Performance and Application of Catalysts

The ammonia synthesis reaction is affected by many factors. The fundamental basis of choosing process conditions is the thermodynamics and kinetics of the ammonia synthesis reaction, and the activity of the catalyst. In selecting the optimum conditions, it is necessary to consider many factors including thermodynamics, reaction kinetics, yields, and energy consumption. Both the process and the equipment need to be considered, all of which must be subjected to the constraints of the catalyst.  

It is well known that the yields (space-time yields) of ammonia can be calculated by (8.1) according to the mass balance of ammonia for reactor. 

Equation (8.2) is the reaction rate based on unit volrnne of catalyst. The reaction rate based on the mass of catalyst can be calculated as follows  

The above equations show that the production of ammonia depends on the inlet gas flow rate, the concentration of ammonia at the outlet and the net values of ammonia at the inlet and outlet of the converter. The production increases with increasing Vj and and from (8.1). The concentration (y ) of ammonia at the outlet is related to the pressme (p), temperature (T), space velocity (S v), H2/N2 ratio, content of inert gases ( i), type (M), volume (Vk), particle size (dp) and reduction R) of catalyst, gas pm-ity (AT), and the concentration of ammonia at the reactor inlet (y o)- These factors can be expressed by the function below. 

This chapter discusses how these factors affect the ammonia concentration at the reactor outlet, as well as how to choose the optimum operating conditions. The effect of reduction (R) had been discussed in detail in Chapter 5. 

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