Study On Catalytic Dehydration Of Ethanol To Ethylene Over Modified HZSM-5Zeolites

Ethylene is one of the major feedstocks in the petrochemical industryConventionally it was produced from the nonrenewable petroleum resources.Recently due to the shortage of natural resources and the rise of crude oil prices,catalytic dehydration of ethanol to ethylene has become an increasingly competitiveand promising route, and therefore has been drawing much attention. This paper istrying to modify the HZSM-5zeolite in order to improve its catalytic performance.A series of modified HZSM-5zeolite catalysts with different metal contents wereprepared through changing the ion-exchange times. The reaction of dehydration ofethanol to ethylene was carried out in a continuous flow fixed-bed reactor. Resultsshowed that Ni-Z-0.12%exhibited the best activity. The catalysts were characterizedby X-ray diffraction （XRD）, pyridine temperature programmed desorption （Py-TPD）,infrared spectra after adsorption of Pyridine（Py-IR），N₂adsorption-desorption andtemperature programmed oxidation （TPO）. Characterization revealed that catalyticperformance was related to the micropore structure and surface acidity, especially thelatter one. It was found that maintaining the ratio of strong acid sites to low acid sitesnear one favor improving the catalyst activity.The preparation conditions of Ni-modified HZSM-5zeolites were studied byorthogonal experiments. The effects of concentration of nickel nitrate solution,temperature and ion-exchange times were discussed. Results showed that theoptimized exchange conditions were as follows: concentration of nickel nitratesolution was0.4mol/L, temperature was80oC, ion-exchange times was twice.The effects of operation parameters on dehydration of ethanol to ethylene werealso investigated, such as reaction temperature, WHSV and concentration of ethanolsolution. The optimized reaction conditions were as follows: reaction temperature was260oC, WHSV was2h^-1, concentration of ethanol solution was50%（V）. The stabilitytest showed that ethanol conversion and ethylene selectivity could be maintainedabove95%within15hours at the optimal reaction conditions.