Enhancement of catalytic lifetime of nanostructured SAPO-34 in conversion of biomethanol to light olefins

• Hydrothermal synthesis of SAPO-34 catalyst at 250 °C in short time.
• Study the effect of crystallization time on properties and catalytic performance at 250 °C.
• Synthesis of spherical particles with accumulation of nano-sized cubic crystals.
• Controlling the crystallinity and particle size via adjustment of crystallization time.
• Enhancement of catalytic lifetime of SAPO-34 in MTO process.

Nanostructured SAPO-34 was synthesized via moderate temperature hydrothermal method in various synthesis times with controlled particle size. The effect of crystallization time on purity and crystallinity of synthesized samples was investigated. The catalysts were characterized by XRD, FESEM, BET, FTIR and EDX techniques. According to the XRD analysis, all the samples have chabazite structure related to SAPO-34. By decreasing crystallization time, pure phase was produced and the particle size reduced. BET analysis illustrated high surface area for all catalysts especially for pure samples. Synthesis at moderate temperature resulted in spherical morphology by the aggregation of nano-sized crystallites. Significant difference was observed in the deactivation behavior of the synthesized catalysts. Samples with high crystallinity and small particles had proper catalytic lifetime. In addition, all synthesized catalysts at moderate temperature had longer lifetime than the synthesized sample at lower temperature and longer crystallization time. The SAPO-34 synthesized at 250 °C and 16 h was found to be the best catalyst regarding to the time on stream performance due to high crystallinity and relevant morphology. This catalyst had 23 h lifetime in the methanol to olefins process while the synthesized sample at low temperature had 4 h lifetime.

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