Effect of SAPO-34 molecular sieve morphology on methanol to olefins performance

SAPO-34 molecular sieve samples with sheet-like and cubic morphology were synthesized under microwave and hydrothermal conditions, respectively. The sheet-like SAPO-34 was 130 nm thick with a Brunauer-Emmett-Teller (BET) surface area of 593 m2/g, while the cubic sample was 1.5–2.5 μm in size with a BET surface area of 708 m2/g. Both samples exhibited a similar density for strong acid sites, while the cubic SAPO-34 possessed less weak acid sites. A methanol to olefins catalytic test carried out at 450 °C and 1.0 h−1 showed that the sheet-like SAPO-34 exhibited a long stability life of 380 min and gave a high ethylene selectivity of 51.77% and a high total selectivity for ethylene, propylene, and butylene of 90.20%. However, the stability life for the cubic SAPO-34 was only 212 min, and the ethylene selectivity and total selectivity for ethylene, propylene, and butylene decreased to 49.84% and 86.81%, respectively. It is thought that the longer stability life and higher olefin selectivity for sheet-like SAPO-34 occur because of the shorter diffusion path that hinders the further conversion of produced olefins and coke formation.

Methanol to olefins performance on SAPO-34 depends on the molecular sieve morphology. The sheet-like SAPO-34 (sample S-1) exhibits a longer lifetime and higher olefin selectivity than the cubic material (sample S-2) because of the shorter diffusion path of the former.Figure optionsDownload as PowerPoint slide