Competitive nucleation and growth in seeded batch crystallization of titanosilicate ETS-10 using Ti(SO4)2

Seeded batch crystallizations were conducted to investigate the competitive nucleation and growth of ETS-10, and to explore seeding as a technique for the growth of large crystals. When used in a “standard” synthesis mixture (5.50SiO2:4.46Na2O:1.00TiO2:xKF:3.35H2SO4:yH2O, x = 1.5, y = 300), seed crystals (particle size distribution (PSD) with a mode 6.1 ± 0.1 μm) grew to be ∼2-2.5 times larger. The amount of growth was determined to depend on the seeding level. The products had bimodal PSDs, indicative of the nucleation of new crystals. Increasing seeding levels from 0.8 to 10.0 wt.% resulted in a decrease in the mode of the PSD for both the seeds (from 14.8 ± 0.3 to 11.8 ± 0.2 μm) and new crystals (from 5.9 ± 0.1 to 5.0 ± 0.1 μm) in the product, and in a decrease in the number of new crystals relative to the number of seed crystals. This suggests the absence of extensive secondary nucleation, and that seeds effectively competed for nutrients with the new crystals that were formed. When crystals grown in a previous experiment were used as seeds in the next experiment (i.e., serially), seed crystals grew to be ∼3 times their original size. However, three such seeding steps resulted in agglomerate formation. Seeding in batches diluted with water (y = 600-750), utilizing seeding levels lower than those used in undiluted batches, resulted in larger seed crystals size increases (∼2.5-3 times), and in fewer new crystals (i.e., nucleation suppressed). Seeding in the KF-free synthesis mixture (x = 0) also resulted in seed crystal size increases (∼2-3 times), but no further elimination of primary nucleation was accomplished. This is hypothesized to be due to the presence of K+ ions in the system, which were likely supplied with the seeds.