Urea, also known as carbamide (carbamide), is composed of carbon, nitrogen, oxygen, hydrogen consisting of an organic compound is a white crystal. What is Urea? One of the simplest organic compounds is the main nitrogen-containing end product of protein metabolism in mammals and certain fish. It is also the nitrogen fertilizer with the highest nitrogen content.
As a neutral fertilizer, urea is suitable for a variety of soils and plants. It is easy to save, convenient to use, and has little damage to the soil. It is a chemical nitrogen fertilizer with a large amount of current use. Industrial use ammonia and carbon dioxide to synthesize urea under certain conditions.
- Chemical formula: CO (NH2)2
- Molecular formula: CH4N2O
- Molecular weight: 60.06
- Exact mass: 60.03240
- PSA: 69.11000
Physical and chemical properties
Properties: colorless or white needle-like or rod-like crystals, industrial or agricultural products are white with reddish solid particles, odorless and tasteless The nitrogen content is about 46.67%.
- Boiling point: 196.6°Cat760mmHg.
- Refractive index: n20 / D 1.40.
- Flashpoint: 72.7°C.
- Density: 1.335.
- Melting point: 132.7°C.
- Water solubility: 1080 g / L (20°C).
Solubility: soluble in water, methanol, formaldehyde, ethanol, liquid ammonia and alcohol, Slightly soluble in ether, chloroform, benzene. Weak alkaline.
It can react with acid to form salt. Has hydrolysis. Condensation can be carried out at high temperature to form biuret, tri-uret and cyanuric acid. It decomposes when heated to 160°C, and ammonia gas is generated and becomes isocyanate at the same time. Because this substance is contained in human urine,
It contains 46% nitrogen (N), the highest nitrogen content among solid nitrogen fertilizers.
It can be hydrolyzed to form ammonia and carbon dioxide under the action of acids, alkalis and enzymes (acids and alkalis need to be heated).
It is unstable to heat, and it will be deaminated into biuret when heated to 150 ~ 160℃. The reaction of copper sulfate and biuret is purple, which can be used to identify urea. If it is heated quickly, it will deaminate and trimerize into six-membered ring compound cyanuric acid. (Mechanism: first deamination to isocyanate (HN = C = O), and then trimerization.)
With acetyl chloride or acetic anhydride, acetyl urea and diacetyl urea can be generated.
Under the action of sodium ethoxide, it reacts with diethyl malonate to form malonyl urea (also known as barbituric acid because of its certain acidity).
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It can react with formaldehyde under the action of basic catalysts such as ammonia to condense into urea-formaldehyde resin.
Interaction with hydrazine hydrate to form semicarbazide.
It is easily soluble in water and can dissolve 105 grams in 100 ml of water at 20°C. The aqueous solution shows a neutral reaction. There are two types of urea products. The crystalline urea has a white needle-like or prismatic crystalline form, has strong hygroscopicity, and agglomerates after moisture absorption, and the moisture absorption speed is 12 times faster than that of granular urea.
Granular urea is a semi-transparent particle with a diameter of 1 to 2 mm. It has a smooth appearance and a significant improvement in hygroscopicity. At 20°C, the critical moisture absorption point is 80% relative humidity, but at 30°C, the critical moisture absorption point drops to 72.5%.
Therefore, urea should be kept open in the humid summer climate. Adding hydrophobic substances such as paraffin to urea production greatly reduces its hygroscopicity.
Ammonium carbamate is synthesized from carbon dioxide and ammonia at high temperature and pressure. After decomposition, absorption and conversion, it is crystallized, separated, and dried.
The preparation method is to mix purified ammonia and carbon dioxide at a molar ratio of 2.8 to 4.5 into the synthesis tower. The pressure in the tower is 13.8 to 24.6 MPa, the temperature is 180 to 200°C, and the reaction material residence time is 25 to 40 min.
The urea solution containing excess ammonia and ammonium carbamate is decompressed and cooled to evaporate the urea liquid after separating ammonia and ammonium carbamate to more than 99.5%, and then granulated in a granulating tower to obtain a urea product.
The final product of mammalian body protein metabolism in urea. In 1922, the industrial production of urea from ammonia and carbon dioxide was realized in Germany. Ammonia reacts with carbon dioxide to form urethane, which is then dehydrated to form urea.
Production method: Industry uses liquid ammonia and carbon dioxide as raw materials to directly synthesize urea under high temperature and pressure conditions. The chemical reaction is as follows:
2NH3 + CO2 → NH2COONH4 → CO(NH2)2 + H2O.
Use of Urea
It can be used as raw materials for the production of melamine, urea-formaldehyde resin, hydrazine hydrate, tetracycline, phenobarbital, caffeine, reduced brown BR, phthalocyanine blue B, phthalocyanine blue Bx, monosodium glutamate and other products in large quantities.
Adjust flower amount
In order to overcome the size of the apple field, at the young age, 5-6 weeks after flowering (the critical period of apple flower bud differentiation, the new shoot growth is slow or stopped, and the leaf nitrogen content shows a downward trend). If sprayed twice, it can increase the nitrogen content in the leaves, accelerate the growth of new shoots, inhibit the flower bud differentiation, and make the annual flower amount suitable.
The flower organs of peach trees are more sensitive to urea but the glutinous response is slower. Therefore, experiments on sparse flowers and fruits of peaches and nectarines with urea were conducted abroad. (7.4%) can show good results, the most suitable concentration is 8% -12%, within 1-2 weeks after spraying, the purpose of thinning flowers and fruits can be achieved.
However, under different land conditions, the response of different periods and different varieties need further testing.
Rice seed production
In the hybrid rice seed production technology, in order to increase the parental outcrossing rate, in order to increase the amount of hybrid rice seed production or the sterile line, the female parent is generally sprayed with red toxin to reduce the female parent’s necking or make Extract it completely; or spray the parent, adjust the growth of the two, so that the flowering period is synchronized. Because gibberellin is more expensive, its seed production cost is high.
People use urea instead of gibberellin for experiments. 1.5% -2% urea is used in the booting stage and heading stage (20% heading). Its breeding effect is similar to gibberellin and it does not increase plant height.
Use urea, washing powder, and clean water at 4: 1: 400. Stir and mix to prevent pests such as aphids, red spiders, and cabbage worms on fruit trees, vegetables, and cotton. The insecticidal effect is more than 90%.
Urea Iron Fertilizer
It forms chelated iron with Fe 2+ in the form of a complex. This organic iron fertilizer has a low cost and has a good effect in preventing iron deficiency and chlorosis. In addition, 0.3% urea is added when a foliar spray of 0.3% ferrous sulfate, and the effect of preventing green loss is better than that of a single spray of 0.3% ferrous sulfate.
- COMPOUND SUMMARY
It is an excellent dye solvent / hygroscopic agent/viscose fiber bulking agent in the textile industry because urea has excellent dissolving dye properties, as well as mild reducing/oxidizing resistance and extremely good hygroscopicity (see attached table). The resin finishing agent has a wide range of uses.
Comparison of hygroscopicity of urea with other hygroscopic agents in the textile industry: weight ratio to itself.
It has a brightening effect on the chemical polishing of steel and stainless steel. It is used as a corrosion inhibitor in metal pickling and also used in the preparation of a palladium activating solution.
It is also used industrially as a raw material for the production of urea-formaldehyde resin, polyurethane, and melamine-formaldehyde resin. When urea is heated to 200°C, solid melamine (ie, cyanuric acid) is formed.
Derivatives of cyanuric acid Trichloroisocyanuric acid, sodium dichloro isocyanate, tris (2-hydroxyethyl) isocyanurate, tris (allyl) isocyanurate, tris (3,5-di tert-butyl-4-hydroxy benzyl) isocyanate, triglycidyl isocyanurate, melamine cyanurate complex, etc. have many important applications.
The former two are new high-end disinfection and bleaching agents. The total production capacity of trichloroisocyanuric acid in the world exceeds 80,000 tons.
Selective reducing agent for denitration of combustion exhaust gas, and urea for vehicles. Its composition is 32.5% high-purity urea and 67.5% deionized water.
Selective catalytic reduction (SCR) exhaust after treatment is a technology that uses the ammonia produced by the pyrolysis reaction of urea in the combustion exhaust gas to perform selective catalytic reduction reaction with nitrogen oxides (NOx) in automobile exhaust.
The key and mainstream technology to reduce NOx, which is a harmful substance in combustion exhaust gases such as combustion boilers and diesel engines.
The SCR system is an indispensable system to meet the strict emission regulations of modern automobiles, such as Euro IV / Euro V / Euro VI (National IV / National V / National VI) regulations. Vehicle urea is called AdBlue in Europe, and DEF (diesel exhaust treatment fluid) in the United States.
- Raw materials for special plastics, especially urea-formaldehyde resins.
- Certain gum raw materials.
- Fertilizer and feed ingredients.
- Instead of spraying antifreeze on the street, the advantage is that it does not corrode the metal.
- Enhance the smell of cigarettes.
- Gives industrially produced pretzels a brown color.
- Ingredients of certain shampoos and cleansers.
- Components of a refrigeration kit for emergency use, because the reaction between urea and water will absorb heat.
- The treatment of exhaust gas from diesel engines, engines, and thermal power plants by vehicle urea can reduce nitrogen oxides in particular.
- The composition of the rain-proofing agent (combined salt).
- Used to separate paraffin, because urea can form inclusion complexes.
- Composition of environmentally friendly engine fuel.
- Ingredients for whitening dental products.
- Chemical fertilizer
- An important adjuvant for dyeing and printing.
Urea can denature proteins very effectively, especially can destroy non-covalently bound proteins very effectively. This feature can increase the solubility of certain proteins, and its concentration can reach 10 moles/volume. Urea can also be used to make urea nitrate.