Synthesis of mordenite with different SiO2/Al2O3 ratios

The effect of the initial mixture composition and crystallization conditions (temperature and time) on the molar ratio SiO₂/Al₂O₃ of mordenite has been investigated. The obtained SiO₂/Al₂O₃ molar ratio in mordenite is directly proportional to the initial mixture (SiO₂/Al₂O₃ × Na₂O/H₂O) composition, always being lower than that. The obtained values increase and tend to approach the initial value only with increasing crystallization temperature and time. The calculated activation energy value for incorporation of SiO₂ into the mordenite lattice is very close to that of crystallization.     

Synthesis of ultrafine zeolites by dry-gel conversion without any organic additive

ZSM-5, mordenite, cancrinite and Y zeolites were successfully crystallized by the dry-gel conversion (DGC) without any organic additive (or template), in which the crystal particles of ZSM-5, mordenite and Y zeolite were well controlled in the range of ultrafine size. With a molar ratio of SiO₂/Al₂O₃ ≤40, the pure ZSM-5 zeolite was obtained at 170 °C at the Na₂O/SiO₂ molar ratio <0.2, but the pure mordenite was formed at 150 °C at the Na₂O/SiO₂ molar ratio >0.25. When the dry-gel with a composition of 5.0Na₂O:Al₂O₃:5.0SiO₂ was crystallized at 140 °C for 24 h, pure cancrinite phase was obtained. TEM images showed that thus-crystallized zeolites consisted of ultrafine particles ranging 35-150 nm for ZSM-5, 50-200 nm for mordenite and 120-200 nm for zeolite Y, respectively. Different from ZSM-5, mordenite and cancrinite zeolites, the DGC synthesis of Y zeolite required more water in the dry-gel before crystallization.     

Synthesis of zeolite omega. Influence of the temperature and the reagents on the crystallization kinetics

The kinetics of the crystallization of zeolite omega in the system Na₂O, TMA₂O, Al₂O₃, SiO₂, H₂O have been determined as a function of the temperature and the nature of the sources of silicon and aluminium. At 100°C, faujasite appears first and is then dissolved while crystals of zeolite omega develop. Sodalite is also formed but pure zeolite omega can be isolated after 15 days. At 135°C the transient formation of faujasite is not observed. The crystallization kinetics of zeolite omega are not sensitive to the nature of the reagents but those of the secondary products (sodalite, analcite, mordenite, cristobalite) depend on their reactivity. Porous silica gel favours the nucleation of sodalite. Reaction mixtures prepared from kaolinite lead to die-shaped monocrystals which are stable in the medium whereas sodium aluminate produces polycrystalline aggregates which are progressively dissolved. Under these conditions pure zeolite omega was obtained after only one day of reaction using sodium aluminate and a non-porous silica gel as starting materials.     

Hydrothermal Synthesis of Nanosized Zeolite T Crystals

In this study, effects of gel formulation parameters such as Na₂O/K₂O molar ratio(from 0.05 up to 3) and tetra methyl ammonium hydroxide (TMAOH) additive in the synthesis of zeolite T (Linde Type T) crystals have been investigated in different SiO₂/Al₂O₃ molar ratios from 5 to 29. Submicron and nanosize crystal of zeolite T from 100 nm up to 25 µm with distinctive crystal shapes from the needle type to cylindrical crystals have been synthesized successfully at the wide range of SiO₂/Al₂O₃ ratios with and without TMAOH. It is shown that Na₂O/K₂O ratio plays the most important role in gel formulation. All synthesized crystalsare characterized by XRD and SEM analysis.     

Preparation of zeolite-coated cordierite honeycombs prepared by an in situ crystallization method

Zeolite thin films were prepared on cordierite (Mg₂Al₄Si₅O₁₈) honeycomb substrates by in situ crystallization using soft hydrothermal conditions. The synthesized zeolite films (zeolite A and ZSM-5) were characterized by XRD, FTIR, SEM, NH₃-TPD, and Ns₂ and propane gas adsorption. Zeolite-A films were prepared by dip-coating on a cordierite substrate in a precursor of molar composition of Na₂O:Al₂O_3: SiO_2: H₂O=4:1:2:100 and heating in an autoclave at 80 °C for 6–10 h. The resultant zeolite-A films consisted of cubic crystals about 2–3 μm in size, achieving a thickness of 20 μm after re-coating. ZSM-5 films were similarly formed using a microporous silica precursor obtained by selective leaching of metakaolinite with tetrapropylammonium hydroxide (TPAOH) as the templating agent. The molar composition of the precursor was NaOH:microporous silica:TPAOH:H₂O=1:10:1:200. The dipped substrate covered with the wet precursor gel was heated in an autoclave at 150 °C for 24 h. The resultant films were composed of short prismatic <1 μm crystals achieving thickness of several to 10 μm after re-coating. The microstructure and porous properties of the ZSM-5 films were found to change according to the chemical composition and surface treatment of the cordierite substrates. The presence of a SiO₂-rich interfacial layer between the substrate and zeolite film increased the amount of zeolite formed and the physical adsorption but decreased the solid acidity and amount of chemisorption.     

Preparation of zeolite-coated cordierite honeycombs prepared by an in situ crystallization method

Zeolite thin films were prepared on cordierite (Mg₂Al₄Si₅O₁₈) honeycomb substrates by in situ crystallization using soft hydrothermal conditions. The synthesized zeolite films (zeolite A and ZSM-5) were characterized by XRD, FTIR, SEM, NH₃-TPD, and Ns₂ and propane gas adsorption. Zeolite-A films were prepared by dip-coating on a cordierite substrate in a precursor of molar composition of Na₂O:Al₂O_3: SiO_2: H₂O = 4:1:2:100 and heating in an autoclave at 80 °C for 6–10 h. The resultant zeolite-A films consisted of cubic crystals about 2–3 μm in size, achieving a thickness of 20 μm after re-coating. ZSM-5 films were similarly formed using a microporous silica precursor obtained by selective leaching of metakaolinite with tetrapropylammonium hydroxide (TPAOH) as the templating agent. The molar composition of the precursor was NaOH:microporous silica:TPAOH:H₂O = 1:10:1:200. The dipped substrate covered with the wet precursor gel was heated in an autoclave at 150 °C for 24 h. The resultant films were composed of short prismatic <1 μm crystals achieving thickness of several to 10 μm after re-coating. The microstructure and porous properties of the ZSM-5 films were found to change according to the chemical composition and surface treatment of the cordierite substrates. The presence of a SiO₂-rich interfacial layer between the substrate and zeolite film increased the amount of zeolite formed and the physical adsorption but decreased the solid acidity and amount of chemisorption.     

FAU-type zeolite membranes synthesized by microwave assisted in situ crystallization

FAU-type zeolite membranes were prepared by an “in situ aging-microwave synthesis” (AM) method using a clear solution with the molar composition of 70Na₂O: 1Al₂O₃: 20SiO₂: 2000H₂O. After two-stage AM synthesis, a defect-free FAU zeolite layer consisted of uniform zeolite crystals was formed on the support surface. The Si/Al ratio was ca. 1.5. The single-gas permeation and single-liquid vapor permeation properties of the as-synthesized zeolite membranes were investigated. The permselectivity of H₂ and N₂ was as high as 4.25 for FAU-type zeolite membranes. Pervaporation measurements were carried out for the dehydration of ethanol and isopropanol aqueous solutions. FAU-type zeolite membranes displayed relatively high permeation flux and water-selectivity.     

High performance dehydration of ethyl acetate/water mixture by pervaporation using NaA zeolite membrane synthesized by vacuum seeding method

High quality NaA zeolite membranes were prepared by vacuum assisted secondary growth. At the first stage in which NaA powder was synthesized, increasing the aging time led to formation of impure and smaller crystals. However, at the aging time of 48 h, pure NaA zeolite particles with average particle size of 1.5 μm were obtained. In the second stage, the outer surface of porous α-Al₂O₃ tubular supports were seeded by vacuum method using 1.5 μm NaA particles. The most stable and uniform seeded layer was obtained at seeding time and suspension concentration of 90 s and 5 g L⁻¹, respectively. Then, 6 h of secondary growth of the zeolite layer on the seeded surface was carried out at 373 K three times. The XRD and SEM results showed the formation of a uniform and dense layer of pure NaA zeolite with an average thickness of 45 μm. Dehydration experiments were conducted on ethyl acetate/water mixtures with 2 wt% water content. The average total fluxes were 0.147, 0.208, and 0.315 kg m⁻² h⁻¹ at 303, 313, and 323 K, respectively. The separation factor was 163,000. This parameter did not change with temperature and it was due to very close activation energies of ethyl acetate and water.     

The influence of γ-Al2O3 and Na2O on the formation of gyrolite in the stirring suspension

Influence of γ-Al₂O₃, Na₂O and hydrothermal synthesis parameters on the gyrolite formation process was established at 200 °C. The molar ratios of primary mixtures were CaO/(SiO₂ + Al₂O₃) = 0.66 and Al₂O₃/(SiO₂ + Al₂O₃) = 0 or 0.025. The amount of NaOH, corresponding to 5% of Na₂O from the mass of dry materials, added in the form of solution. It was determined that in the stirred suspensions under favourable synthesis conditions (active SiO₂ component, dispersive starting materials) gyrolite already forms after 16 h of isothermal curing at 200°C. The stirring affects the sequence of intermediate compounds: gyrolite crystallizes together with Z-phase. γ-Al₂O₃, as the additive in gyrolite synthesis is not usable, because it stimulates other calcium silicate hydrates formation. Na₂O additive positively affects gyrolite synthesis because the duration of gyrolite synthesis shortens almost 2–3 times (6 h, 200°C) to compare with pure mixtures. However, gyrolite is not stable in the mixture with Na₂O and begins to turn into pectolite already after 16 h of isothermal curing. Moreover, the presence of (Na₂O + γ-Al₂O₃) additive stabilizes gyrolite and prevents its transformation to pectolite. Obtained results were confirmed by XRD, DSC and SEM/EDS analysis methods.     

Effects of H2O/Na2O molar ratio on the strength of alkaline activated ground blast furnace slag-ultrafine palm oil fuel ash based concrete

Effects of H₂O/Na₂O molar ratios (MRs) on the developed alkaline activated pozzolanic solid wastes (PMs)-ultrafine palm oil fuel ash (UPOFA) and ground blast furnace slag (GBFS)-were studied by using the constant mass of combined activators (10 M NaOH_aq + Na₂SiO_3aq of silica-modulus (Ms = SiO₂/Na₂O) of 3.3).The free water content (FWC) expressed as FWC/(PMs) varied from 0.02 to 0.1 by mass while the total H₂O/Na₂O MRs ranged from 18.9 to 23.1 The findings revealed that increase in H₂O/Na₂O MRs negatively affects the strength but positively impact the mixture workability (consistency). The microstructural morphology examination using Scanning Electron Microscope coupled with Energy dispersive spectroscopy (SEM + EDS) reveals the contribution of H₂O/Na₂O MRs to the product nature, compactness, and the reactivity of Ca²⁺ and Al³⁺ while Fourier transform infra-red (FTIR) spectroscopy indicates that H₂O/Na₂O ratios contributed to the product amorphousity and carbonation process but sparingly affected its formed polymerized structural units (SiQⁿ(mAl), n = 2 and 3).     

One-pot synthesis of Ni-SSZ-13 zeolite using a nickel-amine complex as an efficient organic template

We show that a nickel-amine complex (nickel-diethylenetriamine, Ni-DETA) is an efficient organic template for the one-pot synthesis of Ni-SSZ-13 zeolite. The effects of the reaction compositions, including the molar ratios of SiO₂/Al₂O₃, H₂O/Al₂O₃, Ni-DETA/Al₂O₃, and Na₂O/Al₂O₃, on the synthesis of the pure product were investigated using different temperatures and synthesis times. Physicochemical characterizations, including XRD, SEM, and ²⁷Al NMR, show that the zeolitic product has good crystallinity, uniform crystals, and contains a tetrahedral Al³⁺ species. The N₂ sorption isotherms, TG–DTA curves, IR spectra, and UV–Vis spectra show that Ni-DETA acts as a template in the product obtained. Interestingly, Ni-SSZ-13 zeolite is obtained by the conversion of Ni-Y zeolite produced in the crystallization process.     

Glass transition temperature of glasses in the SiO2-Na2O-CaO-P2O5-Al2O3-B2O3 system

A total of 24 glasses in or near the bioactive region in the system SiO₂-Na₂O-CaO-P₂O₅-Al₂O₃-B₂O₃ were studied. By differential thermal analysis their glass transition temperatures,T _g, were determined. On basis of an experimental plan for 16 glasses, two phenomenological equations describing the relationship betweenT _g and glass composition were developed. The equations describeT _g within the compositional ranges: SiO₂, 38.0–65.5 Na₂O, 15.0–30.0; CaO, 10.0–25.0; P₂O₅, 0–8.0; B₂O₃, 0–3.0; Al₂O₃, 0–3.0 wt%. The glass transition temperature shows a linear dependence of the Na₂O content. The higher the Na₂O content, the lower theT _g. Compositional alterations not including Na₂O influencesT _g little in comparison with changes in the Na₂O content.     

Alkali silicate binders: effect of SiO2/Na2O ratio and alkali metal ion type on the structure and mechanical properties

The influence of SiO₂:Na₂O molar ratio and the nature of an alkali metal (Na vs. K) in commercial aqueous alkali silicate on the microstructure, textural properties, phase composition, and hydrolytic stability of an alkali silicate binder have been investigated using scanning electron microscopy, nitrogen adsorption/desorption technique, X-ray diffractometry, thermal analysis, and dissolution tests. It has been found that microstructure and textural properties of the alkali silicate binder depend both on silica to alkali molar ratio and type of alkali metal (Na vs. K). Sodium silicate binder obtained from commercial silicate solution with lower SiO₂:Na₂O molar ratio (2.2) exhibits a globular microstructure of silica xerogel with high content of micropores, whereas the binder formulated with SiO₂:Na₂O molar ratio 3.2 is characterized by more open cluster structure with lower content of micropores. It is observed that surface specific area estimated by Brunauer, Emmett, and Teller method and mesopore volume obtained by the Barrett–Joyner–Halenda method for sodium silicate binder are substantially higher than those for potassium silicate binder. The ultimate hydrolytic stability of the sodium silicate binder increases slightly with increase in the silica to alkali molar ratio within the studied range. Decreasing in SiO₂:Na₂O molar ratio and replacement of sodium silicate solution by potassium silicate solution in the corresponding filled composition lead to the improvement of mechanical properties and decrease in open porosity.     

Synthesis and characterization of low-cost zeolite NaA from coal gangue by hydrothermal method

Through this investigation, we have demonstrated a low-cost preparation method of zeolite NaA from coal gangue. The well-developed zeolite NaA of 87.56% crystallinity was successfully prepared by hydrothermal alkali activation method, which required low alkali concentration (1.8 mol/L) compared to other researches (3–6 mol/L). The characterization results of product prepared at different conditions suggest that the purity and crystallinity of zeolite NaA are high at low alkali concentration and longer crystallization time. The Ca²⁺ exchange value of synthesized zeolite attained 265 mg CaCO₃/g compared to commercial zeolite, which is typically 340 mg CaCO₃/g. The basic structure parameters and thermal stability have also been studied. The results suggest that the obtained zeolite has a potential to be used as hard water softening agent. Moreover, the result of Rietveld quantitative phase analysis and Box-Behnken's response surface methodology showed that the weight fraction of zeolite NaA in product can reach 71.9%, and the crystallinity can attain 88.14% at the optimal condition of n(SiO2)/n(Al2O3) of 2.60, NaOH(aq) concentration of 1.86 mol/L at 95 °C for 10.08 h.     

Phase selection controlled by sodium ions in the synthesis of FAU/LTA composite zeolite

Abstract

Zeolite faujasite (FAU), Linde type A (LTA) and FAU/LTA composite have been synthesized using tetramethylammonium cation (TMA⁺) as template, by adjusting only the concentration of Na⁺ ions in the initial solution (1.00 Al₂O₃ 4.36 SiO₂ : 2.39 (TMA)₂ O : β Na₂ O : 249.00H₂ O). Na⁺ ions alter the phase composition of the product more than TMA⁺ or OH^? ions. When Na₂ O concentration [Na₂ O] increases from 0.024 to 0.168, the product gradually changes from pure FAU to pure LTA via the formation of FAU/LTA composite with increasing LTA fraction. Interestingly, the induction periods of FAU and LTA in the FAU/LTA composite zeolite ([Na₂ O] is 0.072) are both 13 h, quite different from the induction periods of their individual pure phases—45 h for FAU and 4 h for LTA. During the crystallization, the LTA/(FAU + LTA) fraction in the composite zeolite decreases in a nearly linear fashion. Scanning electron microscopy, thermogravimetry and differential thermal analysis indicate some difference between the properties of the FAU/LTA composite zeolite and of the mechanical mixture.     

Synthesis of LTA zeolite beads using alum sludge and silica rich wastes

This study successfully recycled alum sludge with either lithium slag or bottle glass to make high purity zeolite LTA beads. The basic synthesis approach was to fuse the waste material with sodium hydroxide then complete hydrothermal crystallization. Separate fusion of individual wastes promoted zeolite LTA formation compared to combined fusion. Preferred synthesis conditions were: 10 Na₂O:Al₂O₃:2.5 SiO₂:300 H₂O; hydrothermal temperature = 80 °C; time = 5 h. Zeolite LTA purity was between 80 and 85 wt% from the two waste combinations. Use of pseudoboehmite and carboxymethyl cellulose favoured granulation/extrusion/spheronization of zeolite LTA powder. However, the beading process decreased calcium exchange capacity (CEC) from 99.5 to 37 mg Ca²⁺/g for alum sludge + lithium slag and from 64.5 to 37 mg Ca²⁺/g for alum sludge + waste glass. Additionally, when using 20 wt% pseudo-boehmite as a binder the ion-exchange equilibrium time increased from 60 to 300 min. The importance of not only making zeolite powder from waste materials but also to extend studies to shaped forms was evident. It is recommended that future studies should also focus on making extrudates or beads as these are the forms used commercially.     

Fast and efficient synthesis of ZSM-5 in a broad range of SiO2/Al2O3 without using seeding gel

ZSM-5 zeolite were synthesized in a wide range of SiO₂/Al₂O₃ molar ratios at temperature ranging from 220 to 230 °C without adding seeding gel in 4-6 h of autoclavation time.     

Conversion of high silicon fly ash to Na-P1 zeolite: Alkaline fusion followed by hydrothermal crystallization

In this research, we converted high silicon fly ash to a high ion-exchange capacity zeolite using a two stages conversion process. Alkaline fusion was applied to collapse the fly ash crystalline phases and release Si content. Then Si/Al ratio of the synthesis sol adjusted with appropriate amount of industrial grade materials. A synthesis solution with the molar ratio of 2.2 SiO₂:Al₂O₃:5.28 Na₂O:106 H₂O was hydrothermally crystallized to Na-P1 zeolite at 120 °C for 4 h. The as-synthesized zeolite characterized by means of X-ray diffraction, infrared spectroscopy, scanning electron microscopy and thermal analysis. Cation exchange capacity of the zeolite was determined using ammonium acetate method. The zeolitization remarkably improved the cation exchange capacity of the final product (e.g. 3.23 meq/g in comparison to the raw fly ash ～0.005–0.02 meq/g).Due to the high CEC and sufficient whiteness of the final product, we suggest that the as-synthesized zeolitic powder is a potential candidate as a detergent builder.     

Synthesis of mordenite zeolite in absence of organic template

Mordenite is a zeolite that has been used as a selective adsorbent and as a catalyst. Mordenite zeolite with crystal diameter 65 nm and crystal length 7 μm was successively synthesized in the absence of organic template by hydrothermal method at 180 °C for 5 days after stirring at high speed and aging in the synthesis mixture with the molar composition of 12Na₂O:100SiO₂:2Al₂O₃:500H₂O. The produced samples were investigated using XRD, SEM, FT-IR, EDS, DTA/TG and BET surface area. The prepared sample, crystallized in needle shape crystals. Total (BET) surface area was 52.14 m²/g whereas, total pore volume was 0.2 cm³/g. Average pore diameter was 24.16 Å. Thermogravimetry analysis (DTA/TG) showed that, at room temperature to 800 °C, mordenite mass loss is 6%.     

In situ preparation of self-bonded zeolite MCM-22 bodies by vapor-phase transport method

Self-bonded bodies of zeolite MCM-22 were prepared by vapor-phase transport method. The resultant materials were characterized by means of X-ray diffraction, scanning electron microscope, mercury porosimetry, and nitrogen porosimetry. Self-bonded MCM-22 bodies were in situ prepared at pH 10.0 with the molar composition of 0.05Na₂O:SiO₂:0.033Al₂O₃. It was found that the bodies, prepared by aluminosilicate gel, had been transformed into zeolite MCM-22. The MCM-22 bodies of which the mechanical resistance was 126 N/cm avoided binder accession. By adding auxiliary chemical–PEG20000 to the aluminosilicate gel, the pore size distributions of MCM-22 bodies could be adjusted. The average pore radius of MCM-22 bodies reached in the 149.41–653.64 nm range when AC/SiO₂ ratio was 1.5 × 10⁻⁴–9.0 × 10⁻⁴.