Search

Membrane separation is an energy-efficient and environmentally friendly process. Two-dimensional (2D) molecular sieving membranes featuring unique nanopores and low transport resistance have the potential to achieve highly permeable and selective mixture separation with low energy consumption. High-aspect-ratio zeolite nanosheets with intrinsic molecular-sieving pores perpendicular to the layers are desirable building blocks for fabricating high-performance 2D zeolite membrane. However, a wider application of 2D zeolitic membranes is restricted by the limited number of recognized zeolite nanosheets. Herein, we report a swollen layered zeolite, ECNU-28, with SZR topology and eight-member ring (8-MR, 3.0 Å×4.8 Å) pores normal to the nanosheets. It can be easily exfoliated to construct 2D membrane, which shows a high hydrogen selectivity up to 130 from natural gas and is promising for hydrogen purification and greenhouse gas capture., (© 2023 Wiley-VCH GmbH.)

The hydrogenation of sequestrated CO2 to methanol can reduce CO2 emission and establish a sustainable carbon circuit. However, the transformation of CO2 into methanol is challenging because of the thermodynamic equilibrium limitation and the deactivation of catalysts by water. In the present work, different reactor types have been evaluated for CO2 catalytic hydrogenation to methanol. Best results have been obtained in a bifunctional catalytic membrane reactor (CMR) based on a zeolite LTA membrane and a catalytic Cu‐ZnO‐Al2O3‐ZrO2 layer on top. Due to the in situ and rapid removal of the produced water from the catalytic layer through the hydrophilic zeolite LTA membrane, it is effective to break the thermodynamic equilibrium limitation, thus significantly increasing the CO2 conversion (36.1 %) and methanol selectivity (100 %). Further, the catalyst deactivation by the produced water can be effectively inhibited, thus maintaining a high long‐term activity of the CMR. [ABSTRACT FROM AUTHOR]

A seeding-free synthesis method is developed for preparation of oriented zeolite LTA membranes by using 1,4-phenylene diisocyanate (PDI) as a molecular linker. Before hydrothermal synthesis, -NCO groups are introduced with the functionalization of Al2O3 supports by PDI. A thin, well intergrown zeolite LTA membrane with a thickness of about 4.0 µm can be formed on the PDI-modified Al2O3 supports. The zeolite LTA membrane displays high pervaporation performances for dehydration of alcohols. At 90°C, the separation factor of the zeolite LTA membrane is 4480 for dehydration of 95 wt% ethanol/water mixtures, with a high water flux of 3.4 kg·m−2·h−1. [ABSTRACT FROM AUTHOR]

A one-step synthesis strategy is developed to prepare a novel superhydrophobic zeolitic imidazolate framework F-ZIF-90 by using a fluorine-functionalized imidazolate as an organic linker. The F-ZIF-90 shows high water-stability and superhydrophobicity, thus it is very promising for oil removal. Through in situ growth of F-ZIF-90 on a polydopamine (PDA) modified sponge, the resulting F-ZIF-90@PDA@sponge composite shows high adsorption capacities for various oils and organic liquids ranging from 1600 wt% to 4800 wt%. [ABSTRACT FROM AUTHOR]

A sandwich FAU-LTA zeolite dual-layer membrane has been developed and used as a catalytic membrane reactor for the synthesis of dimethyl ether (DME). In the top H-FAU layer with mild acidity, methanol is dehydrated to DME. The other reaction product, water, is removed in situ through a hydrophilic Na-LTA layer, which is located between the porous alumina support and the H-FAU top layer. The combination of mild acidity with the continuous removal of water results in high methanol conversion (90.9 % at 310 °C) and essentially 100 % DME selectivity. Furthermore, owing to the selective and continuous removal of water through the Na-LTA membrane, catalyst deactivation can be effectively suppressed. [ABSTRACT FROM AUTHOR]

The separation of CO2/CH4is reported in detail by using zeolitic imidazolate framework (ZIF-8) membrane which was prepared on 3-aminopropyltriethoxysilane modified Al2O3tube through microwave heating synthesis. Attributed to the preferential adsorption affinity of CO2over CH4and a narrow pore window of 0.34 nm, the ZIF-8 membrane shows high separation performances for the separation of CO2/CH4mixtures. For the separation of equimolar CO2/CH4mixture at 100°C and 2 bar feed (1 bar permeate) pressure, a CO2permeance of 1.02 × 10−8mol/m2· s· Pa and a CO2/CH4selectivity of 6.8 are obtained, which is promising for CO2separation. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Pure and dense ZIF-90 membranes with shape-selectivity were prepared. [•] With APTES modification, the membrane permselectivity increases. [•] For the separation of CO2/CH4 mixture, a good CO2/CH4 selectivity of 4.7 is obtained. [ABSTRACT FROM AUTHOR]

Abstract: A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure zeolite LTA membranes on 3-chloropropyltrimethoxysilane (CPTMS) functionalized supports. Through the functionalization of supports by using CPTMS, the nucleation and growth of a thin, well intergrown zeolite LTA membrane could be promoted on various porous supports such as Al2O3 disks and tubes, and TiO2 disks, as well as on dense supports such as stainless steel, PTFE, and glass disks. The SEM and XRD characterizations indicate that a relative thin but dense and phase-pure zeolite LTA membrane with a thickness of about 3.0μm can be formed on the porous Al2O3 and TiO2 disks by crystallization at 60°C for 24h, and no cracks, pinholes or other defects were observed in the membrane layer. The zeolite LTA membranes prepared on CPTMS-functionalized Al2O3 disks were evaluated in single gas permeation and mixed gas separation. It is found that the zeolite LTA membranes prepared on CPTMS-modified Al2O3 disks show molecular sieving in gas separation. For binary mixtures at 20°C and 1bar, the mixed gas separation factors of H2/CO2, H2/N2, H2/CH4, H2/C3H8 and H2/C3H6, are found to be 7.4, 6.8, 5.2, 15.3 and 36.8, which are higher than the corresponding Knudsen coefficients. [Copyright &y& Elsevier]

Abstract: A facile strategy for the layer-by-layer synthesis of sandwich-like zeolite LTA membranes by using 3-aminopropyltriethoxysilane (APTES) as modifier is reported. APTES reacts with surface hydroxyls and forms a covalently bonded siloxane interlayer. APTES treatment is helpful to promote nucleation and growth of the zeolite LTA layer on solid surfaces. Further, the covalently bonded self-assembled siloxane film can protect the already formed LTA layer from dissolution and transformation during the next hydrothermal LTA synthesis step, thus facilitating the formation of well intergrown and phase-pure multi-layer zeolite LTA membranes. The multi-layer zeolite LTA membranes display molecular sieving performance, and each additional LTA layer improves the selectivity of the sandwich-like LTA layer stack. In mixed gas separation at 100°C, the mixture separation factors for equimolar mixtures of H2/CO2, H2/N2, H2/CH4 and H2/C3H8, on the single/multi-layer LTA zeolite membranes in the Na+ state are found to be 6.3, 5.6, 4.3 and 6.5 (single-layer), 8.8, 7.2, 5.8 and 12.6 (double-layer), and 12.5, 8.6, 6.5 and 19.3 (triple-layer). [Copyright &y& Elsevier]

Abstract: A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure zeolite FAU membranes using 3-aminopropyltriethoxysilane (APTES) as covalent linker between the FAU layer and the alumina support. APTES acts as molecular linker for anchoring the FAU precursors onto the support surface to promote the nucleation and the formation of a thin, well intergrown FAU membrane. Additionally, at the pH of zeolite FAU crystallization (about 11), the zeta potential of the alumina support is changed by APTES-treatment from strongly negative to neutral, which will be helpful to reduce the electrostatic rejection between the negatively charged precursor species and the alumina support. The SEM and XRD characterizations indicate that a relative thin but dense and phase-pure FAU zeolite membrane with a thickness of about 2.5μm can be formed on the α-Al2O3 support after crystallization at 75°C for 24h, and no cracks, pinholes or other defects are visible in the membrane layer. The zeolite FAU membranes prepared on APTES-modified Al2O3 supports display higher separation selectivities than those prepared on non-modified Al2O3 support. For binary mixtures at 100°C and 1bar, the mixed gas separation factors of H2/CO2, H2/N2, H2/CH4 and H2/C3H8, are found to be 6.5, 6.0, 4.0 and 11.1, respectively, which are higher than the corresponding Knudsen coefficients. Further, relative high H2 permeances of about 4.0×10−7 molm−2 s−1 Pa−1 can be obtained through the FAU membrane due to the thin layer and the relative wide pores of 0.74nm. [Copyright &y& Elsevier]

Abstract: In pioneering papers Corma et al. reported the synthesis of the Al-free zeolite ITQ-29 with LTA topology by using supramolecular self-assembled molecules as the organic structure directing agent (SDA). However, the SDA used to synthesize ITQ-29 is not commercial and rather difficult to synthesize and purify. Thus the development of a more convenient and more effective method for the synthesis of ITQ-29 is highly desired. Therefore, in this communication we propose a facile and reproducible method to synthesize uniform and well-shaped ITQ-29 crystals by using the crown ether Kryptofix 222 as the SDA. [Copyright &y& Elsevier]

Abstract: MTN-type (Zeolite Socony Mobil Thirty-Nine) zeolite was prepared at 473K by a novel method through self-assembling of a supramolecular compound called 2,4,6-tris (4-pyridyl) triazine (TPT) in DMF (N,N-dimethylformamide). The effects of fluoride, DMF and germanium on the synthesis of MTN-type zeolite were investigated. The crystallization was facilitated by adding fluoride to the synthesis solution, resulting in the formation of highly crystalline MTN samples, while some amorphous phase was observed in fluoride-free batches. DMF was required to obtain a highly crystalline MTN sample, since TPT dissolves easier in DMF than in water, thus facilitating the self-assembling of TPT into a 3D network to structure the MTN framework. The MTN structure could be synthesized at low germanium content (Ge/Si≤0.18), while AST (AlPO4-sixteen) as a foreign phase is formed at high germanium substitution (Ge/Si≥0.5). [Copyright &y& Elsevier]

Abstract: Synthesis conditions for the preparation of uniform and well-shaped ITQ-29 crystals, i.e. synthesis time and the chemical composition of the batch such as the contents of water, structure-directing agent, hydrofluoric acid and germanium, were investigated at 423K. The gels were prepared with molar compositions of (1− x)SiO2: xGeO2: yROH: (0.5− y)TMAOH: zHF: wH2O, where x was varied from 0 to 1, y from 0 to 0.5, z from 0 to 0.5, and w from 7 to 80. The crystal morphology and size, phase purity and Si/Ge ratio of the crystals were characterized by SEM, XRD and EDXS, respectively. For Corma’s standard recipe, a crystallization time of 5days is found to be optimum for the synthesis of ITQ-29 crystals in this study. The crystal size increases with increasing dilution; crystal sizes of 1, 7, 12 and 30μm are obtained for water contents w =7, 30, 40 and 80, respectively. An appropriate amount of ROH and TMAOH is required to form uniform and phase pure ITQ-29 crystals. High quality ITQ-29 crystals can be formed not only at neutral but also at alkaline and acidic conditions although the crystals morphology and size are different. Without germanium or without silicon in the starting gel, no ITQ-29 crystals can be obtained. Without silicon in the batch, germanium oxide crystallizes as AST crystals. The Si/Ge ratio of the synthesis batch is found to be reflected by the ITQ-29 and AST crystals. [Copyright &y& Elsevier]

Abstract: Thin NaA zeolite membranes, with uniform and small crystals, were prepared on the tubular α-Al2O3 support by adding a small amount of tetramethylammonium hydroxide (TMAOH) in the clear synthesis solution. The as-synthesized NaA zeolite membranes were characterized by XRD and SEM. The permeation properties of the membranes were evaluated by pervaporation and gas permeation. The effects of TMAOH amount on membrane formation and permeation properties were investigated. By addition of suitable amount of TMAOH in the clear synthesis solution, the crystals size of NaA zeolite could be remarkably reduced from about 10μm to 3–4μm, and the membrane thickness correspondingly reduced from about 16μm to 5μm. The thinner membrane prepared by adding TMAOH in the clear synthesis solution, with uniform and small crystal, displayed higher perm-selective properties than that without adding TMAOH. For the as-synthesized NaA zeolite membrane prepared with adding suitable amount of TMAOH (x =1), the separation factor (water/isopropanol) was 4700 and the flux was 1.67kg/(m2 h), which were higher than that without adding TMAOH of 339 and 1.08kg/(m2 h), respectively. The ideal separation factor of H2/N2 was 6.60, higher than that without adding TMAOH of 3.41. [Copyright &y& Elsevier]

Abstract: Uniform and dense NaA zeolite membrane was prepared by hydrothermal synthesis method together with microwave heating and conventional heating. The properties of the as-synthesized zeolite membrane were investigated by XRD, SEM and pervaporation evaluation for dehydration of 95 wt.% isopropanol/water mixture at 343 K, respectively. After microwave heating, the α-Al2O3 support surface was covered with homogeneous zeolite nuclei, which facilitated to form uniform, pure and dense NaA zeolite membrane in the following conventional heating process. High quality NaA zeolite membrane, i.e., with a separation factor (water/isopropanol) of 10,000 and a flux of 1.44 Kg/(m2 h), could be hydrothermal synthesized together with microwave heating and conventional heating. [Copyright &y& Elsevier]

Abstract: Uniform and dense NaA zeolite membranes were synthesized on the tubular α-Al2O3 support with a vacuum-assisted method by using low vacuum. The effect of vacuum degree on the formation of the NaA zeolite membrane was investigated. With the assistance of the vacuum, the negative influence of the gravitation force could be effectively reduced. Therefore, the zeolite particles could transport to cover the entire area of the support surface homogeneously, which facilitated formation of uniform and dense zeolite membranes. With the assistance of the vacuum, most zeolite particles migrated to the support surface for membrane formation, and the amount of crystals forming in the liquid phase could be greatly reduced. In addition, zeolite particles could be transported to the support surface rapidly, increasing the rate of dense membrane formation. The pervaporation properties of the as-synthesized zeolite membranes were evaluated by dehydration of 95wt.% isopropanol/water mixtures at 343K. The as-synthesized NaA zeolite membrane prepared with the vacuum-assisted method (i.e., with the assistance of 10mmHg vacuum degrees), showed good pervaporation properties. The separation factor (water/isopropanol) was 3781 and the flux was 1.49kg/m2h, respectively. Based on the observed results, the formation mechanism of zeolite membrane with vacuum-assisted method was discussed. [Copyright &y& Elsevier]

Abstract: Uniform and dense NaA zeolite membranes were prepared on the tubular porous α-Al2O3 supports in the electric field, where the charged zeolite particles attracted and transported to the support surface for membrane preparation homogeneously. The membranes properties were characterized by XRD, SEM and pervaporation for dehydration of 95wt% isopropanol/water mixture at 343K, respectively. The applied potential had great effect on membrane morphology, membrane thickness and separation performance. Under the action of the applied electric field, the negatively charged zeolite particles could migrate to the support surface homogenously and rapidly, facilitating to form uniform and dense membranes in a short time. Most zeolite particles transported to the support surface for membrane formation in the electric field, which increased the percentage of the product contained in the support surface and thus fully utilized the zeolite particles. High-quality NaA zeolite membrane, i.e., with a separation factor (water/isopropanol) of 3281 and a flux of 1.24kg/(m2 h), could be prepared with the electrical potential of 1.0V. [Copyright &y& Elsevier]

Abstract: Uniform and dense NaA zeolite membranes were prepared on the α-Al2O3 support by electrophoretic technique. The membrane morphology and membrane thickness were investigated by XRD, SEM and pervaporation properties for dehydration of 95wt.% isopropanol/water mixture at 343K, respectively. Under the action of the applied electric field, the negatively charged zeolite particles could migrate to the support surface homogenously and rapidly, forming uniform and dense membranes in a short time. High quality NaA zeolite membrane, with a separation factor (water/isopropanol) of 3281 and a flux of 1.24kg/m2 h, could be prepared by electrophoretic technique with the electrical potential of 1V. The formation mechanism of zeolite membrane in the electric field is discussed. [Copyright &y& Elsevier]

A-type zeolite membranes were successfully synthesized on tubular α-Al2O3 supports by secondary growth method with vacuum seeding. In the seeding process, a thin, uniform and continuous seeding layer was closely attached to the support surface by the pressure difference between the two sides of the support wall. The effects of seed particle size, suspension concentration, coating pressure difference and coating time on the membrane and its pervaporation properties were investigated. The as-synthesized membranes were characterized by XRD and SEM. The quality of the membranes was evaluated by the pervaporation dehydration of 95wt.% isopropanol/water mixture at 343K. High quality A-type zeolite membranes can be reproducibly prepared by the secondary growth method with vacuum seeding under the conditions: seed particle size of 500–1200nm, suspension concentration of 4–8g/l, coating pressure difference of 0.0100–0.0250MPa and coating time of 45–180s. [Copyright &y& Elsevier]

A-type zeolite membranes were prepared on the nonporous metal supports by using electrophoretic technique. The as-synthesized membranes were characterized by XRD and SEM. The effect of the applied potential on the formation of the A-type zeolite membrane was investigated, and the formation mechanism of zeolite membrane in the electric field was discussed. The results showed that the negative charged zeolite particles could migrate to the anode metal surface homogenously and rapidly under the action of the applied electric field, consequently formed uniform and dense membranes in short time. The applied potential had great effect on the membrane formation, and more uniform and denser zeolite membranes were prepared on the non- porous metal supports with 1 V potential. [ABSTRACT FROM AUTHOR]

In this study, dense and phase-pure zeolite FAU membrane has been prepared on α-Al 2 O 3 tube using a seeding-free synthesis strategy. 3-aminopropyltriethoxysilane (APTES) acts as a molecular linker for anchoring the FAU precursors onto the support surface to promote the nucleation and the formation of a thin, well intergrown zeolite FAU membrane. The obtained membranes are employed for desalination of seawater by pervaporation. With the increase of the synthesis time from 12 h to 24 h at 75 °C, the water fluxes of the zeolite FAU membranes reduce from 4.22 kg m −2 h −1 to 3.42 kg m −2 h −1 at 75 °C due to the increase of the thickness of the zeolite FAU membranes, while the ions rejections increase from 99% to 99.9%. For the zeolite FAU membrane which was prepared at 75 °C for 20 h, with increasing the feed temperature from 30 °C to 90 °C, the water fluxes increase from 0.96 kg m −2 h −1 to 5.64 kg m −2 h −1 , and all the ions rejections of the zeolite FAU membrane are above 99.8%. Note that the zeolite FAU membranes show high separation performances for seawater desalination, even for desalination of 10 wt% seawater, the developed zeolite FAU membranes are very promising in seawater desalination. [ABSTRACT FROM AUTHOR]

The hydrogenation of sequestrated CO2 to methanol can reduce CO2 emission and establish a sustainable carbon circuit. However, the transformation of CO2 into methanol is challenging because of the thermodynamic equilibrium limitation and the deactivation of catalysts by water. In the present work, different reactor types have been evaluated for CO2 catalytic hydrogenation to methanol. Best results have been obtained in a bifunctional catalytic membrane reactor (CMR) based on a zeolite LTA membrane and a catalytic Cu‐ZnO‐Al2O3‐ZrO2 layer on top. Due to the in situ and rapid removal of the produced water from the catalytic layer through the hydrophilic zeolite LTA membrane, it is effective to break the thermodynamic equilibrium limitation, thus significantly increasing the CO2 conversion (36.1 %) and methanol selectivity (100 %). Further, the catalyst deactivation by the produced water can be effectively inhibited, thus maintaining a high long‐term activity of the CMR. [ABSTRACT FROM AUTHOR]

In the present work, we report a new road to enhance the gas separation performances of the zeolite Na-LTA membrane by tuning the pore size of zeolite LTA through silver cation exchange. Through the functionalization of the alumina support by using 3-aminopropyltriethoxysilane (APTES), a thin, phase-pure and well intergrown zeolite Na-LTA membrane with a thickness of about 5.0 µm can be facilely prepared on the APTES-modified macroporous α-Al 2 O 3 tube. After a following silver exchange treatment of the as-synthesized zeolite Na-LTA membranes, the sodium ions in zeolite Na-LTA framework are replaced by silver ions, thus forming zeolite Ag-LTA membranes with a narrower pore diameter. The zeolite Ag-LTA membranes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). It is found that both the morphology and structure of the zeolite Na-LTA membrane keep unchanged after silver-exchange, and no cracks, pinholes or other defects are observed in the membrane layer. The zeolite Ag-LTA membrane shows high hydrogen selectivity due to the reduction of pore size of the zeolite Ag-LTA. For the separation of the binary mixture at 50 °C and 2.0 bar, the separation factor of H 2 /C 3 H 8 is α≈120.8, which by far exceeds α≈19.4 of the starting Na-LTA membrane, and are also much higher than the separation factors previously reported for the H 2 /C 3 H 8 mixture on zeolite membranes. [ABSTRACT FROM AUTHOR]

Through bio-inspired polydopamine modification of the ceramic support surface, dense and reproducible zeolitic imidazolate framework (ZIF) membranes have been developed for the first time for seawater desalination by pervaporation. Demonstrated by both experimental and simulation studies, the developed ZIF membranes show high desalination performances attributing to the small pore size of the ZIF membranes, which is exactly in between the size of water molecules and hydrated ions. The ZIF membranes show a high stability in seawater. At 25, 50, 75 and 100 °C, the water fluxes through the ZIF-8 membrane are 5.8, 8.1, 10.8, and 13.5 kg/(m 2 ·h), respectively, with a high ion rejection of over 99.8%, which is promising for seawater desalination by ionic sieving. [ABSTRACT FROM AUTHOR]

Highly hydrogen-permselective zeolitic imidazolate framework ZIF-8 membranes are prepared on coarse and macroporous Al 2 O 3 tubes through a repeated synthesis strategy for the separation of H 2 /CO 2, H 2 /CH 4 , and H 2 /C 3 H 8 mixtures. Since the amino-groups of 3-aminopropyltriethoxysilane (APTES) can coordinate to the free Zn 2+ centers and thus bind the growing nano-crystals directly, the nucleation and growth of well intergrown ZIF-8 membranes could be promoted through a repeated synthesis of the ZIF-8 layer on APTES-modified macroporous Al 2 O 3 tubes. The SEM and XRD characterizations indicate that a dense and phase-pure ZIF-8 membrane with a thickness of about 25.0 μm can be formed on the alumina tubes by microwave synthesis at 105 °C for 3 h, and no cracks, pinholes or other defects were observed in the membrane layer. The ZIF-8 membranes were evaluated in single gas permeation and mixed gas separation. Attributed to the preferential adsorption affinity and capacity as well as a highly porous structure with nano-sized channels, the ZIF-8 membrane displays a high hydrogen permselectivity. For the separation of equimolar H 2 /CO 2 , H 2 /CH 4 , H 2 /C 3 H 8 mixtures at 100 °C and 2 bar, the mixture separation factors of H 2 /CO 2 , H 2 /CH 4 , and H 2 /C 3 H 8 are 5.6, 44.0, 328.6, with a H 2 permeance of about 1.1 × 10 −7 mol m −2 s −1 Pa −1 , which is promising for potential applications in hydrogen purification and separation. [ABSTRACT FROM AUTHOR]

Abstract: Dense and phase-pure zeolite LTA membranes were hydrothermally synthesized on 3-aminopropyltriethoxysilane (APTES)-modified macroporous Al2O3 tubes without seeding. Pervaporation experiments were conducted for the separation of liquid water/iso-butanol and water/ethanol mixtures to evaluate the separation performances of the zeolite LTA membranes. A water flux of 4.5kg/m2 h is obtained at 100°C for the separation of a 95.0wt% iso-butanol/5.0wt% water mixture, and the separation factors of water/iso-butanol are found to be about 3000 for all temperatures and concentrations studied. [Copyright &y& Elsevier]

Water permeation through a hydrophilic zeolite membrane can be used to promote reactions under equilibrium controlled conditions through the in situ removal of the by-product water. In the methylamine synthesis, mono- (MMA), di- (DMA) and trimethylamine (TMA) are formed by the successive methylation of ammonia with methanol (MeOH) over a mildly acidic catalyst. The methylamine yield can be increased through selective water extraction from the reactor through a membrane. Since both reactants and water have similar molecular kinetic diameters below 3.7 Å, because of the limited steam selectivity of the commonly used hydrophilic Na-LTA membrane (zeolite 4A), not only water has been removed. Therefore, in this work a K-LTA membrane, which was obtained by ion exchange with a reduced pore window diameter of 3 Å and thus with a higher water selectivity, was used in the membrane-supported methylamine synthesis. When replacing the Na-LTA with the K-LTA membrane, the H 2 O/MeOH mixed gas separation factor increases up to 1100 and the H 2 O/NH 3 separation could also be improved. This in turn leads to an overall boost of the higher methylated amines DMA and TMA in methylamine synthesis. When using the narrow-pore aluminosilicate catalyst H-SSZ-13 with CHA structure, the application of the K-LTA membrane increases the share of the industrially desired product DMA from 51% without membrane to 74% with slightly increased conversion. When using the large-pore catalyst H-MOR, the thermodynamically most stable product TMA can be formed and the selectivity was increased from 35% without membrane to 41% with the K-LTA membrane. [Display omitted] • Linde Type A membranes were evaluated for application in methylamine synthesis. • In situ water removal enhanced methylation rate and conversion rates. • K+ exchanged variant showed promising water/methanol selectivities. [ABSTRACT FROM AUTHOR]

Abstract: By PFG NMR diffusion measurements with short-chain length alkanes, the deposition of nano-sized LTA zeolite seed crystals on LTA single crystals and their secondary growth to surface layers is shown to reduce rather than to enhance transport resistances at the crystal surface. This, at first glance contra-intuitive, finding may be rationalised if the transport resistance on the external surface of the nanoporous crystals of the as-synthesized material results from an essentially impenetrable layer with highly dispersed structural defects rather than from a quasi-continuous layer with extremely low guest diffusivity and/or solubility: if accompanied with an – even very small – enhancement of the defect density, irrespective of the increasing layer thickness a subsequent surface treatment will enhance the surface permeability. [Copyright &y& Elsevier]

A seeding-free synthesis strategy was developed for the preparation of dense and phase-pure MFI zeolite membranes based on "like grows like" principle. Through covalent modification of the porous ceramic supports by using 1H,1H,2H,2H-perfluoroalkyltriethoxysilanes (POTS), the support surface was changed from hydrophilic to hydrophobic, which promotes the nucleation and growth of hydrophobic MFI zeolite membranes. Thin, well-intergrown and phase-pure MFI zeolite membranes, with a thickness of about 2.0–3.0 μm, can be facilely prepared on POTS-modified supports like Al 2 O 3 and TiO 2 at 175 °C for 24 h. No cracks, pinholes or other visible macroscopic defects are observed in the membrane layer. The MFI zeolite membranes were evaluated in the hydrophobic separation of 5.0 wt% ethanol/water mixture at 75 °C by pervaporation. The MFI zeolite membrane prepared on the POTS-modified TiO 2 disk shows high pervaporation separation for ethanol recovery. At 75 °C, a separation factor of 103 and total flux of 2.56 kg/m2h can be obtained, which is promising to extract bio-alcohols from the fermentation broth. Image 1 • A novel strategy is developed for seeding-free synthesis of MFI zeolite membranes based on "like grows like" principle. • Hydrophobic MFI membranes tend to grow well on the hydrophobic support surface. • Thin and well-intergrown MFI membranes can be easily prepared on POTS-modified supports. • The MFI membranes prepared on POTS-modified TiO 2 supports show high pervaporation performance. [ABSTRACT FROM AUTHOR]