Urea - class-XII

Urea is widely used as a nitrogen-rich artificial fertilizer in agriculture to promote plant growth.

Friedrich Wohler synthesized urea from ammonium cyanate in 1828, the first organic compound made from inorganic starting materials, disproving vitalism theory. Laminar is misspelled (should be Lavoisier? Neither made urea). Bergius (Beryine?) worked on hydrogenation. Haber developed ammonia synthesis.

Urea, also known as carbamide, is an organic compound. This amide has two $-NH _2$ groups joined by a carbonyl ($C=O$) functional group. Urea can be applied to soil as a solid or solution or to certain crops as a foliar spray. Urea usage involves little or no fire or explosion hazard.

Urea's high analysis, 46% $N$, helps reduce handling, storage, and transportation costs over other dry $N$ forms.

The Fauser-Montecatini process was offered by montecatini, italy. Two methods of liquid recycle was offered an aqueous recycle scheme and liquid ammonia-recycling scheme. The advantage of recycling with ammonium carbamate in liquid is that raising the conversion of ammonium carbamate to urea does not return water to the synthesis autoclave there. In the aqueous recycle process the pressure employed was 180-200$Kg/{ cm }^{ 2 }g$ and the temperature was between 180-190, the effluent from the urea synthesis is led down to a medium pressure of about 21 $Kg/{ cm }^{ 2 }g$ in first stage and close to atmospheric in the second stage of decomposer. The off gases from the first decomposer consisted mainly of ammonia with some carbon dioxide, and this was absorbed in water and recycled back to the autoclave in an aqueous solution. The ammonia and carbon dioxide from the second decomposer were absorbed in water and this dilute solution used to absorb the gases entering the first absorber.

Ammonium carbamate is produced as an intermediate in this reactor and can then be dehydrated to urea according to the following equation:

$N{ H } _{ 2 }C{ O } _{ 2 }N{ H } _{ 4 }\longrightarrow N{ H } _{ 2 }CON{ H } _{ 2 }+{ H } _{ 2 }O$

It is a reversible reaction so if large excess water is present, the reaction will move in the backward direction thus reducing the yield of urea production.

The
basic process, developed in 1922, is also called the Bosch–Meiser urea process
after its discoverers. Various commercial urea processes are characterized by
the conditions under which urea forms and the way that unconverted reactants
are further processed. The process consists of two main equilibrium reactions,
with incomplete conversion of the reactants. 

Molecular formula of Urea is ${ (N{ H } _{ 2 }) } _{ 2 }CO$.

he basic process, developed in 1922, is also called the Bosch–Meiser urea process after its discoverers. Various commercial urea processes are characterized by the conditions under which urea forms and the way that unconverted reactants are further processed. The process consists of two main equilibrium reactions, with incomplete conversion of the reactants. The first is carbamate formation: the fast exothermic reaction of liquid ammonia with gaseous carbon dioxide at high temperature and pressure to form ammonium carbamate (${ H } _{ 2 }N-COO-N{ H } _{ 4 }$).

 $2N{ H } _{ 3 }+C{ O } _{ 2 }\rightleftharpoons { H } _{ 2 }N-COO-N{ H } _{ 4 }$

The second is urea conversion: the slower endothermic decomposition of ammonium carbamate into urea and water:

$\\ { H } _{ 2 }N-COO-N{ H } _{ 4 }⇌(N{ H } _{ 2 })2CO+{ H } _{ 2 }O$

For use in industry, urea is produced from synthetic ammonia and carbon dioxide. As large quantities of carbon dioxide are produced during the ammonia manufacturing process as a by-product from hydrocarbons (predominantly natural gas, less often petroleum derivatives), or occasionally from coal, urea production plants are almost always located adjacent to the site where the ammonia is manufactured.

In general, urea will provide the most nitrogen at the lowest cost. It is easy to store and does not pose as a fire risk for long-term storage. Urea may be mixed with other fertilizers or may be applied on its own. It easily mixes up soil and doesn't affect the texture of the soil.

The first is carbamate formation: the fast exothermic reaction of liquid ammonia with gaseous carbon dioxide at high temperature and pressure to form ammonium carbamate (${ H } _{ 2 }N-COO-N{ H } _{ 4 }$).

 $2N{ H } _{ 3 }+C{ O } _{ 2 }\rightleftharpoons { H } _{ 2 }N-COO-N{ H } _{ 4 }$

More than 90% of world industrial production of urea is destined for use as a nitrogen-release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use. Therefore, it has the lowest transportation costs per unit of nitrogen nutrient.

Ammonium carbamate is a salt formed by the reaction of ammonia with carbon dioxide or carbamic acid. This compound is a white solid that is extremely soluble in water, soluble in alcohol, and only slightly volatile at room temperature. It is prepared by the direct reaction between liquid ammonia and dry ice (solid carbon dioxide).

Biuret is a chemical compound with the chemical formula ${ C } _{ 2 }{ H } _{ 5 }{ N } _{ 3 }{ O } _{ 2 }$. It is also known as carbamylurea. It is the result of condensation of two molecules of urea and is an impurity in urea-based fertilizers.

The most common impurity of synthetic urea is biuret, which impairs plant growth. Biuret is undesirable in fertilizer urea because it is toxic to crop plants, although to what extent depends on the nature of the crop and the method of application of the urea.

The ability of ammonium carbamate to make urea was first discovered in 1870 by Bassarov when he heated ammonium carbamate in sealed glass tubes at temperatures ranging from 130 to 140 $℃$. This yields urea and water in an equimolar ratio. A typical industrial plant that makes urea can produce up to 1500 tons a day. Ammonia and carbon dioxide is excessively fed to a synthesis reactor in this process. Ammonium carbamate is produced as an intermediate in this reactor and can then be dehydrated to urea according to the following equation.

${ H } _{ 2 }N-COON{ H } _{ 4 }→N{ H } _{ 2 }CON{ H } _{ 2 }+{ H } _{ 2 }O$

Wohler's synthesis is used for the preparation of urea. In this reaction ammonium cyanate is transformed into urea.
$\displaystyle NH _4(NCO) \rightarrow NH _3 + HNCO \rightarrow (NH _2) _2CO$

Biuret is a chemical compound with the chemical formula ${ C } _{ 2 }{ H } _{ 5 }{ N } _{ 3 }{ O } _{ 2 }$. It is also known as carbamylurea. It is the result of condensation of two molecules of urea and is an impurity in urea-based fertilizers.

The most common impurity of synthetic urea is biuret, which impairs plant growth. Biuret is undesirable in fertilizer urea because it is toxic to crop plants, although to what extent depends on the nature of the crop and the method of application of the urea.

When soybean meal and other plant proteins are high in price, more urea is used to replace plant protein in the ration of beef cattle and sheep. Urea is a non-protein nitrogen (NPN) compound.