REDUKSI PENGGUNAAN SENYAWA PENGARAH STRUKTUR MENUJU SINTESIS ZEOLITE SOCONY MOBIL–5 (ZSM-5) BERPORI HIRARKI BEBAS SENYAWA ORGANIK

• Main Author: Rilyanti, Mita
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/32821
• Institution: Institut Teknologi Bandung

Hierarchical ZSM-5 zeolites are MFI-structured zeolite that have additional mesopores (meso-scale). Hierarchical ZSM-5 zeolites are widely used as catalysts, especially for bulky molecules. These zeolites also give chance for the reactants to move faster, so that it will provide better catalytic activity as compared to the conventional zeolites that only have microporous system (pore size <2 nm). Generally, the synthesis of hierarchical porous MFI zeolites uses organic compounds such as structure directing agent (SDA) and surfactant. However, these compounds are rare and expensive in the market. Morever, in the final synthesis procedure, in order to remove the organic compounds to allow formation of pores in zeolite, calcination has to done, where it will contribute to environmental pollution. Consequently, alternative synthesis methods that are more efficient, effective and environment friendly are needed. The purpose of this research is to produce hierarchical zeolite materials with high crystallinity by steam-assisted crystallization (SAC) method with and without additional of organic compound (SDA and surfactant). ZSM-5 zeolites have been synthesized using SAC with molar composition of 1SiO2: 0.13NaOH:0.025Al2O3:0.24TPA:37.5H2O. All the samples were prepared in a two-steps procedure. In the first step, a homogeneous synthesis solution was prepared from the raw materials. The precursor solutions were evaporated at room temperature in the course of 6 h and at 100 °C for 4-5 h in order to obtain an amorphous dry gel. The second step involved putting 0.3 g of the amorphous dry gel in a teflon support and into a teflon-lined stainless steel autoclave. Then, 5 cm3 of water was added into the bottom of the autoclave. The reaction was carried out for several days under static conditions in a convection oven preheated at 150 °C. The final materials obtained were normally in the monolithic form after washing with distillated water and drying at 60 °C. The as-synthesis zeolites were characterized by X-ray powder diffraction (XRD) for crystallinity, nitrogen physisorption for pore distribution and scanning electron microscopy (SEM) for morphology studies. The hierarchical porous ZSM-5 that was synthesized by SAC method at 150 °C for 5 days using low concentration of SDA gel that was dried at 100 °C. By comparison with the conventional hydrothermal method (HT), SAC method proved to be a more effective method to synthesize ZSM-5 zeolite by using low concentration of SDA. The synthesis of hierarchical zeolite materials without the addition of organic compound (SDA-free) has also been carried out using seeding-steam-assisted crystallization method. Precursor gel with the molar composition of 1SiO2:0.025Al2O3:0.13NaOH:37.5H2O crystallized very well with 1 % (w/w) seed (ZSM-5 or silicalite-1) added. The as-synthesis ZSM-5 zeolite has mesoporosity with pore diameter of about 2-3 nm. The formation of ZSM-5 in the precursor gel without organic compound using seeding-SAC method occurred through several steps. The starting step was seed crystallite dissolution. Aluminosilicate amorph that was formed due to seed crystal dissolution can undergo nucleation (secondary amorph). Seed residues and the seeds were formed by secondary amorph nucleation which were crystallized by the nutrients in the gel precursor. Nucleation will produce small crystals (nano-crystal). During the hydrothermal process by the SAC method, nanocrystal aggregated to generate large zeolite particles. This aggregation creates the observed mesoporosity from interparticle voids.