What is the harm of the formation of nickel carbonyl to methanation catalysts? How should it be avoided?

It will permanently deactivate the methanation catalyst

The formation of nickel carbonyl poses a threat to methanation catalysts: it causes the active component, nickel, to be lost； Reduce catalyst activity ； If nickel carbonyl is released into the atmosphere and inhaled by humans, it can affect human health. How should it be avoided? 1. Before the gas enters the methanation reactor, its temperature is first raised to above 150 degrees, so as to allow the catalyst bed temperature to increase rapidly.

The formation of nickel carbonyl reduces the active component of the catalyst, thereby decreasing its activity. Nickel carbide is a highly harmful substance to the human body. Its freezing point is 25°C, its boiling point is 43°C, and its vapor pressure at 20°C is 320.6 mm of mercury. The vapors released into the air can cause the lungs to become inflamed; the symptoms of poisoning include dizziness, nausea, vomiting, high fever, and difficulty breathing. The main method to prevent the formation of nickel carbonyl is to prevent CO from coming into contact with nickel at temperatures below 200°C (200°C being the limit temperature below which nickel carbonyl does not form at higher CO partial pressures). If the process gas contains CO, the methanizer must be purged with N2 before the temperature drops to 200°C. When starting up at temperatures below 120°C, if an alkaline scrubbing gas containing CO is used for heating, the partial pressure of CO in the gas must be reduced to below 0.0035 MPa, which is equivalent to approximately the pressure in the methanizer

Regarding the hazards of nickel carbide, what was said above is very clear. Generally, methaneation catalysts can exert a catalytic effect mainly due to the metallic nickel component present in them. If nickel carbonyl is formed, then this nickel component will be carried out of the methaneation reactor along with the process gas, resulting in the loss of the active components in the catalyst, a decrease in its catalytic activity, and a shorter lifespan for the catalyst. As for methods to prevent the formation of nickel carbonyl, it is possible to restrict it by controlling the conditions under which it forms: 1. Maintain a temperature between 150–200 degrees and pass the gas through quickly to reduce the formation of nickel carbonyl; 2. When the methaneation reactor is in a low-temperature zone, do not introduce process gas containing CO, instead use nitrogen to raise the temperature to 300 degrees before introducing the process gas; 3. Nickel carbonyl can only form when all three factors—temperature, CO gas, and metallic nickel—are present. Therefore, in production, we can employ effective measures to avoid the formation of nickel carbonyl. Furthermore, when loading catalysts in methaneation reactors, the amount used is generally higher than the designed level in order to ensure a production margin; with proper personal safety measures in place, even if a small amount of nickel carbonyl is generated, it has little impact on production

Use an inert gas to raise the catalyst layer to over 200 degrees; this prevents problems in no time, and then process gas can be introduced – everything will be fine shortly. Is it really necessary to use process gas?

The production of nickel hydroxide is a reversible reaction; generally, its equilibrium concentration is below the ppb level, so it is considered that no nickel hydroxide is formed – it’s just present in such small amounts that it goes unnoticed. Under normal conditions of methanation, it is difficult for this to have any significant impact. Therefore, in actual production, there is no need to worry about color changes caused by nickel hydroxide; it is sufficient to keep the duration of exposure to conditions that lead to the formation of large amounts of nickel hydroxide as short as possible, as this will not have any noticeable effect on humans or the performance of the catalyst.