Synthesis of 5A zeolite nanocrystals using kaolin via nanoemulsion-ultrasonic technique and study of its sorption using a known kerosene cut

摘要

In this research, 5A zeolite nanocrystals were synthesized and the effects of the controlling parameters such as, temperature, composition of the reactants, and effects of ultrasound on morphological and crystal size modifications were investigated. Nanoemulsion-ultrasonic technique was used in preparation of 4A (Na-A) zeolite which is the precursor of 5A (Ca-A) zeolite. Kaolin and/or aluminate derived from kaolin were utilized as the main sources of Al. X-ray fluorescence (XRF) were used to identify SiO2/Al2O3 ratio in kaolin and X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), were used to confirm zeolite crystallinity, crystal size and morphology, and phase purity. The optimal conditions were SiO2/Al2O3 ratio of 2.2, temperature 75 °C, heating time of 8 h, and ultra-sound rate 4000 rpm (ca 67 Hz) for 15 min. Then, the sample that was prepared at optimal conditions and possessed the highest crystallinity and an average crystal size of about 260 nm was subject to dead-end batch sorption tests using a special cut of kerosene composed of C_(10)-C_(13) linear and branched paraffinic hydrocarbons and sorption and sieving properties of the zeolite were studied by Gas Chromatography Mass Spectroscopy (GC-MS). The results show that the microanoemulsion technique induces rapid growth, and formation of 4A zeolite goes to completion within 2 h of the synthesis time, compared to 8-24 h for the samples that were not prepared by this technique. Since 4A zeolite is the precursor for 5A zeolite, reduced synthesis time of the precursor would accordingly lead into decreased preparation time course of the final desired product 5A zeolite. In addition, the results show that the application of ultrasound plays a great role in reducing the crystal size, and could reduce the crystal size by as much as 62%. Nanoemulsion-ultrasonic method produces smaller, more uniform, and purer zeolite nanocrystals with greater ion exchange capacity than the conventional synthesis methods. Furthermore, the sorption property of the 5A zeolite is improved on average about 15%.