Editing Nitrophosphate process (section)

{{Short description|Method to produce nitrogen fertilizers}}
The '''nitrophosphate process''' (also known as the '''Odda process''') is a method for the industrial production of [[nitrogen]] [[fertilizer]]s invented by [[Erling Johnson]] in the municipality of [[Odda, Norway]] around 1927.

The process involves acidifying [[phosphate rock]] with dilute [[nitric acid]] to produce a mixture of [[phosphoric acid]] and [[calcium nitrate]].

:<chem>Ca5(PO4)3OH + 10 HNO3 -> 3 H3PO4 + 5 Ca(NO3)2 + H2O</chem>

The mixture is cooled to below 0&nbsp;°C, where the calcium nitrate crystallizes and can be separated from the phosphoric acid.

:<chem>2 H3PO4 + 3 Ca(NO3)2 + 12 H2O -> 2 H3PO4 + 3 Ca(NO3)2.4H2O</chem>

The resulting calcium nitrate produces nitrogen fertilizer.  The filtrate is composed mainly of phosphoric acid with some nitric acid and traces of calcium nitrate, and this is neutralized with [[ammonia]] to produce a compound fertilizer.

:<chem>Ca(NO3)2 + 4 H3PO4 + 8 NH3 -> CaHPO4 + 2 NH4NO3 + 3(NH4)2HPO4</chem>

If [[potassium chloride]] or [[potassium sulfate]] is added, the result will be NPK fertilizer.  The process was an innovation for requiring neither the expensive [[sulfuric acid]] nor producing [[gypsum]] waste (known in the context of phosphate production as [[phosphogypsum]]).

The calcium nitrate mentioned before, can as said be worked up as calcium nitrate fertilizer but often it is converted into [[ammonium nitrate]] and [[calcium carbonate]] using [[carbon dioxide]] and ammonia.

:<chem>Ca(NO3)2 +  2 NH3 + CO2 + H2O -> 2 NH4NO3 + CaCO3</chem>

Both products can be worked up together as straight nitrogen fertilizer.

Although Johnson created the process while working for the [[Odda Smelteverk]], his company never employed it.  Instead, it licensed the process to [[Norsk Hydro]], [[BASF]], [[Hoechst AG|Hoechst]], and DSM.  Each of these companies used the process, introduced variations, and licensed it to other companies.  Today, only a few companies (e.g. [[Yara International|Yara]] (Norsk Hydro), [[Acron Group|Acron]], [[EuroChem]], [[Borealis AG|Borealis Agrolinz Melamine GmbH]], Omnia, [[Gujarat Narmada Valley Fertilisers & Chemicals|GNFC]]) still use the Odda process.  Due to the alterations of the process by the various companies who employed it, the process is now generally referred to as the nitrophosphate process.