Urea Product Introduction
Urea, also known as carbamide, is an organic compound composed of carbon, nitrogen, oxygen and hydrogen. It is a white crystal. It is one of the simplest organic compounds and the main nitrogen-containing end product of protein metabolism and decomposition in mammals and some fish. It is also the nitrogen fertilizer with the highest nitrogen content. As a neutral fertilizer, urea is suitable for various soils and plants. It is easy to store, easy to use, and has little destructive effect on the soil. It is currently a chemical nitrogen fertilizer with a large amount of use. In industry, urea is synthesized with ammonia and carbon dioxide under certain conditions.
1. Physical properties of urea:
Chemical formula: CO(NH2)2, molecular weight 60.06, CO(NH2)2 is colorless or white needle-shaped or rod-shaped crystals, industrial or agricultural products are white slightly reddish solid particles, odorless and tasteless. Nitrogen content is about 46.67%. Density 1.335g/cm3. Melting point 132.7℃. Soluble in water and alcohol, insoluble in ether and chloroform. Weakly alkaline.
Urea can be hydrolyzed into ammonia and carbon dioxide under the action of acid, alkali and enzyme (acid and alkali require heating).
It is unstable to heat and will deaminate to biuret when heated to 150~160℃. If heated rapidly, it will deaminate and trimerize to form a six-membered ring compound, cyanuric acid. (Mechanism: first deaminate to form isocyanic acid (HN=C=O), then trimerize.)
It can react with acetyl chloride or acetic anhydride to form acetylurea and diacetyl urea.
It reacts with diethyl malonate under the action of sodium ethoxide to form malonyl urea (also known as barbituric acid, because it has a certain acidity).
It can react with formaldehyde under the action of alkaline catalysts such as ammonia water to condense into urea-formaldehyde resin.
It reacts with hydrazine hydrate to form semicarbazide.
Urea is easily soluble in water. At 20°C, 105 grams can be dissolved in 100 ml of water, and the aqueous solution is neutral. There are two types of urea products. Crystalline urea is white needle-shaped or prismatic crystal with strong hygroscopicity. Granular urea is a translucent particle with a particle size of 1 to 2 mm, with a smooth appearance and significantly improved hygroscopicity. At 20°C, the critical hygroscopicity point is 80% relative humidity, but at 30°C, the critical hygroscopicity point drops to 72.5%, so urea should avoid being stored open in the humid climate of midsummer. At present, hydrophobic substances such as paraffin are added in urea production, and its hygroscopicity is greatly reduced.
2. Agricultural application of urea:
Urea is a high-concentration ammonia fertilizer, 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. In animal husbandry, it can be used as a "feed for ruminants". However, excessively high temperatures during granulation will produce a small amount of biuret, also known as biuret, which has an inhibitory effect on crops. my country stipulates that the biuret content of urea fertilizer should be less than 0.5%. When the biuret content exceeds 1%, it cannot be used as seed fertilizer, seedling fertilizer or foliar fertilizer. The urea content in other application periods should not be too much or too concentrated.
Urea is an organic nitrogen fertilizer. It can only be absorbed and utilized by crops after being hydrolyzed into ammonium carbonate or ammonium bicarbonate by urease in the soil. Therefore, urea should be applied 4 to 8 days before the crop's fertilizer-requiring period.
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