Synthesis and Characterizations of High Crystallized Clinoptilolite by Structure Directing Agent Method and its Crystallization Kinetics

Abstract

The clinoptilolites (CPs) with high purity were prepared via structure directing agent (SDA) method combining with hydrothermal method using silica sol as the silica source and aluminum hydroxide as the aluminum source. Their structural features were characterized by X-ray diffraction (XRD) patterns, Fourier transform infrared (FT-IR) spectra, thermal gravimetric (TG) analysis, scanning electron micrograph (SEM) images, 29 Si nuclear magnetic resonance (NMR) profiles. The effects of additive amount and aging time of used SDA, as well as synthetic parameters such as crystallization temperature and crystallization time on their structure and performance were emphasized. Particularly, the activation energies of their crystallization kinetics at different stages of induction period and growth period were calculated on the basis of Arrhenius equation. The results demonstrated that the obtained CPs presented the highest relative crystallinity when the additive amount of used SDA was 1 mL at aging periods of 2 d, otherwise, their relative crystallinity degree was low due to existences of a large number of heterocrystal impurities. Particularly, the apparent activation energy values for induction (E n) and growth (E g) profile were calculated by the Arrhenius equation. The E n value (86.46 kJ/mol) of induction period was much higher than that E g value (9.64 kJ/mol) of growth stage, suggesting that the induction period was the main controlling step during the synthetic CP. Finally, the synthetic CP was employed to preliminarily assess its performances for CH 4 /N 2 separation. These demonstrations provide a promising method for the synthesis of CPs.