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.