Investigation of synthesis time and type of seed along with reduction of template consumption in the preparation of SAPO-34 catalyst and its performance in the MTO reaction

摘要

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.