Synthesis Processes and Catalysts

It is known from analysis of the thermodynamics that the process of synthesis ammonia from H2 and N2 is hmited by the thermodynamic equilibrium, so the outlet content of ammonia obtained is below about 15% imder general industrial conditions. In order to increase the utilization ratio of H2 and N2, the un-reacted H2 and N2 should be recycled. Therefore, the product of ammonia should be separated from the mixed gas, and then the im-reacted H2 and N2 are circulated by circle-compressor for next reaction. The sjmthesis of ammonia, separation of ammonia and the recycle of unreacted H2 and N2 make up the recycle process flow for the ammonia synthesis. 

The process flow of sjmthesis ammonia has changed a lot in one century, but so far the basic steps are the same including the final purifying of the syngas, the synthesis of ammonia, the utihzation of reaction heat, separation of ammonia, recompression of the recycle gas, the discharge of the inert gas, the callback, use of H2 and so on. 

Catalysts Process Synthesis pressure/MPa Energy consumption/(GJ t ) 

Classical iron Small- and medium-scale plant 30.4 54 

---

The top reaction, between carbon monoxide and hydrogen to form methanol, is the basis for all conunercial methanol synthesis plants, and is desirable. This reaction is carried out using a heterogeneous catalyst containing copper and zinc oxide, and is quite reversible at conunercial reaction conditions. The bottom, undesirable reaction is referred to as methanation. It is relatively slow with today s methanol synthesis processes and catalysts. However, methanation can be important if die catalyst becomes contaminated with elements such as nickel and iron, which catalyze the methanation reaction. 

---