Effect of phosphorus on methane production in LPG catalytic cracking over modified-structure ZSM-5

• Significant reduction of methane by loading phosphorus on zeolite ZSM-5 in LPG catalytic cracking reactions.
• Generating of ZSM-5 zeolite mesopores by carbon nanotubes in order to increase availability of active site.
• Decreasing coke formation in the mesopores and increasing activity of the micropores in ZSM-5 by regulating steam timing.

Phosphorus was loaded by wet impregnation method on zeolite ZSM-5 created by template-free technique. Mesopores were produced using 30 wt.% of carbon nanotube template. The synthesized catalysts were characterized by means of XRD, XRF, FE-SEM, BET and NH3-TPD techniques. LPG catalytic cracking was conducted in fixed-bed reactor by using P-impregnated ZSM-5 zeolite. Since methane production was related to P amount, the amount of this element on the synthesized zeolite was optimized. Minimum methane production occurred with 0.5 wt.% of phosphorus. The resulting mesopores not only increase the availability of materials to catalyst active sites, but also increase the coke yield and deactivation of catalyst at reaction initiation, as well. Hence, to decrease coke formation, the steaming process dealuminated the mesopores while leaving micropores untouched, and so, mesopores were deactivated for coke formation. Modification of zeolite by phosphorus and steaming process increased light olefins yield and selectivity to 50% and 60%, respectively. In addition, coke formation declined from 14% on ZSM-5 to 7% on ZSM-5 CNT(30) P(0.5) steam (1 h) zeolite.

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