Na-A Type Zeolite Research Articles

Synthesis of NaA-type Zeolite and its sorption properties

In the article, the synthesis of NaA-type zeolite, its processing with alkali and acid, and the sorption capacity of the synthesized sorbent (composition: NaA type zeolite:clay=1:1) concerning Fe3+, Ni2+, Cr3+, Cu2+ were studied. The use of modified clays leads to significant changes in the structural and mechanical properties of the samples. Increasing the pH value of NaA-type zeolite-based moulding materials increases the proportion of plastic deformations by 1.5 times. An increase in the content of NaA-type zeolite in the forming materials sharply increases the percentage of elastic deformations and, as a result, worsens their formation. In turn, changing the type of binder plasticizer, in this case from clay to kaolin, leads to excessive development of plastic deformations, which leads to the appearance of defects during the moulding process. To improve the formation of NaA-type zeolite and clay-based materials, they can be modified with alkali. During the research, it was found that the optimal ratio of zeolite and clay sorbent is 1:1. It was found that replacing the plasticizer with 1M NaOH solution increases the sorption capacity of the recommended sorbent based on NaA type zeolite, and acid treatment of NaA type zeolite causes its crystal structure to be disturbed. It was conducted on a DRON-3M diffractometer. A standard graphite monochromator is attached to the primary X-ray beam. Differential thermal analysis was performed on a Q-1500D (MOM company) derivatography. The heating rate of the samples in the air was 5 and 10 ℃ per minute. Purpose of work- synthesis of NaA-type zeolites and study of their sorption properties.

Influence of Organic Solvent Species on Dehydration Behaviors of NaA-Type Zeolite Membrane.

In this study, an NaA-type zeolite membrane was prepared, and the dehydration performances of the membrane were determined by the pervaporation for several organic solvents to understand the lower dehydration performances of zeolite membranes for NMP solutions than those for alcohols. For a 90 wt% ethanol solution at 348 K, the permeation flux and separation factor of the membrane were 3.82 kg m−2 h−1 and 73,800, respectively. The high dehydration performances were also obtained for alcohols and low boiling solvents (acetonitrile, acetone, methyl ethyl ketone (MEK) and tetrahydrofuran (THF)). However, the permeation flux and separation factors decreased significantly for high boiling solvents, such as N,N-dimethylacetamide (DMA), N,N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP). The influences of the water content and temperature on the dehydration performances for the NMP solutions were determined to understand the lower dehydration performances for those solvents. Those results suggest that the lower dehydration performances for the high boiling solvents were attributed to the lower vapor pressures of water and the higher permeances of those solvents. Furthermore, this study proposes that the permeation behaviors through zeolite membranes could be understood by the determination of the effect of temperature on the permeance of individual components.

Facile preparation of zeolite-activated carbon composite from coal gangue with enhanced adsorption performance

A composite structure of the zeolite and activated carbon is successfully synthesized through CO2 activation followed by the hydrothermal synthesis method using coal gangue as the raw material. The zeolite-activated carbon composite is used as an adsorbent for the removal of heavy metal ions and macromolecular organics. The integrative adsorption property of the composite could be improved by adding a certain amount of powdered coal into coal gangue as the extra carbon source. The specific surface area of a so-prepared composite is 669.4 m2/g, which is much larger than that of the pure NaA type zeolite (249.3 m2/g). As a result, the zeolite-activated carbon shows high adsorptive efficiencies for Cu2+ (92.8%) and Rh-B (94.2%). The thermodynamic and kinetic processes for adsorption of Cu2+ and Rh-B onto pure zeolite and zeolite-activated carbon are also investigated systematically. The mechanistic study of zeolite-activated carbon indicates that the uniform micropores in zeolite are suitable for the adsorption of heavy metal ions and the multilevel porous structure of activated carbon could accommodate macromolecular organics. The high value-added product prepared from coal gangue is a good alternative to treat industrial waste water.

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

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

Synthesis of Coal Fly Ash Zeolite with Copper Oxide Load for Acid Red GR Wastewater Treatment

The waste coal fly ash was utilized to synthesize zeolite by alkaline fusion method through orthogonal test. The copper oxide was loaded on the zeolite by dipping method. The optimal ratio of coal fly ash to sodium hydroxide, ratio of liquid to solid, calcining temperature and crystallization time were determined to be 1.2, 9, 700°C and 10 h, respectively. The CuO dipped zeolite was applied to treat the acid red GR wastewater and the obtained color and COD removal rates were 83.80% and 99.88%, respectively. The XRD pattern showed that the NaA type zeolite phase was formed in the experiment.

Preparation and characterization of surface-modified zeolite-polyamide thin film nanocomposite membranes for desalination

NaA type zeolites were surface modified with octadecyltrichlorosilane (OTS) and then added in polyamide layer of thin film composite (TFC) membranes to prepare surface-modified zeolite-polyamide thin film nanocomposite (TFN) membranes for desalination. The zeolites were characterized by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The properties of membranes were characterized by scanning electron microscopy (SEM), contact angle measurement, and the permeation experiment, respectively. The results showed that zeolites were successfully surface-modified with OTS without changing of its structure. The SEM images depicted that the membrane morphology was more homogeneous and the zeolites aggregation in membranes was ameliorated after the zeolites were surface modified. The results of contact angle measurement indicated that the hydrophilic property of membranes was not changed after the zeolites were modified with the long alkyl chain organosilane. The RO performance results verified that the flux of the modified-zeoliteTFN membranes was all higher than that of the original-zeolite TFN membranes under the same conditions whereas the salt rejection was improved slightly. The flux of the TFN membranes with 0.05% (w/v) zeolite loading was increased from 28.5 to 40.9 l/m2h, while the salt rejection was increased from 97.8% to 98.5% after the zeolite modification. The experimental results revealed that the modification of zeolites made the molecular sieve zeolite nanocrystals well dispersed in the polyamide thin film layer, and hence improved the water permeation while maintaining high solute rejection.

Formation of high flux CHA-type zeolite membranes and their application to the dehydration of alcohol solutions

CHA-type zeolite membranes have excellent dehydration performance and acid stability. However, the permeation flux of the membrane is still lower than that of commercially available NaA-type zeolite membranes. In this paper, the influences of the crystal growth conditions and the support properties on the dehydration performance were determined in order to prepare high flux CHA-type zeolite membranes. As a result, the permeation flux increased to 14.0 kg m −2 h −1 for a 90 wt% ethanol solution at 348 K (separation factor > 10,000). The membrane was also used to dehydrate methanol and 2-propanol. The results suggest that the CHA-type zeolite membranes are effective for the separation of water from organic solvents.

Influence of acid on the permeation properties of NaA-type zeolite membranes

The acid stability of the NaA-type zeolite membrane was evaluated in this study. For the rapid evaluation of membrane stability, the change in the permeation fluxes of the membrane was monitored in real-time by using a mass spectrometer during pervaporation. When sulfuric acid was added to the feed solution, the permeation flux of water decreased dramatically immediately after the acid addition (step (I)), then decreased slightly (step (II)), and finally increased significantly (step (III)). The permeation flux of ethanol also increased significantly in step (III). As a result, the NaA-type zeolite membrane lost its separation ability for an equimolar mixture of water and ethanol at 313 K in 10 min after the addition of 1.0 mL sulfuric acid. Hydrolysis reaction and dissolution occurred in steps (I)–(III). Furthermore, we also discuss the influence of the amount of added acid and ethanol content of the feed solution on the destruction of the zeolite membrane.

Synthesis of Ordered Cage-like Mesoporous Aluminosilicates from Na-A Zeolite Precursors Dissolved in HCl

Abstract Highly ordered cubic mesoporous aluminosilicates were synthesized using PEO106PPO70PEO106 triblock copolymer and aluminosilicate sols containing Si–O–Al bonds, which are obtained by dissolving Na-A type zeolite in HCl, under mild acidic conditions (pH 1.9–3.2).

A non-equilibrium thermodynamics approach to model mass and heat transport for water pervaporation through a zeolite membrane

Pervaporation through zeolite membranes involves local heat effects and combined heat and mass transport. The current state-of-the-art Maxwell–Stefan (M–S) models do not take these effects into account. In this study, transport equations for the coupled heat and mass transport through a zeolite membrane are derived from the framework of non-equilibrium thermodynamics (NET). Moreover, the assumption of equilibrium between the adjacent bulk phases at the feed and permeate sides of the zeolite layer is abandoned in favor of local equilibrium. The equations have been used to model pervaporation of water through a 2 μ m thick NaA type zeolite membrane, deposited on an asymmetric α -alumina support, at a feed temperature of 348 K. Assuming a flux of 10 kg m −2 h −1(0.15 mol m −2 s −1), the transport through the zeolite layer, as well as the liquid feed side boundary layer and the support layers is modeled. The activity, fugacity, and temperature profiles are calculated with and without taking coupling effects and surfaces into account. The profiles show distinct differences between the two cases. Including the surface effects leads to discontinuities in the activity and temperature at the membrane interfaces. A significantly higher temperature drop of 1.3 K is calculated across the zeolite, compared to 0.4 K when surface and coupling effects are not accounted for. The calculated decrease in temperature over the zeolite layer is dominated by the surfaces. This could indicate that temperature polarization is, to a large extent, a surface effect. The heat flux induces an extra driving force for mass transport, reducing the activity difference over the membrane. A positive jump in activity is observed at the interfaces, revealing the mass transport across the interfaces is governed by the coupling with the heat flux. The support layers contribute significantly to the total mass transport resistance.

Adsorption of Toxic Gases on Iron-Incorporated Na-A Zeolites Synthesized from Melting Slag

Iron incorporated zeolites were prepared from Na-A type zeolite synthesized from melting slag and FeCl3 solution and applied as adsorbents for NH3 and H2S gases. Iron incorporated zeolite was pelletized, calcined and used for gas adsorption experiment. XRD analyses of the zeolite revealed that Fe 3þ concentration of solution more than 90 mM could destruct the zeolite network structure. It was observed that the gas adsorption capacities of these zeolite pellets depend significantly on iron concentration of solution and calcination temperature. The type of binders affected a little on gas adsorption capacities. From adsorption results, adsorption capacity for NH3 was proportional to Fe 3þ concentration and it was increased with calcination temperature up to 500 � C, but it was decreased over 600 � C. Pellets prepared from 56 mM Fe 3þ solution calcined at 500 � C showed highest ammonia adsorption capacity (3.7%). This iron incorporated Na-A type zeolites showed much higher adsorption capacities for NH3 (2:4� 3:7%) than commercially available activated carbons (0:16� 0:44%) and zeolites (0:23� 0:60%). In the case of adsorption capacities for H2S, adsorption capacity was proportional to Fe3þ concentration and inversely proportional to calcination temperature. Pellets prepared from 78 mM Fe 3þ solution calcined at 200 � C showed highest hydrogen sulfide adsorption capacity (1.5%). Adsorption capacity (0:2� 1:5%) was found to be lower than that of the commercial activated carbons (1:2� 2:4%) and higher than that of commercial zeolites 4A (0.15%) and 13X (0.91%). Higher ammonia adsorption in iron incorporated Na-A zeolites could be possibly due to development of number of acid sites on the zeolites surface due to incorporation of Fe 3þ ion. [doi:10.2320/matertrans.M2009175]

Conventional hydrothermal synthesis of Na-A zeolite from cupola slag and aluminum sludge

Na-A type zeolites were prepared from two industrial wastes: the solid by-product of cupola slag and aluminum sludge from an aluminum plating plant. Two preparation methods using the same starting material compositions were carried out. In the first method, alkaline fusion was introduced, followed by the hydrothermal treatment to obtain sodium aluminosilicate which was then crystallized in NaOH solution under the condition of 90 ± 3 °C for 1–9 h with different H 2O/SiO 2 ratios. The result shows that higher H 2O/SiO 2 ratio increases the rate of crystallization. The largest amount of crystallinity for Na-A was found at 3 h. In the second method, alkaline hydrothermal treatment without fusion was carried out in the same condition as the first method. No Na-A zeolite was obtained by this method. The changes of the dissolved amounts of Si 4+ and Al 3+ in 3 M NaOH were investigated during the hydrothermal reaction.

Performance of Mitsui NaA type zeolite membranes for the dehydration of organic solvents in comparison with commercial polymeric pervaporation membranes

The dehydration performance of a commercial NaA type zeolite membrane (supplied by Mitsui engineering) was investigated for dehydration of the binary mixtures isopropanol/water, acetonitril/water and methylethylketon/water. For each solvent the dehydration performance was compared with alternative commercial polymeric membranes from two different suppliers: Celfa and Sulzer. All experiments were performed at 70 °C. For all the solvents tested, the zeolite membrane shows the best dehydration properties at water concentrations in the azeotropic region and below. For isopropanol dehydration, the polymeric Celfa membrane type CMC-VS-11V also shows very good results. The advantage of the Mitsui zeolite membrane is that it shows a higher temperature and mechanical stability than the polymeric membranes making pervaporation in harsh conditions possible. The higher fluxes and selectivities obtained with the Mitsui membranes even at low feed water concentrations, makes it possible to pervaporate up to low feed water concentrations. The disadvantage of the zeolite membrane is that it cannot withstand low pH values and that it is more expensive than the polymeric membranes, although prices are expected to decrease when more membranes are produced in the future.

Dynamical properties of liquids in restricted geometries

Raman scattering and Fourier-transform infrared (FT-IR) absorption results on confined water are presented. The aim is to characterize different porous materials, studying the vibrational properties of water inserted in their porous structure, and determining the relationship between these two aspects. Confinement has been realized by using a sol–gel silica glass, GelSil, with 26 Å diameter pores of huge hydrophilic inner surface, and NaA type zeolites, with 10 Å diameter pores in which 27 H 2O molecules can be located. The O–H stretching spectral range (2800–3800 cm −1), as a function of temperature and for different water contents, has been explored. From a comparison of the data in these two cases, we put into evidence the structure breaker role of GelSil, as revealed by the slowing down of the collective contribution to the polarized O–H stretching band, indicating that the tetrabonded H 2O network is destroyed. On the other side, NaA zeolites will be proofed to play a structure breaker effect on physisorbed water, since the contribution to the O–H stretching band linked to the tetrahedral ice-like arrangement is present even at the lowest hydration conditions.

Economic comparison between azeotropic distillation and different hybrid systems combining distillation with pervaporation for the dehydration of isopropanol

Abstract An economic analysis was performed comparing different processes for the dehydration of isopropanol/water. Traditional azeotropic distillation was compared with a hybrid system consisting of distillation followed by pervaporation and a hybrid system consisting of distillation followed by pervaporation followed by a second distillation. In the hybrid combinations pervaporation with both polymeric (PERVAP® 2510, Sulzer Chemtech GmbH) and ceramic membranes (NaA type zeolite, Mitsui & Co.) was investigated. Both membranes were tested for the dehydration of isopropanol at 70 and 90 °C. Based on these experimental results, calculations were performed with the PV design calculation program (RWTH Aachen) to obtain economic data on the pervaporation processes. For the simulations of the distillation processes, Aspen Plus 11.1 was used. It was found that the hybrid system distillation–pervaporation with ceramic membranes was the most interesting process from economic point of view and could lead to a saving in total costs of 49% compared to azeotropic distillation.

Structure and dynamics of radicals in zeolite matrices: ESR and theoretical studies

Amine radical cations of the type R3N·+ and [R3NCH2]·+, R=CH3, C3H7, and nitric oxide, NO, have been used to probe the bonding to the surface and the dynamics of the radicals trapped in the confined space of cages or channels in the zeolite. Regular continuous-wave electron spin resonance (ESR) was employed to study the internal motion of the cation radicals formed by γ-irradiation of amines and related ammonium ions, introduced during the synthesis of the zeolites Al-offretite, SAPO-37, SAPO-42 and AlPO4-5. The ESR spectra of [(CH3)3NCH2]·+ radical cation in several studied systems changed reversibly with temperature, indicating dynamical effects. Free rotation about the >N−CH2 bond of the [(CH3)3NCH2]·+ species was found to occur in the temperature range of 110 to 300 K, while the rotation about the >N−CH3 bonds was hindered. The observations confirm the theoretical prediction on the basis of density functional theory calculations, which indicate that the corresponding barriers are of the order of 0.3 and 7 kJ/mol, respectively. The radical cations of the type R3N·+ with R=C2H5, C3H7 were found to undergo a different type of dynamics, involving a two-jump process of the methylene hydrogens next to the nitrogen. A cage or channel size effect on the stability and molecular dynamics was inferred in some cases. Pulsed ESR was employed to study the (NO)2 triplet-state dimers in Na-A type zeolite, with the purpose to resolve the interaction with surface groups, and to elucidate the role of the zeolite on stabilizing the triplet rather than the usual singlet state. Measurements performed at 5 K gave rise to Fourier transform spectra that were assigned to the dimer species interacting with one or more23Na nuclei, with approximative parameters A(23Na)=(4.6, 4.6, 8.2) MHz and Q(23Na)=(−0.3, −0.3, 0.6) MHz for the hyperfine and nuclear quadrupole coupling tensors, respectively. The values are of similar magnitude as those determined for the NO−Na+ complex. The stability of the triplet-state structure was attributed to unusual geometric structure imposed by the zeolite matrix, with the N−O bonds along a line as in [O−N−Na+−N−O], which according to UHF ab initio calculations has a triplet ground

IPA purification for lens cleaning by vapor permeation using zeolite membrane

Abstract Vapor permeation (VP) properties of commercial NaA-type zeolite membranes were examined using the alcohol/water systems, before equipments to purify isopropanol (IPA) from lens cleaning process were designed. The membranes displayed excellent water-permselective performance for water/organic solutions in the VP. With an increase in feed temperature, both the permeation flux Q and the separation factor α increased, and the membrane performance was the same for pervaporation as for VP over 0.7 relative vapor pressure p / p s . In VP of alcohol mixtures with 5 wt.% water over p / p s =0.7 at 120 °C, Q values were 2.64, 4.3 and 5.6 kg m −2 h −1 and α value were 4000, 5600 and 6000 for the water/methanol (MeOH), water/ethanol (EtOH) and water/IPA solutions, respectively. The repeated experiment of IPA purification by VP with a zeolite NaA membrane was carried out in waste IPA liquid. The substances (acids, particles, etc.) in the waste IPA hardly influenced membrane performance in the VP. The IPA purification plant with approximately 0.72 m 2 membrane areas was composed of 24 double tube-type modules. This plant which can purify 10 l h −1 of IPA at less than 0.5 wt.% water from 88.6 wt.% IPA at 120 °C has been put into lens cleaning operation.

Evaluation of dual-bed pressure swing adsorption for CO2 recovery from boiler exhaust gas

Abstract Dual-bed CO2 adsorption using zeolite was studied experimentally and theoretically. Boiler exhaust gas (13 vol% CO2, 79 vol% N2 and 8 vol% O2) was used as a feed gas for the eight-step four-bed PSA process. Na-X type zeolite (NaX) and Na-A type zeolite (NaA) were selected in the break-through test. NaX has higher CO2 adsorption capacity than other adsorbents. NaA has the highest selectivity among all adsorbents tested. In the simulations, a NaX-to-NaA ratio affected the recovery efficiency and the concentration of recovery gas. Moreover, in the dual-bed PSA process of NaX-to-NaA ratio=2/1, the recovery efficiency and CO2 concentration of recovery gas were higher than those in a single-adsorbent PSA process. Simulated results by the dynamic model agreed well with the PSA experimental results.

GAS PERMEATION PROPERTIES OF ION-EXCHANGED LTA-TYPE ZEOLITE MEMBRANES

NaA-type zeolite membranes were prepared on a 1.7-mm i.d. porous α-alumina tube by repeating a hydrothermal reaction. The membranes, which were prepared by four repetitions, were ion-exchanged with Ca2+ and K+, and the permeation for single-component and mixed gases were investigated at 35°C. The NaA-type membrane showed a hydrogen permeance of (0.8–2.6) × 10−8 mol · m−2 s−1 Pa−1 and a hydrogen/n-butane ideal separation factor of 12–15. The permeability properties of the membrane for binary mixtures were dependent on the size of the permeating molecules and their adsorptivity to the zeolite. The KA-type zeolite membrane showed a higher ideal separation factor for a hydrogen/nitrogen system than did the NaA- and CaA-type zeolite membranes. The pores of the CaA-type zeolite membrane were larger than those in the NaA- and KA-type zeolite membranes, and showed higher permeances to n-butane and i-butane. All the zeolite membranes contained non-zeolitic pores, which decreased the selectivity of permeation.

Oxygen Selectivity on Partially K Exchanged Na-A Type Zeolite at Low Temperature

In previous work by the authors on Na-A zeolite (Izumi et al., Japan Patent Toku-Kou-Shou 63-058614, 1988), it was shown that the combination of high-temperature calcination and operation of the adsorption step at low temperatures improved the selectivity for oxygen over nitrogen from air (Izumi et al., CATS J Meeting Abstracts, 31(2A), 10, 1989; Izumi and Suzuki, Adsorption, 6, 2000). Berlin discloses in his U.S. Patent 3282028 (1966) that the partial exchange of potassium ions for sodium ions in the Na-A type zeolite also improved selectivity for oxygen by reducing the uptake rate of nitrogen. It was therefore expected that the oxygen selectivity of Na-K-A with high-temperature calcination and low-temperature adsorption might be enhanced. For the confirmation of optimum conditions for the appearance of oxygen selectivity on Na-K-A, samples were prepared with a K exchange ratio varied from 0–20 mol% (0–2.4 K ions/unit cell), and a calcination temperature varied from 923 to 1073 K, and an experiment concerning oxygen and nitrogen adsorption on Na-K-A was undertaken with a small adsorbent column under pressure swing adsorption (PSA) conditions at adsorption temperatures from room temperature to 213 K. It was found that (a) the K exchange ratio of 7 mol% (0.84 K ions/unit cell), and (b) the calcination temperature of 993 K, resulted in a remarkable increase in oxygen selectivity. Under optimum conditions for Na-K-A, the oxygen separation factor was about 8. Na-K-A has the potential to effectively separate oxygen and nitrogen from air by means of PSA.