Urea

Abstract

Urea was discoverd in urine by Rouelle in 1773 and first synthesized from ammonia and cyanic acid by Woehler in 1828. This was the first synthesis of an organic compound from an inorganic compound, and it dealt a death blow to the vital force theory. 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. The two reactions are usually carried out simultaneously in a high pressure reactor. Most urea plants are licensed by Snamprogetti, Stamicarbon, or Toyo Engineering. Their processes are discussed in detail. Urea's biggest use is as a fertilizer. It is also used in animal feeds, in the manufacture of resins, and in reducing automotive emissions by catalytic reduction. Urea is classified as a nontoxiic compound.

An Integrated Process Analysis for Producing Glycerol Carbonate from CO2 and Glycerol

“…This gaseous effluent is then recycled to the urea synthesis section passing through the high‐pressure carbamate condenser. In this unit, ammonia and CO 2 are condensed resulting in a highly exothermic reaction producing ammonium carbamate, which is then fed into the urea reactor [30] . This reaction is strongly controlled by the amount of heat removed in the condenser.…”

“…Urea can be produced according to a two‐step reaction. In the first one, see Figure 4a, ammonium carbamate is obtained under supercritical conditions using ammonia and CO 2 [30] . The second reaction results in the formation of urea and water from the dehydration of ammonium carbamate.…”

“…The second reaction results in the formation of urea and water from the dehydration of ammonium carbamate. The first reaction is characterized by being fast and highly exothermic, requiring heat removal [30] . The heat removal process, as well as the ammonium carbamate formation reaction are carried out in the carbamate condenser where conversion is controlled by cooling.…”

Putting carbon dioxide to work

“…Current ecological theory states that, as ecosystems approach critical thresholds (also referred to as tipping points), they become unstable and respond more acutely to external perturbations 2 . Knowledge of these thresholds is key to the sustainable management of ecosystems and to anticipating irreversible changes and/or ecological collapse.…”

“…CO 2 has been used as a raw material by the chemical industry in the past 2,3 , albeit rather sparingly, to make urea (a fertilizer and building block for the chemical industry) and cyclic carbonate (a solvent). The processes were commercialized not because they were more sustainable than other routes, but because the chemistry was available to make these valuable products economically.…”