Mordenite Membranes Research Articles

Preparation of high-performance zeolite membrane on a macroporous support by novel intermittent hydrothermal synthesis

Constructing high-quality zeolite membrane by regulating solely the kinetics of zeolite nucleation and growth is desired because of its simplicity and potential industrial viability. Herein, a high-performance mordenite membrane was prepared without using organic template successfully on a macroporous tubular α-alumina support using a novel and simple intermittent hydrothermal synthesis (IHS) method. We aimed at regulating membrane synthesis kinetics by adjusting the concentration of the synthetic gel by introducing an unheated period of the oven in the middle stage of the synthesis process. In the proposed IHS method, the power supply of the oven can be switched off and on with the aid of a smart socket without manual operation, ensuring its feasibility and convenience. A thin and dense membrane layer was formed via the appropriate adjustment of presynthesis time, unheated time, and resynthesis time. The effects of each duration on the morphologies, microstructures, and pervaporation performances of the prepared mordenite membranes were investigated. Under optimized conditions, the as-synthesized mordenite membrane showed high pervaporation performance with a permeation flux and separation factor of 5.57 kg m−2 h−1 and >10000, respectively, in the dehydration of 90 wt% isopropanol/water mixture at 75 °C. This work provides a novel, simple, and feasible method for the preparation of high-performance zeolite membrane.

Industrial-scale fabrication of mordenite membranes by dual heating method for production of ethyl acetate in an industrial VP-esterification plant

High-performance industrial-scale mordenite membranes were successfully prepared on 100-cm-long tubular macroporous mullite supports using a large autoclave containing 50 pieces (membrane area: 1.88 m 2 ) by a dual heating method. The effects of different heating methods on temperature and concentration distribution in the industrial autoclave were discussed in detail. Mordenite membranes prepared using a dual heating method by eliminating the temperature and concentration gradients showed excellent reproducibility, with an average flux of more than 2 kg m −2 h −1 for separation of a 90 wt% HAc/H 2 O mixture at 90 °C. The qualification rate of industrial-scale membranes produced in a single autoclave was more than 90%. Additionally, 345 pieces of industrial-scale mordenite membranes with a total membrane area of ca. 12.6 m 2 were assembled into 3 membrane modules in an industrial vapor permeation (VP) plant to intensify esterification of acetic acid and ethanol by rapid dehydration. The industrial VP-esterification plant produced 99.5 wt% ethyl acetate with a product flow rate of about 140 kg h −1 and the annual output exceeded 1000 tons. Importantly, the industrial plant showed an excellent stability for operating over 100 d, illustrating that the industrial-scale mordenite membranes had a high stability in industrial application of esterification of acetic acid and ethanol to produce ethyl acetate. • 50 pieces of 100-cm-long mordenite membranes were prepared in a single autoclave. • Reproducible industrial-scale membranes were synthesized by a dual heating method. • Ethyl acetate was produced by coupling of esterification with VP in an industrial plant. • Industrial VP-esterification plant showed a good stability for operating over 100 d.

A green synthesis of MOR zeolite membranes by wet gel conversion for dehydration of water-acetic acid mixtures

High performance mordenite (MOR) membranes were successfully synthesized by wet gel conversion (WGC) route using organic template-free and fluoride-free gels on seeded macroporous Al2O3 tubes. The seeded Al2O3 tubes were dipped into the gel solution with a composition of SiO2: 0.0045Al2O3: 0.19 Na2O: 27.76 H2O and then directly crystallized at 150 °C for 8 h without any extra solvent or solution in autoclave. The concentration of MOR seeds, crystallization time, composition of gels and crystallization way (hydrothermal growth or WGC) significantly influenced the membrane performance for dehydration of acetic acid (AA) mixtures by pervaporation. The prepared MOR membranes displayed a high water flux and good selectivity in long-term dehydration of 90 wt.% AA/H2O at 75 °C with the steay-state flux of 0.70 kg m−2 h−1 and separation factor increasing to 5000 after 200 h test. The WGC approach reduced the consumption of gel by about 96% with almost “zero” waste liquid. This WGC method is demonstrated as an efficient, green route to synthesze zeolite membranes and to possess potentiality for industrial dehydration applications.

Mono- and di-valent ion exchange of mordenite membranes for dehydration of acetic acid by pervaporation

The conventional Na-mordenite (Na-MOR) zeolite membranes prepared on α-Al2O3 tubes by secondary hydrothermal growth method. To improve membrane performances in dehydration of acetic acid by pervaporation, the Na+ as counter ions in MOR membranes were exchanged by a series of mono- and di-valent cations to adjusted the channel structure and water affinity. Langmuir surface areas for monovalent ion-exchanged MOR zeolites were consistent with the reverse order of ion radii as H+>Li+>Na+>K+>Cs+, while for those exchanged by divalent ions the zeolites surface areas followed the reverse order of hydrated ion radii instead of natural radii as Ba2+>Ca2+>Mg2+. The water adsorption of MOR by mono- and di-valent cations exchange were all disordered, and H+, K+ and Ca2+ exchanged MOR showed higher water capacity than that of Na-MOR. In pervaporation, monovalent ion-exchanged membranes with molecular sieving effect showed higher performances than those of divalent ion-exchanged membranes with augmented steric effect and weakened molecular sieving. Among these membranes, H-MOR showed the largest flux of 3.68 kg m−2 h−1 with a normal separation factor of 472 in pervaporation of 90 wt% acetic acid/water under 348 K due to a larger pore size and higher water adsorption, which were supplemented for acid-treated membranes. To get better separation ability, H+ exchange conditions on MOR membranes were investigated in detail. The optimized H-MOR membrane showed a flux of 1.52 kg m−2·h−1and separation factor of 1443 with good stability for 100 h. A simple water wash with a recovered performance proved a previously reported phenomenon that reduced flux with time was affected by acetic acid blockage.

Optimization of Mordenite Membranes Using Sucrose Precursor for Pervaporation of Water-Ethanol Mixtures.

Post-treated mordenite membranes were prepared using sucrose (C12H22O11) as a carbon precursor to block any pinholes and defects in the zeolite layer. The pervaporation (PV) process was used to separate ethanol from the water. The effects of the sucrose concentration and the pyrolysis temperature (650–850 °C) were investigated, and the resulting high separation performance compared to those post/pre-treated membranes was reported in the literature. In this study, mordenite carbon membranes yielded a water/ethanol separation factor of 990.37 at a water flux of 9.10 g/m2h. The influence of the operating temperature on the performance of the membrane also was considered. It was concluded that the selective adsorption of water through zeolite pores was achieved. The entire preparation procedure was achieved using a rapid, low-cost preparation process.

Microwave synthesis of high-quality mordenite membrane by a two-stage varying heating-rate procedure

High performance mordenite membranes were successfully prepared on porous α-Al2O3 tubes by a novel two-stage varying heating-rate procedure under microwave assisted heating. The effect of heating rate on microstructure and performance of mordenite membrane was first time to be investigated. It was found that slowing down the heating rate at lower temperature range can improve the nucleation process, and further enhance compactness as well as performance of mordenite membrane. Crystallization time was also optimized for the preparation of high-quality mordenite membrane and it was reduced to only 75 min in this work. The as-synthesized M14 exhibits an excellent PV performance for dehydration of 90 wt% acetic acid/water mixture at 75 °C with a flux of 1.48 kg m−2 h−1 and a separation factor of larger than 10,000, which shows an excellent potential for dehydration of acetic acid aqueous solutions in industrial separation applications. Our work also provides a new idea for regulating microstructure and performance of zeolite membrane.

Fabrication and stability exploration of hollow fiber mordenite zeolite membranes for isopropanol/water mixture separation

Abstract High performance mordenite zeolite membranes were fabricated on four-channel Al2O3 hollow fiber substrates for the first time by using ball-milled mordenite particles as seeds. It was found that the particle size of seed played a vital part in the growth of membrane layers. The mordenite particles with a size of approximately 300 nm via ball milling enabled the growth of zeolite to form a uniform and defect-free zeolite membrane. The as-fabricated membranes showed high performance for isopropanol (IPA)/water mixtures separation. For IPA/H2O (90/10 wt%) mixture dehydration at 75 °C by pervaporation, the permeation flux of 1.43 kg m−2 h−1 and the separation selectivity of >10000 were achieved. The influence of feed water content on the separation performance of mordenite membrane was studied in detail. In addition to good dehydration performance at a low feed water content, the mordenite zeolite membranes also demonstrated long time stable separation performance for high feed water content systems. Permporosimetry measurements and molecular simulations showed that, unlike NaA zeolite crystal, the adsorbate water affected the expansion/contraction of MOR zeolite crystal framework weakly. Our research shows that MOR zeolite membrane shows good potential for the industrial solvent dehydration applications.

Scale-up of high performance mordenite membranes for dehydration of water-acetic acid mixtures

Mordenite membranes have been successfully synthesized on 80-cm-long mullite supports by secondary growth method. The morphology and quality of mordenite membrane were greatly affected by fluoride concentration, water content and crystallization mode. Compact and high-flux mordenite membranes were obtained with the addition of NaF in precursor gel, which also exhibited a long-term acid stability for a 90 wt% HAc/H2O mixture at 75 °C. Typically, 80-cm-long mordenite membrane prepared with transverse crystallization displayed a permeation flux of ca. 0.97 kg m−2 h−1 and separation factor of ca. 1200 for separating a 90 wt% HAc/H2O mixture at 75 °C. The pervaporation performance was better than that of membranes prepared with vertical crystallization due to the negligible impact of gravity and temperature gradients. These scaled-up mordenite membranes with high reproducibility showed a promising industrial application for dehydration of water-acetic acid mixtures.

Influences of Synthesis Parameters on Preparation of Acid-Stable and Reproducible Mordenite Membrane

Long-term acid-resistant mordenite membranes are prepared on the porous mullite supports by secondary hydrothermal synthesis in this study. Influences of the preparation conditions (fluoride, synthesis time, molar composition of precursor synthesis gel, and alkaline of the precursor synthesis gel) on the growth and pervaporation performance of the mordenite crystals and membranes are studied in detail. The fluorides containing the precursor gel could improve the acid stability and hydrophilicity of the mordenite membrane greatly. The Si/Al ratio, separation performance, and mordenite crystals morphology of the mordenite membranes depend on the Si/Al ratio of the initial synthesis gels, and medium alkalinity is crucial to prepare the compactness mordenite membrane layer by OH– and F– as mineral agents. As the molar ratio of the initial synthesis gel is SiO2:0.01KF:0.08Al2O3:0.2Na2O:35H2O, the mordenite membranes have good dehydration performance and reproducibility for dehydrating a 90 wt % acetic acid/wat...

Synthesis of high performance mordenite membranes from fluoride-containing dilute solution under microwave-assisted heating

High performance mordenite membranes were successfully prepared in a short synthesis time from fluoride-containing dilute solution without organic template under microwave-assisted heating. The effects of crystallization temperature, fluoride ion and aluminum source on the membrane morphology and separation performance for dehydration of acetic acid by pervaporation were systematically investigated. High performance mordenite membranes with a thickness about 5µm could be prepared from dilute solution with composition of SiO2: 0.06Al2O3:0.24Na2O:0.3NaF:120H2O at 165°C for 4h using various aluminum sources. These mordenite membranes exhibited high fluxes of 0.87±0.06kgm−2h−1 and excellent selectivities, that is only pure water was detected in the permeate side for dehydration of 90wt% acetic acid aqueous mixtures at 75°C. The reproducibility of mordenite membranes was high, using the fluoride-containing dilute solution under microwave-assisted heating, which forebodes a promising prospect for industrial applications in preferential separation of water from acetic acid aqueous solutions.

Application of a mordenite membrane to the esterification of acetic acid and alcohol using sulfuric acid catalyst

The well acid-stable and hydrophilic mordenite membrane is applied as a “membrane extractor reactor” for the esterification of acetic acid and alcohol with the H2SO4 as catalyst. The mordenite membrane reactors are placed into the reaction mixtures and continuously remove water from the esterification mixture by pervaporation, which could greatly improve the alcohol conversions of esterification. Besides, the effects of the reaction conditions (such as temperature, molar ratio of acetic acid/alcohol, and catalyst loading) on the ethanol conversion are investigated in details. As the reactional temperature, the molar ratio of acetic acid/alcohol, the catalyst loading, and the ratio of effective membrane surface area to esterification mixture volume are 85 °C, 1.5, 0.05 wt% (0.005 mol/L), and 0.31 cm2/cm3, the ethanol and n-butanol conversions of esterifications are up to 98.13% and 98.73%, respectively. Even if the mordenite membrane is applied to pervaporation-esterification for 8 times (96 h), the mordenite membranes are still kept the typical diffraction peaks and morphology by XRD and SEM characterization, and the dehydration performance of the membrane for 90 wt% HAc/H2O mixture at 75 °C is almost the same as the as-synthesized mordenite membranes, and the flux and separation factor of the mordenite membrane after 8 times PV-esterification are 0.44 kg m−2 h−1 and 627.

Preparation and optimization of mordenite nanocrystal-layered membrane for dehydration by pervaporation

Mordenite nanocrystal-layered membranes consisting of a mordenite nanocrystal layer and protection layer were successfully prepared. The obtained mordenite membranes were applied to the separation of water from water/organic solutions (organic solvents: ethanol, acetone, iso-propanol, or acetic acid) using a pervaporation method at temperatures from 60 to 100 °C. Water permeance through the mordenite membrane in each water/organic solution system was almost identical regardless of organic solvent types in the feed solution. In contrast, the permeance of the organic molecules depended on their polarities. The pre-aging temperature of the mother liquid and the heating rate for formation of the protection layer affected the secondary growth process that formed the protection layer, leading to different morphologies and sizes of the crystals in the protection layer. Water flux increased with decreasing crystal size in the protection layer because the number of non-zeolitic pores among the mordenite crystal increased as the crystal size decreased.

Rapid Preparation of Acid-Stable and High Dehydration Performance Mordenite Membranes

Highly intergrown mordenite membranes were rapidly prepared on seeded aluminum supports by microwave-assisted synthesis. Both the thicknesses of the zeolite layer and the sizes of the zeolite crystals of the mordenite membranes were highly dependent on the synthesis time. With a SiO2:0.08Al2O3:0.2Na2O:0.1NaF:35H2O precursor synthesis gel, a compact and 0.75 μm thick mordenite crystal layer was successfully prepared on the aluminum support at 170 °C for 3 h. The as-synthesized mordenite membrane exhibited excellent water perm-selectivity and long-term stability for dehydration of alcohol/water, acetic acid/water, and acetic acid/ethanol/water/ethyl ester mixtures by pervaporation. For dehydration of 90 wt % acetic acid/water solution, the corresponding flux and separation factor (water over acetic acid) of the membrane remained at 0.44 kg·m–2·h–1 and 2300, respectively, at 75 °C even after 59 days of immersion.

Stabilisation of the water permeability of mineral ultrafiltration membranes: An empirical modelling of surface and pore hydration

Abstract This work focuses on the study of the hydration phenomenon operating in Na–mordenite membranes during the conditioning step (stabilisation of filtration properties). First, experimental (filtration of pure water) tests are carried out immediately after putting the membrane in its casing and until the stabilization of the membrane permeation flux. The evolution of the hydraulic permeability shows that there are two separate steps during the conditioning of the membrane. A numerical approximation of the hydraulic permeability during the conditioning step was carried out. The first part of the equation expresses a fast decrease in the membrane's permeability during the beginning of the conditioning step (several hours). This behaviour is attributed to a surface hydration of the membrane and also to a modification of the crystalline framework. The second one is a slower phenomenon that takes place until the end of the conditioning step. It is attributed to the (intra-crystalline) hydration of micropores.

Understanding of Ion Transport in a Na–Mordenite Membrane: Use of Numerical Modeling To Estimate Surface–Solute Interactions in the Pore

A mordenite membrane was prepared and surface characterizations were performed on the synthesized mordenite (as powder form). The surface charge remained constant when mordenite powder was in contact with the studied solutions. A pore diameter of 5.8 × 10–9 m was estimated. Filtration tests of single salt–water solutions (NaCl, NaF, and Na2SO4) were carried with the mordenite membrane. No rejection was observed. After an alkaline treatment, the rejections were observed: NaF = Na2SO4 = 5–6%, while NaCl = 0%. New filtration tests of mixed salt–water solutions were carried out (Na2SO4 + NaCl and Na2SO4 + NaF). The sulfate ion was retained by a majority (up to 16%) whatever the halide ion in solution. The rejection rate of sulfate ion in mixtures decreases with the applied pressure, which actually cannot be explained (no observable polarization layer effect). A preferential transport is observed for chloride ions and the rejection rate of the fluoride ions remained constant. A numerical modeling (Nernst–Planc...

Preparation of low thermal expansion coefficient porous ceramic support for thermostable mordenite membrane

Low thermal expansion coefficient porous ceramic support (PCS) with secondary building units (SBUs) of mordenite for thermostable mordenite membrane was successfully prepared from mordenite powder by cold isotatic pressing-calcination technique. The sintered temperature of 1120K and the calcination holding time of 1h were used to keep the SBUs which could direct the mordenite crystals in the membrane to grow from the surface of PCS and make the mordenite membrane and PCS to be an organic whole. The as-synthesized mordenite membrane, combined to the PCS by strong chemical bonds, had been proven to have a good integrity and thermal stability, which contributes to the application in the high temperature environment.

Fabrication and characterization of highly crystalline mordenite membranes on α-alumina disks via a seeded in situ template-free hydrothermal treatment

A template-free seeded short-time in situ hydrothermal treatment was carried out in a brass autoclave to synthesize crystalline mordenite (MOR) membranes on alumina-silicate disk supports with micro-scale pores. According to XRD analysis, MOR was the only zeolitic material present in the membrane layers on the supports. SEM examination of the membranes showed three different layers of the membrane thickness: (i) support sub-layer, (ii) mix penetrated mid-layer, the MOR crystals filling the pores among the support (about 4–5 μm), and (iii) MOR top-layer (about 4–5 μm). The crystalline bonds between MOR crystals of the membrane top-layer and the crystals of the support were clearly observed within the mid-layer. The continuous top-layer of zeolitic membrane was formed by many large and well-shaped crystals. The seeding treatment significantly enhanced the formation of MOR crystals onto the surface of the supports. EDAX analysis showed a Si/Al ratio of 6.8 for the MOR layer of the membrane. Due to their hydrophilic natures, the polycrystalline MOR membranes were found to be selective for continuous dehydration of different EtOH–water mixtures through an adsorption–diffusion–desorption mechanism. Both total permeation flux and separation factor of the membrane were found to increase by increasing temperature and water concentration of feed. The continuity and high crystallinity of the membrane top-layer led to the fairly high dehydration of EtOH. It was found that there was no pinhole within the layer and the morphology of the membrane was almost defect-free.

Microstructural optimization of mordenite membrane for pervaporation dehydration of acetic acid

Abstract The crystallization of defect-free, acid-proof film microstructure is consistently pursued for making hydrophilic pervaperation (PV) membranes popular in process industries. We show that a novel modified secondary growth method can fabricate high-PV-performance, excellent-acid-stability mordenite membranes by eliminating grain boundary defects, dramatically by optimizing film microstructure. This method consists of growing the assembled nanocrystals of an ultrathin seed layer to a well-intergrown film directly on a macroporous support at a relatively low crystallization temperature (150 °C) by avoiding events that lead to an acid nonresistant film microstructure, such as the formation of Al-rich film surface and grain boundaries. Fluoride anions are used as mordenite crystal structure modifiers to optimize distribution of aluminum atoms in zeolitic film, so grain boundaries can be kept intact for long-term acidic corrosion. The polycrystalline films are ultrathin (3–4 μm), and oriented with different Si/Al ratios (5.6–20.1). Comparison with conventional synthesized membranes shows that these microstructurally optimized membranes have superior PV performance and acid stability for the dehydration of high-concentration acetic acid (AcOH) mixtures.

Preparation and microstructural analysis of high-performance mordenite membranes in fluoride media

High-performance mordenite membranes were prepared in fluoride media on porous tubular mullite supports by a single hydrothermal synthesis. Mordenite membranes and powders were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), magic-angle spinning nuclear magnetic resonance (MAS NMR) and contact angle with water droplets. The microstructure (i.e. hydrophilicity and crystal morphology) and pervaporation (PV) performance were influenced by the fluoride source and synthesis temperature. The 19F MAS NMR evidence shows the fluorine anion is present in channels of the mordenite crystal as a counterion of cations. Eight mordenite membranes (M-3 serial) prepared using NH4F-modified gels exhibited high fluxes of 1.50±0.25kgm−2h−1 together with high separation factors of 1380±110 for a water/ethanol (10/90wt.%) mixture at 75°C. The membranes also displayed good water-selective for the water/i-propanol mixture. The high performance is attributed to the thin zeolite layer and good surface hydrophilicity of mordenite membranes prepared in fluoride media.

Description of the preferential transport of monovalent salts through Na–mordenite membrane: Physico-chemical aspects

A Na–mordenite membrane was prepared by using sol–gel synthesis protocol, and spin-coating was chosen as the impregnation methodology. The gel was impregnated onto commercial ceramic tubular support (α-alumina) and surface characterizations were carried out on Na–mordenite powder prepared with the same gel. The Na–mordenite surface charge is not appreciably modified by a contact with monovalent or divalent salts. The average pore diameter was estimated in the range of 8nm. Previous results showed that monovalent salts were not retained by the stabilized Na–mordenite membrane while after an alkaline treatment, rejections were observed according to the order of hydration energies (NaF>NaCl>NaBr>NaI). After an acid cleaning, the membrane recovered its initial properties. A new estimation of average pore radius proved that steric effects were not responsible for rejection themselves. A new filtration test of mixed monovalent salt solution was carried out. Fluoride ions were retained by a majority while the others were almost not retained. Infrared characterizations indicate that, after an alkaline treatment, surface chemistry modifications may be at the origin of these interactions. Especially, the apparition of an ultrapolar layer all over the Na–mordenite surface greatly modifies Van der Waals interactions between the hydrated anions and the Na–mordenite surface.