Pressure Swing Adsorption

Pressure Swing Adsorption

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Pressure Swing Adsorption

Pressure swing adsorption (PSA) is a technology used to separate some gas species from a mixture of gases under pressure according to the species’ molecular characteristics and affinity for an adsorbent material. It operates at near-ambient temperatures and differs significantly from cryogenic distillation techniques of gas separation. Specific adsorptive materials (e.g., zeolites, activated carbon, molecular sieves, etc.) are used as a trap, preferentially adsorbing the target gas species at high pressure. The process then swings to low pressure to desorb the adsorbed material.

Pressure Swing Adsorption processes take advantage of the fact that certain gases under high pressure tend to be adsorbed to the surfaces of adsorbents and solids, and therefore adsorb the desired gas. As the pressure applied during the process increases, the quantity of the gas adsorbed by the adsorbent also increases. When the applied pressure is reduced or removed, the adsorbed gas is released or we can say it has desorbed, and finally the separation process will be completed. Pressure Swing Adsorption processes can be used to separate gases from a gas mixture because because different gases tend to be attracted to different solid surfaces more or less strongly and by applying the appropriate amount pf pressure, the desired gas can be separated from other gases in the mixture.

If we pass a gaseous mixture such as air through a container containing a zeolitic adsorbent under high pressure and this adsorbent adsorbs nitrogen more intensely than oxygen, it can be expected that the exit gas is richer in oxygen because air passes through the bed and the adsorbent adsorbs most or all of the nitrogen present in the air. When the adsorbent bed reaches the end of its work cycle; That is, when its capacity to adsorb nitrogen is filled, the adsorbed nitrogen can be desorbed by reducing the pressure applied to the bed, and in addition to completing the gas separation process, the adsorbent bed can also be regenerated for reuse. In this case, the regenerated bed can be returned to produce the oxygen-rich from air cycle.

Regardless of the ability of adsorbents to differentiate between different gases, the adsorbents of pressure oscillation absorption systems are usually highly porous materials that are selected due to their high specific surface area. Common adsorbents used in the process of pressure swing adsorption are materials such as activated carbon, silica gel, alumina, resin and zeolite. Although the gas adsorbed on the surface of these adsorbents may consist of a layer as thick as one or at most several molecules, their specific surface area of ​​a few hundred square meters per gram allows the adsorbent to adsorb gas many times its own weight. In addition to being selective towards gases in a mixture, these adsorbents, specially a special type of adsorbent known as molecular sieves, separate gases based on their molecular size. In this case, the ability of the adsorbent to adsorb larger molecules is limited and we must use the appropriate model of this type of adsorbent based on the final target and the type of gas we want to separate.

The most common application of pressure swing adsorption technology is to provide hospital oxygen. Another application of this technology is its ability to remove carbon dioxide as the last step in the industrial hydrogen synthesis process. This hydrogen will eventually be used in oil refineries and ammonia production. Oil and gas refineries often use pressure swing adsorption technology to remove hydrogen sulfide from the hydrogen feed and recycle stream of water treatment and hydrocracking units. Another application of this technology is the separation of carbon dioxide from biogas to increase the proportion of methane in it. With the help of PSA technology, the quality of biogas can be improved to a quality similar to natural gas.

Zirsakht Tadbir Arian (ZETA) Company, with the help of experts in the field of gas separation, is able to use pressure swing separation/adsorption technology in order to adsorb the desired gases from a mixture of gases, and is responsible for all stages of the whole process from equipment preparation to their application.

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