Oxidation Dehydrogenation Of Ethane To Ethylene On The Nickel-Based Catalysts

Ethylene is an important chemical in petrochemical industry. With the development of economy, the demand of ethylene increases. Ethane widely exists in natural gas, liquefied petroleum gas (LPG), coke oven gas and refinery gas. The preparation of ethylene from ethane can effectively relieve the shortage of petroleum resources and it has the vital significance to our petrochemical industry. At present, the production technology of ethylene is mainly from steam cracking and catalytic cracking olefin, and the reaction temperature is more than900℃. The cracking process is a strong endothermic reaction, which consumes much energy and restrictes by thermodynamic equilibrium. On the contratry, ethane oxidative dehydrogenation reaction is an exothermic reaction in thermodynamics, and ethylene can be obtained at low temperature. Therefore, it is important to explore low-temperature catalysts with high performance of the oxidative dehydrogenation of ethane to ethylene (ODHE).As a potential low temperature catalyst, nanosized NiO exhibited good ODHE catalytic performance, therefore in this thesis NiO-based catalysts were investigated. Nanoflake nickel oxide, with high concentration of urea as precipitation, was prepared by homogeneous precipitation method. By adding different additives, nanoflake composite NiMeO catalysts were prepared and they were evaluated for ODHE reaction and characterized by XRD, SEM, BET, H2-TPR, O2-TPD, CO2-TPD and XPS methods. The results showed that the doped Na, Mg ions did not enter into the NiO catalyst, so the catalytic performance is similar to the pure NiO. By contrast, the doped Al and Zr could partially substitute the Ni ion in lattice and had a strong interaction with Ni, boosting the alkalinity of catalyst, consequently improved the ethane cleavage-resistance, and affected the physical and chemical properties of catalysts and their catalytic activity. The adding of Zr element makes catalyst adsorption more O" species, which helps to improve ethylene selectivity. Among the NiMeO catalysys, NiZrO catalyst exhibited the best performance with the ethylene selectivity and yield of60.7%and29.2%at360℃respectively. Then a series of NiZrO catalysts with different Zr amount was prepared and studied. The results showed that the strong interaction between Ni and Zr and the particles size have effect on the catalytic performance.10%NiZrO catalyst exhibited the highest ethylene yield with ethane conversion of48.7%and ethylene selectivity of68.8%at350℃.In addition, NiZrO catalysts with different morphologies were also prepared by various ways. The effect of morphorlogy on their ODHE performance was stuided. Under the same experimental conditions, the catalytic performances of NiZrO catalysts were in the foollowing order:template method> sol-gel> precipitation> direct calcination> hydrothermal. Compared with the other catalysts, the NiZrO catalyst prepared by template method had larger specific surface areas, the higher Zr content on the surface, the suitable amount of alkalinity and better reduction properties, and thus showed better ODHE catalytic performance.