Small pore SAPO-14-based zeolites with improved propylene selectivity in the methanol to olefins process

The methanol to olefins (MTO) process is an important non-petroleum route to prepare light olefins, however, it still remains a challenge to improve the one-pass propylene selectivity over the industrial SAPO-34 catalyst. The acidity (Si content) and pore structure (pore size and cage) of the catalyst are the vital factors for product selectivity. In this work, SAPO-14 zeolite (AFN zeotype) with a small-pore and ultra-small cage structure, as well as a high Si content (about 9%) has been successfully synthesized. It presents a short catalytic lifetime of 26 min, but high propylene selectivity with a P/E ratio up to 4.17 at 450 degrees C and WHSV = 0.5 h(-1). Furthermore, for the first time, SAPO-34/SAPO-14 composite zeolites are prepared using traditional SAPO-34 zeolites as seeds and varying the seed amount in the reaction system of SAPO-14. Such zeolites exhibit improved MTO performance, and the catalytic lifetime and selectivity for light olefins can reach 226 min and 82% at 400 degrees C and WHSV = 2 h(-1), and the P/E ratio reaches 2.7 or 1.3. This work demonstrates a feasible method for the design and synthesis of composite zeolite catalysts for controlling the product selectivity for MTO conversion.

Automated summary

The influence of catalysts on product selectivity in the methanol to olefins (MTO) process was studied in this work. SAPO-14 zeolite catalysts with high selectivity and SAPO-34/SAPO-14 composite zeolite catalysts were successfully synthesized. The results showed that controlling the acidity and pore structure of the catalysts could effectively improve the selectivity for light olefins.