Urea Superphosphate USP

A newcomer in this field is the USP process disclosed by AZF GRANDE PAROISSE at the IFA technical meeting in Amman [20] in 1994. 

Even though mixing urea and superphosphate is not recommended because the products react to form lumps and a sticky mixture, GRANDE PAROISSE and their partner ARMINES found that as early as 1934 Dalman [21] had reported that urea and sulfuric acid form the following complexes  

The preparation of the mixtures of urea, sulfuric acid, and water at the mole ratios, 3.6 1 and 1.8 1, is exothermic in both cases. Heat release with the first ratio is lower than vnth the second one and allows the preparation of the mixture under stable and reliable conditions at an equilibrium temperature of 60 -70°C, which is ideal to acidulate phosphate rock. 

In the manufacture of USP, the reaction of acidub--titnrmay-bewritteri-as-follows. 

It will be noticed that urea is associated with caldum sulfate rather than water of hydration [22]. But the sulfuric acid to rock ratio has not changed. 

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