The hydrothermal stability of the alkali-treated ZSM-5 and it’s catalytic performance in catalytic cracking of VGO
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To enhance the heavy oil cracking ability of ZSM-5, desilication by alkali has been adopted in this study. The results showed that desilication by NaOH, NaOH/Al(NO3)3, NaOH/(NH4)3PO4 solutions all can induce some mesoporous structure to ZSM-5 zeolite. Among them, the sample ZSM-5/NaOH/(NH4)3PO4-F showed the highest mesoporous surface area. The hydrothermal stability of the desilicated ZSM-5 samples was also measured. The NaOH-modified ZSM-5 sample exhibited worse hydrothermal stability than the parent ZSM-5, while NaOH/(NH4)3PO4 modified ZSM-5 sample maintained the higher relative crystallinity and more acidic sites than the parent ZSM-5 after the hydrothermal treatment. The micro-activity tests showed that the NaOH/Al(NO3)3, NaOH/(NH4)3PO4-modified ZSM-5 samples exhibited higher catalytic activity than the parent ZSM-5 sample and NaOH-modified ZSM-5 sample in catalytic cracking of vacuum gas oil (VGO). Especially, for the sample ZSM-5/NaOH/(NH4)3PO4, the conversion of VGO increased from 78.91 to 85.13%, and the yield of propylene increased from 15.01 to 18.83% compared to the unmodified ZSM-5 catalyst.