Problem of synthetic catalyst deactivation

It’s not clear, but based on the instructions, I estimate that the air velocity should be fairly high; oxygen should be added slowly to prevent combustion in the catalyst bed.

I haven’t heard that methanol catalysts need to be passivated; only ammonia synthesis catalysts are said to require passivation. Because after the methanol catalyst is deactivated, it suffers from severe powdering upon removal, and its activity is greatly reduced after being taken out. In normal production, since some manufacturers need to shut down for extended periods, the catalyst must be passivated for protection. In such cases, a mixture of pure nitrogen and oxygen (air can also be used) is generally employed; the pressure should be kept as low as possible while maintaining a high space velocity. On this premise, as oxygenation continues, the end of reduction is considered to be reached when the oxygen content finally reaches 21%. After passivation is complete, nitrogen replacement is also required to maintain a certain positive pressure in order to protect the catalyst. Due to the special structure of the copper catalyst, even after such protection, the catalyst suffers a significant loss in activity upon reduction. But it might be a bit cheaper than replacing the catalyst.

Reply 3# The passivation of catalysts is the reverse process of catalyst reduction, and it also requires to be carried out under relatively stable conditions. Copper-based bifunctional catalysts are generally removed by direct removal. In low-pressure methanol synthesis plants, to protect the methanol synthesis tower, copper-based low-pressure methanol catalysts are usually removed at the end of their usage period, after the catalyst has been passivated. For relatively common shell-and-tube reactors, there are usually no specific requirements regarding the volume of circulating gas, but the initial concentration of O2 added for passivation is generally kept below 1% in order to prevent intense oxidation reactions that could lead to overheating and sintering of the remaining catalyst trapped in the insulation layer of the upper tube sheet, after the reduced volume of catalyst on that tube sheet has contracted.

The passivation of a catalyst is the reverse process of catalyst reduction, and it also requires to take place under relatively stable conditions. Copper-based methanol catalysts are generally removed by direct removal. In low-pressure methanol synthesis units, to protect the methanol synthesis tower, copper-based low-pressure methanol catalysts are usually removed at the end of their service life, after the catalyst has been passivated. For relatively common shell-and-tube reactors, there are usually no specific requirements regarding the volume of circulating gas. However, the initial concentration of O2 introduced for passivation is generally kept below 0.5%, and the pressure is around 0.5 MPa, in order to prevent intense oxidation reactions that could lead to overheating and sintering of the remaining catalyst trapped in the insulation layer of the upper tube sheet, after the reduced volume of that catalyst has contracted.

The system reduces the temperature of the catalyst bed to below 100°C, and after nitrogen purging is completed successfully (H2+CH4