Mixed Gas Permeation Experiments Research Articles

Long-term pure- and mixed-gas performance of carbon molecular sieve membranes derived from a tetraphenylethylene-based ladder polymer of intrinsic microporosity (TPE-PIM) for propylene/propane separation

Continuous long-term evaluation of propylene and propane permeation through narrow slit carbon molecular sieve (CMS) membranes is essential for an in-depth study of their steady-state separation performance. CMS membranes are characterized by finely tuned ultramicroporous structures, exceptional thermal and chemical stability, and hold great promise for the energy-intensive separation of propylene and propane. However, the gradual changes in their performance over time due to penetrant-induced structural chain rearrangements have often been overlooked. In this study, we prepared CMS membranes using a polymer of intrinsic microporosity (PIM) with a highly aromatic tetraphenylethylene (TPE) based building block. The presence of bulky and sterically hindered TPE repeat units renders this polymer an excellent precursor for the fabrication of high-performance CMS membranes. The TPE-PIM-based precursor underwent pyrolysis at temperatures ranging from 550 to 700 °C for 1 h. Pure- and mixed-gas permeation tests were accompanied by various characterization techniques to assess the carbonization state of the CMS materials. The CMS pyrolyzed at 700 °C exhibited a decline in pure-gas C3H6/C3H8 selectivity from an initial value of 300 to 161 at steady state over a 20-day period. Even more notable, under equimolar mixed-gas feed conditions, the isotropic CMS film displayed a substantial C3H6/C3H8 selectivity reduction from 214 to 62 over a 24-day period. This performance decline can be attributed to competitive sorption and very slow dilation kinetics, which led to moderately reduced propylene permeability while significantly enhancing propane permeability. Our study suggests that long-term, continuously performed mixed-gas permeation experiments are essential to assess the ‘steady-state’ performance of CMS membranes for mixtures containing highly sorbing feed components, as observed for propylene/propane separation.

Mixed Matrix Membranes Using Porous Organic Polymers (POPs)-Influence of Textural Properties on CO2/CH4 Separation.

Mixed matrix membranes (MMMs) provide the opportunity to test new porous materials in challenging applications. A series of low-cost porous organic polymer (POPs) networks, possessing tunable porosity and high CO2 uptake, has been obtained by aromatic electrophilic substitution reactions of biphenyl, 9,10-dihydro-9,10-dimethyl-9,10-ethanoanthracene (DMDHA), triptycene and 1,3,5-triphenylbenzene (135TPB) with dimethoxymethane (DMM). These materials have been characterized by FTIR, 13C NMR, WAXD, TGA, SEM, and CO2 uptake. Finally, different loadings of these POPs have been introduced into Matrimid, Pebax, and chitosan:polyvinyl alcohol blends as polymeric matrices to prepare MMMs. The CO2/CH4 separation performance of these MMMs has been evaluated by single and mixed gas permeation experiments at 4 bar and room temperature. The effect of the porosity of the porous fillers on the membrane separation behavior and the compatibility between them and the different polymer matrices on membrane design and fabrication has been studied by Maxwell model equations as a function of the gas permeability of the pure polymers, porosity, and loading of the fillers in the MMMs. Although the gas transport properties showed an increasing deviation from ideal Maxwell equation prediction with increasing porosity of the POP fillers and increasing hydrophilicity of the polymer matrices, the behavior of biopolymer-based CS:PVA MMMs approached that of Pebax-based MMMs, giving scope to not only new filler materials but also sustainable polymer choices to find a place in membrane technology.

Thin-Film Composite Matrimid-Based Hollow Fiber Membranes for Oxygen/Nitrogen Separation by Gas Permeation.

In recent years, the need to reduce energy consumption worldwide to move towards sustainable development has led many of the conventional technologies used in the industry to evolve or to be replaced by new alternatives. Oxygen is a compound with diverse industrial and medical applications. For this reason, obtaining it from air is one of the most interesting separations, traditionally performed by cryogenic distillation and pressure swing adsorption, two techniques which are very energetically expensive. In this sense, the implementation of membranes in a hollow fiber configuration is presented as a much more efficient alternative to carry out this separation. The aim of this work is to develop cost-effective multilayer hollow fiber composite membranes made of Matrimid and polydimethylsiloxane (PDMS) for the separation of oxygen and nitrogen from air. PDMS is used as a cover layer but can also enhance the performance of the membrane. In order to compare these two materials, three different configurations are studied. First, integral asymmetric Matrimid hollow fiber membranes were produced using the spinning method. Secondly, by using dip-coating method, a PDMS dense selective layer was deposited on a self-made polyvinylidene fluoride (PVDF) hollow fiber support. Finally, the performance of a dual-layer hollow fiber membrane of Matrimid and PDMS was studied. Membrane morphology was characterized by SEM and separation performance of the membranes was evaluated by mixed-gas permeation experiments. The novelty presented in this work is the manufacture of hollow fiber membranes and the way Matrimid is treated. This makes it possible to develop much thinner dense layers than in the case of flat-sheet membranes, which leads to higher permeance values. This is a key factor when implementing this technology on an industrial scale. Membranes prepared in this work were compared to the current state of the art, reporting quite good performance for the dual-layer membrane, reaching O2 permeance of 30.8 GPU and O2/N2 selectivity of 4.7, with a thickness of about 5-10 μm (counting both selective layers). In addition, the effect of operating temperature on the membrane permeances has been studied experimentally; we analyze its influence on the selectivity of the separation process.

MXene assisted preparation of well-intergrown ZIF-67 membrane for helium separation

Well-intergrown ZIF-67 membranes were prepared by the assistance of laminarly stacked MXene films. Several analytic methods have found that the MXene films, despite being as thin as 90 nm, could host a high amount of Co (II) ions. The Co (II)-MXene films acted as buffer layer and provided anchor sites for nucleation. After solvothermal synthesis, well-intergrown ZIF-67 membranes with a thickness about 4 μm were formed on Co (II)-MXene modified α-Al2O3 disks. Single-gas and mixed-gas permeation experiments showed that the ZIF-67 membranes exhibited excellent gas separation performance and long-term chemical (against CO2 and H2O) and thermal stabilities with a He permeance greater than 6.6 × 10−8 mol m–2 s–1 Pa–1 and selectivities above 13 for the gas mixtures He/N2 and He/CH4, superior to the state-of-the-art MOF membranes.

Influence of ionic liquid-like cationic pendants composition in cellulose based polyelectrolytes on membrane-based CO2 separation

Cellulose acetate (CA) is an attractive membrane polymer for CO2 capture market. However, its low CO2 permeability hampers its application as part of a membrane for most relevant types of CO2 containing feeds. This work investigates the enhancement of CA separation performance by incorporating ionic liquid-like pendants (1-methylimidazol, 1-methylpyrrolidine, and 2-hydroxyethyldimethylamine (HEDMA) on the CA backbone. These CA-based polyelectrolytes (PEs), synthesised by covalent grafting of cationic pendants with anion metathesis, were characterised by NMR, FTIR, DSC/TGA, and processed into thin-film composite membranes. The membrane performance in CO2/N2 mixed-gas permeation experiments shows a decrease in CO2 and N2 permeability and an initial decrease and then gradual increase in CO2/N2 selectivity with increasing HEDMA content. The amount of HEDMA attached to the CA backbone determines overall separation process in bifunctional PEs. This indicates that the hydroxy-substituted cationic pendants alter interactions between PEs network and permeating CO2 molecules, suggesting possibilities for further improvements.

Unprecedentedly Low CO2 Transport through Vertically Aligned, Conical Silicon Nanotube Membranes.

Nanotube membranes could show significantly enhanced permeance and selectivity for gas separations. Up until now, studies have primarily focused on applying carbon nanotubes to membranes to achieve ultrafast mass transport. Here, we report the first preparation of silicon nanotube (SiNT) membranes via a template-assisted method and investigate the gas transport behavior through these SiNT membranes using single- and mixed-gas permeation experiments. The SiNT membranes consist of conical cylinder-shaped nanotubes vertically aligned on a porous silicon wafer substrate. The diameter of the SiNT pore mouths are 10 and 30 nm, and the average inner diameter of the tube body is 80 nm. Interestingly, among the gases tested, we found an unprecedentedly low CO2 permeance through the SiNT membranes in single-gas permeation experiments, exceeding the theoretical Knudsen selectivity toward small gases/CO2 separation. This behavior was caused by the reduction of CO2 permeability through the blocking effect of CO2 adsorbed in the narrow pore channels of the SiNT cone regions, indicating that CO2 molecules have a high affinity to the native silicon oxide layer (∼2 nm) that is formed on the inner walls of SiNTs. SiNT membranes also exhibited enhanced gas permeance and water flux as compared to classic theoretical models and, as such, may prove useful as a new type of nanotube material for use in membrane applications.

Gas Transport in Mixed Matrix Membranes: Two Methods for Time Lag Determination

The most widely used method to measure the transport properties of dense polymeric membranes is the time lag method in a constant volume/pressure increase instrument. Although simple and quick, this method provides only relatively superficial, averaged data of the permeability, diffusivity, and solubility of gas or vapor species in the membrane. The present manuscript discusses a more sophisticated computational method to determine the transport properties on the basis of a fit of the entire permeation curve, including the transient period. The traditional tangent method and the fitting procedure were compared for the transport of six light gases (H2, He, O2, N2, CH4, and CO2) and ethane and ethylene in mixed matrix membranes (MMM) based on Pebax®1657 and the metal–organic framework (MOF) CuII2(S,S)-hismox·5H2O. Deviations of the experimental data from the theoretical curve could be attributed to the particular MOF structure, with cavities of different sizes. The fitting procedure revealed two different effective diffusion coefficients for the same gas in the case of methane and ethylene, due to the unusual void morphology in the MOFs. The method was furthermore applied to mixed gas permeation in an innovative constant-pressure/variable-volume setup with continuous analysis of the permeate composition by an on-line mass-spectrometric residual gas analyzer. This method can provide the diffusion coefficient of individual gas species in a mixture, during mixed gas permeation experiments. Such information was previously inaccessible, and it will greatly enhance insight into the mixed gas transport in polymeric or mixed matrix membranes.

A lithium–aluminosilicate zeolite membrane for separation of CO2 from simulated blast furnace gas

In this study, for the first time, the small pore size (0.28 × 0.37 nm) Li–aluminosilicate zeolite membrane was synthesized for separation of CO2 from H2–CO2 and H2–CO2–N2–CO (simulated blast furnace gas) gas mixtures. Li–aluminosilicate membranes were prepared on porous clay alumina tubes by sonication mediated hydrothermal method using pre synthesized zeolite powders as seeds. The zeolite formation was confirmed by X-ray diffraction pattern and FESEM analysis. The scanning electron micrograph of the membrane, suggested the uniformity of the dense structure of the membrane. Single-gas and mixed-gas permeation experiments through membranes were carried out at 25 °C using H2, CO2 and N2 single-component gases and mixture of H2–CO2, H2–CO2–N2–CO for simulated blast furnace gas composition. Synthesized Li–aluminosilicate zeolite shows appreciable CO2 adsorption capacity at liquid nitrogen temperature compared with other reported zeolites. In case of single gas permeation, membrane shows usual pattern of permeation. For mixture gas, separation efficiency of Li–zeolite membrane increased abruptly compared to the other zeolite membranes. The maximum CO2–H2, CO2–N2 and CO2–CO separation selectivities were found to be 78, 8.7 and 67.3 respectively, with permeance of H2, CO2 and N2 2.21 × 10−7, 1.01 × 10−7 and 0.8 × 10−7 mol m−2 s−1 Pa−1 at 25 °C respectively.

Mixed matrix membranes based on MIL-101 metal–organic frameworks in polymer of intrinsic microporosity PIM-1

This work presents a study on mixed matrix membranes (MMMs) of the polymer of intrinsic microporosity PIM-1, embedding the crystalline Cr-terephthalate metal-organic framework (MOF), known as MIL-101. Different kinds of MIL-101 were used: MIL-101 with an average particle size of ca. 0.2 µm, NanoMIL-101 (ca. 50 nm), ED-MIL-101 (MIL-101 functionalized with ethylene diamine) and NH2-MIL-101 (MIL-101 synthesized using 2-aminoterephthalic acid instead of terephthalic acid). Permeability, diffusion and solubility coefficients and their corresponding ideal selectivities were determined for the gases He, H2, O2, N2, CH4 and CO2 on the “as-cast” samples and after alcohol treatment. The performance of the MMMs was evaluated in relation to the Maxwell model. The addition of NH2-MIL-101 and ED-MIL-101 does not increase the membrane performance for the CO2/N2 and CO2/CH4 separation because of an initial decrease in selectivity at low MOF content, whereas the O2 and N2 permeability both increase for NH2-MIL-101. In contrast, MIL-101 and NanoMIL-101 cause a strong shift to higher permeability in the Robeson diagrams for all gas pairs, especially for CO2, without significant change in selectivity. Unprecedented CO2 permeabilities up to 35,600 Barrer were achieved, which are among the highest values reached with PIM-1 based mixed matrix membranes. For various gas pairs, the permeability and selectivity were far above the Robeson upper bound after alcohol treatment. Short to medium time aging shows that alcohol treated samples with MIL-101 maintain a systematically higher permeability in time. Mixed gas permeation experiments on an aged as-cast sample with 47 vol% MIL-101 reveal that the MMM sample maintains an excellent combination of permeability and selectivity, far above the Robeson upper bound (CO2 = 3500–3800 Barrer, CO2/N2 = 25–27; CO2/CH4 = 21–24). This suggests good perspectives for these materials in thin film composite membranes for real applications.

Effect of Ethylene Oxide Functional Groups in PEBA-CNT Membranes on CO2/CH4 Mixed Gas Separation

Poly (ether-block-amide) /poly (ethylene glycol)/ carbon nanotubes mixed matrix membranes have been successfully fabricated using solvent evaporation method to determine the effect of ethylene oxide groups on the performance of produced membranes. The effects of CNTs (2-8 wt%) and PEG (up to 50 wt%)were investigated in both single and mixed gas test setup in different temperature and pressure. Finally the membranes were structurally characterized using Scanning Electron Microscopy, X-Ray Diffraction, Fourier Transform Infrared Spectroscopy, and Atomic Force Microscopy.Results showed that addition of carbon nanotubes enhanced the gas separation performance of membranes and presences of ether groups in poly ethylene glycol improved the CO2 permeability. Membrane containing 8 wt % carbon nanotubes and 50 wt % poly ethylene glycol showed the best performance with CO2/CH4 selectivity of 45 and CO2permeability of 302 at pressure of 14 bars. Also, mixed gas permeation experiments were carried out and results showed dramatic decrease in CO2 selectivity due to membrane plasticizing. The permeability of CO2 in mixed gas test for membrane containing 50 wt% pol ethylene glycol and 8 wt% was 193 with CO2/CH4 selectivity of 19 in room temperature. Furthermore, membranes produced by 6 and 8 wt% carbon nanotubes and 50 wt% poly ethylene glycol placed above Robeson’s trade-off line. The effect of temperature on performance of fabricated membrane was finally investigated. Results showed an increase in permeability and decrease in selectivity for all membranes.

Tuning the gas separation performance of fluorinated and sulfonated PEEK membranes by incorporation of zeolite 4A

ABSTRACTMixed matrix membranes (MMMs) containing fluorinated‐sulfonated poly(ether ether ketone) (F‐SPEEK) and zeolite 4A filler, were prepared by solution casting. F‐SPEEK with a fixed degree of sulfonation (40%) was used for membrane synthesis. The SEM pictures showed good interfacial adhesion between filler particles and polymer, which was also confirmed by the increase in glass transition temperature of MMMs with increase in filler particles. Pure and mixed gas permeation experiments were carried out to investigate the potential of this membrane material. The results revealed that addition of zeolite 4A fillers enhanced both permeability and selectivity owing to the intrinsic nature of polymer and modified membrane morphology due to filler. The highest permeability obtained for CO2 at 30% filler loading was 49.2 Barrer, while highest selectivities obtained for CO2/CH4 and CO2/N2 were 55 and 58 compared to 47 and 51 for the unfilled polymer, respectively. Intrinsic CO2 solubility of F‐SPEEK was observed to be decreased from 10.7 to 1.9 (10−2) cm3 (STP)/cm3 cmHg with the addition of Zeolite 4A. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45952.

Synthesis and gas permeation properties of a novel thermally-rearranged polybenzoxazole made from an intrinsically microporous hydroxyl-functionalized triptycene-based polyimide precursor

A hydroxyl-functionalized triptycene-based polyimide of intrinsic microporosity (TDA1-APAF) was converted to a polybenzoxazole (PBO) by heat treatment at 460 °C under nitrogen atmosphere. TDA1-APAF treated for 15 min (TR 460) resulted in a PBO conversion of 95% based on a theoretical weight loss of 11.7 wt% of the polyimide precursor. The BET surface area of the TR 460 (680 m2 g−1) was significantly higher than that of the TDA1-APAF polyimide (260 m2 g−1) as determined by nitrogen adsorption at −196 °C. Heating TDA1-APAF for 30 min (TRC 460) resulted in a weight loss of 13.5 wt%, indicating full conversion to PBO and partial main-chain degradation. The TR 460 membrane displayed excellent O2 permeability of 311 Barrer coupled with an O2/N2 selectivity of 5.4 and CO2 permeability of 1328 Barrer with a CO2/CH4 selectivity of 27. Interestingly, physical aging over 150 days resulted in enhanced O2/N2 selectivity of 6.3 with an O2 permeability of 185 Barrer. The novel triptycene-based TR 460 PBO outperformed all previously reported APAF-polyimide-based PBOs with gas permeation performance close to recently reported polymers located on the 2015 O2/N2 upper bound. Based on this study, thermally-rearranged membranes from hydroxyl-functionalized triptycene-based polyimides are promising candidate membrane materials for air separation, specifically in applications where space and weight of membrane systems are of utmost importance such as nitrogen production for inert atmospheres in fuel lines and tanks on aircrafts and off-shore oil- or natural gas platforms. Mixed-gas permeation experiments also demonstrated good performance of the TR 460 membrane for natural gas sweetening with a CO2 permeability of ∼1000 Barrer and CO2/CH4 selectivity of 22 at a typical CO2 wellhead partial pressure of 10 bar.

A Novel Copper(I)-Based Supported Ionic Liquid Membrane with High Permeability for Ethylene/Ethane Separation

For the separation of an ethylene/ethane mixture, a novel copper(I)-based supported ionic liquid membrane (SILM) with high permeability has been fabricated. This SILM was prepared from a polyvinylidene fluoride microporous membrane impregnating the copper(I) based IL which formed by the cuprous chloride (CuCl) and 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]). Scanning electron microscopy, attenuated total reflection Fourier transform infrared spectroscopy, and time of flight mass spectroscopy were used to characterize the SILM. Pure and mixed gas permeation experiments were carried out to investigate the influences of ILs composition, trans-membrane pressure, temperature, and time upon the separation performance. This SILM showed comparable C2H4 permselectivity but outstanding permeability with a long-term stability beyond the reported polymeric membrane upper bound. At the CuCl/[Bmim][Cl] ratio of 2, the C2H4 permeability and permselectivity reached 2653 barrer and 11.8, respectively. Furthermore, t...

Preparation and characterization of ceramic supported ultra-thin (~1 µm) Pd-Ag membranes

This work reports the preparation and characterization of ultra-thin (~1µm thick) Pd-Ag supported membranes for hydrogen purification. Ultra-thin membranes with different thicknesses (ranging from 0.46 to 1.29µm) have been prepared by electroless plating (ELP) technique onto asymmetric tubular porous alumina supports. The membranes have been characterized by single gas and mixed gas permeation experiments at temperatures between 300 and 500°C obtaining a correlation for the membrane permeation as a function of the activation energy and the membrane thickness. Hydrogen permeation results of the ultra-thin Pd-Ag membranes have been compared with other highly permeable membranes reported in the literature and they show some of the highest H2 permeance values. A 1.29µm thick membrane has been tested for 1000h at 400°C and has shown a stable H2 permeance of 9.0−9.4×10−6molm−2s−1Pa−1 with a H2/N2 perm-selectivity between 3300 and 2000 at 100kPa transmembrane pressure difference. The same membrane has been tested with a feed gas mixture of H2/N2/CO with a 15% CO content and H2 binary mixtures containing N2, CH4 and CO2. When tested in a catalyst fluidization environment during 100h, the 1.29µm thick membrane showed stable H2 permeance and H2/N2 perm-selectivity.

Novel sulfonated and fluorinated PEEK membranes for CO2 separation

Abstract Polymeric membranes containing sulfonated and fluorinated poly (ether ether ketone) were prepared by solution casting method. The monomers were pre-sulfonated before the polymerization to avoid the side-effects of polymer post-sulfonation, like low degree of sulfonation and poor mechanical and thermal properties. The degree of sulfonation was varied from 20% to 40% to study its influence on the membrane performance. Pure and mixed gas permeation experiments were performed to evaluate the potential of this novel polymer in separation of CO2 from mixtures containing CH4 and N2. Increasing degree of sulfonation improved the CO2 permeability and selectivity for both gas pairs. The incorporation of fluorinated groups further enhanced the performance of membranes by simultaneous increase in gas permeability and selectivity. Diffusion and solubility measurements were also performed in order to get further insight into the role of sulfonic and fluorinated groups in membrane performance. The comparison of results with literature revealed the promising characteristics of the polymer in industrially relevant gas separations.

A Novel Chemical Surface Modification for the Fabrication of PEBA/SiO2 Nanocomposite Membranes To Separate CO2 from Syngas and Natural Gas Streams

In this work, a novel chemical modification is introduced to fabricate poly(ether-block-amide)/silica (PEBA/SiO2) nanocomposite membranes for the separation of CO2 from syngas and natural gas streams. cis-9-Octadecenoic acid (OA) was utilized for surface modification of the nanoparticles to restrict their agglomeration within the polymeric matrix. To our best knowledge, there is no evidence about the application of this modifier agent for the fabrication of nanocomposite membranes. The separation performance of fabricated membranes was investigated by pure and mixed gas permeation experiments. The incorporation of modified nanoparticles into the polymeric matrix improved the separation performance of the fabricated nanocomposite membranes. For instance, by increasing the loading content of the SiO2 nanoparticles from 0 wt % (the neat PEBA membrane) to 8 wt %, at 25 °C and 2 bar, the ideal selectivity values of CO2/H2, CO2/CH4, and CO2/N2 were improved from 9, 18, and 61 to 17, 45, and 137, respectively.

Mixed-linker zeolitic imidazolate framework mixed-matrix membranes for aggressive CO2 separation from natural gas

Zeolitic imidazolate framework (ZIF) materials are a promising subclass of metal–organic frameworks (MOF) for gas separations. However, due to the deleterious effects of gate-opening phenomena associated with organic linker rotation near the limiting pore apertures of ZIFs, there have been few demonstrations of improved gas separation properties over pure polymer membranes when utilizing ZIF materials in composite membranes for CO2-based gas separations. Here, we report a study of composite ZIF/polymer membranes, containing mixed-linker ZIF materials with ZIF-8 crystal topologies but composed of different organic linker compositions. Characterization of the mixed-linker ZIFs shows that the mixed linker approach offers control over the porosity and pore size distribution of the materials, as determined from nitrogen physisorption and Horváth–Kawazoe analysis. Single gas permeation measurements on mixed-matrix membranes reveal that inclusion of mixed-linker ZIFs yields membranes with better ideal CO2/CH4 selectivity than membranes containing ZIF-8. This improvement is shown to likely occur from enhancement in the diffusion selectivity of the membranes associated with controlling the pore size distribution of the ZIF filler. Mixed-gas permeation experiments show that membranes with mixed-linker ZIFs display an effective plasticization resistance that is not typical of the pure polymeric matrix. Overall, we demonstrate that mixed-linker ZIFs can improve the gas separation properties in composite membranes and may be applicable to aggressive CO2 concentrations in natural gas feeds.

Modeling syngas permeation through a poly dimethyl siloxane membrane by Flory–Rehner theory

Poly dimethyl siloxane (PDMS) membranes show potential for the separation of carbon dioxide from hydrogen in syngas applications due to their strong affinity for CO2. The Flory–Rehner theory of mixing enables the sorption of gases within such a rubbery membrane to be modeled, as long as the Flory–Huggins interaction parameters are known. In this work, mixed gas permeation experiments are used to determine interaction parameters for a range of relevant gas pairs. For the N2–H2 system, the mixed gas performance is comparable to pure gas measurements and indicates that H2 does not interfere with the permeation of N2 through the membrane. In contrast, for the CO2–H2 system, the CO2 permeability falls with increasing H2 partial pressure, attributed to competitive sorption. The effect of a typical hydrocarbon impurity, toluene, upon CO2 and N2 permeability through PDMS was also measured. The addition of this aromatic hydrocarbon caused significant polymer swelling, which required solubility modeling with the Flory–Rehner model. A concentration dependent diffusivity was also required to fit the permeation data. The parameters determined from the laboratory experiments were used to model pilot plant results for a PDMS membrane separating CO2 from syngas, as part of the CO2CRC Mulgrave Project. It was found that the model could effectively predict experimental CO2, N2 and H2 permeabilities.

Copper(I)-containing supported ionic liquid membranes for carbon monoxide/nitrogen separation

In this work, facilitated transport supported ionic liquid membranes (SILMs) were prepared with the room temperature ionic liquid (RTIL) 1-hexyl-3-methylimidazolium chloride ([hmim][Cl]) and the cuprous chloride (CuCl) copper(I) salt to perform the selective separation of CO from N2. Previously, we reported that this solute-carrier system provides large CO/N2 solubility selectivity due to the reversible formation of a CO–copper(I) complex. The RTIL was impregnated in a porous PVDF membrane and pure and mixed gas permeation experiments were performed with continuous gas flow at constant pressure. The effects of different operating conditions were tested, namely pressure, temperature, sweep gas flow rate and liquid membrane composition. The CO permeability through the copper(I)-based SILMs increases with respect to pure [hmim][Cl]–SILMs owing to the CO carrier-mediated transport. On the contrary, the N2 flux is not affected, and therefore, the CO/N2 selectivity is increased. The CO transport through the reactive SILMs is enhanced at higher temperatures and copper(I) concentration. However, mixed gas experiments revealed a slight decrease of CO/N2 selectivity. Regarding membrane stability, SILMs were continuously operated for two weeks without any loss of performance. Additionally, gas diffusion coefficients (~10−10m2s−1) and solute-carrier complex diffusivity (~10–11m2s−1) were calculated in the RTIL media.

Fabrication and testing of a planar microstructured concept module with integrated palladium membranes

A planar microstructured hydrogen separation module has been fabricated to study the hydrogen permeation through free-standing palladium-based membranes (Pd, PdCu and PdAg) with minimal influence by concentration polarization.The membranes were laser-welded directly between two face-to-face arranged stainless-steel sheets with 10 microchannels each (width×depth×length of the channels: 500μm×300μm×2cm).Single gas hydrogen and mixed gas permeation experiments (H2/N2) were conducted between 300 and 400°C. The permeabilities and activation energies of the membranes in this temperature range were calculated.The 12.5μm thick membrane was successfully tested up to 650kPa, indicating that the microchannel plates provide a good mechanical support even for very thin membranes. However, settling of the film into the microchannels on the permeate side was observed due to the overpressure on the retentate side suggesting even finer channels and eventually the use of an additional porous support for very high differential pressure.The concentration polarization effects in the membrane module were evaluated in terms of the film effectiveness factor η which is a familiar concept from heterogeneous catalysis. It could be shown that the microchannel configuration effectively decreases concentration polarization.