Ammonia synthesis exothermic nature

Synthesis Temperature. Because of the exothermic nature of the ammonia synthesis reaction, higher temperatures increase reaction rates, but the equihbrium amount of ammonia decreases. Thermal degradation of the catalyst also increases with temperature. 

The reverse of reaction (2.1) is methanation. Used to remove residual CO traces from ammonia synthesis feedstocks, it was also developed as an important source of substitute natural gas (SNG) in the synthetic fuels industry. Since this reaction is exothermic, equilibrium yields are better at low temperatures (300-500 C). Thus, high activity is critical. Nickel must be highly dispersed. Preparational methods are required to produce small nickel crystallites. This high metal area must be maintained in the presence of extreme exothermicity, so that sintering must be avoided. This is partially accomplished through proper catalyst design, but process reactor type must also be considered. Recycle, fluidized, and slurry reactors are appropriate. 

The heart of the ammonia synthesis loop is the ammonia converter. The ammonia converter normally comprises a basket (internals) enclosed in a pressure shell. In the ammonia synthesis converter(s), due to the exothermal nature of the reaction taking place, it is normally not possible to go from the inlet to, the outlet conditions in the reactor in one adiabatic step, if a reasonable conversion is desired. Therefore, some type of cooling is required. In principle, the cooling can be applied in three different ways ... 

Reactions of ammonia and carbon dioxide forming ammonium carbamate constituted the first step, which is exothermic in nature. This is followed by the endothermic decomposition of ammonium carbamate, through dehydration, in the second step to form urea. Recently, Xiang et al. [280] reported urea synthesis at atmosphere pressure and ambient temperature. 

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