(532bh) Enhancing the Propylene Selectivity in the Methanol-to-Olefins Reaction over SAT-Type Molecular Sieves
AIChE Annual Meeting
2022
2022 Annual Meeting
Catalysis and Reaction Engineering Division
Poster Session: Catalysis and Reaction Engineering (CRE) Division
Wednesday, November 16, 2022 - 3:30pm to 5:00pm
Molecular sieves containing Brønsted acid sites are at the nexus of the MTO process, with SAPO-34 (CHA) being the catalyst deployed industrially. In MTO, framework structure and composition (acidity) together with reaction conditions determine the reaction intermediates that form as a part of the dual-cycle mechanism, which ultimately dictate product selectivity. In prior reports, enhancing propylene selectivity was primarily achieved by utilizing (i) 10- or 12-member ring (MB) zeolites (e.g., MFI and *BEA) with high Si/Al (i.e., low acid sites) in order to suppress the aromatics cycle and improve the alkene cycle, or (ii) 8-MR molecular sieves with cages larger than CHA (e.g., AEI and DDR), in order to accommodate higher substituted methylbenzenes.
In this work, we present an alternative approach for enhancing P/E by utilizing a low acidity small-pore catalyst with a cage that is significantly narrower than CHA. We report the synthesis and characterization of several SAT-type molecular sieves (e.g., MgAPO, CoAPO and SAPO), and their MTO behavior over a wide range of reaction conditions. Our results show that the combination of low acidity and unique structural features of the narrow SAT-cage lead to a catalytic pathway and a mechanism that predominantly favors propylene formation (P/E=2-4.2; P=40-50%).