ENVIRONMENTALLY-FRIENDLY SYNTHESIS OF ZSM-5 ZEOLITE FROM RICE HUSK ASH IN THE ABSENCE OF SOLVENT AND OSDA

• Main Author: Juli Azhari, Noerma
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/51977
• Institution: Institut Teknologi Bandung

ZSM-5, an MFI (Mordenite Framework Inverted) type of zeolite, is widely used as a heterogeneous catalyst in industrial applications such as cracking, isomerization, alkylation, acylation, etc. Generally, it was synthesized by hydrothermal method from a mixture of alumina-silica precursor in alkaline media in the presence of water as solvent and OSDA (Organic Structure Directing Agent) i.e. organic compound containing TPA+ (tetrapropylammonium) ions. However, this method is low efficient process both economically and environmentally due to the high cost of OSDA, low yields, the emergence of autogenous pressure from the solvent, high energy consumption, as well as producing liquid waste and gases that are harmful to the environment. In this research, zeolite was synthesized using an environmentally-friendly and sustainable method. Rice husk ash was used as a silica source to synthesize zeolite in solvent-free and OSDA-free conditions. The silica was extracted through an acid-base treatment. Then, the seeds are added to the initial precursor mixture to accelerate the crystallization process. Zeolite crystallization was carried out at three different temperatures, i.e., 160 ?????, 180 ?????, and 200 ?????. Furthermore, the kinetic parameters and the activation energy for each crystallization stage were determined using the Avrami and Arrhenius equation. In this study, the crystallization at 180 ?C was used as a model for studying the transformation of structure and morphology during the synthesis process through characterization technique, i.e. XRD, FTIR, and SEM. The results showed the pure crystalline phase of zeolite ZSM-5 could be obtained in a relatively short time (10 hours at T = 180 ?C) and produced a yield > 95%. The prolongation of the synthesis period > 10 h causes the transformation of the ZSM-5 phase into mordenite and quartz phases. The zeolite product has a cube morphology with a size of ca. 500 nm. It is much smaller than the seed used, which indicates the formation of new crystals through secondary nucleation mechanisms. At all temperatures, zeolite crystallization followed the sigmoid curve pattern. The flat line at the beginning of the synthesis period represents the induction stage. When the nuclei formed is stable enough in the induction period (t0), the curve begins to rise, indicating the start of the transition period (ttr). At this stage, the crystallization process occurs very slowly. The crystal growth period (tc) was observed by the acceleration of the crystallization rate. It was represented by the slope change in the crystallization curve. Based on the results of curve fitting using Avrami's non-linear equation, the zeolite crystallization speed increases with increasing synthesis temperature. It was indicated by the shorter time parameters and the higher reaction constant (k) and reaction rate (v) values for each crystallization stage for higher temperatures. Furthermore, the Avrami constant (n) ~ 3 indicates the occurrence of 3-dimensional crystal growth through the instant nucleation pathway. Based on the result, it was found that the nucleation stage is the rate-determining step in the zeolite crystallization process with the value of the activation energy for the induction, transition, and crystal growth stages, respectively, En1 = 136.87 kJ/mol, En2 = 50.74 kJ/mol and Ec = 50.61 kJ/mol. Based on the results described above, this study provides a model for a better understanding of solvent-free and OSDA-free zeolite synthesis. Besides, this research also gives an extensive insight into realizing a sustainable and environmentally-friendly synthesis of zeolite