Pressure swing adsorption

Overview
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 so differs from cryogenic distillation techniques of gas separation. Special adsorptive materials (e.g., zeolites) are used as a molecular sieve, preferentially adsorbing the target gas species at high pressure. The process then swings to low pressure to desorb the adsorbent material.

Using two adsorbent vessels allows near-continuous production of the target gas. It also permits so-called pressure equalisation, where the gas leaving the vessel being depressured is used to partially pressurise the second vessel. This results in significant energy savings, and is common industrial practice.

Applications of the PSA technology
One of the primary applications of PSA is in the removal of carbon dioxide (CO2) as the final step in the large-scale commercial synthesis of hydrogen (H2) for use in oil refineries and in the production of ammonia (NH3). Another application of PSA is the separation of carbon dioxide from biogas to increase the methane (CH4) content. Through PSA the biogas can be upgraded to a quality similar to natural gas.

Research is currently underway for PSA to capture CO2 in large quantities from coal-fired power plants prior to geosequestration, in order to reduce greenhouse gas production from these plants.

PSA is an economic choice for small-scale production of reasonable purity oxygen or nitrogen from air. PSA technology has a major use in the medical industry to produce oxygen, particularly in remote or inaccessible parts of the world where bulk cryogenic or compressed cylinder storage are not possible.

PSA has also been discussed as a future alternative to the non-regenerable sorbent technology used in space suit Primary Life Support Systems, in order to save weight and extend the operating time of the suit.