Urea, also known as carbamide (carbamide), is composed of carbon, nitrogen, oxygen, hydrogen consisting of an organic compound is a white crystal. One of the simplest organic compounds is the main nitrogen-containing end product of protein metabolism in mammals and certain fish species. It is also the nitrogen fertilizer with the highest nitrogen content. urea uses

Urea

As a neutral fertilizer, urea is suitable for a variety of soils and plants. It is easy to store, easy to use and has little effect on soil destruction. It is a chemical nitrogen fertilizer that is currently used in large quantities. Industrially, ammonia and carbon dioxide are used to synthesize urea under certain conditions.

Discovery Journey

In 1773, Hilaire Rouelle discovered urea. In 1828, the German chemist Friedrich Weiler first synthesized urea with inorganic ammonium cyanate (NH 4 CNO, an inorganic compound, which can be obtained by reacting ammonium chloride with silver cyanate) with Ammonium Sulfate.

Originally he intended to synthesize ammonium cyanate but got urea. The synthesis of urea unveiled the prelude to synthetic organic matter. urea uses

Thus, it proves that the error of vitality actually opens up organic chemistry (the theory of vitality believes that inorganic matter and organic matter are fundamentally different, so the inorganic matter cannot be turned into organic matter, and organic compounds can only be made by biological cells in a special kind.

It is impossible to produce by force – vitality. Mammals in mammals, amphibians and some fish contain urea; birds and reptiles emit uric acid because the amount of water used in nitrogen metabolism is relatively small.

Compound introduction

Basic Information

Chemical formula: CO (NH 22

English alias: Carbamide; Urea solution; Urea, USP Grade Carbamide, USP Grade; Urea, MB Grade (1.12007); Urea (Medical); Urea-12C; 10-Hydroxy-2-trans-Decenoic Acid

CAS No.: 57-13-6

EINECS number: 200-315-5

Molecular formula: CH 4 N 2 O

Molecular weight: 60.06

Exact quality: 60.03240

PSA: 69.11000

LogP: 0.42440

Physicochemical Properties

Properties: colorless or white needle-like or rod-like crystals, industrial or agricultural products are white with slightly reddish solid particles, odorless and tasteless. The nitrogen content is about 46.67%. urea uses

Boiling point: 196.6 ° Cat 760 mmHg.

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. Weakly alkaline.

Chemical Properties

It can form a salt with an acid. Has hydrolysis. The condensation reaction can be carried out at a high temperature to form a biuret, a Triuret, and a cyanuric acid. It is decomposed by heating to 160 ° C to produce ammonia gas and become isocyanic acid. Because it contains this substance in human urine.

urea

Named urea. Urea contains 46% nitrogen (N), which is the highest nitrogen content in solid nitrogen fertilizer.

Urea can be hydrolyzed to form ammonia and carbon dioxide under the action of acid, alkali, an enzyme (acid and alkali need to be heated).

It is unstable to heat and will be deaminated to biuret when heated to 150~160 °C. The reaction between copper sulfate and biuret is purple and can be used to identify urea. If heated rapidly, it will be deaminated to be trimeric into a six-membered ring compound cyanuric acid. (Mechanism: the first deamination to form isocyanic acid (HN=C=O), and then trimer.)

The action of acetyl chloride or acetic anhydride produces Acetylurea and Diacetylurea.

It reacts with diethyl malonate under the action of sodium ethoxide to form malonylurea (also known as barbituric acid because it has some acidity). urea uses

It can react with formaldehyde under the action of an alkaline catalyst such as ammonia to polycondense into a urea-formaldehyde resin.

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It reacts with hydrazine to form semicarbazide.

Urea is easily soluble in water and can dissolve 105 grams in 100 ml of water at 20 ° C. The aqueous solution is neutral. There are two types of urea products. Crystalline urea has a white needle shape or a prismatic crystal shape, which has strong hygroscopicity and agglomerates after moisture absorption, and the moisture absorption rate is 12 times faster than that of granular urea.

Granular urea is a translucent particle with a particle size of 1-2 mm. The appearance is smooth and the hygroscopicity is significantly improved. At 20 ° C, the critical moisture absorption point is 80% relative humidity, but at 30 ° C, the critical moisture absorption point is reduced to 72.5%, so urea should be kept open and stored in the humid summer climate. The addition of hydrophobic substances such as paraffin to the production of urea greatly reduces the hygroscopicity.

Urea Preparation

Method 1

The ammonium carbamate is synthesized by using carbon dioxide and ammonia at a high temperature and a high pressure and is formed by decomposition, absorption, transformation, crystallization, and separation and drying.

Method 2

The method is prepared by mixing the purified ammonia with carbon dioxide by a molar ratio of 2.8 to 4.5 into a synthesis tower, the pressure in the column is 13.8 to 24.6 MPa, the temperature is 180 to 200 ° C, and the residence time of the reaction material is 25 to 40 min. The urea solution containing excess Ammonia and ammonium carbamate is cooled under reduced pressure, and the urea solution after separating ammonia and ammonium carbamate is evaporated to 99.5% or more, and then granulated in a prilling tower to obtain a finished urea product.

Method 3

The final product of protein metabolism in mammals in urea. In 1922, industrial production of urea with ammonia and carbon dioxide was realized in Germany. Ammonia reacts with carbon dioxide to form a carbamate amine, which is then dehydrated to form urea. urea uses

urea

Industrial law

Production method: industrially use liquid ammonia and carbon dioxide as raw materials, directly synthesize urea under high temperature and high-pressure conditions, the chemical reaction is as follows:

2NH3 + CO2 →  NH2COONH4 →  CO(NH2)2 + H2O

 

Application field

Medical field

Dermatology uses certain agents that contain urea to increase the humidity of the skin. The occlusive dressing used for non-surgical removal of nails contains 40% urea.

The carbon-14-expiratory test for the presence of H. pylori was tested using urea containing carbon 14 or carbon 13 labeling. Because Helicobacter pylori urease uses urea to make ammonia to increase the pH in its surrounding stomach. The same principle can also test similar bacteria living in the stomach of animals.

Agricultural field

Urea is a high-concentration nitrogen fertilizer, which is a neutral quick-acting fertilizer and can also be used to produce a variety of compound fertilizers. No harmful substances remain in the soil, and long-term application has no adverse effects. Animal husbandry can be used as a feed for ruminants. urea uses

However, if the temperature is too high in the granulation, a small amount of biuret, also known as biuret, will be produced, which has an inhibitory effect on the crop. In China, the urea biuret content of fertilizers should be less than 0.5%. When the biuret content exceeds 1%, it is not possible to use seed fertilizer, seedling fertilizer, and foliar fertilizer. The urea content in other application periods should not be too much or too concentrated.

Urea

Urea is an organic Nitrogen Fertilizer. After being hydrolyzed into ammonium carbonate or ammonium hydrogen carbonate by urease in the soil, it can be absorbed and utilized by crops. Therefore, urea should be applied 4 to 8 days before the fertilizer requirement period of the crop.

Urea is suitable for use as base fertilizer and top dressing, and sometimes as a seed fertilizer. Urea is molecular in nature before conversion and cannot be absorbed by the soil. It should be prevented from being lost with water.

The ammonia formed after conversion is also volatile, so urea should be applied deep. (Soil conversion is applied to a small part of the soil dissolved in the soil solution in a molecular state, adsorbed by the soil by hydrogen bonding, and most of the other are hydrolyzed to ammonium carbonate by urease to form carbonic acid and ammonium hydroxide.

Then ammonium the root ion can be absorbed by the plant and adsorbed by the soil colloid, and the bicarbonate ion can also be absorbed by the plant. Therefore, the urea does not leave any harmful components after being applied to the soil. In addition, the biuret contained in the urea can be decomposed by the action of urease.

Ammonia and carbonic acid, the conversion of urea in the soil are affected by soil pH, temperature and moisture, and it is neutral in soil. The higher the soil temperature is, the faster the transformation is. When the soil temperature is 10 °C, the area is completely converted into ammonium. Nitrogen needs 7-10 days, 4-5 days at 20 °C, 2-3 days at 30 °C. Urea is hydrolyzed to form ammonium nitrogen, which will cause ammonia volatilization, especially alkaline or alkali. Sexual soil is more serious, so the application of urea should be applied deep, and the paddy field should be applied deep to the reducing layer.

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Urea is suitable for all crops and all soils and can be used as base fertilizer and top dressing. Since urea can accumulate a large number of ammonium ions in the soil, it will cause the pH to increase by 2-3 units. In addition, the area itself contains a certain amount of biuret. When the concentration is 500ppm, the roots of the crop will be the shoots act as inhibitors, so urea is not suitable for use as a seed fertilizer.

Urea (nitrogen fertilizer) can promote cell division and growth, making branches and leaves grow lush.

Urea uses

It can be used as a raw material for many products such as melamine, urea-formaldehyde, hydrazine hydrate, tetracycline, phenobarbital, caffeine, reduced brown BR, indigo blue B, indigo blue Bx, and MSG.

Adjust the Number of Flowers

In order to overcome the size of apples, in the small years, 5-6 weeks after flowering (the critical period of apple flower bud differentiation, the growth of new shoots is slow or stopped, the nitrogen content of leaves is decreasing), and 0.5% urea aqueous solution is sprayed on the leaves. Even spraying twice can increase the nitrogen content of the leaves, accelerate the growth of new shoots and inhibit the differentiation of flower buds, so that the annual flowering amount is suitable.

Thinning and Thinning

The flower organs of peach trees are sensitive to urea but the reaction of kneading is slow. Therefore, the use of urea to test the peach and nectarines in foreign countries has shown that the peach and nectarines need to be concentrated. (7.4%) can show good results, the most suitable concentration is 8%-12%, within 1-2 weeks after spraying, it can achieve the purpose of thinning flowers and fruit. However, under different land conditions, the response of different periods and different varieties need further testing. urea uses

Rice seed production

In the hybrid rice seed production technology, in order to increase the parental rate of heterosexuality, in order to increase the amount of hybrid rice seed production or the number of sterile lines, the erythropotox is used to reduce the degree of maternal neck or Completely withdraw; or spray parental, adjust the growth of both, so that the flowering period is synchronized.

urea

Because of the relatively high price of gibberellin, the cost of seed production is high. People used urea instead of gibberellin for experiments. 1.5%-2% urea was used at the booting stage and at the beginning of the earing stage (20% heading). The breeding effect was similar to that of gibberellin and did not increase the plant height.

Pest Control

4:1:400 parts of urea, washing powder and water can be mixed to prevent pests such as aphids, red spiders and cabbage caterpillars on fruit trees, vegetables and cotton, and the insecticidal effect is over 90%.

Urea iron fertilizer

Urea forms chelated iron with Fe 2+ in the form of a complex. This organic iron fertilizer has a low cost and is effective in preventing iron deficiency and chlorosis. In addition, 0.3% urea was added to the foliar spray of 0.3% ferrous sulfate, and the effect of controlling chlorosis was better than that of single-spraying 0.3% ferrous sulfate.

Because urea has excellent dissolving dye properties, mild reducing/oxidizing resistance, and excellent hygroscopicity (see attached table), it is an excellent dye solvent/hygroscopic agent/viscose fiber expanding agent in the textile industry. , resin finishing agent, has a wide range of uses. urea uses

The hygroscopicity of urea in the textile industry compared to other moisture absorbents: the weight ratio to itself.

Industrial application

For steel, stainless steel chemical polishing has a lightening effect, used as a corrosion inhibitor in metal pickling, also used in the preparation of palladium activation solution.

It is also used industrially as a raw material for the manufacture of urea-formaldehyde, polyurethane, and melamine-formaldehyde resins. When urea is heated to 200 ° C, solid tripolychloric acid (ie, cyanuric acid) is formed. Derivatives of cyanuric acid trichloroisocyanuric acid, sodium dichloroisocyanate, tris(2-hydroxyethyl) isocyanurate, tris(allyl) isocyanurate, tris(3,5-di There are many important applications for tert-butyl-4-hydroxybenzyl)isocyanate, triglycidyl isocyanurate, and melamine cyanurate complex. The former two are new high-grade disinfection and bleaching agents, and the total production capacity of trichloroisocyanuric acid in the world exceeds 80,000 tons.

A selective reducing agent for denitration of combustion exhaust gas, and urea for vehicles having a composition of 32.5% high purity urea and 67.5% deionized water.

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Selective Catalytic Reduction (SCR) exhaust after treatment is a technique for selective catalytic reduction of nitrogen oxides (NOx) in the automobile exhaust gas by ammonia produced by pyrolysis of urea in the combustion exhaust gas. A key and mainstream technology for reducing NOx in combustion gases such as combustion boilers and diesel engines.

The SCR system is an essential system for meeting the strict emission regulations of modern vehicles such as Euro IV/European V/Euro VI (Country IV/Country V/Country VI) regulations. Vehicle urea is called AdBlue (Ten Blue Liquid) in Europe and DEF (Diesel Exhaust Treatment Liquid) in the United States.

Commercial areas

Special plastic raw materials, especially urea formaldehyde resin;

Raw materials for certain gums;

Fertilizer and feed ingredients;

Instead of antifreeze, the salt is scattered on the street. The advantage is that it does not corrode the metal;

Strengthen the smell of cigarettes;

Giving industrial production of pretzel brown;

Some shampoos, detergent ingredients;

The composition of the first-aid refrigeration package, because the reaction of urea with water will absorb heat;

The treatment of exhaust gas from diesel engines, engines and thermal power plants with urea in vehicles can especially reduce its nitrogen oxides;

The composition of the raining agent <match salt>

Used to separate paraffin in the past because urea can form clathrates;

Refractory material

The composition of the environmentally friendly engine fuel;

The ingredients of whitening dental products;

For chemical fertilizers;

An important adjuvant for dyeing and printing.

Laboratory application:

Urea is very effective in denaturation of proteins, especially in non-covalently bound proteins. This feature can increase the solubility of certain proteins at concentrations up to 10 moles/vol. Urea can also be used to make urea nitrate.

Feed additives:

The shortage of human food resources and protein has also caused a major problem in the feed industry. The industry is actively looking for new sources of protein and expanding sources of nitrogen other than proteins, such as urea with high nitrogen content.

In 1897, Waesk et al. proposed the idea that ruminants can convert non-protein nitrogen into bacterial proteins. In 1949, CJ Watson et al. fed sheep with N15-labeled urea capsules and tested N15-containing proteins in sheep blood, liver, and kidneys four days later.

This confirms that ruminants can utilize non-protein nitrogen. In the same year, JK Looli et al. used urea as the sole nitrogen source to feed sheep and found that the sheep were able to balance the positive nitrogen, indicating that the microorganisms in the rumen of the sheep can use urea to synthesize the 10 essential amino acids required for their growth. Since then, urea and urea compounds have become feed additives for ruminants.

Application in cosmetics:

Urea is a very good moisturizing ingredient. It is found in the stratum corneum of the skin and is a major component of the skin’s natural moisturizing factor NMF. For the skin, urea has moisturizing and soft keratin, so it can prevent the stratum corneum from blocking the pores, thereby improving the problem of acne. It is used to add moisturizing ingredients to masks, skin care lotions, creams, hand creams, and other products. The addition ratio is 3-5%.