Abstract
SAPO-34 catalysts were synthesized through the seeding approach under different seed conditions. The different seed synthesis times (6 h, 12 h, and 24 h) and three types of seeds were evaluated: the dried seed, the calcined seed, and the mother liquor from an unseeded synthesis, called the solution seed. Pure SAPO-34 was obtained using 12 h and 24 h solution seeds, in which a 40% reduction of template consumption was achieved simultaneously. All seeding induced samples represented higher catalytic performance in the MTO process than conventional SAPO-34 due to the smaller crystallite/particle sizes and larger external surface areas and mesopore volume. Furthermore, the changes in the acidity of samples affect their performance. The maximum olefin selectivity under industrial feed conditions (72 wt% methanol in water) was 91.79% for the sample prepared from the 12 h solution seed, which was 14.43% higher than the unseeded sample. Although this sample did not have the longest lifetime, it showed a 330 min lifespan, which was at least twice more than that of the conventional one (150 min). The sample prepared from the 6 h solution seed showed the longest lifetime of more than 500 min among all catalysts, although it was contaminated with a little SAPO-5.
Highlights
Ethylene and propylene are the primary building blocks in the chemical industry and are mainly produced by uid catalytic cracking (FCC) and steam cracking
We investigated the effect of seed synthesis time and three types of seeds on the physicochemical properties and the catalytic performance of SAPO-34 zeolites in the methanol conversion to light ole ns (MTO) reaction
Pure SAPO-34 was obtained with consuming 40% less template by applying 12 h solution seed
Summary
Ethylene and propylene are the primary building blocks in the chemical industry and are mainly produced by uid catalytic cracking (FCC) and steam cracking. Sun et al.[14] synthesized nano-sized hierarchical SAPO-34 samples via a seed assisted method using different concentrations of triethylamine (TEA). Using seeds resulted in (1) increasing crystallization rate, (2) decreasing the formation of an undesirable phase, (3) decreasing the synthesis time, and (4) controlled the particle size.[18,19] Sun et al.[20] succeeded in synthesizing pure SAPO-34 through a seeding-induced method applying TEA as the sole template. The seeding method was used in the synthesis of SAPO-34 using three types of seeds (solution, dried and calcined seed) and three different seed synthesis times (6 h,12 h, and 24 h), to decrease the template consumption without signi cant impact on the zeolites crystallinity and their catalytic performance. There has been no report about the effects of seed synthesis times and different types of seeds on the preparation of SAPO34 up to now
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