A301 ammonia synthesis catalyst

The value of tortuosity factor depends on the composition and preparation methods of catalysts. The values measmed for Fei xO-based A301 ammonia synthesis catalyst are Porosity 0 = 0.36, average radius of pore is 16 nm, and tortuosity factor is 3.28.230... 

Bingchen Zhu et al used the d3mamic method and determined the twist-factor of ammonia synthesis catalyst A301 in SPSRM. The twist-factor of catalyst A301 obtained is 3.28. 

One of the keys to achieve the synthesis process at 7.5 MPa is to use ammonia synthesis catalyst used in low temperature and low pressure. A301 and ZA-5 catalysts with wiistite as precursors have very high activity at low temperature and low pressure, which establish a good foundation for developing ammonia synthetic process at low pressure and created favorable conditions. Tables 9.4-9.7 have shown the operating data of A301 loaded in the bypass device in a plant which was measured in the actual industrial conditions. 

In 1986, Zhejiang University of Technology made an important breakthrough on iron catalyst, invented a novel Fei j 0 based catalyst system.In 1992, the first Fei a 0 based catalyst (A301) at low temperatures and pressures was successfully developed, which was superior to the best magnetite-based catalysts in the world. In 1998, they further developed ZA-5 catalyst, and the running temperature was further decreased, which established the technical foundation for low pressure ammonia synthesis process. 

The basic technical characteristics of the wiistite-based catalyst (A301 and ZA-5) for ammonia synthesis are high activity at low-temperatme, and easy reduction. The following results could be obtained by comparison with the magnetite-based catalyst under the same conditions. 

In order to investigate the catalytic activity of Ru catalysts, and compare with iron catalyst, we choose the representative iron catalyst A301 with wiistite as precursor as the reference sample. A301 has the highest activity among all of the iron-based catalysts for ammonia synthesis and now it has been widely used in ammonia synthesis industry. In order to get the reliable and comparable data of the evaluation of catalytic activity, the experiment was conducted under the same conditions and four samples were filled in four reactor contained in one shell. The results were shown in Table 6.41 and Figs. 6.56-6.58. 

Ammonia synthesis is a volume-reduced reaction. In view of the thermodynamics and kinetics of the reaction, the reaction rate can be enhanced by raising the reaction pressure. Therefore, the reaction pressure should be chosen according to the catalytic activity. Figure 8.1 illustrates the relationship between activity and pressure. Figure 8.2 shows the effect of pressure on the activity of A301 catalyst. ... 

It is seen from Fig. 8.2 that the outlet ammonia concentration on A30I catalyst at 15 MPa, 400°C and 0.6 x 10 h achieved 26%, indicating A301 (ZA-5) is an excellent catalyst at low-temperature and low-pressure for ammonia synthesis. 

The ammonia synthesis reaction temperature depends on the active temperature of catalyst hence the process operator should know the active temperature of catalyst. Tables 8.3 and 8.4, and Fig. 8.4 show the relationships between the activity and temperature of ZA-5, A301, ICI74-1 and AllO-2 catalysts. 

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. 

According to the estimation from some relative experts, it is economic when the net value of ammonia is more than 8.4% in low-pressure ammonia synthesis. When the A301 catalyst is in the conditions of 7.0 MPa and space velocity of 4000-8000 h , and the net value of ammonia is 10%-12%, it can meet the needs of economy to net value. Table 9.5 shows the amoimt of inlet syngas (S in) and catalyst volume (V at) needed at isotonic pressure ammonia plant with capacity of 1000 t/d at 7.0-7.5MPa. 

Fortunately, since 1960s, the author has discerned the development of ammonia synthesis industry in China, and has joined in the research of Fes04-based, Fes04-cobalt-based, Fei xO-based and ruthenium-based catalysts. The author and his co-workers have first invented a novel generation of Fei-xO-based catalysts which is more active than the best magnetite-based catalysts in the world, and have developed successfully a series of new catalysts such as AllO-2, A301 and ZA-5 etc that are widely used in industry. 

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