Single-mode Focused Microwave Synthesis Of Small Crystal NaA Zeolite

Microwave energy has been employed in many chemical reaction and zeolite synthsis. Single-mode microwave synthesis have many advantages such as short production cycle, low energy costing, high efficiency, clean, nonpollution. Small crystal size of Na A zeolite not only has abundant pores, high specific surface area and high ion-exchange capacity, but also has excellent performance in heat resistance, acid resistance, alkali resistance and so on. Small crystal size of Na A zeolite has higher catalytic activity and selectivity in the catalytic cracking, hydrocracking and isomerization reaction comparing with conventional zeolite. Thus, it is a research focus to synthesize small particle size of Na A zeolite which has characteristics of particle size small and uniform, well-defined crystal by single-mode microwave synthesis method.The small crystal size of Na A zeolite was prepared by single-mode microwave synthesis method using solid silicone and colloidal silica as silicon sources and sodium metaaluminate as aluminum source. The influences of n(Si O2)/n(Al2O3) ratios,microwave power, microwave synthesis temperature and time, alkalinity, aging temperature and time on product were investigated. The phase composition, crystallinity,morphology, skeletal structure, particle size and distribution of crystalline products were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM),transmission electron microscope(TEM), fourier transform infrared spectroscopy(FT-IR) and laser particle size analyzer. The optimal conditions on synthesis of small crystal of Na A zeolite by Single-mode microwave synthesis method were explored. The crystal growth mechanism of Na A zeolite was discussed. Ag-loaded zeolite was prepared using small crystal size of Na A zeolite as carrier. The effects of the amont of Ag NO3, reaction temperature and time on the amount of silver supported on Na A zeolite were investigated. The antibacterial properties were measured by spectroturbidity method. The main research result listed in the following.1. When solid silicone was used as the silicon source, the optimal experiment parameters was as follows: n(Si O2)/n(Al2O3)=1.7, n(H2O)/n(Na2O)=30,n(Na2O)/n(Si O2)=2/1.7, aging temperature was 30°C, aging time was 24 h, microwave synthesis temperature was 120°C, microwave synthesis time was 10 min. The Na A zeolite with well-defined crystal and uniform particle size of 300~400 nm were obtained under the optimal reaction parameters.2. When colloidal silica was used as the silicon source, the optimal synthesis parameters were that n(H2O)/n(Na2O)=30, aging temperature was 30°C, aging time was8 h, microwave synthesis temperature was 120°C, microwave synthesis time was 6 minand the max microwave power was 100 W. The Na A zeolite synthesized under the optimal synthesis conditions had small particle size of 200~300nm and had good thermal stability before 900°C.3. Microwave energy increases the heating rate of the synthesis mixture, leads to a more uniform heating of the synthesis mixture, promotes the dissolving of the precursor gel and reduces the apparent activation energy of the crystallization reaction during the synthesis process of small crystal Na A zeolite by single-mode microwave synthesis method. The microwave radiation heating took 45 s to achieve the desired crystallization temperature, while traditional hydrothermal method required 30 min to reach the same temperature. Single-mode microwave energy rapid increases the heating rate. Compared with traditional hydrothermal synthesis crystallization time of 2h, single-mode microwave radiation synthesis small crystal Na A Zeolite only needed 6 min. It largely saves time, shortens the reaction cycle time and improves productivity by single-mode microwave synthesis method.4. Ag-loaded zeolite was prepared using Na A zeolite of 200~300nm as carrier prepared using colloidal silica as the silicon source. The amount of silver supported on Na A zeolite was affected by the amount of Ag NO3, reaction time and reaction temperature. The amount of silver supported on Na A zeolite increased with the improving of the amont of Ag NO3. When the ratio of n(NH4A) and n(Ag NO3) was less than 1/2, the amount of sliver improved linearly; When it was more than 1/2, the amount of sliver increased slowly. When reaction time was 4h, the content of silver reached saturation. When reaction temperature was 400°C, the amount of silver reached a maximum value. The amount of silver was 41.08% under the optimal conditions. The antibacterial properties of Ag-loaded zeolite prepared under different conditions were tested. The optimal conditions of preparation of Ag-loaded zeolite were that the ratio of n(NH4A) and n(Ag NO3) was 1/2, reaction time was 4h, reaction temperature was 400°C.The MIC for Escherichia coli was 10.42 ppm.