Patent Application
20190358594
The invention generally relates to membranes and membrane modules and more particular the manufacture and arrangement of membrane modules and uses therefor.
Membrane-based fluid separation systems (for example, osmosis and pervaporation) are generally known in the prior art. Typically, these systems include a number of components that are plumbed together, which can increase the complexity and overall size of the systems. Additionally, needing to plumb the various components together results in the need for still more components (e.g., valves, fittings, etc.) and results in additional drawbacks for such systems (e.g., additional component costs and plumbing leaks).
Furthermore, those conventional systems tend to be arranged for single applications (e.g., a single pass or type of process). So in cases where multiple processes need to be performed and/or additional stages of a single type of process are desired, additional componentry and plumbing is required, again adding to the complexity and size of the systems. Specifically, multiple modules would need to be plumbed in series and/or parallel to suit a particular application, and once constructed, would not be easy to modify to, for example, accommodate a change in the system's requirements or repair a defect.
Additionally, the membranes used in the afore-mentioned fluid separation systems/processes typically include a thin film barrier layer disposed on a porous support layer. Traditionally, the membrane layers have been manufactured to suit a particular application and via traditional processes. See, for example, U.S. Pat. No. 7,882,963, the disclosure of which is hereby incorporated by reference herein in its entirety. Generally, membranes are put in service, and other than periodic cleaning, perform their intended functions for their useful life. Various modifications can be made to improve the performance of the membranes, for example, the incorporation of nanoparticles into a layer of the finished membrane to enhance fouling resistance and improve flux; however, the mere introduction of nanoparticles into a membrane does not automatically improve the performance of a typical membrane for every application. In addition, by virtue of the assembly/arrangement of a forward osmosis membrane module, the various membrane layers can be at risk of being damaged, where the damage can result in the passage of various solutes through the membrane. Accordingly, there remains a need for solutions to improving the performance of membranes, in particular forward osmosis membranes, which operate differently and have different requirements for optimization than conventional membranes (e.g., nanofiltration or reverse osmosis membranes).
Generally, the membranes and membrane cartridges/modules described herein can be used alone or in combinations and can be disposed within an enclosed housing or submerged in a tank, either an open or closed tank. In addition, the various membranes can be arranged in plate and frame or spiral wound configurations. Examples of various membrane configurations can be found in U.S. Pat. No. 8,181,794, U.S. Patent Publication No. 2011/0036774, and PCT Publication No. WO2013/022945, the disclosures of which are hereby incorporated by reference herein in their entireties. Furthermore, the various membranes described herein can be incorporated into a variety of osmotically driven membrane systems/processes. Examples of osmotically driven membrane processes are disclosed in U.S. Pat. Nos. 6,391,205 and 7,560,029; and U.S. Patent Publication Nos. 2012/0067819, 2011/0203994, 2012/0273417, and 2012/0267306; the disclosures of which are hereby incorporated herein by reference in their entireties.
In one aspect, the invention relates to a forward osmosis membrane module. The forward osmosis membrane module includes a membrane sheet comprising at least a support layer and a barrier layer disposed thereon, a first mesh screen disposed adjacent to the barrier layer of the membrane sheet, a second mesh screen disposed proximate the support layer of the membrane sheet, and a protective layer disposed between the second mesh screen and the support layer of the membrane sheet. The protective layer reduces or eliminates contact between the second mesh screen and the support layer of the membrane sheet. The membrane sheet is configured for passing a solvent therethrough via forward osmosis principles.
In various embodiments of the foregoing aspect of the invention, the protective layer expands over substantially an entire surface of the barrier layer and includes a nonwoven fabric layer having a thickness of about 1.5 mils to about 20 mils. The protective layer can be made from polyethylene terephthalate (PET) or similar material. In some embodiments, the protective layer has a basis weight of about 50 to about 100 g/m2 and/or a Frazier air permeability of about 100 to about 1000 cfm/ft2. In one or more embodiments, the first mesh screen has a thickness of about 0.020 inches with a strand spacing of 16 strands per inch and a strand orientation of 90 degrees, and the second mesh screen has a thickness of about 0.034 inches with a strand spacing of 18 strands per inch and a strand orientation of 90 degrees. One or more of the first mesh screen, the second mesh screen, or the protective layer can be secured to the membrane sheet via an adhesive, such as a small amount glue about the periphery of the membrane so as not to interfere with the active area of the membrane. Heat sealing and/or sonic welding are also contemplated. In various embodiments, the membrane module can be wrapped around a center tube to form a spiral would membrane assembly.
In another aspect, the invention relates to a membrane assembly including a forward osmosis membrane module and a housing at least partially enclosing the forward osmosis membrane module. The forward osmosis membrane module includes a membrane sheet having at least a support layer and a barrier layer disposed thereon, a first mesh screen disposed adjacent to the barrier layer of the membrane sheet, a second mesh screen disposed proximate the support layer of the membrane sheet, and a protective layer disposed between the second mesh screen and the support layer of the membrane sheet. The protective layer reduces or eliminates contact between the second mesh screen and the support layer of the membrane sheet. The membrane sheet is configured for passing a solvent therethrough via forward osmosis principles. The housing can include means for fluid ingress and fluid egress. In addition, the housing can be a vessel that completely encloses the membrane module in, for example, a spiral wound or plate and frame configuration. Alternatively, the housing can be configured to only partially enclose the membrane module or may consist of a skeleton or framework for holding the modules together for use in an immersed application.
In various embodiments of the foregoing aspect, the means for fluid ingress include a first inlet for introducing a feed solution to one side of the membrane module and a second inlet for introducing a draw solution to an opposite side of the membrane module. The means for fluid egress include a first outlet for discharging a concentrated feed solution from one side of the membrane module and a second outlet for discharging a dilute draw solution from the opposite side of the membrane module. In one or more embodiments, the housing is a pressure vessel and the membrane module is wrapped around a center tube to form a spiral wound membrane assembly. In an alternative embodiment, the membrane module has a substantially planar configuration and is assembled in a plate and frame configuration.
In another aspect, the invention relates to a forward osmosis membrane with improved rejection characteristics. The membrane includes a substantially planar substrate, a polymeric support layer disposed on the substantially planar substrate, and a polymeric barrier layer disposed on the polymeric support layer. The barrier layer includes a plurality of layered double hydroxide nanoparticles substantially evenly dispersed within the barrier layer. Generally, the phrase “evenly dispersed” is used to denote that the nanoparticles have not settled onto the polymeric support layer, but instead are generally situated above the junction between the support layer and the barrier layer. In some embodiments, a surfactant can be added to the first bath with the nanoparticles to prevent the nanoparticles from stratifying in the top or bottom layers.
In various embodiments of the foregoing aspect, the substantially planar substrate can include a polymeric paper or other type of non-woven substrate. The support and barrier layers can be deposited onto the membrane assembly via, for example, interfacial polymerization or other suitable means. In one or more embodiments, the layered double hydroxide nanoparticles comprise flakes of Mg/Al-LDH, for example, MgnAln-1(OH)2. The nanoparticle flakes may include a longitudinal axis and the longitudinal axes are oriented horizontally or in parallel relative to the barrier layer (i.e., the flakes essentially lie “flat” within the barrier layer). In various embodiments, the layered double hydroxide nanoparticles include Magnesium (Mg) and Aluminum (Al) in a ratio of about 1:1 to about 10:1. In a particular embodiment, the ratio is 3:1.
In yet another aspect, the invention relates to a method of manufacturing a forward osmosis membrane. The method includes the steps of providing a substantially planar substrate, casting a polymeric support layer onto the substantially planar substrate, and casting a polymeric barrier layer onto the polymeric support layer. The barrier layer includes a plurality of layered double hydroxide nanoparticles substantially evenly dispersed within the barrier layer.
In various embodiments of the foregoing aspect, the step of casting the barrier layer includes the steps of introducing the layered double hydroxide nanoparticles into a solvent bath comprising a first monomer, introducing the substantially planar substrate and support layer to the solvent bath, subjecting the substantially planar substrate and support layer to means for dispersing the layered double hydroxide nanoparticles, introducing the substantially planar substrate and support layer to a second bath, wherein the second bath comprises a second monomer, and reacting the monomers to form the barrier layer and set the nanoparticles in place within the barrier layer. The means for dispersing can include subjecting the solvent bath to an energy field, such as ultrasonic, electro-magnetic, or thermal, applied constantly or in a pulsed manner. The means for dispersing can be applied to the solvent bath continuously as the membrane substrate and support layer are passed therethrough. Alternatively or additionally, the means for dispersing can be applied directly to the membrane substrate, for example, as it passes from the first bath to the second bath.
In additional aspects, the invention relates to forward osmosis membrane systems and/or methods of facilitating a forward osmosis separation operation that may include any of the membrane modules described herein.
Osmotic separation processes generally involve generating water flux across a semipermeable membrane based on osmotic pressure differentials. Solute may be rejected by the membrane and retained on either side due to the greater permeability of water than the solute with respect to the selective barrier of the membrane. Solutes may be undesirable and therefore removed from a process stream via membrane separation for purification, or desirable in which case they may be concentrated and collected via a membrane separation process. Membranes may be used in various osmotically driven separation processes, such as but not limited to desalination, wastewater purification and reuse, FO or PRO bioreactors, concentration or dewatering of various liquid streams, concentration in pharmaceutical and food-grade applications, PRO energy generation and energy generation via an osmotic heat engine.
Typically, polymeric membranes typically include a porous support structure that provides mechanical and structural support for a selective layer. Membranes may be formed in various shapes including spiral wound, hollow fiber, tubular and flat sheet depending on an intended application. Membrane characteristics should be customized to achieve ideal performance and may vary between specific applications. For example, in FO and PRO applications, the effectiveness of a separation process may be enhanced by reducing the thickness and tortuosity of the membrane, while increasing its porosity and hydrophilicity, without sacrificing strength, salt rejection, and water permeability properties.
A selective (i.e., barrier) or otherwise active layer may be applied to the support material of a substrate during a membrane manufacturing process. In some embodiments, a semipermeable layer may be applied as the active layer. The semipermeable layer may comprise a polymer. In certain embodiments, the semipermeable layer may comprise a polyamide, such as polyamide urea, a block co-polymer, or polypiperazine. In some non-limiting embodiments, a polysulfone layer may be applied to a PET support layer of a bilayer substrate.
The substrate material may be conveyed to a polymer application device which applies a solution of polymer, for example polysulfone, in a solvent, for example dimethylformamide. Upon coating, the substrate may enter a quenching bath in which the polymer precipitates into the top layer of the bilayer material. The temperature of the quenching bath may vary and may impact one or more properties of a resultant membrane. In at least some preferred non-limiting embodiments, improved properties of forward osmosis membranes may be associated with quenching bath temperature in the range of 100° F. to 110° F.
In accordance with one or more embodiments, the selective barrier in the disclosed thin-film composite membranes may be a semipermeable three-dimensional polymer network, such as an aliphatic or aromatic polyamide, aromatic polyhydrazide, poly-bensimidazolone, polyepiamine/amide, polyepiamine/urea, polyethyleneimine/urea, sulfonated polyfurane, polybenzimidazole, polypiperazine isophtalamide, a polyether, a polyether-urea, a polyester, or a polyimide or a copolymer thereof or a mixture of any of them. In certain embodiments, the selective barrier may be an aromatic or non-aromatic polyamide, such as residues of a phthaloyl (e.g., isophthaloyl or terephthaloyl) halide, a trimesyl halide, or a mixture thereof. In another example, the polyamide may be residues of diaminobenzene, triaminobenzene, polyetherimine, piperazine or poly-piperazine or residues of a trimesoyl halide and residues of a diaminobenzene. The selective barrier may also comprise residues of trimesoyl chloride and m-phenylenediamine. Further, the selective barrier may be the reaction product of trimesoyl chloride and m-phenylenediamine.
In accordance with one or more embodiments, the selective barrier may be characterized by a thickness adequate to impart desired salt rejection and water permeability properties while generally minimizing overall membrane thickness. In certain embodiments, the selective barrier may have an average thickness from about 50 nm and about 200 nm. The thickness of the barrier layer is desired to be as limited as possible, but also thick enough to prevent defects in the coating surface. The practice of polyamide membrane formation for pressure driven semi-permeable membranes may inform the selection of the appropriate barrier membrane thickness. The selective barrier may be formed on the surface of a porous support via polymerization, for example, via interfacial polymerization.
Polymers that may be suitable for use as porous supports in accordance with one or more embodiments include polysulfone, polyethersulfone, poly(ether sulfone ketone), poly(ether ethyl ketone), poly(phthalazinone ether sulfone ketone), polyacrylonitrile, polypropylene, poly(vinyl fluoride), polyetherimide, cellulose acetate, cellulose diacetate, and cellulose triacetate polyacrylonitrile.
In accordance with one or more embodiments, the support layer may be characterized by a thickness adequate to provide support and structural stability to a membrane during manufacture and use while generally minimizing overall membrane thickness. In certain embodiments, the polymer support may have an average thickness from about 10 μm and to about 75 μm. It is generally desirable for the support to be as thin as possible without compromising the quality of the support surface for interfacial polymerization of the barrier layer. The smoother the support layer is, the less thickness of support material is generally required for this criterion. In at least some preferred embodiments, this layer is less than approximately 40 μm. In certain embodiments, the porous support comprises a first side (active side) with a first plurality of pores, and a second side (support side) with a second plurality of pores. In certain embodiments, the first plurality of pores and the second plurality of pores are fluidly connected to each other. In one embodiment, polymeric additives are dispersed within the porous support. Additives may enhance hydrophilicity, strength or other desirable properties.
A desired degree of cross-linking may be achieved within the active layer, such as to improve the barrier properties of the membrane. Inducing cross linking in the polyamide layer is generally desirable to improve salt rejection and overall performance. In accordance with one or more embodiments, cross-linking is achieved in a manner such that the hydrophilic materials are not reduced in their performance, and are maintained in a wet state throughout the manufacturing and treatment process. In some embodiments, hot water annealing may be used to facilitate cross-linking. In other embodiments, heat treatment may occur in one or more of the immersion steps of the membrane fabrication process, during or after the active layer deposition or formation process. In other embodiments, chemical treatment may be used. In at least one embodiment, heat drying, such as oven drying, is not used. In some such embodiments, the membranes will readily rewet by immersion in water, and in some embodiments, they will rewet by exposure to a wetting agent in conjunction with water, such that they will be substantially wet when ready for use. In some embodiments, the membranes may be characterized as having a salt rejection of at least 99% or greater. The forward osmosis membranes may generally be relatively thin and characterized by high porosity, low tortuosity, and high wettability. The membranes may find use in a variety of applications including osmotic-driven water purification and filtration, desalination of seawater, purification of contaminated aqueous waste streams, separation of various aqueous streams, osmotic power generation and the like.
In some embodiments, phase inversion of a polymer coated on or around a material intended primarily to give the polymer resistance to deformation with strain may be used to create a membrane support. For example, a very open and thin woven or non-woven material may be surrounded by the polymer, rather than underneath it. Interfacial polymerization of a rejecting polymer may then be carried out on this support structure. In accordance with one or more embodiments, a forward osmosis membrane may be a hydrophilic phase inversion membrane on a woven or non-woven fabric. The hydrophilic material may be PAN in some non-limiting embodiments, alone or mixed with other monomers. The fabric layer may be of any desired thickness. In some non-limiting embodiments, the fabric may be about 25 micrometers in thickness. The forward osmosis membrane may be further characterized by polyamide interfacial polymerization on its surface. A polyamide active layer may be applied so as to result in a membrane of any desired thickness. In some non-limiting embodiments, the membrane may be approximately 25 micrometers thick. The active layer of the forward osmosis membrane may be modified to enhance rejection of draw solutes. The support film may be nonwoven and made of any material, but thinness, high porosity, low tortuosity, and hydrophilicity are generally desirable. The thickness of the support film may vary. In some embodiments, the support film may be less than about 100 micrometers, less than about 80 micrometers, less than about 50 micrometers or thinner. In at least one embodiment, a porous polyester nonwoven support film may be used as a substrate.
In accordance with one or more embodiments, a forward osmosis membrane may be formed by first creating a support layer. In some non-limiting embodiments, a thin fabric backing layer of less than about 30 micrometers may be coated with a polysulfone solution of about 10% to about 20%, preferably about 12% to 16%, and more preferably about 13.5% to 15% in dimethylformamide. Lower concentrations of polysulfone may be used to further improve forward osmosis membrane properties, including flux. In some embodiments, the amount of polysulfone coating may generally be less than about 16 g/m2 to minimize the impact of the support layer on diffusion. The resulting support layer precursor may then be immersed in room temperature water causing the phase inversion of the polymer. Immersion in temperatures greater than 90° F. may be used to improve the pore size characteristics of the support layer. This may produce a thin, micro-porous, open support structure with an embedded web giving the polymer strength for rolling and handling. The active layer may then be applied to the support structure. One example of the coating of this support structure with the active layer would be the immersion of the support in a solution containing polyamide or other desired active material. In one embodiment, the support structure may be immersed in a 3.4% solution of 1-3 phenylenediamine in room temperature water. The concentration of the solution may vary based on desired characteristics of the applied active layer. Duration of immersion may also vary. In some embodiments, the duration may be less than about 5 minutes. In one exemplary embodiment, the duration of immersion may be about 2 minutes. Excess solution from the surface of the membrane may be removed, for example with a roller or air knife.
The membrane may then be briefly immersed in another solution to induce the polymerization of the polyamide rejecting layer by combination of the diamine in the aqueous phase and, for example, acid chloride in the non-aqueous phase, at the surface of the support material where the phases meet. In some embodiments, the membrane may be immersed in the solution for about 2 minutes. In one embodiment, a 0.15% solution of 98% 3,5 benzenetricarbonyltrichloride in Isopar® C or G at room temperature may be used. The membrane may then be removed and the Isopar® allowed to evaporate from the membrane for a period of time, for example less than about 5 minutes. In some embodiments, the duration of the evaporation step may be about 2 minutes. In some embodiments, immersion may take the form of a dip coating process, such as one in which substantially only the surface of the membrane comes into contact with a solution. In other embodiments, the entire membrane may be submerged in the bath. In some embodiments, a combination of these techniques may be used, such as in a sequence of different immersion steps. In other embodiments, the heat treatment of the membrane may occur in any or several immersion steps intended for other purposes, such as during or after the active layer polymerization or deposition step.
These and other objects, along with advantages and features of the present invention herein disclosed, will become apparent through reference to the following description and the accompanying drawings. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations.
In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention and are not intended as a definition of the limits of the invention. For purposes of clarity, not every component may be labeled in every drawing. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:
The membrane plates 12, 14 include complimentary shapes and flow paths, as discussed below, and are arranged in an alternating fashion to direct different process streams along predetermined flow paths. The bulkheads 17 and body 15 include a plurality of ports 22, 23 providing inlets and outlets for the various flows. As shown in
In accordance with one or more embodiments, the membranes are configured in a flat sheet forward osmosis membrane module design 200. A flat sheet membrane envelope may facilitate draw solution flow inside a membrane envelope. A membrane sheet 201 may be glued between two plastic frames 203 that provide structural support as illustrated in
In at least some embodiments, the draw solution may increase substantially in volume as it flows through the envelope as a result of water transport across the membrane. With such a flow configuration, the velocity of the draw solution through the module 200 may increase as the volume increases, which may lead to increased pressure drop and required pumping energy. In accordance with one or more embodiments, a relatively constant draw solution velocity may be beneficially maintained as the volume increases from the inlet to outlet of the module 200. Alternatively, as illustrated in
In accordance with one or more embodiments, membrane envelopes may be configured into a module consisting of multiple envelopes. Final spacing between envelopes and the dimensions of the module may be determined during product development. For example, in one non-limiting embodiment, three envelopes per inch of module width may be used for estimating membrane area per unit volume. With respect to
As also shown in
In some embodiments, the combined frame 303′ and spacer 307′ can be formed by incorporating (e.g., via injection molding) a molten plastic into the perimeter of a soft mesh screen (i.e., the spacer), where the hardened plastic will form the frame 303′ and be sufficiently rigid that the membrane sheets can be secured thereto (e.g., by sonic welding or heat sealing). The hardened plastic will also allow for the interfacing with additional plates or membrane assemblies and will provide rigidity to the entire assembly. Additionally, the molten plastic can applied to the mesh screen and molded as necessary to also form flow channels, manifolds, and ports that can replace the multiple plates, manifolds, ports, etc. described elsewhere herein.
The module 400 of
The module 400 of
Generally, the channel widths will be selected to suit a particular application, e.g., flow requirements, dimensions of spacers, etc. and will typically be determined by the dimensions of the frames. In one or more embodiments, the draw channels are about 0.010 to about 0.50 inches thick, preferably about 0.018 to about 0.060 inches thick. In one embodiment, the frame is about 0.034 inches thick to accommodate a 0.034 thick spacer. The feed channels may have similar dimensions (although are typically larger) and are generally sized to provide room for the flow of feed solution and possibly provide space for substances that may precipitate out of the solution. In the case of multiple single modules disposed, for example in a tank, the feed channel spacing will be determined by the placement of the modules within the tank and the draw channel spacing (i.e., module interior space) will be determined by the spacers and any necessary protective layers.
The module 700 can also include means 723 for attaching or otherwise securing the module to a tank or other modules. In one embodiment, the means for attachment 723 are arms that extend from the frame and include receptacles and/or protuberances that correspond to similar structures on the tank. In one embodiment, the attachment means 723 are simple hooks for engaging the tank sidewalls. The attachment means 723 can be constructed as part of the frames 703 or be optional pieces that can be attached to the frames. In one or more embodiments, the attachment means 723 can include hardware 725, such as mechanical fasteners or clamps, that assist in securing the modules to the tank or one another or, in some cases, the attachment means 723 to the frames/modules. Additionally or alternatively, the tank may include structure (e.g., baffles or other protuberances) for maintaining a membrane module within the tank in a specific orientation and/or secure the module thereto.
In alternative embodiments, the tank has a closed design, which allows for the pressurization of the solution (e.g., feed solution) within the tank. This can assist the overall process by increasing the flux through the membranes and can reduce or eliminate any issues with the membranes bulging under the pressure of the solution (e.g., draw solution) within the membrane module. Alternatively or additionally, the (draw) solution can be “pulled” through the membrane modules under vacuum.
The membrane 851 has a feed side that typically corresponds to the membrane barrier layer and a permeate side that typically corresponds to the membrane support layer. Typically for a forward osmosis application, the feed side is at a higher pressure than the draw side, which tends to push the membrane away from the feed and into contact with the draw screen. (For a PRO application, the draw side, which would then be the barrier layer side of the membrane, would be at the higher pressure) In the case of very thin membranes, and in particular those that have a very thin support layer such as those made in accordance with the present assignee's commonly owned U.S. Pat. No. 8,181,794, the high points on the surface of the draw screen can pierce the support layer and barrier layer and damage the membrane, especially in the spiral wound configuration. Generally, the feed and draw screens 853, 855 are relatively porous and resilient as they need to maintain the spacing between layers of membrane. As such, it is not possible to replace or eliminate the draw screen, and an additional protective layer 857 is necessary between the draw screen 855 and the membrane sheet 851. However, the protective layer 857 must balance protecting the fragile membrane 851 and not impeding flux or the flow of draw solution.
In one or more embodiments, the protective layer is a nonwoven fabric layer having a thickness of about 1.5 mils to about 20 mils, preferably about 5 mils to about 15 mils, and more preferably about 7 mils to about 10 mils. The layer is typically made of PET; however, other polymers that are compatible with the various solutions are contemplated and considered within the scope of the invention. In addition, the protective layer 857 will have a basis weight of about 50 to 100 g/m2, preferably about 60 to 80 g/m2, and more preferably about 70 to 75 g/m2 and a Frazier air permeability of about 100 to 1000 cfm/ft2, preferably 200 to 500 cfm/ft2, and more preferably about 350 to 400 cfm/ft2. In one or more embodiments, the draw screen has a thickness of about 10 mils to about 60 mils, preferably about 20 mils to about 40 mils and more preferably 34 mils (i.e., 0.034 inches), with a strand spacing of about 8-24 strands per inch (SPI), preferably 12-20 SPI, and more preferably 18 SPI with a strand orientation angle of about 90 degrees. In one or more embodiments, the feed screen has a thickness of about of about 10 mils to about 60 mils, preferably about 20 mils to about 40 mils and more preferably 20 mils (i.e., 0.020 inches), with a strand spacing of about 8-24 SPI, preferably 12-20 SPI, and more preferably 16 SPI with a strand orientation angle of about 90 degrees. The screens 853, 855 are typically made of polypropylene; however, other compatible polymers are also possible.
Various components of the modules can be manufactured from a variety of materials including, for example, polymers, polymer blends, and block co-polymers and can be manufactured by, for example, molding, extrusion, stamping, or other known manufacturing techniques. The various membrane sheets can be manufactured from any suitable materials, such as those disclosed in U.S. Patent Publication Nos. 2007/0163951, 2011/0036774, 2011/0073540; and 2012/0073795; the disclosures of which are hereby incorporated by reference herein in their entireties. The particular materials used will be selected to suit a particular application and should be able to withstand the various process conditions, for example, high temperatures, and for fluid compatibility.
The overall size and number of membrane modules and membranes will be selected to suit a particular application with a focus on providing a specific total membrane surface area. In addition, the membrane parameters will also be selected to suit a particular application with a focus on obtaining a particular flux rate, where flux (JW)=A (Δπ−ΔP), where A=specific permeability (m/s/atm); Δπ=osmotic pressure difference at surface of membrane selective layer, and ΔP=pressure across membrane. The flux rate will also be impacted by the flow rates of the draw and feed solutions, which will be chosen to maximize residence time, but minimize concentration polarization (CP). In one example, an assembly having 50 membrane modules, each having an active membrane area of about 1′ by 3′ (3 ft2) will result in an approximate total effective membrane surface area of 150 ft2. If used, for example, with a thin film composite polyamide membrane designed for osmotically driven flux, a flux of approximately 1500 gallons per day would be expected from an assembly of this type used in a seawater desalination environment with an average flux of about 10 gallons per ft2 per day (GFD).
One example of a suitable membrane is disclosed in the incorporated U.S. Pat. No. 8,181,794. The membrane disclosed therein can be further enhanced by, for example, using polyethersulfone support structures, which may produce a different pore structure and provide improved flux/rejection properties in FO or RO applications. Additionally, the charge on one of the membrane layers, for example, the barrier layer, can be changed, which may also improve the performance of the membrane. Also, the various layers of the membrane can be modified by the incorporation of nanoparticles or anti-microbial substances. For example, layered double hydroxide (LDH) nanoparticles can be incorporated into the barrier layer to improve the flux/rejection characteristics of the membrane. These various modifications may also improve the reverse salt flux performance of the membrane. Additionally, these various improvements are also applicable to hollow fiber type membranes.
In one or more embodiments, the membrane includes a LDH in the form of MgnAln-1 (OH)2. The ratio of Mg to Al may be about 1:1 to about 10:1, preferably about 2:1 to about 5:1, and more preferably 3:1; however, the specific ratio will be selected to suit a particular application. In some embodiments, the nanoparticles are organo-metallic compounds. This particular composition is represented in
Typically, there is a feed solution 911 on one side of the membrane 900 and a draw solution 912 on the other side. Solvent (e.g., water) will flux through the barrier and dilute the draw solution 912. Solutes 908 within the feed solution 911 are generally rejected by the barrier layer. Generally, in prior art systems, solutes from the draw solution will attempt to reverse flux through the membrane into the feed solution. With the additional charge at the juncture between the barrier layer 904 and the support layer 902, certain of the solutes 914 within the draw solution 912 will be repelled/rejected by the charge provided by the nanoparticles. In the embodiment shown, the nanoparticles provide a negative charge; however, other nanoparticle compositions can be used to provide a positive charge to preferentially reject other solutes 914. Additionally, certain support layer materials can also be selected to provide a charge therein, which can be cumulative with the charge of the nanoparticles to provide a particularly strong rejecting force. For example, a polyethersulfone, which is more hydrophilic, may give a greater negative charge, which will be additive to the charge of the nanoparticles, thereby creating a double electrical layer. Generally, the membrane materials, draw solutes, and membrane charge can be selected to suit a particular application.
The support layer 1002 is then feed through a second bath 1008 having THC in solution with hexane or Isopar G, although other solvents are contemplated and considered within the scope of the invention. The introduction of the monomer from the first bath with the monomer of the second bath creates the polymeric barrier layer (e.g., polyamide) with the nanoparticles at least partially dispersed therein and fixed in place. The membrane (support layer and barrier layer) can then be directed to additional, conventional processes (e.g., wash, quench, etc.) to complete the membrane manufacturing process.
Having now described some illustrative embodiments of the invention, it should be apparent to those skilled in the art that the foregoing is merely illustrative and not limiting, having been presented by way of example only. Numerous modifications and other embodiments are within the scope of one of ordinary skill in the art and are contemplated as falling within the scope of the invention. In particular, although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objectives.
Moreover, it should also be appreciated that the invention is directed to each feature, system, subsystem, or technique described herein and any combination of two or more features, systems, subsystems, or techniques described herein and any combination of two or more features, systems, subsystems, and/or methods, if such features, systems, subsystems, and techniques are not mutually inconsistent, is considered to be within the scope of the invention as embodied in any claims. Further, acts, elements, and features discussed only in connection with one embodiment are not intended to be excluded from a similar role in other embodiments.
Furthermore, those skilled in the art should appreciate that the parameters and configurations described herein are exemplary and that actual parameters and/or configurations will depend on the specific application in which the systems and techniques of the invention are used. Those skilled in the art should also recognize or be able to ascertain, using no more than routine experimentation, equivalents to the specific embodiments of the invention. It is, therefore, to be understood that the embodiments described herein are presented by way of example only and that the invention may be practiced otherwise than as specifically described.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/793,184, filed Mar. 15, 2013; the entire disclosure of which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61793184 | Mar 2013 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14204433 | Mar 2014 | US |
| Child | 15860997 | US |
