Why does a catalyst that performs well under normal pressure completely deactivate under pressure?
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When our catalyst is under normal pressure and the temperature is 250°C, the CO conversion rate on the nickel-based catalyst is 98%. However, when the pressure is 3MPa, the conversion rate is zero. When the reaction temperature increased to 500 oC, the conversion rate increased. Please ask the experts to help analyze the reasons. Could it be that at low temperature and high CO concentration, carbon-based nickel was generated and the catalyst was poisoned and deactivated? What other possible reasons could there be?
Under high pressure conditions, what is your initial reaction temperature? If the temperature is 200-230 degrees, nickel carbonyl is likely to be generated. When the temperature rises to 500 degrees, part of the nickel carbonyl will decompose and restore some activity.
Thanks for the reply, it makes sense. We initially used an initial reaction temperature of 100 oC and found that at 30 atm, the catalyst with low nickel content was completely inactive. Later, we increased the initial temperature to 300 oC and it became normal. However, for catalysts with higher nickel content, even if a lower starting temperature is used, the reaction activity is acceptable compared with normal pressure. Could it be that part of the nickel was converted into carbon-based nickel with such a high CO concentration? Isn't it enough to deactivate all active sites? I also suspect this is the reason. Are there any other factors other than this?
This post was last edited by liujingangren on 2011-9-23 08:46 3# honglvdou The starting temperature of methanation reaction on Ni catalyst must be at least 200~300 degrees, otherwise nickel carbonyl will definitely be generated. The lower the temperature and the higher the pressure, the more conducive to the formation of nickel carbonyl. The reaction conversion rate is low, and kinetic factors also need to be considered.
What is generated is nickel hydroxyl. At 230 degrees, when it is in the reactor, the inlet should be around 330 and the outlet should be 620 degrees. Therefore, it will quickly exceed 230 degrees in the early stage. The generated nickel hydroxyl is harmful to humans and poisonous to the catalyst. The conversion rate you mentioned is determined based on the temperature-pressure curve and has something to do with the catalyst!