Effect of Next-Nearest-Neighbor Aluminum Atoms in the HZSM-5 Framework Synthesized with Various Aluminum Sources on Liquefied Petroleum Gas Transformation to Light Olefins
2018
Abbasizadeh, Saeed | Karimzadeh, Ramin
HZSM-5 catalysts with various aluminum distributions in their frameworks and different Si/Algₑₗ ratios were synthesized to investigate the product distribution in liquefied petroleum gas cracking. The characterization of synthesized zeolites was performed by X-ray diffraction (XRD), Brunauer, Emmett, and Teller (BET) method, (scanning electron microscopy) SEM, NH₃-TPD, X-ray fluorescence (XRF), and direct reflectance (DR) UV–visible, and ²⁷Al MAS NMR analyses. The maximum proportion of 0NNN aluminum atoms (90.6–92.6%) were found in HZSM-5 synthesized with aluminum nitrate. The higher 0NNN aluminum atoms in the zeolite framework and lower content of aluminum at channel intersections enhanced the olefin yield and decreased the C₅⁺ yield. The amount of coke increased with increase of the 1NNN Al atoms. The optimum olefin yields for HZSM-5 synthesized with aluminum nitrate, aluminum chloride and aluminum hydroxide were found to be 47.22% with Si/Algₑₗ 50, 45.47% with Si/Algₑₗ 30, and 44.32% with Si/Algₑₗ 30, respectively. The propylene to ethylene ratio and catalytic stability increased with decrease of the acid strength distribution.
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