Urea

Maybe there are few people who are not familiar with urea. This chemical substance is very popular among chemicals due to its existence and great importance in the human body, as well as its many uses in various industries and occupations, especially agriculture. In this article, we are trying to introduce it and its different roles.

Urea, also called carbamide, is an organic compound with chemical formula CO(NH2). This amide has two amino groups (–NH2) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.

Specifications of urea

Melting temperature: 133 to 135 degrees Celsius
Density: 2.13 grams per cubic centimeter
Solvents: water, glycerol, ethanol and acetonitrile
Chemical formula of urea: CO(NH2)2

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Urea is also known as carbamide. This amide has two amine groups attached to a carbonyl functional group. Urea plays an important role in the metabolism of nitrogen-containing compounds in animals. Urea is the main nitrogen-containing substance in the urine of mammals.

Pure solid urea is colorless and highly soluble in water and non-toxic. This chemical compound is soluble in water and insoluble in acid and alkali. The body uses this substance in many processes, including nitrogen excretion.

The liver forms this substance through the combination of two molecules of ammonia with a molecule of carbon dioxide in the urea cycle, but in the human liver, ammonia is produced during the deamination process of amino acids. It is the main end product of protein catabolism (change in shape and structure of chemicals as a result of metabolism) and constitutes about half of the total solids in urine.

Injecting urea into the body increases the osmolality of the blood plasma, which increases the flow of water from the tissues to the intracellular plasma. This increase in water flow reduces the pressure in the tissues and also increases the amount of urine.

This substance is widely used in fertilizer as a source of nitrogen and is an important raw material in the chemical industry. This compound can be created from minerals. In the laboratory, pure urea can be produced without biological raw materials. The most common impurity in urea production is biorite, which slows down plant growth.

blood urea

Urea is formed in the liver, then goes into the blood. For this substance, no significant physiological function has been observed yet, and it is separated from the blood in the kidney and enters the urine. Also, a small amount of this substance (along with sodium chloride and water) is excreted through sweat.

Blood urea (BUN) levels for adults have been reported to be around 6 to 24 mg/dL. Sometimes due to the use of certain drugs, the level of urea in the blood can change. The high or low level of urea in the blood can be caused by the lack of proper functioning of some body organs such as the heart and liver, which is diagnosed by the doctor.

Applications of urea in various industries

This material is mainly used in the production of solid fertilizers, liquid fertilizers, animal feed supplements, plastics and adhesives. Nitrogen is one of the necessary and important substances for the growth of plants, and one of the best sources for providing this element in plants is urea. Among nitrogenous compounds, urea has the highest production volume among different materials. The use of this material is constantly increasing and it is considered as the best nitrogen fertilizer in the world.

Urea in agriculture:
More than 90% of the industrial production of this substance in the world is used as a nitrogen-releasing fertilizer. Many soil bacteria have urease enzyme that catalyzes its conversion to ammonia (NH3) or ammonium ion (NH+4) and bicarbonate ion (HCO-3). Therefore, urea fertilizers are quickly converted into ammonium form in the soil.

Urea in the chemical industry:
This combination is a raw material for making two main classes of materials:

• Urea-formaldehyde resins
• Urea-melamine-formaldehyde used in marine plywood.

Urea in explosives:
This substance can be used to prepare urea nitrate, an explosive substance that is used industrially and as a part of some explosives. This substance is a stabilizer of nitrocellulose explosives.

Urea in automotive systems:
It is used to reduce NOx pollutants in exhaust gases.
In the catalytic converter, ammonia resulting from the hydrolysis of urea reacts with the release of nitrogen oxide and turns into nitrogen and water.
Cars that use these catalytic converters need to prepare diesel exhaust fluids, a solution of urea in water.

Laboratory use of urea:
This substance in concentrations of up to 10M is a powerful protein excreting substance. This property is used to increase the solubility of some proteins.

Medical use of urea:
Creams containing medicinal urea are used as topical skin products to strengthen body water. It has also been investigated as a diuretic

Other uses of urea:
Other uses of this substance include the following:

• The use of medicinal urea in cosmetic products (moisturizing cream, hair conditioner, shampoo, and hair dryers)
• Production of urea formaldehyde resin, urea formaldehyde, melamine and urea nitrate
• In fire extinguishers as a fire resistant agent
• As a yeast nutrient for fermenting sugars to ethanol
• Anticorrosive alternative to antifreeze salt
• A rich source of hydrogen in fuel cells
• Reduction of nitrogen oxide pollutants
• Using medicinal urea in teeth whitening products
• as synthetic protein
• Fabric dyeing and printing
• Diagnosis of kidney function
• in the cultivation of cereals and cotton
• Dishwashing Liquid
• humidity absorber
• Animal feed
• gardening

Uses of medicinal urea:

Medicinal urea causes hydration and is mainly used topically in the treatment of ichthyosis and hyperkeratotic skin disorders. In intravenous use, it has osmotic diuretic properties similar to mannitol and is used in the treatment of acute increase in intracerebral pressure.

Cases caused by cerebral edema and also used to reduce intraocular pressure in acute glaucoma. It is used intra-amniotically in the termination of pregnancy. In local use, this drug has hydrating and keratolytic properties. Medicinal urea is used to diagnose Helicobacter pylori infection.

Stages of urea production:

Industrial production of urea is only from ammonia and carbon dioxide. Because carbon dioxide is produced as a by-product in the production of hydrogen from natural gas or crude oil to be used in ammonia synthesis, hence the urea production unit is often connected to an ammonia synthesis unit.

In the first step, ammonium carbamate is formed from ammonia and carbon dioxide:

CO2(g) + 2NH3(l) → NH2COONH4(l)

At high pressures, this reaction is partial. Ammonium carbamate and water are in equilibrium:

NH2COONH4(l) ↔ H2NCONH2(l) + H2O(l)

At a molar ratio of ammonia to carbon dioxide of 4 to 1, temperature of 200 degrees Celsius and pressure of 200 bar, about 70% of carbon dioxide will be converted into urea.

Unconverted ammonium carbamate and unreacted ammonia should be removed from the reaction mixture (aqueous solution of urea, ammonium carbamate and ammonia). Many industrial processes for the production of this chemical compound differ from each other, especially in terms of the method of separation and the method of recovering ammonia and carbon dioxide. Minimizing the energy consumption of these large production units is very important.

One-pass production
In the first factories that used the “one-pass” process, the mixture of ammonia and carbon dioxide resulting from pressure release and thermal decomposition of ammonium carbamate was converted into ammonium nitrate or sulfate and carbon dioxide was sent out.

In modern factories, complete recovery of carbon dioxide and ammonia is carried out, so that the efficiency of ammonia reaches 99%. Because considerable product loss occurs in the subsequent pelleting step, the actual yield of the reaction is therefore even higher than this value. Current methods include:

• Return the solution
  Extraction processes (precipitation or removal)

Production of urea by solution recovery method:
In this way, the pressure of the synthesis solution after leaving the reactor is gradually released, and the released ammonia and carbon dioxide are dissolved under their own pressure in an absorbing device, in water or, conversely, in the mother solution of urea. become The pressure of the absorption solution increases step by step until the synthesis pressure is restored. By this type of reverse pressure absorption, a concentrated solution of carbamate containing a small amount of water is produced and thus the balance shifts towards the formation of urea. In those recovery processes where the first stage of decomposition is carried out at a pressure of 60 to 80 bar, less heat is required.

Production of urea by extraction method
In extraction processes, after leaving the reactor, the solution is injected on top of a layered evaporation device. In this device, the solution that flows downwards is in reverse contact with all the carbon dioxide required by the process. The gases that exit from the upper part of the evaporator along with a part of the primary ammonia are partially condensed in the compressed solution that enters from the low pressure separator, and the result is a mixture of liquid and gas. It becomes a reactor.

Because about 85% of carbamate is decomposed in the precipitation chamber, therefore, a low pressure decomposition unit is sufficient to complete the separation process. The heat produced in the high pressure condenser is converted to steam and used to operate the low pressure decomposer. Instead of precipitation with carbon dioxide, ammonia can also be used. Precipitation processes are somewhat more energetically favorable than recovery processes with high pressure decomposers.

Urea fertilizer production

The 72-77% urea solutions prepared by the above processes, after pre-treatment (for example, with the help of activated carbon to remove oil), are evaporated under vacuum to carry out the crystallization process, or in layered evaporation devices. They evaporate to form molten urea (132.7 °C). Usually, pure melted urea or molten crystals will be in the form of tablets, or granular urea is also produced. Urea fertilizers with 46% nitrogen are widely used for agricultural purposes.

This chemical compound for use as fertilizer is mainly produced in the form of small round seeds (pills) and is subjected to post-treatment to prevent the seeds from sticking together. This material easily turns into a cake due to storage. This behavior can be improved by post-treatment with formaldehyde.

Amount of Everett:
As a result of heating urea, biurethane is formed:

H2NCONH2 → H2NCONHCONH2 + NH3

The presence of this substance is harmful for some plants. Therefore, the amount of biurethane in this material should be kept low (commercial urea contains 0.3-1% biurethane).

Dangers of Urea (MSDS Urea)

This substance can irritate the skin, eyes and respiratory system. Frequent or long-term contact of the skin with fertilizers containing urea causes dermatitis. Pure urea with high concentration in the blood can be harmful. The presence of small amounts of this substance, like the amount of urea in human urine, is not dangerous. Swallowing a small amount of this chemical compound with plenty of water for an acceptable amount of time is not dangerous.

The amount of this substance in the urine of animals is more than that of humans, and this amount can be dangerous. This combination can cause algal blooms and lead to poison production. The presence of this substance in the soil obtained from the land containing fertilizers can play an important role in increasing the bloom of toxic algae.

Urea decomposes when exposed to heat and heat above its melting point, producing toxic gases and reacting violently with strong oxidants, nitrites, mineral chlorides, chlorites, and perchlorates, causing fires and explosions.

Safety guide for working with urea

Generally, materials are divided into three categories including high, medium and low toxicity in terms of toxicity. The type of dealing with the substance from a safety point of view depends on the toxicity and physical form of the substance. The most dangerous way to enter the toxic substance into the body is the respiratory system, so proper ventilation systems must be set up. In conditions of moderate toxicity, the use of normal masks works, and the presence of ventilation systems along with personal protective equipment can be more effective. Under conditions of low toxicity, the risk is eliminated.

Urea fertilizer in agriculture (for saffron and citrus fruits)

Characteristics of urea chemical fertilizer:
This organic fertilizer has the following characteristics:

• This fertilizer can be said to have replaced ammonium nitrate.
• Urea has 46% nitrogen.
• It is used as an additive for animal feed and fertilizer.
• It is the most widely used fertilizers.
• Urea is produced from the reaction between liquid ammonia and carbon dioxide.
• This fertilizer is highly effective in Asia due to the numerous rice fields. Urea fertilizer is one of the most widely used fertilizers.

Introduction of urea chemical fertilizers:

Urea is one of the chemical fertilizers widely used by farmers for soil fertility and plant growth .

In general, this fertilizer can be divided into three types:

• Urea fertilizer: This type of fertilizer has 26% nitrogen. This fertilizer is suitable for lawns because of its acidification.
• Urea fertilizer with sulfur coating: this fertilizer has 35% nitrogen. Acidic and recommended for light soils. Its price is reasonable and it is resistant to washing.
• Urea fertilizer: contains 46% nitrogen and is suitable for most soils. This type of fertilizer is not acidic.

Benefits of urea chemical fertilizer

• It improves product performance.
• Urea reduces environmental pollutants.
• The presence of 46% nitrogen in urea helps to reduce transportation costs.
• Urea does not catch fire.
• Urea is used in both solution and solid forms