Synthesis of Zeolites from Bolivian Raw Materials for Catalysis and Detergency Applications

Abstract: Zeolites are very useful in many technological applications such as catalysis, separation and purification of gases and solvents, ion-exchange, etc. The production of zeolites is nowadays carried out with a variety of reagents, such starting materials render large scale production of zeolites expensive. Hence alternative synthesis routes for zeolite production at a lower cost are currently under investigation. One of these routes involves the use of natural aluminosilicate raw materials which have many advantages such as their availability, low price, workability, etc. The aim of the present work was to provide routes to produce synthetic zeolites of industrial attractiveness derived from non-expensive Bolivian raw materials like clays and diatomites. In particular, the work was focused on the synthesis of intermediate- and low-silica zeolites: zeolite Y and zeolite A. The raw materials as well as intermediate materials and final zeolite products were characterized by scanning electron microscopy (SEM),X-ray diffraction (XRD), nitrogen gas adsorption, inductively coupled plasma mass spectrometry (ICP-SFMS), and UV-VIS spectroscopy.The first part of the study addressed the synthesis and characterization of intermediate silica zeolite Y from diatomite. Prior to synthesis, the diatomite was leached in sulfuric acid to remove impurities, but this step also resulted in dealumination. Therefore, aluminum sulfate was used as an extra source of aluminum. The raw materials were reacted hydrothermally at 373 K in aqueous medium with sodium hydroxide. Variations in parameters like the Na2O/SiO2 ratio and synthesis time were investigated. As a result, micro-sized crystals of zeolite Y were obtained. It was possible to achieve high zeolite yield at a Na2O/SiO2 ratio of 0.9, which produced zeolite Y with a SiO2/Al2O3 ratio of 3.9. Also, synthesis of almost pure zeolite Y with a SiO2/Al2O3 ratio of 5.3 in low yield at a Na2O/SiO2 ratio of 0.6 was achieved. In this respect, diatomite behaved similarly to colloidal silica in traditional syntheses, with both sources of silica having a high degree of polymerization. Zeolite Y with the latter SiO2/Al2O3 ratio might be useful for the production of ultra-stable zeolite Y for use as FCC catalyst. A similar acid leaching procedure, this time with hydrochloric acid, was used for dealumination of diatomite to increase the SiO2/Al2O3 ratio and to reduce the amount of iron in producing well-crystallized ZSM-5 from diatomite in combination with sodium hydroxide and n-butyl amine under appropriate synthesis conditions.The second part of this study dealt with the synthesis of low silica zeolite A from Bolivian montmorillonite-type clay. This clay did contain significant amounts of quartz. Hence, an alkali fusion treatment was applied to the clay by fusing the clay at high temperature with NaOH to make the material more reactive and to take advantage of all the silica present in the clay. The raw clay had a SiO2/Al2O3 ratio of 4, and sodium aluminate was added to the mixture to decrease this ratio to 2. An optimization of the synthesis time was performed. The final zeolite product exhibited high brightness despite the presence of iron in appreciable amount in the starting material and the final product. This was attributed to the magnesium in the raw material, which exerted a masking effect on iron. The latter was incorporated into extraneous magnesium aluminosilica compounds, thereby increasing brightness and strongly decreasing the overall yellowness. This simple method appears as a promising alternative to the complex and costly techniques suggested to reduce the iron content in natural raw materials, especially kaolin.To summarize, this work reports the synthesis of zeolites with promising characteristics from Bolivian raw materials. However, further optimization is required to qualify these products for industrial applications. Moreover, this study might help in the development of poor regions of the Bolivian Altiplano and open up for large scale production, since the methodsdeveloped in this work are simple and non-expensive and other impurities for synthesis of high silica ZSM-5 zeolite. This procedure was successful in producing well-crystallized ZSM-5 from diatomite in combination with sodium hydroxide and n-butyl amine under appropriate synthesis conditions.The second part of this study dealt with the synthesis of low silica zeolite A from Bolivian montmorillonite-type clay. This clay did contain significant amounts of quartz. Hence, an alkali fusion treatment was applied to the clay by fusing the clay at high temperature with NaOH to make the material more reactive and to take advantage of all the silica present in the clay. The raw clay had a SiO2/Al2O3 ratio of 4, and sodium aluminate was added to the mixture to decrease this ratio to 2. An optimization of the synthesis time was performed. The final zeolite product exhibited high brightness despite the presence of iron in appreciable amount in the starting material and the final product. This was attributed to the magnesium in the raw material, which exerted a masking effect on iron. The latter was incorporated into extraneous magnesium aluminosilica compounds, thereby increasing brightness and strongly decreasing the overall yellowness. This simple method appears as a promising alternative to the complex and costly techniques suggested to reduce the iron content in natural raw materials, especially kaolin. To summarize, this work reports the synthesis of zeolites with promising characteristics from Bolivian raw materials. However, further optimization is required to qualify these products for industrial applications. Moreover, this study might help in the development of poor regions of the Bolivian Altiplano and open up for large scale production, since the methods developed in this work are simple and non-expensive.