Preparation of zeolites by different bases with 1 . 5 of initial ratio Si / Al : the effect of crystallization temperature (original) (raw)
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Zeolite A Synthesis under Dynamic Conditions, after Hydrogel Ageing
Croatica Chemica Acta, 2012
ABSTRACT Zeolites are crystalline, microporous, alumo-silicate materials (around 400 types) which are used in many applications. Each field of usage (catalysis, ion exchange, sorption, molecular sieving, etc.) has demands regarding crystals' structural and particulate properties. Detailed understanding of the mechanisms of crystals' formation and growth enables the control of these properties. Hydrogels of the starting composition 3.2 Na2O x 2 SiO2 x 1.05 Al2O3 x 250 H2O were heated in stainless steel reactor at 80 degrees C under dynamic conditions, after ageing for t(A) = 0-209 h at 25 degrees C. Solid phase samples were characterized using microscopy (OM, SEM), PXRD and laser light scattering (LLS). Specific number of zeolite A crystals was calculated from particle size distributions. It was shown that the some particulate properties: specific number of crystals and crystal size distribution, are changing towards higher number of crystals and wider size distribution while the morphology of the crystals remains the same. Also, the crystal growth rate is higher in the systems which are treated under dynamic conditions. Obtained results were compared with data of systems crystallized under static conditions and commented on the grounds of the autocatalytic nucleation theory. (doi: 10.5562/cca2055)
Influence of Alcalinity on Synthesis of Zeolite a
2011
Two different systems were examined: (1) homogeneous (optically clear solution saturated with Na + , aluminate, silicate and alumosilicate species) and (2) heterogeneous (hydrogel – saturated solution with precipitated gel). Hydrothermal transformation of samples in both systems was made by heating of HDPE reactors (flasks) with samples at 80°C. All systems were prepared adding of the basic sodium silicate solution into the basic sodium aluminate solution. Both solutions were prepared by dissolving of appropriate amounts of sodium silicate (Fluka, > 97% Na2O SiO2 × 5H2O) or sodium aluminate (Riedel de Haën, 54% Al2O3; 41% Na2O) with NaOH (Kemika, 98% NaOH) in deionized water. In order to remove impurities from the sodium aluminate solutions, they were centrifuged and only clear supernatant was used for preparation of starting system. After preparation and ageing for 24 h, starting solution of systems 1 (1a, 1b, 1c) and hydrogel of systems 2 (2a, 2b, 2c) were divided among needed ...
Microporous and Mesoporous Materials, 2007
An aqueous aluminosilicate hydrogel having oxide molar composition: 4.72Na 2 O AE Al 2 O 3 AE 1.93SiO 2 AE 254.86H 2 O was treated in two ways: (1) the hydrogel (system S NL ) was heated at 80°C until the entire amount of amorphous aluminosilicate precursor (gel) has been transformed to zeolite A, (2) the hydrogel was frozen in liquid air and freeze-dried; solid liophilizate was poured in an appropriate volume of water, and the obtained suspension (system S L ) was treated in the same way as the system S NL . The drastic treatment of hydrogel did not substantially change the distribution of nuclei in the matrix of the amorphous aluminosilicate precursor (gel) established during its precipitation. The consequence is that, in accordance with the principles of the gel ''memory'' effect, the crystal size distributions of the crystalline end product (zeolite A) obtained from both the systems (S NL and S L ) are almost the same. On the other hand, the above mentioned treatment of hydrogel changes the concentrations of aluminium and silicon in the liquid phase and caused that the rate of crystal growth is somewhat higher in system S L than in system S NL . Population balance analysis of the crystallization processes has shown that the difference of the kinetics of crystallization of zeolite A from the systems S NL and S L is in larger extent caused by the small difference in the crystal growth rate and in the smaller extent by the particulate processes determined by the specific number of nuclei N S and distribution of nuclei in the gel matrix.
Influence of alkalinity of the starting system on size and morphology of the zeolite A crystals
Materials Chemistry and Physics, 2012
The performance of zeolite crystals in different industrial processes often depends on their size and shape. Several physico-chemical parameters can have significant impact on their particulate properties (especially morphology). Amongst the chemical parameters the Si/Al ratio is one of most important variable together with the Na + ions (alkalinity) content. The present study is devoted to the effect of Na on the morphology of zeolite A (LTA-type) crystals. Initial hydrogels were heated at 80 • C in reactors made of HDPE, under static conditions. After separation by centrifugation, samples of solid and liquid phase were characterized using several analytical methods such as: atomic absorption spectroscopy, Xray diffraction, laser light scattering, optical, scanning and transmission electron microscopy. The results show that the increase of alkalinity in starting system causes two effects: (a) increase of the number of nuclei (crystals) in system through additional nucleation at surface and subsurface area of gel particles, and (b) the growth of crystals which have more irregular shape (rounded edges).
Journal of Porous Materials, 2013
A number of investigations have demonstrated that zeolite NaA could be synthesized using Si, extracted from rice husk ash; however, experiments on direct extraction of Si from rice husk (RH) are scarce. The main objective of the present study was to explore the possibility to synthesize high-quality zeolite NaA from RH and waste aluminium cans (as a source of Al), applying different procedures for the preparation of initial hydrogel and a unified procedure for crystallization of zeolite NaA. Products were characterized by SEM-EDX and XRD analyses. The investigation demonstrated that Si could be extracted directly from RH, avoiding the process of RH burning. Practically complete dissolution of Si from RH was achieved by alkali treatment (with 10 % NaOH for 7 h) at boiling temperature and atmospheric pressure, i.e. using refluxing system instead of autoclave for the preparation of Si-gel. Zeolite NaA samples synthesized from such Si-gels were pure, highly crystalline and white. Furthermore, it was found that the direct dissolution of Al in Si-gel did not affect the quality of the final product. Although this investigation was not focused on the mechanism of zeolite NaA crystallization, the results obtained indicated clearly that the history of Si-gel preparation played an important role in the nucleation and growth of zeolite NaA crystals and influenced their yield, size, and shape. Therefore, the optimization of Si-gel preparation procedure has to be considered as essential not only for the economy of the synthesis of NaA from RH, but also for the quality of the final product.
Microporous and Mesoporous Materials, 2011
Influence of the batch molar ratio, y [SiO 2 /Al 2 O 3 ] b , on the size and shape of zeolite A crystals at three different molar ratios [SiO 2 /H 2 O] b and [Na 2 O/H 2 O] b was investigated. Four different morphological entities of zeolite A, namely regular cubic crystals with sharp edges and apexes, cubic crystals with truncated edges, cubic crystals with ''rounded" edges and apexes and pseudo-spherical, face-less particles, were observed in the crystalline end products obtained by hydrothermal treatment (heating at 80°C) of the hydrogels having 1.0 6 [SiO 2 /Al 2 O 3 ] b 6 2.2, 0.006 6 [SiO 2 /H 2 O] b 6 0.0186 and 0.0136 6 [Na 2 O/H 2 O] b 6 0.0424. The chemical conditions with respect to the values of [SiO for obtaining the particular morphological entities of zeolite A are defined, and the possible mechanisms of their formation are discussed. The influence of the mentioned factors on the crystal size and the surface properties of crystallized zeolites is also considered.
CRYSTALLIZATION TEMPERATURE OF NaA ZEOLITE PREPARED FROM SILICA GEL AND ALUMINUM HYDROXIDE
CHEMISTRY PROGRESS, 2019
Wuntu, A. D. et al. 2011. Suhu kristalisasi zaolit NaA yang disintesis dari silica gel dan aluminium hidroksida. Pengaruh suhu dalam tahap kristalisasi zeolit NaA telah dikaji dalam penelitian ini. Sintesis zeolit NaA dikerjakan pada kondisi hidrotermal konvensional menggunakan silika gel dan aluminium hidroksida sebagai bahan dasar dan kristalisasi dikondisikan pada suhu 60 oC, 75 oC, 90 oC, 105 oC, dan 120 oC. Kristalisasi zeolit NaA selanjutnya dianalisis dengan teknik spektroskopi infra merah. Hasil yang diperoleh memperlihatkan bahwa pada suhu 60 oC belum terbentuk kristal zeolit yang ditunjukkan dengan tidak adanya pita serapan yang menjadi karakteristik zeolit A pada spektra infra merah. Pita serapan khas zeolit A muncul pada spektra infra merah zeolit yang diperlakukan pada suhu kristalisasi 75 oC hingga 120 oC. Kata kunci : kristalisasi, suhu, zeolite NaA, silika gel
Microporous and Mesoporous Materials, 2008
Zeolite [Ti, Al]-Beta has been synthesized by two methods (Method I and II) using aluminum (Al(NO 3 ) 3 Á 9H 2 O) and varying the initial gel alkalinities (OH À /T IV O 2 ). Both methods employed silica (SiO 2 ), hexafluorotitanic acid (H 2 TiF 6 ), tetraethylammonium hydroxide (TEAOH) and ammonium fluoride (NH 4 F) as silicon and titanium sources, template and crystallization additive, respectively. X-ray powder diffraction and chemical analyses were used to examine crystallinity and framework elements composition in the solid samples. DR-IR/DF-UVis spectroscopy and scanning electron microscopy (SEM) were used to study the influence of initial gel alkalinity in the particle size and crystallization mechanism of solid samples. In general, higher solid yields were obtained for relatively shorter crystallization times in samples crystallized from more alkaline gels (Method I). No zeolite Beta crystallized from gels with OH À /T IV O 2 lower than 0.42 using Method II. Samples of higher crystallinity were obtained for crystallization times >132 h using Method II. Samples of Method I synthesized from less alkaline gels contained higher Ti and lower Al contents. The intensification of the IR band at 960 cm À1 and the UV absorption at 212 nm observed in calcined samples proved tetrahedral Ti in the Beta framework. SEM micrographies revealed smaller average zeolite particle size in samples crystallized from more alkaline gels using Method I.
The crystal morphology of zeolite A. The effects of the source of the reagents
Microporous Materials, 1997
This study investigates the effects of the variation in reagents on the synthesis of zeolite A. The synthesis was attempted under autogenic conditions and at temperatures of 100 (±1)°C and 70 (±1 )°C, using various aluminium and silicon sources. Preparation of the gels used silica and aluminium to form mixed systems of organic and inorganic reagent sources. Products formed were analysed and characterised instrumentally using X-ray diffraction, X-ray fluorescence, Fourier transform infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Systems using aluminium isopropoxide consistently produced uniformly sized crystals, each having deep, chamfered edges. Sodium reagent sources produced sharp edged crystals. The system using tetraethyl-orthosilicate with aluminium powder produced a hexagonal morphology. The change in the hydroxide concentrations, relative to the systems using sodium silicate and sodium aluminate sources was also monitored, and while it had a marked effect on crystallinity and stability, the crystal morphology remained consistent. © 1997 Elsevier Science B.V.