Almost all industrial gases, whether they are inert, flammable, acid, reactive, or oxidizing, can be purified or dried using what is commonly known as adsorption technology. Adsorption technology is used to remove targeted impurities or separate bulk mixtures. This technology is used in many industrial gas treatment processes including biogas separation and purification, hydrogen recovery, air separation, and oxygen enrichment for medical applications as well as drying applications for air, natural gas, carbon monoxide, carbon dioxide, sulfur dioxide, acetylene, propylene, propane, and syngas
Adsorption is a process that occurs when a gas or liquid (solute) accumulates on the surface of a solid or a liquid (adsorbent) forming a film of molecules or atoms (adsorbate). This process differs from the absorption process, in which a substance diffuses into a liquid or a solid to form a solution.
Adsorbents are a class of materials that have the property whereby gas molecules adhere to their surface. Because some molecules will adhere preferentially over others, by selecting the right adsorbent material it is possible to selectively remove an impurity from a gas stream. To maximize capacity, adsorbents are made with an extremely high porosity, with the result that for a small quantity of adsorbent material, there is a very high surface area available for the impurities to be adsorbed. Once an adsorbent is laden with adsorbed molecules, it can be regenerated for re use in two ways. The first method is to reduce the pressure from normal operating conditions of 80 pounds per square inch to 160 pounds per square inch down to between 0 and 1 pound per square inch, at which point most of the adsorbed molecules are released. The second method is to regenerate using heat. By raising the adsorbent to temperatures of 200°C or higher, the adsorbed molecules are driven off. The adsorbent must then be cooled down to be ready for the next cycle.
The adsorbents and zeolites used by Xebec differ from conventional adsorbents in that their pore sizes are smaller and more orderly structured. This means that some molecules are physically too large to enter the pore, so that the selectivity for adsorption is determined by which molecules can actually enter the zeolite pore. In this way they act just like a sieve, therefore their common name - molecular sieve. One important property of adsorbents is their ability to remove impurities at very low concentrations. This means they can be used to purify a gas to a very high degree of purification. Certain adsorbents have larger pore sizes and are both used for removal of bulk quantities of impurities since they have a high loading capacity needed when impurity concentrations are high.
The purification of a gas implies the removal of a trace impurity or contaminant. The drying of air can be classified in this category since water molecules, considered as the contaminant in drying applications, are selectively adsorbed onto an adsorbent material as air passes over it. The impure moist air passes through the adsorbent material and the purified dry air is then released. Once the adsorbent material is saturated with water molecules, the adsorbed water can be released by changing the conditions under which it originally adhered in the first place. This regenerates the adsorbent so it can be used again. The principles of adsorption are not limited to the extraction of water, extending too many more types of gas purification. For instance, if the appropriate adsorbent material is used and other conditions are favorable, it is possible to selectively remove the carbon dioxide from air, to separate nitrogen from oxygen, or to dry any other gas such as natural gas.