Passivation of methanol synthesis catalysts

There’s something wrong with your question – if the catalyst is still highly active, who would go ahead and deactivate it? It is passivated only when not in use, or during necessary maintenance work. Passivation certainly has an impact on the activity of catalysts. I don’t have specific figures to indicate exactly how large it is.

The impact on synthetic ammonia catalysts is minimal, but the effect on copper catalysts can be significant. If passivation is necessary, it is recommended to use N2 from air separation combined with pure oxygen for passivation, rather than air.

Generally, catalysts that have been passivated are not intended for use; if they are used anyway, the losses can be even greater. Due to repeated oxidation-reduction processes, the internal grains grow larger, resulting in a reduction in the specific surface area. If it has been in use for a long time, the catalyst is likely to be poisoned, for example, the sulfur content may be very high. If the equipment leaks or the catalyst needs to be removed for other reasons, most of it is no longer useful; of course, there is no loss in activity as mentioned by the original poster. This question might need to be explained by experts in catalysts.

My humble opinion: 1. No matter what the space velocity is during passivation, dead zones will always exist; as a result, when the catalyst is removed, it’s inevitable that some of its activity and quantity will be lost. I’ve had such an experience myself； 2. The operating temperature of the copper catalyst ranges from 210 to 300 degrees, with it usually being kept between 210 and 270 degrees. During passivation, intense heat is released, and the temperature is difficult to control; this leads to grain growth and a decrease in the internal specific surface area, which severely affects the activity of the material after regeneration. Even if it can be used after regeneration, the low one-way conversion rate of methanol leads to catalyst deactivation, reducing its value for reuse and possibly making it not worth it ； 3. During the catalyst deactivation process, toxins can enter the catalyst; under normal conditions, 0.3% of toxins is sufficient to cause the catalyst to become inactive. Controlling this process during deactivation is also a challenge. 4. If the catalyst is to be passivated, it is usually done when the equipment malfunctions and the catalyst has already suffered severe damage; whether passivation is necessary is debatable ； 5. Before replacing the catalyst, it must be passivated, which is not considered here.

For copper-based catalysts used in methanol synthesis, the impact is significant; however, in most cases, passivation occurs when it’s time to replace the catalyst. For example, in cases of burn damage or permanent poisoning, it has to be passivated only when removing him from there

Passivation is a form of destructive protection, and it is generally not applied after production has begun.

How great is the loss? Are there any relevant data?

There probably aren’t any specific figures, as no one would use a usable catalyst for experiments. Nor would anyone use this method to “protect” the catalyst. It is only passivated when removal is necessary when it is not active, but this is not for protection either; rather, it is done because removing it without passivation would cause it to react with oxygen in the air and release a large amount of heat. For safety reasons, it is passivated before being removed.

The deactivation of catalysts is not only used for catalyst replacement; there are many other possibilities as well, such as shutting down the reaction process or regenerating the catalyst； There is specialized research on passivation; the amount of loss depends on the specific control conditions