Fig. 5. XRD patterns of four ZSM-5 samples obtained by
different operating processes.
Fig. 5 presents XRD patterns of ZSM-5 samples obtained by RPB premix -
static crystallization (ZSM-5-RS), RPB premix - dynamic crystallization
(ZSM-5-RD), STR premix - static crystallization (ZSM-5-SS) and STR
premix - dynamic crystallization (ZSM-5-SD). All the obtained samples
are assigned to highly crystallized ZSM-5 corresponding to the typical
MFI topology. Independently of micromixing intensity, the crystal form
and growth face of ZSM-5 samples have no obvious differences in the four
operating routes mentioned above, indicating the crystal form and growth
face main determined by reaction temperature rather than micromixing
effect.
The morphological properties of four ZSM-5 samples are shown in Fig. 6.
All ZSM-5 samples exhibited spherical morphologies but the particle size
distributions were not consistent. The ZSM-5 samples pretreated by RPB
premix displayed narrower particle
size distributions and smaller average particle sizes compared with
those by STR premix, indicating that the uniform distribution of
structural units and TPA+ could facilitate the
increase of nucleation sites. The number of structural units and
TPA+ are certain in the whole reaction system, the
more crystal nucleus assembled by structural units, the fewer remaining
structural units for crystal growth, resulting in the decrease of final
particle sizes. Moreover, under the same premixing process, dynamic
crystallization results in narrower particle size distributions of ZSM-5
samples with less crystallization time because of the uniform growth of
zeolites in a relatively homogeneous crystallization environment.
ZSM-5-RD showed the narrowest size distribution ranging from 160 to 400
nm with an average size of 290 nm.