How is oxygen made?

Oxygen production

1. Industrial oxygen production

1. Air freezing separation method

The main components in the air are oxygen and Nitrogen. Making use of the different boiling points of oxygen and nitrogen to produce oxygen from air is called air separation. First, the air is pre-cooled and purified (to remove a small amount of moisture, carbon dioxide, acetylene, hydrocarbons and other gases and dust and other impurities in the air), and then compressed and cooled to turn it into liquid air. Then, using the difference in the boiling points of oxygen and nitrogen, the liquid air is evaporated and condensed multiple times in the distillation tower to separate the oxygen and nitrogen to obtain pure oxygen (which can reach 99.6% purity) and pure nitrogen (which can reach 99.6% purity). 99.9% purity). If you add some additional devices, you can also extract argon, neon, helium, krypton, xenon and other rare inert gases that have 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 put into high-pressure cylinders for storage, or directly transported to factories and workshops through pipelines for use. Although using this method to produce oxygen requires large-scale complete sets of equipment and strict safety operating techniques, the output is high and can produce several dry or ten thousand cubic meters of oxygen per hour, and the raw materials consumed are only unnecessary and unnecessary. It does not transport air stored in warehouses, so since the first cryogenic air separation oxygen generator was developed in 1903, this oxygen generation method has been the most widely used.

2. Molecular sieve oxygen production method (adsorption method)

Using the characteristic that nitrogen molecules are larger than oxygen molecules, special molecular sieves are used to separate oxygen in the air. First, a compressor is used to force dry air through the molecular sieve into the vacuumed adsorber. The nitrogen molecules in the air are adsorbed by the molecular sieve, and oxygen enters the adsorber. When the oxygen in the adsorber reaches a certain amount (the pressure reaches a certain level ), you can open the oxygen valve to release oxygen. After a period of time, the nitrogen adsorbed by the molecular sieve gradually increases, the adsorption capacity weakens, and the purity of the oxygen produced decreases. It is necessary to use a vacuum pump to extract the nitrogen adsorbed on the molecular sieve, and then repeat the above process. This method of producing oxygen is also called adsorption method. Recently, small oxygen concentrators that use the adsorption method to produce oxygen have been developed for home use.

3. Electrolytic oxygen production method

Put water into the electrolyzer, add sodium hydroxide or potassium hydroxide to increase the electrolysis degree of the water, and then pass in direct current, and the water will Decomposes into oxygen and hydrogen. For every cubic meter of oxygen produced, two cubic meters of hydrogen are obtained. Producing one cubic meter of oxygen by electrolysis consumes 12-15 kilowatt hours of electricity, 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-scale oxygen production. In addition, if the hydrogen gas produced at the same time is not collected properly, it will accumulate in the air and, if mixed with oxygen, it will easily cause an extremely violent explosion. Therefore, the electrolysis method is not suitable for home oxygen production methods.

2. Chemical Oxygen Production

Industrial and medical oxygen are purchased from self-produced oxygen plants. The raw material for oxygen production in factories is air, so the price is very cheap. However, it is not convenient to store oxygen (cylinders are used for high-pressure oxygen and special storage tanks for liquid oxygen), transport and use. Therefore, it is difficult to transport in remote mountainous areas far away from oxygen plants. In addition, it is extremely inconvenient to carry huge and heavy cylinders in special environments such as patients' homes, high-altitude flights, underwater submarines, diving operations, and mine rescues. Small cylinders have a small oxygen storage capacity and a long service time. Short, so the chemical oxygen production method appeared. Among the compounds, inorganic peroxides contain the most oxygen and are easy to release. At present, chemical oxygen production mostly uses peroxides to produce oxygen.

Scientific research on inorganic peroxide compounds began in the 18th century. In 1798, German natural scientist Alexander von Humboldt prepared barium peroxide by oxidizing barium oxide at high temperatures. In 1810, French chemists Joseph-Louis Gay-Lussac and Louis-Jacques Thenard collaborated to prepare sodium peroxide and potassium peroxide. In 1818, Tanner treated barium peroxide with acid, and then discovered hydrogen peroxide through distillation. Over the past 200 years, chemists have continued to study and discovered a large number of inorganic peroxide compounds. These peroxides can easily release oxygen when exposed to heat, water or other chemical reagents.

Commonly used peroxides include the following:

1. Liquid peroxide (liquid oxygen generator)-hydrogen peroxide

The chemical name of hydrogen peroxide is hydrogen peroxide (H2O2). It is a colorless and transparent liquid with a weak special ozone smell. It is a very unstable substance and will accelerate decomposition when exposed to heat, alkali, mixed with impurities, etc. For every 5°C increase in temperature, its decomposition rate increases by 1.5 times. Even diluted hydrogen peroxide with a concentration of 35% will undergo rapid decomposition if the pH value increases (for example, when stored in an alkali-containing glass bottle) for more than 6 hours. A small amount of impurities (such as iron, copper, brass, bronze, lead, silver, chromium, manganese and other metal powders or their salts) mixed in hydrogen peroxide 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 generator recognized by scientists from various countries. Hydrogen peroxide has the advantages of large oxygen production (in a 30% dilution, the effective oxygen content is 14.1%) and low cost. However, hydrogen peroxide is a strong corrosive and can cause personal injury if not careful. In many cases, it can also cause explosions or combustion. It is a dangerous product whether in use, storage or transportation. For example: under normal pressure, when the vapor concentration of hydrogen peroxide reaches more than 40%, there is a danger of explosion if the temperature is too high. Mixing hydrogen peroxide with organic matter can produce sensitive and powerful explosives. When hydrogen peroxide is mixed with organic matter such as alcohols and glycerin, an extremely dangerous and explosive mixture is formed. Hydrogen peroxide is a strong oxidizing agent, corrosive to organic matter, especially textiles and paper, and can burn spontaneously when in contact with most combustibles.