Proper use of catalysts

The performance of a catalyst for ammonia s3mthesis is related to its quality, the reduced conditions, its proper use and maintenance. Scientifically sound management and use of a catalyst will not only slow down the decline in catalytic activity, but also render its operation economically. 

A catalyst just after reduction should not bear a prematurely increased the load of production the operation temperature should not be too high or fluctuates too often. The inlet temperature and hot spots in the catalyst bed should be controlled well, and the amount of poisons in the S3mthesis gas kept low to prevent poisoning. Stabilizing the proportion of H2/N2 ratio should be controlled within a small range, so as not to cause the bed temperature to fluctuate. 

The hot spot temperature of the catalyst used in different period(s) is shown in Table 8.41. Under the condition of steady production capacity and stable catalytic activity, the hot spot temperature should be maintained as low as possible. This will not only benefit in maintaining the low-temperature activity of the catalyst, but also enhances the equilibrium of the ammonia synthesis reaction. Especially for the A301, ZA-5 and other low-temperature and low-pressure catalysts, because the temperature for high activity is low, the hot spot temperature should be strictly controlled and should not exceed the designed limit. When operators who were used to using the medium-temperatme catalyst change to the new low-temperature catalyst, they are not accustomed to operate the process at low temperatures. They might raise the hot spot temperatme intentionally or unintentionally, which would reduce the catalyst utilization efficiency and shorten the catalyst life. This issue has been discussed in Section 8.1.2.4. 

Type (heat transfer way) initial stage middle stage end stage 

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The hydrogenation of phenols may proceed more readily than other aromatic compounds under proper use of catalyst and conditions. Over Ni-kieselguhr, hydroxyben-zenes such as phenol, catechol, and resorcinol are hydrogenated rapidly at 120-150°C under high pressure. Usually, the yields of the corresponding cyclohexanols are quantitative except for resorcinol, which gave only a 90% yield of cyclohexane-1,3-diol.70 An example is shown in eq. 11.11 for the hydrogenation of phenol. 

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