What are the methods for separating oxygen in the air？

    The main components in the air are oxygen and nitrogen, which exist in molecular states respectively. Molecules are the smallest particles that maintain their original properties. The diameter is in the order of 10-8cm, and the number of molecules is very large, and they are constantly in irregular motion. Therefore, the oxygen, nitrogen and other molecules in the air are uniformly It is more difficult to separate the ones that are mixed with each other. There are currently three separation methods.

(1) Low temperature method (liquid oxygen plant)

The air is first compressed and expanded to cool down. Until the air is liquefied, the vaporization temperatures (boiling points) of oxygen and nitrogen are different (under atmospheric pressure, the boiling point of oxygen is 90K, and the boiling point of nitrogen is 77K). Nitrogen with a low boiling point is relatively low. Due to the feature that oxygen is easy to vaporize, the higher temperature vapor and the lower temperature liquid are kept in contact with each other in the rectification tower. More nitrogen in the liquid evaporates, and more oxygen in the gas condenses. Makes it rise. The nitrogen content in the vapor continues to increase, and the oxygen content in the downstream liquid continues to increase, so as to achieve the separation of air. To liquefy air, it is necessary to cool the air to a temperature below 100K. This type of refrigeration is called deep freezing; and the process of separating liquid and air by using the boiling point difference is called rectification. The low-temperature method to achieve air separation is a combination of deep cooling and rectification. Is currently the most widely used air separation method

(2) Adsorption method (PSA oxygen generator)

It allows air to pass through an adsorption tower filled with a certain porous material and one-separated sieve. It uses molecular sieves to selectively adsorb different molecules. Some molecular sieves have strong adsorption performance for nitrogen, allowing oxygen molecules to pass through. Therefore, oxygen with higher purity can be obtained; because the adsorption capacity of the adsorbent is limited, when the adsorption of a certain molecule reaches saturation, there is no ability to continue adsorption, and the adsorbed material needs to be driven out to restore the adsorption capacity. This process is called "regeneration". Therefore, in order to ensure continuous gas supply, more than two adsorption towers need to be used alternately. The method of regeneration can be the pressure reduction method ((PSA). This method has a simple process, convenient operation and low operating cost, but it is more difficult to obtain high-purity products. The oxygen purity of the product is about 93%. Moreover, it is It is only suitable for separation devices with a capacity that is not too large (less than 4000m3/h).

(3) Membrane separation method

It uses the permeation selectivity of some organic polymer membranes. When air passes through the membrane (0.1μm) or hollow fiber membrane, the rate of oxygen passing through the membrane is about 4 to 5 times that of nitrogen, thereby achieving oxygen and nitrogen The separation method is simple in device, convenient in operation, fast in start-up, and low investment. However, the oxygen-enriched concentration is generally suitable for medium and small-sized, so it is only suitable for oxygen-enriched combustion and ceremonial health care.