable properties of both polymers and organic/inorganic filler as important materials. In this work, synthesized zeolitic imidazolate framework (ZIF-8) suspension (10–50 wt%) was directly incorporated into a [poly (amide-b-ethylene oxide) Pebax^® 1657] matrix in order to improve the gas separation performance of the membrane. Dynamic light scattering (DLS) analysis showed an average diameter of 77.4 nm for the prepared nanoparticles. The transparent membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffractometry (XRD). These indicated excellent dispersion of nanoparticles, which was achieved by ultrasonication before casting the solution. Incorporation of ZIF-8 as filler in the polymer matrix led to improved thermal and mechanical stability of the membranes. This was confirmed by TGA and tensile analyses, indicating good contacts provided at the polymer/filler interfaces. The effect of ZIF-8 loading (up to 50 wt%) on membrane performance was investigated and it showed an optimum loading of 30 %. Single gas (CO₂, N₂ and CH₄) permeation tests revealed rapid, enhanced permeability of the nanocomposite membranes without significant changes in selectivity (compared to those of the pristine polymeric membrane). The permeability increases for CO₂, CH₄ and N₂ in the optimum Pebax^® 1657/ZIF-8 (30 wt%) membrane were found in the stated order as 111, 88 and 99 %. The study revealed that Pebax^® 1657/ZIF-8 membranes displayed better gas permeation properties compared to those of Pebax^® 1657.     

Gas‐separation properties of amine‐crosslinked polyimide membranes modified by amine vapor

The modification of a polyimide (PI) membrane by aromatic amine vapor was performed in this work to increase the crosslinking of the membrane and to study the effect on gas permeability and the corresponding selectivity. The single‐gas permeability of the membranes at 35 °C was probed for H₂, O₂, N₂, CO₂, and CH₄. From the relationship between the combinations of gases and ideal permselectivities, this study showed that amine‐crosslinked PI membranes tended to increase gas permselectivities exponentially with the increasing difference in gas kinetic diameter. Moreover, this study illustrated that the permeability of the membranes was influenced by the formation rate of amine‐crosslinked networks or chemical structures after the reaction. The membranes had the highest level of permselectivities among crosslinked PI membranes for O₂/N₂, and the H₂/CH₄ permselectivity increased 26 times after vapor modification. Furthermore, the modification method that used aromatic amine vapor produced thin and strongly modified layers. These findings indicate that modification is an advantageous technique for improving gas‐separation performance, even considering thinning. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44569.