Patent Application
20070262027
The present invention relates to a filter and method for making such filter for use in treatment of contaminated fluids, and more particularly, to a layered filter incorporating the use of self-assembled monolayers on mesoporous supports in the removal of toxic heavy metals from contaminated fluids.
Produced fluid, such as water from offshore oil platforms can contain toxic heavy metals, for instance, mercury. In the Gulf of Mexico, mercury levels rarely exceed 100 parts per billion (ppb). However, in the Gulf of Thailand, the average concentration of mercury in produced water can range from about 200 ppb to about 2,000 ppb.
Discharge of mercury into the marine environment in U.S. territorial waters is currently regulated by the U.S. Environmental Protection Agency (EPA) under the Clean Water Act via the National Pollutant Discharge Elimination System permit process. According to environmental standards under 40 CFR § 131.36 for marine environment, limits include about 1800 ppb for acute exposure and about 25 ppb for chronic exposure. International standards for mercury discharges in produced water, on the other hand, range from about 5 ppb in Thailand to about 300 ppb in the North Sea.
Produced water often contains oil that was removed with the water during the bulk oil/water separation process. As an example, the produced water from the North Sea fields contains about 15-30 parts per million (ppm) dispersed oil with benzene, toluene, ethylbenzene, and xylene (BTEX); naphthalene, phenanthrene, dibenzothiophene (NPD), polycyclic aromatic hydrocarbon (PAH), phenol, and organic acid concentrations ranging from about 0.06 ppm to about 760 ppm. Additionally, these produced waters contain toxic heavy metals, such as mercury, cadmium, lead, and copper in concentrations ranging from less than about 0.1 ppb to about 82 ppb. The presence of a complex mix of constituents coupled with a high concentration of dissolved salts can present a challenge for heavy metal removal using currently available conventional technologies.
In particular, existing technologies for metal and mercury removal from diluted wastewater include activated carbon adsorption, sulfur-impregnated activated carbon, microemulsion liquid membranes, ion exchange, and colloid precipitate flotation. These technologies may not be suitable for water treatment because of poor metal loading (e.g., metal uptake less than 20% of the mass of the adsorber material) and selectivity, (interference from other abundant ions in groundwater). In addition, mercury may be present in species other than elemental. So the method must be able to remove these other species, such as methyl mercury, etc. Furthermore, they lack stability for metal-laden products so that they are not disposable directly as a permanent waste form. As a result, secondary treatment is required to dispose or stabilize the separated mercury or the mercury-laden products. Mercury removal from non-aqueous sludge, adsorbed liquids, or partially- or fully-stabilized sludges, and mercury-contaminated soil is difficult because (1) the non-aqueous nature of some wastes prevents the easy access of leaching agents, (2) some waste streams with large volumes make the thermal desorption process expensive, and (3) the treatment of some waste streams are technically difficult because of the nature of the wastes.
Mercury removal from offgas in vitrifiers and in mercury thermal desorption processes is usually accomplished through active carbon adsorption. However, the carbon-based adsorbents are only effective enough to remove 75 to 99.9% of the mercury with a loading capacity equivalent to 1-20% of the mass of the adsorber material. A last step, mercury amalgamation using expensive gold, usually is needed to achieve the EPA air release standard. A carbon bed usually is used later in the offgas system, where the temperature is generally lower than 250° F. In the sulfur impregnated carbon process, mercury is adsorbed to the carbon, which is much weaker than the covalent bond formed with, for instance, surface functionalized mesoporous material. As a result, the adsorbed mercury needs secondary stabilization because the mercury-laden carbon does not have the desired long-term chemical durability due to the weak bonding between the mercury and activated carbon. In addition, a large portion of the pores in the active carbon are large enough for the entry of microbes to solubilize the adsorbed mercury-sulfur compounds. The mercury loading is limited to about 0.2 g/g of the materials.
The microemulsion liquid membrane technique uses an oleic acid microemulsion liquid membrane containing sulfuric acid as the internal phase to reduce the wastewater mercury concentration from about 460 ppm to about 0.84 ppm. However, it involves multiple steps of extraction, stripping, demulsification, and recovery of mercury by electrolysis and uses large volumes of organic solvents. The liquid membrane swelling has a negative impact on extraction efficiency.
The slow kinetics of the metal-ion exchanger reaction requires long contacting times. This process also generates large volumes of organic secondary wastes. One ion exchange process utilizes Duolite™ GT-73 ion exchange organic resin to reduce the mercury level in wastewater from about 2 ppm to below about 10 ppb. Oxidation of the resin results in substantially reduced resin life and an inability to reduce the mercury level to below the permitted level of less than about 0.1 ppb. The mercury loading is also limited because the high binding capacity of most soils to mercury cations makes the ion-exchange process ineffective, especially when the large amounts of Ca2+ from soil saturate the cation capacity of the ion exchanger. In addition, the mercury-laden organic resin does not have the ability to resist microbe attack. Thus, mercury can be released into the environment if it is disposed of as a waste form. In addition to interference from other cations in the solution besides the mercury-containing ions, the ion exchange process is simply not effective in removing neutral mercury compounds, such as HgCl2, Hg(OH)2, and organic mercury species, such as methylmercury, which is the most toxic form of mercury. This ion-exchange process is also not effective in removing mercury from non-aqueous solutions and adsorbing liquids.
The reported removal of metal from water by colloid precipitate flotation reduces mercury concentration from about 160 ppb to about 1.6 ppb. This process involves the addition of HCl to adjust the wastewater to pH 1, addition of Na2S and oleic acid solutions to the wastewater, and removal of colloids from the wastewater. In this process, the treated wastewater is potentially contaminated with the Na2S, oleic acid, and HCl. The separated mercury needs further treatment to be stabilized as a permanent waste form.
Acidic halide solution leaching and oxidative extractions can also be used in mobilizing mercury in soils. For example KI/I2 solutions enhance dissolution of mercury by oxidization and complexation. Other oxidative extractants based on hypochlorite solutions have also been used in mobilizing mercury from solid wastes. Nevertheless, no effective treatment technology has been developed for removing the mercury contained in these wastes. Since leaching technologies rely upon a solubilization process wherein the solubilized target (e.g. mercury) reaches a dissolution/precipitation equilibrium between the solution and solid wastes, further dissolution of the contaminants from the solid wastes is prevented once equilibrium is reached. In addition, soils are usually a good target ion absorber that inhibits the transfer of the target ion from soils to solution.
The removal of mercury from nonaqueous liquids, adsorbed liquids, soils, or partially-or-fully-stabilized sludge at prototypic process rates has been lacking. This is mainly because the mercury contaminants in actual wastes are much more complicated than the mercury systems addressed by many laboratory-scale tests that are usually developed based on some simple mercury salts. The actual mercury contaminants in any actual wastes almost always contain inorganic mercury (e.g., divalent cation Hg2+, monovalent Hg22+, and neutral compounds such as HgCl2, Hg[OH]2,); organic mercury, such as methylmercury (e.g., CH3 HgCH3 or CH3 Hg+) as a result of enzymatic reaction in the sludge; and metallic mercury, because of reduction. Since many laboratory technologies are developed for only one form of mercury, demonstrations using actual wastes are not be successful.
Other metals that are of interest for remediation and industrial separations include but are not limited to silver, lead, uranium, plutonium, neptunium, americium, cadmium and combinations thereof. Present methods of separation include but are not limited to ion exchangers, precipitation, membrane separations, and combinations thereof. These methods usually have the disadvantages of low efficiencies, complex procedures, and high operation costs.
Accordingly, it would be advantageous to provide an apparatus and method that can be used to remove heavy metals, such as mercury, cadmium, and lead from complex waste fluids, such as produced water, in a significant amount and in a cost effective manner.
The present invention, in one embodiment, provides a filter for use in the treatment of contaminated fluid. The filter, in an embodiment, includes two filter elements, each substantially flat in shape, for use in removing certain contaminants from the fluid flow. The filter further includes a waste adsorbent material, positioned between the two filter elements for use in removing additional contaminants within the fluid flowing across the filter elements. The waste adsorbent material, in an embodiment, may be a nanosorbent material manufactured from self-assembled monolayers on mesoporous supports (SAMMS). The filter can be enlarged by overlapping or by ultrasonically joing a plurality of filters to one another. The filter can form a barrier through which contaminated fluid flows, so that targeted contaminants can be removed.
The present invention, in another embodiment, a method of manufacturing a filter for use in the treatment of contaminated fluid. The method includes providing a two filter elements, each having an inner surface and an outer surface, for use in removing certain contaminants from the fluid flow. In an embodiment, each of the filter elements can be substantially flat in shape, similar to a sheet. Next, one of the filter elements can be placed onto a surface, so that its inner surface can be exposed. Thereafter, a layer of a waste adsorbent material may be placed on to the exposed inner surface of the one filter element. The thickness and uniformity of the layer of adsorbent material can be controlled, depending on the application. Subsequently, the other filter element can be positioned on top of the layer of adsorbent material, such that its inner surface directly contacts the layer of adsorbent material. The assembled filter may then be heated, so that a bond can be created between the tow filter elements to trap the layer of adsorbent material therebetween. Should a longer or wider filter be desired, multiple filters can be placed adjacent one another and joined together using method known in the art.
The present invention further provides a method for treatment of contaminated fluid. The method includes providing a filter having a first sheet of filter element, a second sheet of filter element in opposing relations thereto, and a layer of a waste adsorbent material disposed between the first and second filter elements. Next, the filter may be placed over a surface of a contaminated area where seepage can be an issue, so as to form a barrier through which contaminated fluid may flow. To the extent desired, multiple filters may be overlapped across the contaminated area. Contaminated fluid may then be allowed to seep across the first filter element directly in contact with the contaminated area, so that contaminants of a certain size can be removed. The fluid may be permitted to continue to seep from the first filter element, across the adsorbent material, so that additional contaminants may be adsorbed by the adsorbent material and removed from the fluid. Thereafter, the fluid treated from the adsorbent material can be allowed to move through the second filter element and away from the filter.
FIGS. 2A-B illustrate, in accordance with another embodiment of the present invention, the filter shown in
With reference to
The filter 100, in an embodiment, includes a first filter element 110 and a second filter element 120. Filter element 110, as illustrated, can be provided with an outer surface 111 and an inner surface 112. Likewise, filter element 120 includes an outer surface 121 and an inner surface 122. Filter elements 110 and 120, in one embodiment, may be a substantially a flat sheet of filtration media designed for removing certain contaminants, for instance, solid and liquid contaminants, from the fluid flow. To that end, the filter elements 110, 120 may be made from a fluid permeable material, such as a synthetic material, e.g., polyester, polypropylene, nylon, or a combination thereof, to permit fluid to flow therethrough. Other materials from which the outer filter element may be made include inorganic components, like fiberglass or ceramic, microglass, melt-blown, micron synthetic, organic cellulose, paper etc. or a combination thereof. In an embodiment, the filter elements 110 and 120 may be made from non-woven material. An example of such a material from which the filter elements may be made is disclosed in U.S. Pat. No. 5,827,430, entitled Coreless and Spirally Wound Non-Woven Filter Element, and in U.S. Pat. No. 5,893,956, entitled Method of Making a Filter Element. Both of these patents are hereby incorporated herein by reference. The material from which the filter elements 110 and 120 may be made can be provided with a substantially tortuous path from an outer surface of each filter to an inner surface of each filter. In that way, fluid flowing across the filter elements can be forced to follow a tortuous path so that contaminants, for instance, solid contaminants of a particular size, can be trapped within the filter element. Although illustrated as being square in shape, it should be appreciated that the filter elements 110 and 120 may be provided in any geometric shape, including rectangular, square, circular, or any shape necessary for the particular application.
In addition, filter elements 110 and 120 of filter 100 may be provided with a thickness sufficient to remove certain solid contaminants. In an embodiment, filter elements 110 and 120 may have a thickness of about 0.1 inch or greater. Of course, the thickness of filter elements 110 and 120, and other size related dimensions, may be varied depending on the particular application, and the environment within which the filter 100 is used.
Filter 100 further includes an adsorbent material 125, positioned between the first filter element 110 and the second filter element 120. The waste adsorbent material 125 may be used for removing contaminants, for example, heavy metals similar to those disclosed above, within the fluid flowing across the first filter element 110 and/or the second filter element 120. It should be appreciated that placement of the adsorbent material 125 between the filter elements 110 and 120 helps to contain and retain the adsorbent material 125 within filter 100. The waste adsorbent material 125, in an embodiment, may be a nanosorbent material manufactured from self-assembled monolayers on mesoporous supports (SAMMS). The support, in an embodiment, may be made from various porous materials, including silica. An example of a SAMMS material that can be used in connection with apparatus 100 of the present invention includes thiol-SAMMS, such as that disclosed in U.S. Pat. No. 6,326,326, which patent is hereby incorporated herein by reference.
In accordance with one embodiment of the present invention, the waste adsorbent material 125 may be porous particles ranging from about 5 microns to about 200 microns in size. In an embodiment, the particles, on average, range from about 50 microns to about 80 microns in size, include a pore size ranging from about 2 nanometers (nm) to about 7 nm, and may be provided with an apparent density of ranging from about 0.2 grams/milliliter to about 0.4 grams/milliliter. Due to the size of the adsorbent material 125, it should be noted that each of the filter elements 110 and 120 may be designed to limit its permeability to the adsorbent material 125, so as to minimize movement of the adsorbent material 125 across the filter elements 110 and 120.
In manufacturing filter 100 of the present invention, the first filter element 110 and second filter element 120 may be made by blending raw fibers of various size, as disclosed in U.S. Pat. Nos. 5,827,430 and 5,893,956, both of which are incorporated by reference. Thereafter, one of the filter elements, for example, filter element 120 can then be positioned on to a surface, for instance, a substantially flat surface, so that its inner surface 122 may be exposed. Once exposed, the inner surface 122 of filter element 120 can be covered with a layer of the adsorbent material 125. Of course, multiple layers of the adsorbent material 125 can be applied. The thickness and uniformity of this layer, as well as the amount of waste adsorbent material 125, can be predetermined and controlled, depending on the commercial application. Alternatively, the adsorbent material 125 can be applied to a sheet (not shown) of a permeable material and the sheet placed on to the inner surface 122 of filter element 120.
It should be appreciated that the adsorbent material, e.g., SAMMS, can be functionalized with a treatment to specifically target a contaminant in a contaminated fluid. This treatment can be done before or after application of the adsorbent material on to filter element 120, or even after the filter 100 has been formed. To the extent desired, the adsorbent material 125 can further include a different substance or material, e.g., carbon, or a differently functionalized SAMMS. This flexibility can allow for different designs of waste adsorbent material to match specified contaminants the may exist in the fluid being treated.
Next, the remaining filter element, for instance, filter element 110, can be situated in opposing relations to filter element 120, so that its inner surface 112 can be in substantial contact with the adsorbent material 125. Placement of filter element 110 and filter element 120 in such a manner allows the adsorbent material 125 to be sandwiched therebetween to form filter 100. The assembled filter 100 can then be heated, so that a bond can be created between the two filter elements 110, 120, thereby trapping the adsorbent material 125 in the middle. In one embodiment, the edges of the filter elements are heated to create a bond between the edges and around the adsorbent material. To enhance the bond between the filter elements 110 and 120, pressure may be applied to one or both filter elements, so as to compress the filter elements toward one another during heating.
The bond between the filter elements 110, 120 can be created because each filter element may be made of a permeable material that contains a combination of components, such that at least one component of the permeable material has a lower melting point than the remainder of the components. This allows the filter elements 110 and 120 to be melted around the adsorbent material 125, thereby forming the layered filter 100. In fact, the filter elements 110 and 120 can be melted more than once, and still maintain their overall matrix integrity. An advantage of using such a permeable material to make filter elements 110, 120, is the ability to blend different fibers, so as to provide a substantially exact matrix composition to best contain and use the adsorbent material 125 in an optimal way.
Once the layered filter 100 has been heated and compressed, it may then be calendared and ready for use. Thereafter, should a wider or longer filter 100 be required, multiple filters 100 can be placed adjacent one another and joined (i.e. attached) together using techniques known in the art. In one example, ultrasonic welding techniques may be employed to join adjacently situated layered filters 1000, such that multiple layered filters 100 can be coupled together, either along the sides or end to end. In this manner, large sheets of layered filters 100, can be assembled on site for convenience.
In application, referring now to
While the invention has been described in connection with the specific embodiments thereof, it will be understood that it is capable of further modification. Furthermore, this application is intended to cover any variations, uses, or adaptations of the invention, including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains.
This application claims priority to U.S. Provisional Patent Application Ser. No. 60/787,950, filed Mar. 31, 2006, which application is hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60787950 | Mar 2006 | US |
