| Propylene is important fundamental chemical material, and it is widly used to produce acrylonitrile, acrylic, polypropylene, acetone, epoxy propane, etc... At present, propylene consumption is greater than supply in the global. However, it is hard to expand propylene production capacity throngh traditional propylene route. Many factors have unfavorable effected on propylene industry and new route of producing propylene is need to exploit urgently. Bio-ethanol provides rich raw material for carbon-neutral process. The conversion of bio-ethanol to propylene has attracted increasing attention, and preparing efficient catalyet is the key of ETP.Now, the study of ETP pay attention to zeolite mainly, which can provide unique acidity and pore structure. Studies have shown that reaction system, reaction conditions, catalyst property and coke effect the catalytic activity. Among these, coke play an important role in effecting catalytic activity、stability and application-prospects. Studying coke deposition on catalyst can contribute to preparing efficient catalyst. We have prepared HZSM-5/SAPO-34composites catalyst for ETP, and discussed the influence of preparation method、composition and reaction conditions to catalytic activity. In order to make the catalyst better, the coke on HZSM-5/SAPO-34composites catalyst was be investigated in this work.In this work, the HZSM-5/SAPO-34composites catalysts with different preparation method and composition have been prepared and their catalytic performance were tested. The structure、 acidity and coke were characterized by X-ray diffraction (XRD), N2isotherm adsorption-desorption (BET), Scanning electron microscopy (SEM), The infrared spectrum analysis(FT-IR),Programmed desorption of ammonia (NH3-TPD),Oxygen temperature programmed oxidation(O2-TPO) and X-ray photoelectron spectroscopy(XPS). Carbon deposited on ZS-MM-4(m(HZSM-5):m(SAPO-34)=4、mechanical mixture) with different reaction time were be investigated. Moreover, catalyst regeneration with oxygen is adopted to prepare ZS-MM-4catalyst.(1) Different preparation methods and composition changed the acidity and pore structure of HZSM-5/SAPO-34composites catalysts, which resulted in different carbon deposition. Strong acid sites and medium acid sites of catalysts were the reactive sites for carbon deposition, meanwhile, coke mainly deposited in mesoporous. As a whole ZS-MM catalyst showed better anti-coking ability than ZS-HS catalyst.(2) A large amount of strong and medium acid sites were exposed in initial stage of ETP on ZS-MM-4, in the meantime sufficient pore space conducived to catalytic reaction and carbon deposition. The rate of carbon deposition was quick and most of strong and medium acid sites were coverd by coke in meseporous. During this period, the change of coke mainly was reflected in the amount of coke. In the late stage of ETP on ZS-MM-4, the driving force of carbon deposition reduced, which caused by the decreases of acid sites and mesoporous space. Some coke spread beyond mesoporous and deposited on the orifice of microporous. In this period the lower species of coke transformed to high species and the change of coke main was reflected in the species of coke.(3) Keeping appropriate oxygen concentration and coke burning temperature could contribute to resume acidity and structure. The regeneration reaction conditions of used ZS-MM-4as follows:oxygen concentration:10%%、heating rate:10℃/min、final temperature:550℃、holding time:1h. The acidity、structure and catalytic activity of regenerated catalysts can be basically recovered, the highest yield of propylene reach32.35wt%on regenerated catalyst and was93%yield of propylene on fresh ZS-MM-4catalyst. |
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