Gas separation can be accomplished by flowing a mixture of gases over an adsorbent that preferentially adsorbs a more readily adsorbed component relative to a less readily adsorbed component of the mixture. Examples of such processes include temperature swing adsorption (TSA) and pressure swing adsorption (PSA). Pressure swing adsorption generally involves coordinated pressure cycling of a gaseous mixture over an adsorbent material. The total pressure is elevated during intervals of flow in a first direction through the adsorbent bed, and is reduced during intervals of flow in the reverse direction. As the cycle is repeated, the less readily adsorbed component is concentrated in the first direction, while the more readily adsorbed component is concentrated in the reverse direction.
In early work in this field, Milton's U.S. Pat. Nos. 2,882,243 and 2,882,244 described the preparation of type A and type X zeolites, and the use of these materials to separate components of gas mixtures. Other workers in the field recognized the importance of using zeolites having small and uniformly sized crystals as adsorbents for gas separation processes. Kostinko's U.S. Pat. No. 4,443,422 describes a zeolite A having an average particle size of less than 1.7 microns and a zeolite X having an average particle size of less than 2.2 microns, and further provides a detailed summary of the patent literature in the field of zeolite preparation.
Commercial gas separation and chemical gas reactor devices typically use a granular or pelletized form to hold the crystals in contact with the fluid flow. In many cases, additional benefits are realized by reducing the containment vessel volume, weight, cost, pressure drop and increasing robustness. A reduction in the volume will increase fluid velocities, which increases fluid forces on the adsorbent particles, increases fluid pressure drop across the length of the device, and also reduces the time available for mass transfer between the fluid and the adsorbent.
Hence, a need developed for rigid, low fluid resistance, high-surface-area adsorbent supports that overcome the limitations of granular adsorbent beds.
Supported adsorbent materials are known for use with TSA processes. For example, corrugated materials having adsorbent material applied thereto are known for use with TSA processes. Rigid, high-surface-area adsorbent structures, such as stacked or spirally wound adsorbent-impregnated sheet material, also are known for use in PSA devices operating at relatively low cycle frequencies. Examples of such adsorbent structures are disclosed in Keefer's U.S. Pat. Nos. 4,702,903, 4,801,308 and 5,082,473, which are incorporated herein by reference. Keefer's U.S. Pat. No. 4,801,308 discloses a PSA apparatus having an adsorbent structure comprising adsorbent sheets. Adsorbent sheets also may be adapted for use in rotary type pressure swing adsorbers. Keefer et al.'s U.S. Pat. No. 6,051,050, for example, which is incorporated herein by reference, discloses a rotating pressure swing adsorption apparatus comprising a rotor adapted to receive a plurality of circumferentially spaced adsorbent structures, each of which comprises multiple adsorbent sheets.
As outlined in U.S. Pat. No. 5,082,473, gas separation by pressure swing adsorption (PSA) is advantageously conducted using laminated, parallel passage adsorbers. These “adsorbent laminate” adsorbers provide high surface area and relatively low-pressure drop. Thin adsorbent sheets are separated by spacers which establish the gap height between adjacent sheets and thus define flow channels between each pair of adjacent sheets.
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