Production methods of industrial gases

I. Air separation method
1. Cryogenic distillation method
- This is one of the most commonly used methods for producing industrial gases. It is based on the difference in boiling points of different gas components in the air. First, the air is compressed, cooled and purified to remove impurities such as water, carbon dioxide, etc. For example, carbon dioxide and water are adsorbed by molecular sieves, and then the air is cooled to a near liquid state. At low temperatures, different gases begin to separate, such as nitrogen, which boils at -195.8°C, and oxygen, which boils at -183°C. Through the distillation tower, the lighter nitrogen is enriched at the top of the tower, and the heavier oxygen is enriched at the bottom of the tower. This method can produce high-purity gases such as oxygen, nitrogen and argon on a large scale. This technology is widely used in many industrial fields, such as steel, chemical and other industries, to provide them with the required industrial gases.
2. Membrane separation method
- The membrane separation method uses the difference in permeability of special polymer membranes to different gases to separate gases. When air passes through the membrane module under a certain pressure, different gases pass through the membrane at different speeds. For example, oxygen permeates through the membrane faster than nitrogen. This method has the advantages of simple operation and compact equipment. However, the purity of the gas produced is relatively low, and it is usually used in places where the gas purity requirements are not particularly high, such as small-scale industrial production or some auxiliary processes. In the food packaging industry, nitrogen produced by membrane separation can be used to preserve food and prevent food oxidation and deterioration.

2. Chemical synthesis method
1. Hydrogen synthesis
- In industry, there are many chemical synthesis methods for the production of hydrogen. Among them, the water-gas shift reaction is a common method. Using coal or natural gas as raw materials, carbon monoxide and hydrogen are first reacted to generate (such as natural gas steam reforming reaction: \(CH_4 + H_2O→CO+ 3H_2\)), and then the water-gas shift reaction \(CO + H_2O→CO_2+ H_2\) is used to further increase the hydrogen production. Hydrogen has a wide range of applications in the fields of petrochemicals, electronics, etc. For example, in the process of petroleum refining, hydrogen is used for hydrogenation refining reactions to remove impurities in petroleum products.
2. Synthesis of ammonia
- Ammonia is synthesized by the Haber-Bosch process. Nitrogen and hydrogen react under high temperature (about 400-500°C), high pressure (150-300 atmospheres) and a catalyst (usually an iron catalyst) to produce ammonia. The reaction equation is \(N_2+3H_2⇌2NH_3\). Ammonia is mainly used in the production of fertilizers and is an important raw material for nitrogen fertilizers. In addition, ammonia also has many applications in the chemical and pharmaceutical industries, such as in the production of chemical products such as nitric acid

III. Electrolysis
1. Water electrolysis to produce hydrogen and oxygen
- Water electrolysis is the decomposition of water into hydrogen and oxygen under the action of direct current. In the electrolytic cell, water is used as the electrolyte, and the electrodes are usually made of precious metals (such as platinum) or graphite. The reaction equation is \(2H_2O→2H_2↑+O_2↑\). The hydrogen produced by this method is of high purity, reaching more than 99.9%. Although the cost of producing hydrogen by water electrolysis is relatively high, it plays an irreplaceable role in some special application fields that require extremely high hydrogen purity, such as the electronics industry, fuel cells, etc. At the same time, the oxygen produced by electrolysis can also be used in some special industrial processes or medical purposes.