Title:
THIN FILM MEMBRANES WITH ADDITIVES FOR FORWARD AND PRESSURE RETARDED OSMOSIS
Kind Code:
A1


Abstract:
A thin film composite or TFC membrane formed by interfacial polymerization of an organic and aqueous phase on a support membrane with nanoparticles in the discrimination layer and/or the support membrane, optimized by the selection of nanoparticles for membrane flux, hydrophilicity and to minimize thickness of the support membrane while maintaining the strength and ruggedness characteristics required for forward osmosis (FO) and/or pressure retarded osmosis (PRO) so that the flux flow paths are less tortuous than conventional support membranes and thereby provide increased flux flow.



Inventors:
Kurth, Christopher James (Eden Prairie, MN, US)
Burk, Robert Leon (Seattle, WA, US)
Application Number:
12/436063
Publication Date:
11/05/2009
Filing Date:
05/05/2009
Assignee:
NANOH20 INC. (Los Angeles, CA, US)
Primary Class:
International Classes:
B01D61/02; C02F1/44
View Patent Images:
Related US Applications:



Primary Examiner:
FORTUNA, ANA M
Attorney, Agent or Firm:
FISH & RICHARDSON P.C. (TC) (PO BOX 1022, MINNEAPOLIS, MN, 55440-1022, US)
Claims:
1. A forward or pressure retarded osmosis process, comprising: providing a porous support membrane having nanoparticles disposed therein; applying a draw solution to a discrimination membrane interfacially polymerized on the porous support membrane; and applying a feed solution to the discrimination layer for diffusion there through to the draw solution to remove contaminants from, or utilize increased pressure in, the draw solution.

2. The forward or pressure retarded osmosis process of claim 1, wherein applying a draw solution to a discrimination membrane interfacially polymerized on the porous support membrane further comprises: applying the draw solution to the porous support membrane for diffusion there through to the discrimination layer.

3. The forward or pressure retarded osmosis process of claim 1, wherein applying a feed solution to the discrimination layer for diffusion there through into the draw solution, comprising: applying the feed solution to the porous support membrane for diffusion there through to the discrimination layer.

4. The forward or pressure retarded osmosis process of claim 1, further comprising: utilizing increased pressure in the draw solution resulting from transport of the feed solution across the discrimination membrane into the draw solution.

5. The forward or pressure retarded osmosis process of claim 1, further comprising: contaminants may be removed from the feed solution resulting from transport of the contaminants across the discrimination membrane into the draw solution.

6. The process of claim 1, wherein providing a porous support membrane having nanoparticles disposed therein further comprises: providing a porous support membrane having the structural strength of a thicker porous support membrane as a result of having the nanoparticles disposed therein.

7. The process of claim 1, wherein providing a porous support membrane having nanoparticles disposed therein further comprises: providing a porous support membrane having the structural strength of a more porous support membrane as a result of having the nanoparticles disposed therein.

8. The process of claim 1, wherein providing a porous support membrane having nanoparticles disposed therein further comprises: providing a thinner porous support membrane having the required structural strength for the process as a result of having the nanoparticles disposed therein.

9. The process of claim 1, wherein providing a porous support membrane having nanoparticles disposed therein further comprises: providing a porous support membrane having less tortuous feed solution transport paths as a result of having the nanoparticles disposed therein.

10. The process of claim 1, wherein providing a porous support membrane having nanoparticles disposed therein further comprises: providing a porous support membrane having increased hydrophilicity as a result of having the nanoparticles disposed therein.

11. The process of claim 1, further comprising: providing the discrimination membrane including additives dispersed therein added to an organic and/or an aqueous phase before the organic and aqueous phases were contacted during the interfacial polymerization so that the discrimination layer has increased solvent permeability as a result of the additives therein.

12. The process of claim 11 wherein providing the discrimination membrane including additives dispersed therein further comprises: providing the discrimination membrane including the same or different nanoparticles dispersed therein.

13. The process of claim 12 wherein providing the discrimination membrane including the same or different nanoparticles dispersed therein further comprises: providing the discrimination membrane also including alkaline earth metals dispersed therein.

14. The process of claim 12 wherein providing the discrimination membrane including the same or different nanoparticles dispersed therein further comprises: providing the discrimination membrane also including alkaline earth metals dispersed therein.

15. The process of claim 13 wherein providing the discrimination membrane also including alkaline earth metals dispersed therein further comprises: providing the discrimination membrane also including mhTMC as an additive dispersed therein.

16. The process of claim 11 wherein providing the discrimination membrane including additives dispersed therein further comprises: providing the discrimination membrane including alkaline earth metals dispersed therein.

17. The process of claim 16 wherein providing the discrimination membrane including alkaline earth metals dispersed therein further comprises: providing the discrimination membrane also including mhTMC as an additive dispersed therein.

18. The process of claim 11 herein providing the discrimination membrane including additives dispersed therein further comprises: providing the discrimination membrane including mhTMC as an additive dispersed therein.

19. The process of the claim 1, further comprising: providing the discrimination membrane including additives dispersed therein added to an organic and/or an aqueous phase before the organic and aqueous phases were contacted during the interfacial polymerization so that the discrimination layer has increased solvent permeability as a result of the additives therein.

20. The process of claim 1, wherein the draw solution is seawater and the feed solution is fresh water.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the priority of provisional application 61/050,572, filed May 5, 2008 and Ser. No.12/424,533 filed Apr. 15, 2009, incorporated in herein in full and attached hereto as Appendix A for that purpose.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is related to thin film composite membranes, which may be called TFC membranes, and more particularly to such membranes used for forward osmosis or FO, for example to purify water, or for pressure retarded osmosis or PRO, for example to generate power from the mixing of salt water and pure water.

2. Description of the Prior Art

RO membranes are often made by interfacial polymerization or IFP of a monomer in a nonpolar (e.g. organic) phase together with a monomer in a polar (e.g. aqueous) phase on a porous support membrane. The support membrane is used for structural support of the IFP membrane during manufacturing and during operation. RO membranes, such as IFP RO membranes (that is, RO membranes made by interfacial polymerization processes), may be used for osmosis where water flows naturally from a pure solvent or feed solution, to a less pure solution or draw solution. However, when IFP RO membranes are used for FO or PRO, the solvent, typically water, and the solute, typically water diluted with inorganic or organic salts, or other soluble molecules, tend to dilute each other and reduce membrane efficiency. Further, the support membrane, which is used primarily for structural support, reduces water flux to some degree, and the solvent and solute become mixed in solution in the thickness of the support membrane structure including a fabric, further reducing membrane efficiency for both FO and PRO processes.

What are needed are improved membranes with enhanced efficiency for use in FO and PRO processes.

SUMMARY OF THE INVENTION

In one aspect, a forward or pressure retarded osmosis process may include providing a porous support membrane having nanoparticles and/or other additives disposed therein, applying a draw solution to one side of a discrimination membrane interfacially polymerized on the porous support membrane and applying a feed solution to another side of the discrimination layer for diffusion there through to remove contaminants from, or utilize increased pressure in, the draw solution. The feed solution may be applied to the porous support membrane for the another side of the discrimination layer.

The increased pressure in the draw solution resulting from transport of the feed solution across the discrimination membrane into the draw solution may be used. Contaminants from the feed solution may be removed resulting from transport of the contaminants across the discrimination membrane into the draw solution.

The porous support membrane may have the structural strength of a thicker porous support membrane or a less porous support membrane as a result of having the nanoparticles and/or other additives disposed therein. A thinner support membrane, and/or a membrane with less tortuous feed solution transport paths may be used as a result of having the nanoparticles and/or other additives disposed therein.

The discrimination membrane may including additives dispersed therein added to an organic and/or an aqueous phase before the organic and aqueous phases were contacted during the interfacial polymerization so that the discrimination layer has increased feed solution permeability as a result of the additives therein. The discrimination membrane may include the same or different nanoparticles and/or alkaline earth metals and/or other metals and/or mhTMC as an additive dispersed therein. The membrane may have increased feed solution permeability as a result of the additives therein. The draw solution may be seawater and the feed solution may be fresh water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded diagrammatic view of membrane 10 during a fabrication processing including nanoparticle/additives 16 in aqueous phase 14 and/or organic phase 18 and/or porous support 12 and/or fabric 20.

FIG. 2 is a cross-sectional view of membrane 10 with nanoparticle/additives 16 dispersed in discrimination layer 24 and support layer 12.

FIG. 3 is a graph of resistance to flow, illustrating compaction as a function of time, during initial operations of control membrane 52—without nanoparticles/additives 16—and for membranes 54, 56 and 58 with nanoparticle/additives 16 dispersed in various layers.

FIG. 4 is a photomicrograph illustrating the operation of the dual beam FIB-SEM technique used for FIGS. 5-7.

FIG. 5 is an FIB-SEM of support membrane 12—with nanoparticle/additives 16 dispersed therein—after 8 hours of operation of membrane 12 at 800 psi.

FIGS. 6,7 are FIB-SEMs of support membrane 64, without nanoparticle/additives 16 dispersed therein, after 1 and 8 hours of operation, respectively.

FIG. 8 is a diagrammatic view of an IFP FO/PRO membrane in a conventional cylindrical housing, canister 66.

FIG. 9 is a diagrammatic view of membrane 10 during operation as an FO or RO membrane including a graph of salinity superimposed thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now to FIG. 1, an exploded view of membrane 10 illustrating the fabrication process is shown in which membrane 10 may include organic phase layer 18, aqueous phase layer 14, porous support membrane 12 and fabric layer 20. One or more types of nanoparticles 16, or other additives as discussed below in greater detail, may be included in aqueous or organic phases 14, 18 before contact there between for interfacial polymerization so that nanoparticles 16 are dispersed in discrimination layer 24 as shown in FIG. 2. Nanoparticles/additives 16 may also be dispersed in support layer 12 and fabric 20.

Referring now also to FIG. 2, a portion of membrane 10 is illustrated after fabrication including nanoparticles and/or other additives 16, in discrimination layer 24 as well as nanoparticles/additives 16 in support layer 12 which may be the same or different than those—if any—used in discrimination layer 24. In a conventional thin film composite or TFC membrane, made without nanoparticles/additives 16, the typical layer thicknesses are as shown, the discrimination layer is on the order of 0.1 microns (100 nm) thick, the support layer is typically on the order of 50 microns thick and the fabric layer is typically on the order of 100 microns thick. These thicknesses of layers are conventionally required for structural support.

Nanoparticles/additives 16, which may used in porous support layer 12 to add strength to support membrane 12, advantageously may permit a substantially thinner support membrane to be used under the same conditions as a conventionally made support membrane is used as discussed in more detail below. Similarly, the same or different nanoparticles 16 may be added to fabric layer 20 to provide further structure support and ease of handling for support membrane 12 and membrane 10. For example, the conventionally used 50 micron thickness of support layer for TFC membranes, such as membrane 10, when strengthened by the addition of nanoparticles 16, provides perhaps twice as much structural strength as provided by the same support layer without nanoparticles/additives 16 and may be replaced by a substantially thinner layer such as a 25 micron layer without any loss of required strength as shown below with regard to FIG. 9. Similarly, when nanoparticles/additives 16 are added, the thickness of fabric 20 may be reduced by perhaps about 25% to 50% as also shown below in FIG. 9.

During fabrication, support membrane 12 is often formed by casting on fabric 20. Nanoparticles/additives 16 may be added to aqueous phase 14 and/or organic phase 18 before such phases are contacted together for IFP. Aqueous phase 14 is typically applied to support 12 and then organic phase 18 is applied to aqueous phase 14 which begins the IFP process, forming discrimination layer 24.

In particular with regard to the process of forming membrane 10 by IFP, aqueous phase 14 may also include one of the reactants or monomers, and other processing aids such as surfactants, drying agents, catalysts, coreactants, cosolvents, etc. A first reactant or monomer can be selected so as to be miscible with a polar liquid to form a polar mixture. Typically, the first monomer can be a dinucleophilic or a polynucleophilic monomer. Generally, the difunctional or polyfunctional nucleophilic monomer can have a primary or secondary amino group and can be aromatic (eg, m-phenylenediamine (MPD), pphenylenediamine, 1,3,5-triaminobenzene, 1,3,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,4-diaminoanisole, and xylylenediamine) or aliphatic (e.g., ethylenediamine, propylenediamine, piperazine, and tris(2-diaminoethyl)amine).

The polar mixture for aqueous phase 14 need not be aqueous, but the polar liquid should be immiscible with the apolar liquid of organic phase 18. Although water is a preferred solvent for aqueous phase 14, non-aqueous solvents can be utilized, such as acetonitrile and dimethylformamide (DMF). The resulting polar mixture typically includes from about 0.1% to about 20% by weight, preferably from about 0.5% to about 6% weight, of amine. The polar mixture can typically be applied to the micro-porous support membrane 12 by dipping, immersing, coating, spraying or other conventional techniques. Once coated on porous support membrane 12, excess polar mixture can be optionally removed by evaporation, drainage, air knife, rubber wiper blade, nip roller, sponge, or other devices or processes.

Organic phase 18 used during IFP may also include one of the reactants and other processing aids such as catalysts, co-reactants, co-solvents, etc. A second monomer can be selected so as to be miscible with an apolar liquid forming an apolar mixture for organic phase 18, although for monomers having sufficient vapor pressure, the monomer can be optionally delivered from a vapor phase. Typically, the second monomer can be a dielectrophilic or a polyelectrophilic monomer. The electrophilic monomer can be aromatic in nature and can contain two or more, for example three, electrophilic groups per molecule. For the case of acyl halide electrophilic monomers, acyl chlorides are generally more suitable than the corresponding bromides or iodides because of the relatively lower cost and greater availability.

Suitable polyfunctional acyl halides include trimesoyl chloride or TMC, trimellitic acid chloride, isophthaloyl chloride, terephthaloyl chloride and similar compounds or blends of suitable acyl halides. The polyfunctional acyl halide can be dissolved in an apolar organic liquid for organic phase 18 in a range of, for example, from about 0.01% to about 10.0% by weight or from about 0.05% to about 3% weight percent, preferably about 08.%-5.0%. Suitable apolar liquids are those which are capable of dissolving the electrophilic monomers, for example polyfunctional acyl halides, and which are immiscible with a polar liquid, for example water. In particular, suitable apolar liquids can include those which do not pose a threat to the ozone layer and yet are sufficiently safe in terms of their flashpoints and flammability to undergo routine processing without having to undertake extreme precautions. Higher boiling hydrocarbons, e.g., those with boiling points greater than about 90° C., such as C8-C24 hydrocarbons and mixtures thereof, have more suitable flashpoints than their C5-C7 counterparts, but they are less volatile. The apolar mixture for organic phase 18 can typically be applied to microporous support membrane 12 by dipping, immersing, coating or other conventional techniques.

During fabrication of membrane 10, interfacial polymerization—or IFP—occurs at the interface between aqueous phase layer 14 and organic phase layer 18 to form discrimination layer 24 shown in FIG. 2. The conventional conditions for the reaction of MPD and TMC to form a fully aromatic, polyamide thin film composite membrane 10 include an MPD to TMC concentration ratio of 10-30 with MPD at about 1% to 6% by weight in polar phase 14, preferably about 2.0-4.0% by weight MPD. The reaction can be carried out at room temperature in an open environment, or the temperature of either the polar or the apolar liquid or both may be controlled.

Once formed, the dense polymer layer, which becomes discrimination layer 24, can advantageously act as a barrier to inhibit the contact between reactants and to slow down the reaction. The selective dense layer, discrimination layer 24 so formed, is typically very thin and permeable to water, but relatively impermeable to dissolved, dispersed, or suspended solids such as salts. Once the polymer layer 24 is formed, the apolar liquid or residue of organic phase 18 can be removed by evaporation or mechanical removal. It is often convenient to remove the residue of organic phase 18 by evaporation at elevated temperatures, for instance in a drying oven.

Nanoparticles/additives 16 may be added to aqueous phase 14 and/or organic phase 18 for several reasons; to increase water permeability, to increase hydrophilicity, and/or to control surface morphology (for example to increase or decrease the smoothness of the membrane surface). Changes to the membrane smoothness can alter the rate at which materials rejected by the membrane are transported from the membrane, that is, higher smoothness can both improve process efficiency and/or reduce fouling.

In some cases, performance can be further improved by the addition of a rinse in a high pH aqueous solution after membrane 10 is formed. For example, membrane 10 can be rinsed in a sodium carbonate solution. The pH is preferably from 8-12, and exposure time may vary from 10 seconds to 30 minutes or more. Alternatively the membrane may be rinsed at high temperatures, or exposed to chlorinating agents.

Support membrane 12, on which discrimination layer 24 is formed by IFP, is typically a polymeric microporous support membrane, which may or may not be supported by a nonwoven or woven fabric, such as fabric 20, for further mechanical strength and structural support. Support membrane 12 may conventionally be made from polysulfone or other suitably porous membranes, such as polyethersulfone, poly(ether sulfone ketone), poly(ether ethyl ketone), poly(phthalazinone ether sulfone ketone), polyacrylonitrile, polypropylene, cellulose acetate, cellulose diacetate, or cellulose triacetate. These conventional microporous support membranes 12 are typically 25-250 microns in thickness, for example 50 microns, and have been found to have the smallest pores located very near their upper surface. Porosity at the surface of membrane 12 is often low, for instance from 5-15% of the total surface area. Nanoparticles/additives 16, such as zeolites, particularly LTA, may be added to support membrane 12 during processing to improve flux by, perhaps, improving porosity, e.g. at the surface of support membrane 12 and/or by making membrane 12 more resistant to compaction and/or mechanical strengthening of the membrane.

Support membrane 12 including nanoparticles/additives 16 will have greater strength and toughness and therefore may be made thinner than conventional support membranes made for the same service. As a result of being thinner, support membranes 12 with nanoparticles/additives 16 imbedded therein are able to minimize mixing within the support and fabric layer, possibly from the decreased diffusion path length. Further, addition of nanoparticles 16 to the support membrane 12 may lead to a more highly porous structure, with fluid transport paths of relatively low tortuosity, when compared with a conventional support membrane.

In other words, support membrane 12 with nanoparticles/additives 16 may be made thinner using less material (and thus possessing more porosity, less thickness and less tortuosity of water flow path) while still providing the required mechanical properties to serve as an appropriate support. In one embodiment, this may be accomplished, for example, by forming porous support membrane 12 from a polymer and nanoparticle/additive solution containing less polymer, for example 5-15%, than would be used in conventional support membranes 12, such as 15-20%. In another embodiment, this may be accomplished, for example, by casting a thinner layer directly, for instance by changing the gap used for slot die or knife over roll casting, or by decreasing the flow rate or increasing the web speed for slot die casting.

Support layers 12—including well dispersed nanoparticles/additives 16 therein—may also be hydrophilic, e.g., with surfaces more readily wet with water and/or displacing air or gasses entrained within the body of support 12. Such entrained gasses may make support 12 less efficient by blocking portions of support 12 to water flow, reducing effective porosity of support 12 to water or other fluid flow. By selecting nanoparticles/additives 16 for use within support membrane 12 that result in hydrophilicity of membrane 12 (for example nanoparticle zeolites such LTA), increased hydrophilicity of support 12 may result in reduced water contact angles at the surfaces of support 12.

In some instances, fabric layer 20 may also have nanoparticles/additives 16 incorporated therein for added strength, as shown for example below with regard to FIG. 9. Fabric layer 20 may be woven or non-woven layers typically of polymeric fibers. It is desirable that fabric layer 20 be permeable to the fluid or water being processed, flat and without stray fibers that could penetrate support 12 and/or thin film 24 and relative thin to decrease cost and to maximize the surface area of membrane 10 for a given diameter housing as discussed below in greater detail with regard to FIG. 8, strong against extension and mechanically resistant to deformation at high pressures which is useful for PRO processes in which the draw solution is often pressurized to enable more efficient system performance. Adding nanoparticles/additives 16 to the polymer fibers of layer 20 produces a more mechanically robust backing that may allow thinner, less expensive, or tougher support layers to be manufactured as well as help increase the surface area of membrane 10 for a given diameter housing as described with regard to FIG. 8. In some cases it may be preferable that fabric layer 20 is contained within the support layer 12.

In some instances, membrane 10 may be used to treat waters that contain materials that have a tendency to accumulate on the membrane surface, decreasing the effective permeability of the membrane. These materials can include but are not limited to natural organic matter, partially insoluble inorganic materials, organic surfactants, silt, colloidal material, microbial species including biofilms, and organic materials either excreted or released from microbial species such as proteins, polysaccharides, nucleic acids, metabolites, and the like. This drop in permeability is often smaller for membranes prepared as disclosed herein than for membranes prepared by conventional techniques due to a decreased amount, density, viability, thickness and/or nature of accumulated material. Membrane surface properties, such as hydrophilicity, charge, and roughness, often affect this accumulation and permeability change.

Generally, membranes with highly hydrophilic, negatively charged and smooth surfaces yield good permeability, rejection, and fouling behavior. The improved resistance to accumulation for membranes of the type disclosed herein can in part be related to the increased hydrophilicity of these membranes. The increased hydrophilicity can be measured by the equilibrium contact angle of the membrane surface with a drop of distilled water at a controlled temperature. Membranes prepared with nanoparticles/additives 16 present during IFP polymerization can have a contact angle that is reduced by 5°, 15° or even 25° or more relative to a similarly prepared membrane without nanoparticles/additives 16. The equilibrium contact angle can be less than 45°, less than 40°, or even less than 25°.

Contact angles of distilled, or DI, water at room temperature may be measured. Membrane 10 may be thoroughly rinsed with water, and then allowed to dry in a vacuum desiccator to dryness. Membrane 10 may be dried in a vertical position to prevent re-deposition of any extracted compounds that may impact contact angle. Due to the occasional variability in contact angle measurements, 12 angles may be measured at different spots on membrane 10 with the high and low angles being excluded and the remaining angles averaged.

Referring now to FIGS. 3-6, the addition of nanoparticles/additives 16 to support layer 12, and/or fabric layer 20, may reduce the tendency of membrane 10 to become compacted overtime and lose permeability during operation.

Compaction is a somewhat different function or result than the increased strength of support membrane 12 discussed above. The increased strength of support 12 discussed above resulting from the addition of nanoparticles/additives 16 refers to the fact that membrane 12 with nanoparticles/additives 16 dispersed therein provides greater support and resistance against damage and distortion. As a result, for example, a typical 50 micron thickness of support membrane 12, fabricated without nanoparticles/additives 16 may be replaced with a 25 micron thickness of the same membrane with nanoparticles/additives 16 dispersed therein without loss of the necessary structural strength or rigidity.

As described immediately below, resistance to compaction refers to the ability of membrane 12, with nanoparticles/additives 16 dispersed therein, to resist being compacted, i.e., being squeezed to a thinner dimension by pressure and remaining at a thinner dimension. As shown below with regard to the graph of FIG. 3, membrane 12 with nanoparticles/additives 16 is substantially less compacted over time during operation as a result of applied pressure. The advantage of resistance to compaction is a reduction in the common loss, after initial operation, of substantial permeability or flux flow. The advantage of increased strength by adding nanoparticles/additives 16 to support membrane 12, and/or fabric 20, is that a thinner support membrane, with shorter and less tortuous flow paths, may be used and provides better operating efficiency for FO and PRO processes both during initial operation and also thereafter.

Referring now in particular to FIG. 3, graph 50 illustrates flow compaction by graphing resistance to flow through membrane 12 with nanoparticles/additives 16, as a function of time. The experimental conditions were a differential pressure of 500 pounds per square inch or psi, a temperature of 25° C. and 585 ppm NaCl. For control membrane 52, a TFC membrane similar to membrane 10 except without nanoparticles/additives 16 dispersed therein was used, as shown by the graph line for membrane 52. Resistance increased from just above 6 units to about 12.5 or so units in about 2 hours. That is, after initial operation, the TFC membrane made in accordance with the present disclosure but without nanoparticles/additives 16 lost about half of its permeability in about 2 hours. Membrane salt rejection was on the order of 91%.

The graph line for membrane 54, with nanoparticles/additives 16 dispersed in discrimination layer 24, indicates that the resistance to flow in membrane 54 started at a much lower resistance to flow, just over 4 units, and lost very little permeability over the 4 hour test. Membrane salt rejection was on the order of 90%.

The graph line for membrane 56, with nanoparticles/additives 16 in support layer 12 and discrimination layer 24, indicates that the resistance to flow in membrane 56 started at an even lower resistance to flow, about 1.5 units, and also lost very little permeability over the 4 hour test. Membrane salt rejection was on the order of 94%.

The graph line for membrane 58, with nanoparticles/additives 16 in support layer 12, indicates that the resistance to flow in membrane 58 started at an even lower resistance to flow, just about 1 unit, and lost a little permeability over the 4 hour test, to reach the same level as membrane 56 in about 1 hour. Membrane salt rejection was on the order of 92%.

Graph lines for the 4 membranes shown in graph 50 illustrate the reduced resistance to flow for a TFC membrane, such as membrane 52, when nanoparticles/additives 16 are added to the various layers in membranes 54, 56 and 58, indicating that the addition of nanoparticles/additives 16 increases the resistance to compaction of these membranes.

Referring now in particular to FIGS. 4-7, a series of photomicrographs are shown of various support membranes taken by a focused ion beam scanning electron microscope or FIB-SEM technique, to illustrate the physical effect of the presence of nanoparticles/additives 16 in support membrane 12 over time. In this technique, as shown in FIG. 4, platinum deposition Pt 60 was made on a sample polysulfone support membrane 64 and a dual ion beam was used to cut a cross sectional view of the polysulfone support to a depth of approximately 5 microns. A portion of cut 62 for 3 different membranes is shown by FIB-SEM in FIGS. 5-7.

Referring now specifically to FIGS. 5-7, a segment of support membrane 12—with nanoparticles/additives 16 dispersed therein—is shown by FIB-SEM after 16 hours of operation at 800 psi. For comparison, control membrane 64, made in the same manner as membrane 12 but without nanoparticles/additives 16, is also shown after 1 hour of operation at 800 psi. The openings in membranes 12 and 64 are generally of the same shape and orientations. FIG. 7 shows membrane 64 after 8 hours of operation at the same pressure, 800 psi. The shape and orientation of the openings within membrane 64 have clearly been degraded during the subsequent operations. In particular, the openings shown in FIG. 7 are primarily in a horizontal orientation indicating that substantial compaction has occurred compared to the openings in membrane 64 shown in FIG. 6.

It is clear by comparing support membrane 12 in FIG. 5 that very little compaction has occurred in the membrane with nanoparticles/additives 16 after 16 hours because at least a fair number of the openings are clearly oriented in a vertical direction as also shown in membrane 64 in FIG. 6 rather than primarily in a horizontal orientation as shown by membrane 64 in FIG. 7 after 8 hours.

In operation, saltwater 26 could also be a relatively high concentration stream of any solute rejected by membrane 10, such as less pure water, and able to generate a spontaneous flow into pure fluid 28. Similarly, pure fluid 28 could be any stream relatively low in concentration of solutes rejected by membrane 10, for example a freshwater solution. In some instances, pure water 28 could even be seawater if a sufficient concentration of solutes are added to saltwater 26 to cause water to flow from fluid 28 to 26. Alternately, saltwater 26 could be relatively pure water with a high quantity of sugars present to desalinate a seawater stream into a potable mixture, or a high quantity of ammonium carbonate which can easily be removed by subsequent processing to generate a purified water stream. In a PRO system, the pressure could be utilized at tap 68.

Support membranes 12 with nanoparticles/additives 16 imbedded therein may be able to minimize mixing losses from purified water 28 and seawater 26 by maximizing diffusive transport of solutes within support 12. Inclusion of nanoparticles/additives 16 in support 12 may add strength and toughness allowing useful support membranes 12 to be created from materials that would conventionally be ineffective such as polypropylene, polyethyleneterepthalate, polyvinylchloride, or polystyrene.

Referring now to FIG. 8, canister 66 may be a conventional membrane canister such as a 8″ diameter, 40″ long sealed tube containing solute, such as seawater 26, surrounding membrane structure 72 wound in a spiral around flow tube 70 carrying the solvent, such as purified water 28. Membrane structure 72 may include one or more sheets of 12″-40″ wide sheets of membrane 10 that are 20″-80″ long, providing a wide range of total surface areas from about 5 square feet to 1600 square feet or more, plus conventional spacers, permitting membrane 10 to be wound in a spiral form. Membrane 10 may include support layer 12 with nanoparticles/additives 16 dispersed therein having a reduced thickness, for example, of 25 microns rather than the conventional 50 microns as shown in FIG. 2 as well as fabric 20 with nanoparticles/additives 16 dispersed therein having a reduced thickness of for example 75 microns rather than the conventional 100 microns also as shown in FIG. 2.

Because of the spiral winding, the benefit of the additional strength provided by nanoparticles/additives 16 reduces the diameter of the spiral wound membrane structure 72 by 50 microns for each winding. A conventional membrane of the same type as membrane 10 having a 50 micron support membrane and a 100 micron fabric backing that would fit in conventional canister 66 would have the same 40″ width as membrane 10 but the total square footage of membrane available for osmosis would be reduced by ˜3-10% compared to a membrane fabricated according to the present disclosure. In other words, the use of nanoparticles/additives 16 in support membrane 12 and/or fabric 20 may provide a ˜3-10% improvement in the membrane area available for osmosis when used in a standard size canister.

Referring now to FIG. 9, FO/PRO membrane 10 is shown in operation between draw solution 26 and feed solution 28 to illustrate a further advantage, related to salinity, of the addition nanoparticles/additives 16 to permit the use of thinner support layers 12 and/or thinner fabric layers 20. Membrane 10 may be used for FO or PRO processes in which feed solution 28 may be allowed to spontaneously flow through membrane 10 to dilute draw solution 26 on the other side of membrane 10. To a small degree, salt or other contaminants from draw solution 26 can also diffuse into feed solution 28 and vice versa. These processes lead to regions within draw solution 26 diluted with feed solution 28 and regions in support membrane 12, fabric 20 and feed solution 28 contaminated with draw solution 26. FIG. 9 includes a graph of salinity 25 superimposed on the illustration of FO/PRO membrane 10 in use.

In the graph, salinity 25 increases from the left hand side to a maximum, such as 32,000 ppm of salt in saltwater 25. The increasing salinity shown is the salinity of the fluid at the vertical position within saltwater 26, membrane 10 including support 12 and fabric 10, and fresh water 28. Graph segment 25a represents a portion of the salinity curve where saltwater 26 contacts discrimination membrane 24. As shown by segment 25a, salinity decreases from the maximum salinity of the saltwater to a lower salinity where pure water 28, having penetrated discrimination membrane 24, is not yet fully in solution with saltwater 26. Below discrimination membrane 24, graph segment 25b illustrates salinity 25 substantially reduced by membrane 10 but still higher than the salinity of pure water 28. The salinity gradually reduces as the salt from saltwater 26, leaking backwards through membrane 10, is dissolved in pure water 28 until it reaches the typically non-zero level of salt in pure water 28. The salinity for segment 25b is also higher than that in pure water 28 from removal of water through the discrimination membrane 24.

Although membrane 10 is shown with discrimination membrane 24 in contact with seawater 26, fabric 20 in contact with fresh water 28, and with support membrane 12 there between, it is conventional in some situations to use membrane 10 in the opposite orientation. That is, discrimination membrane 24 may be in contact with fresh water 28, fabric 20 in contact with seawater 26, and support membrane 12 there between.

Referring again to the orientation shown in FIG. 9, the presence of pure water 28 in saltwater 26 above membrane 10, and of salt from saltwater 26 in pure water 28 near the bottom of discrimination layer 24, reduces the efficiency of FO and PRO processes across membrane 10 by reducing the salinity differential there across. It should be noted that among the advantages of membrane 10 as described herein, the presence of nanoparticles/additives 16 in support layer 12 (and/or fabric 20) enhance the strength of these structural layers permitting the use of thinner layers. Further, in addition to support layer 12 being thinner, the water transport paths there through may become less tortuous, i.e., less resistant to flow, and therefore make support layer 12 more permeable than a conventional porous support membrane.

Although the exact thickness dimensions of the various layers of conventional FO and PRO membranes depend on many factors, the following table shows some relatively reasonable, representative values of the thicknesses and salinity of conventional IFP RO membranes and IFP RO membranes 10—with nanoparticles/additives 16 dispersed therein—in accordance with the present disclosure as a guide to one of the improvement provided by the present design. A salinity of 32,000 parts per million, or ppm, for saltwater 26 and 500 ppm for fresh water 28 was used.

Salinity ppm at
IFP FO/PROSupportFabricMembrane 10Salinity
Membranes(in Microns)TopBottomDifferential
Conventional507525K  5K  20K
Nanoparticle255025K1.5K23.5K

Although the mixing of fresh water and salt water in FO and PRO processes conventionally leads to decreased driving forces for water transport, leading to decreased process efficiencies, the use of nanoparticles in discrimination layer 24, support layer 12 and/or in other layers such as fabric layer 20, as described herein, may increase the concentration driving force and improve process efficiencies. For example, use of nanoparticles and/or other additives dispersed in discrimination layer 24 and/or support layer 12 may lead to increased flux flow or permeability to further increase process efficiencies.

Referring now to Appendix A, and in particular to Section D: Tables I-XII, Examples 1-172, pages 66-77, par.s [00047]-[000259], the related portions of the specification and drawings of Appendix A, and FIGS. 1 and 2 of the present application, nanoparticles/additives 16, particularly for addition to aqueous phase 14 and/or organic phase 18 before IFP in order to be dispersed in discrimination layer 24, may include

    • LTA nanoparticles 16 in aqueous phase 14 as indicated in examples 23-25 and/or in organic phase 18 as shown in examples 26-28;
    • CuMOF nanoparticles in organic phase 18 as indicated in example 36;
    • SiO2 nanoparticles 16 in aqueous phase 14 as indicated in example 38;
    • Zeolite BETA nanoparticles 16 in aqueous phase 14 as indicated in example 40;
    • additives such as Al, Fe, Sn, Cu, Co, Pr, Zn, Cr, In, V, Sn, Ru, Mo, Cd, Pd, Hf, Nd, Na, Yb, Er, Zn, K and/or Li in organic phase 18 as indicated in examples 94-118;
    • mhTMC in organic phase 18 as indicated in examples 122-136;
    • Alkaline earth additives in organic phase 18, such as Ca, Sr, Mg or Be as indicated in examples 29-34;
    • Nanotubes in organic phase 18 as indicated in example 44;
    • mhTMC (monohydrolyzed TMC) in organic phase 18 as shown in examples 122-136; as well as
    • combinations of these nanoparticle/additives, such as nanoparticles (including FAU) or nanotubes with metal additives or alkaline earth additive and/or with mhTMC as indicated in the remaining examples in Tables I-X.

Further, the concentration of TMC may be adjusted in accordance with the ranges indicated in examples 137-166 in Table XI, as described in greater detail in Appendix A, and the MPD to TMC ratio may be adjusted in accordance with the ratios shown in Table XII, as described in greater detail in Appendix A.

Further, the combination of nanoparticle and other additive reduces flux loss during initial operation as shown in FIG. 5, as described in greater detail in Appendix A.

Still further, the concentration of additives and combinations thereof, such as mhTMC, can be adjusted, tested and compared to identify the deflection point as shown in FIG. 26, as described in greater detail in Appendix A. Knowledge of the deflection point, where one can be clearly determined, for a particular additive or combination of additives, permits optimizing the select of the additives, whether nanoparticles or tubes, alkaline earth or other metals, mhTMC and/or various combinations thereof.