NaA Zeolite Research Articles

Optimization of Pretreatment and Hydrothermal Process of Na-X Zeolite from Kaolin and Metakaolin

Synthesis of Na-X zeolite was conducted from kaolin and metakaolin. Synthesis varied in its pretreatment method and hydrothermal conditions. The pretreatment methods used were: conventional alkaline, alkaline fusion and conventional fluoride. Hydrothermal conditions for the experiments were gradual temperature 40 oC (6h), 60 oC (6h), 80 oC (12h), and constant temperature 80 oC for 24 h, 100 oC for 24 and 100 oC for 48 h. Synthesized products were characterized by X-Ray Diffraction (XRD), Fourier Transform InfraRed (FTIR), Scanning Electron Microscopy-Energy Dispersive X-Ray (SEM-EDX), and N2 Isotherm Adsorption/Desorption method. The result showed that pre-treatment by conventional fluoride could not produce Na-X zeolite, synthesis by conventional alkaline and alkaline fusion with hydrothermal at 100 oC (48h), 100 oC (24 h), and gradual temperature produce Na-X zeolite with Na-P1 or Na-A zeolite as impurities, while synthesis from metakaolin by conventional alkaline with hydrothermal at 80 oC for 24 hours produced pure Na-X zeolite. Na-X zeolite and NaP1 zeolite with hierarchical pores were synthesized through alkali fusion with hydrothermal at 100 oC for 24 hours.

Synthesis, characterisation and CO2 adsorption potential of NaA and NaX zeolites and hydrotalcite obtained from the same coal fly ash

Hydrotalcites and zeolites are materials characterised by a high capacity for CO2 adsorption and can therefore be useful adsorbents for the capture of CO2 from flue gases. In this study, two types of zeolites (NaXFA and NaAFA) were successfully synthesised from South African coal combustion fly ash. Their CO2 adsorption properties, as well as those of a hydrotalcite (HTFA) synthesized from the same fly ash in our previous work, were investigated and compared. In addition, this paper reports the CO2 adsorption capacity of a novel hierarchical morphology NaX-type zeolite (NaXFA) made from fly ash. This material was characterized by plate-like structures arranged in ball-like clusters with crystal widths of between 63 nm and 99 nm. NaXFA was characterised by very high CO2 physisorption properties and was therefore the most suitable candidate for low temperature and pressure swing adsorption generally required in short-term CO2 adsorption applications. In contrast, both physisorption and chemisorption properties were observed for NaAFA and HTFA. However, HTFA was the most suitable material for chemisorption of CO2. The findings demonstrated the suitability of utilising HTFA for both short- and long-term capture of CO2.

Blocking defects of zeolite membranes with WS2 nanosheets for vapor permeation dehydration of low water content isopropanol

It is difficult for zeolite membrane to behave good separation selectivity in dehydration of low water content isopropanol (IPA) by vapor permeation (VP) because capillary condensation in small intercrystalline defects is usually insufficient for excluding IPA molecules and adsorbate-induced contraction of zeolite crystals open new defects at low water content. To address this issue, a facile and high-efficiency modification strategy was proposed to block defects of NaA zeolite membranes on hollow fibers by using WS2 nanosheets. Effect of nanosheets thickness on VP separation performance of modified membranes was investigated. It showed that the separation factor of membrane was improved by more than two orders of magnitude (from 60 to >10000) after modified with the few-layer WS2 nanosheets while the loss in water flux was only 18.6% in VP dehydration of 10 wt% water/IPA mixture at 373 K. Moreover, the modified membrane still maintained a high separation factor of ~5000 rather than that of pristine membrane (336) even when the feed water content lowered to 0.5 wt%, indicating that not only intrinsic defects but also the crystal contraction-induced defects were blocked simultaneously by the thin WS2 nanosheets.

Surface modification of mesoporous silica nanoparticle with 4-triethoxysilylaniline to enhance seawater desalination properties of thin-film nanocomposite reverse osmosis membranes

Mesoporous silica nanoparticles (MSN), with higher water permeability than NaA zeolite, were used to fabricate thin-film nanocomposite (TFN) reverse osmosis (RO) membranes. However, only aminoalkyl-modified MSN and low-pressure (less than 2.1 MPa) RO membrane were investigated. In this study, aminophenyl-modified MSN (AMSN) were synthesized and used to fabricate high-pressure (5.52 MPa) RO membranes. With the increasing of AMSN dosage, the crosslinking degree of the aromatic polyamide decreased, while the hydrophilicity of the membranes increased. The membrane morphology was maintained to show a ridge-and-valley structure, with only a slight increase in membrane surface roughness. At the optimum conditions (AMSN dosage of 0.25 g/L), when compared with the pure polyamide RO membrane, the water flux of the TFN RO membrane (55.67 L/m2/h) was increased by about 21.6%, while NaCl rejection (98.97%) was slightly decreased by only 0.29%. However, the water flux of the membranes was much lower than expected. We considered that the enhancement of RO membrane permeability is attributed to the reduction of the effective thickness of the PA layer.

Membrane dehydration-enhanced esterification for biodiesel production from a potential feedstock of Firmiana platanifolia L.f. seed oil

A two-step acid/alkali-catalysis method was developed to produce biodiesel from Firmiana platanifolia L.f. seed oil obtained from continuous-screw squeezing and solvent extraction by absolute ethanol. The esterification of Firmiana platanifolia L.f. seed oil with ethanol was carried out with the strong-acid cation exchange resin to decrease the content of free fatty acids (FFAs) below 1wt. %. A NaA zeolite membrane was used for dehydration in the coupled reactor. Alkali-catalysis transesterification was performed with 0.08% (m/m oil) of KOH and 6:1 of molar ratio of methanol to oil, reaction time of 30min, and reaction temperature of 60°C. Results showed that the combination of esterification with vapor permeation (VP) or pervaporation (PV) could greatly shift the reaction equilibrium forward. The FFAs conversion rates higher than 99.0% were obtained under the conditions of ethanol to oil molar ratio of 15:1, catalyst dosage of 40.0wt.% and temperature of 78°C, and operation time of 7h. Moreover, the properties of the biodiesel meet the standards of American Society for Testing Material (ASTM), European Norm (EN) and Chinese Standard (GB).

Organic-free one-step synthesis of macro/microporous LTA zeolite and its encapsulation of metal nanoparticles

Abstract Micrometer-sized hierarchical LTA-type zeolite crystals with uniform embedded macropores were synthesized via steam-assisted conversion (SAC) of spherical mesoporous silica particles (MSPs) impregnated with alkaline aluminate. The one-pot synthesis was achieved by direct transformation without the need of organic structure directing agents or pre-formed seeds. The obtained cubic hierarchical NaA zeolite materials were 2–5 μm in size which possessed a core-shell structure with a microporous wall in the shell and multi-hollow macropores about 400 nm in the core. Time-series studies revealed the in situ dissolution–crystallization formation mechanism, in which the mesoporous silica particles functioned as silica source as well as “space-filling” template. When the starting MSPs were pre-loaded with metal precursors, multi-hollow zeolite nanoreactor crystals with encapsulated metals were successfully synthesized by this strategy. The present study provides an organic-free way to fabricate hierarchical aluminosilicate zeolites with embedded macropore system.

Enhancing the removal performance of Cd(Ⅱ) from aqueous solutions by NaA zeolite through doped thiourea reduced GO which is trapped within zeolite crystals

In this study, thiourea reduced graphene oxide/NaA zeolite composite (tGO-Zeo) was successfully prepared by a facile two-step synthetic route and used as an efficient adsorbent for removal of Cd(II) from aqueous solution. Characterization of the composite material showed that tGO was entrapped within zeolite crystalline particles and intimately interacted with the zeolite framework. Furthermore, the presence of tGO considerably reduced zeolite crystal size and altered crystal morphology, turning cubic zeolite crystals of micrometer size into nanometer irregular particles. Batch adsorption experiment for Cd(II) removal was conducted and the adsorption performance of tGO-Zeo and Zeo (zeolite) were determined. It was shown that doped tGO significantly enhanced the adsorption capacity of zeolite by 31.54%. The adsorption mechanism differs for tGO-Zeo and Zeo, and tGO-Zeo has higher affinity for Cd(II). The adsorption capacity of tGO-Zeo with a tGO doping amount of 1.26% (wt%) was estimated to be 196 mg/g (1.74 mM/g) at 30 °C and superior to most previously reported zeolite based composites, which often contain large amounts of dopants. The effects of pH and ionic strength on adsorption suggest that ion exchange and coordination are responsible for Cd(II) adsorption by tGO-Zeo. Humic acid can slightly increase Cd(II) adsorption performance of tGO-Zeo, which may be due to tGO-Zeo—humic acid—Cd(II) complexes formation. Therefore, tGO-Zeo composite is a cost-effective and eco-friendly adsorbent for efficient removal of Cd(II) ions from aqueous solutions.

Synthesis of kaolin-based zeolite NaA and its crystallization mechanism

The zeolite NaA was successfully synthesized by hydrothermal method using kaolin as a raw material. In order to study the crystallization mechanism, the products and intermediates of different crystallization stages were systematically characterized using x-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM)-energy-dispersive spectrometry (EDS). The results show that the metakaolin is completely dissolved during the first hour of the crystallization process, forming a rich crystal nucleus. As the crystallization time increases, the nucleus grows rapidly to form zeolite NaA crystals. When the crystallization time reaches 3 h, the percentage crystallinity of zeolite NaA reaches a maximum. Therefore, it can be concluded that the optimum crystallization time of zeolite NaA is 3 h. Meanwhile, we can come to the conclusion that the synthesis of zeolite NaA from kaolin is a liquid phase transition mechanism. The microstructure of zeolite NaA synthesized at 3 h of crystallization was further investigated by transmission electron microscopy (TEM) technique. The SAED patterns indicate the polycrystallinity of the zeolite NaA structure. The electron diffraction pattern indicates that the crystal structure type of the zeolite NaA belongs to the body center cube (BCC). The textural properties of the zeolite NaA synthesized at 3 h of crystallization were studied by nitrogen adsorption technique. It can be concluded that the BET surface area of the zeolite NaA obtained by the BET method is 21.106 m2·g−1. Meanwhile, from the BJH method, it is found that the microporous surface area and micropore volume of the zeolite NaA are 13.929 m2·g−1 and 0.052 cm3·g−1, respectively.

Fabrication of stainless steel hollow fiber supported NaA zeolite membrane by self-assembly of submicron seeds

Submicron NaA zeolite seeds were coated on the stainless steel (SS) hollow fiber support by self-assembly method, and then the hydrothermal crystallization and autoclave technique were used to synthesize NaA zeolite membranes. The effects of grafting temperature, grafting time and the size of induction seeds on the membrane performance were extensively investigated. The as-synthesized membranes and zeolite crystals were then characterized by X-ray diffraction, and the morphology and thickness of membranes were examined by scanning electron microscopy. The separation performance of the membrane was evaluated by pervaporation dehydration of 90 wt% ethanol/water mixtures at 75 °C. It was found that the seed-layer should be uniformly coated to induce good continuity for the NaA zeolite membrane layer, where the seeding effect was clearly affected by grafting time, grafting temperature and seed size. The optimal seeding condition was found for a grafting time of 6 h under a temperature of 110 °C, using a seed size of 150 nm. A continuous zeolite membrane layer could be obtained on the surface of the SS hollow fiber, with a separation factor above 10,000 and a permeation flux of 4.22 kg∙m−2∙h−1. The proposed self-assembly method could be readily operated and extended to the seeding process during the preparation of other supported zeolite membranes, providing a good prospect in batch-scale production of SS hollow fiber supported NaA zeolite membranes.

Hydrothermal synthesis of Zeolite NaA from Kaolin

Zeolite NaA was successfully synthesized from low-grade kaolin via hydrothermal synthesis method. The properties of the zeolite NaA were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray fluorescence (XRF), scanning electron microscopy (SEM)-energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and thermogravimetry (TG)-differential thermal analysis (DTA). TEM analysis indicated the formation of body-centered cubic crystal zeolite NaA and the polycrystallinity of the zeolite NaA structure. The textural properties of the zeolite NaA were further studied by N2 adsorption-desorption technique. In addition, the TG-DTA study confirmed that the heat treatment temperature of the zeolite NaA should be controlled below 600∘C.

Selective adsorption of Co(II)/Mn(II) by zeolites from purified terephthalic acid wastewater containing dissolved aromatic organic compounds and metal ions

Selective separation and recovery of Co(II)/Mn(II) from purified terephthalic acid (PTA) production wastewater is very important to reduce the Co(II)/Mn(II) catalysts consumption and control the pollutant discharge. This work employed zeolites NaA, NaX, and HZSM-5 with different pore sizes and Na(I) contents to selectively separate and recover Co(II)/Mn(II) from PTA wastewater and to understand the adsorption mechanism. It is found that only NaA can exclusively adsorb Co(II)/Mn(II) through ion-exchange without adsorbing any aromatic organic compound (AOC); oppositely, HZSM-5 shows the highest adsorption capacity for AOCs but almost no adsorption for Co(II)/Mn(II); and NaX exhibits moderate adsorption capacities for both Co(II)/Mn(II) and AOCs. Moreover, pH can significantly impact the adsorption of both Co(II)/Mn(II) and AOCs due to the competitive adsorption between H(I) and Co(II)/Mn(II) and the electrostatic repulsion between AOCs and zeolites. The adsorption kinetics, isotherms, and thermodynamics were also investigated to lay a good basis for process development. Importantly, bench-scale experiments for simulating the industrial operation were carried out, and the results show that the adsorption capacity of the NaA particles for Co(II)/Mn(II) from the industrial PTA wastewater is 9.1/8.6 mg/g, respectively, without adsorbing any AOC. Therefore, an efficient strategy to selectively separate and recover Co(II)/Mn(II) from PTA wastewater was successfully developed.

The effects of metakaolinization and fused-metakaolinization on zeolites synthesized from quartz rich natural clays

Abstract A variety of zeolites have been synthesized by performing either metakaolinization or fused-metakaolinization of natural clays prior to the hydrothermal synthesis step. To understand the differences arising from performing fused metakaolinization rather than simple metakaolinization, the calcination conditions, gel composition, gelling and crystallization conditions were kept similar for both methods. The original clay material, a kaolinite group mineral with Si/Al molar ratio of 1, had a high content of quartz as impurity. The two treatment methods gave different zeolites of high crystallinity and relatively similar Si/Al molar ratio. Zeolite Na-A with 98% crystallinity was produced from the metakaolinization method within 8 h, while Na-X with 96% crystallinity was generated from the fused-metakaolinization (fusion) method within 48 h. In the fusion method, sodalite was formed at or beyond 48 h of hydrothermal reaction, while in the metakaolinite method, apart from a slight decrease in intensities of XRD peaks, no phase change was observed even after 168 h of hydrothermal reaction. Modification of the synthesis gel by increasing the Si/Al molar ratio via addition of fumed silica resulted in mixed zeolite products via the metakaolinite method, while Na–Y was the major product for the fusion method. Except for Na-A, all zeolite products had high surface area of up to 600 m2/g and micropore volume of 0.18 cm3/g. Our findings demonstrate the crucial role of the pre-treatment step in the synthesis of zeolites from clay minerals, and that a variety of high quality zeolites are achievable via choice of pre-treatment protocols.

Incorporation of strontium and calcium in geopolymer gels

Radioactive waste streams containing 90Sr, from nuclear power generation and environmental cleanup operations, are often immobilised in cements to limit radionuclide leaching. Due to poor compatibility of certain wastes with Portland cement, alternatives such as alkali aluminosilicate ‘geopolymers’ are being investigated. Here, we show that the disordered geopolymers ((N,K)-A-S-H gels) formed by alkali-activation of metakaolin can readily accommodate the alkaline earth cations Sr2+ and Ca2+ into their aluminosilicate framework structure. The main reaction product identified in gels cured at both 20 °C and 80 °C is a fully polymerised Al-rich (N,K)-A-S-H gel comprising Al and Si in tetrahedral coordination, with Si in Q4(4Al) and Q4(3Al) sites, and Na+ and K+ balancing the negative charge resulting from Al3+ in tetrahedral coordination. Faujasite-Na and partially Sr-substituted zeolite Na-A form within the gels cured at 80 °C. Incorporation of Sr2+ or Ca2+ displaces some Na+ and K+ from the charge-balancing sites, with a slight decrease in the Si/Al ratio of the (N,K)-A-S-H gel. Ca2+ and Sr2+ induce essentially the same structural changes in the gels. This is important for understanding the mechanism of incorporation of Sr2+ and Ca2+ in geopolymer cements, and suggests that geopolymer gels are excellent candidates for immobilisation of radioactive waste containing 90Sr.

The study on the coupled process of column distillation and vapor permeation by NaA zeolite membrane for ethanol dehydration

A pilot was used to experimentally study the ethanol dehydration process, based on the coupled process of distillation and vapor permeation by NaA zeolite membrane, and the effects of the water content in the feed, reflux ratio, mass flow, the product purity of the distill and the operating stability were systematically analyzed. It was found that due to the placement of NaA membrane, the operation zone of the original column could be significantly extended in the coupling, which in return could reduce the column facility investment. Based on the interplay among the operation parameters, it was found that the water content of the distilled product from the column could be used as a critical parameter to balance the energy consumption of the column and the membrane facility investment, and a value of 20wt.% was recommended for the coupling. During the steady test of the coupling, the results indicated that the pilot plant could be continuously operated for 18h to dehydrate the feed (water/ethanol) from 60wt.% to 8wt.%, where the steady state was further validated in process simulation of Aspen plus. In summary, the parameters suitable for the stable operation of the distillation-vapor permeation coupling were investigated for the given condition. This research paves a foundation for the large-scale industrial design and application of the distillation-vapor permeation coupling.

Methods for quantitative determination of filler weight fraction and filler dispersion degree in polymer composites: example of low-density polyethylene and NaA zeolite composite

Novel methods for the determination of filler weight fraction and filler dispersion degree in polymer composite have been established. The XRD and FTIR methods used for the determination of zeolite weight fraction are based on measurement of selected integral area of one of the XRD diffraction peaks and one of the FTIR absorption bands, respectively. Filler dispersion degree was determined from the calculation of weight fraction of zeolite in randomly selected points of composite sample. Powdery calibration mixtures of low-density polyethylene and NaA zeolite were prepared with the certain zeolite weight fraction ranging from 5 to 30 wt%. The XRD patterns and FTIR spectra of calibration mixtures were recorded. The effect of zeolite weight fraction on the integral area and full width on half maximum of the diffraction peaks and absorption bands of the NaA zeolite were evaluated. The composite samples in the form of plates which contains from 5 to 30 wt% of zeolite were prepared by the compression moulding technique. Weight fraction and dispersion degree of zeolite in the composite, as well as the errors for their determination, were established.

A method for NaA zeolite synthesis from coal fly ash and its application in warm mix asphalt

Fly ash (FA) can be a powerful substitute for conventional sources towards synthesis of zeolites, a class of aluminossilicates that can be used as additives in the production of warm mix asphalt (WMA). The use of zeolite has proved to enhance asphalt workability by water releasing. In this work, it is presented a new synthesis route for zeolite NaA based on fly ash as the primary source of silica and alumina, in which different sources of fly ash were applied. The composition of FA samples was determined by means of X-ray fluorescence (XRF) and the zeolite synthesis was confirmed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The rheological properties of the pure and modified asphalt cement (AC) assessed by a dynamical shear rheometer (DSR) did not show significative differences. The mechanical tests of tensile strength (TS), resilience modulus (RM), dynamic creep (DC) and pull-off tensile strength (POTS) for mixtures with modified AC showed subtle positive differences when compared to mixtures with unmodified AC.

Adsorption and Desorption Characteristics of Sr, Cs, and Na Ions with Na-A Zeolite Synthesized from Coal Fly Ash in Low-Alkali Condition

Adsorption and Desorption Characteristics of Sr, Cs, and Na Ions with Na-A Zeolite Synthesized from Coal Fly Ash in Low-Alkali Condition

Mass produced NaA zeolite membranes for pervaporative recycling of spent N-Methyl-2-Pyrrolidone in the manufacturing process for lithium-ion battery

N-methyl pyrrolidone (NMP) is a colorless and odorless liquid that has been heavily used in the manufacturing process of lithium ion batteries. The development of efficient technology for the on-site recycling of NMP is extremely significant in the lithium ion battery manufacturing plant. The pervaporation dehydration by mass produced NaA zeolite membranes followed by vacuum flash vaporization has proven to be an effective and economic way for recovering spent NMP in this paper. The pilot-scale pervaporation plant containing 225 tubular NaA zeolite membranes with a total membrane area of ca. 7.3 m2 was established for dehydration of actual industrial recovered NMP solution from a lithium battery production line. All technical indicators of the retentate (NMP ≥ 99.9%, H2O ≤ 105 ppm, color 10 Hz, refractive index 1.4694) have fully met the requirements of electronic-grade NMP for lithium-ion battery industry. Owing to the excellent molecular sieving effect of NaA zeolite membrane at extremely low water concentration, the NMP recovery yield was far better than the reported values in literature. These results suggested that the mass produced NaA zeolite membranes showed technical feasibility for the recycling of NMP in the lithium ion battery manufacturing process.

Synthesis of Na-A zeolite from water treatment residue using hydrothermal and microwave techniques

Na-A zeolite was synthesized from water treatment residue (WTR) using hydrothermal and microwave techniques. WTR was brought from Metropolitan Waterworks Authority (Thailand) and was activated by firing at 700 °C for 3 h in an electric furnace. The activated WTR was reacted with 3 M NaOH solution in a reactor under a controlled temperature of 80, 90 and 100 °C for 8, 10, 12, and 14 h. SEM (Scanning electron microscopy) images reveal the cubic crystal of zeolite. The highest cation exchange capacity (CEC) was obtained from sample synthesized at 90 °C for 14 h and gave the CEC value of 3.14 meq/g Ca2+. For the microwave technique, the raw materials were reacted at 80 90 and 100°C for 30, 60, and 120 min. Results showed that the sample obtained at 80 °C for 30 min represented the highest CEC value of 0.29 meq/g Ca2+.

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.