Preparation and characterization of NaY zeolite in a rotating packed bed

Petroleum Science, Mar 2012

NaY Zeolite was synthesized in a rotating packed bed (RPB) for the first time. A Si-Al gel with a specific composition was used as the structure-directing agent. The as-synthesized NaY Zeolite was characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD) and specific surface area (BET). The characterization result showed that the NaY Zeolite had a particle size of approximately 200 nm, n(SiO2)/n(Al2O3) ratio of 5.03, crystallinity of 96% and specific surface area of 714 m2/g. The experimental results indicated that the structure of NaY Zeolite was related to the synthesis conditions (such as reactors, crystallization time and so on). The micromixing efficiency was proven to be the most important factor for synthesis of NaY Zeolite in the high-gravity environment in RPB.

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Preparation and characterization of NaY zeolite in a rotating packed bed

Received April Preparation and characterization of NaY zeolite in a rotating packed bed Xu Yongquan 0 1 Cai Lianguo 0 1 Shao Lei 0 1 Chen Jianfeng 0 1 0 050018 , China 1 Technology , Beijing100029 , China 1 Introduction attention owing to its valuable properties, such as high catalytic activity, high surface-atom ratio, large specific surface area and high surface energy (Wang et al, 2002; Camblor et al, 1989). Fluid catalytic cracking (FCC) catalysts have high catalytic activity and can be used in the refining of residual and heavy oils (Gilson and Derouane, 1984; catalytic cracking selectivity, reduce coke formation, increase the yield of diesel oil and improve gasoline quality; and industry (Yang et al, 1999; Kyotani et al, 2003; Albemarle to develop a feasible technology for preparation of small apparatus for better multiphase contact, can generate an acceleration of 1-3 orders of magnitude larger than the gravitational acceleration on the earth (Chen et al, 1996; Foley, 1995). Since this apparatus can intensify gas-liquid or liquid-liquid mass transfer and micromixing, it has been successfully applied to the synthesis of well-defined nano inorganic powders, such as calcium carbonate, silica and 2/g. The experimental pseudoboehmite, by the reactive precipitation method (Chen the conventional reactors in production of nano inorganic powders, such as short reaction time, small particle size, on microporous structure was confirmed by comparison hydrothermal synthesis. The effect of high-gravity level on 2 Experimental 2.1 Synthesis All the chemicals used in this work were A.R. grade. The reaction apparatus is shown in Fig. 1. 2.1.1 Preparation of structure-directing agent Sodium aluminate solution (with a concentration of 20 wt%) was intensively mixed with sodium silicate solution (with a concentration of 30 wt%) for 10 min in directing agent was obtained with a typical composition of 2 2 3 2 2 2.1.2 Preparation of initial solution Sodium aluminate solution (with a concentration of 30 wt%) was intensively mixed with sodium hydroxide solution (with a concentration of 7 wt%) and sodium silicate solution the initial solution was obtained with a typical composition 8 1 2 6 7 3 5 4 under a High-Gravity level of 170 g and the agitating tank. Then the directing agent was slowly added into this solution accurately. 2.1.4 Crystallization and calcination The resulting gel-like mixture was aged for 24 h and crystallized at 100 °C for 12 h, and then calcined at 450 °C for 3 h in air. 2.2 Characterization zeolite were recorded on a Siemens D500 diffractometer using CuKa radiation ( =0.154 nm). The crystallinity of the peaks in the X-ray diffraction patterns (Shimazu, Japan). Limited Company, China). Scanning electron microscopy (Hitachi, Japan). 3 Results and discussion 3.1 Comparison of NaY zeolite synthesized in RPB and by conventional hydrothermal method 20kv 15 001 S nm and exhibited uniform particle size distribution, indicating that high-gravity technology is superior to hydrothermal mass transfer and micromixing property than hydrothermal synthesis, resulting in homogenous mixing of structuredirecting agent with initial solution, so that the size of the nuclei is small, and the number is large. Thus the crystal adsorbing solute on their surface for crystallization. The grain Compared with the conventional hydrothermal method, stress exists, a large number of silicate and aluminum ions collide at the same time, and a large number of nucleation events occur in the system. The larger the number of nuclei with size smaller than the critical size in the synthesis system, the smaller the crystals that are generated. The size of molecular sieve grains also depends on the crystal growth rate crystal growth rate, the size of synthesized molecular sieve is small and tends to be uniform. Because the nuclei greater than the threshold can grow to crystals almost at the same time, and new generated grains are allowed to exist until they reach a rapid growth period. Under high gravity, the nucleation rate is accelerated, the induction period is shortened, and the nucleation rate is faster than the crystal growth rate, so the to investigate the effect of crystallization time on its structure. structure, synthesized by a conventional hydrothermal method as shown in Table 1. 3 . 2 S y n t h e s i s o f N a Y z e o l i t e w i t h d i f f e r e n t crystallization times m e t h o d s h a s a r e g u l a r s t r u c t u r e a n d w o r k s w e l l i n applications. But the synthesis time is long, especially the hydrothermal synthesis, with different crystallization times, Crystallization time, h n 2)/n(Al2 3) Crystallinity, % Surface area, m2/g 12 2.19 42 425 20 3.28 91 703 24 3.24 90 711 method had higher Si-Al ratio and crystallinity. The surface area is 703 m2/g. Crystallization time of 20 h is the optimal time for the conventional hydrothermal synthesis method. the conventional hydrothermal method (i.e. the Si-Al ratios of structure-directing agent and mother liquor, crystallization, aging time, etc.), is shown in Table 2. of 5.03, crystallinity of 96% and surface area of 714 m2/g. by the conventional hydrothermal method. with crystallization time of 9 h, 12 h and 24 h are shown in Fig. 5. 30 3.17 84 609 18 4.8 89.0 608 40 3.21 67 543 24 4.3 67.0 596 2nm provides a promising and efficient pathway for mass Acknowledgements can be regarded as a continuation of the growth process, but Kyotani T, Ma Z X and Tomita A. Templated synthesis of novel porous Zeolite crystallization is a micromixing process and a and aluminum crystallization does not occur quickly and completely. Thus it will greatly prolong the crystallization the mass transfer and micromixing. A high-gravity reactor can enhance the mass transfer and mixing between silica and aluminum sols in the nucleation process and the reaction system will be uniformly mixed in a very short time, which will greatly shorten the crystallization time and improve the crystallinity of the molecular sieve. As a result the zeolite particles will be small and uniform. Grain growth process can be divided into three stages. concentration of silicon tetrahedral structure and aluminum tetrahedral structure at this time has not yet reached the minimum saturation C*min required for grain nucleation, and this point the concentration is higher than C*min, and a large number of nuclei forms. With the formation of nuclei, the when the nuclei grow and become grains. To obtain small and uniform grains, nucleation rate must be as high as possible, silicon and aluminum are highly decentralized, and can instantly reach the minimum saturation C*min required for grain stage — nucleation phase, and a large number of small nuclei are produced. Competition occurs between nucleation and crystal growth. The faster the rate of nucleation, the slower the growth rate of corresponding grains, as a result the grains number of nuclei is formed at the early stage and particle size is small, resulting in large surface area and a large number of growing points, crystallization will be completed in a short time. 4 Conclusions a uniform particle size distribution was synthesized in a has a much smaller particle size and higher surface area, suggesting higher catalytic performance. The experimental 2813-2826 micromixing which was the most important condition for 541 1459 2005-10 -05 Benefits in activity and selectivity of small Y zeolite crystallites stabilized by a higher silicon-to-aluminium ratio by synthesis . on particle size distribution in reactive precipitation. Chemical hydroxide in novel rotating packed bed reactor . Chemical 3 by high-gravity reactive precipitation . Acta Metallurgica Sinica . 1999 . 388 (in Chinese) Yamamura M , Chaki K , Wakatsuki T , et al. Synthesis of ZSM-5 zeolite with small crystal size and its catalytic performance for ethylene


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Yongquan Xu, Lianguo Cai, Lei Shao, Jianfeng Chen. Preparation and characterization of NaY zeolite in a rotating packed bed, Petroleum Science, 2012, 106-109, DOI: 10.1007/s12182-012-0190-0