What is Urea or Nitrogen 46% Fertilizer?

Urea or Nitrogen 46%
Urea, also known as Nitrogen 46%, is a white, odorless crystalline solid with a low melting point and high water solubility. Produced primarily from natural gas and petroleum feedstocks, it is classified as a petrochemical product.

Neutral in nature—neither acidic nor alkaline—urea has a density of about 1.32 g/cm³ at room temperature. Because it contains a high concentration of nitrogen, it is one of the most widely used fertilizers in agriculture, providing an essential nutrient for healthy plant growth.

History of Urea
The story of urea dates back to 1828, when German chemist Friedrich Wöhler first synthesized it in a laboratory. He created this organic compound by converting the mineral substance ammonium cyanate, a discovery that marked a milestone in organic chemistry.

Industrial-scale production later advanced with the Bosch–Meiser process, developed in the early 20th century. (The process is often linked to work from the 1920s, though some sources cite later refinements.) In this method, urea is produced by reacting ammonia and carbon dioxide under high pressure and temperature.

Today, several modern techniques are used to manufacture urea, but they all rely on the same basic principle of combining ammonia with carbon dioxide to create this essential nitrogen-rich compound.

Different Methods of Producing Urea

Several industrial methods are used to manufacture urea. The two primary processes are outlined below:

1. Bosch–Meiser Process

In this method, ammonia (NH₃) and carbon dioxide (CO₂) react under high temperature and pressure to form ammonium carbamate. This intermediate compound then decomposes into urea and water.

2. Haber–Bosch Process

The Haber–Bosch process is used first to synthesize ammonia. Here, nitrogen (N₂) from the air reacts with hydrogen (H₂) at high pressure and temperature in the presence of an iron catalyst. The ammonia produced is then fed into the Bosch–Meiser urea process to create urea.

This method is particularly important because it taps into atmospheric nitrogen, making large-scale nitrogen fertilizer production possible.

Urea Manufacturing Process (Haber–Bosch Method)

The production of urea begins with the reaction of ammonia (NH₃) and carbon dioxide (CO₂) to form ammonium carbonate, which then decomposes into urea and water.

To concentrate the urea solution, industries use techniques such as vacuum concentration, evaporation, or crystallization. During this stage, the molten urea is transformed into a solid form.

In the final solidification step, the product is shaped into either granular or prilled urea, depending on the intended application.

Difference Between Granular and Prilled Urea

Granular Urea
Granular urea is produced by cooling molten urea on a plate and then crushing it into particles measuring about 1–4 mm in diameter. Its larger size and resistance to moisture make it especially popular in agriculture, where it performs well in a variety of soil and crop conditions. For more details on its physical properties, refer to the urea 46 specification.

Prilled Urea
Prilled urea is made by spraying molten urea from a prill tower, forming small spherical particles typically 0.85–2.8 mm in diameter. Its smaller size makes it easier to handle, transport, and dissolve, which is why it is commonly used in the manufacture of plastics, resins, and adhesives.

Screening and Packaging
After formation, both types undergo a screening process to ensure uniform particle size. The finished urea is then either packaged or shipped in bulk for industrial and agricultural applications.