Urea

Abstract

Urea was discovered in urine by Rouelle in 1773 and first synthesized from ammonia and cyanic acid by Wöhler in 1828. Commercially, urea is produced by the direct dehydration of ammonium carbamate at elevated temperature and pressure. Ammonium carbamate is obtained by direct reaction of ammonia and carbon dioxide. Most urea plants are licensed by Saipem, Stamicarbon, or Toyo Engineering Corporation. Their processes are discussed in detail. Urea's biggest use is as a fertilizer. Further, it is also used in animal feeds, in the manufacture of resins, and in reducing NO x emissions by catalytic reduction. Urea is classified as a nontoxic compound.

Towards a low-carbon future: exploring green urea synthesis for sustainable agriculture

“…It is estimated that 183 °C is the optimal temperature for urea synthesis. 18,19 Since the R2 reaches equilibrium slowly, the dehydration reaction does not go to completion in the urea reactor. It is therefore necessary to recover the unconverted components from the reactor effluents.…”

“…There are two main urea synthesis technologies: Stamicarbon and Saipem. 17,19 In this study, we used the Stamicarbon technology due to its advantages over Saipem, including: (1) elimination of MP section due to higher recovery of ammonia through carbon dioxide stripping, (2) exclusion of additional water for carbamate recirculation due to its maximum recovery in synthesis section, and (3) reduction in steam requirement due to pro-duction of LP steam in HP carbamate condenser. 19 The Stamicarbon technology consists of four sections: synthesis/ high pressure, low pressure, evaporation, and hydrolysis sections, as shown in Fig.…”

“…To achieve maximum conversion, a nitrogen-to-carbon molar ratio of 3.0 is maintained in the carbamate condenser. 19,20 The reaction occurs at 138.2 bar and 167 °C, resulting in the formation of carbamate and LP steam. 18 Notably, the LP steam is produced by utilizing the heat of reaction (ΔH = −117 kJ mol −1 ) released during the carbamate synthesis.…”

A comparative overview of the electrochemical valorization and incorporation of CO2 in industrially relevant compounds

“…Thermodynamic limitations on the conversion per pass through the urea reactor, a corrosive ammonium carbamate intermediate, hydrolysis of urea and biuret formation side reactions require specific equipment and precise design of operating and recycling conditions. 165,166 In addition, the energetically voracious Haber–Bosch process and the immense urea production scale justify the quest for more sustainable urea synthesis protocols, as nowadays approximately 2% of the annual global energy consumption is attributed to urea synthesis alone.…”