ABSTRACT
Heat produced by the exotheric carbamate step is used in the endothermic urea step. Initially urea was produced from calcium cyanamide, but the ready availability of ammonia and improvements in high pressure technology led to the development of ammonia-carbon dioxide based processes. Urea processes can be categorized under two main groupings: external solution recycle systems and internal solution stripping systems. Ammonia and carbon dioxide are fed through a feed pump and compressor respectively into the urea synthesis reactor. Urea is stable at room temperature but will react violently with sodium hypochlorite. The aqueous urea solution is concentrated either by direct evaporation or by crystallization followed by centrifuging. Urea is used in the manufacture of urea-formaldehyde resins produced by the condensation reaction between urea and formaldehyde. Urea is a constituent of animal feeds. It is also a useful viscosity modifier for casein or starch-based paper coatings and an explosive stabilizer.
