Influence Of Crystallization Time Research Articles

Influences of crystallization time, batch molar ratios Al2O3/SiO2 and Na2O/SiO2 on particulate properties of sodalite crystals prepared under room-temperature conditions

Sodalite crystals were prepared by the hydrothermal method under room-temperature conditions. The influences of crystallization time, batch molar ratios Al2O3/SiO2 and Na2O/SiO2 on the crystalline end products were investigated. For comparison, an experiment was also carried out in which sodalite was synthesized at 90 °C for 10 h. The results revealed that with the prolongation of crystallization time from 1 h to 14 days, the crystallization followed a sequence of phase transformations from an amorphous phase to zeolite NaA, and finally to sodalite. Spherical sodalite crystals composed of very small crystallites were obtained after 10 h of room-temperature crystallization. Whereas, with the same gel composition, the sodalite synthesized at 90 °C for 10 h was large lepispherical particles. High Al2O3/SiO2 molar ratio favored the generation of smaller individual sodalite nanocrystals, which resulted in the formation of larger steady congregated agglomerates. Moreover, alkalinity circumstance determined whether or not sodalite was formed. Well-developed cubic zeolite NaA particles were obtained at Na2O/SiO2 = 1.4; when the Na2O/SiO2 was increased to 8.0, zeolite NaZ-21 crystals were generated, meanwhile, the decomposition of wool ball-like sodalite particles into nanorods was also observed.

Influences of crystallization time and molar composition of hydrogel on the preparation of sodalite, cancrinite and analcime

Sodalite, cancrinite and analcime were synthesized via hydrothermal processes, the influences of crystallization time and molar composition of hydrogel on the crystalline end products were investigated. The results revealed that with the prolongation of crystallization time from 3 min to 80 min, the crystallization followed a sequence of phase transformations from amorphous to zeolite NaA, sodalite and cancrinite. Well-crystallized cancrinite crystals were achieved at Al2O3/SiO2 molar ratios of 0.12, 0.34 and 0.76. However, with the Al2O3/SiO2 molar ratio was increased to 0.95, pure-form sodalite was formed. A gradual increase in the crystallinity of cancrinite was observed with increasing H2O/SiO2 molar ratio, while too high H2O/SiO2 resulted in analcime generated. Also, when the Na2O/SiO2 molar ratios of the hydrogel were 0.70, 1.22 and 4.75, the corresponding products obtained were pure phases of analcime, cancrinite and sodalite, respectively

The relationship between the preparation conditions and the crystallinity of ZSM-5 and the adsorption performance of sulfide in nature gas

ABSTRACT The preparation conditions of zeolite are the key factors affecting the adsorption performance of organic sulfur from natural gas. The influence of crystallization time, pH and Si/Al ratio of ZSM-5 zeolite preparation on the crystallinity, which is further related to the dimethyl sulfide adsorption performance in gas was explored for the first time. After conditional screening, the suitable conditions for organic sulfur adsorption are crystallization time of 36 h, Si/Al of 50, and pH as 13, and the breakthrough capacity of ZSM-5 is 8.23 mg/g. The Si/Al ratio has the greatest impact on the adsorption performance. With Si/Al ratio reduced from 200 to 50, the breakthrough time increased by 146%. The breakthrough time of ZSM-5 in methane is reduced by 12.5% compared with nitrogen. After the 5 cycles, the breakthrough time of the ZSM-5 decreases by less than 5%, indicating that the ZSM-5 can be reused for a long time in the natural gas purification industrial application process. This research provides research directions and guidance for the optimization of zeolite preparation conditions and the development of new organic sulfur adsorbents.

INVESTIGATIONS ON HYDROTHERMAL SYNTHESIS PARAMETERS IN PREPARATION OF ZEOLITE W

Zeolite W crystals were synthesized via hydrothermal process, the influence of crystallization time, aging time and temperature, the molar ratios Al2O3/SiO2 and K2O/SiO2 on the crystalline final products were studied. The results revealed that well-developed twin-ball shaped morphology zeolite W crystals were obtained after 6 h of crystallization, the longer crystallization time would not result in substantial changes in crystal morphology and size of end products. However, the crystals transferred from twin-ball to bouquet-like in shape with increasing aging time, while the high aging temperature resulted in zeolite F developed. Also, the Al2O3/SiO2 and K2O/SiO2 molar ratios of the hydrogel had major influences on synthesis of pure form zeolite W. Well-crystallized pure phase zeolite W products were obtained with Al2O3/SiO2=0.20, which were composed of many square pillars crystals, with average width in the range of 0.2–0.5 μm and length approximately 10 μm. Mild alkalinity circumstance was in favor of zeolite W crystallization, when the K2O/SiO2 molar ratio was increased to 9.42, the product obtained was pure phase of zeolite LTJ.

Fast synthesis of zeolite NaP by crystallizing the NaY gel under microwave irradiation

Zeolite P in sodium form (NaP) is useful in the separation of small gases. However, the synthesis of NaP is slow due to a long crystallization time. Here, we report the fast synthesis of NaP by crystallization of the gel of NaY under microwave irradiation without any template. The influence of crystallization time and temperature on the zeolite morphology, the character of water desorption and functional vibration are confirmed by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy. The suitable condition producing pure NaP crystalline is at 150 °C for 1 h. This is the shortest crystallization time to produce pure phase NaP.

Green energy-efficient synthesis of Fe-ZSM-5 zeolite and its application for hydroxylation of phenol

Abstract Currently, there remains a great challenge to synthesize zeolites in an energy-saving and environmentally friendly manner. Herein we report a novel solvent-free route of synthesizing Fe-ZSM-5 zeolite, which is featured by using Fenton's reagent as a promoter. The influences of crystallization time, amount of hydrogen peroxide and low-temperature pretreatment on the synthesis of Fe-ZSM-5 zeolite were investigated in detail. The results indicate that the combination of solvent-free synthesis with Fenton's reagent can facilitate the rapid crystallization of Fe-ZSM-5 zeolite. The resultant Fe-ZSM-5 zeolite was used as a catalyst for phenol hydroxylation, and characterized by XRD, SEM, ICP-AES, N2 physisorption and UV–Vis diffuse reflectance spectroscopy. Notably, it exhibits a much better catalytic performance as compared with the reference catalyst by conventional solvent-free method. The observed enhanced catalytic performance for this Fe-ZSM-5 catalyst is attributed to its larger BET surface area and mesoporous volume as well as enrichment towards phenol.

Influence of Crystallization Time on Energy-Storage Density and Efficiency of Lead-Free Bi0.5(Na0.8K0.2)0.5TiO3 Thin Films

Lead-free Bi0.5(Na0.80K0.20)0.5TiO3 (BNKT) ferroelectric films were synthesized on Pt/Ti/SiO2/Si substrates via chemical solution deposition. The influence of crystallization time on the microstructures and ferroelectric and energy-storage properties of the films was investigated in detail. The XRD analysis showed that the BNKT films have well crystallized corresponding to the single-phase perovskite structure at 700°C. Ferroelectric and energy-storage properties of the films were significantly enhanced by increasing crystallization time. With crystallization time of 60 min, the remnant polarization (Pr), maximum polarization (Pm), and Pm-Pr values reached the highest values of 7.9 µC/cm2, 28.9 µC/cm2, and 21.0 µC/cm2, respectively, under the electric field of 400 kV/cm. Thanks to the strong enhancement in Pm and the large Pma-Pr value, the highest recoverable energy-storage density (Jreco) gets the value of 2.9 J/cm3. The obtained results indicate that the BNKT films have application potentials in advanced capacitors.

Synthesis of core–shell structured FAU/SBA-15 composite molecular sieves and their performance in catalytic cracking of polystyrene

Composite molecular sieves, FAU/SBA-15, having core-shell structure were synthesized. The synthesized composite sieves were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), pyrolysis fourier transform infrared (Py-FTIR) spectroscopy, temperature programmed desorption spectra (NH3-TPD), UV Raman spectroscopy, nuclear magnetic resonance (NMR) and other techniques. XRD, SEM, TEM, N2 adsorption-desorption, mass spectrometry, NMR and EDS results showed that the composite molecular sieve contained two pore channels. Py-FTIR results showed that the addition of HY molecular sieves improved the acidity of the composite zeolite. The crystallization mechanism during the growth of FAU/SBA-15 shell was deduced from the influence of crystallization time on the synthesis of FAU/SBA-15 core-shell structured composite molecular sieve. HY dissociated partially in H2SO4 solution, and consisted of secondary structural units. This framework structure was more stable than its presence in the isolated form on the same ring or in the absence of Al. Thus it played a guiding role and connected with SBA-15 closely through the Si-O bond. This resulted in the gradual covering of the exterior surface of FAU phase by SBA-15 molecular sieves. The presence of SBA-15 restricted the formation of the other high mass components and increased the selectivity towards ethylbenzene.

Synthesis of ZSM-5 Zeolite without Organic Template

ZSM-5 zeolite was synthesized via a template-free method. The influence of crystallization time was investigated. The obtained samples were characterized by XRD, SEM and FTIR. Results shown that with the ratio of 8 Na2O : 80 SiO2 : 2 Al2O3 : 2500 H2O, the crystallization for ZSM-5 began at ca. 9 h. And fine ZSM-5 zeolite (ca. 10~15 μm) could be obtained by crystallizing at 190 °C for 10 h. Further increasing time would lead to the appearance of quartz.

Influence of Synthesis Parameters on the Formation of SAPO-5 from Metakaolin

SAPO-5 molecular sieves was hydrothermally synthesized using metakaolin simultaneously as silica and aluminum sources, triethylamine as template agent, and phosphoric acid as phosphorous source. The influence of crystallization time, amount of triethylamine, hydrofluoric acid, and water on the structure and composition of crystalline phase were investigated. The structure and composition of product were analyzed by means of XRD, and BET. It was showed that the SAPO-5 molecular sieves with high crystallinity and well-defined morphology can be synthesized with a molar ratio of MK:P2O5:2.5TEA: 0.1HF:70H2O in the final reaction mixture at 200°C for 24h.

A Study of HZSM-5 Membrane Synthesis on α-Al<sub>2</sub>O<sub>3</sub> Supports

Porous α-alumina supports were seeded with monodisperse nanocrystalline HZSM-5 zeolite and calcined. The supports were treated in a synthesis solution to grow the seeds into HZSM-5 membrane with aluminum nitrate (Al (NO3)3), tetraethyl orthosilicate (TEOS), and tetrapropyl ammonium hydroxide (TPAOH) as raw materials. X-ray diffraction (XRD) characterization results showed that the membranes consisted of well-crystallizedH ZSM-5. The influence of crystallization time on morphology of HZSM-5 membranes was represented by scanning electronic microscopy (SEM) characterization: the HZSM-5 zeolite membranes on the supports were defect free and the membrane thickness was increased with the crystallization time prolonged.

Synthesis of NaX zeolite: Influence of crystallization time, temperature and batch molar ratio SiO2/Al2O3 on the particulate properties of zeolite crystals

Abstract In this study, the effects of crystallization time, temperature and SiO 2 /Al 2 O 3 molar ratio in the synthesis gel on the end products (NaX zeolite) were investigated. The results revealed that crystallization time and temperature determined whether or not NaX zeolite was formed. Furthermore, SiO 2 /Al 2 O 3 molar ratio was found to play a significant role in the particulate properties of the crystalline end products. A single phase NaX zeolite was obtained only with the SiO 2 /Al 2 O 3 molar ratio of 1.5–4.0; the NaA zeolite was developed at SiO 2 /Al 2 O 3 = 1.0 in addition to the NaX zeolite. However, at SiO 2 /Al 2 O 3 = 0.5, a single phase NaA zeolite was generated. The Si/Al molar ratios of NaX zeolites were tested to be 1.38, 1.33, 1.29, 1.24 and 1.18 for the SiO 2 /Al 2 O 3 molar ratios of 4.0, 3.5, 2.9, 2.0 and 1.5. The corresponding samples had the mean particle sizes of 464, 548, 689, 836 and 980 nm, with the particle size distribution ranges of 120–810, 202–815, 445–975, 605–1096 and 770–1218 nm, respectively. N 2 adsorption–desorption results showed that the BET surface areas and micropore volume of the end product increased with the decrease of SiO 2 /Al 2 O 3 molar ratio in synthesis gel, but all the NaX zeolite particles have relatively high total pore volumes. In addition, the effect of molar ratio of SiO 2 /Al 2 O 3 on the amount of NaX zeolite formed in the products was also considered.

Synthesis of Single-Phase Zeolite 4A from by-Products of Polysilicon Production Process

In this paper, pure,single phase and high crystalline zeolite 4A samples were synthesized by hydrothermal treating by-products of polysilicon production process. The influence of crystallization time and the molar ratio of SiO2/Al2O3 on degree of crystallinity of synthesized zeolite 4A samples was studied. The degree of crystallinity, skeleton structure and particles morphology of zeolite 4A samples were characterized by XRD,FT-IR,SEM,respectively.The results show that synthesized zeolite 4A samples were identical with commodity zeolite 4A.

Hydrothermal synthesis of size-controlled silicalite-1 crystals

The objective of this work was to evaluate the use of hydrothermal method for the synthesis of small and homogeneous silicalite-1 zeolite. The influences of crystallization time, crystallization temperature, different organic solvents and different TPAOH template concentrations were investigated. The results showed these parameters had played important roles in controlling particle size of silicalite-1 zeolite.

Multiple melting behaviour of poly( l-lactide- co-glycolide) investigated by DSC

The melting behaviour of poly( l-lactide- co-glycolide) (PLGA) isothermally crystallized from the glassy state was investigated by differential scanning calorimetry (DSC). Triple, double or single melting endotherms were observed in subsequent heating scans for the samples isothermally crystallized at different temperatures. These endothermic peaks were labelled as I, II, and III for low-, middle-, and high-temperature melting endotherms, respectively. The observations of the independence of endotherm III from the crystallization temperature, and the heating rate dependence of endotherm III, indicated that endotherm III was due to the remelting of recrystallized lamellar during a heating scan. The influence of crystallization time on the melting behaviour of PLGA showed that secondary crystallization appeared even at an early stage of crystallization, since endotherm II was still developing with time after the appearance of endotherm I. Further investigation showed that the peak temperature of endotherm I increased linearly with the logarithm of the crystallization time. It is suggested that endotherm II is attributed to the melting of the primary lamellae, while endotherm I is assigned to the melting of secondary lamellae.

Synthesis of mordenite using kaolin as Si and Al source

The main purpose of this work was to study mordenite synthesis using kaolin as a Si and Al source. The influence of crystallization time and seed addition were studied. The obtained zeolites were characterized by: XRD, SEM, nitrogen adsorption and chemical analysis. Kaolin showed to be a promising source of Si and Al for mordenite synthesis. Seed addition led to more highly crystalline phases. Kaolin yielded mordenite whereas ZSM-5 was obtained from calcined kaolin. Longer synthesis times and seed addition favored mordenite formation.

Thermal analysis of the multiple melting behavior of poly(butylene succinate‐co‐adipate)

AbstractThe melting behavior of poly(butylene succinate‐co‐adipate) (PBSA) isothermally crystallized from the melt was investigated by differential scanning calorimetry. Triple, double, or single melting endotherms were observed in subsequent heating scan for the samples isothermally crystallized at different temperatures. These endothermic peaks were labeled as I, II, and III for low‐, middle‐, and high‐temperature melting endotherms, respectively. The independence of endotherm III to the crystallization temperature, the existence of an exothermic crystallization peak just below the endotherm III, and the heating rate dependence of endotherm III indicated that endotherm III was due to the remelting of recrystallized lamellar during a heating scan. The influence of crystallization time on the melting behavior of PBSA showed that endotherms II and III developed prior to endotherm I; endotherm III developed rather simultaneously with endotherm II. Further investigation showed that the peak temperature of endotherm I increased linearly with the logarithm of the crystallization time. It suggested that endotherm II was attributed to the melting of the primary lamellae, while endotherm I was due to the melting of secondary lamellae. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3077–3082, 2005

Separation of the Soluble Salts KNO 3 and NH 4Cl by Flotation with Oleic Acid

A flotation study was performed for the soluble salts KNO3 and NH4C1 using oleic acid as the collector agent and various pH modifiers. Flotation was performed in one- and two-stage processes. The results of this study show that, as a collector agent, oleic acid enables flotation of NH4Cl and thus makes separation of these soluble salts possible. The best results, moreover, have been found at pH = 8 with gas ammonium as a regulator where three-stage flotation was performed with reflotation of concentrate and tailing obtaining 93% recovery of KNO3 in the tailing with a content of 98%. The influence of crystallization time on the size of the crystals in the soluble salts prior to flotation has also been examined. The most favourable particle size was found between 4 and 6 hours.