Single Gas Permeation Experiments Research Articles

Single-file diffusion and its influence on membrane gas separation: A case study on UTSA-280

Gas permeation in metal-organic framework-based (MOF-based) membranes is often elucidated through the solution-diffusion model, where the adsorption and diffusion of gases play equally vital roles. This study draws attention to a unique phenomenon known as single-file diffusion (SFD) occurring within MOF membranes that possess ultramicropores with dimensions comparable to the gas molecules themselves. When SFD takes place, the separation performance becomes solely reliant on the adsorption quantities on the feed side of the membrane. As a proof of concept, we fabricated a UTSA-280 membrane and subjected it to testing using gas mixtures of CO2/N2 and CO2/CH4. Two crucial observations substantiate the occurrence of single-file diffusion. Firstly, in the gas mixtures, the diffusion coefficients of N2 or CH4 were observed to align closely with that of CO2, despite the intrinsic diffusion coefficients of CO2, N2, and CH4, as determined from single-gas permeation experiments, exhibiting differences. Secondly, the CO2 mole fractions within the adsorption phase closely mirrored those in the gas phase on the permeate side. Given the high adsorption selectivity of UTSA-280 for CO2, the UTSA-280 membrane delivers outstanding permeation selectivity for CO2/N2 (611) and CO2/CH4 (80.7). Our experimental findings are supported by mesoscale kinetic Monte Carlo simulations, which confirmed the relation between the CO2 compositions in the adsorption phase on the feed side and in the gas phase on the permeate side. Furthermore, density functional theory calculations revealed high energy barriers associated with CO2 surpassing its counterparts, rendering such processes unfavorable, thereby reinforcing our experimental findings regarding single-file diffusion.

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.

Nonaqueous Interfacial Polymerization-Derived Polyphosphazene Films for Sieving or Blocking Hydrogen Gas.

A series of cyclomatrix polyphosphazene films have been prepared by nonaqueous interfacial polymerization (IP) of small aromatic hydroxyl compounds in a potassium hydroxide dimethylsulfoxide solution and hexachlorocyclotriphosphazene in cyclohexane on top of ceramic supports. Via the amount of dissolved potassium hydroxide, the extent of deprotonation of the aromatic hydroxyl compounds can be changed, in turn affecting the molecular structure and permselective properties of the thin polymer networks ranging from hydrogen/oxygen barriers to membranes with persisting hydrogen permselectivities at high temperatures. Barrier films are obtained with a high potassium hydroxide concentration, revealing permeabilities as low as 9.4 × 10-17 cm3 cm cm-2 s-1 Pa-1 for hydrogen and 1.1 × 10-16 cm3 cm cm-2 s-1 Pa-1 for oxygen. For films obtained with a lower concentration of potassium hydroxide, single gas permeation experiments reveal a molecular sieving behavior, with a hydrogen permeance of around 10-8 mol m-2 s-1 Pa-1 and permselectivities of H2/N2 (52.8), H2/CH4 (100), and H2/CO2 (10.1) at 200 °C.

Ultra-thin zeolite CHA and FAU membranes for desalination by pervaporation

In the present work, ultra-thin zeolite CHA and FAU membranes, with thicknesses of 600 and 500 nm, respectively, were evaluated for desalination by pervaporation at various temperatures. Single gas permeation experiments were employed to verify high quality of the membranes. At 90 °C, the observed water fluxes for CHA and FAU membranes were as high as 24 and 28 kg/(m2‧h), respectively. A mathematical model was used to estimate the effect of the support. The results showed that the mass transfer resistance of the support reduced the flux. The water flux corrected for the mass transfer resistance over the support was as high as 40 and 51 kg/(m2‧h) at 90 °C for CHA and FAU membranes, respectively. To the best of our knowledge, these are the highest reported water fluxes for desalination by zeolite membranes in a pervaporation process.

Cr-based MOF/IL composites as fillers in mixed matrix membranes for CO2 separation

New composite materials made of bromide-based ionic liquids (ILs) and metal–organic framework (MOF) MIL-101(Cr) were produced using two different ILs. The powdered composites [PMIM][Br]@MIL-101(Cr) and [BMIM][Br]@MIL-101(Cr) were rigorously characterized, and it was confirmed that both ILs were incorporated into the MOF structure. Single-component CO2 and N2 adsorption–desorption isotherms for the pristine MIL-101(Cr) and [BMIM][Br]@MIL-101(Cr), at 303 K and up to 10 bar, showed that the composite has lower gas adsorption capacity and selectivity when compared with the pristine MOF due to the IL incorporation. Mixed Matrix membranes (MMMs) were prepared by the solvent evaporation method, using Matrimid®5218 as the polymeric matrix, and MIL-101(Cr) and [email protected](Cr) composites as fillers with different loadings (10, 20 and 30 wt%). All prepared membranes were dense, except for the Matrimid®5218/[PMIM][Br]@MIL-101(Cr) ones, and their mechanical properties were improved by the presence of the IL in the composite fillers. Single-gas permeation experiments with CO2 and N2 were performed at 303 K for the Matrimid®5218/MIL-101(Cr) and Matrimid®5218/[BMIM][Br]@MIL-101(Cr) membranes, as the Matrimid®5218/[PMIM][Br]@MIL-101(Cr) showed voids. Independently of the filler percentage, the Matrimid®5218/MIL-101(Cr) membranes showed superior CO2 permeability than the Matrimid®5218/[BMIM][Br]@MIL-101(Cr) ones. In every case, the best CO2/N2 selectivity was achieved with a 20 wt% of filler loading, which indicates the existence of an optimum loading that yields the best membrane separation performance.

Poly (ether-block amide) thin-film membranes containing functionalized MIL-101 MOFs for efficient separation of CO2/CH4

In this study, a post-synthesis modification method was used to graft tetraethylenepentamine (TEPA) on MIL-101(Cr) metal organic framework (MOF). The post-modified amine grafted MIL-101(Cr) was incorporated into poly (ether-block amide) (Pebax® 1657) to fabricate thin-film nanocomposite (TFN) membrane. A series of single gas permeation experiments were carried out through the synthesized membranes to evaluate the effect of amine functional groups on the gas permeability and selectivity. BET, FT-IR, XRD, and FE-SEM results indicated that the amine groups were grafted on MIL-101(Cr) successfully. Moreover, the morphological studies of synthesized membranes demonstrated the formation of uniform and non-defected composite selective layer over the polyethersulfone sublayer. Gas permeation tests revealed that the best performance of TFN membranes obtained for sample containing 5 wt% TEPA-MIL-101 at 4 bar; in which the CO2 permeability increased by 63% (34.6 Barrer) as compared with Pebax neat membrane (21.8 Barrer). Meanwhile, an outstanding CO2/CH4 selectivity of 46.3 was achieved, which was 110% greater than the parent neat Pebax membrane (21.1). The results showed that TFN membranes have great potential in CO2 separation at low pressure.

Characterization of defect-containing zeolite membranes by single gas permeation experiments before and after calcination

The synthesis of defect-free zeolite gas separation membranes is challenging. In addition to the desired transport by surface and Knudsen diffusion through the zeolite pores, the undesired transport by Knudsen and viscous flows through the defects are typically present to a different extent. This paper proposes a method to assess the extent of the undesirable defect-transport in zeolite membranes, which is essential for fine-tuning membrane synthesis protocols. Also, knowing the undesirable defect transport contribution allows determining the corrected diffusivity of gases in the zeolite crystals incorporated in the membrane. The latter is the intrinsic property of the zeolite. The method relies on gas permeation tests with not-adsorbed and adsorbed gases before and after the membrane's calcination. The adsorption isotherms of the gases with the zeolite crystals incorporated into the membrane are also required.We have demonstrated the proposed characterization method using silicalite-1 zeolite membranes prepared by a pore-plugging method inside porous TiO2 supports. The validity of the parameters, which characterize the crystal and defect transport, were verified by comparing the experimental and predicted permeances of He, N2, CO2 and CH4 at different pressures. Also, the calculated corrected diffusivity values of CO2 and CH4 in the silicalite crystals of 1.69⋅10−8m2⋅s−1 and 6.51⋅10−8m2⋅s−1, respectively, are comparable to the values reported in the literature.

Polyoctahedral Silsesquioxane Hexachlorocyclotriphosphazene Membranes for Hot Gas Separation.

There is a need for gas separation membranes that can perform at high temperatures, for example, for CO2 capture in industrial processes. Polyphosphazenes classify as interesting materials for use under these conditions because of their high thermal stability, hybrid nature, and postfunctionalization options. In this work, thin-film composite cyclomatrix polyphosphazene membranes are prepared via the interfacial polymerization reaction between polyhedral oligomeric silsesquioxane and hexachlorocyclotriphosphazene on top of a ceramic support. The prepared polyphosphazene networks are highly crosslinked and show excellent thermal stability until 340 °C. Single gas permeation experiments at temperatures ranging from 50 to 250 °C reveal a molecular sieving behavior, with permselectivities as high as 130 for H2/CH4 at the low temperatures. The permselectivities of the membranes persist at the higher temperatures; at 250 °C H2/N2 (40), H2/CH4 (31) H2/CO2 (7), and CO2/CH4 (4), respectively, while maintaining permeances in the order of 10–7 to 10–8 mol m–2 s–1 Pa–1. Compared to other types of polymer-based membranes, especially the H2/N2 and H2/CH4 selectivities are high, with similar permeances. Consequently, the hybrid polyphosphazene membranes have great potential for use in high-temperature gas separation applications.

CO2/N2 and O2/N2 Separation Using Mixed‐Matrix Membranes with MOF‐74 Nanocrystals Synthesized Via Microwave Reactions

Due to their large surface areas and unique gas adsorption properties, mixed‐matrix membranes (MMMs) with metal–organic frameworks (MOFs) have been extensively studied in relation to various gas separations. In the present paper, we report the quick synthesis of MOF‐74 (M = Mg, Mn, Co, Ni) nanocrystals by microwave reactions and the fabrication of MMMs for use in CO2/N2 and O2/N2 separation. The scanning electron microscopy and energy dispersive X‐ray spectroscopy analysis revealed the homogenous distribution of the MOF‐74 nanocrystals within the polydimethylsiloxane (PDMS). The single gas permeation experiments showed the enhanced CO2/N2 and O2/N2 selectivity by adding the MOF‐74 nanocrystals to the PDMS. This enhanced CO2/N2 and O2/N2 selectivity may be due to the affinity of CO2 and O2 toward the Lewis acidic sites of the MOF‐74.

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.

Effect of Thermal Soak Time Towards Polyimide Based-Carbon Tubular Membrane

Tubular carbon membrane (TCM) was prepared form BTDA-TDI/MDI (P-84) polyimide (PI) has a main precursor that combines with nanocrystalline cellulose (NCC) through controlled carbonization condition. Consideration of the thermal soaking time through the heating process is needed to maintain the proficiency of resultant TCM’s. Thermal soaking time of 30 minutes, 60 minutes, 90 minutes, and 120 minutes was investigated to study the gas properties of the final TCM’s. In the course of TCM’s separation, single gas permeation experiments of CO2 and N2 are performed to investigate the transport mechanism. The PI / NCC TCM’s developed at 120 min of thermal soak time from this study showed the most impressive CO2/N2 performance, selectivity of 66.32±2.18 respectively.

Synthesis and evaluation of a nanocomposite hydroxy sodalite/ceramic (HS/ceramic) membrane for pre-combustion CO2 capture: Characterization and permeation test during CO2/H2 separation

Greenhouse gases (GHGs), secondary products from combustion of fossil fuel, have been instrumental to global warming which causes climate change. However, carbon capture, storage and utilization (CCSU) is one of the promising ways to reducing CO2 emission from large point sources via pre-combustion CO2 capture. Membrane technology has been identified as one of the promising technologies for pre-combustion CO2 capture, but availability of membranes with high membrane integrity (high CO2 flux, high selectivity, good chemical and thermal stability) is a major challenge in advancing this technology. Against this background, synthesis and gas permeation of a nanocomposite hydroxy sodalite/ceramic (HS/α-Al2O3) membrane, prepared via pore-plugging hydrothermal synthesis technique (PPH), are hereby reported. Morphology, purity of the sodalite particles (obtained from the bottom of the autoclave) and quality of the as-prepared membrane were checked using scanning electron microscopy (SEM), X-ray Diffraction (XRD), and Basic Desorption Quality Test (BDQT) (for the membrane). Single gas permeation experiments were carried out on the membrane at 298 K via Wicke-Kallenbach method (W-K) using pure component CO2 and H2 to gain insight into separation performance of the membrane. The single gas permeation results reveal H2 permeance and CO2 permeance of 7.37 × 10−8 mol·s−1·m−2·Pa−1 and 1.14 × 10−8 mol·s−1·m−2·Pa−1, respectively, with ideal selectivity of 6.46. In addition, H2 permeation through the membrane was adequately described with the well-known Maxwell-Stefan (M-S) model.

Temperature-Dependent Gas Transport Behavior in Cross-Linked Liquid Crystalline Polyacrylate Membranes

Stable, cross-linked, liquid crystalline polymer (LCP) films for membrane separation applications have been fabricated from the mesogenic monomer 11-(4-cyanobiphenyl-4′-yloxy) undecyl methacrylate (CNBPh), non-mesogenic monomer 2-ethylhexyl acrylate (2-EHA), and cross-linker ethylene glycol dimethacrylate (EGDMA) using an in-situ free radical polymerization technique with UV initiation. The phase behavior of the LCP membranes was characterized using differential scanning calorimetry (DSC) and X-ray scattering, and indicated the formation of a nematic liquid crystalline (LC) phase above the glass transition temperature. The single gas transport behavior of CO2, CH4, propane, and propylene in the cross-linked LCP membranes was investigated for a range of temperatures in the LC mesophase and the isotropic phase. Solubility of the gases was dependent not only on the condensability in the LC mesophase, but also on favorable molecular interactions of penetrant gas molecules exhibiting a charge separation, such as CO2 and propylene, with the ordered polar mesogenic side chains of the LCP. Selectivities for various gas pairs generally decreased with increasing temperature and were discontinuous across the nematic–sotropic transition. Sorption behavior of CO2 and propylene exhibited a significant change due to a decrease in favorable intermolecular interactions in the disordered isotropic phase. Higher cross-link densities in the membrane generally led to decreased selectivity at low temperatures when the main chain motion was limited by the lack of mesogen mobility in the ordered nematic phase. However, at higher temperatures, increasing the cross-link density increased selectivity as the cross-links acted to limit chain mobility. Mixed gas permeation measurements for propylene and propane showed close agreement with the results of the single gas permeation experiments.

Highly permeable and selective tubular zeolite CHA membranes

Highly permeable and selective tubular zeolite CHA membranes with a thickness of about 450 nm and a length of 100 mm and an inner diameter of 7 mm were evaluated by single gas permeation experiments and for separation of an equimolar CO2/CH4 mixture. The membranes displayed high H2 and CO2 single gas permeances of 55 × 10−7 mol m−2 s−1 Pa−1 and 94 × 10−7 mol m−2 s−1 Pa−1, respectively, and a very low SF6 permeance of 3 × 10−9 mol m−2 s−1 Pa−1. The highest observed mixture separation factor was 99 with CO2 permeance of 60 × 10−7 mol m−2 s−1 Pa−1 at a feed pressure of 5 bar and permeate pressure of 0.12 bar. The corresponding CO2 flux was 1.46 mol m−2 s−1. The highest observed flux was 1.98 mol m−2 s−1 with a separation factor of 52 at a feed pressure of 10 bar and permeate pressure of 0.12 bar at room temperature. To the best of our knowledge, this is the first report describing highly permeable and selective tubular CHA membranes. The results indicate that the membranes have a great potential for industrial separation of CO2 from natural gas and biogas.

Synthesis of graphene oxide membranes on polyester substrate by spray coating for gas separation

Graphene oxide (GO) membranes have shown promising gas separation characteristics specially for hydrogen showing potential for industrial applications. However, GO membranes made by filtration, the most common synthesis method, contain wrinkles affecting their gas separation characteristics and the method itself is difficult to scale up. In this work, high quality GO membranes are made from GO suspension by easily scalable spray coating technique (and also by filtration method for comparison) on hydrophilic polyester track etch substrates. GO sheet suspensions of large sheet average size (33 µm) and dilute concentrations are used to minimize GO sheet edge-to-edge interactions and minimize extrinsic wrinkle formation. Single gas permeation and separation experiments of equimolar H2/CO2 binary mixture were conducted to evaluate the permeation and separation characteristics of prepared membranes. GO membranes prepared by spray coating offer gas characteristics similar to those made by filtration, however using dilute GO suspension in spray coating reduces the formation of extrinsic wrinkles causing reduction in the porosity of the inter-sheet pathway where the transport of large gas molecules dominates. This study demonstrates an efficient, scalable and cost-effective approach for synthesizing large area GO membranes with enhanced hydrogen separation.

Bis(triethoxysilyl)ethane (BTESE)-derived silica membranes: pore formation mechanism and gas permeation properties

Based on their high performance in gas and liquid-phase separations, 1,2-bis(triethoxysilyl)ethane (BTESE)-derived organosilica membranes have attracted much attention. To improve performance, we focused on the acid molar ratio (AR) in sol preparation and its effect on the pore formation mechanism during sol-gel processing. BTESE-derived sols with AR = 10−4–100 were prepared, and the effect of the AR on the gel structure was evaluated in detail via FT-IR, nuclear magnetic resonance (NMR), N2 adsorption, and positron annihilation lifetime (PAL) measurements. The chemical structure of the gels was confirmed by FT-IR and NMR and showed that sols with the largest number of silanol groups (AR = 10−2) experienced a significant increase in condensation during the firing process. The porous structures of fired gels characterized by N2 adsorption and PAL measurement showed that the AR = 10−2 fired gel consisted of a larger number of small pores that had formed during the firing process. Single-gas permeation experiments showed high H2 permeance (5–9 × 10−7 mol/(m2 Pa s)) and H2/CF4 selectivity (700–20,000). The gas permselectivity (He/H2, H2/N2, and H2/CF4) was highest for the intermediate AR (=10−2), which corresponded to the greatest amount of silanol groups in unfired gels and confirmed that small pores had formed from the condensation of silanol groups during firing.

Investigation and comparison of mixed matrix membranes composed of polyimide matrimid with ZIF – 8, silicalite, and SAPO – 34

Mixed Matrix type membranes (MMMs) containing 10wt% of either silicalite, SAPO – 34, and ZIF – 8 in polyimide Matrimid were fabricated and tested for their suitability to separate a number of gas mixtures by conducting single gas permeation experiments using H2, CO2, N2, and CH4 gases. The transport of these gases through the polymeric and inorganic membrane phases, as well as their interfacial voids, have additionally been distinguished from each other by fabricating MMMs containing non-calcined fillers of silicalite and SAPO-34. The ideal selectivities that have been calculated using the experimentally determined permeabilities can be attributed to the relative pore size and volume of the fillers in each membrane, as well as changes to the mobility of polymer chains in the vicinity of fillers. Due to its large pore volume as well as simultaneous reductions of interfacial voids and polymer chain mobility, ideal selectivities and gas permeabilities that are higher than those achieved by a neat Matrimid membrane have been achieved using ZIF – 8 containing MMMs. For the ZIF – 8 containing membranes, the largest permeabilities for H2, CO2, N2, and CH4 were found to be 51.1, 15.5, 0.64, and 0.54 barrer, respectively. This H2 permeability in particular was found to be the most outstanding out of all of the membranes that have been tested, and ideal selectivities for the separation of H2/N2, and H2/CH4, were found to be 80.3 and 102, respectively. The performance of the membranes that were fabricated using uncalcined silicalite and SAPO-34 also suggest that the structure of the Matrimid phase is altered by the addition of these fillers as greater selectivities at the expense of permeability were also achieved using these MMMs in comparison to a neat Matrimid membrane.

Synthesis and characterization of nanocomposite SAPO‐34/ceramic membrane for post‐combustion CO2 capture

AbstractThin‐film SAPO‐34 membranes can separate CO2 efficiently. However, crack formation due to thermal expansion mismatch between the SAPO‐34 crystals and the support occurs at high operating temperatures, thereby resulting in a dramatic loss. Nanocomposite architecture SAPO‐34 membranes prepared via pore‐plugging hydrothermal synthesis could overcome this problem. In this study, nanocomposite SAPO‐34 membranes were synthesized via pore‐plugging hydrothermal and evaluated for N2/CO2 separation. Physico‐chemical property of the as‐synthesized membranes was checked with X‐ray diffraction, scanning electron microscope, thermal gravimetric analyser, and Fourier transform infrared. The X‐ray diffraction pattern reveals characteristic peaks associated with the rhombohedral crystal type of SAPO‐34; thermal gravimetric analyser shows a high thermal stability, Fourier transform infrared spectra indicate the presence of the D6R and T–O vibrations which form an essential part of the SAPO‐34 structure, and scanning electron microscope images of the membranes reveal cubic morphology of the SAPO‐34 crystals embedded in the ceramic support. Single gas permeation experiments using pure component of CO2 and N2 conducted to evaluate the separation performance of the membranes during post‐combustion CO2 capture reveal that ideal selectivity increased significantly for multistage pore‐plugging hydrothermal synthesis. The Maxwell–Stefan model describes adequately the CO2 permeation behaviour through the membrane as well. However, the membrane flux reduced owing to increase in membrane thickness. © 2017 Curtin University and John Wiley & Sons, Ltd.

Enhanced gas transport properties of mixed matrix membranes consisting of Matrimid and RHO type ZIF-12 particles

Zeolitic imidazolate frameworks (ZIF) have been showed as potential active inorganic fillers in high-performance gas separation membranes. Among them, zeolitic imidazolate framework-12 crystals were synthesized as a porous filler material by alcohol-based solution method using benzimidazole–toluene interactions and they were incorporated into a commercial glassy polyimide Matrimid 5218 with various ZIF-12 loadings (0, 10, 20, 30, 40wt.%), as the continuous phase. As-synthesized ZIF-12 was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), multipoint Brunauer–Emmett–Teller (BET) surface analysis, Fourier Transform Infrared Spectroscopy (FT-IR) and Thermogravimetric Analysis (TGA). SEM images of ZIF-12 particles assert regular external surfaces with a rhombic dodecahedron structure. Matrimid mixed matrix membranes (MMMs) loaded with different amounts of ZIF-12 were prepared by solution casting method and characterized by XRD, FT-IR, TGA and SEM analyses. Our findings showed that there was a good dispersion and wetting of ZIF-12 particles in the continuous phase. Gas transport properties of the membranes were investigated by single gas permeation experiments of H2, CO2 and CH4 at 4bar feed pressure and 35°C. The permeability values increased as the ZIF-12 loading increased up to 20wt.%. However, at higher loadings, 30 and 40wt.%, the permeability decreased for all gases and the CO2/CH4 and H2/CH4 selectivities increased depending on the influence of the ZIF-12 filler. The maximum ideal separation factor for CO2/CH4 and H2/CH4 were found about 66.70 and 212.00, significantly higher than the pure polymer ideal separation factor.

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.