Study On Ni-based Catalysts For Methanation At Low Temperature

Hydrogen-rich fraction was separated from the hydrogen/methane separation tank during the process of cracking naphtha and light hydrocarbons to produce ethylene,which inevitably contained some amount of CO and CO₂.The concentration of CO should be below to 1 ppm in order to avoid poisoning the catalyst in downstream plants.Methanation is one of the most widely used methods to get rid of CO from hydrogen-rich gas.Nowadays,the reaction temperature of high-temperature methanation catalyst used in the industry is about 280?350 ?.Nevertheless,the reaction temperature of the methanation catalyst at low temperature is generally below 200 ?.Using low-temperature methanation catalysts can save a lot of high-pressure steam.Therefore,it is quite necessary to develop a kind of methanation catalyst,which has high activity and long life under low temperature conditions.Due to its large specific surface area,adjustable pore size and good stability,alumina carrier is one of the most widely used catalyst support materials in the industry.Nickel catalyst has good hydrogenation activity and perfect advantages in economy.So it is widely used in the industry.In this paper,nickel-based catalysts were mainly prepared by impregnation method and systematically evaluated in continuous fixed-bed reactors.Several factors in the methanation reaction were mainly investigated,including the calcination temperature of the carrier,the influence of different kinds of promoters?La,Ce,Pr,Mn,and Mg?and its contents,the contents of active components and reaction process conditions.The experimental results demonstrated that the catalyst prepared by the support calcined at 600 °C has a larger specific surface area and a smaller pore size distribution,and it has the best methanation reaction activity.When the influence of contents and its contents was investigated,it was found that addition of La,Pr,Mn and Mg can promote the dispersion of the active component Ni and increase the methanation reaction activity.The optimum addition amounts of La,Pr,and Mn are 6 wt%,and meantime the reaction temperature is 190 °C when CO is completely converted to methanation.All of these contents play a role in reducing the reduction temperature of the catalyst,especially Mn contents.Adding of the Mg has a significantly effect on increasing the specific surface area of the catalyst,and with the increasement of the Mg contents,the reaction activity will gradually decrease.The optimum addition level of is 1 wt% and at this time,the complete conversion temperature of CO is 205 °C.Excess Mg contents are unfavorable to the catalyst reduction.The addition of Ce with different contents will reduce the methanation reaction activity and the higher the contents of Ce contents,the faster the reactivity declines.With the increasement of Ni contents,the activity of the catalyst is also gradually increased.When the content of active component is 50 wt%,the reaction temperature for CO complete conversion is 175 °C.The optimum process conditions of 50Ni2 La catalyst are as follows: the reaction pressure 2 MPa,and the optimal space velocity 5000 h^-1.