Permeation Of He Research Articles

Gas permeation properties of bridged-type organosilica membranes at extremely low temperatures and the application to oxygen separation

A bridged-type organosilica, bis(triethoxysilyl)methane (BTESM) membrane was evaluated in detail for single-gas permeation at temperatures ranging from −130 to −200 °C, and for binary (O2/He, O2/N2) separation at 30 and -115 °C, respectively. The permeance of He, Ar, and N2 demonstrated a trend of activated diffusion as permeance increased with an increase in the temperature; O2 permeance, however, reached its maximum value at about −80 °C. O2 permeance increased with a decrease in the temperature (30 to −80 °C), and permeance then gradually decreased (−80 to −130 °C), which demonstrates surface diffusion. In the case of O2/He binary separation, both O2 and He permeated according to molecular sieving at 30 °C, but at −115 °C, O2/He selectivity was enhanced approximately 10-fold due to permeation blockage by adsorbed O2. On the other hand, in the case of O2/N2 binary separation at −115 °C, the effect of permeation blocking by adsorbed O2 permeance was lessened due to the effect of competitive adsorption, which translated to a level of O2/N2 selectivity that was only 1.5-fold higher than that at 30 °C.

Gas Transport Mechanisms through Molecular Thin Carbon Nanomembranes.

Molecular thin carbon nanomembranes (CNMs) synthesized by electron irradiation induced cross-linking of aromatic self-assembled monolayers (SAMs) are promising 2D materials for the next generation of filtration technologies. Their unique properties including ultimately low thickness of ≈1nm, sub-nanometer porosity, mechanical and chemical stability are attractive for the development of innovative filters with low energy consumption, improved selectivity, and robustness. However, the permeation mechanisms through CNMs resulting in, e.g., an ≈1000 times higher fluxes of water in comparison to helium have not been yet understood. Here, a study of the permeation of He, Ne, D2 , CO2 , Ar, O2 and D2 O using mass spectrometry in the temperature range from room temperature to ≈120°C is studied. As a model system, CNMs made from [1″,4',1',1]-terphenyl-4-thiol SAMs are investigated. It is found out that all studied gases experience an activation energy barrier upon the permeation which scales with their kinetic diameters. Moreover, their permeation rates are dependent on the adsorption on the nanomembrane surface. These findings enable to rationalize the permeation mechanisms and establish a model, which paves the way toward the rational design not only of CNMs but also of other organic and inorganic 2D materials for energy-efficient and highly selective filtration applications.

Design, synthesis and characterization of novel fluorinated polyimide membranes with bulky pendant for gas transport

AbstractThree novel fluorinated polyimides (PIs) were synthesized via one‐step solution polycondensation from a new diamine monomer, 4‐(3‐methoxy‐4‐(difluoromethoxy)phenyl)‐2,6‐bis(4‐aminophenyl)pyridine, and three commercially available aromatic dianhydrides. The solubility, thermal, optical, hydrophobic and gas transport properties of the obtained PIs were investigated. The results demonstrated that these polymers present good solubility in dimethylformamide, N‐methylpyrrolidone, dimethylsulfoxide, dimethylacrylamide, CHCl3, tetrahydrofuran and CH2Cl2 at room temperature or upon heating. Meanwhile, they displayed excellent thermal properties with glass transition temperature of 261–345 °C, weight loss temperatures at 10% of 518–523 °C as well as char yield of 60–62% at 800 °C in nitrogen atmosphere. Furthermore, the PI membranes have good hydrophobic properties with water contact angle value in the range 90.1–92.0°. Moreover, they show excellent optical properties, with cut‐off wavelength (λcut‐off) values of 368–381 nm and wavelength values at 80% transmittance (λ80%) of 421–462 nm. The pure gas permeabilities of He, CO2, O2 and N2 of the PI membranes were measured by the method of constant volume–variable pressure. The PI containing 4,4′‐(hexafluoroisopropyl)diphthalic anhydride moiety exhibits the largest molecular chain spacing and free volume, giving the best gas transport performance in this work. Molecular simulation results show that the introduction of fluorine‐containing structure and bulky pendant into polymer backbones is beneficial for gas transport. © 2023 Society of Industrial Chemistry.

Machine learning enables interpretable discovery of innovative polymers for gas separation membranes.

Polymer membranes perform innumerable separations with far-reaching environmental implications. Despite decades of research, design of new membrane materials remains a largely Edisonian process. To address this shortcoming, we demonstrate a generalizable, accurate machine learning (ML) implementation for the discovery of innovative polymers with ideal performance. Specifically, multitask ML models are trained on experimental data to link polymer chemistry to gas permeabilities of He, H2, O2, N2, CO2, and CH4. We interpret the ML models and extract valuable insights into the contributions of different chemical moieties to permeability and selectivity. We then screen over 9 million hypothetical polymers and identify thousands that lie well above current performance upper bounds, including hundreds of never-before-seen ultrapermeable polymer membranes with O2 and CO2 permeability greater than 104 and 105 Barrers, respectively. High-fidelity molecular dynamics simulations confirm the ML-predicted gas permeabilities of the promising candidates, which suggests that many can be translated to reality.

High-throughput computational screening of Covalent−Organic framework membranes for helium purification

Currently, helium purification is carried out by the heat-driven cryogenic distillation process, which is prohibitively energy-intensive and capital-intensive. As an alternative, covalent-organic frameworks (COFs)-based membrane separation technology is considered to be cost-efficient and technically feasible. In this study, a high-throughput computational screening strategy was proposed for the rapid determination of high-performing COF membranes for this particular application. A geometric analysis-based prescreening process was carried out on 688 experimentally synthesized COFs, resulting in 665 COF candidates with pore limited diameter (PLD) no less than 3.8 Å. Subsequently, molecular simulations were performed to estimate the henry coefficients and self-diffusion coefficients of N2, H2, and CH4 in each COF. Based on the results, the membrane selectivity and permeability of all the COFs were calculated, from which 23 high-performing COF membranes were identified. Additionally, the performances of these 23 COF membranes for a ternary mixture of He/N2/CH4 were computationally examined, five of which were highly preferable to permeate He over N2 or CH4. The results indicated that a large number of COF membranes exceeded the performance upper limit of polymer membranes owing to their high He permeability. Additionally, the relation between the PLD of COFs and the corresponding separation performances was investigated. Finally, He permeability, as well as He/CH4 and He/N2 selectivity of mixed matrix membranes were estimated by using the Maxwell model. The results revealed that the addition of COFs into pure polymers significantly improved the permeability of He up to 11689 Barrer.

Gas Permeability, Fractional Free Volume and Molecular Kinetic Diameters: The Effect of Thermal Rearrangement on ortho-hydroxy Polyamide Membranes Loaded with a Porous Polymer Network.

Mixed-matrix membranes (MMMs) consisting of an ortho-hydroxy polyamide (HPA) matrix, and variable loads of a porous polymer network (PPN) were thermally treated to induce the transformation of HPA to polybenzoxazole (β-TR-PBO). Two different HPAs were synthesized to be used as a matrix, 6FCl-APAF and tBTpCl-APAF, while the PPN used as a filler was prepared by reacting triptycene and trifluoroacetophenone. The permeability of He, H2, N2, O2, CH4 and CO2 gases through these MMMs are analyzed as a function of the fraction of free volume (FFV) of the membrane and the kinetic diameter of the gas, allowing for the evaluation of the free volume. Thermal rearrangement entails an increase in the FFV. Both before and after thermal rearrangement, the free volume increases with the PPN content very similarly for both polymeric matrices. It is shown that there is a portion of free volume that is inaccessible to permeation (occluded volume), probably due to it being trapped within the filler. In fact, permeability and selectivity change below what could be expected according to densities, when the fraction of occluded volume increases. A higher filler load increases the percentage of inaccessible or trapped free volume, probably due to the increasing agglomeration of the filler. On the other hand, the phenomenon is slightly affected by thermal rearrangement. The fraction of trapped free volume seems to be lower for membranes in which the tBTpCl-APAF is used as a matrix than for those with a 6FCl-APAF matrix, possibly because tBTpCl-APAF could approach the PPN better. The application of an effective medium theory for permeability allowed us to extrapolate for a 100% filler, giving the same value for both thermally rearranged and non-rearranged MMMs. The pure filler could also be extrapolated by assuming the same tendency as in the Robeson’s plots for MMMs with low filler content.

Improving Gas Selectivity in Membranes Using Polymer-Grafted Silica Nanoparticles

Herein, we demonstrate that tuning of structural parameters and material chemistry enables control of the permeability and selectivity of gases (CO2, He, and CH4) in membranes based on poly(butyl methacrylate)-grafted nanoparticles (PGNs). Our data show that the presence of nanoparticles and the overall dense packing of grafted chains noticeable in PGNs with low grafting density have an adverse effect on the diffusivity of gases. This effect is compensated by an improvement in the solubility of CO2 gas promoted by the silica nanoparticle surface, yielding a substantial improvement in the permeability of CO2 versus CH4. In membranes with high grafting density, changes in the structural arrangements and alterations in the membrane porosity, evident from small-angle X-ray scattering and positron annihilation lifetime spectroscopy, positively influence the permeability of He and CO2 gases. In contrast, CH4 permeability in the same membranes is significantly suppressed, suggesting the formation of a unique, highly selective environment for gas separation. As a result, an improvement of up to 50% in selectivity for gas pairs containing large CH4 molecules is observed. Our studies provide fundamental insights into the role that structural parameters play in gas transport through polymer membranes, laying a foundation for the rational design of membranes with improved permeability and selectivity.

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.

ZIF-95 as a filler for enhanced gas separation performance of polysulfone membrane.

Metal–organic frameworks (MOFs) are found to be promising porous crystalline materials for application in gas separation. Considering that mixed matrix membranes usually increase the gas separation performance of a polymer by increasing selectivity, permeability, or both (i.e., perm-selectivity), the zeolitic imidazole framework-95 (ZIF-95) MOF was dispersed for the first time in polysulfone (PSF) polymer to form mixed matrix membranes (MMMs), namely, ZIF-95/PSF. The fabricated ZIF-95/PSF membranes were examined for the separation of various gases. The characterization of solvothermally synthesized ZIF-95 was carried out using different analyses such as powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), porosity measurements, etc. ZIF-95 was mixed with PSF at 8%, 16%, 24%, and 32% weight percent to form different loading MMMs. SEM analysis of membranes revealed good compatibility/adhesion between the MOF and polymer. The permeability of He, H2, O2, CO2, N2, and CH4 were measured for the pure and composite membranes. The ideal selectivity of different gas pairs were calculated and compared with reported mixed matrix membranes. The maximum increases in permeabilities were observed in 32% loaded membrane; nevertheless, these performance/permeability increases were at the expense of a slight decrease of selectivity. In the optimally loaded membrane (i.e., 24 wt% loaded membrane), the permeability of H2, O2, and CO2 increased by 80.2%, 78.0%, and 67.2%, respectively, as compared to the pure membrane. Moreover, the selectivity of H2/CH4, O2/N2, and H2/CO2 gas pairs also increased by 16%, 15%, and 8% in the 24% loaded membrane, respectively.

Nanocomposites of polyimide with Various Modified LDHs: Synthesis, characterisation and towards improvement of, morphology, thermal stabilities, mechanical properties, gas permeation and gas selectivity

ABSTRACT Novel polyimide (PI) nanocomposite films were synthesised from diamine monomer (diamine 1B) and Pyromellitic dianhydride (PMDA) with various modified layered double hydroxides (LDHs) particles via solution intercalation polymerisation to poly(amic acid)s, followed by thermal imidization. Modified LDHs particles, including LDH-amino benzoate (M-LDHs) were prepared with the coprecipitation method. The intercalation of PI chains among the LDHs particles was examined using wide-angle X-ray diffraction (XRD) and electron microscopy (TEM) techniques. TEM photographs showed that most LDH layers were dispersed homogeneously into the matrix polymer on the nanoscale, although some particles of LDHs were agglomerated. Moreover, the addition of only a small amount of LDHs particles was enough to improve the thermal stabilities and mechanical properties of PI hybrid films. The thermo-optical properties were measured by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and ultraviolet-visible (UV–vis) spectrometry. As anticipated, though the gas permeability of pure gases, viz., He, N2, CH4 and CO2 exhibited decrease, it was not monotonous. A marked decrease in permeability of gases like CO2 and CH4, in comparison to relatively lower decrease in permeability of He was observed, especially at higher LDH loading. An increase in selectivity: α(He/CO2) and α(He/CH4), especially at higher LDH loading indicated the capability of nanocomposites to tune the selectivity favourably.

Polyimide based mixed matrix membranes incorporating Cu-BDC nanosheets for impressive helium separation

Incompatibility between particles and polymers has the adverse consequence on the performance of mixed matrix membranes (MMMs).To overcome this problem, MMMs containing Cu-BDC nanosheets with two various polyimides (6FDA-DAM and Matrimid) were fabricated and tested for He separation. High aspect ratio of nanosheets (more than 100) was confirmed by TEM and AFM Analyses. FESEM images of MMMs showed that the nanosheets were uniformly distributed all over the matrices and there was no symptom of micro scale polymer-filler phase void up to 15 wt%. Also due to the interface interaction established between two phases, rigidification of chains happened and resulted in increasing Tg and decreasing FFV of polymers. Addition of particles to matrices led to the permeability of He increased slightly until 9 wt% loading, but it was reduced at 12 and 15 wt%. Actually, the oriented stacking of nanosheets caused the permeability of CH4 and N2 reduced significantly and gave rise to developed ideal selectivities. The best MMMs for both polymers was observed at loading of 15 wt%, so that for 6FDA-DAM based MMM, He/CH4 and He/N2 ideal selectivities enhanced by 2570 and 2320% compared to pure 6FDA-DAM and surpassed the 2008 Robeson upper bound.

Gas transport properties of PDMS-coated reverse osmosis membranes

We report a systematic study of the adaptation of polyamide reverse osmosis (RO) membranes for gas separation applications. The RO membranes examined in this study contained defects or pores in the polyamide selective layer that compromised gas selectivity. These membranes were surface-coated with poly(dimethylsiloxane) (PDMS) to caulk the defects, and pure-gas permeances of He, H2, CO2, and CH4 were measured at 35 °C, and upstream pressure ranging from 3 to 16 atm. After a PDMS coating was applied, the pure-gas selectivities increased and were comparable to those of typical aromatic polyamide membranes. Pure-gas permeances of coated RO membranes were also constant or slightly decreased with increasing upstream pressure, suggesting that PDMS had filled and eliminated the defects. In addition, CO2 and CH4 mixed-gas (50/50) permeation tests were performed at 35 °C and fugacities ranging from 3 to 15 atm. CO2 did not appear to plasticize the thin polyamide selective layer of the coated RO membranes. CO2/CH4 mixed-gas selectivities were about 20% higher than pure-gas selectivities, presumably due to dual-mode competitive sorption effects.

Matrimid® 5218 based mixed matrix membranes containing metal organic frameworks (MOFs) for helium separation

Mixed matrix membranes (MMMs) based on two different MOFs (Cu-BTC and Cu-BDC) dispersed in Matrimid® 5218 were studied. The synthesized particles were characterized by N2 sorption measurements, FTIR, SEM, TGA and XRD. Also, SEM, XRD, TGA, FTIR and DSC analyses were used to evaluate the structure of the prepared membranes. The MMMs were tested in separation of helium from CH4 and N2 at 35 °C and feed pressure of 5 bar. The effect of operating temperature and feed pressure on the separation performance of MMMs was investigated. The cross sectional SEM micrographs showed good adhesion between fillers and the polymer, however at 30 wt. % loading of Cu-BTC, non-selective voids were found in some areas. For the MMMs with 20 wt. % loading of Cu-BTC, permeability of He was found 49.7 Barrer and ideal selectivities for He/CH4 and He /N2 were 217.1 and 168.5, respectively. The MMM comprising 30 wt. % of Cu-BDC was chosen as the best membrane with ideal selectivities of He/CH4 = 257.9 and He /N2 = 193.4, which developed by 96.7 and 96.2 % compared to pure Matrimid.

Effects of surface pretreatment and deposition conditions on the gas permeation properties and flexibility of Al2O3 films on polymer substrates by atomic layer deposition

The effects of surface pretreatment and deposition conditions on the gas permeation properties—including permeability of He, O2, and H2O; the size; and the density of permeation-enhancing defects—and mechanical flexibility of Al2O3 films on polymer substrates by atomic layer deposition (ALD) were investigated to develop flexible gas barrier films for organic and flexible electronics. Pretreating polyimide (PI) and poly(ethylene terephthalate) (PET) substrates with an aqueous KOH solution greatly lowered the gas permeability of the ALD Al2O3 films as a result of improved affinity between the substrate surface and the ALD precursors. Varying the ALD conditions—including lengthening the precursor exposure, elevating the deposition temperature, and changing the precursor sequence—enhanced physisorption of ALD precursors on the polymer substrate, which improved nucleation of the ALD films to reduce defects in the films and lower their gas permeability. Activation energy for permeation determined from the temperature dependence of the permeability of the ALD films indicated that the ALD films deposited under the optimized condition contained smaller and few permeation-enhancing defects. The optimized ALD films possessed a low water vapor transmission rate of ~ 10−6 g/m2 day that met the stringent requirement of organic and flexible electronics, while also exhibiting excellent mechanical flexibility by withstanding repeated bending with small increases in gas permeability. Our results provide valuable insights into the development of flexible barrier thin films for the encapsulation of organic and flexible electronics.

Polymer of Intrinsic Microporosity (PIM-1) Membranes Treated with Supercritical CO2

Polymers of intrinsic microporosity (PIMs) are a promising membrane material for gas separation, because of their high free volume and micro-cavity size distribution. This is countered by PIMs-based membranes being highly susceptible to physical aging, which dramatically reduces their permselectivity over extended periods of time. Supercritical carbon dioxide is known to plasticize and partially solubilise polymers, altering the underlying membrane morphology, and hence impacting the gas separation properties. This investigation reports on the change in PIM-1 membranes after being exposed to supercritical CO2 for two- and eight-hour intervals, followed by two depressurization protocols, a rapid depressurization and a slow depressurization. The exposure times enables the impact contact time with supercritical CO2 has on the membrane morphology to be investigated, as well as the subsequent depressurization event. The density of the post supercritical CO2 exposed membranes, irrespective of exposure time and depressurization, were greater than the untreated membrane. This indicated that supercritical CO2 had solubilised the polymer chain, enabling PIM-1 to rearrange and contract the free volume micro-cavities present. As a consequence, the permeabilities of He, CH4, O2 and CO2 were all reduced for the supercritical CO2-treated membranes compared to the original membrane, while N2 permeability remained unchanged. Importantly, the physical aging properties of the supercritical CO2-treated membranes altered, with only minor reductions in N2, CH4 and O2 permeabilities observed over extended periods of time. In contrast, He and CO2 permeabilities experienced similar physical aging in the supercritical treated membranes to that of the original membrane. This was interpreted as the supercritical CO2 treatment enabling micro-cavity contraction to favour the smaller CO2 molecule, due to size exclusion of the larger N2, CH4 and O2 molecules. Therefore, physical aging of the treated membranes only had minor impact on N2, CH4 and O2 permeability; while the smaller He and CO2 gases experience greater permeability loss. This result implies that supercritical CO2 exposure has potential to limit physical aging performance loss in PIM-1 based membranes for O2/N2 separation.

Experimental investigation of the ideal selectivity of MFI-ZSM-5 zeolite-type membranes for a first evaluation of the separation of hydrogen isotopologues from helium

In future fusion power plants, the tritium (T) breeding inside the reactor is a key aspect to ensure the so-called tritium self-sufficiency. The continuous availability of the fuel for further fusion reactions requires the continuous separation of small molecules such as hydrogen isotopologues (e.g., HT) from helium. Pressure-driven separation with membranes is a promising method to fulfill these requirements, especially if molecular-sieving membranes are available to separate these gas species. In this work, the single gas permeances of He, H2 and D2 were measured with a MFI-ZSM-5 zeolite-type tubular membrane. These experiments were performed in the membrane’s temperature range: 298–398K. At these temperatures, a transition in the transport regime was observed at 360K, which is attributed to the transition from surface-diffusion dominant to gas-translational diffusion dominant. Using the measured permeances, the permselectivities for H2/He and D2/He were calculated. In the temperature range tested, the permselectivities exceed the Knudsen selectivity, indicating that the membrane is of rather high-quality. Instead, the H2/D2 permeances ratio was around the Knudsen ratio (i.e., ∼1.41). Moreover, the permeances of the binary mixture H2/D2, at the whole concentration range, were also measured at 298K to study the isotopic effects on the transport through the MFI-ZSM-5 membrane. We found that the mixed gas behaves macroscopically as a hydrogen isotopologue molecule, and its permeance falls with Meff-0.5, where Meff is the effective mass of the mixture determined by the concentrations of H2 and D2. Using this result, the Q2 permeances and the Q2/He permselectivities (where Q = H, D, T) for the other hydrogen isotopologues (i.e., HD, HT, DT and T2) were also calculated.

Mechanistic insights into porous graphene membranes for helium separation and hydrogen purification

Porous graphene (PG) and nitrogen-substituted PG monolayers of 3N-PG and 6N-PG were designed as effective membranes for the separation of He and H2 over Ne, Ar, N2, CO, and CH4 by using density functional theory. Results showed that PG and 3N-PG exhibited suitable pore sizes and relatively high stabilities for He and H2 separation. PG and 3N-PG membranes also presented excellent He and H2 selectivities over Ne, Ar, N2, CO and CH4 at a wide temperature range. 6N-PG membrane exerted unexceptionable permeances of the studied gases, especially He and H2, which could remarkably improve the separation efficiency of He and H2. Analyses on the most stable adsorption configurations and maximum adsorption energies indicated weak Van der Waals interactions between the gases and the three PG-based membranes. Microscopic permeation process analyses based on the minimum energy pathway, energy profiles, and electron density isosurfaces elucidated the remarkable selectivities of He over Ne/CO/N2/Ar/CH4 and H2 over CO/N2/CH4 and the high permeances of He and H2 passing through the three PG-based membranes. This work not only highlighted the potential use of the three PG-based membranes for He separation and H2 purification but also provided a superior alternative strategy to design and screen membrane materials for gas separation.

Sol-gel processed magnesium-doped silica membranes with improved H2/CO2 separation

Magnesium-doped silica membranes were synthesized and a large increase in H2/CO2 permselectivity is achieved as compared to undoped silica membranes. Three magnesium concentrations were studied, namely 10, 15 and 20mol%, in order to find the optimal Mg-concentration for the highest H2/CO2 separation performance. The physical properties of these sol-gel derived Mg-doped silica gels and membranes were characterized by dynamic light scattering, X-ray diffraction and high-resolution scanning electron microscopy. After the incorporation of magnesium into amorphous silica network, the membrane structure remained amorphous. Membrane performance was tested by single gas permeance of He, H2, CO2, N2 and CH4. With 20mol% Mg doping, H2/CO2 permselectivity values of more than 350 were achieved with a H2 permeance of 70 × 10−9molm−2s−1Pa−1. For pure silica membranes, a H2/CO2 permselectivity of 9 was observed with a H2 permeance of 526 × 10−9molm−2s−1Pa−1.

Poly(vinylalcohol)-Tetraethoxysilane based NaA Zeolite Composite Membrane by Primary Growth Technique: Gas Permeation and Water-Ethanol Pervaporation Study

ABSTRACTPoly(vinylalcohol)-tetraethoxysilane based NaA zeolite composite membranes were prepared onto the inner side of porous alumina support tube via primary crystallization processes at 100°C for 4 h. Crystallization behaviour of the prepared NaA zeolite membranes was confirmed by XRD and FTIR studies. FESEM analysis revealed dense microstructure of the membrane with thickness of 15-20 µm. Single gas permeation of He, N2 and CO2 was measured with NaA zeolite membrane. Maximum permselectivity values of He/N2 and He/CO2 were found to be 43.55 and 46.27, respectively. Pervaporation behaviour for the separation of ethanol/water mixture was studied with the membrane. Starting with 90% ethanol, 95.2% ethanol concentration was achieved within 600 min of pervaporation experiment.

Synthesis and Transport Properties of Novel MOF/PIM-1/MOF Sandwich Membranes for Gas Separation.

Metal-organic frameworks (MOFs) were supported on polymer membrane substrates for the fabrication of composite polymer membranes based on unmodified and modified polymer of intrinsic microporosity (PIM-1). Layers of two different MOFs, zeolitic imidazolate framework-8 (ZIF-8) and Copper benzene tricarboxylate ((HKUST-1), were grown onto neat PIM-1, amide surface-modified PIM-1 and hexamethylenediamine (HMDA) -modified PIM-1. The surface-grown crystalline MOFs were characterized by a combination of several techniques, including powder X-ray diffraction, infrared spectroscopy and scanning electron microscopy to investigate the film morphology on the neat and modified PIM-1 membranes. The pure gas permeabilities of He, H2, O2, N2, CH4, CO2 were studied to understand the effect of the surface modification on the basic transport properties and evaluate the potential use of these membranes for industrially relevant gas separations. The pure gas transport was discussed in terms of permeability and selectivity, highlighting the effect of the MOF growth on the diffusion coefficients of the gas in the new composite polymer membranes. The results confirm that the growth of MOFs on polymer membranes can enhance the selectivity of the appropriately functionalized PIM-1, without a dramatic decrease of the permeability.