Urea, a widely used chemical fertilizer globally, plays a vital role in modern agricultural production. It is not only a key substance for increasing crop yields and promoting agricultural development, but also an important component of the chemical industry. However, for many, the process of urea production remains relatively unfamiliar. This article will delve into the urea production process, revealing the underlying scientific principles and industrial technologies to help readers gain a comprehensive understanding of this important chemical manufacturing process.

The synthesis of urea can be traced back to 1828, when German chemist Friedrich Wöhler first synthesized urea in his laboratory by heating ammonium urea cyanate. This discovery marked a major breakthrough in the field of organic chemical synthesis and laid the foundation for the industrial production of urea. However, early laboratory preparation methods were inefficient and could not meet the needs of large-scale agricultural production. It wasn't until the early 20th century, with the invention and application of the Haber-Bosch process, that urea production truly became industrialized.

The Haber-Bosch process is a key technology for ammonia synthesis and is also the foundation of urea production. Fritz Haber and Carl Bosch, the inventors of this method, were awarded the Nobel Prize in Chemistry. The Haber-Bosch process, by reacting nitrogen (N₂) and hydrogen (H₂) under high temperature and pressure with a catalyst to produce ammonia (NH₃), provides the necessary raw materials for urea production. This process requires specific reaction conditions, including high temperature (approximately 500-600°C), high pressure (approximately 150-200 atmospheres), and the use of an iron-based catalyst.

In urea production, ammonia synthesis is the first crucial step. Air is the primary source of nitrogen, while hydrogen is typically produced through natural gas reforming. Natural gas is mainly composed of methane (CH₄), which reacts with water vapor at high temperature in the presence of steam to produce carbon monoxide (CO) and hydrogen (H₂). This reaction process is called steam reforming, and its chemical equation is: CH₄ + H₂O → CO + 3H₂. The produced hydrogen gas, after purification, is mixed with nitrogen gas obtained from liquefied air separation, and then reacts under high temperature and pressure in a Haber-Bosch reactor to produce ammonia gas. The reaction equation is: N₂ + 3H₂ ⇌ 2NH₃. This reaction is reversible. To improve the ammonia yield, a recycling process is required, meaning that unreacted nitrogen and hydrogen gas are reintroduced into the reactor for further reaction.