NaY Zeolite Membrane Research Articles

Effects of ion-exchange on the pervaporation performance and microstructure of NaY zeolite membrane

Pervaporation performance of NaY zeolite membranes is improved by ion-exchange with di-valent nitrate salt. Different nitrate salts, including Co(NO3)2, Mg(NO3)2, Zn(NO3)2, Ca(NO3)2, Cu(NO3)2, KNO3, and AgNO3, have great effects on the channel structure and water affinity of the NaY zeolite membrane. When the concentration of nitrate salt, ion-exchange temperature and time are 0.1 mol·L−1, 50 °C and 2 h, the ion-exchange degree order of NaY zeolites is Ag+ > K+ > Ca2+> Zn2+ ≫ Co2+ > Mg2+. Especially, Ag+ and K+ cation exchange degree of NaY zeolites are achieved to 96.54% and 82.77% in this work. BET surface, total pore capacity, pore size distribution and water contact angle of the ion-exchanged NaY zeolites are all disordered by mono- and di-valent cations. Di-valent nitrate salt is favor for increasing the dehydration performance of NaY zeolite membranes by ion-exchange. When the ion-exchange solution is Zn(NO3)2, the total flux variation and separation factor variation of the NaY membrane (M-5) are −45% and 230% for separation of 10% (mass) H2O/EtOH mixture by pervaporation, and the ion-exchanged membranes showed good reproducibility.

Growth process and short chain alcohol separation performance of fluoride-containing NaY zeolite membrane

Growth process of the NaY zeolite membranes was investigated by fluoride-containing precursor synthesis gel. Compared with the fluoride-free precursor synthesis gel, the irregular NaY zeolite crystals were dissolved into amorphous by the fluoride-containing precursor synthesis gel initially, the amorphous contained the Y-type zeolite characteristic bands by the IR characterization. The fine square NaY zeolite crystals arose from the amorphous, which were accumulated and gradually grew into a dense NaY zeolite layer on the support surface after 6.5 h. Because the excessive NaY zeolites were dissolved by the strong alkaline and fluoride-containing precursor synthesis gel, there was plenty of amorphous on NaY zeolites layer for prolonging the crystallization time. The as-synthesized NaY zeolite membranes had a good separation performance and repeatability for separation of 10 wt% methanol (MeOH)/methyl methacrylate (MMA) mixture by pervaporation, the flux and separation factor were (1.27 ± 0.07) kg ∙ m−2 ∙ h−1 and (4900 ± 1500) at 323 K, respectively. Besides, the NaY zeolite membranes were applied to separate the other short chain alcohol from the various alcohol/organic ester and alcohol/organic ether mixtures, the NaY zeolite membranes showed high short chain alcohol perm-selectivity.

Formation of NaY zeolite membrane: influence of intermediate layer and its characterization

In the synthesis process of zeolite membranes, the zeolites crystals are crystallized and grow during crystallization period to form polycrystalline film.Secondary growth method is an effective method to synthesis high quality zeolite membranes which involves two main steps which are coating and hydrothermal treatment (HT) synthesis. There are several problems associated with the coating process in secondary growth method such as lack of good adherence of the seeds, rough surface of the support, and thermal mismatch between the zeolite seeds and supports during hydrothermal process. In order to solve these issues, an intermediate layer (buffer layer) could be applied between the support and the seeds layer hence to reduce the defects forms during the hydrothermal treatment (HT) synthesis process. In current study, two different types of intermediate layer were studied and results were compared in terms of zeolite seeds coverage on the surface of the support and zeolite layer formed during subsequent hydrothermal treatment (HT) to form zeolite membranes. The formed zeolite membranes were characterized with X-Ray diffraction (XRD) and scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDX).

Cation-exchanged NaY Zeolite: Effect of temperature and ion concentration to membrane performance

Zeolite membranes possess well defined pore structures which able to separate gasses with high selectivity. The separation between adsorptive and non-adsortive gasses depends on the affinity of permeating gas molecules with the zeolites structures whereby different types of cations resides in the zeolitic framework will affect the permeselectivity of the membranes. Several efforts have been made to modify zeolite membranes in order to enhance their capability in gas separation by ion exchange process. Here, investigations were performed on the ion exchange process of zeolite NaY membrane with Ag+ cation at different concentrations (0.1M, 0.025M) and temperatures (ambient temperature and 80°C). The results revealed that temperature plays significant role in maintaining the morphologies of zeolite NaY membranes. Dealumination process was also observed to occur simultaneously with the ion exchange process. Overall, CO2/CH4 selectivity of the cation-exchanged NaY zeolite membranes increased by 100% with less CO2 flux reductions were recorded by samples which had been ion exchanged with less concentrated ion exchange solution i.e. 0.0125M at ambient temperature. Nevertheless, CO2/CH4 selectivity decreased for membrane samples which had been ion exchanged at higher temperature (80°C) due to dissolution of the zeolite membranes layer.

Effect of flouride on preparation and pervaporation performance of NaY zeolite membrane for EtOH/ETBE mixture

Good separation performance NaY zeolite membrane was successfully prepared on the tubular mullite support by fluoride-containing precursor synthesis gel. The fluoride source had a great influence on NaY zeolite membrane growth and separation performance for EtOH/ETBE mixture, the NaF containing precursor gel was benefit for preparing high Si/Al ratio, fine reproduction quality and long-term stable NaY zeolite membrane. Solid state 19F MAS NMR characterization results indicated that the fluorine existed in the channel of NaY zeolite crystals. Both flux and separation factor of the NaY zeolite membrane were greatly depended on the separation temperature and composition of EtOH/ETBE mixtures. The NaY zeolite membrane presented eminent long-term stability for separating 20 wt% EtOH/ETBE mixture at 60 °C, even if the test time was prolonged to 80 h, the flux and separation factor were kept 1.30 kg m−2 h−1 and 1100.

Studies on Different Support Seeding Conditions Applied in the Formation of NaY Zeolite Membrane

Abstract Exploring the efficient synthesis method is essential in producing zeolite membranes with minimum defects. Seeding prior hydrothermal synthesis (HT) is the major parameters that affecting the quality of zeolite membrane formed. The colloidal stability of the NaY seed solution and its attachment to the support were studied by varying the pH of the seed solutions. Three seeding methods, including dip-coating, spin coating and vacuum coating, were studied in forming NaY zeolite seed layer. Then, the seeded alumina supports were subjected to hydrothermal treatment (HT) in order to form NaY zeolite membranes. The effect of NaY seeds solution colloidal stability, electrostatic attachment between seeds and support and the seeding methods on the properties of the quality of the formed NaY zeolite membranes were investigated. The zeta potential of the seed solution was measured with respect to different pH of the seed solution. The formed NaY zeolite membrane samples were characterized with X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) and Energy dispersive X-Ray spectroscopy (EDX). Spin coating and vacuum coating displayed better seeds coverage onto the alumina support due to the vacuum lock mechanism however excessive seeds accumulation onto the alumina support will inhibit zeolite growth and expansion hence to produce NaY zeolite membranes with cracks. Nonetheless, seeded supports by dip coating method display less coverage on the support however with a proper selection pH of the seeding solution with relates to its zeta potential, stable aqueous colloidal dispersion of the seeds solution and better attachment between the zeolite seeds and the support could be achieved in order to form zeolite NaY membranes with least defects.

CO2/H2 Selectivity Prediction of NaY, DD3R, and Silicalite Zeolite Membranes

Using DD3R, silicalite and NaY zeolite membrane for gas separation is an attractive prospect for the development of a sustainable green process industry. The interest in CO2 and H2 lies in their relatively strong and weak adsorption in zeolite, respectively, causing a peculiar behavior of membrane selectivity, which is here evaluated in a wide range of temperature (273–573 K), feed pressure (100–500 kPa) and CO2 molar fraction (0.05–0.95). As a result, CO2/H2 selectivity of the considered zeolite is found to be high at a low temperature owing to the relatively strong CO2 adsorption with respect to the weak H2 one. Differently, selectivity is much lower at a higher temperature because of the reduced adsorption strength. The temperature strongly affects the membrane selectivity through surface diffusion closely correlated to gas adsorption, and CO2 adsorption results responsible for the high membrane selectivity in the low-temperature range.

Discrimination among gas translation, surface and Knudsen diffusion in permeation through zeolite membranes

Gas translation diffusion is proposed to compete with surface diffusion for describing the permeation of light gases (He, H2, CO2 and CO) through zeolite membranes. The analysis for both DD3R and NaY zeolite membranes shows some differences in H2, CO and CO2 permeation for both binary/ternary gas mixture and single gas.The permeation description through gas translation of weakly adsorbed species such as, e.g., H2, specifically at low temperatures, is more accurate than that obtained by Knudsen diffusion in a previous work. Gas translation paired to surface diffusion well reproduces the maximum in H2 flux, which was missed by the Knudsen diffusion (Caravella et al., 2016) [13]. The strongly adsorbed species are less dependent on gas translation or Knudsen diffusion since the surface diffusion is very significant in the whole temperature range investigated.The gas translation was demonstrated to reproduce the permeation through zeolite membranes better than Knudsen diffusion.This paper attempts to discriminate the operating mechanisms among gas translation, surface and Knudsen diffusion in gas mixture permeation through zeolite membranes.

C-doped Cr2O3/NaY composite membrane supported on stainless steel mesh with enhanced photocatalytic activity for cyclohexane oxidation

In this study, a C-doped Cr2O3/NaY composite membrane supported on stainless steel mesh with layer-by-layer structure was successfully synthesized and used in the partial oxidation of cyclohexane. In the composite membrane, NaY zeolite membrane acted as absorbent and the C-doped Cr2O3 behaved as photocatalyst, which was successfully prepared using a chromium-containing MOF as precursor. The supported composite membrane was characterized by a series of analysis techniques. Comparing with the stainless steel mesh-supported C-doped Cr2O3 membrane, the supported C-doped Cr2O3/NaY composite membrane exhibited superior visible-light-driven photocatalytic performance for cyclohexane oxidation. This is due to its layer-by-layer structure and NaY membrane with high surface areas and polarity which can preferentially adsorb KA oil products, avoiding their overoxidation.

Seed‐Free Synthesis and Characterization of Zeolite Faujasite Aluminosilicate Coating on α‐Alumina Supports

NaY zeolite was synthesized by a simple sol–gel technique. NaY zeolite membrane was formed on the alumina substrate using optimized solution composition and synthesis conditions. The formation of the NaY zeolite was ascertained by X‐ray powder diffraction, which showed that the crystallinity improved with annealing. The high‐resolution transmission electron microscopy images of samples annealed at 300°C showed the formation of cubic structure corresponding to NaY zeolite. Brunauer–Emmett–Teller analysis revealed that the synthesized zeolite is a well crystallized NaY zeolite. The SEM images revealed the formation of fine structure NaY zeolite membrane on α‐alumina substrate.

A novel modelling approach to surface and Knudsen multicomponent diffusion through NaY zeolite membranes

A novel pairing between Knudsen and surface diffusion is developed for multicomponent mass transport in NaY zeolite membranes considering the actual conditions inside the pores owing to competitive adsorption of the species. The motivation behind this study starts from the consideration that the adsorption of the species, in particular of the most strongly adsorbed ones (like CO2), can significantly influence the Knudsen permeation. This occurs because the pore geometrical parameters affecting permeation, i.e., porosity, tortuosity and mean diameter, are modified by the steric effect owing to the presence of the adsorbed molecules, whose size is close to pore diameter. Therefore, in the present work, all these geometrical parameters are expressed as functions of the adsorption loading. This leads to a model that correctly predicts the blocking effect on the Knudsen diffusion mechanism at a low temperature, where the adsorption strength is sufficiently high to cause a severe occupation of the channel cross-section. As a consequence, such a model allows membrane selectivity to be predicted in a wide range of temperature and pressure. For instance, the CO2/H2 selectivity is observed to change from 25 to 0.3 when the temperature goes from 303 to 673 K. Hence, this novel approach, which is well-validated in both binary- and ternary-mixture conditions, is a useful tool for the analysis of the mass transport of multicomponent mixtures through NaY zeolite membranes, particularly at lower temperatures, where the adsorption strength provides a higher selectivity.

Preparation of a novel composite electrode based on N-doped TiO2-coated NaY zeolite membrane and its photoelectrocatalytic performance

Abstract For the first time the preparation of the N-doped TiO 2 -coated NaY zeolite membrane (N-doped TiO 2 /NaY zeolite membrane) as an electrode material for photoelectrocatalysis has been achieved and reported. The XRD, SEM, UV–vis and XPS techniques were used to characterize the structure of the N-doped TiO 2 /NaY zeolite membrane. The results verified that the surface of the N-doped TiO 2 /NaY zeolite membrane was coated by TiO 2 nanoparticles of ca. 20 nm size and exhibited a distinct red-shift in the UV–vis spectra compared to N-doped TiO 2 . The photoelectrocatalysis performance of the N-doped TiO 2 /NaY zeolite membrane electrode was evaluated by phenol degradation. The results revealed it is a promising novel electrode material for application of photoelectrocatalysis in the removal of organic contaminants in waste water.

Preparation and photoelectrocatalytic performance of N-doped TiO2/NaY zeolite membrane composite electrode material.

A novel composite electrode material based on a N-doped TiO2-loaded NaY zeolite membrane (N-doped TiO2/NaY zeolite membrane) for photoelectrocatalysis was presented. X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible (UV-vis) and X-ray photoelectron spectroscopy (XPS) characterization techniques were used to analyze the structure of the N-doped TiO2/NaY zeolite membrane. The XRD and SEM results verified that the N-doped TiO2 nanoparticles with the size of ca. 20 nm have been successfully loaded on the porous stainless steel-supported NaY zeolite membrane. The UV-vis result showed that the N-doped TiO2/NaY zeolite membrane exhibited a more obvious red-shift than that of N-TiO2 nanoparticles. The XPS characterization revealed that the doping of N element into TiO2 was successfully achieved. The photoelectrocatalysis performance of the N-doped TiO2/NaY zeolite membrane composite electrode material was evaluated by phenol removal and also the effects of reaction conditions on the catalytic performance were investigated. Owing to exhibiting an excellent catalytic activity and good recycling stability, the N-doped TiO2/NaY zeolite membrane composite electrode material was of promising application for photoelectrocatalysis in wastewater treatment.

Microwave synthesis of high-flux NaY zeolite membranes in fluoride media

High-flux NaY zeolite membranes were synthesized using low-cost mullite supports by microwave heating in fluoride media.

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 of NaY zeolite membranes in fluoride media and their application in dehydration of bio-alcohols

Improved NaY zeolite membranes were prepared in the presence of ammonium fluoride. The crystallization and separation performance of fluoride-derived NaY zeolite membranes were studied in comparison with fluoride-free membranes. The addition of ammonium fluoride in gel influenced the crystallization and the morphologies of NaY zeolite and zeolite layers, and effectively suppressed the formation of the impurity phase of P-type zeolite in NaY zeolite layers. The fluoride-derived NaY zeolite membranes had thinner zeolite layers and displayed both higher fluxes and separation factors for the dehydration of bio-alcohols (ethanol and butanol) than the fluoride-free membranes. The separation factors increased with the increasing kinetic diameters of alcohols for the methanol, ethanol, i-propanol and n-butanol aqueous solutions. Synthesis reproducibility of fluoride-derived membranes and membrane stability during the dehydration process were also investigated. 29Si and 19F MAS NMR results confirmed that fluorine anions were not included in FAU crystals.

NaY zeolite membranes with high performance prepared by a variable-temperature synthesis

NaY zeolite membranes were synthesized by the secondary growth method on the surface of α-Al2O3 and mullite tubular supports. Influence of the different thermal profiles during the hydrothermal synthesis was investigated. In addition to the conventional constant temperature (CT) at 100 and 140°C syntheses, a variable-temperature syntheses were applied where the temperature was increased from 100 to 140°C (VT-LH) and decreased from 140 to 100°C (VT-HL) during the hydrothermal syntheses. Synthesized membranes were characterized by XRD, SEM and EPMA. The pervaporation (PV) performance of the NaY zeolite membranes was examined with water/alcohol (ethanol or isopropanol) mixtures and alcohol/organic mixtures such as methanol/dimethly carbonate (DMC), /methyl methacrylate (MMA), /methyl tert-butyl ether (MTBE), /methyl isobutyrate (MIB), /methyl acrylate (MA), /methyl propionate (MP) and ethanol/ethyl tert-butyl ether (ETBE) mixtures. NaY zeolite membranes showed dehydration properties and alcohol selectivity from alcohol/organic mixtures. The highest PV results were obtained with membranes prepared on α-Al2O3 supports with the VT-HL thermal profile: separation factors over 5000 with fluxes over 3kgm−2h−1 were obtained in the separation of methanol/MMA (10/90wt.%) and methanol/MA (10/90wt.%) mixtures at 60°C. The remarkably high perm-selectivity makes the NaY zeolite membrane an attractive candidate in alcohol/organic separations.

Optimization of NaY zeolite membrane preparation for the separation of methanol/methyl methacrylate mixtures

NaY zeolite membranes were prepared on porous mullite supports by secondary hydrothermal growth for pervaporation separation of thermal-sensitive methanol/methyl methacrylate (MMA) mixtures. Effects of synthesis parameters (synthesis time, gel composition, aging treatment and silica source) and separation conditions (feed temperature and composition) on the separation performance of NaY zeolite membranes were investigated. Under optimized membrane synthesis conditions (6.5h crystallization time, 10–16h aging time at 303–323K, and gel composition of 1SiO2: 0.04Al2O3: 0.88Na2O: 40H2O), NaY zeolite membranes without the impurity phase of P-type zeolite could be formed on the porous supports. The best membrane displayed fluxes of 0.55–2.35kgm−2h−1 and separation factors of 1000–3600 for the 5–50wt.% methanol/MMA mixtures at 323K. The preparation of NaY zeolite membranes under optimized conditions showed a good reproducibility. The high methanol/MMA pervaporation separation performance of NaY zeolite membranes can be attributed to the selective sorption and molecular sieve of zeolite layers.

Preferential Oxidation of CO in a Hydrogen-Rich Gas Through Au/NaY Catalytic Membranes

This paper describes novel Au/NaY catalytic membranes for preferential oxidation of CO (CO-PROX) in an H 2-rich gas. NaY zeolite membranes with a high CO 2/N 2 separation factor were loaded with nanosized Au particles using an ion-exchanged method. X-ray diffraction analyses showed that the structure of the NaY zeolite was not damaged by the ion exchange process. CO-PROX experiments showed that the catalytic membranes had excellent catalytic performance for selective oxidation of CO. The CO/H 2 molar ratio on the permeate side decreased with increasing operating temperature in the range of 80–200°C. At 200°C, almost no CO was detected from the permeate stream of a catalytic membrane with the feed containing 0.67% CO, 1.33% O 2, 32.67% H 2, and He in balance. Thus, these Au/NaY catalytic membranes show a promise for CO removal from hydrogen fuels.

Seeded synthesis of small polycrystalline NaY zeolite membrane using zeolite structure-directing agent and its pervaporation performance

Continuous and polycrystalline NaY zeolite membranes were synthesized successfully on porous α-Al2O3 tubes by zeolite structure-directing agent (ZSDA) method. This ZSDA method consists of two steps: preparation of NaY ZSDA and growth of NaY zeolite membranes with ZSDA by the secondary hydrothermal treatment. The synthesis parameters, such as aging time, aging temperature and the amount of ZSDA added, etc. were investigated. Scanning electron microscopy and X-ray diffraction technology were used to characterize the morphology and the crystal structure of the as-synthesized zeolite membranes, respectively. The results indicated that the growth of NaY zeolite membranes on the supports depended strongly on ZSDA, which could not only accelerate the formation of NaY zeolite membranes but also inhibit the transformation of NaY zeolite phase. It was also found that the prolonged aging time, the lower aging temperature and the increasing amount of ZSDA resulted in a crystal size diminution of the product, thus linking the aging process directly to the increasing number of formed nuclei. Compared with the larger crystal NaY zeolite membrane, the small crystal NaY zeolite membrane exhibited much higher separation selectivity. At 308 K, the highest separation selectivities achieved towards 1,3-propanediol/glycerol and 1,3-propanediol/glucose were 80 and 2,400, respectively.