What are the conditions of ammonia synthesis?

The synthesis of ammonia is a reversible reaction in which heat is released and the total volume of gas is reduced. Based on our knowledge of chemical reaction rates, we know that increasing the temperature, increasing the pressure, and using a catalyst can all increase the chemical reaction rate for ammonia synthesis.

Pressure:

　　Some studies have shown that at 400 ° C, pressure over 200 MPa, without the use of catalysts, ammonia can be successfully synthesised, but the actual production, too much pressure requires a large amount of power, the material requirements will be higher, which increases the production cost, therefore, affected by the power materials and equipment, China's ammonia synthesis plant is generally used in the 20MPa ~ 50MPa.

Temperature:

　　From the ideal conditions, the synthesis of ammonia at a lower temperature is favourable, but the temperature is too low, the reaction rate will be very small, so in actual production, the general selection of 500 ° C.

Catalyst:

Iron catalysts (iron based, mixed catalysts) are used, and iron catalysts are most active at 500°C, which is why ammonia synthesis is selected at 500°C. 　Finally, the amount of ammonia produced is not too much, and rapid cooling can also be taken to change the gaseous ammonia into liquid ammonia. The raw material can also be reused. However, for the iron catalyst in the ammonia reaction, O2, CO, CO2 and water vapour can poison the catalyst. But the use of pure hydrogen, nitrogen gas mixture through the poisoning of the catalyst, the catalyst activity can be restored, so this poisoning is temporary poisoning. On the contrary, compounds containing P, S, As can make the iron catalyst permanently poisoned. After poisoning, the catalyst often loses its activity completely, and even if the catalyst is treated with pure hydrogen and nitrogen gas mixture, the activity is difficult to recover. Catalyst poisoning will seriously affect the normal production. In order to prevent catalyst poisoning in industry, the reactant material should be purified to remove the poison, which will increase the equipment and raise the cost. Therefore, the development of new catalysts with strong anti-poisoning ability is an important topic.