Effect of aluminum concentration on crystal size and morphology in the synthesis of a NaAl zeolite (original) (raw)
Related papers
2003
1 µm crystal-size Na A zeolite (LTA) is successfully synthesized via the sol-gel process and microwave heating technique using alumatrane and silatrane as precursors. The optimal conditions to obtain LTA were 1:1:3:410 SiO 2 :Al 2 O 3 :Na 2 O:H 2 O ratio, microwave heating temperature and a time of 110°C and 160 min, respectively. Under the same conditions, increasing the Na 2 O concentration exponentially reduces the microwave heating time from 160 min at a Na 2 O:SiO 2 ratio of 3:1 to 5 min at a Na 2 O:SiO 2 ratio of 9:1. Increasing the Na 2 O concentration strongly affects the particle size and particle size distribution, but does not affect the product composition. Increasing the amount of water increased the average particle size and also the number of irregular cubic shape crystals. Increasing the aging temperature from 90° to 150°C, everything else being the same (one hour heating time and the loading ratio of SiO 2 :Al 2 O 3 :5Na 2 O:410H 2 O), only amorphous product was produced at 90°C and between 110°-150°C only LTA was produced.
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.
Morphology-Controlled Synthesis of Zeolite and Physicochemical Properties
Engineering Journal, 2012
Zeolite L is a crystalline aluminosilicate compound and a typical chemical composition of K9Al9Si27O72•nH2O (n = 0-36). The structure and chemical properties, as well as their sizes and morphologies of zeolite L has led to various applications in different fields. The aim of this study is to investigate the effects of chemical compositions of the starting gel on the synthesis, size and morphology of zeolite L crystals. Zeolite L had been synthesized hydrothermally at 180 ˚C for 2 days, from gels with the molar compositions of 2.62-3.78 K2O: 0.8-1.4 Al2O3: 8-12 SiO2: 80-200 H2O. The variation of chemical compositions led to the differences in morphologies and crystal sizes. Their morphologies varied from ice hockey to cylindrical shapes and their crystal sizes varying from 1.50-7.53 µm. With an increase in H2O and SiO2, the crystal size was also increased but decreased with an increase in K2O. In varying Al2O3, there was no effect on their shapes which were still cylindrical but with different crystal sizes. Moreover, the adsorption of ethylene on zeolite L samples depended significantly on crystal shapes and sizes.
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).
Synthesis and characterization of Na-X, Na-A, Hydroxisodalite and Na-P zeolites from metakaolinite
D. NOVEMBRE, B. DI SABATINO, D. GIMENO, C. PACE (2011) Synthesis and characterization of Na-X, Na-A, Hydroxisodalite and Na-P zeolites from metakaolinite. Clay Minerals, 46: 336-354, 2011
The present work deals with the hydrothermal synthesis of Na zeolites (Na-A, Na-X and Na-P) and hydroxysodalite using kaolinite calcined at 650ºC as starting material. The focus was on definition of the most favourable conditions for the synthesis of zeolite Na-A and Na-X from metakaolin in order to economize on both energy (i.e. synthesis temperatures) and reaction time and to enlarge the field of pure and isolated synthesized phases. Metakaolin was mixed with calculated amounts of NaOH solution and sodium silicate and five sets of experiments were carried out at ambient pressure and 6880.1ºC varying the SiO2/Al2O3 ratio from 2.2 to 7. Optimal conditions for crystallization of Na-A zeolite from kaolinite were reached with a SiO2/Al2O3 ratio of 2.2 plus 4 M NaOH without adding sodium silicate; transformation into hydroxysodalite develops after ~8 h. For SiO2/Al2O3 ratios between 4 and 7, crystallization of the separate Na-X zeolite phase could be achieved and transformation into Na-P and hydroxysodalite occurred after 382 h and 190 h, respectively. For SiO2/Al2O3 ratios between 5 and 6, transformation of metakaolin into Na-X plus Na-A, hydroxysodalite and Na-P occurred, and the field within which Na-A and Na-X zeolite exists overlapped that of the other zeolites. The products of synthesis were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma optical emission spectrometry (ICP-OES), infrared spectroscopy (IR) and thermal analyses (TG-DTG-DTA). Obtaining pure Na-A and Na-X zeolite from kaolinite treated at low metakaolinitization temperature (650ºC) and low hydrothermal synthesis temperature (68ºC) represents a considerable economic advantage in terms of both energy and time.
AB ST R ACT : The present work deals with the hydrothermal synthesis of Na zeolites (Na-A, Na-X and Na-P) and hydroxysodalite using kaolinite calcined at 650ºC as starting material. The focus was on definition of the most favourable conditions for the synthesis of zeolite Na-A and Na-X from metakaolin in order to economize on both energy (i.e. synthesis temperatures) and reaction time and to enlarge the field of pure and isolated synthesized phases. Metakaolin was mixed with calculated amounts of NaOH solution and sodium silicate and five sets of experiments were carried out at ambient pressure and 68Ô0.1ºC varying the SiO 2 /Al 2 O 3 ratio from 2.2 to 7. Optimal conditions for crystallization of Na-A zeolite from kaolinite were reached with a SiO 2 /Al 2 O 3 ratio of 2.2 plus 4 M NaOH without adding sodium silicate; transformation into hydroxysodalite develops after~8 h. For SiO 2 /Al 2 O 3 ratios between 4 and 7, crystallization of the separate Na-X zeolite phase could be achieved and transformation into Na-P and hydroxysodalite occurred after 382 h and 190 h, respectively. For SiO 2 /Al 2 O 3 ratios between 5 and 6, transformation of metakaolin into Na-X plus Na-A, hydroxysodalite and Na-P occurred, and the field within which Na-A and Na-X zeolite exists overlapped that of the other zeolites.
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 ...
Powder Technology, 2011
Hydrothermal synthesis of zeolite T in aqueous alkaline solutions without using templates was investigated. Zeolite T crystals were prepared via hydrothermal synthesis using milk-like aluminosilicate gel with a composition of aSiO 2 :bAl 2 O 3 :cNa 2 O:dK 2 O:xH 2 O. The effects of molar compositions including silicon module (n RM = a/b) and relative alkalinity (α = OH/SiO 2), and crystallization conditions including crystallization temperature (T) and time (t) on the yield of T-type crystals were investigated. This research work examines changes in the yield of crystalline zeolite phases by varying the gel composition parameters (n RM =20-25, and α = 0.71-0.82) and crystallization process temperature and time (T = 100°−140°C, t = 120-216 h), while keeping constant the parameters [OH] = 2.77 m, U RM (Na/Na + K) = 0.75, stirring time = 24 h , stirring temperature = 30°C, and drying temperature = 100°C. The crystal species of zeolite T were characterized by XRD (X-ray diffraction) and SEM (Scanning Electron Microscope).
Effect of Crystallization Time on the Hydrothermal Synthesis of Zeolites from Kaolin and Bauxite
2014
— Kaolin and bauxite were used as alumina and silica sources to synthesize zeolites hydrothermally. The source materials as well as the synthesized zeolites were characterized by X-ray diffraction (XRD) scanning electron microscopy (SEM), energy dispersive x-ray analysis (EDX) and Fourier transformed infrared spectroscopy (FTIR). XRD spectra of the bauxite showed Gibbsite phase whereas that of kaolin gave 32.4 % quartz and 67.6 %. The main phases of zeolites obtained after hydrothermal crystallizations were zeolite types LTA, analcime and zeolite X. Longer crystallization time resulted in phase change of the zeolites into sodalite. Hence, natural raw materials such as bauxite and kaolin have the attractive features of providing the staring reagents for the synthesis of ultrapure synthetic zeolites.