The Mixed-Acid Process

The first step of the process is the digestion of phosphate rock with nitric acid, which results in a solution of phosphoric add and calcium nitrate (first reactor). 

Depending on the type of phosphate rock, formation of add gases containing, for example, nitrogen oxides and compounds of fluorine takes place during the digestion. In the second reactor the overflow from the first reactor is ammoniated, and scrubber liquor is added. 

The acid slurry is ammoniated with gaseous ammonia along the following reactions. 

H3PO4 + 2NH3 (NH4)2 HPO4 + 33.52 kcal (9) 2H3PO4 + Ca(N03)2 + 4NHs CaHP04 + 

The third reactor provides for final ammoniation of overflow from the second reactor. Phosphoric and sulfuric acids are added and the KCl dissolved (when NPK is produced). 

---

Environmental aspects, as well as the requirement of efficient mixing in the mixed acid process, have led to the development of single-phase nitrations. These can be divided into Hquid- and vapor-phase nitrations. One Hquid-phase technique involves the use of > 98% by weight nitric acid, with temperatures of 20—60°C and atmospheric pressure (21). The molar ratios of nitric acid benzene are 2 1 to 4 1. After the reaction is complete, excess nitric acid is vacuum distilled and recycled. An analogous process is used to simultaneously produce a nitrobenzene and dinitrotoluene mixture (22). A conversion of 100% is obtained without the formation of nitrophenols or nitrocresols. The nitrobenzene and dinitrotoluene are separated by distillation. 

---