IN SITU OIL CLEANUP AND RECOVERY USING SMART POLYMER INTEGRATED SURFACE VESSELS

Abstract

Smart membranes (14) are integrated into a small, unmanned surface vessel (20) to enable the efficient, automated cleanup of oil spills. Such a vessel (20) has the potential to provide a low-cost, modular solution for day-to-day oil-spill cleanup operations, especially in confined aquatic areas, such as under piers and in the small spaces between marine vessels and piers. The smart membranes (14) are provided on the surface of a conveyor belt (34) that circulates the membranes (14) through the surrounding body of water (10) for oil collection, as well as through an internal reduction chamber (22) of the vessel (20) for oil release. The smart membranes (14) are adapted to attract and repel oil (12) in response to low-voltage commands applied across the conveyor belt (34), using a process that is repeatable for a number of cycles, offering high efficiency and long durability (FIG. 5).

Claims

1. A membrane adapted for use as an oil-collection agent, said membrane comprising an exposed surface which includes a conjugated polymer that is capable of functioning to collect oil on said exposed surface when said conjugated polymer is oxidized and that is capable of functioning to release oil from said exposed surface when said conjugated polymer is reduced.

2. The membrane of claim 1, wherein said conjugated polymer is capable of being oxidized and reduced electrochemically.

3. The membrane of claim 2, wherein said conjugated polymer is capable of being electrochemically oxidized by applying a positive electric voltage to said conjugated polymer and wherein said conjugated polymer is capable of being electrochemically reduced by applying a negative electric voltage to said conjugated polymer.

4. The membrane of claim 3, wherein said positive electric voltage lies in a range of from greater than 0 volts to about 1.5 volts and wherein said negative electric voltage lies in a range of from about −0.6 volts to about −1.5 volts.

5. The membrane of claim 4, wherein said conjugated polymer exhibits a wettability characteristic variable in response to the voltages selected from said positive and negative electric voltage ranges.

6. The membrane of claim 1, wherein said conjugated polymer is a surfactant-doped conjugated polymer film.

7. The membrane of claim 1, wherein said conjugated polymer is dodecylbenzenesulfonate-doped polypyrrole.

8. The membrane of claim 1, wherein said conjugated polymer is a freestanding, porous film.

9. The membrane of claim 8, wherein said freestanding, porous film is fabricated via 3D printing of said conjugated polymer.

10. The membrane of claim 1, further comprising a substrate which cooperates with said conjugated polymer to form a composite structure.

11. The membrane of claim 10, wherein said substrate includes a stainless steel mesh.

12. The membrane of claim 11, wherein said substrate further includes carbon nanotubes.

13. The membrane of claim 12, wherein said carbon nanotubes are grown on said stainless steel mesh via chemical vapor deposition.

14. The membrane of claim 13, wherein said conjugated polymer is coated on said carbon nanotubes via electropolymerization.

15. The membrane of claim 10, wherein said substrate includes electrically conductive carbon foam having a porous 3D structure.

16. The membrane of claim 1, wherein said membrane is integrated into a surface vessel adapted to perform an oil cleanup and recovery operation on a body of oil-contaminated water.

17. The membrane of claim 16, wherein said surface vessel includes a reduction chamber, which includes a first reservoir of electrolyte and a first set of electrodes; an oxidation chamber, which includes a second reservoir of electrolyte and a second set of electrodes; a conveyor belt, which includes said membrane; and motive means for moving said conveyor belt such that said membrane (i) passes beneath said surface vessel and through a body of oil-contaminated water to collect oil thereon, (ii) passes through said first reservoir of electrolyte in said reduction chamber after passing through the body of oil-contaminated water, and (iii) passes through said second reservoir of electrolyte in said oxidation chamber after passing through said first reservoir of electrolyte in said reduction chamber.

18. The membrane of claim 17, wherein said membrane is electrochemically reduced by applying a negative electric voltage to said first set of electrodes as said conveyor belt carries said membrane through said first reservoir of electrolyte in said reduction chamber and wherein said membrane is electrochemically oxidized by applying a positive electric voltage to said second set of electrodes as said conveyor belt carries said membrane through said second reservoir of electrolyte in said oxidation chamber.

19. The membrane of claim 18, wherein said first reservoir of electrolyte in said reduction chamber is separated from said second reservoir of electrolyte in said oxidation chamber by a partition positioned between said oxidation chamber and said reduction chamber.

20. The membrane of claim 19, wherein said partition inhibits oil collected in said reduction chamber from migrating into said oxidation chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] For a better understanding of the present invention, reference is made to the following detailed description of various exemplary embodiments considered in conjunction with the accompanying drawings, in which like structures are referred to by the like reference numerals throughout the several views, and in which:

[0020] FIG. 1 is a schematic illustration of a body of oil-contaminated water;

[0021] FIG. 2 is a schematic illustration of a plurality of oxidized polymer mesh membranes constructed in accordance with an embodiment of the present invention and operating to collect oil as a conveyor transports the membranes through the body of oil-contaminated water shown in FIG. 1;

[0022] FIG. 2A is a detailed schematic illustration showing an oil droplet adhered to the oxidized polymer surface of one of the mesh membranes illustrated in FIG. 2;

[0023] FIG. 2B is an alternate view of the schematic illustration of FIG. 2A, showing a close-up view of the mesh membrane;

[0024] FIG. 3 is a schematic illustration showing the polymer mesh membranes of FIG. 2 in a reduced stated in which collected oil is being released therefrom and therethrough;

[0025] FIG. 3A is a detailed schematic illustration showing an oil droplet being released from (e.g., by sliding or permeating) the reduced polymer surface of one of the mesh membranes illustrated in FIG. 3;

[0026] FIG. 4 is a schematic illustration showing the polymer mesh membranes of FIG. 3 in an oxidized state and ready for reuse after they have been regenerated;

[0027] FIG. 5 is a schematic illustration of an oil-cleaning surface vessel constructed in accordance with an embodiment of the present invention and showing the vessel's oxidation and reduction chambers and their interactions with a conveyor belt which comprises membranes that are similar in construction and function to those illustrated in FIGS. 2-4; and

[0028] FIG. 6 is a rear schematic illustration of the surface vessel depicted in FIG. 5 showing the vessel's catamaran hull form and steering mechanism.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0029] The following disclosure is presented to provide an illustration of the general principles of the present invention and is not meant to limit, in any way, the inventive concepts and embodiments contained herein. All terms defined herein should be afforded their broadest possible interpretation, including any implied meanings as dictated by a reading of the specification as well as any words that a person having skill in the art and/or a dictionary, treatise, or similar authority would assign thereto.

[0030] Further, it should be noted that, as recited herein, the singular forms “a”, “an”, and “the” include the plural referents unless otherwise stated. Additionally, the terms “comprises”, “comprising”, “includes”, “including”, “has” and the like, when used herein specify that certain features are present in that embodiment; however, such terms should not be interpreted to preclude the presence or addition of additional steps, operations, features, components, and/or groups thereof.

[0031] With specific reference now to the accompanying drawings, FIGS. 1-4 represent schematic illustrations of a method involving the trap-and-release of oils and the regeneration of smart membrane surfaces in accordance with one embodiment of the present invention. In FIG. 1, a body of water (e.g., seawater) 10 is contaminated with oil 12, which is shown schematically in the form of bubbles or droplets. FIG. 2 shows the oil 12 trapped within oxidized mesh membranes 14. FIG. 2A shows an oil droplet 12 adhered to the oxidized polymer surface of one of the mesh membranes 14 illustrated in FIG. 2, wherein a DBS group 16 of the polymer has its hydrophobic tail exposed. As shown in FIG. 3, reduced polymer surfaces of the membranes 14 cause collected oil droplets 12 to be released from the membranes 14 (through sliding or permeating). FIG. 3A shows an oil droplet 12 being released from (e.g., by sliding or permeating) the reduced polymer surface of one of the mesh membranes 14 illustrated in FIG. 3, wherein the DBS group 16 of the polymer has its hydrophilic head exposed. FIG. 4 shows the membranes 14 after they have been oxidized to thereby regenerate their membrane surfaces in preparation for reuse of the membranes 14 as oil collection agents.

[0032] In an embodiment, a substrate cooperates with a conjugated polymer to form a composite mesh structure. The result is a smart membrane that includes: (1) conjugated polymer; (2) CNTs; and (3) SS mesh. On the SS mesh, CNTs 17a (See FIG. 2B) are directly grown using chemical vapor deposition to form the substrate for the conjugated polymer. Finally, the surfactant-doped conjugated polymer film is coated atop the CNTs 17a using electropolymerization to complete the composite mesh structure.

[0033] In an embodiment, multiwalled carbon nanotubes (CNTs) 17a can be directly grown from 304 stainless steel (SS) meshes (Size 200×200, McMaster-Carr, Robbinsville, N.J.) using atmospheric pressure chemical vapor deposition (APCVD). SS meshes were cut, rinsed, dried and then placed in the center of a 200 quartz tube in a horizontal three zone chemical vapor deposition (CVD) furnace and heated to 750° C. under the flow of 60 sccm hydrogen (H2, Praxair, Newark, N.J.) and 500 sccm Argon (Ar, Praxair, Newark, N.J.). Then, additional ethylene (C2H4, Praxair, Newark, N.J.) was fed through the system at flow rates of 100 sccm for 7 mins for CNTs growth. Subsequently, the samples were rapidly cooled to room temperature by blowing air into the furnace.

[0034] After CNT growth, PPy(DBS) film was electropolymerized atop the CNT-covered SS mesh surface. First, 1 mL pyrrole monomer (reagent grade, 98%, Sigma-Aldrich, St. Louis, Mo.) was thoroughly mixed with 150 mL 0.1 mol/L sodium dodecylbenzenesulfonate (NaDBS, technical grade, Sigma-Aldrich, St. Louis, Mo.) solution. Then, a CNT-covered SS mesh, a saturated calomel electrode (SCE, Fisher Scientific Inc., Pittsburgh, Pa.), and another SS mesh (5 cm×5 cm) were submerged in the solution as the working, reference, and counter electrode, respectively. The coating of PPy(DBS) surfaces was carried out using a potentiostat (263A, Princeton Applied Research, Oak Ridge, Tenn.) by applying 0.7 V to the working electrode (vs. SCE) and stopped once surface charge density reached 1 C./cm.sup.2. Instead of CNTs, SS meshes were deposited with 10 nm chromium (Cr) and 30 nm gold (Au) films using an e-beam evaporator (Explorer 14, Denton Vacuum, Moorestown, N.J.), and then also coated with PPy(DBS) surfaces. After fabrication, the PPy(DBS) mesh surfaces were rinsed and dried in air overnight before any further characterizations.

[0035] It should be noted that CNTs are optional in the foregoing embodiment. However, the CNTs are preferred, as the in situ switch time decreases because the CNTs allow for a higher surface area, which increases the amount of DBS molecules desorbed from PPy(DBS) surfaces under reduction, thereby facilitating more rapid decrease of oil/water interfacial tension and retention force.

[0036] In another embodiment, a conductive carbon foam 17b can be used directly for PPy(DBS) electropolymerization after necessary cutting and dicing (See FIG. 2B). The pristine carbon foam 17b is extremely porous and has a 3D microstructure. It is also lightweight. The 2.5×0.5×0.2 cm carbon foam weighs only 0.025 g, compared to a 2×3 cm PPy(DBS) mesh, which weighs 0.2 g. After PPy(DBS) electropolymerization, the whole surface of carbon foam 17b can be evenly and uniformly covered with PPy(DBS) surfaces. Results show that the PPy(DBS) surface inherits the 3D porous structure of the carbon foam 17b without blocking the pores. In testing conductive carbon foam as a substrate for PPy(DBS) electropolymerization, results further show that the resulting PPy(DBS) foam exhibits much higher absorbing capacity compared with the PPy(DBS) mesh. To summarize, the PPy(DBS) foam had 3 times more absorption capacity with only 1/10 of the weight, versus the PPy(DBS) mesh. Such higher absorption capacity is attributed to the abundant surface area in the 3D porous structure of the foam 17b. By fabricating PPy(DBS) surfaces on conductive carbon foam, the absorption capacity of absorbent made of PPy(DBS) material significantly increases.

[0037] The PPy(DBS) foam's longevity was tested, and it still absorbed and released DCM oil after 100 redox cycles. Additionally, the foam proved in tests its ability to absorb and release hexane and diesel. Such 3D printed PPy(DBS) has the potential for further improving the absorbing capacity and tailoring absorbent structure for different oil cleanup scenarios, as well as the development of other applications using PPy(DBS) surfaces and its wettability characteristic that can be varied in response to changing parameters (i.e., tunable wettability).

[0038] In another embodiment, 3D printing is used to directly print PPy(DBS) materials with a 3D porous structure to form PPy(DBS) absorbents. In this way, the structure and physical/mechanical properties of PPy(DBS) absorbents can be tailored and the mass production of PPy(DBS) absorbents will be possible. In order to test the feasibility of 3D printing of PPy(DBS), the PPy(DBS) solution was prepared and later cast on flat substrates (i.e., glass slides, Au-coated Si) to form freestanding PPy(DBS) films. Then, the resulting freestanding PPy(DBS) films were tested for their tunable wettability and switchable adhesion toward oils.

[0039] To prepare the PPy(DBS) solution, PPy(DBS) surfaces must be dissolved in organic solvents. However, it is suggested that electropolymerized PPy(DBS) is insoluble in either organic or inorganic solvents due to its high degree of cross-linking. Thus, electrochemical oxidization is used instead to prepare PPy(DBS) material, in which the polymerization is started by adding oxidants (e.g., iron(III) chloride, FeCl.sub.3) into the solution with pyrrole monomer and NaDBS.

[0040] With careful controlling of the molecular ratio/concentration of pyrrole/NaDBS/FeCl.sub.3 and the polymerization duration, PPy(DBS) particles were synthesized and precipitated, which were then filtered out and thoroughly rinsed and dried. For example, 0.5 mL (0.0075 mL) of pyrrole monomer was mixed with 75 mL of 0.1 mol/L NaDBS solution for one hour. Then, 5 mL of 0.25 mol/L FeCl.sub.3 solution was added dropwise to start the polymerization process. After 10 minutes, the precipitates were filtered out using centrifugation, washed extensively with water three times, and dried in air at 60° C. for 72 hours. Subsequently, the PPy(DBS) particles were dissolved in dimethylformamide (DMF) to form a stable suspension. To test the tunable wettability of PPy(DBS) made from electrochemical oxidization, one drop of such suspension was applied on a glass slide and dried overnight to form a freestanding film. The resulting PPy(DBS) freestanding film was then tested for tunable wettability.

[0041] This initial result suggests that the PPy(DBS) films made by a casting PPy(DBS) particle solution also exhibit tunable wettability, demonstrating the feasibility of making an oil absorbent via the 3D printing of PPy(DBS). Thus, with a careful design of the structure based on the oil cleanup requirement, the PPy(DBS) oil absorbent can be fabricated using 3D printing. Such oil absorbent can have both high absorbing capacity, as well as in situ surface regeneration ability, making it suitable for highly efficient next generation oil cleanup technology.

[0042] By way of example, DCM droplets on freestanding PPy(DBS) surfaces are characterized by a spherical shape and contact angle of ˜60° when no voltage was applied to the surface. However, when −0.9V was applied, the DCM droplet exhibited flattening behavior, similar to the shape change observed in those droplets on the reduced electropolymerized PPy(DBS) surface. A DCM droplet once adhered to the oxidized PPy(DBS) surface rolled away after 60 seconds of reduction, demonstrating tunable adhesion.

[0043] Any of the smart membranes described hereinabove can be incorporated into an unmanned, robotic surface vessel adapted for oil cleaning and recovery from a body of oil-contaminated water. For purposes of discussion only, the membranes 14 will be described in connection with one practical, potentially commercial embodiment of such a vessel 20, which is shown schematically in FIGS. 5 and 6.

[0044] With particular reference now to FIGS. 5 and 6, the vessel 20 includes a reduction chamber 22 with a reservoir 24 of electrolyte and a plurality of electrodes 26 in the form of passive rollers having a negative electric voltage. The vessel 20 also includes an oxidation chamber 28 with a reservoir 30 of electrolyte and a plurality of electrodes 32 in the form of passive rollers having a positive electric voltage.

[0045] A conveyor belt 34 includes a plurality of the smart membranes 14, which are spaced apart and electrically insulated from one another along the entire length of the conveyor belt 34. Active (i.e., driven) rollers 36 function as motive means for assisting in the performance of a method which includes the following steps: (i) passing the oxidized membranes 14 through the body of oil-contaminated water 10, where the lowest submerged portion of the membranes' surface (stable in the oxidized state) collects oil droplets 12 from the body of water 10; (ii) passing the membranes 14 through the reservoir 24 of electrolyte in the reduction chamber 22, where the membranes 14 are electrochemically reduced to thereby release collected oil droplets 12 with an assist from the simultaneous application of a dynamic pressure; and (iii) passing the membranes 14 through the reservoir 30 of electrolyte in the oxidation chamber 28, where the membranes 14 are oxidized to thereby regenerate them for reuse as oil-collection agents when they are subsequently passed back into the body of oil-contaminated water 10.

[0046] In connection with the performance of the aforementioned method, the membranes 14 can be reduced in the reduction chamber 22 by applying a negative voltage (e.g., −0.9 volts) to the rollers/electrodes 26 versus a 13 mm×35 mm platinum (Pt) mesh (i.e., counter-electrode).The subsequent oxidation of the membranes 14 can be achieved by applying a positive voltage (e.g., 0.1 volt) to the rollers/electrodes 32 versus a 13 mm×35 mm platinum (Pt) mesh (i.e., counter-electrode).

[0047] A partition 38 between the reduction chamber 22 and the oxidation chamber 28 electrically insulates the two chambers from each other so that the requisite and appropriate negative and positive voltages may be applied to the membranes 14 as they pass between the reduction chamber 22 and the oxidation chamber 28, respectively. The partition 38 also creates a physical barrier that inhibits collected oil 40 in the reduction chamber 22 from migrating to the oxidation chamber 28. The collected oil 40 may be cleaned in the reduction chamber 22 to thereby avoid re-contaminating the body of water 10 outside the vessel 20.

[0048] The rollers/electrodes 26, 32 are arranged inside the reduction and oxidation chambers, 22, 28 respectively, so as to maximize the amount of collected oil 40 housed within the vessel 20. The rollers/electrodes 26, 32 also serve to support the conveyor belt 34 as it passes through the reduction and oxidation chambers 22, 28, respectively.

[0049] In addition to the active rollers 36, which function as motive means (i.e., a drive system) for the conveyor belt 34, the vessel 20 includes a simple electric propulsion system (not shown), an onboard microcontroller (not shown) supporting remote control of the drive and propulsion systems, and a lithium polymer battery (not shown). The vessel 20 is designed to be sufficiently positively buoyant to take on additional weight during the performance of an oil-collection operation.

[0050] It will be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as defined in the appended claims.