Ammonia manufacturing process

Raw materials :

  • NH3 1000 kg (85% yield)
  • Hydrogen → 210 kg (synthesis gas) 
  • Nitrogen →960 kg (air or air liquefaction process)
  • Catalyst →0.2 kg 

Raw material sources:

  • Nitrogen – it is taken form air 
  • Hydrogen – It can be synthesized from  feed stock like Natural gas,Coke oven gas 

Catalysts used :

  • Iron with added promoters e.g. oxides of aluminium, zirconium or silicon at about 3% concentration and potassium oxide at about 1%.
  • Promoters prevent sintering and make the catalyst more porous.
  • Iron catalysts lose their activity rapidly, if heated above 520°C.
  • Also, is deactivated by contact with copper, phosphorous, arsenic, sulfur and CO.

Purification of raw gases :

  • The liquid nitrogen wash has the function to remove residual impurities like CO, Ar and CH4 from a crude hydrogen stream and to establish a stoichiometric ratio H2/N2 = 3:1.
  • CO must be completely removed, since it is poisonous for the NH3 synthesis catalyst.

Manufacturing process:

  • Ammonia is manufactured by passing mixture of pure H2 and N2 in the proportion of 3:1 by volume under pressure (100–1000 atm depending on conversion required).
  • Reaction  :  N2(g) + 3H2(g) → 2NH3(g)    ΔH = -22.0 kcals
  • N2 and H2 are first passed through filter to remove compression oil and additionally through a high temperature guard converter (convert CO and CO2 into CH4 and remove traces of H2O, H2S, P and As).
  • The relatively cool gas is added along the outside of converter tube walls to provide cooling.
  • The preheated gas flows next through the inside of the tube which contains promoted iron catalyst at 500-550 0C.
  • The NH3 product, with 8-30% conversion depending on aprocess conditions, is removed by condensation, first with water cooling and then NH3 refrigeration.
  • The unconverted N2–H2 mixture is recirculated to allow an 85-90% yield.