Patent Application
20080047436
Like reference numerals will be used to refer to like parts from Figure to Figure in the following description of the drawings.
A rotary adsorber wheel according to the invention comprises an electrically-conductive adsorbent in the physical form of a monolith having internal passageways, notably a honeycomb or other suitable form, configured as a wheel. For most applications, the adsorbent in the honeycomb includes largely an activated carbon material, notably activated carbon fibers, bonded with a suitable organic or inorganic binder. A fluid stream, typically air, containing the target volatile organic (or inorganic) species to be separated is passed through the adsorption zone (typically 330 degrees of arc) of the rotating wheel, where certain of the species are adsorbed on the adsorbent. The porosity and surface chemistry of the adsorbent are tailored to the capture of specific chemical species. Species not adsorbed pass through the wheel, thereby achieving separation. Further separations on the species discharged from the adsorption zone could be achieved by passing the effluent gas stream through a second wheel (or even more wheels), the properties of which would be specifically tailored to the adsorption of those species. Release of the captured species in the first (and subsequent wheels) is accomplished by passing a low voltage current through the adsorbent media as it passes through the desorption (regeneration) zone of the wheel (typically 30 degrees of arc). In principle, only that amount of electrical energy equivalent to the heat of adsorption of the adsorbed species need be applied, with an appropriate flow of air (or inert gas). Thus, a temperature rise, per se, to remove the adsorbed species (regenerate the adsorbent) is not necessarily required to affect removal of the adsorbed species from the adsorbent media. Through this means, yet further separation of the volatile organic compounds in the original influent gas stream is achieved.
Similar concepts can be applied to liquid phase separations. For example, a liquid stream can be passed through a rotating adsorbent wheel, resulting in adsorption of target species and rejection (separation) of others. Desorption of the adsorbed species can be accomplished by passing a clean liquid stream (aqueous or organic) through the wheel in the regeneration zone. Depending on the nature of the eluting liquid stream, electrical swing techniques can be applied to facilitate desorption.
Referring now to
The apparatus 10 includes an adsorption zone that encompasses adsorption blocks 12B to 12L in
An adsorption fluid stream is provided by a fluid delivery system to the adsorption zone. The fluid delivery system has appropriate seals and manifolds such that the fluid stream flows through the adsorption blocks in the adsorption zone. As the fluid stream contacts the adsorbent structures in the adsorption blocks in the adsorption zone, a target species of interest in the fluid stream is adsorbed on the adsorbent structures 14.
Looking now at
Thus, as the rotary wheel rotates, each adsorption block sequentially moves through the adsorption zone and the desorption zone as follows. Upon entering the adsorption zone, an adsorption block will receive an influent adsorption fluid stream provided by the fluid delivery system for the adsorption zone. The fluid stream enters one end of the adsorption block and contacts the adsorbent structures 14 in the adsorption block. The fluid stream then exits an opposite end of the adsorption block. Throughout the 330° arc of the adsorption zone, the adsorbent structures 14 adsorb a target species of interest from the fluid stream. After leaving the adsorption zone, the adsorption block enters the desorption zone as shown in
The adsorbent structures 14 can be manufactured using known extrusion methods. One such method is shown in U.S. Pat. No. 5,914,294 (which is incorporated herein by reference along with all other documents cited herein). As disclosed in U.S. Pat. No. 5,914,294, an adsorbent structure is made by mixing together activated carbon, ceramic forming material, flux material, binder, and water to make an extrudable mixture. The extrudable mixture is extruded through an extrusion die to form the monolith having the honeycomb structure. After extrusion, the extruded honeycomb monolith retains its shape while it is dried and then fired at a temperature and for a time period sufficient to react the ceramic forming materials to form a honeycomb monolith having activated carbon dispersed throughout the honeycomb structure and having sufficient strength for its intended use. In the present invention, activated carbon fibers (or other suitable adsorbents, such as zeolites) are used in place of the activated carbon powder mentioned in U.S. Pat. No. 5,914,294. Appropriate activated carbon fibers include those derived from isotropic or mesophase pitch precursors, or from other suitable materials. In general, suitable activated carbon fibers have a diameter in the range of approximately 10-50 microns. The fibers preferably have a length in the range of approximately 100-1000 microns, and more preferably in the range of 100 to 400 microns.
Many VOCs of even moderate molecular weight necessitate the use of mesoporous activated carbon for adsorption, and this alternative process is amenable to the production of wider pore carbons or the very high surface area products which can be produced through chemical activation techniques (e.g., as high as about 3,000 m2/g as measured by nitrogen BET). The adsorbent structures produced by this method provide for carbon fibers having more mesopore volume than micropore volume which aids in the adsorption of VOCs. Preferably, the adsorbent structures produced by this method provide for carbon fibers having a surface area of greater than 1,000 m2/g, preferably greater than about 2,000 m2/g, and most preferably greater than about 3,000 m2/g, the surface area being measured by a nitrogen BET method.
Looking at
In one aspect of the invention, the adsorbent structure 14 is prepared using extrusion processing conditions in which the activated carbon fibers are predominantly aligned in a preferred single direction. Looking at
Therefore, it can be seen that the invention provides an adsorption system for continuous bulk separation of volatile organic compounds, separation of gases, purification of gases, separation of organic compounds in solution, purification of organic compounds in solution, separation of inorganic compounds in solution, and purification of inorganic compounds in solution.
Although the invention has been described in considerable detail with reference to certain embodiments, one skilled in the art will appreciate that the present invention can be practiced by other than the described embodiments, which have been presented for purposes of illustration and not of limitation. Therefore, the scope of the appended claims should not be limited to the description of the embodiments contained herein.
This invention was made with United States Government support under Contract No. DE-AC05-00OR22725 between the United States Department of Energy and U.T. Battelle, LLC. The United States Government has certain rights in this invention.
