Hydrothermal Synthesis of High Crystalline Silicalite from Rice Husk Ash

Chaiwat Kongmanklang,Kunwadee Rangsriwatananon

doi:10.1155/2015/696513

Abstract

The objective of this research work was to evaluate the hydrothermal synthesis of silicalite with high crystallinity within a small particle size. The current study focused on investigating the effects of silica sources such as rice husk ash (RHA) and silica gel (SG), crystallization time, and ratios of NaOH/SiO2, H2O/NaOH, and SiO2/TPABr. The crystallinity, particle size, and morphology were characterized by FT-IR, XRD, particle size analyser, and SEM. The conclusion of the main findings indicated that the XRD patterns of these samples clearly showed a pure phase of MFI structure corresponding to FT-IR spectra with vibration mode at 550 and 1223 cm−1. The highest crystallinity was obtained at reaction time only 6 hours with the mole ratios of NaOH/SiO2, H2O/NaOH and SiO2/TPABr as 0.24, 155, and 30, respectively. When SG was used as a silica source, it was found that the particle size was smaller than that from RHA. The morphologies of all silicalite samples were coffin and cubic-like shape.

Highlights

Silicalite or high silica ZSM-5 is MFI structure
Silicalites are synthesized by the hydrothermal method from the gel compositions of silica, alkaline, and organic cation as a template
TEOS, fumed silica and colloidal silica are much more expensive compared to rice husk ash which is a potential silica source containing amorphous silica about 20% (w/w) [8] considered as a byproduct in form of an industrial waste abundance in agricultural countries

Summary

Introduction

Silicalite or high silica ZSM-5 is MFI structure. It contains two intersecting channel systems composed of 10-membered ring straight and sinusoidal channels with a unique pore structure dimension of 0.54–0.56 nm. TEOS, fumed silica and colloidal silica are much more expensive compared to rice husk ash which is a potential silica source containing amorphous silica about 20% (w/w) [8] considered as a byproduct in form of an industrial waste abundance in agricultural countries. Another benefit of silica from rice husk is that it is highly reactive silica which can be extracted to be highly purifying silica (about 98%) by digesting with dilute acid and burning at 700∘C for 4 hours [9]

Methods

Results

Conclusion