Synthesis Of Zeolite Membranes Research Articles

MFI Zeolite Membranes and PV Separation of Isopropanol-Water Azeotropic Mixtures

Membrane separation process has become one of the emerging technologies that undergo a rapid growth since few decades. Pervaporation (PV) is one among the membrane separation processes which gained foremost interest in the chemical and allied industries. It is an effective and energy-efficient technology that carries out separations, which are difficult to achieve by conventional separation processes. Inorganic membranes such as zeolite membranes with uniform, molecular-sized pores, selective adsorption and molecular sieving action offer unique type of pervaporation membrane for a number of separation processes. This paper presents the role of MFI-zeolite membrane and its progress in the pervaporation process. The fundamental aspects of pervaporation over different types of membranes are reviewed and compared. The focus of this paper is on zeolite membrane synthesis, membrane characterization and pervaporation studies. The transport mechanism during pervaporation is discussed and the issues related with pervaporation are addressed. Innovation and future development of zeolite membrane in pervaporation are also presented.

Room-Temperature Synthesis of Zeolite Membranes toward Optimized Microstructure and Enhanced Butane Isomer Separation Performance.

Room temperature (RT) synthesis of high-performance zeolite membranes, which is profound from techno-economic and eco-friendly perspectives, remains a grand challenge. In this work, we pioneered the RT preparation of well-intergrown pure-silica MFI zeolite (Si-MFI) membranes, which was realized through adopting highly reactive NH4F-mediated gel as nutrient during epitaxial growth. Benefiting from the introduction of fluoride anions as mineralizing agent as well as precisely tuned nucleation and growth kinetics at RT, both their grain boundary structure and thickness could be deliberately controlled, resulting in the formation of Si-MFI membranes showing unprecedented n-/i-butane separation factor (96.7) and n-butane permeance (5.16 × 10-7 mol m-2 s-1 Pa-1) in the case of a feed molar ratio of 10/90, which well transcended the state-of-the-art membranes reported in the literature. This RT synthetic protocol was also proven effective for preparing highly b-oriented Si-MFI film, thus showing great promise for the preparation of diverse zeolite membranes with optimized microstructure and superior performance.

A super-permeable and highly-oriented SAPO-34 thin membrane prepared by a green gel-less method using high-aspect-ratio nanosheets for efficient CO2 capture

High-efficient and green preparation of super permeable zeolite membranes is highly desired for scientific and application purposes. The normal gel-filled synthesis of zeolite membrane raises the problems including environment, safety and efficiency issues. Herein, tubular and preferentially oriented CHA-type SAPO-34 membranes with controllable thickness of 0.3–2.5 μm are prepared by a gel-less method with few liquid wastes. The membrane synthesis has a good reproducibility and high efficiency. Perpendicular, ordered and short nanochannels in the SAPO-34 membrane supply the fast path for CO2 permeation. The highly-oriented SAPO-34 membrane displays CO2 permeances as high as 1.0 × 10-5 mol(m2 s Pa)-1 and CO2/CH4 and CO2/N2 selectivities of 129 and 29, respectively, in the CO2/CH4 and CO2/N2 separation at 0.2 MPa pressure drop and 298 K. Such super-permeable SAPO-34 membrane prepared by simple and gel-less method is attractive for highly efficient CO2 capture.

A novel preparation of high permeation SiC supports for NaA zeolite membrane by in situ reaction bonding

The performance of zeolite membrane supports directly determines the synthesis performance and industrial application of zeolite membranes. In this study, a novel and high permeation SiC supports for NaA zeolite membrane were prepared by carrying out in situ reaction bonding at high temperature in the air atmosphere to coat the SiC particles with aluminum sol. The effects of process parameters on the formation of porous structure of SiC supports were systematically investigated, and the underlying mechanism was explored. During the sintering process, high-temperature Al2O3 from aluminum sol reacted with SiO2 generated by oxidation of the surface of SiC particles to form mullite, which exhibited excellent chemical stability and improved the mechanical properties and chemical stability of the supports. The porous SiC supports for zeolite membrane displayed obvious three-dimensional connected pore structure, with smooth inner surface of the pores and obvious connection neck between the particles. The porous SiC supports for zeolite membrane showed good in situ mullite bonding between the particles, and high permeability. It has a porosity of 36.3%, an average pore size of 1.42 µm and a bending strength of 32.4 MPa. All these figures indicate good comprehensive properties that are consistent with the rigorous requirements of zeolite membrane synthesis and industrial application.

Research on the Modification of Silane/Zeolite Composite Anticorrosive Membrane on Ti-6Al-4V Alloy Surface by Graphene Oxide and Its Mechanism

The zeolite membrane as a corrosion-resistant membrane has green environmental protection, high-temperature resistance, high-mechanical strength, and other characteristics, which has attracted much attention. However, due to the very different surface properties between metals and inorganics, the embodiment of high-binding force membrane is a major difficulty in the current zeolite membrane synthesis technology. Research has been conducted on the silane (YDH-151)/zeolite (TS-1) composite anticorrosive membrane in Ti-6Al-4V alloy surface, and on the modification effect by using graphene oxide (GO), as well as the membrane formation mechanism after being modified. Scanning electron microscope and 3D laser confocal microscope (3D LCSM) were used to study the effect of GO on the modified silane/zeolite composite anticorrosion membrane, and electrochemical methods, contact angle, bonding force, Fourier transform infrared ray were used to study the modification effect and the membrane formation mechanism and process after being modified. Microscopic observations show that GO causes the zeolite particles to accelerate to accumulate, hinders the lateral membrane formation of TS-1 zeolite which forms thus non-negligible pores or defects. It also reduces the density of the zeolite membrane, and the hydrophobicity and binding force of the composite membrane. However, GO can effectively decrease the corrosion current density and greatly enhance the corrosion resistance of the membrane. YDH-151 undergoes dehydration condensation reaction with metal surface and zeolite, and graft reaction with GO, forming a dense YDH-151/GO/TS-1 composite membrane on the surface of Ti-6Al-4V alloy, with a corrosion resistance rate of 99.8%.

Reaction of methanol to olefin using a membrane contactor on a silica substrate

A MFI zeolite membrane was synthesized on a porous silica substrate. The defect-free MFI zeolite membrane was synthesized via a secondary growth method using seed crystals (Si/Al = 20) on a silica substrate in a parent gel of Si/Al = 100. The silica substrate prevented the dissolution of the seed crystals during the synthesis to promote the MFI zeolite membrane synthesis. The MFI zeolite membranes were employed for a contactor-type reactor for methanol-to-olefins (MTO) reactions to produce olefins, such as propylene. The methanol conversion was 99.9% with the selectivity of ethylene - pentene at 91.5% for the permeate side of the membrane contactor. The propylene selectivity was high at 48.5% with the C3H6/C3H8 ratio at 236.

Gel-Modulated Growth of High-Quality Zeolite Membranes

Trade-off between thickness (and thus gas permeance) and quality (and thus selectivity) of zeolite membranes significantly restricts their wide application. It is challenging to maintain the membrane thickness while minimizing nonselective defects in the selective membrane layer. Currently, continuous change of the synthesis gel concentration during membrane synthesis, instead of high gel concentration for membrane "skeleton" growth and low gel concentration for slow crystal growth to merge "skeleton" crystals, usually leads to thick membranes to compensate for the low selectivity. In this work, we report a gel-modulated synthesis approach to engineer the zeolite membrane synthesis. The gel concentration was suddenly reduced by a quenching process in the middle of the membrane synthesis, leading to reduced nuclei formation and crystal growth rate in the following synthesis process. Membrane quality was significantly improved without increasing membrane thickness, leading to a great increase in membrane selectivity but without sacrifice of gas permeance. Moreover, as an example, highly reproducible SAPO-34 membranes were successfully prepared by the gel-modulated growth method. We expect this novel synthesis strategy might be a viable and economic way of growing thin and high-quality zeolite membranes.

Gas permeation properties of NaA zeolite membranes: effect of silica source on hydrogel synthesis and layer thickness

NaA zeolite membranes were prepared on the inner surfaces of ceramic α-alumina tubes based on an aqueous phase synthesis in order to investigate the influence of different silica sources on NaA zeolite membrane synthesis and zeolite layer thickness with reference to the gas separation properties. SEM and XRD results indicated that zeolite prepared with sodium metasilicate as the silica source can be synthesized for a NaA zeolite membrane, leading to uniform zeolite layers and good thermal stability. The H2 permeance at 25 °C was 4.99 × 10−7 mol m−2 s−1 Pa−1, and the H2/Ar and H2/He permselectivities were 3.78 and 1.36, respectively. The morphologies and single gas permeation properties of the NaA zeolite membranes prepared through repeated aqueous phase synthesis treatments were also studied. When the zeolite layer thickness increased from 2.9 to 53 µm, the H2 permeance gradually decreased, while the permselectivities increased from 3.78 to 5.17. The gas permeance was mainly controlled by the Knudsen diffusion in our NaA zeolite membrane.

Development of LTA zeolite membrane from clay by sonication assisted method at room temperature for H2-CO2 and CO2-CH4 separation

In this work, sodium aluminosilicate zeolite powder and membranes were synthesized by ultrasonic irradiation at room temperature using montmorillonite clay as precursor material. For comparison, same zeolite powder and membranes were synthesized at 100 °C also. The synthesized zeolites were characterized by X-ray diffraction (XRD), infrared (IR) spectral analysis, and field-emission scanning electron microscopy (FESEM). XRD and IR results showed that phase pure mainly LTA phase was formed after 15 days of aging at room temperature. By using the zeolite powders as seeds, membranes were synthesized on clay alumina support tubes at room temperature and also at 100 °C. In both the cases membranes were formed on support surface. The membrane thickness was found to be 15 μm. The performances of the membranes were evaluated by single gas as well as mixture gas permeation measurement for H2-CO2 and CO2-CH4 respectively. The H2–CO2 and CO2-CH4 separation selectivity for the mixture gas of the membrane was found to 16.2 and 20.9 at room temperature respectively. To the best of our knowledge, there is no report of synthesis of zeolite membrane at room temperature using clay as raw materials. For the first time we have reported the synthesis of alumino-silicate zeolite membrane on clay alumina support surface using clay as starting material by sonochemical method at room temperature.

Synthesis of zeolite membranes on calcium silicate support and their bioactive response

The synthesis of calcium silicate supported zeolite membrane was carried out by second growth method. The chemical nature of the functionalizing agent on the formation of homogenous zeolite membrane was evaluated. One monomer and two cationic polymers were used: 3-aminopropyltriethoxysilane (APS), polyethylenimine (PEI) and polydiallyldimethylammonium chloride (PDDA). The support was subjected to chemical functionalization and then it was rubbed with zeolite crystals. The W zeolite was used as zeolite seed in two different Si/Al ratios. The functionalized and rubbed supports were submitted to hydrothermal treatment at 150 °C for 48 h. The bioactivity of the homogeneous zeolite membranes was evaluated by the biomimetic method through the membranes soaking in a simulated body fluid (SBF) at 37 °C for 21 days. Two immersion methods were evaluated. The products were characterized by XRD and SEM techniques. The results indicated that the supported functionalization with PDDA and the Si/Al ratio (higher than 1.8) of zeolite enhanced the interaction between the support and the zeolite precursor enhancing the formation of homogeneous zeolite membrane on the surface. The presence of the functional groups of PDDA on the membrane was detected by FTIR. After immersion in SBF, the zeolite membrane was stable and led to the formation of Ca–P layer on its surface. The re-immersion method led to the formation of richer Ca/P layer (1.36). These findings allowed generating a zeolite membrane with combined properties of calcium silicate and the controllable porosity of zeolitic material making it potentially useful for bone regeneration and drug releasing.

Synthesis of zeolite membrane (NaY/alumina): Effect of precursor of ceramic support and its application in the process of oil–water separation

Abstract The aim of this work was to evaluate the properties of support ceramic (gamma or alpha-alumina) for emulsion oil/water separation. Zeolite membrane (NaY/alumina) was prepared on alumina disk by secondary method (rubbing) and the influence of the ceramic supports have been investigated. The materials were characterized by X-ray diffraction, Mercury porosimetry, Mechanical strength, Scanning electron microscopy, Method Bubble point, contact angle and permeation with water pure. The separation of emulsion oil–water emulsion was evaluated on a stainless steel module. From the XRD results of the individual materials, it can be observed the formation of all the characteristic peaks for each material. From the SEM image of these materials, it can be seen that the surface of the alpha-alumina or gamma-alumina is completely covered with Y zeolite crystals. In the contact angle, it was noticed that the ceramic supports and the zeolitic membranes presented an angle equal to zero, corresponding to a strong hydrophilicity. The performance in the selectivity for fabricated membranes demonstrated that zeolite membranes NaY/alpha-alumina and NaY/gamma-alumina showed excellent results due to the formation of the selective zeolite NaY layer formed on the surface of the alpha and gamma alumina ceramic supports. The cleaning process on reused membranes proved to be efficient, obtaining more than 90% of its recovered flux.

Contaminants Removal in Wastewater Using Membrane Adsorbents Zeolite Y/Alpha-Alumina

This study was prepared by the secondary growth method the zeolite membrane Y and evaluate its use in the emulsion removal of oil / water. The prepared materials: zeolite Y, zeolite membrane alpha-alumina ceramic membrane and Y were characterized by the techniques of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). powder pressing method for compression of alpha-alumina ceramic membrane and the secondary growth method for the preparation of zeolitic membranes Y/alpha-alumina was used. Through XRD analysis, it was observed that the method was effective in the synthesis of zeolite membrane. By spectrophotometric analysis it was possible to observe a significant reduction in oil concentration in the permeate for the Y zeolite membrane / alpha-alumina, thus showing that they have the potential for this application.

Synthesis and preliminary gas permeation studies of a tubular NaA zeolite membrane (NZM)

ABSTRACTDifferent from traditional seeded method, NaA zeolite membranes (NZMs) were prepared by in situ synthesis onto the inner side of porous α-alumina tubular supports in a hydrothermal synthesis reactor. The influences of pretreatment of porous tubular support, temperature, time, and synthetic cycle for the synthesis of the zeolite membranes were investigated. The operating conditions were optimized. Characterization of the membranes by scanning electron microscopy and X-ray diffraction showed that the crystalline materials on the inner surface of the porous α-alumina tubes were NaA-type zeolite. Single- and binary-gas permeation tests were conducted. Single-component permeabilities of hydrogen and nitrogen through the NZM changed slightly when the transmembrane pressure difference varied from 80 to 420 kPa. Its selectivity for H2 relative to N2 was about 5.3, which was greater than that of the Knudsen diffusion. The separation factors of binary gases H2/N2 and H2/CO2 at 473 K were 3.9 and 5.7, respectively, again exceeding the Knudsen diffusion level. The separation of binary gases suggests that the NaA-type zeolite membranes on α-alumina substrate were defect free and able to provide molecular sieving. The results demonstrate that the unseeded synthetic method presented in this work is successful and reliable.

One-Step Synthesis of Zeolite Membranes Containing Catalytic Metal Nanoclusters.

Metal-loaded zeolitic membranes are promising candidates as catalytic membrane reactors. We report a one-step synthesis method to synthesize zeolite membranes containing metal nanoclusters, that has advantages in comparison to multistep methods such as impregnation and ion exchange. Pure-silica MFI zeolite-Pt hybrid membranes were prepared by hydrothermal synthesis with addition of 3-mercaptopropyl-trimethoxysilane (MPS) and a platinum precursor. Composition analysis and mapping by energy-dispersive X-ray spectroscopy (EDX) reveal that Pt ions/clusters are uniformly distributed along the membrane cross-section. High-magnification scanning transmission electron microscopy (STEM) analysis shows that Pt metal clusters in the hybrid zeolite membrane have a diameter distribution in the range of 0.5-2.0 nm. In contrast, a pure-silica MFI membrane synthesized from an MPS-free solution shows negligible incorporation of Pt metal clusters. To characterize the properties of the hybrid (zeolite/metal) membrane, it was used as a catalytic membrane reactor (CMR) for high-temperature propane dehydrogenation (PDH) at 600 °C and 1 atm. The results indicate that Pt metal clusters formed within the MFI zeolite membrane can serve as effective catalysts for high-temperature PDH reaction along with H2 removal via membrane permeation, thereby increasing both conversion and selectivity in relation to a conventional membrane reactor containing an equivalent amount of packed Pt catalyst in contact with an MFI membrane. The hybrid zeolite-Pt CMR also showed stable conversion and selectivity upon extended high-temperature operation (12 h), indicating that encapsulation in the zeolite allowed thermal stabilization of the Pt nanoclusters and reduced catalyst deactivation.

Crystallization and assembling of FAU nanozeolites on porous ceramic supports for zeolite membrane synthesis

In this study, a novel route for preparing nanocrystalline porous FAU layers s stably supported on porous α-Al2O3 tubular substrates is reported. A highly reactive sodium hydroxide rich hydrogel was used to promote the nucleation process on the support surface. After 24 h of treatment at near ambient condition, a heavily nucleated quasi-solid gel layer containing nanozeolite precursor species was first formed on the support surface. This matrix was used as starting material for the synthesis of nanozeolite-based membranes. The support coated with the extensively nucleated gel phase was isolated and cured at higher temperature in different conditions. A rapid and diffuse crystallization was observed by treating the gel matrix with a synthesis solution of lower alkalinity, leading to the formation of a dense nanocrystalline FAU layer firmly adhered to the substrate surface. The FAU layers (Si/Al ratio of ca. 2) have a thickness of ca. 2 μm and are constituted by closely packed, well intergrown nanocrystals (crystallite dimension of ca. 20–30 nm). The results of this study indicate that supersaturation as well as the elevate amount of sodium ions synergistically contribute to induce the assembling of soluble aluminosilicate species on the support surface and to effectively promote the heterogeneous nucleation process.

DDR-type zeolite membrane synthesis, modification and gas permeation studies

DDR-type zeolite membrane was synthesized on porous α-alumina substrate by hydrothermal treatment of a ball-milled Sigmal-1 crystal seed layer in an aluminum-free precursor solution containing 1-Adamantylamine as the structure directing agent (SDA). The as-synthesized DDR zeolite membranes were defect-free but the supported zeolite layers were susceptible to crack development during the subsequent high-temperature SDA removal process. The cracks were effectively eliminated by the liquid phase chemical deposition method using tetramethoxysilane as the precursor for silica deposits. The modified membrane was extensively studied for H2, He, O2, N2, CO2, CH4, and i-C4H10 pure gas permeation and CO2/CH4 mixture separation. At 297K and 2-bar feed gas pressure, the membrane achieved a CO2/CH4 separation factor of ~92 for a feed containing 90% CO2, which decreased to 62 for a feed containing 10% CO2 with the CO2 permeance virtually unchanged at ~1.8×10−7mol/m2sPa regardless of the feed composition. It also exhibited an O2/N2 permselectivity of 1.8 at 297K. The gas permeation behaviors of the current aluminum-containing DDR type zeolite membrane are generally in good agreement with the findings in both experimental and theoretical studies on the pure-silica DDR membranes in recent literature.

Fabrication of zeolite/polymer composite membranes in a roller assembly

Membranes are cost-effective solutions for many industrial separations. Polymer membranes are widely used in gas separations. Because of the solubility-diffusion mechanism of transport, the permeance and selectivity of polymer membranes are inversely related, and is considered a limitation. Zeolite membranes do not have this limitation, but zeolite membrane synthesis is a batch process with long synthesis times and presence of defects. The resulting high costs of manufacture make zeolite membranes non-competitive for most applications. In this study, we present a roll-to-roll method for zeolite synthesis on a polymer support exploiting a gel that leads to rapid zeolite crystallization and a bendable zeolite membrane structure. Membranes were grown under both compressive and tensile stress, and with zeolite structure both on top and within the pores of the polyethersulfone (PES) support. The structure of the membranes was evaluated by electron microscopy. Membranes were coated with a thin layer of polydimethylsiloxane, and evaluated for CO2/N2 separation, relevant for CO2 capture from flue gas of power plants. As long as the zeolite membrane is grown within the PES support, highly reproducible CO2/N2 separation performance with CO2 permeance of 1881 ± 204 GPU and CO2/N2 selectivity of 34 ± 4 was observed immaterial of the stress conditions under which it was grown. For zeolite membrane grown on top of the PES support, the compressive stress resulted in crack formation, with poor transport properties. Demonstration of zeolite membrane fabrication with roll-to-roll method has the potential for industrial level scale up.

Synthesis of zeolite membrane (MCM-22/α-alumina) and its application in the process of oil-water separation

AbstractZeolite membrane (MCM-22/α-Al2O3) was prepared on α-Al2O3 disk by synthesis method (rubbing) and investigated through water separation and oily water recovery. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury porosimetry. Thereafter, the separation of oil-water emulsion was evaluated. The crystallization behavior of the particles of the zeolite membrane is observed through the XRD. The images obtained by SEM of the zeolite membrane (MCM-22/α-Al2O3) showed that the method used for the synthesis of the zeolite membrane was effective since it showed the formation of a homogeneous surface with no cracks or defects on the surface of the porous support of α-Al2O3. Oil rejection was monitored. Fouling occurred as a layer on the membrane surface. The test showed that the MCM-22 zeolite membrane has potential for oil-water separation.

Synthesis of NaA and NaX Zeolite Membranes by Fumed Silica Via Clear Solution Gel

NaA zeolite membranes have been used for dehydration of organic solvents in laboratory and commercial scales. There are many synthesis methods and conditions for manufacturing the membranes. The use of lactescent and clear gel solutions are two of the most important choices for high quality hydrothermal synthesis of NaA zeolite membrane in gas separation or dehydration of organic solvents. In this article, effect of hydrothermal synthesis time was investigated using the clear gel solution (Al2O3:5SiO2:50Na2O:1000H2O). Phase transformation from NaA to NaX was recognized as the most possible event when the clear gel solution was used. XRD spectra, SEM images, and GC analyses were used for evaluation of zeolite crystal phase, the membrane layer quality, and the contents of organic substances (ethanol or 2-propanol) in feed and permeate streams in pervaporation tests, respectively. From synthesis of zeolite membrane at different times, it was revealed that for achieving the pure NaA zeolite phase the synthesis time should not exceed 3 h at 100°C.

Rapid crystallization of faujasitic zeolites: mechanism and application to zeolite membrane growth on polymer supports.

Zeolites are microporous, crystalline aluminosilicates with the framework made up of T-O-T (T = Si, Al) bonds and enclosed cages and channels of molecular dimensions. Influencing and manipulating the nucleation and growth characteristics of zeolites can lead to novel frameworks and morphologies, as well as decreased crystallization time. In this study, we show that manipulating the supersaturation during synthesis of zeolite X/Y (FAU) via dehydration led to extensive nucleation. Controlled addition of water to this nucleated state promotes the transport of nutrients, with a 4-fold increase in the rate of crystal growth, as compared to conventional hydrothermal process. Structural signature of the nucleated state was obtained by electron microscopy, NMR, and Raman spectroscopy. This extensively intermediate nucleated state was isolated and used as the starting material for zeolite membrane synthesis on porous polymer supports, with membrane formation occurring within an hour. With this time frame for growth, it becomes practical to fabricate zeolite/polymer membranes using roll-to-roll technology, thus making possible new commercial applications.