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Procedia 00 (2008) 000–000 PhysicsPhysics Procedia 2 (2009) 1081–1086 www.elsevier.com/locate/XXX www.elsevier.com/locate/procedia
Proceedings of the JMSM 2008 Conference
Synthesis process of zeolite P using a poorly crystallized kaolinite M. Meftaha*, W.Oueslatia, A. Ben Haj Amaraa a
LPMNMH Laboratoire de Physique des Matériaux Lamillaires et Nanomatériaux Hybrides -Faculté des Sciences de Bizerte Zarzouna 7021, Tunisia Elsevier use only: Received date here; revised date here; accepted date here
Received 1 January 2009; received in revised form 31 July 2009; accepted 31 August 2009
Abstract Poorly crystallized kaolinite KGa2 and metakaolinites derived from them were studied under hydrothermal conditions in an aqueous sodium hydroxide solution. Reaction was obtained in a specific reactor allowing a continuous agitation and pH and temperature controls. Metakaolinte were derived from heated kaolinite at 500°C and 900°C. Using kaolinite and metakaolinite obtained after heating at 500°C the main formed products were zeolite P. When metakaolinte obtained at 900°C reacted with NaOH solution zeolite A (LTA) is the first synthesized product and a prolonged treatment (72hours) leads to synthesize zeolite P. Intermediate and homogeneous phases were characterized by XRD analysis and MAS NMR spectroscopy. © 2009 Elsevier B.V. All rights reserved 61.05.cp; 61.05.Qr Keywords: kaolinite, metakaolinite, zeolites P, PXRD
1. Introduction The term zeolite is used to denote crystalline aluminum silicates of natural or synthetic origin. The general structural formula is given by: Mx/m[Al x, (Si (2-x)O4)] ,n H 2 O
Where m is the valence of cations M, n the water content and 0x1. The flexibility of the zeolite Si-O-Si bond explains the fact that more than 200 structures have been determined. Several properties account for their commercial use: they are strong absorbents, they show a very high selectivity and they are excellent solid acid catalysts. Today, synthetic zeolites are employed in wide range of industries (i.e. in the separation of gaseous and liquid compounds, detergent for their high ion-exchange capacities, fluid cracking (FCC)…). Since 1980 zeolite is designed as a phosphate substitute for purely ecological reasons. Zeolites of types P, X, A have been recently introduced into the market; they have significantly different crystalline structures. Among synthetic zeolites, zeolite P was developed with a x value of nearly 1.0 and a high calcium exchange capacity [1]. As
* Corresponding author. Tel.: 216-20-467-333; fax: +0-000-000-0000 . E-mail address:
[email protected].
doi:10.1016/j.phpro.2009.11.066
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a result of the somewhat narrower pores of approximately 0.3 nm, and the more flexible and adaptable crystal structure, the calcium ions are firmly more bound than the case of zeolite A. The cations M are exchangeable and give rise to the rich ion-exchange chemistry of these materials. The newness of zeolites stems from their microporosity and is a result of topology of the framework. Several studies [2-6] showed that the nature of raw materials used in the synthesis of a zeolite is a key factor governing its purity and quality. Zeolites with Si:Al ratio 1 can be synthesized using kaolinite or metakaolinite with NaOH and colloidal silica as described in various publications and patents [4,7]. The main propose of this work concerns the synthesis of zeolite P using kaolinite and metakaolinites as Si and Al source. The intermediate phases and final products were characterized by XRD and ( 29Si and 27Al) MAS NMR spectroscopy. 2. Material and methods We used for this investigation a poorly crystallized KGa2 kaolinite (CMS standard). Kaolinite was first treated by 1N NaCl solution and rinsed with distilled water to remove some impurities. Natural kaolinite and metakaolinites were reacted with NaOH using hydrothermal method at 90°C: 20g of sample and 200ml of 1N NaOH solution were placed in a reactor constituted allowing the control of pH, the temperature and the continuous magnetic agitation. Some controls are effectuated at different period of times. For each control the sample is rinsed and centrifuged at 4500 rpm until the washing reached a pH of 7 and dried at 100°C overnight. Metakaolinites were obtained by heating kaolinites at 500°C and 900°C. Samples were respectively labeled KGa2_500 and KGa2_900 and by the same experimental protocol, as used to synthesize zeolite from natural kaolinite. The zeolitic phases in synthetic products were identified using X-ray diffraction (XRD). X-ray powder diffraction is the most common method to determine the zeolite structure evolution as well as its purity [8]. XRD patterns were obtained by reflection setting with D8 Advance Bruker equipment using Cu-KĮ1 radiation (1.5406 ǖ). Intensities were measured at 50s counting time per step of 0.02° (2-theta). Many important properties of zeolites are strongly dependent of the location of Si and Al in the tetrahedral framework. (29Si and 27Al) NMR have a great potential in the direct determination of local Si, Al orderings. The NMR spectra were recorded using a spectrometer BRUKER-300 MHz Ulrashield. The magnetic field H0 used is equal to 7.1 T and corresponded to the frequencies of resonance of (78.22 MHz) and (59.62 MHz) respectively for 27 Al and 29Si. 3. Results and discussion
3.1 XRD analysis
3.1.1 Natural kaolinite XRD patterns of the natural (Fig. 1a) and treated kaolinite KGa2 by NaOH solution during 72h (Fig. 1b), 168h (Fig. 1c) and at 264h (Fig. 1d) shows that whatever the duration of the treatment is a single-phase is obtained and corresponds to zeolite P. The examination of the fig. 1d shows clearly that the kaolinite-zeolite transformation is not completely achieved (presence of hkl reflection corresponding to the starting material and situated at 20° (2ș)).
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(d ) (c ) (b ) (a )
10
20
30
°2 θ (C u -K α ) Fig. 1. XRD patterns of the KGa2 kaolinite treated with NaOH T=90°C during (a) 24h (b)72h, (c)168h and (d) 264h
3.1.2 Metakaolinite KGa2_ 500 The XRD patterns of metakaolinites obtained by heating the kaolinite at 500°C show a broad featureless band corresponding to the metakaolinite. The observed reflection at 25° (2ș) corresponds to anatase phase (fig. 2a). Zeolite P was formed after 144 hours of treatment (Fig. 2b).
*
I(u.a)
* *
*
(b)
*
**
(a) 5
10
15
20
25
30
35
°2 θ (Cu-K α )
Fig. 2. XRD patterns of metakaolinite KGa2_500 treated with NaOH T=90°C during: 72h (a) and 144h (b) *characteristic line of zeolite P ** Anatase phase
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3.1.3 Metakaolinte KGa2_ 900 XRD patterns of the heated kaolinite at 900°C and treated with NaOH solution during 3h indicate formation of zeolite A [6] (Fig. 3a). By increasing the reaction time of treatment zeolite A lose its XRD intensities and after 72h zeolite P was formed. This study clearly demonstrates the effect of the reaction time on the final zeolite type [6].
Fig. 3. XRD patterns of metakaolinite MK_900 treated with NaOH, T=90°C during: 3h(a), 4h(b), 72h(c) and 144h(d)
3.2 29Si and 27Al MAS NMR analysis NMR spectrum of 29Si (Fig. 4) displays five chemical shifts characteristic of zeolite P situated between -107.36 to 87.49 ppm [3,11].
Fig. 4. 29Si MAS NMR spectrum of zeolite P 27
Al MAS-RMN spectrum (fig. 5) shows one chemical shift at around 57.69 ppm corresponding to zeolite P [3, 11].
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Fig. 5. 27Al MAS NMR spectrum of zeolite P
Results of structural studies and treatments are summarized in table1 Table 1. XRD identification of products during treatments
sample
NaOH solution temp °C
Heating temp °C
Time reaction /h
XRD analysis
NMR spectroscopy Si/Al ratio
Kaolinite KGa2
90
*
264
Zeolites P
§1
KGa2_500
90
500
72h
Amourphous complexe
*
144
Zeolites P
§1
KGa2_900
90
900 72
Zeolites P
§1
4. Conclusion Using specific hydrothermal treatments, zeolite P has been synthesized using a poorly crystallized kaolinite and metakaolinites derived from the heated kaolinite at 500°C and 900°C for 3 hours. Our results indicate that: The untreated kaolinite reacts with NaOH to form zeolite P after 264 hours The metakaolinites MK_500 and MK_900 react differently with NaOH (*) using MK_500, zeolite P was synthesized after 72h reaction. (**) when MK_900 is used as the starting material, the sample reacts with NaOH to form zeolite A after 3 hours reaction. The extra time of treatment leads to form zeolite P.
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