Pressure swing adsorption

Pressure swing adsorption (PSA - Pressure Swing Adsorption ) is a physical process for the separation of gas mixtures by adsorption under pressure.

Special porous materials (such as zeolites, activated carbon ) can be used as an adsorbent. The separation efficiency can be based on two different principles: the separation due to the equilibrium adsorption or separation due to the molecular sieving effect. In the first case one of the components to be separated is adsorbed more strongly than another, characterized an enrichment of the less adsorbed component in the gas phase instead. In the latter case certain molecules penetrate quickly the porous structure of the adsorbent. The adsorbent is then passed through a reactor bed of the gas mixture, as required, the component which penetrates less into the pores, less time to flow past, that is more likely to reach the output of the reactor bed.

Litigation

The gas is at elevated pressure (typically 6-10 bar) in a fixed bed reactor which is filled with the adsorbent, is introduced so that it flows through. One or more components of the mixture ( the so-called heavy component ) will now be adsorbed. At the exit of the bed can be removed the so-called "light component ". After a while, the adsorbent bed is largely saturated, and there is a part of the heavy component with. At this moment, the process is switched so that the output of the light component is closed and an outlet for the heavy component is opened by valves. This is accompanied by a reduction in pressure. At the low pressure, the adsorbed gas is then desorbed and can be recovered at the outlet. Two mutually loaded and unloaded adsorbent thereby allowing continuous operation. To eliminate supernatant of desorbed heavy component from the adsorbent bed is rinsed with a portion of the desired product, to avoid contamination.

The precise regulation of the changeover takes place on the desired purity of the gases. Their increase in a component always occurs at the expense of its recoverable amount and the purity of the other component.

Is carried out at pressures below atmospheric pressure, the method is referred to as VSA ( Vacuum Swing Adsorption ), a pressure above atmospheric pressure and a lower, then of VPSA (vacuum pressure swing adsorption) is spoken. However, except for the pressure range used, and the measures required by these processes are all the same.

Applications

Separation of air for the production of N2 ( > 99.9%), O2 (< 97%) and argon as well as extraction / purification of hydrogen, for example, for fuel cells. A further application is the removal of CO2 from biogas or the removal of water from compressed air.

Air separation was formerly exclusively by the Linde process, but there are still the membrane process.