Lab Nitrogen Generator

How to Get nitrogen by Pressure Swing Adsorption

Mar 08, 2024

A nitrogen generator refers to a device that uses air as a raw material and uses physical methods to separate oxygen and nitrogen to obtain nitrogen. According to the different preparation methods, it can be divided into: cryogenic air separation, molecular sieve air separation (PSA), and membrane air separation.

 PSA nitrogen production uses air as raw material, carbon molecular sieve as adsorbent, and pressure swing adsorption principle to selectively adsorb oxygen and nitrogen through carbon molecular sieve, resulting in the separation of nitrogen and oxygen. This method is a new nitrogen production technology that rapidly developed in the 1970s.

Compared with traditional nitrogen production methods, it has the characteristics of simple process flow, high degree of automation, fast gas production (15-30 minutes), low energy consumption, adjustable product purity within a large range according to user needs, convenient operation and maintenance, low operating costs, and strong device adaptability. Therefore, it is quite competitive in nitrogen production equipment below 1000Nm3/h and is increasingly popular among small and medium-sized nitrogen users.

PSA nitrogen production has become the preferred method for small and medium-sized nitrogen users. Carbon molecular sieve can simultaneously adsorb oxygen and nitrogen in the air, and its adsorption capacity also increases with the increase of pressure, and there is no significant difference in the equilibrium adsorption capacity of oxygen and nitrogen at the same pressure. Therefore, it is difficult to achieve effective separation of oxygen and nitrogen solely based on changes in pressure. If the adsorption rate is further considered, the adsorption characteristics of oxygen and nitrogen can be effectively distinguished. Oxygen molecules have a smaller diameter than nitrogen molecules, so their diffusion rate is hundreds of times faster than nitrogen. Therefore, carbon molecular sieves also adsorb oxygen quickly, reaching over 90% in about one minute; At this point, the adsorption capacity of nitrogen is only about 5%, so the adsorbed material is mostly oxygen, while the remaining material is mostly nitrogen. In this way, if the adsorption time is controlled within 1 minute, oxygen and nitrogen can be preliminarily separated, which means that adsorption and desorption are achieved by pressure difference. When the pressure increases, adsorption occurs, and when the pressure decreases, desorption occurs. The distinction between oxygen and nitrogen relies on the difference in adsorption speed between the two, achieved by controlling the adsorption time. The time is controlled very short, and oxygen has been fully adsorbed, while nitrogen has not yet had time to adsorb, stopping the adsorption process. Therefore, pressure swing adsorption nitrogen production requires a change in pressure and the time should be controlled within 1 minute.

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