The February 2009 Process Paper of presents the history of the urea process;  the large scale manufacture of urea in modern times has been based on synthesis from ammonia and carbon dioxide. This process as originally suggested by Basaroff was first translated into industrial manufacture by German chemists in I. G. Farben in about 1920. 
There are two main reactions involved in the synthesis of urea from carbon dioxide and ammonia; the formation of ammonium carbamate from carbon dioxide and ammonia, and the conversion of ammonium carbamate into urea.
The June 2009 Process paper of discusses the thermodynamics of the urea process. The thermodynamic models of Frejacques and Lemkowitz, de Cooker and van de Berg were presented and the influence of various process parameters like N/C, H/C, temperature and pressure were discussed.
This paper is a follow up of these two papers and discusses the Phase Diagrams of the Urea Process; 
Together with Thermodynamics (Chemical Equilibria), Phase Diagrams (Physical Equilibria) play an important role in the urea production process. The set up of any urea plant is determined by these two aspects and to fully understand the urea process one has to understand its Phase Diagrams. 
This paper will also discuss the background of the optimum design operating parameters of the different urea processes.