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Modification Of HZSM-5 Zeolite And Catalytic Performances For Conversion Of Methanol To Gasoline

Posted on:2016-06-25Degree:MasterType:Thesis
Country:ChinaCandidate:Z H SunFull Text:PDF
GTID:2311330485959628Subject:Chemical Engineering
Abstract/Summary:PDF Full Text Request
Gasoline is an important consumable product for energy with a recorded consumption of over 100 million tons in 2014 in China, of which the majority was produced from petroleum via chemical routes. Methanol to gasoline(MTG) is an important alternative to the petrochemical routes for gasoline production. The core of MTG technology is the preparation of HZSM-5 zeolite with excellent performance, and modification to improve the catalytic activity and lifespan and increase methanol conversion and gasoline selectivity.Micro-sized M-HZSM-5(ca 3 ?m) was prepared by two-stage, temperature controlled crystallization, giving a product of regular crystal structure and clear outline with high crystallinity. Nano-sized N-HZSM-5(ca 500 nm) was prepared by multi-stage crystal seed induction method(an amine-free method). The product had regular crystal structure and high crystallinity but with the phenomenon of agglomeration. In comparison, N-HZSM-5 had larger specific surface area, higher mesoporous content and stronger acidity than M-HZSM-5. When used for catalyzing MTG reaction, M-HZSM-5 exhibited better catalytic performances but still had the problems of low catalyst lifespan, low gasoline selectivity and excessive content of aromatics in the gasoline product. Therefore, further modification to improve its catalytic performances is essential.N-HZSM-5 was first modified with Ag and Zn at a load of 4%(w/w) followed by stream treatment at 500 °C to get the modified catalysts AgH2O/N-HZSM-5 and ZnH2O/N-HZSM-5, respectively. Compared to N-HZSM-5, AgH2O/N-HZSM-5 and ZnH2O/N-HZSM-5 increased the catalyst lifespan by 41.2% and 52.9%, respectively, for the MTG reaction. After 6 h, their gasoline selectivity increased by 19.1% and 15.5%, respectively. Both loads of Ag and Zn promoted the aromatization, leading to an aromatics content of 61.9% and 55.4% in the gasoline products, respectively, which far exceeds the national standard for gasoline V. The gasoline products thus prepared need to be reconciled before use.The P-loaded HZSM-5, which is usually used for converting methanol to alkenes, was modified to get an excellent MTG catalyst(PH2O/N-HZSM-5) with a P load of 0.8%(w/w) treated by stream at 500 °C to make use of the synergistic action of L and B acids. In comparison with N-HZSM-5, PH2O/N-HZSM-5 increased the lifespan by 64.7% for MTG. After 6 h's reaction, the gasoline selectivity was increased by 16% and the aromatics selectivity dropped to 39%. The product meets the national standard for gasoline V, so PH2O/N-HZSM-5 is a better catalyst for MTG.The analysis of catalyst deactivation and regeneration showed that the oxidation of deposited carbon by 4 stages of temperature increase almost completely removed the deposited carbon, leading to the good activity recovery of the deactivated catalyst. After further stream treatment at high temperatures, the anti-coke deactivation ability of the catalyst was significantly improved. Both loads of Ag and Zn increased the hydrothermal stability of HZSM-5, reduced the irreversible inactivation during the deactivation- regeneration process and increased the number of its recycled usage. PH2O/N-HZSM-5 has the strongest anti-coke deactivation ability, and the irreversible inactivation caused during the deactivation- regeneration process significantly affects the catalytic performances of PH2O/N-HZSM-5, reducing its number of recycled usage.
Keywords/Search Tags:HZSM-5, MTG, gasoline selectivity, aromatics content, deactivation-regeneration
PDF Full Text Request
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