NaA Zeolite Research Articles

Reaction of Na-A zeolite with molecular fluorine

NaA zeolite reacts rapidly with molecular fluorine at room temperature forming a mixture of amorphous material and of residual crystalline materials. The extent of the reaction depends on the gaseous pressure. The amorphous material contains fluorinated octahedral aluminum complex, sodium and silica. The crystalline fraction keeps the same unit cell parameter as the initial sample.

Improved desorption performance of NaA zeolite by rare earth (Re = La, Nd) ion exchange

With a characteristic of type I water adsorption isotherms, NaA zeolite has been considered as a very promising candidate for the utilization in adsorptive rotary wheel dehumidification system for deep dehumidification. However, high desorption temperature of the zeolite is not conducive to the system energy saving. In this research, the La-modified, Nd-modified and the binary La/Nd-modified NaA zeolites were synthesized by microwave-assisted ionexchangemethod to reduce the desorption temperature. The structural and the composition of the modified products were characterized using X-ray diffraction (XRD) and X-ray Energy Dispersive Spectrometry (EDS), and their adsorption/desorption performances were evaluated by static adsorption, thermogravimetry (TG) and temperature programmed desorption (TPD). TG results exhibited that, Nd-modified zeolite with the highest ion-exchange degree (α) of 63.35% was more effective in reducing the desorption temperature of NaA zeolite. TPD analysis also demonstrated that the binary modified adsorbent had a lower desorption activation energy (Ed), which indicates that the binary modified zeolite as deep dehumidification adsorbent has an excellent desorption performance.

Recent advances in acid-resistant zeolite T membranes for dehydration of organics

Abstract Zeolite membranes offer outstanding potentials in separation of many molecular mixtures due to their molecular sieving selectivity and the high thermal and mechanical stability that allow them to operate at harsh conditions. Development of durable and high separation performance membranes with lower fabrication and operation cost are highly demanded for industrial applications. Zeolite T membrane possesses good acid-resistance with excellent hydrophilic properties as compared to NaA zeolite membrane and can be extended to industrial organic dehydrations under an acidic environment. In the present review the research advances in development of zeolite T membranes for the dehydration of organic mixtures in acidic conditions are summarized. Especially the low temperature synthesis, and epitaxial growth of the zeolite membrane with high performance are well addressed, besides emphasis is particularly placed on ensemble synthesis of hollow fiber zeolite T membrane module and its future prospects for industrial separations.

Synthesis of zeolite from sugarcane bagasse fly ash and its application as a low-cost adsorbent to remove heavy metals

A new clean and sustainable procedure to synthesize low-cost zeolites from sugarcane bagasse fly ash (BFA), an industrial waste, is presented. BFA is used as source of Al and Si to obtain aluminosilicates with distinguished ion exchange capacity, confirmed by copper uptake. After the fly ash has been calcined and submitted to hydrothermal treatment employing NaOH as mineralizing agent, the XRD patterns of the as-synthesized samples revealed the formation of zeolite Na-A. Temperature and calcination time are key parameters affecting the ion-exchange capacity (q) of the zeolitic materials. Calcination at 600 °C for 8 h, under oxygen atmosphere, ensures that all carbon from fly ash has been removed and optimizes the ion-exchange properties. As a strategy to further improve q, Al isopropoxide was added to the synthesis medium, reducing the Si/Al ratio in the zeolite and generating more ion exchange sites. The hydrothermal treatment and addition of Al modify the structure and morphology of the zeolitic material, leading to a maximized adsorption capacity (142 mg Cu2+ g-1) at 1.71 Si/Al, which is much higher than the observed for a commercial polymeric resin (46.6 mg g-1).

Thermo-kinetics and product analysis of the catalytic pyrolysis of Pongamia residual cake

Catalytic fast pyrolysis of Pongamia residual cake (PRC) and the kinetics of this were evaluated using thermogravimetry and pyrolysis-gas chromatography/mass spectrometry analyses. The influence of the heating rate on the devolatilization process was studied to obtain corresponding kinetic information. Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) model-free isoconversion methods were used to predict the kinetic parameters. The major thermal degradation of PRC occurred around 150–550 °C with an activation energy of 97.2–394.3 kJ/mol or 114.5–412.2 kJ/mol as determined by the KAS and FWO methods, respectively. Micro-scale pyrolysis trials were performed to determine the effects of the PRC particle size, reaction temperature and PRC: catalyst weight ratio on the pyrolytic product distribution and upgraded pyrolytic vapor properties for the 5 wt% Ni impregnated on activated carbon (AC), aluminium(III) oxide (Al2O3), kaolin and zeolite NaA supports. The results indicated that using a 1:5 PRC: Ni/AC catalyst weight ratio with medium-sized PRC particles (125–425 μm) was the most effective condition for the conversion of oxygenated (O)-compounds to hydrocarbons (HCs) through decarbonylation, decarboxylation and dehydration reactions, giving the highest decrease (99%) in O-compounds. Increased HC yields, to more than 58%, were also obtained with this catalyst. Similarly, using the other synthesized Ni catalysts resulted in a reduction in the O-compounds and production of favorable HC species, albeit to a lesser extent. Therefore, the catalytic pyrolysis process of this residue, especially with a Ni/AC catalyst, has the potential to be a viable option for producing upgraded pyrolysis oil, which may be applied as a quality alternative biofuel.

Influence of an aging step on the synthesis of zeolite NaA from Brazilian Amazon kaolin waste

The synthesis of zeolite NaA from kaolin waste was conducted subjecting the reaction mixture to an aging step before autoclaving at high temperature. This waste, from Brasilian Amazon, is deposited in large basins and display excellent quality. In this aging step, the reaction mixture was agitated for 24h at room temperature, and after this time, the synthesis was performed for varying times of 1, 2, 3, 4, 6, 12, 18, 20 and 24h at a constant temperature of 110°C. The kaolin waste and synthesis products were characterized through X-ray diffractometry, scanning electron microscopy and chemical analysis. The results showed that the kaolin waste consists primarily of kaolinite. Zeolite NaA was obtained after 4h. However, zeolite NaA was obtained with a high degree of purity and a high degree of structural order only for times of 6, 12, 18, 20 and 24h. This study showed that zeolite NaA can be produced in shorter times through the synthesis route used. The production of zeolite NaA from kaolin waste could be an excellent way to minimize environmental impacts and decrease processing costs.

Scale-up of NaA zeolite membranes using reusable stainless steel tubes for dehydration in an industrial plant

Large-scale NaA zeolite membranes in a length of 1000 mm were successfully synthesized for the first time on macroporous tubular stainless steel (MTSS) supports in this work. The influencing factors for membrane synthesis, such as pre-treatment, synthesis time, synthesis temperature, Na2O/SiO2 ratio, synthesis reproducibility, membrane stability and support reusability, were investigated systematically. The experimental results revealed that the high-flux NaA membranes prepared on the reusable MTSS supports exhibits a high total flux of 8.28 kg m−2 h−1 and a separation factor of 11,000 for the dehydration of a 90 wt% ethanol solution through pervaporation. The MTSS tubes can be used for at least 8 synthesis-rinse-synthesis circles, and the as-synthesized membranes still maintain high competitive pervaporation performance. Additionally, 93 pieces of membrane samples were assembled in an industrial plant that can produce approximate 99.8 wt% ethanol from 93 wt% ethanol mixtures with a product flow rate of about 60 kg h−1. Importantly, the membrane showed a high stability for running over a whole month, demonstrating that the MTSS-supported membranes have reliable stability for industrial applications.

Ion exchange of zeolite coatings for adsorption heat pump applications

Coatings of NaA and NaX zeolites with various thicknesses were grown by direct crystallization on stainless steel plates. As a next step, ion exchange was applied to obtain the Li forms of the coatings. The materials obtained were characterized by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEGSEM), inductively coupled plasma (ICP), thermal gravimetry (TG), and N2 adsorption. The stabilities of the coatings in the ion exchange process were also determined. Li+ ions were observed to be readily exchanged with Na+ ions in zeolite coatings of various thicknesses but the percentage of exchange did not attain 100%. Favorable ion exchange conditions for obtaining both zeolite LiNaA and LiNaX coatings were determined. After Li exchange, the surface area of zeolite X increased by about 56% while the water capacities of zeolites X and A were enhanced by about 15 and 14%, respectively, for the conditions investigated. The ion exchange process resulted in some detachment from the coatings, which increased with enhanced coating thickness. Significant improvement was obtained in coating stability by using plates with roughened surfaces. Zeolite coatings in Li form may improve the performances of adsorption heat pumps, provided that relatively thick coatings remain stable to a desired extent during ion exchange.

Single‐step process without organic template for the formation of zeolite A from RHA

AbstractDice‐shaped zeolite A (NaA) was prepared via direct dissolution of rice husk ash (96.5% SiO2) in the presence of NaOH and sodium aluminate solution by autoclave process at 90°C/6 h without using any templating agent. The prepared particles were characterized by DTA/TG, XRD, FTIR, N2 adsorption‐desorption physisorption analysis, FESEM, and TEM. XRD results confirmed crystallization of pure NaA zeolite phase. FTIR study shows the characteristic bands at 554 cm−1 for double 4 membered ring (D4R) of NaA zeolite. The total BET surface area of the product was found to be 31.6 m2 g−1. FESEM and TEM images show dice shaped NaA particles of size around 1 μm which is formed via oriented crystalline aggregation of primary particles (30‐40 nm). A tentative mechanism was proposed for the formation of NaA crystals through direct dissolution of rice husk ash. The synthesized NaA zeolite could be used for purification of alcohol and separation of toxic and radioactive ions from waste water via a cost‐effective process.

Structural and adsorptive properties of silica-alumina and clay materials of mineral and synthetic origin

Location on territory of Ukraine of great deposits of aluminosilicates together with good facilities for their processing and standardization promotes the study of this raw material, results of which could be useful for the developers of enterosorbents. For search the specific sorptive activity a comparative examination of several materials of silica-alumina and clay nature has been carried out in this work.
 The X-ray phase analysis, a measuring of specific surface area by the low temperature adsorption–desorption of nitrogen and the method of isotherm of adsorption have been used.
 It is shown that silica-alumina and clay materials have much less specific surface as compared to silica gel Syloid® 244 FP and carbon sorbent SCN. The sorbents of montmorillonite type (smectite, saponite) are characterized by the highest adsorptive capacity in relation to methylene blue and congo red dyes. Synthetic zeolites NaA and NaX effectively absorb the ions of zinc from solution, significantly overcoming Syloid® 244 FP and SCN which were taken as preparations of comparison. Therefore, on the basis of NaA and NaX the selective enterosorbents for elimination from the organism of toxic metals could be created.

Synthesis of Ceramic and Glass Ceramic Matrices with Immobilized Cesium Radionuclides for Active Zones of Ionizing Radiation Sources

The present study was devoted to the development of alternative solutions related to replacement of highly dispersed powder of cesium chloride (137CsCl) used as a filler of active zones of g-radiation IRSs (ionizing radiation sources of the closed type) by safer and more efficient in operation highly compacted ceramic or glass ceramic material. An advanced method of fabrication of highly compacted (density of ~99.8 % of the theoretical one) aluminosilicate (artificial NaA zeolites) ceramic and glass ceramic matrices characterized with high construction strength (compression strength ~149 MPa) applicable for reliable immobilization of cesium radionuclides (leaching rate <10-5–10-6g/cm2×day) has been suggested. Unique matrices properties are ensured by advanced features of the technology of Spark Plasma Sintering (SPS) based on high-rate electro-pulse consolidation of the radioactive charge (adsorbed cesium content ~22.16 mass %) into thermodynamically stable ceramics or glass ceramics. The earlier unstudied features of the SPS consolidation of natural zeolite powders sorption-saturated with a radioactive cesium simulant are presented, including the dynamics of their compaction and specifics of phase and structural transformations under effect of irreversible spark plasma conditions.

Characterisation of NAA zeolite made from Malaysian kaolin

In this study, as an alternative to the pure chemical used to prepare zeolite NaA, the clay mineral kaolinite was used as the source material for NaA-zeolite preparation. Kaolin as an alternative low cost material and as a potential precursor to zeolite A synthesis via metakaolinisation of kaolin at 900 °C to a reactive amorphous material called metakaolin and hydrothermal treatment of metakaolin with an aqueous alkali. Before this reaction takes place however, raw kaolin undergoes a pretreatment process to increase its purity through the removal of impurities. This research intends to prepare zeolite A from Malaysian kaolin. A series of composition and structural characterisations of both the starting material (kaolin) and the final product (zeolite A) were carried out using powder X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) to confirm the formation of NaA-zeolite. From the characterisation studies, it was found that high-purity NaA-zeolite can be produced from local kaolin. These findings enable us to answer the fundamental question regarding the structural characteristics of NaA-zeolites synthesised from Malaysian kaolin.

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.

EVALUATION OF MODIFIED FLY ASH BASED NAA-ZEOLITE: EFFECT OF CRYSTALLINITY ON CO2 ADSORPTION CAPACITY

NaA zeolite was successfully synthesised from fly ash through hydrothermal process. The synthesised NaA zeolite was modified with Li+, Ca2+ and Mg2+ through ion exchange at a temperature of 60 C and contact times of 1 h and 4 h. In this study the crystallinity of the synthesised NaA as well as its modified (LiA, CaA and MgA) was evaluated towards CO2 adsorption capacity using temperature programmed desorption (TPD) process at low temperature (40-150 C) and high temperature (150-700 C). The mineral phase and structural characteristics of zeolites were examined using XRD and FT-IR. The results from XRD and FT-IR spectra revealed unique structural alterations influenced by the intrinsic characteristic of individual cation incorporated in NaA zeolite. Monovalent cations displayed highest crystallinity compared to divalent cations (downward order: NaA > LiA > MgA > CaA). Low and high temperature CO2-TPD profiles were independent of the degree of crystallinity of the zeolites and a significant amounts of CO2 desorption occur at low temperature indicating that physisorption is the most prominent adsorption mode in NaA, LiA, CaA and MgA zeolite.

One-Pot Preparation of NaA Zeolite Microspheres for Highly Selective and Continuous Removal of Sr(II) from Aqueous Solution

This paper describes a synthesis method and adsorption properties of geopolymer microspheres toward strontium ions; first, it was prepared by a dispersion–pelletizing–solidification (DPS) method followed by transformation into NaA zeolite microspheres (about 100 μm) through an in situ heat curing process. The adsorption experiments were investigated and the experimental data were fitted well by the pseudo-second-order kinetic model and Freundlich isotherm model. Loading experiments were performed by batch and column process techniques. The maximum adsorption capacity in the batch process was assigned to be 106.28 mg/g, the zeolite microspheres’ adsorption of strontium ions reached adsorption equilibrium in approximately 15 min. In the dynamic column, the most suitable flow rate was found to be 4 mL/min; this was higher compared with other sorbents with the same particle size. Moreover, the zeolite microspheres have a good dynamic separation effect, the concentration of the outlet Sr(II) ions from the colu...

Pt encapsulated into NaA zeolite as catalyst for the WGS reaction

Pt catalysts were prepared by encapsulating the active metal in the NaA zeolite structure. The catalysts were prepared by hydrothermal synthesis using two heating sources, conventional heating through a thermal bath and microwave radiation. The synthesis time was significantly reduced using microwave radiation without affecting the crystallinity or metallic content of the solids obtained. By X-ray diffraction the presence of the pure NaA zeolite phase was confirmed in all the samples. XRD, XPS and TEM results suggested the presence of Pt particles preferentially located inside the crystalline structure.Pt_NaA catalysts were active and selective for the water gas shift reaction at 673 K. No methane formation was detected in any of the samples under the reaction conditions studied. The Pt_NaA catalyst with low Pt content (0.6% wt.) achieved a high conversion of CO (ca. 70%).

CFD simulation of hollow fiber supported NaA zeolite membrane modules

NaA zeolite membranes have exhibited excellent performance in pervaporation dehydration of organic solvents. However, the industrial applications based on tubular NaA zeolite membranes are limited due to the high fabrication cost and low permeation flux. Hollow fiber supported zeolite membranes have great advantages of high permeation flux and large packing density, which are beneficial to further reduce the membrane cost. For practical application, it is of great significance to design membrane modules with optimized geometric configuration for the hollow fibers. Here, a hollow fiber membrane module equipped with seven bundles of hollow fiber NaA zeolite membranes and several baffles was designed by computational fluid dynamics (CFD) technique. The effect of baffles on flow field distribution of the membrane module was investigated. The results showed that the membrane module with two radial baffles and four axial baffles not only showed uniform flow distributions inside the module, but also improved the axial velocities along the hollow fibers, which could alleviate concentration polarization. The improved separation efficiency of the membrane module was further confirmed by the experimental characterization.

Preparation of nanosized NaA zeolite and its surface modification by KH-550

Abstract Nanosized NaA zeolite was successfully synthesized by hydrothermal method using tetraethyl orthosilicate (TEOS) and aluminum isopropoxide (AIP) as the main raw materials. The surface modification of NaA zeolite was carried out by silane coupling agent 3-aminopropyltriethoxysilane (KH-550). The effects of silane coupling agent dosage, reaction temperature, reaction time, hydrolysis time and pH value on grafting rate of NaA zeolite were investigated in detail. The zeolites were characterized by XRD, SEM-EDS, FT-IR and TG-DTA. The results showed that the surface of NaA zeolite was modified successfully by KH-550. The optimal modification conditions obtained were as follows: the dosage of coupling agent in 95 % ethanol – 1.6 %, reaction temperature − 70 °C, reaction time – 2 h, hydrolysis time – 20 min, and pH value – 3.5. Under these conditions, the grafting rate of modified NaA zeolite was 3.95 %.

Formation of pure NaX zeolite: Effect of ageing and hydrothermal synthesis parameters

Among the challenges of synthesizing NaX zeolite is the formation of competing phases during the hydrothermal process which results with impurities in the product. The competing phases of NaX zeolite may include NaP zeolite, hydroxylsodalite and NaA zeolite. In this paper, relationships between the preparation parameters and hydrothermal synthesis parameters towards the formation of high purity of NaX zeolite are studied. The studied parameters include ageing duration, hydrothermal synthesis temperature and hydrothermal synthesis duration. Sodium silicate, sodium aluminate, sodium hydroxide and distilled water are used as the main reactant sources at a fixed molar ratio. The morphology, Si/Al ratio and zeolite phase of the resultant particles were characterized using field emission scanning electron microscope (FESEM), energy-dispersive x-ray spectroscopy (EDS) and X-ray diffraction analyser (XRD), respectively. Hydrothermal synthesis temperature of 90°C and synthesis duration of 16 hours were identified as the optimum synthesis parameters for producing high crystalline, single phase NaX zeolite. In addition, the relationships between synthesis parameters and NaX zeolite produced were also studied. Longer ageing duration and longer hydrothermal synthesis duration results in high crystalline product with potential impurities phases, while higher hydrothermal synthesis temperature produced pure NaX zeolite at shorter hydrothermal synthesis duration.

Binderless zeolite NaX microspheres with enhanced CO2 adsorption selectivity

Abstract Zeolite NaX@NaA core-shell microspheres were prepared via a post-treatment secondary growth of zeolite NaA films on outer surface of binderless zeolite NaX microspheres. The obtained core-shell microspheres were composed of intergrown octahedral NaX particles inside, with particles size of ca. 500–750 nm, and continuous zeolite NaA films on the outer surface with the thickness of about 2 μm. Higher CO2 separation performance was observed for the core-shell microspheres comparing to the parental binderless zeolite NaX microspheres. The ideal separation factors of zeolite NaX@NaA core-shell microspheres for CO2/CH4 and CO2/N2 were 13 and 47, and the adsorption selectivities for the corresponding binary mixtures were 308 and 923, significantly higher than the binderless zeolite NaX microspheres of 9 and 19 as well as 264 and 735, respectively. After K+ ion exchanging, the core-shell zeolite microspheres have even higher adsorption selectivities of 326 and 1109 for CO2/CH4 and CO2/N2 binary mixtures. The crushing strength of the binderless zeolite NaX microspheres was increased from 0.46 MPa to 3.42 MPa after the secondary growth. In addition, the growth of zeolite A film was resultant from interzeolite conversion and the interzeolite conversion was investigated by the conversion of zeolite NaX to NaA crystals in NaA membrane synthesis gel.