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. th (...truncated)