SYNTHESIS AND CHARACTERIZATION OF ZEOLITES FROM SODIUM ALUMINOSILICATE SOLUTION by SITI AIDA BINTI IBRAHIM Thesis submitted in fulfillment of the requirements for the degree of Master of Science August 2007 ACKNOWLEDGEMENTS Thank you to Allah for His Blessing and giving me an ability and strength to complete this thesis. Firstly, I would like to express my deepest gratitude to my supervisor Dr. Norlia Baharun for her expert guidance, constant attention, valuable suggestions, enthusiastic support and personal concern during the research and through the course of my study.
Her fruitful ideas throughout the research project has helped me accomplished this work successfully. Special thanks to the Dean of School of Material and Mineral Resources Engineering, Associate Professor Dr. Khairun Azizi Azizli for her permission to let me use all the brilliant facilities and equipment in completing my project. Under her leadership, she has created a healthy learning environment in the school. I would also like to extend my sincere appreciation for all the lecturers in the school especially to Associate Professor Dr. Azizan Aziz for his support and guidance throughout my study.
I would like to thank the technical staffs of School of Materials and Mineral Resources Engineering, especially to Mdm. Fong Lee Lee, Mr. Shaarani, Miss Mahani and Mr. Hasnor for their various contributions in one way or another. To my dear friends, Nurul’Ain, Norwanis, Roshazita , Faizul, Shahrizam, Suhaina, Dr. Hasmaliza, Dr. Zuhailawati and all close members of postgraduate room of School of Materials and Mineral Resources Engineering, thank you for making my life in USM so colorful and enjoyable. The memory of our friendship will forever stay inside my heart. ii
Last, but not least to my family especially to my ever-loving mother whom are always on my side, Hajjah Rinah Binti Mohd. Jirin, Thank you for the support and the encouragement you gave me to pursue my dreams. Not to forget, my family members who always be there for me through my thick and thin. May ALLAH bless all of us and only HE, the Almighty could repay all my debts to all of you. Wassalamu’alaikum warahmatullah wabarakatuh. iii TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ii TABLE OF CONTENTS iv LIST OF TABLES vii LIST OF FIGURES ix LIST OF PLATES xi LIST OF SYMBOLS xii LIST OF ABBREVIATION xiii LIST OF APPENDICES xiv
LIST OF PUBLICATIONS & SEMINARS xiv ABSTRAK iv xvii ABSTRACT CHAPTER ONE : INTRODUCTION 1. 1 Background 1 1. 2 The importance of research 4 1. 3 The objectives of the research 5 1. 4 Scope of the research 6 CHAPTER TWO : LITERATURE REVIEW 2. 1 Introduction 8 2. 2 Structure 9 2. 3 Properties 15 2. 4 Natural Occurrence of Zeolite 17 2. 5 Synthesis of Zeolite 19 2. 6 Application 23 2. 6. 1 Zeolite in Adsorption and Separation 23 2. 6. 2 Zeolite in Ion Exchange 25 2. 6. 3 Zeolite in Catalysis 31 2. 6. 4 Other Application 33 2. 7 Comparison Between Natural and Synthetic Zeolite 34 2. 8 Sol-Gel Processing on Hydrothermal Condition 8 2. 8. 1 General Description 38 iv 2. 8. 2 Application to Zeolite Synthesis 42 2. 8. 3 Factors Affecting The Zeolite Synthesis 46 CHAPTER THREE : MATERIALS AND EXPERIMENTAL WORK 3. 1 56 3. 1. 3 Anhydrous sodium aluminate 57 Sample Preparation and Experimental Procedure 57 3. 2. 1 Solution Preparation and Composition 58 3. 2. 2 Sequence of Mixing Order 61 3. 2. 3 Hydrothermal Treatment 61 3. 2. 4 Filtration, Washing and Drying 63 Characterization of The Synthesized Zeolite 64 3. 3. 1 X-Ray Diffraction (XRD) 64 3. 3. 2 Particle Size Analyzer 65 3. 3. 3 Determination of Specific Surface Area (BET) 65 . 3. 4 Fourier Transformed Infra Red (FT-IR) Spectroscopy 66 3. 3. 5 Pycnometer Density 67 3. 3. 6 Scanning Electron Microscopy (SEM) 68 3. 3. 7 Transmission Electron Microscopy (TEM) 68 Application 69 3. 4. 1 Cation Exchange Capacity Analysis (CEC) 3. 4 56 3. 1. 2 Sodium Hydroxide Pellet Anhydrous (NaOH) 3. 3 55 3. 1. 1 Fumed silica 3. 2 Reagent and Chemicals 69 CHAPTER FOUR : RESULTS AND DISCUSSIONS 4. 1 71 4. 1. 1. Gelation and Crystallization Time 4. 2 Zeolite Synthesis 74 Characterization 80 4. 2. 1. XRD analysis 80 4. 2. 1. 1. Phase identification 80 4. 2. 1. 2. Crystallite size 89 4. 2. 2.
Physico-chemical characteristic 90 4. 2. 2. 1. Particle size analysis 90 4. 2. 2. 2. Specific surface area 94 4. 2. 2. 3. FTIR studies 97 v 4. 2. 3. Morphological studies 103 4. 2. 3. 1. SEM analysis 4. 2. 3. 2. TEM analysis 4. 3 103 110 Application of synthetic aluminosilicate solution zeolite produced from sodium 4. 3. 1. Ammonium removal by ion exchange 112 112 CHAPTER FIVE : CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH 5. 1 Conclusion 114 5. 2 Recommendation for future work 116 REFERENCES 118 APPENDICES 126 Appendix A [Procedures for solution preparation] 127 Appendix B [Calculation of CEC values] 132
Appendix C [Experimental setup for CEC analysis] 135 Appendix D [References of XRD Pattern] 136 Appendix E [Publications and Seminars] 144 vi LIST OF TABLES Page 2. 1 Coordination of cation with oxygen in silicate structures 11 2. 2 Physico-chemical properties of zeolite and molecular sieves 16 2. 3 Physical properties of four types of zeolite 16 2. 4 Trends in the properties of zeolites as a function of the Si/Al ratio 17 2. 5 Genetic types of occurrence of zeolite 18 2. 6 Summary of principal proposals for zeolite synthesis mechanism, 1959-2004 22 2. 7 Application and advantages of zeolite as ion exchanger 27 2. 8
Application of zeolite in catalysis 32 2. 9 Health science and zeolite 34 2. 10 Comparison between natural and synthetic zeolite 35 2. 11 Synthetic counterparts of natural zeolites—Alkaline Metal 36 2. 12 Synthetic counterparts of natural zeolites—Alkaline Earths 36 2. 13 Synthetic counterparts of natural zeolites—Alkylammonium 37 2. 14 Natural zeolites with no synthetic counterpart 37 2. 15 The effect of SiO2/Al2O3 on physical properties of zeolite 47 3. 1 The specification of chemical reagent used in this research 55 3. 2 The properties of fumed silica (SiO2) 56 3. 3 The properties of anhydrous sodium hydroxide (NaOH) 56 . 4 Some properties of anhydrous sodium aluminate (NaAlO2) 57 3. 5 The composition and ratio of Si:Al:Alk used for sodium aluminosilicate solution preparation 58 3. 6 The sample identification and coding used for various reaction conditions in zeolite synthesis from aluminosilicate solution 59 3. 7 Reactor specification (Model Parr Mini Reactor, Series 4563), (Parr Operating Instruction, USA) 62 vii 4. 1 Framework densities of zeolite products 81 4. 2 Phase identification of zeolite produced through Method A 86 4. 3 Phase identification of zeolite produced through Method B. 87 4. 4 Results of particle size distribution 1 4. 5 Summarization of IR spectra for synthetic zeolite powders (Method A and B) 98 4. 6 The assigned of zeolite lattice vibration (internal tetrahedra) observed for synthesized zeolites. (Method A) 99 4. 7 The assigned of zeolite lattice vibration (external linkages) observed for synthesized zeolites (Method A) 99 4. 8 The assignment of zeolite lattice vibration (internal tetrahedra) observed for synthesized zeolites (Method B) 102 4. 9 The assignment of zeolite lattice vibration (external linkages) observed for synthesized zeolites (Method B) 102 4. 10 The relationship between crystal size and Si/Al Ratio 07 4. 11 Pore size of zeolite produced with Si/Al ratio of 1 111 4. 12 Pore size of zeolite produced with Si/Al ratio of 2 111 4. 13 The results of cation exchange capacity value (CEC) for synthetic zeolite against ammonium 113 viii LIST OF FIGURES Page 2. 1 Basic structure of zeolite frameworks 10 2. 2 Basic structure of zeolite frameworks 10 2. 3 (a) Distinct gap between zeolite type and dense tetrahedral framework structure. (b) Correlation between pore size of molecular sieves and the diameter (? ) of various molecules. 12 2. 4 Development of zeolite structures 14 2. 5 Three different zeolites 15 . 6 Zoning patterns of zeolites and feldspars in tuffs of saline, alkaline lakes; and deep sediments 18 2. 7 Zoning patterns of zeolites and feldspars in tuffs where zonation is (a) of open system type; (b) hydrothermal; and (c) a result of the burial diagenesis 19 2. 8 Hydrothermal zeolite synthesis. 21 2. 9 (a) A schematic illustration in agricultural industry without using zeolite (b) A schematic illustration in agricultural industry with using zeolite 29 2. 10 Simplified chart of sol-gel processes 39 2. 11 Fractal polymer made by branching of polyfunctional monomer with functionality >2 39 2. 12
Polymerization behaviour of aqueous silica. A = in presence of salts / acidic medium, B = alkaline medium 41 2. 13 Colloidal particles formed by condensing monomers to form closed rings 41 2. 14 SEM showing Ostwald ripening. The arrowheads indicated the smaller particles precipitated on the larger particles. 42 2. 15 Rate of nucleation as a function of degree of undercooling and hence also of viscosity 44 ix 13 30 2. 16 Conceptual diagram of nucleation and crystallization of zeolite A 44 2. 17 Elimination of a high index surface (a) by straightforward more rapid growth of the high index than the neighbouring lower ndex faces; and (b) by step formation. 45 3. 1 Schematic diagram showing the synthesis route of zeolite via sol gel using the hydrothermal treatment 54 3. 2 The schematic diagram showing the filtration process of gel crystal 63 4. 1 A schematic diagram representing zeolite crystallization process 73 4. 2 Gelation time observed for sodium aluminosilicate solution prepared through the Method A and B 75 4. 3 Gelation time of sodium aluminosilicates prepared through the Method A 77 4. 4 (i) Schematic illustration of the solution-mediated transport mechanism (ii) Schematic illustration of the solid-phase transformation mechanism 8 4. 5 The dependence of crystallization time in the synthesis of zeolite at room temperature 80 4. 6 The diffractograms for Na-aluminosilicates zeolites prepared at T= 80°C with Si/Al ratio of (a) 1; (b) 3 ; (c) 5 and (d) 7 respectively 82 4. 7 The diffractograms for Na-aluminosilicates zeolites prepared at T= 80°C with Si/Al ratio of (a) 1; (b) 3 ; (c) 5 and (d) 7 respectively 84 4. 8 Comparison of synthetic zeolite from varying Si concentration using Method A 87 4. 9 Comparison of synthetic zeolite from varying Si concentration using Method B. 87 4. 10 Comparison of XRD phases by the effect of mixing order etween Method A and B for zeolite batch AID1 and AID2 88 4. 11 Comparison of XRD phases by the effect of mixing order between Method A and B for zeolite batch AID3 and AID4 88 4. 12 Crystallite size of zeolite produced at T= 80°C with varying Si concentration 90 x 79 4. 13 Particle size distribution of AID1 92 4. 14 Particle size distribution of AID3 92 4. 15 Particle size distribution of AID5 93 4. 16 Particle size distribution of AID7 93 4. 17 Specific surface area of synthetic zeolite by Method A 94 4. 18 Specific surface area of synthetic zeolite by Method B 95 4. 19
Comparison of specific surface area using Method A and Method B of synthetic zeolite 96 4. 20 IR results from KBr supported samples for AID1A, AID3A, AID5A and AID7A zeolite powders (Method A). 98 4. 21 IR results from KBr supported samples for AID1B, AID3B, AID5B and AID7B zeolite powders (Method B) 101 4. 22 Scanning electron photomicrographs of zeolite synthesized at room temperature with varying Si/Al ratio of (a) 1; (b) 3 and (c) 5 respectively 104 4. 23 Scanning electron photomicrographs of zeolite product at 80°C with varying Si/Al ratio of (a) 4; (b) 5 ; (c) 6 and (d) 8, respectively. 106 4. 24
Scanning electron photomicrographs of zeolite product at 80°C with Si/Al ratio of 5 (Method A and Method B) 108 4. 25 (a) Scanning electron photomicrographs of zeolite product at T=80°C with Si/Al ratio 1 in unstirred condition (b) Scanning electron photomicrographs of zeolite product at T=80°C with Si/Al ratio 1 in stirred condition 109 4. 26 TEM photomicrograph of mesoporous zeolite obtained with Si/Al ratio of 1 110 4. 27 TEM photomicrograph of mesoporous zeolite obtained with Si/Al ratio of 2 111 109 LIST OF PLATES Page 3. 1 Hydrothermal Equipment 62 C-1 Equipment setup for CEC analysis 135 xi LIST OF SYMBOLS °C Celcius
A Angstron (1 x 10-10) nm nanometer (1 x 10-9) µm micrometer (1 x 10-6) cm Centimeter (1 x 10-2) cm 3 Centimeter cube mg milligram gram /liter g/l g/cm 3 gram/centimeter cube M molar meq/100g Milliequivalents/100gram xii LIST OF ABBREVIATION NaOH Sodium Hydroxide SiO2 Fumed Silica NaAlO2 Sodium Aluminate Anhydrous HCl Hydrochloric Acid H3BO3 Boric Acid MgO Magnesium Oxide Na2CO3 Sodium Carbonate Anhydrous H3BO3 Boric Acid CH3COONH4 Ammonium acetate CH3OH Methyl Alcohol N2 OFN gas (oxygen free nitrogen) C21H14Br4O5S Bromocresol green indicator KBr Potassium Bromate XRD X-ray Diffraction SEM Scanning Electron Microscope
TEM Transmission Electron Microscope BET Brunauer, Emett and Teller CEC Cation Exchange Capacity FTIR Fourier Transform Infrared Spectrophotometer VPT Vapor Phase Transport PSD Particle size distribution FAU Faujasite SOD Sodalite GIS Gismondine LTA Lynde Type A xiii LIST OF APPENDICES Page 1. 1 Appendix A: Procedures for solution preparation 127 1. 2 Appendix B: Calculation of CEC values 132 1. 3 Appendix C: Experimental setup for CEC analysis 135 1. 4 Appendix D: References of XRD Pattern 136 1. 5 Appendix E: Publications and Seminars 144 LIST OF PUBLICATIONS Page 1. 1 Synthesis and Characterization of Zeolite From
Na-Aluminosilicate Solutions and Gels 144 1. 2 Room Temperature Synthesis of Mesoporous Zeolite 150 1. 3 Mesoporous Aluminosilicate Synthesis Via Sol-Gel Technique 157 xiv SINTESIS DAN PENCIRIAN ZEOLIT DARIPADA LARUTAN NATRIUM ALUMINOSILIKAT ABSTRAK Rangkaian siri sintetik zeolit telah berjaya disintesiskan daripada larutan natrium aluminosilikat dengan kepekatan Si dari 1 hingga 8 molar menggunakan habuk halus silika (fumed silica) dan natrium aluminat. Kesan daripada tertib percampuran sumber sintesis dan penggunaan pelbagai kepekatan Si terhadap penjelan, penghabluran, fasa, ciri kimia-fizikal dan morfologi yang terhasil dilaporkan. aripada Data pemantauan in-situ perlakuan gel natrium aluminosilikat dan masa penghabluran yang terhasil pada suhu bilik turut dilaporkan dalam kajian ini. Keputusan XRD menunjukkan kehadiran fasa zeolit dengan kerangka kerja sama seperti FAU, LTA, SOD, dan GIS dalam sintetik zeolit yang disintesiskan dengan saiz kristalit dianggarkan antara 3 hingga 20nm. Ciri-ciri kimia-fizikal sintetik zeolit pula diperolehi daripada analisis saiz partikel Malvern, BET dan FTIR. Daripada analisis Malvern, purata saiz partikel (d50) adalah dari 12 hingga 95 mikron manakala analisis BET memberikan luas permukaan sintetik zeolit yang tertinggi pada 9. 4m2/g. Spektra FTIR pula membuktikan kehadiran getaran dalaman merujuk kepada Si-O-(Si) dan Si-O(Al) dalam struktur tetrahedranya pada julat getaran 1200-400cm-1, manakala kehadiran air dalam zeolit ditunjukkan dalam julat getaran 1600-3700cm-1. Spektra FTIR juga menunjukkan wujudnya getaran kekisi-pseudo (pseudo-lattice) dalam struktur unit sintetik zeolite iaitu pada julat 500-700cm-1. Kajian morfologi permukaan daripada fotomigrograf SEM menunjukkan serbuk sintetik zeolit yang terhasil mempunyai struktur berbentuk lamela dangan pinggir sisinya berbentuk kubik. Saiz kristal pula dianggarkan berada antara 1 hingga 12 mikron.
TEM fotomikrograf menunjukkan kehadiran liang-liang halus dengan anggaran saiz liang adalah 13 hingga xv 23nm (lebar) dan 18 hingga 43nm (panjang). Akhir sekali, nilai CEC tertinggi yang diperolehi bagi zeolit yang disintesiskan adalah pada 66. 3meq/100g dan nilai yang paling rendah pula pada 7. 65meq/100g dengan masa kontak selama 12 jam. xvi SYNTHESIS AND CHARACTERIZATION OF ZEOLITES FROM SODIUM ALUMINOSILICATE SOLUTION ABSTRACT A series of synthetic zeolites were successfully synthesized from sodium aluminosilicate solutions with varying Si concentration from 1 to 8 molar using fumed silica and sodium aluminate.
The order of mixing and the effect of varying amount of Si in the sodium aluminosilicate solution towards gelation, crystallization, phases, physico-chemical characteristics and surface morphology were studied. xvii Data concerning the in-situ monitoring of sodium aluminosilicate gelation behavior and the crystallization time at room temperature are reported. XRD results showed that the phases of zeolites synthesized are similar to FAU, LTA, SOD and GIS framework. The crystallite size was found to vary from 3 to nearly 20 nm. The physico-chemical haracteristics of the product were obtained from Malvern particle size analyzer, BET and FTIR. From Malvern analysis, it was found that the average particle sizes (d50) of synthetic zeolites were varied from 12 micron to 95 micron while the highest surface area values obtained from BET was about 9. 84 m2/g. Meanwhile, FTIR spectra exhibited the presence of internal Si-O-(Si) and Si-O-(Al) vibrations in the tetrahedra or alumino- and silico-oxygen bridge in the range of 1200 – 400 cm-1, while the presence of zeolite water in the range of 1600- 3700 cm-1 and the pseudo-lattice vibrations of structural unit in the range of 500-700 cm-1.
Surface morphological studies obtained from SEM photomicrographs showed the powdered synthetic zeolite have a lamellar structure with cubical edge and the crystal size was estimated to be 1 to 1. 2 micron. TEM photomicrographs showed the presence of pores with the pore sizes estimation at 13-23 nm (width) and 18-43 nm (length). Finally, the highest CEC value of the synthesized zeolites against ammonium was obtained at 66. 3 meq/100g meanwhile the lowest was at 7. 65 meq/100g at optimum contact of 12 hours. xviii CHAPTER 1
INTRODUCTION 1. 1 Background Malaysia is now at the mid point of its journey towards becoming a developed country by 2020. Since the global environment is changing, the Prime Minister, Datuk Seri Abdullah Ahmad Badawi has announced that the nation needs to improve and upgrade the country’s domestic condition (Ninth Malaysia Plan, 2006). The National Mission is presented by the government as a policy and implementation framework that outlines the country’s priorities for the next 15 years along with the Ninth Malaysia Plan.
One of the objectives in the National Mission is to move the economy up to the value chain. It is noted that to be successful in the increasingly competitive global market, Malaysia must move out from its “middle development” stage towards human capital driven economy. This can be achieved by several step listed in the National Vision which one of it is to increase the productivity, competitiveness and value add of the established activities in agriculture, manufacturing and service sector.
Even though it is necessary for the nation to move up the economy value chain, the needs to balance between the development needs and the environment must be maintained. This can be achieved by better management in environment stewardship since a better quality environment will contribute towards improving the quality of life. During the Eight Plan Period, the government have emphasized on improving environmental quality through better management particularly in air and water quality, solid waste management as well as the utilization of cleaner technologies.
Nowadays, through the advancement of modern science and technology, zeolites can contribute to a cleaner, safer environment in a great numbers of ways (Bell, 2001). In powder 1 detergents, zeolites have replaced the harmful phosphate builder, which have been banned in many countries due to the water pollution risks. In petroleum and hydrocarbon industry, the chemical process can be more efficient with zeolite acting as the catalyst, thus saving the energy and indirectly reduced the pollution. The processes can be carried out in a fewer step and minimizing unnecessary waste and by-products.
Furthermore, zeolite can also act as solid acids which could reduce the need for corrosive liquid acids and as redox catalyst and sorbents where they can remove atmospheric pollutants such as engine exhaust gases and ozone depleting CFCs (Monticelli et al. , 1999 and Chatterjee et al. , 2003). Zeolite can also be used to separate harmful organics from water (Wang et al. , 2006 and Park et al. , 2002) and removing heavy metal ions including those produced by nuclear fission from water (Nah et al. , 2006 and Ursini et al. 2006). Zeolites are hydrated aluminosilicates of the alkaline and alkaline-earth metals with fully cross-linked open framework structures made up of corner sharing SiO4 and AlO4 tetrahedra. There are about 40 natural zeolites which have been identified during the past 200 years and more than 150 zeolites have been synthesized. The most common of natural zeolite are analcime, chabazite, clinoptilolite, erionite, mordenite and phillipsite while as for synthetic zeolites; the most common are zeolites A, X, Y and ZSM-5.
Both natural and synthetic zeolites are used commercially because of their unique adsorption, ion-exchange, molecular sieve and catalytic properties. The naturally occurred zeolite is formed as a result of the chemical reaction between volcanic glass and saline water. The temperatures favoring the natural reaction are ranges between 27°C to 55°C with pH between 9 and 10. However, nature requires 50 to 50,000 years to complete the reaction with rarely phase-pure state of zeolite. This type of zeolites are contaminated to varying degrees by other minerals such as Fe2+, quartz, SO4-, other zeolites and amorphous glass. Synthetic zeolites on the other hand, hold some advantages over their natural analogs. The synthetics can, of course, be manufactured in a uniform phase-pure state. It is also possible to manufacture desirable structure which does not appear in nature such as zeolite A. Since the principal raw materials used to manufacture zeolite are silica and alumina, which are among the abundant mineral components on earth, the potential to supply zeolite is virtually unlimited. Finally, zeolites manufacturing rocesses engineered by humankind require significantly less time than 50 to 50,000 years as prescribed by nature. In year 1974, Breck, have declared that rarely in our technology society does the discovery of a new class of inorganic materials results in such wide scientific interest and kaleidoscopic development of applications as what happened with the zeolite molecular sieve. The declaration was 30 years ago after the commercial introduction of synthetic zeolites. During that time, the number of areas utilizing zeolites had grown phenomenally.
Since then, the variety of applications and zeolites types available has continued to increase. As zeolites are already well established in such environmentally driven applications, therefore, it is used as phosphate-free ion exchangers for detergent water softening and as the production of lead-free octane enhancer for gasoline. Not only that, zeolite is also well-known used as ammonia and ammonium removal in water, and other heavy metal removal in wastewater since it has a capability as ion exchanger. Today, zeolites are being considered for a variety of important environmental services.
To put the potential zeolites into perspective, this research work looks at the properties of zeolites and how the material is synthesized. 3 1. 2 Importance of Research A considerable research and development effort is being made to produce a tailor made zeolite synthesis. This is because natural zeolites are rarely in phasepure zeolite and contaminated to varying degrees of other minerals such as quartz, SO4- and amorphous glass. Thus, for this reason, natural zeolites are excluded from many important commercial applications where uniformity and purity are essential.
On the other hand, synthetic zeolite could be manufactured in a uniform phase-pure state. Furthermore, it is also possible to engineer a desirable structure zeolite which does not appear in nature such as Zeolite A and ZSM-5. By better understanding on the mechanism responsible for its formation from its precursor, a tailor made zeolite synthesis could be manufactured. It is necessary to know the mechanism process since a desirable structure zeolite can be engineered due to its application. The changes made in synthesis process can affect the tructure and type of zeolite produced. As an example, the varying degrees of Si concentration and the source of Si used can produce a different type of zeolite. Therefore, it is necessary to have a vast knowledge on its fundamental process because a specific tailor made zeolite is depended on its application whether used as ion exchanger for water and wastewater treatment or as catalyst used in hydrocarbon industry. The type of cation present not only influences the ion-exchange properties of zeolite, but also is a factor in its adsorptive and catalytic properties.
High purity synthetic zeolites exhibit uniform pore sizes that can be further tailored to specific molecular dimensions by changing the nature of the cation after synthesis. For example, the greatest volume use for zeolite is due to their ion exchange properties. As we know, hard water causes poor performance in laundry 4 detergents. Zeolite A with Na+ cations is widely used in laundry detergent as a replacement for environmentally undesirable phosphates as detergent water softener. Another example is the used of zeolite in the removal of ammonium in water and wastewater.
Therefore, the production of zeolite from sodium aluminosilicate can contribute to a cleaner environment where the stewardship towards waste management is maintained since the applicability of the zeolite acting as ion exchanger (for the removal of an ammonium and other heavy metal in water or wastewater) is widely known. 1. 3 Objective of the research The aim of this research was to study the structure and properties of zeolite synthesized from aluminosilicate solutions and gels. To achieve this, a study was carried out with the following objectives: . To synthesize zeolites from sodium aluminosilicate solution via hydrothermal sol gel process. ii. To study the effect of varying Si concentration and the sequence of mixing order in the solution towards the development of zeolite crystallization. iii. To examine the characteristic of the synthetic zeolite produced (i. e. morphology, physico-chemical and phases identification) via SEM, TEM, FTIR , XRD and others iv. To evaluate the potential of the produced synthetic zeolite on its capacity as an ion exchanger. 5 1. 4
Scope of the research Due to the industrial important of zeolite, much effort is made to unravel the mechanism responsible for its formation from its precursors. The art of creating zeolite synthesis has become a scientific interest because the process can be engineered to produce a tailor made synthesized zeolite. In zeolite synthesis, the needs to imitate the natural geological process are necessary. However, it is not possible since zeolite formation took thousands of years while commercially, zeolite must be produced in hours or days.
Therefore, the scientist must replicate the best condition of zeolite synthesis to achieve the desirable zeolite with certain properties within a shorter time. The use of hydrothermal process in zeolite synthesis is one of the major interest techniques adopted by the scientist. This is mainly due to the lower production costs and convenience for approach. The major aim of the work presented in this thesis is to investigate the synthesis of zeolites from sodium aluminosilicate solution.
The synthesis was carried out by solgel process and under the confined hydrothermal condition at a temperature of 80°C for two weeks. In this study, the sodium aluminosilicate solution was prepared using silicate solution (at varying amount of Si), aluminate solutions (amount of Al remains constant) and sodium hydroxide (NaOH) solution. The presence of NaOH was to create a caustic environment for the synthesis process. The solid is separated by filtration, washed several times with distilled water and then dried overnight at 50° – 60° C to a constant weight.
At the end of the process, the solid product was recovered for further characterization and analysis. In this study, the investigation on the effect of varying Si concentration (1 to 8 molar) and the sequence of mixing order in the zeolite produced has been carried out. The gelation and the crystallization time of zeolite are measured to study the influence 6 of Si/Al ratio and the sequence of mixing order. Studies on the surface morphology of the zeolite produced are carried out via SEM and TEM while the identification of mineral phases are carried out by using XRD.
The physico-chemical properties of synthetic zeolite such as the specific surface area, density, particle size and lattice vibration are obtained with BET, Particle Size Analyzer (Malvern) and FTIR respectively. The cation exchange capacity (CEC) value was also determined using standard procedures. Details explanation of these experimental procedures was discussed in Chapter 3. This research was conducted according to the method that had been used by Harvey and Glasser (1989).
Some modifications have been made for the synthesis conditions where by different ratios of Si/Al, the type of inorganic cation and the amount of alkali concentration (NaOH) were used. A study on the CEC values has also been done to evaluate the potential of synthesized zeolite for ammonium removal. 7 CHAPTER 2 Literature Review 2. 1 Introduction Zeolite are crystalline aluminosilicates containing pores and channels of molecular dimensions that are widely used in industry as ion exchange resins, molecular sieves, sorbents and catalysts.
Generally they contain silicon, aluminium and oxygen in their framework and cations, water and/or other molecules within their pores. Many occur naturally as minerals, and are extensively mined in many parts of the world. Others are synthetic, and are made commercially for specific uses, or produced by research scientist trying to understand their chemistry. The zeolite history began with the discovery of stilbite by Cronstedt, a Swedish mineralogist in year 1756. Upon heating the zeolite released occluded water, which gave the materials their general name, zeolite, after the Greek words, “??? ” (zeo) , to boil, and “??? o? ” (lithos), stone. A representative empirical formula of a zeolite is M2/nO . Al2O3 . xSiO2. yH2O (2. 1) where M represents the exchangeable cation of valence n. M is generally a Group I or II ion, although other metal, non-metal and organic cations may also balance the negative charge created by the presence of Al in the structure. The framework may contain cages and channels of discrete size, which are normally occupied by water (Ghobarkar et al. , 1999). 8 There are about 40 natural zeolites that have been identified during the past 200 years.
The most common are analcime, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite, and phillipsite. There are also more than 150 zeolites that have been synthesized and the most common are zeolites A, X, Y, and ZMS-5. Natural and synthetic zeolites are used commercially because of their unique adsorption, ion-exchange, molecular sieve, and catalytic properties. 2. 2 Structure Zeolite structure contains two types of building units namely, primary and secondary. A primary building unit (PBU) is the simpler building compared to econdary one. This is because, in PBU, a tetrahedron of (TO4) of 4 oxygen ions surrounding a central ion of either Si4+ or Al3+. These PBU are linked together to form a three-dimensional framework and nearly all oxygen ions are shared by two tetrahedral. Zeolite framework is based on an extensive three dimensional network in which the polyhedral sites, usually tetrahedral, are linked by oxygen atoms. Different combinations of the same secondary building unit (SBU) may give numerous distinctive structural polyhedra formed from smaller ring units. The net egative charge on the framework is balanced by the presence of the cations in most cases Ca, Na or K, which are situated in cavities within it. The zeolite framework is almost structurally independent of the (Na, Ca, K) cations and as the latter do not fill all the cavities replacement of the type Ca-2 (Na, K) can also occur. Figures 2. 1 and 2. 2 show the basic structure of zeolite framework. The complexity of zeolites structure is due to the various ways in tetrahedral group which are linked by the common sharing of oxygen ions to form polynuclear complexes. As listed in Table 2. 1, a considerable variation in the chemical composition results from the substitution of cations. Due to this, they give rise to zeolite and zeolite like materials of a very wide diversity. Figure 2. 1. Basic structure of zeolite frameworks (Byrappa and Yoshimura, 2001) Figure 2. 2. Basic structure of zeolite frameworks (Byrappa and Yoshimura, 2001) 10 Table 2. 1. Coordination of cation with oxygen in silicate structures (Byrappa and Yoshimura, 2001) There are some simple criteria that are used to establish the zeolite frameworks.
The most important one is the framework density (FD), which means the number of T-atoms (temperature atoms) per 1000°A3. The distribution of these values for the porous and dense frameworks whose structures are well established is showed in Figure 2. 3(a) and (b). Thus, the FD is obviously related to the pore volume, but does not reflect the size of the openings and to some extent it depends on the composition for the structural and chemical reason. 11 Framework density (FD)/[T-atoms]/1000A3 Size of smallest ring Figure 2. 3. a) Framework density of selected zeolites in respect to normal tectosilicates (Ghobarkar et al. , 1999) 12 Figure 2. 3. (b) Pore sizes of zeolites and ALPOs (Van der Waal and Bekkum, 1998) Figure 2. 4 shows the development of zeolite structure as follows: the primary building (SiO4)4- tetrahedron (Figure 2. 4a) and the tetrahedral are connected through their corners of shared oxygen atoms to form a wide range of small secondary building as in Figure 2. 4b. In Figure 2. 4c, a wide range of polyhedra is formed due to the interconnection of the building units.
In turn, it is connect to form the extended frameworks of the various specific zeolite crystal structures. Figures 2. 4a-d shows the structure of zeolites, the corners of the polyhedra represent Si or Al atoms and the connecting lines represent the shared oxygen atoms. Individual structures may comprise only one basic unit or many of them such as mineral paulingite which contains five such polyhedra. 13 Figure 2. 4. Development of zeolite structures (Byrappa and Yoshimura, 2001) The same secondary building unit but with different combination may give numerous distinctive zeolite structures.
Figure 2. 5 shows an example of three different zeolites that have the same structural polyhedron (cubo-octaheron) but probably form from smaller ring units. In accordance with the IUPAC recommendations on the chemical nomenclature of zeolites and related materials, topologically distinct framework types are represented by a mnemonic code consisting of three capital letters. This is subjected to review and clearance by the IZA Structure Commission according to a decision of the IZA Council, where took place at 7th IZC in Tokyo in 1986 (Byrappa and Yoshimura, 2001).
Generally, these codes derived from the name of the type species for example FAU for faujasite or SOD for sodalite. These symbols describe all variants of a framework with a given topology, irrespective of composition, Si, and Al distribution, cell dimension and symmetry. 14 Figure 2. 5. Three different zeolites (Byrappa and Yoshimura, 2001) 2. 3 Properties Mineral species such as zeolite has unique properties which are dependent upon its crystal structures and thus the type of inner cavities such as the pores, their size and form.
Many of these properties are especially desirable for environmental protection, such as cation exchange capacity, adsorption properties, acid stability, ammonium capacity and wet attrition resistance. In Table 2. 2, we can see a microporous solid with a broad range of physico-chemical properties of zeolites and related materials, such as phosphate-based molecular sieves. Table 2. 3 briefly the description of each type of common zeolites properties. 15