Question

How is urea manufactured? What are the other nitrogenous fertilizers?

Short answer

The urea manufacturing process involves four main steps: 1. Preparation of feedstock: Ammonia and carbon dioxide are produced as the primary feedstock for urea production. 2. Formation of ammonium carbamate: Ammonia and carbon dioxide combine under high pressure and moderate temperature to form ammonium carbamate. 3. Conversion to urea: Ammonium carbamate is converted into urea by applying more heat and a slight reduction in pressure, resulting in the removal of water. 4. Recovery and purification of urea: The solid urea crystals are separated from the unreacted substances and water through crystallization and further processed for sale as fertilizer. Some other nitrogenous fertilizers include ammonium nitrate, ammonium sulfate, calcium ammonium nitrate, and diammonium phosphate.

Step-by-step solution

Introduction

Urea is an organic compound with the chemical formula (NH2)2CO, and it is widely used as a nitrogenous fertilizer in agriculture. It is produced through a chemical reaction between ammonia and carbon dioxide. We will now go through the manufacturing process, step by step.

Preparation of Feedstock

First, ammonia (NH3) and carbon dioxide (CO2) are prepared as the primary feedstock for the production of urea. Ammonia is typically produced in the Haber-Bosch process, which involves the reaction of nitrogen and hydrogen. Carbon dioxide is obtained from various sources, such as fossil fuel combustion or natural gas production.

Formation of Ammonium Carbamate

Ammonia and carbon dioxide are combined under high pressure (about 150-200 atm) and moderate temperature (180-210°C) to form ammonium carbamate (NH4COONH2). This reaction is exothermic, meaning it releases heat. The reaction can be represented as: NH3 + CO2 → NH4COONH2

Conversion to Urea

Ammonium carbamate is then converted into urea by the application of more heat and a slight reduction in pressure. During this process, water is removed from the ammonium carbamate, and the urea molecule is formed. The reaction can be represented as: NH4COONH2 → (NH2)2CO + H2O

Recovery and Purification of Urea

After the formation of urea, the mixture is cooled, and the solid urea crystals are separated from the unreacted substances and water through a process called crystallization. The remaining liquid may undergo further processing to recover any remaining urea. The urea crystals obtained are usually around 95-99% pure. These crystals can be further purified, granulated and packaged for sale as a fertilizer.

Other Nitrogenous Fertilizers

In addition to urea, there are several other nitrogenous fertilizers used in agriculture. Some of these include: 1. Ammonium nitrate (NH4NO3) - It is created by the reaction of ammonia with nitric acid and is a common nitrogen fertilizer due to its high nitrogen content and good solubility in water. 2. Ammonium sulfate [(NH4)2SO4] - Produced by reacting ammonia with sulfuric acid, it is another popular nitrogen fertilizer, particularly in acidic soils. 3. Calcium ammonium nitrate (Ca(NO3)2 • NH4NO3) - A mixture of ammonium nitrate and calcium carbonate, it is less prone to caking compared to pure ammonium nitrate and provides both nitrogen and calcium to plants. 4. Diammonium phosphate [(NH4)2HPO4] - Formed by reacting ammonia with phosphoric acid, it provides both nitrogen and phosphorous, making it an effective multi-nutrient fertilizer. These are just a few examples of other nitrogenous fertilizers available for agricultural use. The choice of fertilizer depends on factors such as soil composition, crop requirements, and environmental conditions.