| Isomerization of straight-chain paraffin is favorable to improve RON of FCC gasoline in hydrodesulfurization process. We chose ZSM-50 zeolite with one-dimensional oval passageway according to reaction mechanism of isomerization of straight-chain paraffin. Modification and isomerization of ZSM-50 zeolite were investigated to produce the catalytic with metal-acid double function which can reduce suffer and improve the RON of FCC gasoline in our country.Dealuminzation of ZSM-50 zeolite using acid was investigated to improve the catalytic properties of ZSM-50 zeolite in isomerization of straight-chain paraffin. The characterization results showed that the effect of dealuminzation is the most obvious using oxalic acid. ZSM-50 zeolite with different ratio of dealuminzation from 10% to 60% can be prepared by changing oxalic acid solution concentration, reaction time and reaction temperature. Oxalic acid treatment can effectively increase the framework SiO2/Al2O3 molar ratio of ZSM-50 zeolite without affecting the relative crystallinity significantly. The mild dealumization can increase the number of acid site, enhance the L/B ratio, and keep the acid intensity. Severe dealumization produces extra aluminum vacancy in the framework and decreases the number of acid site.The isomerization performance of ZSM-50 zeolites modified by oxalic acid was evaluated in a fixed-bed reactor using n-heptane as model compound. The evaluation results show that, the mild dealumization can reduce the cracking ratio of n-heptane while improving isomerization performance of ZSM-50 zeolite. Severe dealumization enhanced the side reactions while lowering the selectivity of isomerization.In addition, metal atoms were introduced in ZSM-50 zeolite after dealumization using oxalic acid. The impact of various metal modification to acid distribution of ZSM-50 zeolite was investigated. The characterization results show that metal modification can effectively change the acidic distribution and acidic strength of the zeolite. |
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