ELECTED WALL EXTRUDED ACTIVATED CARBON FILTER FIELD OF THE INVENTION The present invention relates to the novel thin-walled extruded activated carbon filter, especially a filter for use in a process of purifying water at room temperature to remove particulate matter. a sub-micron size. BACKGROUND OF THE INVENTION Currently used in filtration systems, where the removal of particles in the range of 99.5% or more of particles of a size from 0.5 μm to 0.8 μm, are ceramic candle filters. Such ceramic filters are designed primarily for high temperature applications. However, due to the lack of availability of suitable filters with lower costs, which still provide the degree of removal of sub-micron particulates, such ceramic filters have also been used for filtration or purification processes even when not high temperatures are required, such as the processes at room temperature for water purification. Such use of ceramic filters, when the properties of high temperatures are not required, result in a greatly increased cost in filtration or purification due to the expensive nature of such ceramic filters.
Although activated carbon filters have been known and used in water purification processes, to date it has not been possible to achieve the level of particulate removal mentioned above, using activated carbon filters. Therefore, it is desirable that the highly effective thin-walled activated carbon filter be available for use in low temperature filtration and purification processes to replace the excessively expensive ceramic filter units currently employed to obtain 99.5% or more of Removal of particulates with a size of 0.5 μm to 0.8 μm. It has been discovered that a thin-walled, extruded activated carbon filter tube capable of removing 99.5% or more of particles with a sub-micron size ranging from 0.5 μm to 0.8 μm of water or other liquids at room temperature is provided in accordance with this invention when extruding such a thin-walled activated carbon filter of a composition comprising an essentially homogeneous mixture of: (a) from about 75% to 85% by weight of the activated carbon particles; and (b) about 15% to 25% by weight of a thermoplastic binder powder having an average particle size of about 5 μm to 25 μm;
wherein the particles of activated carbon comprise: (a) about 18% to 50% by weight of the activated carbon particles passing through a 325 mesh screen, ie a fraction of -325 mesh, and (b) about 50% to 82% by weight of the activated carbon particles passing through a 200 mesh screen and retained in a 325 mesh screen, ie a fraction of -200 to +325 mesh. By a thin-walled filter tube of the present invention means that the activated carbon filter tube has a wall thickness of 12.7 mm (0.5 inches), or less, more preferably 7.62 mm (0.3 inches) or less. A thin-walled activated carbon filter can be extruded from said composition by the continuous extrusion process disclosed in my U.S. Pat. previous 5, 189, 092, and will have a sufficient density to remove 99.5% of particles of a size of 3 microns or larger, preferably sufficient to remove 99.5% of particles of an approximate size of 0.5 μm to 0.8 μm. BRIEF DESCRIPTION OF THE DRAWINGS The Figure is a cross-sectional view of an activated carbon filter of the present invention.
Although my prior patent 5,189,092 discloses the extrusion of compositions comprising particles of activated carbon and a thermoplastic binder powder to produce the filtration articles, the activated carbon filters produced in said patent were not able to remove the particulate of 99.5% or more than particles of a size from 0.5 μm to 0.8 μm, nor was it considered possible to produce activated carbon tubes having a wall thickness of less than 12.7 mm (0.5 inches) and especially such tubes have a wall thickness of 7.62 mm (0.3 inches) or less. It has been found that with the aforementioned homogeneous mixture of the two activated carbon particles of different size, ie from about 75% to 85% by weight from about 18% to 50% by weight of the activated carbon particles of -325 meshes and about 50% to 82% by weight of activated carbon particles of from -200 to +325, employed with about 15% to 25% by weight of a thermoplastic powder having an average particle size of approximately 5 μm to 25 μm. μm, the extrusion of such a thin-walled filter tube can be achieved to provide a filter element capable of removing 99.5% or more of the particles of a size from 0.5 μm to 0.8 μm. Any of the activated carbon particles of the aforementioned sizes can be employed in producing the thin-walled filter tubes of this invention. Among these activated carbon particles suitable for use and available by Calgon Carbon Corporation is activated carbon type TOG-NDS, which are understood to be particles of activated carbon based on acid-washed bituminous mineral carbon. Although about 18% to 50% by weight of the activated carbon particles of -325 mesh can be employed, it is preferred that the amount of said -325 mesh particles be approximately 28% by weight of the activated carbon particles and that 72% by weight of the activated carbon particles are particles of -200 to +325 meshes. Also, it is preferred that the amount of the activated carbon particles comprise about 81% by weight of the essentially homogeneous mixture and the binder powder comprises about 19% by weight of said mixture. The thermoplastic binder can be composed of almost any thermoplastic material including, for example, polyolefins, such as polyethylene, polypropylene, polybutene-1 and poly-4-methyl-pentene-1.; polyvinyls such as polyvinyl chloride, polyvinyl fluoride and polyvinylidene chloride, polyvinyl esters such as polyvinyl acetate, polyvinyl propionate, and polyvinyl pyrrolidone, polyvinyl ethers; polyvinyl sulfates;
polyvinyl phosphates; polyvinyl amines; polioxidiazoles; polytriazoles; polycarbodiimides; copolymers and block interpolymers, such as ethylene vinyl acetate copolymers, polysulfones, polycarbonates, polyethers, such as polyethylene oxide, polymethylene oxide and polypropylene oxide; polyarylene oxides, polyesters, including polyarylates, such as polyethylene terphthalate, nylon polyimides and the variation of these and other polymers having substituted groups, such as hydroxyl, halogen, lower alkyl groups, lower alkoxy groups, monocyclic aryl and the like and other meltable solid materials. Polyethylene, poly (ethylene vinyl acetate) and nylons are preferred. Especially preferred as the binder is polyethylene, particularly a SN 510 grade polyethylene from USl Division of Quantum Chemical Corporation. If desired, a small amount of about 75% to 85% by weight of the activated carbon particles in the essentially homogeneous mixture can be replaced with an additional particulate or powder additive materials to increase the filter performance. For example, approximately between 6 to 20% by weight of zeolite can be added to increase the absorption of heavy metals, such as lead, from the water or other liquid to be filtered. An especially preferred zeolite which can be used as an additive is titanium silicate zeolite ATS with a high specific characteristic for absorbing lead, said zeolite is available from Engelhard Corporation. As examples of other additives that can be used in small amounts, generally in minor amounts of about 10% by weight, mention may be made of diatomaceous earth, ceramics, ion exchange resins and the like. The components of the extrudable composition that are to be mixed in an essentially uniform mixture prior to the extrusion of the mixture into the desired thin-walled carbon tubes. After they have been blended into an essentially homogeneous mixture, the mixture can be extruded into the thin-walled carbon tubes by extrusion according to the process and with the apparatus described in my U.S. Pat. 5,189,092. The extruded thin walled carbon tubes of the present invention will generally have a density of about 0.65 to 0.75 g / cm 3. For example, in accordance with this invention, it is possible to produce an activated carbon filter tube with an average density of 0.72 g / cm 3 having an outer diameter (OD) of 50.8 mm (2.0 inches) and an internal diameter (ID). of 35.56 mm (1.4 inches), that is, a wall thickness of 7.62 mm (0.3 inches). The tube can be continuously extruded and cut into any desired length, for example, such as 254 mm (10 inches long). In accordance with this invention, such an extruded thin walled activated carbon tube is produced in accordance with US Pat. No. 5,189,092, is cut to the desired length and then the tube is assembled or attached to the two appropriate end caps or to an end cap and mounted in the appropriate cartridge housing or some similar configuration suitable for the filters. The typical thin-walled filter tube element of the present invention mounted on a cartridge and suitable for use as a unit for purifying water at sub-micron particle size levels is illustrated in the Figure. It is recognized that the thin-walled filter tubes of the present invention can be used in any suitable environment and that their description of being housed in the cartridge of the Figure is only an exemplary and non-limiting embodiment. The filtration unit 10 of the Figure comprises a cartridge 12 housing a thin-walled extruded filter tube 14 of the present invention. The cartridge 12 can be made of any suitable material, such as, for example, a metal or plastic, such as polypropylene or the like. The cartridge 12 comprises a hollow substantially cylindrical housing having a side wall 16, which at a first end 18, such as a lower end, can be slightly widened to fit at the base suitable for mounting the filter unit 10 to the source of the water or liquid to be purified. The lower end 18 is closed by a base wall 20. The base 20 includes an axial passage 22 inside the hollow cartridge 12. A duct or tube 24 is mounted in the axial passage 22 to allow the water or other purified liquid , filtered out from the inside of the hollow cartridge 12. If desired or necessary, the side wall 16 can be provided with an external groove 26 with a circular gasket or O-ring 28 mounted thereon to seal the unit sealingly. filtration 10 in a water or liquid supply source (not shown). A radial passage 30 is provided in the side wall to allow water or other liquid to be filtered to enter the interior of the hollow cartridge. A porous, thin-walled extruded carbon filter tube 14 of the present invention is provided with a cover disc 32 at one end to close said end of the filter tube. The disc 32 has a central projection 34 that extends into the hollow tubular passage 36 of the filter tube 14 for the purpose of alignment. The disc 32 is also provided with a peripheral edge 38 for aligning the filter tube 14 and closing the end of said filter tube. The function of the disc 32 is to prevent water or other liquid from passing axially to the hollow tubular axial passage 36 of the filter tube 14. At the second end or upper end of the side wall 16, the cartridge 12 is closed with an end cap 40 provided with a central recess 42 for receiving, holding and aligning the cover disc 32 by coupling an elevated central hub 44 on the disc. The disc 32 can be provided with a plurality of radial ribs 46, which can also assist in the alignment process. The thin-walled filter tube 14, provided with a cover disc 32 at one end of the filter tube, is inserted into the cartridge 12, with the open end of the passage axially surrounding the filter tube and the outlet conduit 24 Subsequently, the cartridge is closed by an end cap 40 by inserting a raised bucket 44 into the disc 32 in the central recess 42 of the end cap. The assembled filtration unit 10 can be employed by installing in a system, by which the water or other liquid to be purified enters the cartridge 12, through the radial passage 30 and flows into the interior space 48 between the side wall of the container. cartridge 16 and the thin-walled filter unit 14. Because the upper end of the tubular axial passage 36 is blocked by a cover disc 32, the water or liquid is forced to flow radially through a thin-walled filter tube , porous and below the axial tubular passage where it enters the conduit 24 at the bottom of the cartridge 12, flowing therealong as water or other purified liquid to a sub-micron level. The invention is further illustrated by the following example of the preparation and testing of a thin-walled activated carbon filter tube of the present invention. EXAMPLE A substantially homogeneous mixture is prepared by mixing about 81% by weight of the particles of activated carbon based on bituminous mineral coal, washing with acid with about 19% by weight of the polyethylene powder of type SN 510 having a particle size within the range of 5 μm to 25 μm. 81% by weight of the activated carbon comprises about 28% by weight of the activated carbon particles of -325 mesh and about 72% by weight of the activated carbon particles of -200 to +325 mesh. The substantially homogeneous mixture was subsequently extruded into a thin-walled hollow tube with an outer diameter (OD) of 50.8 mm (2 inches) c 35.56 mm (1.4 inches) of internal diameter (ID) and having an average dry density approximately 0.72 g / cm3 through the extrusion process and apparatus disclosed in the US Patent 5, 189, 092 mentioned above. The substantially homogeneous mixture was heated for approximately 5 minutes in the hot zone of the extruder maintained at a temperature of about 190 ° C (375 ° F), and cooled for about 3 minutes in the cooling zone of the extruder at an approximate temperature of 35 ° C (95 ° F), before it is extruded as a thin-walled hollow tube. The thin-walled hollow tube is then cut to suitable lengths of approximately 254 mm (10 inches) to be used in tests as a filter to remove particles with a sub-micron size. Using water contaminated with a fine PTI test dust ash, the filter tubes of this invention were tested for a particulate removal with a sub-micron size. When such contaminated water flows at 0.5 gal / min through the thin-walled filter tubes produced, mounted on an appropriate cartridge and having a pressure that decreases through the filter by approximately 14 psi causing the purified water that comes out that has a 99.9% reduction in pollution dust particles from a size of approximately 0.5 μm to 0.8 μm, measured using a laser line particle counting technique. When a thin-walled filter tube of a similar type having an average dry density of 0.67 g / cm3 is produced and tested with said water contaminated with powder flowing at 0.5 gal / min with a pressure that decreases through the 7.5 psid filter, 99.8% of the particles with a size range of 0.8 μm to 1 μm were removed, measured by the laser line particle counting technique. The extruded thin-walled activated carbon filter tubes of the present invention are characterized by the fact that the surface of the extruded tubes is extremely hard and smooth and as a result the particles filtered to the outside on the outer surface of the extruded tubes are Quickly removed, which allows repeated use of the filter tubes after cleaning. Additionally, the hard / smooth surface of the extruded, thin-walled activated carbon filter tubes of the present invention prevent the release of the carbon particles from the inner surface of the tubular filters and the water or other purified liquid. With the above description of the invention, those skilled in the art will appreciate that modifications can be made to the invention without departing from the spirit of the invention. Therefore, it is not intended that the scope of the invention be limited by the specific embodiments illustrated and described.