Industrial oxygen production refers to the production of a large amount of oxygen, which can be roughly divided into the following methods.
1. Air freezing separation method
The main components of air are oxygen and nitrogen. Using the different boiling points of oxygen and nitrogen, oxygen is prepared from air, which is called air separation method. First, the air is pre-cooled and purified (a small amount of moisture, carbon dioxide, acetylene, hydrocarbons and other gases and dust impurities are removed from the air), and then compressed and cooled to become liquid air. Then, using the difference in boiling points of oxygen and nitrogen, the liquid air is evaporated and condensed in the distillation column many times to separate oxygen and nitrogen to obtain pure oxygen (99.6% purity) and pure nitrogen (99.9% purity). If some additional devices are added, rare inert gases such as argon, neon, helium, krypton, and xenon can also be extracted with very little content in the air. The oxygen produced by the air separation device is compressed by the compressor, and finally the compressed oxygen is loaded into high-pressure cylinders for storage, or directly transported to factories and workshops through pipelines. The use of this method to produce oxygen, although it requires a large set of equipment and strict safety operation technology, but the output is high, several dry, 10,000 cubic meters of oxygen can be produced per hour, and the raw materials consumed are only air that does not need to be bought, transported, or stored in warehouses, so since the development of the first cryogenic air separation oxygen concentrator in 1903, this oxygen generation method has been the most widely used.
2. Molecular sieve oxygen generation method (adsorption method)
Taking advantage of the characteristics of nitrogen molecules being larger than oxygen molecules, special molecular sieves are used to separate oxygen in the air. First, the compressor is used to force the dry air through the molecular sieve into the vacuum adsorber, the nitrogen molecules in the air are adsorbed by the molecular sieve, and the oxygen enters the adsorber. After a period of time, the nitrogen adsorbed by the zeolite gradually increases, the adsorption capacity weakens, and the oxygen purity produced decreases. This method of oxygen production is also called adsorption method. Recently, small oxygen concentrators that use adsorption to generate oxygen have been developed for home use.
3. Electrolytic oxygen generation method
Water is put into an electrolyzer, sodium hydroxide or potassium hydroxide is added to improve the electrolysis of water, and then direct current is passed through, and the water is decomposed into oxygen and hydrogen. For each preparation, one cubic meter of oxygen is obtained, and two cubic meters of hydrogen are obtained at the same time. The electrolysis method to produce one cubic meter of oxygen consumes 12-15 kilowatt-hours, which is very uneconomical compared with the power consumption of the above two methods (0.55-0.60 kilowatt-hours). Therefore, electrolysis is not suitable for large amounts of oxygen production. In addition, if the hydrogen generated at the same time is not properly collected, it will gather in the air, such as mixing with oxygen, and it is easy to cause an extremely violent explosion. Therefore, the electrolysis method is not suitable for home oxygen generation.
(2) Chemical oxygen production
Industrial and medical oxygen are purchased from oxygen production plants. The raw material for factory oxygen production is air, so the price is very cheap. However, the storage of oxygen (cylinders for high-pressure oxygen, special tanks for liquid oxygen), transportation and use are not very convenient. Therefore, it is difficult to transport remote mountainous areas away from oxygen plants, and some special environments such as patients' homes, high-altitude flights, submarines sailing underwater, diving operations, mine rescue, etc. are extremely inconvenient to carry huge and bulky cylinders, small cylinders have small oxygen storage capacity and short use time, so there is a chemical oxygen production method, in the compound with the largest oxygen content and easy to release, at present, chemical oxygen production mostly uses peroxide to produce oxygen.
Scientific research on inorganic peroxy compounds began in the 18th century. In 1798, the German natural scientist Alexander von Humboldt used the method of oxidizing barium oxide at high temperature to prepare barium peroxide. In 1810, French chemists Joseph-Louis Gay-Lussac and Louis-Jacques Thenard collaborated to produce sodium peroxide and potassium peroxide. In 1818, Tenar treated barium peroxide with acid, and then distilled it to discover hydrogen peroxide. For 200 years, chemists have been studying and discovering a large number of inorganic peroxy compounds. These peroxides are easy to predate oxygen when exposed to heat, water, or other chemical reagents. Commonly used peroxides are as follows:
1. Liquid peroxide (liquid oxygen producer) - hydrogen peroxide
The chemical name of hydrogen peroxide is hydrogen peroxide (H2O2), which is a colorless transparent liquid with a faint special ozone odor and is a very unstable substance, which will accelerate decomposition in many situations such as heat, alkali, and impurities. For every 5°C increase in temperature, its decomposition rate increases by 1.5 times. Even hydrogen peroxide with a concentration of 35% after dilution will decompose rapidly after more than 6 hours of pH increase (e.g. stored in alkali-containing glass bottles). Hydrogen peroxide mixed with a small amount of impurities (such as iron, copper, brass, bronze, lead, silver, chromium, manganese and other metal powders or their salts) will cause rapid decomposition and produce oxygen even at room temperature.
Hydrogen peroxide is the most basic substance in peroxide, and it is also the earliest chemical oxygen producer recognized by scientists from all over the world. Hydrogen peroxide has the benefits of higher oxygen production (14.1% available oxygen in a 30% dilution) and lower cost. However, hydrogen peroxide is a strong corrosive agent, which can cause personal injury if you are not careful, and in many cases can also cause explosion or combustion, whether it is used, stored or transported, it is a dangerous good. For example, when the vapor concentration of hydrogen peroxide reaches more than 40% under normal pressure, there is a risk of explosion if the temperature is too high. Hydrogen peroxide mixes with organic matter to produce sensitive and strong high-efficiency explosives. Hydrogen peroxide mixes with alcohols, glycerin and other organic matter, forming an extremely dangerous explosive mixture. Hydrogen peroxide is a strong oxidizing agent, corrosive to organic matter, especially textiles and paper, and can burn itself on its own when in contact with most combustibles.