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The urea cycle converts highly toxic ammonia to urea for excretion. [1] This cycle was the first metabolic cycle to be discovered by Hans Krebs and Kurt Henseleit in 1932, [2] [3] [4] five years before the discovery of the TCA cycle. The urea cycle was described in more detail later on by Ratner and Cohen.
Ammonia volatilization reduces the economic efficiency of agricultural cropping systems. Either yield will be reduced or additional costs will be incurred from additional nitrogen fertilizer. The amount of ammonia volatilization depends on several environmental factors, including temperature, pH, and the soil water content.
The structure of the molecule of urea is O=C(−NH 2) 2.The urea molecule is planar when in a solid crystal because of sp 2 hybridization of the N orbitals. [8] [9] It is non-planar with C 2 symmetry when in the gas phase [10] or in aqueous solution, [9] with C–N–H and H–N–H bond angles that are intermediate between the trigonal planar angle of 120° and the tetrahedral angle of 109.5°.
Ammonia occurs in nature and has been detected in the interstellar medium. In many countries, it is classified as an extremely hazardous substance. [15] Ammonia is produced biologically in a process called nitrogen fixation, but even more is generated industrially by the Haber process. The process helped revolutionize agriculture by providing ...
The excretion of urea is called ureotelism. Land animals, mainly amphibians and mammals, convert ammonia into urea, a process which occurs in the liver and kidney. These animals are called ureotelic. [3] Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion.
DEF is a 32.5% solution of urea, (NH 2) 2 CO. When it is injected into the hot exhaust gas stream, the water evaporates and the urea thermally decomposes [13] to form ammonia (NH 3) and isocyanic acid (HNCO): (NH 2) 2 CO → NH 3 + HNCO. The isocyanic acid reacts with the water vapor and hydrolyses to carbon dioxide and ammonia: HNCO + H 2 O ...
While many details about Vivance’s design remain proprietary, the company uses an enzyme to convert urea to ammonia, and a sorbent mixture to remove the ammonia and other ions. In late 2023 ...
Urea is the safest to store, but requires conversion to ammonia through thermal decomposition. [ 8 ] At the end of the process, the purified exhaust gasses are sent to the boiler or condenser or other equipment, or discharged into the atmosphere.