Preparation And Application Of Ethylene Catalysts For Dehydration Of Ethanol

The oil energy crisis has restrained the development of the ethylene production process using petroleum as raw materials,and the production of ethylene from non-oil energy ethanol has become an inevitable trend of current and future economic development.The key technology for the ethylene production from bio-ethanol is the preparation of new catalysts.Currently,activated alumina,HZSM-5 and SAPO-34 are commonly used.However,active alumina and HZSM-5 catalystshave problems such as harsh reaction conditions,high energy consumption,and poor resistance to carbon deposition.In recent years,SAPO-34 has received more attention due to its mild surface acidity,good coke-proof ability and high ethylene selectivity,but its poor thermal stability has limited its wide application.In order to further improve the anti-coking capacity,catalytic activity of SAPO-34 molecular sieves and thermal stability of SAPO-34 catalysts,the MeSAPO-34 catalysts modified by Fe or Co were prepared by the same crystal substitution method in this paper,and the activity and stability of these catalysts for ethanol dehydration to ethylene were studied.The main research content is as follows:(1)MeSAPO-34 catalyst was characterized by TG,XRD,NH3-TPD,N2 adsorption-desorption and SEM.The results showed that the loading of metal(Co or Fe)did not change the CHA topology of the SAPO-34 molecular sieve,but the metal Co or Fe partially replaces[PO4]+ and[AlO4]-tetrahedron in SAPO-34 to form metal cage structure and to enhance acid strength.The metal cage structure stabilizes the catalyst framework while allowing the metal Co or Fe to stably exist in the framework,which enhanced the acidity of the catalyst and optimized the hydro-thermally stable acid sites of the catalyst.The acid strength had a significant effect on the activity of the catalyst.(2)Ethylene was produced in a fixed-bed reactor.The optimum conditions for the ethanol-to-ethylene reaction of MeSAPO-34 molecular sieves were studied on evaluating catalytic activity by calculating the conversion of ethanol and the selectivity ethylene.the CoSAPO-34 catalyst shows 0.08CoSAPO-34 on the conditions of the the temperature at 360 ℃,the weight hourly space velocity of 3h-1 and the volume of ethanol of 2ml with a concentration of 99.7%,which makes the conversion of ethanol and the selectivity of the ethylene to 99.2%and 98.1%respectively.the CoFeSAPO-34 catalyst shows the best catalytic activity with a composition of 0.04Co0.08FeSAPO-34 on the conditions of the temperature at 280 ℃,the weight hourly space velocity of 3h-1 and the volume of ethanol of 2ml with a concentration of 99.7%,which makes the conversion of ethanol and the selectivity of the ethylene to 99.3%and 98.87%respectively.The results show that the modification of SAPO-34 by metal(Co or Fe)not only makes the reaction conditions mild,but also has excellent catalytic activity.(3)Ethylene was produced in a fixed bed reactor.The stability of the ethanol-to-ethylene reaction of MeSAPO-34 catalyst were studied on evaluating catalytic activity by calculating the conversion of ethanol and the selectivity of ethylene.According to the stability experiments,it was found that CoSAPO-34 and CoFeSAPO-34 catalysts had the best catalytic at 400 ℃ and 380 ℃,respectively,and did not change with time.In summary,MeSAPO-34 catalyst modified by to Fe and Co can not only enhance the strength of the acid but also optimize the hydro-thermally stable acid sites of the catalyst,which enhances the catalytic activity of the catalyst,the reaction conditions are milder,and the anti-coking ability is stronger.