Optimization of Synthesis Procedure for Nanocrystalline MFI Zeolite Using Taguchi’s DOE Method

Zeolites are crystalline, microporous aluminosilicates with well-defined pores of molecular dimensions. In powder form they are used in a broad variety of applications such gas separation processes (molecular sieving), catalysis as well as adsorbents and ion exchangers with high capacities and selectivities. When zeolites are grown as films, they offer the potential for continuous separation of industrially important gas/vapor mixtures, and can be used as for applications in membrane reactors, as sensitive chemical sensors, and in electronic and thermoelectric applications.Among all the zeolites, medium pore-size ZSM-5 represents a continuing area of interest for processes involving petrochemicals and fluid catalytic cracking. This molecular sieve with MFI structure is synthesized from hydrogels containing precursors of silicon and aluminum at autogenous pressure and temperatures above 100°C.The efficiency of the zeolites as catalysts is related to their morphological and particular property (crystalline structure, high internal surface areas, uniform pores and good thermal stability) which leads to shape-selective catalysis for reactions occurring within the micropore system. According to the relevant role of surface area in the catalytic behavior, zeolites with small crystal size should be advantageous.The pathway of the crystallization process as well as the morphology and singular properties (crystal size and distribution) of MFI-type zeolites are influenced by different variables: the silicon and aluminum source [1], the aluminum content [2], the template/silicon ratio [3], the nature of cations present in the synthesis medium [1], the alkalinity [1], the temperature of crystallization [4], the presence of seeds [5], the water content [2].In this work, Nanocrystalline MFI has been synthesized by hydrothermal crystallization of clear synthesis mixtures at low temperature under atmospheric pressure. By taguchi design, the influence of crystallization temperature, aluminum content, template/silica mole ratio, water content and presence of alkaline cations on the properties of the final nanocrystalline zeolites have been studied