Type Zeolite Membranes Research Articles

Understanding the performance of RHO type zeolite membrane for CH4/N2 separation based on molecular dynamics and deep neural network methods

This study shows a molecular dynamics (MD) simulation study on the performance of the RHO zeolite membrane for separating nitrogen from methane/nitrogen gas mixtures. The contamination of natural gas, predominantly composed of methane, with nitrogen diminishes its value. Zeolite membranes offer promising prospects for gas separation due to their stability, rigid pore structure, and molecular sieving properties. The study investigates the impact of pressure difference (up to 30 MPa), feed composition, and membrane thickness on the separation rate at a system temperature of 298 K. Results demonstrate that the RHO zeolite membrane exhibits high permeability and selectivity for N2 separation, surpassing the upper limit defined by Robson with a maximum permeability of 2.14 × 105 GPU (Gas Permeation Units). Exceptional selectivity of N2 over CH4 molecules is observed. Additionally, altering the feed composition and membrane thickness positively influences the membrane's separation performance, thereby enhancing its efficiency. The findings contribute to the advancement of separation technologies, providing valuable insights into the potential application of zeolite membranes for efficient N2 separation from CH4/N2 gas mixtures in natural gas processing. Furthermore, the study explores the use of Deep Neural Network (DNN) models to predict the membrane's performance under diverse operating conditions. The DNN models, trained using simulation data from MD simulations, exhibit high accuracy with a coefficient of determination (R2) exceeding 0.9, ensuring reliable predictions. The integration of DNN models facilitates the optimization of zeolite membrane-based gas separation systems, improving their design and operation.

Estimation of CO2 Separation Performances through CHA-Type Zeolite Membranes Using Molecular Simulation.

Chabazite (CHA)-type zeolite membranes are a potential material for CO2 separations because of their small pore aperture, large pore volume, and low aluminum content. In this study, the permeation and separation properties were evaluated using a molecular simulation technique with a focus on improving the CO2 separation performance. The adsorption isotherms of CO2 and CH4 on CHA-type zeolite with Si/Al = 18.2 were predicted by grand canonical Monte Carlo, and the diffusivities in zeolite micropores were simulated by molecular dynamics. The CO2 separation performance of the CHA-type zeolite membrane was estimated by a Maxwell-Stefan equation, accounting for mass transfer through the support tube. The results indicated that the permeances of CO2 and CH4 were influenced mainly by the porosity of the support, with the CO2 permeance reduced due to preferential adsorption with increasing pressure drop. In contrast, it was important for estimation of the CH4 permeance to predict the amounts of adsorbed CH4. Using molecular simulation and the Maxwell-Stefan equation is shown to be a useful technique for estimating the permeation properties of zeolite membranes, although some problems such as predicting accurate adsorption terms remain.

Low-temperature ozone treatment for p-xylene perm-selective MFI type zeolite membranes: Unprecedented revelation of performance-negating cracks larger than 10 nm in polycrystalline membrane structures

We report that low-temperature ozone calcination allowed MFI type polycrystalline zeolite membranes to maximize their p-/o-xylene separation factor (as high as ca. 2000) by suppressing defect formation. Conventional high-temperature calcination and rapid thermal processing, which provide poor and marked p-/o-xylene separation abilities, respectively, were used for comparison. The corresponding defect structures were quantitatively analyzed by image processing of fluorescence confocal optical microscopy images combined with membrane permeation modeling, revealing the main defects (grain boundary defects and cracks) and their tortuosity, porosity, and size. To the best of our knowledge, we, for the first time, demonstrated that in contrast to common belief, the minor portion of wider cracks instead of the major portion of narrower grain boundary defects determined the final permeation rates. Specifically, the MFI membrane prepared by high-temperature calcination contained many grain boundary defects (narrow; ca. 1 nm) and few cracks (wide; ca. 20 nm) that accounted for ca. 0.1% and 99.8%, respectively, of the slowly permeating o-xylene molar flux. In contrast, the ozone-treated MFI membranes, which only possessed grain boundary defects, achieved the high p-/o-xylene separation performance, underlining the need for the selective reduction in the number of wider cracks rather than ubiquitous, narrow grain boundary defects.

Small-Pore Zeolite Membranes: A Review of Gas Separation Applications and Membrane Preparation

There have been significant advancements in small-pore zeolite membranes in recent years. With pore size closely related to many energy- or environment-related gas molecules, small-pore zeolite membranes have demonstrated great potential for the separation of some interested gas pairs, such as CO2/CH4, CO2/N2 and N2/CH4. Small-pore zeolite membranes share some characteristics but also have distinctive differences depending on their framework, structure and zeolite chemistry. Through this mini review, the separation performance of different types of zeolite membranes with respect to interested gas pairs will be compared. We aim to give readers an idea of membrane separation status. A few representative synthesis conditions are arbitrarily chosen and summarized, along with the corresponding separation performance. This review can be used as a quick reference with respect to the influence of synthesis conditions on membrane quality. At the end, some general findings and perspectives will be discussed.

Application of Zeolite Membranes to Dehydrate a Bio-Ethanol Solution Produced by High-Temperature Fermentation

The combination of high-temperature fermentation and membrane separation has the potential to realize a simple on-site process to produce concentrated bioethanol. The performance of dehydration membranes in separating bioethanol was investigated in this study. Three types of zeolite membranes, LTA, MFI, and MOR, were synthesized. Their dehydration ability was compared using a bioethanol solution produced by high-temperature fermentation followed by vacuum distillation. The LTA zeolite membranes deformed and became amorphous while treating the distillate. On the contrary, no significant changes were observed in the MFI and MOR zeolite membranes analyzed by X-ray diffraction after treating the distillate. However, the flux declined when the membranes were in contact with the distillate (pH = 3.8). Neutralizing the distillate to pH 6.6 with sodium hydroxide did not prevent the flux decline. Even though flux decreased by about 20–30%, the MOR membrane showed quite high water-selectivity, with a water concentration of over 99.9% in the permeate, suggesting the feasibility of its application to concentrate bioethanol.

Pervaporative Dehydration of Organic Solvents Using High-Silica CHA-Type Zeolite Membrane.

A high-silica chabazite (CHA) type zeolite membrane was prepared on the porous α-Al2O3 support tube by the secondary growth of seed particles. The dehydration performances of the membrane were determined using methanol, ethanol, 2-propanol, acetone, acetic acid, methyl ethyl ketone (MEK), tetrahydrofuran (THF), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrolidone (NMP) at 303–373 K. As a result, the dehydration performances of the membrane were categorized to following three types: (1) 2-propanol, acetone, THF, and MEK; (2) ethanol and acetic acid; and (3) methanol, DMF, and DMSO, and NMP. The adsorption isotherms of water, methanol, ethanol, and 2-propanol were determined to discuss the influences of the organic solvents on the permeation and separation performances of the membrane. For 2-propanol, acetone, MEK, and THF solutions, the high permeation fluxes and separation factors were obtained because of the preferential adsorption of water due to molecular sieving. In contrast, the permeation fluxes and separation factors were relatively low for methanol, DMF, and DMSO, and NMP solutions. The lower dehydration performance for the methanol solution was due to the adsorption of methanol. The permeation fluxes for ethanol and acetic acid solution were ca. 1 kg m−2 h−1. The significantly low flux was attributed to the similar molecular diameter to the micropore size of CHA-type zeolite.

An Extrinsic-Pore-Containing Molecular Sieve Film: A Robust, High-Throughput Membrane Filter.

MFI type zeolites with 10-membered-ring pores (ca. 0.55 nm) have the ability to separate p-xylene (ca. 0.58 nm) from its bulkier isomers. Here, we introduced non-zeolitic micropores (ca. 0.6-1.5 nm) and mesopores (ca. 2-7 nm) to a conventional microporous MFI type zeolite membrane, yielding an unprecedented hierarchical membrane structure. The uniform, embedded non-zeolitic pores decreased defect formation considerably and facilitated molecular transport, resulting in high p-xylene perm-selectivity and molar flux. Specifically, compared to a conventional, crack network-containing MFI membranes of similar thickness (ca. 1 μm), the mesoporous MFI membranes showed almost double p-xylene permeance (ca. 1.6±0.4×10-7 mol m-2 s-1 Pa-1 ) and a high p-/o-xylene separation factor (ca. 53.8±7.3 vs. 3.5±0.5 in the conventional MFI membrane) at 225 °C. The embedded non-zeolitic pores allowed for decreasing the separation performance degradation, which was apparently related to coke formation.

An Extrinsic‐Pore‐Containing Molecular Sieve Film: A Robust, High‐Throughput Membrane Filter

AbstractMFI type zeolites with 10‐membered‐ring pores (ca. 0.55 nm) have the ability to separate p‐xylene (ca. 0.58 nm) from its bulkier isomers. Here, we introduced non‐zeolitic micropores (ca. 0.6–1.5 nm) and mesopores (ca. 2–7 nm) to a conventional microporous MFI type zeolite membrane, yielding an unprecedented hierarchical membrane structure. The uniform, embedded non‐zeolitic pores decreased defect formation considerably and facilitated molecular transport, resulting in high p‐xylene perm‐selectivity and molar flux. Specifically, compared to a conventional, crack network‐containing MFI membranes of similar thickness (ca. 1 μm), the mesoporous MFI membranes showed almost double p‐xylene permeance (ca. 1.6±0.4×10−7 mol m−2 s−1 Pa−1) and a high p‐/o‐xylene separation factor (ca. 53.8±7.3 vs. 3.5±0.5 in the conventional MFI membrane) at 225 °C. The embedded non‐zeolitic pores allowed for decreasing the separation performance degradation, which was apparently related to coke formation.

Preparation of a high-silica chabazite-type zeolite membrane with high CO2 permeability using tetraethylammonium hydroxide

High-silica chabazite (CHA)-type zeolite (HS-CHA) crystals and membranes were prepared using tetraethyl ammonium hydroxide (TEAOH) as an organic structure-directing agent. The effect of the hydrothermal synthesis time used for preparation of the HS-CHA crystals on various properties was studied. The crystal structures, Si/Al ratios, amounts of incorporated TEAOH, and morphologies were characterized by X-ray diffractometry, energy dispersive X-ray analysis, thermogravimetry/differential thermal analysis, and scanning electron microscopy, respectively. The results suggested that the CHA-type zeolite crystals were formed after 12 h of hydrothermal synthesis. After 36 h the faujasite (FAU)-type zeolite, which is a precursor of CHA-type zeolite, was transformed completely to HS-CHA crystals. HS-CHA membranes were successfully prepared on an α-alumina support by the secondary growth method using TEAOH. This membrane exhibited high CO2 permeance of 3.5 × 10−6 mol m−2 s−1 Pa−1 with an ideal selectivity (CO2/CH4) of 91. This CO2 permeance is twice that of the HS-CHA membrane prepared using N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH), which is the conventional organic structure-directing agent for HS-CHA. In addition, TEAOH in the HS-CHA membrane was removed at a temperature 70 °C lower than that required to remove TMAdaOH (430 °C).

Olefin Purification by Ag–exchanged X–type Zeolite Membrane

Olefin Purification by Ag–exchanged X–type Zeolite Membrane

Synthesis and gas permeation properties of chabazite-type titanosilicate membranes synthesized using nano-sized seed crystals

Abstract Chabazite (CHA)-type zeolite membranes have received considerable attention regarding their high permeance and separation performance. A recent report detailing a unique preparation procedure for a CHA-type titanosilicate (Ti-CHA) zeolite—in which titanium heteroatoms were incorporated into the zeolite framework by substitution of aluminum—demonstrates excellent physico-chemical properties when compared with conventional aluminosilicate CHA-type zeolites. In this study, the synthesis of Ti-CHA zeolite membranes (Ti-CHA membrane) was investigated. The Ti-CHA membrane was synthesized on an alumina support via a secondary growth method using Ti-CHA zeolite seed crystals. The Ti-CHA membrane properties were studied as a function of seed crystal size. The average particle diameter was observed to reduce from 2.3 μm to 450 nm by increasing the loading of Ti-CHA into the synthesis gel. Regardless of the seed crystal particle size, the presence of CHA-type zeolites on the alumina support was confirmed by x-ray diffraction. UV–Vis demonstrated the incorporation of titanium heteroatoms into the zeolite framework. The results indicated the successful synthesis of the Ti-CHA membrane regardless of the seed crystal particle size. Additionally, the membrane thickness decreased by using the seed crystal. Single gas permeation tests showed that the thinnest Ti-CHA membrane prepared in this study exhibited a relatively high CO2 permeance of 1.5 × 10−6 mol m−2 s−1 Pa−1, compared with that of previously reported CHA-type zeolite membranes. The influence of moisture on the separation performance of the Ti-CHA membrane was evaluated in the presence of gas mixtures composed of CO2, methane and H2O ranging from 0.1 to 5 vol%. In the presence of 1 vol% H2O, the CO2 permeance and selectivity were only marginally reduced as a result of the highly hydrophobic pore structure.

Organic template-free synthesis of high-quality CHA type zeolite membranes for carbon dioxide separation

Microporous chabazite (CHA) zeolite is very promising for CO2 capture because of its appropriate pores with molecular dimensions for the preferential adsorption of CO2 molecules. Herein, CHA type zeolite particles and membranes were prepared by using a seeded growth method in the absence of an organic structure directing agent (OSDA) or template. After substantial effort to find appropriate and reliable conditions for obtaining continuous CHA type zeolite membranes, it was recognized that the formation of these membranes is a highly sensitive function of the Si/Al ratio in the synthetic precursor. Using the appropriate Si/Al ratio of ~50, OSDA-free CHA type zeolite membranes were manufactured with high reproducibility. The resulting OSDA-free CHA type zeolite membranes showed maximum CO2/N2 and CO2/CH4 separation factors of ~12.5 ± 3.8 and ~28.8 ± 6.9, respectively, with a moderate CO2 permeance of ~1 × 10−7molm−2s−1Pa−1. Notably, under more realistic wet conditions (i.e., in the presence of H2O vapor), the separation performance at temperatures above 75°C was comparable to that obtained under dry conditions, although permeation was hindered below 50°C, apparently due to the strong adsorption of H2O vapor.

Fabrication of high-performance silicalite-1 membrane by a novel seeding method using zeolite-dispersed polymer film

A highly reproducible silicalite-1 membrane with high pervaporation performance was successfully prepared on a tubular silica support by a novel seeding method using a zeolite-dispersed polymer film. The proposed seeding method (film seeding) allowed for the formation of a uniform and continuous zeolite seed layer with high reproducibility on the support surface in a single seeding step, resulting in a membrane with high separation performance. The synthesized membrane had a continuous and dense zeolite layer with a thickness of approximately 12 μm and exhibited an ethanol/water separation factor of 120 and flux of 3.16 kg m−2 h−1 for 10 wt% ethanol/water mixtures at 323 K by pervaporation. This novel seeding method should lead to the development of new processes for synthesizing zeolite membranes that show both high performance and reproducibility. Moreover, given the simplicity and effectiveness of the method, it has immense potential for use in the commercial production of various types of zeolite membranes.

Synthesis of ZSM-5 and SAPO-34 membranes in a high temperature-pressure recirculating-flow system

MFI and SAPO-34 type zeolite membranes were prepared on tubular alumina supports in a recirculating flow system at elevated temperatures and reported for the first time in the literature. During membrane synthesis, the synthesis mixture flowed between the reservoir and the membrane module, which includes the membrane support. The highest synthesis temperatures were 180°C and 220°C, and the corresponding system pressures were approximately 20 and 30bar for MFI and SAPO-34, respectively. The best performing MFI membrane had a CH4 single gas permeance of 2.8×10−7mol/m2sPa and CH4/n-C4H10 ideal selectivity of 24 at 25°C. The n-C4H10/CH4 separation selectivity was 43.6 with n-C4H10 permeance of 8×10−7mol/m2sPa at 25°C. The ideal selectivities of CO2/CH4 of SAPO-34 membranes synthesized at 220 and 200°C in an autoclave without flow were 227 and >1000, respectively. However, the membranes synthesized by flow-induced crystallization exhibit CO2/CH4 ideal selectivities of less than 10.

Removal of chromium from synthetic wastewater using MFI zeolite membrane supported on inexpensive tubular ceramic substrate

A mordenite framework inverted (MFI) type zeolite membrane was produced on inexpensive tubular ceramic substrate through hydrothermal synthesis and applied for the removal of chromium from synthetic wastewater. The fabricated ceramic substrate and membrane was characterized by diverse standard techniques such as X-ray diffraction, field emission scanning electron microscope, porosity, water permeability and pore size measurements. The porosity of the ceramic substrate (53%) was reduced by the deposition of MFI (51%) zeolite layer. The pore size and water permeability of the membrane was evaluated as 0.272 μm and 4.43 × 10–7 m3/m2s.kPa, respectively, which are lower than that of the substrate pore size (0.309 μm) and water permeability (5.93 × 10–7 m3/m2s.kPa) values. To identify the effectiveness of the prepared membrane, the applied pressure of the filtration process and initial chromium concentration and cross flow rate were varied to study their influence on the permeate flux and percentage of removal. The maximum removal of chromium achieved was 78% under an applied pressure of 345 kPa and an initial feed concentration of 1,000 ppm. Finally, the efficiency of the membrane for chromium removal was assessed with other membranes reported in the literature.

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.

Recent Progress in Zeolite/Zeotype Membranes

This is a comprehensive review of the recent progresses made in the field of zeolite membranes. It describes zeolitic materials and methods of membrane fabrication, followed by a summary of applications for gas separation, pervaporation and separation of liquid mixtures. Special attention is called to polymer mixed matrix membranes (MMMs) and membranes based on metal organic frame works (MOFs). In this comprehensive survey, the following trends were observed during the past 5 – 10 years. New zeolitic materials and new synthesis methods, such as hydrothermal synthesis, seeding and microwave heating, have been continuously reported in the literature. Many efforts have been devoted to the synthesis of hybrid or mixed matrix membranes (MMMs) since MMMs clearly outperformed polymeric membranes. MOFs also showed improved performance in gas separation. Many attempts have been made to develop thin (1µm) supported zeolite layers on a variety of carriers such as capillaries, fibers, tubes, etc. The assembly of nanozeolite building blocks and nanosheets is the starting point for the synthesis of thin defect free zeolite membranes. The present review presents the recent progresses made in the field of zeolite/zeotype membranes. Different types of zeolite membranes, methods of preparation and application aspects especially for separation of gases have been focused on, including the individual zeolites which are in use or are to be used as inorganic fillers in mixed matrix membranes (MMMs). Despite the enormous efforts of researchers, the commercialization of zeolite membranes has been achieved only in a limited area. The future works necessary to change the current situation are hence suggested.

Continuous dehydration of IPA–water mixture by vapor permeation using Y type zeolite membrane in a recycling system

Industrially alcohol dehydration is carried out by a distillation process, thereby requiring a large amount of energy. In an IPA/water system, since producing an azeotrope, two more distillation towers should be added. Therefore, a large amount of energy saving will be expected when the IPA concentration by applying vapor permeation (VP) with membrane becomes possible. Recently, zeolite membrane separation has been attracting much interest in terms of lower energy consumption and higher separation performance.In this study, a composite type of NaY (Faujasite) zeolite membrane with high dehydration performance was synthesized, and VP tests were carried out for IPA/water mixtures. Furthermore, a continuous recycled VP (CVP) apparatus was set up and operated to analyze the enriching process of IPA. As a result, a two-step method, where two membranes with different performances are exchanged along the concentrating way, or operation temperature or feed rate was increased stepwise, was proposed. It was shown that such a new operation method could shorten the time of concentrating IPA.

Preparation and characterization of nanoporous ceramic membranes for separation of water from ethanol

In this work, high performance nanoporous Linde Type A (LTA)-type zeolite membranes were synthesized via secondary growth method. The used substrate for growing membrane layer was porous mullite. To synthesize defect-free zeolite film on porous mullite discs, synthesis duration was optimized for hydrothermal treatment. The morphology and structure of synthesized zeolite membranes were characterized by scanning electron microscopy and X-ray diffraction. The defect-free LTA-type zeolite membranes were obtained at synthesis duration of 3 h and synthesis temperature of 100°C. The separation performance of synthesized LTA-type zeolite membranes were evaluated in dehydration of ethanol using pervaporation process. Influence of feed composition on separation performance of LTA membranes was also investigated. The best membranes showed a separation factor of 9,400 and total flux of 9.8 kg m−2 h−1 for dehydration of 10:90 (wt.%) water/ethanol mixture.

T型ゼオライト膜を用いた膜支援型エステル化反応

T型ゼオライト膜を用いた膜支援型エステル化反応