Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1999-10-05
2001-03-13
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S688000, C502S071000, C502S527190
Reexamination Certificate
active
06200483
ABSTRACT:
This invention relates to monolithic structures for removing contaminants from liquid streams using inorganic purifying agents.
BACKGROUND OF THE INVENTION
Various ion exchange materials, both organic and inorganic, are widely acknowledged as having the ability to remove certain metal ions such as lead from aqueous solutions. The use of organic ion exchange materials is popular in current carafe or gravity filter products. One of the disadvantages of organic ion exchange materials is that they swell when in contact with water while inorganic materials do not swell. The organic ion exchange materials are not stable at high temperatures. Most of the organic ion exchange materials are expensive and used in a packed bed form.
The use of inorganic materials such as crystalline zeolites and amorphous gels is much less popular. In the water treatment industry inorganics find use in lead removal, but appear to be in particulate or granular form. For example, it is well known that inorganic ion-exchange materials can provide the same function as organic ion exchange resins. Commercially available carbon block filters, made from granular activated carbon (GAC), commonly mix amorphous titanium-silicate powders with their GAC and polymer binders before forming. The amorphous titanium-silicate powders are used for lead and other heavy metal removal in drinking water. These powders are held in place by the polymer binders and the GAC.
There are some claims of inorganic ion exchange materials being attached to other support materials, such as carbon granules. However, the support in such cases is still a particle or granule itself. Unfortunately, the bonding between the ion exchange material and the granular carbon support has typically been quite poor, resulting in continual sloughing off of the ion exchange material. As a result, large amounts of water are needed to wash the filter before the water is clear enough for consumption.
There is never a guarantee that the water is completely free of ion exchange material. The continual sloughing off shortens the life of the device and may have adverse effects on the health of individuals drinking such treated water.
A common method for ion exchange purification is to run the feed solution through a column filled with the ion exchange material. In order to accomplish significant ion exchange, columns of considerable length are sometimes required. However, with increasing column length, the flow rate decreases. Also, such columns develop channeling of the feed solution, which decreases the ion exchange efficiency.
Accordingly, a need exists for efficient liquid purification devices in which the disadvantages of loose powder or granular or loosely bound materials are eliminated and in which the disadvantages of decreased flow due to channeling are eliminated.
The present invention provides such structured materials and methods.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided a monolithic structure having active material that includes at least inorganic ion exchange material, for purifying a liquid stream of contaminants such as heavy metals, chlorine, volatile organics, pesticides, herbicides, and/or parasites, etc. The structure has an inlet end and an outlet end and a multiplicity of cells extending from inlet to outlet end. The cells are separated from one another by porous walls that are alternatively plugged at each end such that a liquid stream that enters the structure, enters through the unplugged cells at the inlet end and passes through porous walls to be purified by the active material, and thereafter passes out of the structure through unplugged cells at the outlet end.
In accordance with another aspect of the invention, there is provided a method of making the above-described structure that involves applying active material as a coating on an alternately plugged substrate. The average particle size of the active material after calcination is greater than the average cell wall pore size of the substrate. The coated substrate is dried at no greater than 200° C., and calcined at no greater than 650° C., to bond the active material to the substrate.
In accordance with another aspect of the invention, the structure can be shaped from a forming mixture of the active materials.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to monolithic structures for purifying liquid streams. The structures have inorganic active purifying material that includes ion exchange material.
The structured materials are in the form of a cellular monolith having an inlet end and an outlet end, the cells running the length of the monolith from inlet end to outlet end. The cells have porous walls through which a liquid stream can pass. The cells are alternately plugged at the inlet and outlet ends, allowing liquid to flow through the cell walls.
The structured materials of this invention are suitable for purification of water containing ionexchangeable materials. These exchangeable species include but are not limited to: lead, copper, chromium, nickel, cadmium, arsenic, mercury, silver, zinc, Ca, Mg, and other hard water minerals. According to this invention chlorine, volatile organic chemical (VOCs), herbicides and/or pesticides can be removed when a carbon-based monolith is used. Structured materials are also suited for particulate and cyst removal (by physical filtration). In the latter applications, the appropriate porosity is created to filter off these contaminants.
The honeycomb geometry, (characterized by a large number of cells per unit area) is especially advantageous for efficiently removing pollutants. Preferably, the cells are symmetric.
Generally honeycomb cell densities range from 235 cells/cm
2
(about 1500 cells/in
2
) to 1.5 cells/cm
2
(about 10 cells/in
2
). Some examples of commonly used honeycombs, although it is to be understood that the invention is not limited to such, are about 94 cells/cm
2
(about 600 cells/in
2
), about 62 cells/cm
2
(about 400 cells/in
2
), or about 47 cells/cm
2
(about 300 cells/in
2
), and those having about 31 cells/cm
2
(about 200 cells/in
2
) and 15 cells/cm
2
(about 100 cells/in
2
). Typical wall thicknesses are for example, about 0.15 mm (about 6 mils) for about 31 cells/cm
2
(about 200 cells/in
2
) honeycombs. Wall (web) thickness range typically from about 0.1 to about 1.5 mm (about 4 to about 60 mils). Honeycombs having about 15 to about 62 cells/cm
2
(about 100 to about 400 cells/in
2
) and about 0.30 to about 0.75 mm (about 12 to about 30 mil) wall thicknesses are especially suited for filter applications. This invention is especially advantageous for honeycombs having appropriate wall pore size in the range of 0.1 to 100 micrometers, with preferred range of 1-20 micrometer, and a wall porosity of 15-75%.
The cells of the multicellular device are selectively plugged to allow maximum contact of their walls with the liquid stream for maximum purification efficiency. Plugging can be done by techniques known in the art using compatible plugging materials that will seal off the cell.
For example, with ceramic materials two part epoxy is suitable.
A wide range of inorganic purifying agents can be used and are selected depending on the pollutants to be removed. For cation exchange, the purifying agent must have an acidic surface (proton on the surface). For anion exchange, the purifying agent must have a basic surface. Some examples of purifying agents, although it is to be understood that the invention is not limited to these, are one or more of the following: zeolites, gamma alumina, clays, zirconia, sulfonated zirconia, heteropoly acids, e.g. heteropoly molybdic acid, amorphous titanium silicates, etc.
Some agents that are especially suited for lead removal are Y-zeolite, gamma alumina, and/or titanium silicate.
This invention can be practiced in several ways. One way is to contact a multicellular substrate with active material either by washcoating a slurry of discrete particles of the active material onto the substrate, or by creating a thin film by
Cutler Willard A.
Tao Tinghong
Torns Jennifer M.
Barry Chester T.
Corning Incorporated
Gheorghiu Anca C.
Herzfeld L. Rita
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