Low-Energy Enhanced Membrane for Pressure-Driven Applications

Abstract

The present disclosure discloses an enhanced flat sheet membrane operable to withstand vacuum pressure and high pressure up to 1500 psi. The enhanced flat sheet membrane comprises: a polymer membrane; a permeate carrier that enhances the polymer membrane and has channels for guiding the permeate stream; wherein the polymer membrane incorporates the permeate carrier therein, and the channel portions of the permeate carrier are exposed on the surface of the polymer membrane. The present disclosure includes a method of manufacturing an enhanced flat sheet membrane. The method includes contacting the permeate carrier with a pre-wetting agent; casting a polymer solution onto the permeate carrier; and forming a polymer membrane from the polymer solution, wherein the permeate carrier is incorporated into the polymer membrane.

Description

[0001] Cross - reference to related applications

[0002] This application claims the priority of Singapore Patent Application No. 10201904021V, filed on May 3, 2019, the content of which is incorporated herein by reference in its entirety for all purposes. Technical field

[0003] The present disclosure relates to an enhanced flat sheet membrane operable to withstand vacuum pressure and high pressure up to 1500 psi. The present disclosure also relates to a method of manufacturing such an enhanced flat sheet membrane. Background art

[0004] In a membrane module for treating liquids (such as wastewater), there is typically a leaf group which, among other components (permeate carrier, spacer, etc.), includes a membrane. The mechanical strength of the membrane and the overall leaf group thickness are key factors affecting the purification performance of pressure - driven membranes in terms of water flux, rejection rate, power density, and reverse salt flux permeability.

[0005] In high - pressure applications, if the mechanical strength of the membrane is insufficient, the membrane area between the feed spacers may deform. In this regard, although commercially available reverse osmosis (RO) membranes tend to have sufficient mechanical strength to operate at high pressures up to 1500 psi, when operating in pressure - retarded osmosis applications, due to the presence of various support layers and their structural parameters, such membranes tend to suffer from severe internal concentration polarization (ICP), which may result in very low permeation rates and power densities.

[0006] For pressure - retarded osmosis (PRO) membranes operating at high pressures (up to 25 bar, approximately 50% of the osmotic pressure), the membrane may be severely deformed, and the resulting water flux may be significantly lower than the theoretically predicted water flux.

[0007] Membranes suitable for pressure - retarded osmosis may need to have a reasonable level of mechanical strength to avoid severe membrane deformation at high pressures. PRO membranes can also have a dense active layer that effectively retains salts, which provides high water flux and low reverse salt permeability. Thus, enhanced membranes can potentially be considered as membranes suitable for PRO and even FO.

[0008] In addition to the mechanical strength of the membrane, the thickness of the leaf pack must also be considered when manufacturing all pressure-driven membrane low-energy spiral wound membrane modules (SWMs). Generally, the leaf pack includes various reticulated materials to provide channels for feed and permeate flow. Due to the high applied pressure in pressure-driven membrane operation, the reticulated materials also act as support materials in the leaf pack to protect membrane integrity. Even when the membrane backing coated with the polymer membrane has sufficient mechanical strength, the polymer membrane may elongate and thus deform due to aging and the higher applied pressure. The reticulated materials potentially reduce the amount of membrane material that can be assembled into the module. In other words, the filtration output is affected due to the installation of various support materials. In addition, the support materials may make module manufacturing difficult and more expensive. For example, using support materials, including membranes, to roll up all the components (i.e., more layers) to fit into a spiral wound module tends to become more difficult.

[0009] Accordingly, there is a need to provide a solution to address one or more of the above limitations. The solution should provide at least one such enhanced flat sheet membrane: having reasonable mechanical strength and thickness to operably withstand the pressure conditions used in various membrane applications (RO, PRO, FO, etc.). SUMMARY OF THE INVENTION

[0010] In a first aspect, there is provided an enhanced flat sheet membrane operable to withstand vacuum pressure and high pressure up to 1500 psi, wherein the enhanced flat sheet membrane comprises:

[0011] A polymer membrane;

[0012] A permeate carrier that enhances the polymer membrane and has channels for guiding permeate flow;

[0013] Wherein the polymer membrane incorporates the permeate carrier therein, and the channel portions of the permeate carrier are exposed on the surface of the polymer membrane.

[0014] In another aspect, there is provided a method of manufacturing an enhanced flat sheet membrane operable to withstand vacuum pressure and high pressure up to 1500 psi, wherein the enhanced flat sheet membrane comprises:

[0015] A polymer membrane;

[0016] A permeate carrier that enhances the polymer membrane and has channels for guiding permeate flow;

[0017] Wherein the polymer membrane incorporates the permeate carrier therein, and the channel portions of the permeate carrier are exposed on the surface of the polymer membrane, and the method comprises:

[0018] Contact the permeate carrier with a pre-wetting agent;

[0019] Cast a polymer solution onto the permeate carrier; and

[0020] Form a polymer film from the polymer solution, wherein the permeate carrier is incorporated into the polymer film. Description of the Drawings

[0021] The drawings are not necessarily to scale, but generally focus on illustrating the principles of the invention. In the following description, various embodiments of the invention will be described with reference to the following drawings, wherein:

[0022] Figure 1 Examples of materials that can be obtained and used as permeate carriers to mechanically reinforce flat polymer films are shown. The first column shows TJ-30 material with pores having an average pore size of 400 microns, which may even include some pore sizes up to 1200 microns or larger. The second column shows P16 material with pores of approximately 300 μm. The third column shows TF800 material with pores of approximately 100 μm. The fourth column shows BW30 material with pores of approximately 400 μm. The actual size is obtained by using the scale shown in the photograph to obtain measurements and dividing the measurements by 4. The top row of the image shows the surface of the permeate carrier that has not been incorporated into the polymer film. The bottom row of the image shows the reverse surface of the permeate carrier that has not been incorporated into the polymer film. When the permeate carrier is incorporated into the polymer film, either surface of the permeate carrier can be exposed on the back side of the polymer film. The back side of the polymer film can be the surface from which the permeate flows out of the polymer film;

[0023] Figure 2 Shows an enhanced flat sheet membrane formed with a permeate carrier in a handframe prior to magnification. The polymer solution used to form the flat sheet membrane is coated on the permeate carrier;

[0024] Figure 3 A shows 60x magnified front and rear views of a conventional flat sheet membrane coated with a polyamide rejection layer. Specifically, Figure 3 A shows a conventional flat sheet membrane formed of a non-woven polyester backing. The top row of images shows the polyamide rejection layer (front view), while the bottom row of images shows the opposite side with the non-woven polyester backing (rear view). The conventional flat sheet membrane here is not reinforced with a mesh, i.e., no permeate carrier is incorporated therein;

[0025] Figure 3 B shows 60x magnified front and rear views of an enhanced flat sheet membrane coated with a polyamide rejection layer. Specifically, Figure 3Figure B shows an enhanced flat sheet membrane formed with a TJ-30 permeate carrier, where the polymer solution is cured to form the flat sheet membrane with the polymer solution facing the direction of gravity (i.e., downward curing). In other words, the permeate channels of the permeate carrier are positioned upward (i.e., in the direction opposite to gravity). The top row of images shows the polyamide rejection layer (front view), while the bottom row of images shows the opposite side of the permeate channels with the TJ-30 permeate carrier (rear view);

[0026] Figure 4 Figure A shows 60x magnified front and rear views of an enhanced flat sheet membrane coated with a polyamide rejection layer. Specifically, Figure 4 Figure A shows an enhanced flat sheet membrane formed with a TJ-30 permeate carrier, where the polymer solution is cured to form the flat sheet membrane with the polymer solution facing the direction opposite to the action of gravity (i.e., upward curing), and an FO formulation is used. In other words, the permeate channels of the permeate carrier are positioned downward (i.e., in the same direction as gravity). The top row of images shows the polyamide rejection layer (front view), while the bottom row of images shows the opposite side of the permeate channels with the TJ-30 permeate carrier (rear view). The term "FO formulation" as used herein refers to a polymer membrane made of similar active components / materials except for compositional differences, including enhanced flat sheet membranes. Specifically, a specific composition of MPD and TMC is used for interfacial polymerization to form the polyamide rejection layer;

[0027] Figure 4 Figure B shows 60x magnified front and rear views of an enhanced flat sheet membrane coated with a polyamide rejection layer. Specifically, Figure 4 Figure B shows an enhanced flat sheet membrane formed with a TJ-30 permeate carrier, where the polymer solution is cured to form the flat sheet membrane with the polymer solution facing the direction of gravity (i.e., downward curing), and an FO formulation is used. In other words, the permeate channels of the permeate carrier are positioned upward (i.e., in the direction opposite to gravity). The top row of images shows the polyamide rejection layer (front view), while the bottom row of images shows the opposite side of the permeate channels with the TJ-30 permeate carrier (rear view);

[0028] Figure 4 Figure C shows Figure 4 a field emission scanning electron microscopy (FESEM) image of a cross-sectional view of the enhanced flat sheet membrane of Figure A. The scale bar represents 100 μm;

[0029] Figure 4 Figure D shows Figure 4FESEM image of the bottom view of the enhanced flat sheet membrane of C, where the bottom view is the side of the permeate channel with the permeate carrier. Scale bar represents 100 μm;

[0030] Figure 5A An industrially scaled enhanced flat sheet membrane of the present disclosure is shown, where the flat sheet membrane is enhanced using a P16 permeate carrier;

[0031] Figure 5B An enhanced flat sheet membrane of the present disclosure is shown, where compared with Figure 4 A to Figure 4 The enhanced flat sheet membrane manufactured on an industrial scale compared to the enhanced flat sheet membrane produced using a smaller-sized manual rack of D. The upper left image shows the polyamide rejection layer, and the scale bar represents 500 μm. The upper right image shows the side (back side) of the permeate channel with the permeate carrier, and the scale bar represents 500 μm. The lower left image is a 10-fold magnification of the upper right image, and the scale bar represents 50 μm. Specifically, the enhanced flat sheet membrane has a significant improvement in the unobstructed permeate channel on the back side of the membrane;

[0032] Figure 5C An enhanced flat sheet membrane manufactured for reverse osmosis (RO) is shown. The upper left image shows the polyamide rejection layer, and the scale bar represents 750 μm. The upper right image shows the side (back side) of the permeate channel with the permeate carrier, and the scale bar represents 250 μm. The bottom image is a 5-fold magnification of the upper right image, and the scale bar represents 50 μm. Specifically, the enhanced flat sheet membrane has a significant improvement in the unobstructed permeate channel on the back side of the membrane;

[0033] Figure 6 A table showing the RO performance of the enhanced flat sheet manufactured on a manual rack tested at 225 psi (15 bar). * refers to the sample of the enhanced membrane IDD050718HF23.4 made with a polyester backing on a manual rack. ** refers to the column titled "Reduction %", which represents the percentage reduction in thickness relative to the reference membrane. The results are based on manual rack data;

[0034] Figure 7It is a table showing the RO performance of an enhanced flat sheet membrane manufactured by phase inversion (PI) during interfacial polymerization (IP) on a handframe. Except for the samples marked with * and ** in the membrane ID, the enhanced flat sheet membranes prepared using Formulation B were tested at a pressure of 225 psi (15 bar), where * represents the resulting enhanced flat sheet membrane made from the polymer coated on a thin film composite (TFC) line, and where Formulation D was used, and ** represents the enhanced flat sheet membrane made using Formulation D. The term "line" in this disclosure refers to a somewhat automated production line involved in manufacturing the resulting enhanced flat sheet membrane. The term "TFC line" refers to the process for manufacturing a salt-rejecting polyamide layer on a polymer membrane. Formulations B and D refer to the chemical compositions used to manufacture the polymer membrane on a phase inversion (PI) line, where polysulfone (PS) is used to manufacture the polymer membrane. Formulations B and D refer to the compositions for manufacturing the polymer membrane, where Formulation B uses 1 wt% more polymer than Formulation D. However, the viscosity of the polymer solution (i.e., the coating) used to form the polymer membrane based on Formulation B is 30% higher than that of Formulation D, even though Formulation B uses an additional 1 wt% of polymer in the polymer solution;

[0035] Figure 8 It is a table showing the power density and reverse salt flux of an enhanced flat sheet membrane (RM) manufactured on a phase inversion (PI) coater line using a handframe (HF) and different polymer coatings (i.e., Formulation B involving polysulfone (PS-B) and Formulation D involving polysulfone (PS-D)) compared to commercially available RO membranes at different pressures. Specifically, the RO performance of this enhanced flat sheet membrane (RM) made on a handframe (HF) and lined with a polysulfone (PS) coating is compared with commercially available RO membranes;

[0036] Figure 9It is a table showing the FO performance of the enhanced flat sheet membranes (Formulation B) of the present disclosure manufactured on a coater line tested under FO. For the FO test, based on the following specifications, the enhanced membranes used were such that interfacial polymerization was carried out on the membranes manufactured using the coater line: line speed: 3 MPM, pump speed: 13 Hz, pre-wetting agent: deionized (DI) water, wetting supplier: peristaltic pump with 4 cartridges (4×50 ml per minute), reinforcing material: TJ-30 permeate carrier (warp knitted). Jw represents the water flux from the feed to the draw solute, and Js represents the reverse salt flux. The FO test was carried out with the active layer facing the feed, while the PRO test was carried out with the active layer facing the draw solute. Coupons A and B refer to two different positions of the enhanced flat sheet membranes used in this example. Specifically, both Coupons A and B are samples of rectangular sheets cut from the enhanced flat sheet membranes with an area of 42 cm 2 This helps to measure the uniformity of the enhanced flat sheet membranes;

[0037] Figure 10A It is a table showing the performance of a 2514 RO element under 15 bar and 2000 ppm of NaCl. The RO element is a spiral wound membrane made using the enhanced flat sheet membrane of the present invention. For the element test, polyamide interfacial polymerization was carried out on the enhanced flat sheet membrane cast on the coater line. The IP mode in the table illustrates whether the interfacial polymerization was carried out using a hand rack (HF) or the coater line (Line). The conditions used for the test are shown in Figure 10A The number 2514 indicates that each RO element has a diameter of 2.5 inches and a length of 14 inches;

[0038] Figure 10B It is a table showing the performance of an 1812 RO element under 3.4 bar and 500 ppm of NaCl. The RO element is a spiral wound membrane made using the enhanced flat sheet membrane of the present invention. For the element test, polyamide interfacial polymerization was carried out on the enhanced flat sheet membrane cast on the coater line. The interfacial polymerization was carried out using the coater line (Line) as shown in the IP mode in the table. The conditions used for the test are shown in Figure 10B The number 1812 indicates that each RO element has a diameter of 1.8 inches and a length of 12 inches;

[0039] Figure 11A A comparison was made between a conventional spiral wound module (left figure) and a spiral wound module incorporating the enhanced flat sheet membrane of the present disclosure. The conventional spiral wound module consists of 3 independent components, which are the feed spacer, the permeate carrier, and the membrane. In contrast, the spiral wound module of the present disclosure has two independent components, namely the feed spacer and the enhanced flat sheet membrane, where the permeate carrier is incorporated into the enhanced flat sheet membrane to form a single component;

[0040] Figure 11B Element 1812 of the spiral wound assembly is shown;

[0041] Figure 11C Element 2514 of the spiral wound assembly is shown;

[0042] Figure 12A A spiral wound leaflet configuration for PRO is shown, where the active layer faces the draw solution;

[0043] Figure 12B A spiral wound leaflet configuration for RO is shown, where the active layer faces the feed solution;

[0044] Figure 13 An enhanced flat sheet membrane prepared without pre - wetting is shown, where the enhanced flat sheet membrane has creases. Detailed Description

[0045] The following detailed description refers to the accompanying drawings, which illustrate by way of example specific details and embodiments in which the invention may be implemented.

[0046] Features described in the context of one embodiment may correspondingly apply to the same or similar features in other embodiments. Features described in the context of one embodiment may correspondingly apply to other embodiments even if not explicitly described in those other embodiments. Additionally, additions and / or combinations and / or substitutions described for a feature in the context of one embodiment may correspondingly apply to the same or similar features in other embodiments.

[0047] The present disclosure relates to an enhanced flat sheet membrane operable for various treatment processes. The treatment processes can involve operating pressures from vacuum to high pressure. Non - limiting examples of treatment processes include reverse osmosis (RO), pressure retarded osmosis (PRO), forward osmosis (FO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (Mf), pervaporation, membrane distillation, and / or gas separation. The enhanced flat sheet membrane of the present invention can be operable to withstand a wide range of operating pressures, including vacuum pressure and high operating pressures, such as from 0 Pa and up to 1500 psi (about 10.34 MPa) or pressures in the range of 1.5x10 -11 psi to 1500 psi, and thus has a wide range of uses.

[0048] The enhanced flat sheet membrane includes a polymer membrane and a permeate carrier bonded to the polymer membrane. In various cases, a dense rejection layer may be formed on the polymer membrane, and the rejection layer is remote from the permeate carrier (i.e., the permeate carrier and the rejection layer are formed on opposite sides of the polymer membrane). The dense rejection layer may be interchangeably referred to herein as a dense selective layer, a dense active layer (or simply an active layer), and an active rejection layer.

[0049] The polymer membrane herein may be interchangeably referred to as a base layer, a support layer, a porous base layer, and a membrane substrate. The polymer membrane is the layer that forms the main body of the enhanced flat sheet membrane. In other words, the polymer membrane contains the permeate carrier.

[0050] The permeate carrier may be a mesh having pores of different sizes or uniform sizes. The pores may be defined by the pores formed between the filaments woven to construct the mesh. The filaments may be woven or aligned to define channels. Such channels are referred to herein as permeate channels. The permeate channels may be configured to direct the permeate flow in a desired direction. The permeate carrier may be substantially embedded in the polymer membrane. For example, the permeate carrier may be partially embedded such that the permeate channels may be substantially exposed (e.g., fully or partially exposed) to direct the permeate flow away from the polymer membrane.

[0051] The enhanced flat sheet membrane is advantageous because the polymer membrane and the permeate carrier are formed as a single component. This is in contrast to conventional configurations in which the polymer membrane and the permeate carrier are used as separate components. Even though the polymer membrane and the permeate carrier are formed as a single component, not only is the mechanical strength of the polymer membrane enhanced, but also the overall thickness of the leaf pack is reduced. In the context of the present disclosure, the leaf pack includes the membrane and other filtration components, such as a feed spacer, a permeate carrier, additional backing material. For example, conventionally, the leaf pack of a spiral wound membrane module may include a feed spacer and a permeate carrier, with the polymer membrane sandwiched between the feed spacer and the permeate carrier. The membrane module may be interchangeably referred to as a spiral wound element. The element may have a housing, where the housing refers to the shell for the spiral wound element.

[0052] Advantageously, forming the permeate carrier in the polymer membrane alleviates or even eliminates deformation of the polymer membrane caused by high pressure and vacuum pressure applied thereto. Deformation of the membrane can at least adversely reduce the filtration output.

[0053] Advantageously, bonding the permeate carrier to the polymer membrane reduces the overall thickness of the leaf pack compared to a conventional leaf pack. Refer to Figure 6As an example, using the same membrane manufacturing method on a manual rack, even when using a 11 mil thick permeate carrier, the overall thickness of the blade set is reduced from 62 mil (D050718HF23.4) to 51 mil (D171218HF33.1), indicating a 17% reduction in the blade set thickness. The unit "mil" used herein refers to one thousandth of an inch. Additionally, a very desirable rejection rate of 97.1% can still be achieved. This allows more of the enhanced flat sheet membranes of the present invention to be installed in the module, at least improving the processing efficiency of each module. Furthermore, by reducing the number of components involved and the thickness of the blade set, the blade set and various components can be more easily curled to fabricate a spiral wound configuration, thereby reducing the manufacturing effort (less energy consumed to produce the same or higher filtration output).

[0054] The method also includes a method for manufacturing an enhanced flat sheet membrane. The method enhances a polymer membrane with a mesh (i.e., permeate carrier) that enables higher water permeability because the binding of the permeate carrier can give the polymer membrane fewer structural parameters, which helps mitigate internal concentration polarization (ICP). The polymer membrane has fewer structural parameters because a portion of the polymer membrane is replaced by the integrated permeate carrier. In contrast, a conventional polymer membrane can have a porous layer and a dense rejection layer formed thereon, and although the porous layer may have more pores than the dense rejection layer, the porous layer is denser and more tortuous than the permeate carrier. The term "structural parameter" herein is an inherent membrane parameter that can be a function of the support layer thickness, tortuosity, and porosity. It can be a parameter that indicates the degree of internal concentration polarization in a porous support structure used, for example, as a forward osmosis membrane, and can be used to evaluate the performance of a membrane (such as a forward osmosis membrane). Regardless of the operating conditions, the structural parameter is generally a consistent parameter. In this case, the support layer can be the permeate carrier incorporated in the polymer membrane.

[0055] The enhanced flat sheet membrane of the present invention can also have a permeate carrier (mesh reinforcement) that replaces a conventional non-woven substrate.

[0056] Details of various embodiments of the enhanced flat sheet membrane, its manufacturing method, and advantages associated with the various embodiments are described below.

[0057] In the present disclosure, an enhanced flat sheet membrane operable to withstand vacuum pressure and high pressure up to 1500 psi is provided. The enhanced flat sheet membrane can include: a polymer membrane; and a permeate carrier that enhances the polymer membrane and has channels for guiding the permeate flow; wherein the polymer membrane incorporates the permeate carrier therein, and the channels of the permeate carrier can be partially exposed on the surface of the polymer membrane.

[0058] In various embodiments, the permeate carrier can include a mesh. The mesh can include a woven mesh, a non-woven mesh, or a warp-knitted mesh. The mesh can be formed from cellulose, polyester, polypropylene, acrylic, nylon, sulfonated polysulfone, polysulfone, polyethersulfone, polyimide, polyamide, polybenzimidazole, polyacrylonitrile, polyarylsulfone, poly(vinyl butyral), polyetherimide, derivatives thereof, or combinations thereof.

[0059] In various embodiments, the mesh can have a pore size in the range of 100 μm to 5000 μm, 200 μm to 5000 μm, 500 μm to 5000 μm, 1000 μm to 5000 μm, 1500 μm to 5000 μm, 100 μm to 200 μm, 100 μm to 500 μm, 100 μm to 1000 μm, 200 μm to 1000 μm, 200 μm to 500 μm, 100 μm to 2000 μm, 200 μm to 2000 μm, 500 μm to 2000 μm, 1000 μm to 2000 μm, etc. In various cases, the pore size can be about 1000 μm or greater than 1000 μm. In various cases, the pore size can be about 500 μm or about 200 μm. Regardless of the pore size of the mesh (i.e., the permeate carrier), enhanced flat sheet membranes can be produced.

[0060] In various embodiments, the polymer membrane can have a porous substrate layer, wherein (i) an active rejection layer can be formed on the porous substrate layer, and / or (ii) the permeate carrier can be incorporated into the porous substrate layer. In various cases, the polymer membrane itself can be used as the porous substrate layer.

[0061] The active rejection layer can include polyamide, polyamine, polyamide-imide, polyol, polyphenol, derivatives thereof, or combinations thereof. Such materials can be readily fabricated by interfacial polymerization or any suitable crosslinking method.

[0062] The porous substrate layer can include cellulose, polyester, polypropylene, acrylic, nylon, sulfonated polysulfone, polysulfone, polyethersulfone, polyimide, polyamide, polybenzimidazole, polyacrylonitrile, polyarylsulfone, poly(vinyl butyral), polyetherimide, derivatives thereof, or combinations thereof.

[0063] In various embodiments, the enhanced flat sheet membrane can have a thickness ranging from 20 μm to 300 μm, 30 μm to 300 μm, 50 μm to 300 μm, 100 μm to 300 μm, 200 μm to 300 μm, 20 μm to 100 μm, 30 μm to 100 μm, 20 μm to 200 μm, or 30 μm to 200 μm, etc. In addition to the reduced thickness relative to polymer membranes and permeate carriers that are typically used as single components, such thickness also provides better water flux without compromising salt rejection. For example, compared to a conventional leaf module having a permeate carrier and a polymer membrane configured as a single component, using the enhanced flat sheet membrane of the present invention can achieve a thickness reduction of at least 17%. Even when the permeate carrier is integrated into the polymer membrane, a rejection rate of at least 97.1% can still be achieved.

[0064] The enhanced flat sheet membrane can also include a pre-wetting agent coated on the permeate carrier. The pre-wetting agent can be applied to the permeate carrier before bringing the permeate carrier into contact with the polymer solution to form a polymer membrane having the permeate carrier therein. The pre-wetting agent renders the permeate carrier suitable for subsequent instantaneous pre-curing after contact with the polymer solution (i.e., polymer coating) prior to phase inversion (complete curing) in a coagulation tank. When the polymer solution coagulates in the presence of the permeate carrier to form a polymer membrane, the pre-wetting agent also alleviates the formation of defects.

[0065] In various embodiments, the enhanced flat sheet membrane can be operable to withstand pressures from 0 psi to 1.5×10 -11 psi, 0 psi to 1000 psi (about 6.89 MPa), 0 psi to 1500 psi, 1.5×10 -11 psi to 1000 psi, or 1.5×10 -11 psi to 1500 psi, etc.

[0066] In various embodiments, the enhanced flat sheet membrane can be operably used for microfiltration, ultrafiltration, nanofiltration, reverse osmosis, pressure retarded osmosis, forward osmosis, pervaporation, membrane distillation, and / or gas separation.

[0067] The embodiments and advantages described for the enhanced flat sheet membrane of the present invention in the first aspect are similarly effective for the method of the present invention for manufacturing the enhanced flat sheet membrane described subsequently herein, and vice versa. Since the various embodiments and advantages have been described above and examples are presented herein, they will not be repeated for the sake of brevity.

[0068] The present disclosure provides a method of manufacturing an enhanced flat sheet membrane that is operable to withstand vacuum pressure and high pressures up to 1500 psi, wherein the enhanced flat sheet membrane can comprise: a polymer membrane; a permeate carrier that enhances the polymer membrane and has channels for guiding the permeate stream; wherein the polymer membrane incorporates the permeate carrier therein, and the channel portions of the permeate carrier are exposed on the surface of the polymer membrane, and wherein the method can comprise: contacting the permeate carrier with a pre-wetting agent; casting a polymer solution onto the permeate carrier; and forming a polymer membrane from the polymer solution, wherein the permeate carrier is incorporated into the polymer membrane.

[0069] In various embodiments, contacting the permeate carrier with a pre-wetting agent can include dispensing the pre-wetting agent onto the permeate carrier at a flow rate of 10 mL / min to 10 L / min, 100 mL / min to 10 L / min, 1 L / min to 10 L / min, etc. Such flow rates facilitate proper control of a sufficient and / or uniform coating of the permeate carrier so that no defects (such as pinhole defects or permeate channel blockages) are formed when the polymer solution is cast thereon. The dispensing of the pre-wetting agent can be done by hand or on an industrial line. The permeate carrier can be placed by hand on a rack where the user can control the rack to dispense the pre-wetting agent thereon. For an industrial line, machines and equipment can be used, such as a conveyor belt for placing the permeate carrier, to move the permeate carrier under a dispensing assembly that dispenses the pre-wetting agent onto the permeate carrier. The method of dispensing the pre-wetting agent onto the permeate carrier can be done in any suitable manner, such as spraying, atomizing, pouring, sponging, slot die coating, roll coating, nip roll coating, drop coating, and soaking.

[0070] The pre-wetting agent can include a liquid or an aerosol. The liquid or aerosol can comprise: (i) an anionic surfactant, wherein the anionic surfactant can include a detergent, a fatty acid, a foaming agent, or a dispersant; or (ii) a non-ionic surfactant, wherein the non-ionic surfactant can include an alcohol, an ester, a phenol, an ether, or an amide; or (iii) a cationic surfactant, wherein the cationic surfactant can include a salt solution, wherein the salt solution can include an organic solvent or an inorganic solvent, wherein the organic solvent can include N-methyl-2-pyrrolidone, dimethylformamide, hexane, or a combination thereof, and wherein the inorganic solvent can include water; or (iv) a combination thereof.

[0071] The method can further include removing excess pre-wetting agent from the permeate carrier. Removing the excess pre-wetting agent can be done by different physical means, such as but not limited to removing it by using a sponge, compressed air, vacuum suction, etc. The removal can be done prior to phase inversion.

[0072] The method may further include dissolving the polymer in an organic solvent to form a polymer solution for casting on the permeate carrier, where the organic solvent may include 1-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide, or a combination thereof.

[0073] The polymer in the organic solvent may have a concentration range of 5 wt% to 50 wt%, 10 wt% to 50 wt%, 20 wt% to 50 wt%, 30 wt% to 50 wt%, 40 wt% to 50 wt%, 10 wt% to 20 wt%, etc. The viscosity of the polymer solution may be in the range of 100 cps to 100,000 cps, 1,000 cps to 100,000 cps, 10,000 cps to 100,000 cps, etc. For example, the polymer solution may have a viscosity in the range of 1,100 to 1,600 cps. This viscosity helps to properly control the sufficient and / or uniform coating of the permeate carrier so that no defects (such as pinhole defects or permeate channel blockages) are formed when the polymer solution is cast thereon.

[0074] In various embodiments, forming the polymer membrane may include coagulating the polymer solution by phase inversion in the presence of a non-solvent, such as water or an aqueous solution of an inorganic salt, where the aqueous solution may contain 20 vol% (or less) of one or more organic solvents. The organic solvents in such an aqueous solution may include, but are not limited to, one or more alcohols, such as isopropyl alcohol, ethanol, polyethylene glycol (PEG), or a combination thereof. In various embodiments, coagulating the polymer solution by phase inversion may include casting the polymer solution onto the permeate carrier and immersing the polymer solution and the permeate carrier in the non-solvent, where the polymer solution and the permeate carrier are arranged such that the polymer solution faces in any direction in the non-solvent. For example, the permeate carrier and the polymer solution may be arranged on a wet mesh carrier for phase inversion, where the polymer solution faces upward, downward, vertically, or at an angle to the surface of the coagulant in the coagulation bath. In other words, the exposed permeate channels face downward, upward, vertically, or at an angle to the surface of the coagulant in the coagulation bath. When the polymer solution or the permeate carrier faces downward, the polymer solution or the permeate carrier faces the direction of the gravitational force. Advantageously, the method is versatile in this regard.

[0075] In various embodiments, forming the polymer membrane can include coagulating a polymer solution by phase inversion within a temperature range of -10°C to 150°C, 10°C to 150°C, 50°C to 150°C, 100°C to 150°C, etc. Such temperature helps to appropriately control the structure of the polymer membrane (i.e., the porous base layer). The coagulant used can contain or can carry with or without an antifreeze. The coagulant can include or can be vapor or supersaturated vapor. In some cases, before phase inversion, the polymer solution can have a layer that has been cured or may be partially cured (partially solidified / coagulated) into a polymer. In various cases, curing (solidification / coagulation) may occur during the phase inversion process.

[0076] The method can also include subjecting the polymer membrane to interfacial polymerization or chemical crosslinking to form an active rejection layer. The active rejection layer can be formed on the polymer membrane away from the permeate carrier incorporated in the polymer membrane such that the channels of the permeate carrier are exposed or partially exposed at the surface of the polymer membrane opposite (i.e., contrary to) the surface where the active rejection layer is formed.

[0077] In addition to the above, various embodiments can include converting a laboratory-scale phase inversion into an industrial-scale phase inversion casting line. Various settings as described above (e.g., temperature, flow rate, viscosity) can be considered to convert laboratory-scale manufacturing into industrial-scale manufacturing, which involves manufacturing reinforced flat sheet membranes with a width range of 0 m to at least 2 m and a length greater than 0 m to at least 2000 m such that the reinforced flat sheet membranes can be readily used for all pressure-driven applications (e.g., reverse osmosis, forward osmosis, and pressure retarded osmosis). As described above, at the industrial scale, a line speed greater than 0 MPM to at least 50 MPM can be considered. Such a line speed helps to appropriately control the adequate and / or uniform coating of the permeate carrier so that no defects (e.g., pinhole defects or permeate channel blockages) are formed when casting the polymer solution thereon, and also controls the coagulation rate and residence time of the polymer solution in the coagulation bath. In addition to the line speed, other parameters determined above (e.g., polymer solution viscosity, mesh aperture, wetting flow rate) help to manufacture reinforced flat sheet membranes with sufficient permeate channels to obtain good permeate flow rates. The method allows for the manufacture of spiral wound membrane elements with a length range of 12” to 2 m and a diameter range of 1” to 12”, where the spiral wound membrane elements include the reinforced flat sheet membranes of the present disclosure.

[0078] In the present disclosure, when used in the context of measurement units, e.g., referring to dimensions or sizes (e.g., length, diameter, surface area), a number accompanied by the symbol ” (e.g., 12”) refers to an inch value. For example, 1” and 12” refer to 1 inch and 12 inches, respectively.

[0079] The term "substantially" does not exclude "completely"; for example, a composition "substantially free" of Y may be completely free of Y. When necessary, the term "substantially" may be omitted from the definition of the present invention.

[0080] In the context of the various embodiments, the articles "a", "an", and "the" as used with respect to a feature or element include references to one or more features or elements.

[0081] In the context of the various embodiments, the term "about" or "approximately" applied to a numerical value encompasses both the exact value and a reasonable variance.

[0082] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0083] Unless otherwise specified, the terms "comprises" and "comprising" and their grammatical variants are intended to be "open-ended" or "inclusive" language, such that they include the recited elements but also permit the inclusion of additional, unrecited elements.

[0084] Examples

[0085] The present disclosure relates to an enhanced flat sheet membrane for low energy pressure driven applications, which can be part of a thinner blade set including the enhanced flat sheet membrane. The present disclosure also relates to a method of manufacturing such an enhanced flat sheet membrane.

[0086] The enhanced flat sheet membrane can be used in pressure driven water purification applications such as reverse osmosis (RO), pressure retarded osmosis (PRO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), and forward osmosis (FO).

[0087] To manufacture the enhanced flat sheet membrane, the porous base layer can be part of a permeate carrier having a mechanically enhanced substrate ( Figure 1 ), wherein the permeate channels of the permeate carrier are substantially exposed on the back side of the enhanced flat sheet membrane. As used herein, the back side of the enhanced flat sheet membrane refers to the side of the enhanced flat sheet membrane that is closer to the permeate stream or the permeate channels. The enhanced flat sheet membrane can be used independently for low pressure applications or can be coated with a dense rejection layer for high pressure salt rejection applications.

[0088] The enhanced flat sheet membrane and its manufacturing method of the present invention are further described in detail by the following non-limiting examples.

[0089] Example 1: General discussion of the enhanced flat sheet membrane and method - pre-wetting of the permeate carrier

[0090] The present disclosure describes a method for stabilizing the manufacture of enhanced flat sheet membranes for pressure-driven applications (e.g., including up to 1500 psi). The resulting membranes have a high salt rejection layer, low reverse salt permeability, high flux permeability, resistance to high-pressure deformation, and a spiral wound blade pack with an overall reduced thickness, all of which contribute to an overall increase in the efficiency of spiral wound elements incorporating the enhanced flat sheet membranes of the present invention.

[0091] The manufacturing method involves casting a polymer solution onto a pre-wetted permeate carrier (e.g., a mesh) and coagulating the polymer from the polymer solution by phase inversion. Advantageously, wetting of the mesh allows the polymer solution to be cast directly onto a mesh with a grid size exceeding 300 microns, which otherwise might result in a membrane with small pores and a mechanically weak reverse phase layer that fails under high pressure. However, direct casting can be applicable to permeate carriers with a smaller grid size of less than 300 microns, bearing in mind that permeate carriers with a smaller grid size may be more expensive and / or less readily available. Direct casting onto permeate carriers with a grid size less than 300 microns may not easily allow for scaling up the membrane to industrial sizes, but this is made possible by the present method involving pre-wetting the permeate carrier. Additionally, in the absence of pre-wetting, the polymer solution may permeate through the permeate carrier and block the channels of the permeate carrier.

[0092] For laboratory-scale manufacture, it may be advantageous to cast membranes that are consistently good, without small pores and blocked permeate channels, for meshes with a pore size exceeding 300 microns ( Figure 3 A), by pre-wetting the mesh with liquids of different compositions before casting and then coagulating the polymer solution to form a porous membrane, especially when casting the polymer solution downward (i.e., in the same direction as the action of gravity). A thin coagulation layer is formed almost immediately after casting and phase inversion, and casting the polymer solution downward helps prevent the polymer solution, which is still in a liquid state, from oozing through the pores of the permeate carrier, thus preventing the formation of small pores, keeping the permeate channels unblocked, and reducing the thickness of the polymer membrane. The coagulation of the membrane can also be carried out with the polymer solution in the direction opposite to the action of gravity (i.e., upward) ( Figure 4 A).

[0093] Thus, for laboratory-scale coating, pre-wetting enables the successful scaling up of the method to an industrial-scale coating line for manufacturing the enhanced flat sheet membranes of the present disclosure. For example, an industrial-scale coating line with a width of 1 m and a length exceeding 100 m can be set up. In such an industrial scale, the polymer solution can be cast onto a substrate (e.g., perpendicular to the substrate) in any direction or at any angle, for example, using a slot die. The method may depend on the control of substrate wetting, drying, polymer coating formulation and viscosity, coating dispenser pressure, pump speed, line speed, coagulation temperature, rinse tank temperature, etc.

[0094] Subsequently, the developed method can be used to test the performance of the resulting membranes, which enables flat sheet flux and salt rejection measurements to be carried out without being affected by leakage from the non-active membrane regions that contain the permeate carrier, where the method does not suffer from permeate leakage or feed flow leakage due to pressure-driven tests or FO / PRO operation tests. This test method can be referred to herein as the flat sheet specimen performance quality test method to prevent leakage from the non-active layer of the enhanced flat sheet membranes of the present invention. Vacuum grease, silicon, blue tack, putty, any removable gel or fluid or malleable solid that may fill the microchannels and / or pores of the warp / weft (i.e., permeate carrier) on the back of the membrane can be carefully applied outside the active area but within the boundaries of the test cell before the performance test.

[0095] Example 2: Detailed discussion of enhanced flat sheet membranes and methods

[0096] In terms of water flux and power density, for example, in PRO, the membrane is one of the factors affecting pressure-driven performance. Conventional membranes for high-pressure applications can be fabricated by directly coating a porous polymer support layer onto a non-woven polyester substrate via phase inversion. The support layer is then interfaced polymerized on another machine to create a dense rejection polyamide layer. The membrane can then be wound into a spiral wound element, where the feed spacer faces the active rejection side and the permeate carrier faces the back of the membrane, where the feed spacer and the permeate carrier are not incorporated (i.e., remain as individual components) into the membrane.

[0097] A key consideration for the enhanced flat sheet membranes of the present invention is to enable the enhanced flat sheet membranes to be fabricated and operated in pressure-driven applications (up to at least 1500 psi), where the enhanced flat sheet membranes can be thin blade sets that have a permeate carrier incorporated into the polymer membrane, which forms a single component rather than existing as separate components. The thin blade sets facilitate the fabrication of low-energy spiral wound modules (SWMs) for pressure-driven membranes because the reduced thickness enables a single thinner component (the polymer membrane with the incorporated permeate carrier) to be rolled up with the feed spacer to form a spiral wound element, significantly reducing the work done due to element rolling ( Figure 11A)。The membrane manufacturing method of the present invention uses a permeate carrier, which can be a mesh material, to enhance the membrane, so as to achieve higher water permeability through fewer structural parameters in the polymer membrane, thereby reducing internal concentration polarization (ICP). Generally, a polymer membrane has a layer with a porous structure that forms the membrane body, and an optional dense rejection layer (i.e., a dense selective layer, a dense active layer). The layer with a porous structure can be referred to as a support layer or a base layer herein. By binding the permeate carrier to the polymer membrane, especially the support layer, the thickness of the support layer can be reduced, which can mitigate ICP. This enhanced flat sheet membrane can avoid using a traditional non-woven substrate because a permeate carrier (mesh reinforcement) has been incorporated, where the permeate channels of the permeate carrier are substantially exposed on the back of the polymer membrane, such that when the enhanced flat sheet membrane is wound into a spiral wound module, it requires lower energy for the same treatment output because more of the enhanced flat sheet membranes of the present disclosure can be wound within the spiral wound module housing. The enhanced flat sheet membrane of the present invention also has a high salt rejection layer, a low reverse salt permeability, a high flux permeability, is not easily deformed under high pressure, is wound into a spiral wound element with less effort, and reduces the overall thickness when all components are combined - allowing more of the enhanced flat sheet membranes of the present invention to be installed in one module.

[0098] In the present disclosure, the permeate carrier can be a hydrophilic or hydrophobic warp-knitted mesh fabric with strong mechanical strength and high porosity, which is embedded in a porous base layer for supporting the entire enhanced flat sheet membrane. A selective thin rejection layer can be formed on top of the enhanced membrane layer, away from the position where the permeate carrier is bound. The enhanced flat sheet membrane can be manufactured in standard element sizes, i.e., 1.8”, 2.5”, 4” and 8” for different applications.

[0099] In PRO, when released from the mixing of seawater and river water in an estuary, the renewable osmotic energy available in nature is estimated to be approximately 2000 Twh per year globally. Industrially, a large amount of brine waste (such as seawater desalination brine) has great osmotic potential. PRO may be a promising technology for harvesting this renewable osmotic energy. When water in the feed solution permeates through the membrane due to the osmotic difference across the membrane, it increases the volume of the pressurized driving solution, which can then be used to drive a turbine for power generation or drive a pressure exchanger to reduce the energy consumption of the seawater desalination process.

[0100] The PRO membrane is a consideration as it affects PRO performance (water flux and power density). However, to date, traditional spiral-wound membranes may not be suitable for PRO, which has hindered the large-scale commercialization of PRO technology. As an alternative, high-performance FO membranes have been considered. However, the drawback of using FO membranes in PRO is that the membranes are severely deformed due to the high operating pressure in PRO. In PRO, the membrane area at the feed spacer grid is typically unsupported and thus prone to deformation under high pressure, even if the membrane has a reasonable level of mechanical strength for FO applications. Severe membrane deformation can have an adverse impact on PRO performance and operation. First, it reduces the membrane separation parameters, such as undesirably increasing membrane solute permeability and decreasing membrane selectivity, which may be reflected in a sharp increase in the reverse solute diffusion rate at elevated pressures. Severe reverse solute diffusion can unfavorably enhance the ICP, thereby reducing the water flux and power density in PRO. Second, the deformed membrane restricts or blocks the feed flow channels, and then unfavorably requires a higher pressure on the feed side to maintain the feed flow, which unfavorably increases the energy consumption for operating PRO.

[0101] Even considering self-supporting hollow fiber membranes, such hollow fiber membranes cannot avoid deformation because of their low mechanical stability and can only operate at a maximum pressure of less than 20 bar. The low operating pressure of PRO affects the high power density with the application of a higher pressure (since the applied pressure for the theoretical peak power density is approximately half of the osmotic pressure difference), and may also reduce the energy conversion efficiency in the later stage of osmotic energy recovery.

[0102] The enhanced flat sheet membrane of the present invention is also beneficial for use in other high-pressure applications, such as RO for seawater desalination in particular, where the pressure can be as high as 1000 psi. The enhanced flat sheet membrane of the present invention eliminates the use of a permeate carrier as a single component in polymer membranes in RO / NF / UF / MF or an additional feed spacer for mechanically supporting the PRO membrane in PRO. This makes it possible to install more membranes within each membrane module, thereby providing more membrane surface area for filtration in pressure-driven applications and making the processing cost per module more effective. If the enhanced flat sheet membrane of the present invention (wherein a permeate carrier is incorporated) is sufficient to avoid the use of low-concentration spacers in PRO, the total blade pack thickness can be reduced by (2×T m1 +T LCS )–2×T m2 (see Figure 6 and Figure 12). In this case, in the context of PRO, the feed spacer may be equivalent to the permeate carrier used in RO. The "feed spacer in PRO" is configured to face the cleaner liquid flow. Figure 6It is shown that with 280 - micron spacers, the RO leaflet sets can save 1% to 4% in thickness. If a thinner permeate carrier of 100 microns is used, such as for RO, the thickness saved per leaflet set can reach up to about 18%, or even about 20%. Considering that more of the enhanced flat - sheet membranes of the present invention can be loaded into one element, even with thinner leaflet sets, the throughput of each spiral - wound element can be significantly increased, thus providing a low - energy membrane spiral - wound element.

[0103] Figure 7 It is shown that based on a series of process settings for casting on 280 - micron warp - knitted spacers with an average mesh size of 400 microns (and possibly including some mesh sizes up to 1200 microns or larger), the enhanced flat - sheet membranes successfully cast using the improved phase - inversion coating line of the present invention have an average flux of 3.1 LMH / bar and a rejection rate of 95%. Larger meshes may result in small holes if pre - wetting of the permeate carrier is exactly omitted. Figure 8 It is shown the power density, reverse salt flux, and reverse osmosis performance of the enhanced flat - sheet membrane of the present invention compared to traditional RO membranes. The structure, material, and chemistry of the polymer support structure and the rejection layer are configured only for reverse osmosis performance, so the power density and reverse salt flux of the enhanced flat - sheet membrane of the present invention can be significantly improved. Figure 9 It is shown the results of FO tests using FO mode and PRO mode (where specimens A and B refer to 2 different membrane samples). For pressure - retarded osmosis (PRO) tests, 2 different modes are used, namely FO mode and PRO mode. In FO mode, the membrane active layer faces the feed solution. In PRO mode, the membrane active layer faces the draw solution. In other words, the difference between FO mode and PRO mode lies in the orientation of the membrane selective layer.

[0104] Example 3: Non - limiting examples of configurations and materials used

[0105] The mesh fabric (i.e., permeate carrier) is partially embedded in the middle porous substrate layer to support the entire enhanced flat - sheet membrane against the applied hydraulic pressure. The permeate carrier can have a tensile modulus of, for example, greater than 100 MPa and is selected from woven, non - woven, warp - knitted fabrics, and their combinations. Each strand of the permeate carrier is a monofilament or multifilament. Non - limiting examples of materials for the permeate carrier include polyester, polypropylene, acrylic resin, nylon, sulfonated polysulfone, and their combinations. The thickness of the permeate carrier is in the range of, for example, 30 μm to 300 μm.

[0106] The permeate carrier is pre-wetted with, for example, water, a solution of one or more surfactants, a solution of one or more salts, one or more solvents, or a combination thereof. The surfactant solution includes, for example, (i) anionic surfactants such as detergents, fatty acids, foaming agents, dispersants; (ii) non-ionic surfactants such as alcohols, esters, phenols, ethers, amides; and / or (iii) cationic surfactants. The solvent can be, for example, water, N-methyl-2-pyrrolidone (NMP), hexane, or a combination thereof. The components used as pre-wetting agents or for forming pre-wetting agents can be in any range from 0% to 100%, with the sum of all components used being 100%. The pre-wetted web can be blown with compressed dry air at 0.1 bar to 10 bar to remove the excess pre-wetting agent.

[0107] The middle porous base layer (i.e., the layer formed between the dense rejection layer and the permeate carrier) is coagulated on the permeate carrier by the phase inversion method. The polymers used to form the base layer are selected from, for example, polymeric materials such as polysulfone (PSU), polyethersulfone (PES), polyacrylonitrile (PAN), polyarylsulfone (PASf), poly(vinyl butyral), sulfonated polysulfone (sPSU), polybenzimidazole (PBI), cellulose, its derivatives, and / or combinations thereof. The concentration of the polymer in the polymer coating (i.e., the polymer solution) ranges from, for example, 5.0 wt.% to 50.0 wt.% (preferably 15.0 wt.% to 20.0 wt.%). As non-limiting examples, the solvents used for the polymer solution can include 1-methyl-2-pyrrolidone (also known as NMP), dimethylacetamide (DMAc), dimethylformamide (DMF), and combinations thereof. Macromolecular organic substances, small molecular organic substances, and inorganic salts such as lithium bromide (LiBr), polyvinylpyrrolidone (PVP), propylene glycol, polyethylene glycol (PEG), acetone, isopropyl alcohol, ethanol, lithium chloride (LiCl), etc. can be used as additives to adjust the membrane porosity or hydrophobicity-hydrophilicity, and their concentration in the polymer solution can range from 0.1 wt.% to 20.0 wt.%.

[0108] The top active layer is formed by interfacial polymerization on top of the base layer or by phase inversion during the formation of the base layer. However, the formation of the top active layer is not limited to these two methods and may include, for example, crosslinking by chemical reaction or other suitable methods. The polymers used for forming the active layer by interfacial polymerization are selected from polyamines, polyols, and polyphenols, which are polymerized from the following monomers: (i) o-phenylenediamine (OPD), m-phenylenediamine (MPD), bisphenol A (BPA), trihydroxypropane, and (ii) molecules having poly-chlorides and / or polysulfonyl chlorides, such as trimesoyl chloride (TMC) and 1,5-naphthalene-disulfonyl chloride, wherein the monomers in (i) and (ii) can be dissolved in organic solvents such as hexane, cyclohexane, Isopar series, etc. or a combination thereof. High molecular weight organic compounds, small molecular weight organic compounds, and surfactants such as dimethyl sulfoxide (DMSO), ε-caprolactam (CL), triethylamine (TEA), camphorsulfonic acid (CSA), sodium dodecyl sulfate (SDS) are used to increase the miscibility of the two immiscible phases during the interfacial polymerization process or to neutralize by-products.

[0109] Example 4A: Warp-knitted permeate carrier (average mesh size – 100 microns), no pre-wetting

[0110] For Examples 4A to 4I, a polymer coating containing an NMP solution of 17 wt% PSU and 1 wt% LiBr was prepared in a round-bottom flask and mixed at 55 ± 5 °C. The coating was cooled to room temperature and degassed under vacuum for 2 hours. The coating was used as the polymer solution, and the coating was cast to form a polymer film.

[0111] In this example, a permeate carrier (TF800) with an average warp-knitted mesh size of 100 microns was cast without pre-wetting. The results are shown in Table 1 below.

[0112] Table 1 - Coating using TF800 permeate carrier mesh

[0113]

[0114] It has better performance when quenched (i.e., coagulated) at room temperature. The cost of TF800 is high, at $4.30 per meter, while the cost of TJ-30 is $2.10 per meter. The thickness of the blade set is reduced by approximately 5.8% (estimated based on the films coated with blade gaps of 100 μm and 150 μm). For a comparison calculation of the blade sets, see the examples below.

[0115] Coating parameters

[0116] Active layer formulation: MPD 2.25 wt%, TMC 0.12 wt%

[0117] Blade gap: 250 μm

[0118] Coating angle: 45°

[0119] Curing direction: Polymer upwards

[0120] Coating density: 1222 cps

[0121] Test conditions

[0122] Feed solution: 2000 ppm NaCl

[0123] Pressure: 225 psi

[0124] Feed temperature: 25 °C

[0125] Example 4B: Warp-knit permeate carrier pre-wetted for RO (average mesh size – greater than 400 microns)

[0126] In this example, a permeate carrier (TJ-30) with an average warp-knit mesh size greater than 400 microns was cast with pre-wetting using DI water. The results are in Table 2 below. Experiments using TJ-30 with this mesh size without pre-wetting can be prone to defective porous support layers and are thus not desirable. In this example, a control with a standard non-woven polyester backing was cast together to calculate the saved leaf-pack thickness (leaf-pack comparison calculation). The leaf-pack thickness was reduced by approximately 1.5%. The term “RO formulation” refers to the MPD and TMC compositions used for interfacial polymerization to form the active layer for RO applications.

[0127] Table 2 - Coating using TJ-30 mesh with RO formulation

[0128]

[0129] Coating parameters

[0130] Active layer formulation: MPD 2.25 wt%, TMC 0.12 wt%

[0131] Leaf gap: 100 μm

[0132] Coating angle: 45°

[0133] Curing direction: Polymer downwards

[0134] Coating density: approximately 1100 cps

[0135] Pre-wetting agent: DI water

[0136] Test conditions

[0137] Feed solution: 2000 ppm NaCl

[0138] Pressure: 225 psi

[0139] Feed temperature: 25 °C

[0140] Example 4C: Warp-knit permeate carrier for pre-wetting in FO (average mesh size - greater than 400 microns)

[0141] In this example, a permeate carrier (TJ30) with an average warp-knit mesh size greater than 400 microns was cast with pre-wetting using DI water with an FO formulation. The results are in Table 3 below. The FO formulation provides higher flux under the same test conditions.

[0142] Table 3 - Coating with TJ-30 mesh with FO formulation

[0143]

[0144] Coating parameters

[0145] Active layer formulation: 1.5 wt% MPD, 0.1 wt% TMC

[0146] Blade gap: 100 μm

[0147] Coating angle: 45°

[0148] Curing direction: Polymer down

[0149] Coating density: Approximately 1100 cps

[0150] Pre-wetting agent: DI water

[0151] Test conditions

[0152] Feed solution: 2000 ppm NaCl

[0153] Pressure: 225 psi

[0154] Feed temperature: 25 °C

[0155] Example 4D: Warp-knit permeate carrier for pre-wetting in RO with polymer up (average mesh size - greater than 400 microns)

[0156] In this example, a permeate carrier with an average warp-knit mesh size of 400 micron pores (which may even include some pore sizes up to 1200 microns or larger) was cast with pre-wetting using DI water and an RO formulation, but cured upward and with a coating angle of 90°. The results are in Table 4 below. The blade stack thickness was reduced by approximately 4.5%.

[0157] Table 4 - Coating with TJ-30 mesh using RO formulation with polymer side up

[0158]

[0159] Coating parameters

[0160] Active layer formulation: MPD 2.25 wt%, TMC 0.12 wt%

[0161] Blade gap: 100 μm

[0162] Coating angle: 90°

[0163] Curing direction: polymer side up

[0164] Coating density: approximately 1100 cps

[0165] Pre-wetting agent: DI water

[0166] Test conditions

[0167] Feed solution: 2000 ppm NaCl

[0168] Pressure: 225 psi

[0169] Feed temperature: 25 °C

[0170] Example 4E: Warp-knit permeate carrier for RO (average mesh size - approximately 64 microns)

[0171] In this example, a permeate carrier with an average rectangular mesh size of approximately 64 microns (Sefar PETEX IEM-07-195 / 70) was cast using and without using DI water for pre-wetting and using an RO formulation, and curing downwards. In this case, the permeate carrier is a polyester mesh that is 45 μm thick and has an open area of approximately 44.5%. The results are in Table 5 below. The membrane cast without pre-wetting (D260718HF26.1) has good rejection, flux and a 10% reduction in blade pack thickness. However, the membrane appears to have creases (see Figure 13 ).

[0172] Table 5 - Coating with ultra-thin Sefar mesh and RO formulation

[0173]

[0174] Coating parameters

[0175] Active layer formulation: MPD 2.25 wt%, TMC 0.12 wt%

[0176] Blade gap: 100μm

[0177] Coating angle: 90°

[0178] Curing direction: Polymer facing up

[0179] Coating density: approximately 1100 cps

[0180] Pre-wetting agent: DI water

[0181] Test conditions

[0182] Feed solution: 2000 ppm NaCl

[0183] Pressure: 225 psi

[0184] Feed temperature: 25°C

[0185] Example 4F: Warp-knitted permeate carrier (average mesh size - greater than 400 microns) pre-wetted with water as solvent and surfactant for RO

[0186] In this example, a permeate carrier (TJ-30) with an average warp-knitted mesh size greater than 400 microns was pre-wetted with an aqueous solution of solvent and an aqueous solution of surfactant, cast, and interfacially polymerized using an RO formulation. For an aqueous solution of 20 wt% NMP, the blade set thickness decreased by approximately 4.5%, and the flux was higher.

[0187] Table 6 - Coating using TJ-30 mesh with RO formulation but polymer facing up

[0188]

[0189] Coating parameters

[0190] Active layer formulation: MPD 2.25 wt%, TMC 0.12 wt%

[0191] Blade gap: 100μm

[0192] Coating angle: 45°

[0193] Curing direction: Polymer facing down

[0194] Coating density: approximately 1100 cps

[0195] Pre-wetting agent: DI aqueous solution of 0.2 wt% SLS and 20 wt% NMP

[0196] Test conditions

[0197] Feed solution: 2000 ppm NaCl

[0198] Pressure: 225 psi

[0199] Feed temperature: 25 °C

[0200] Example 4G: Pre-wetted P16 Permeate Carrier for RO (Average Mesh Size - Approximately 300 microns)

[0201] In this example, a permeate carrier (P16) with an average warp-knit mesh size of approximately 300 microns was pre-wetted with DI water, cast, and interfacially polymerized using an RO formulation. The results are in Table 7 below. The pre-wetted membrane had good rejection and flux.

[0202] Table 7 - Coating with P16 Permeate Carrier with RO Formulation

[0203]

[0204] Coating parameters

[0205] Active layer formulation: MPD 2.25 wt%, TMC 0.12 wt%

[0206] Blade gap: 200 μm

[0207] Coating angle: 45°

[0208] Curing direction: Polymer down

[0209] Coating density: Approximately 1600 cps

[0210] Pre-wetting agent: DI water

[0211] Test conditions

[0212] Feed solution: 2000 ppm NaCl

[0213] Pressure: 225 psi

[0214] Feed temperature: 25 °C

[0215] Example 4H: Phase Inversion P16 Permeate Carrier Used (Average Mesh Size - Approximately 300 microns)

[0216] In this example, a permeate carrier (P16) with an average warp-knit mesh size of approximately 300 microns was cast on a currently retrofitted industrial phase inversion casting line. The permeate carrier was pre-wetted and cast using a slot die at a coating angle of 90 °C. The results are in Table 8 below. Compared with *RO250918-01 coated on a non-woven backing, the thickness of the enhanced membrane was reduced by 2.9% to 9.6%.

[0217] Table 8 - Coating with P16 permeate carrier on the currently retrofitted industrial phase inversion casting line, where * indicates interfacial polymerization using an active layer formulation containing 2.25 wt% MPD and 0.12 wt% TMC for interfacial polymerization on the thin film composite (TFC) line. ** refers to an active layer formulation improved with small molecule additives (such as sodium dodecyl sulfate (SDS), isopropyl alcohol, etc.).

[0218]

[0219] Coating parameters

[0220] Active layer formulation: 2.25 wt% MPD, 0.12 wt% TMC

[0221] Slot die lip gap: 100 μm

[0222] Coating angle: 90°

[0223] Coating density: about 1600 cps

[0224] Pre - wetting agent: DI water

[0225] Test conditions

[0226] Feed solution: 2000 ppm NaCl

[0227] Pressure: 225 psi

[0228] Feed temperature: 25 °C

[0229] Example 4I: Reinforced flat sheet membrane in 1812 spiral wound element

[0230] In this example, interfacial polymerization of the reinforced flat sheet membrane was carried out using the RO formulation on an industrial - scale interfacial polymerization (IP) line. The results are in Table 9 and Table 10 below. The fabricated reinforced flat sheet membranes were wound into full - size 1812 elements. In this example, a P16 permeate carrier with an average grid size of about 300 microns was used.

[0231] Table 9 - Interfacial polymerization (IP) of reinforced flat sheet membranes on an industrial - scale IP line

[0232]

[0233] Table 10 - Element curling of interfacially polymerized reinforced flat sheet membranes

[0234]

[0235] Coating parameters

[0236] Active layer formulation: 2.25 wt% MPD, 0.12 wt% TMC

[0237] Slot die gap: 100 μm

[0238] Coating angle: 90°

[0239] Coating density: approximately 1600 cps

[0240] Pre - wetting agent: DI water

[0241] Test conditions

[0242] Feed solution: 2000 ppm NaCl

[0243] Pressure: 225 psi

[0244] Feed temperature: 25 °C

[0245] The rejection layers of the FO and RO membranes are polymerized using Formulations B, C, and D, which consist of DI aqueous solutions of metaphenylenediamine (MPD) and hexane solutions or isopar series of trimesoyl chloride with different amounts of small molecule additives such as sodium dodecyl sulfate (SDS), isopropyl alcohol, etc. Formulations B, C, and D differ in solvent type, composition of MPD and TMC, and the amount of additives, all of which are adjusted for different applications such as FO and RO.

[0246] Example 5: Commercial and potential applications

[0247] The present technology relates to the structure of a membrane configurable for a spiral - wound membrane module to increase productivity and reduce costs. Specifically, the present disclosure relates to an enhanced flat - sheet membrane that can be used in a spiral - wound membrane module, where the enhanced flat - sheet membrane can be curled to form a spiral - wound element. Since the enhanced flat - sheet membrane includes a polymer membrane having a permeate carrier formed as a single piece, a thinner leaf set is produced, which provides a higher active area in pressure - driven water purification applications with low energy requirements.

[0248] In summary, the present disclosure includes enhanced flat sheet membranes for PRO or FO processes. The enhanced flat sheet membranes can include: (a) a low concentration (LC) spacer having permeate channels as a first layer; (b) a porous substrate / support layer as a second layer, which is adjacent to and / or partially merged into the first layer; (c) wherein the LC spacer can be partially embedded in the multi-substrate / support layer; (d) a selective layer / active layer as a third layer, which is adjacent to and / or partially merged into the second layer, and / or a draw spacer adjacent to the third layer. The draw spacer can be used in PRO or FO, where the spacer is placed in or near the draw solution, and thus is called a draw spacer.

[0249] In some embodiments, the enhanced flat sheet membranes for RO, UF or MF processes can include: (a) a permeate carrier as a first layer; (b) a porous substrate / support layer as a second layer, which is adjacent to and / or partially merged into the first layer, wherein the permeate carrier can be partially embedded in the porous substrate / support layer; (c) a selective layer / active layer as a third layer, which is adjacent to and / or partially merged into the second layer; and (d) a feed spacer adjacent to the third layer.

[0250] The present disclosure also includes a method for manufacturing enhanced flat sheet membranes. The method can include: (a) pre-wetting the low concentration spacer or the permeate carrier with a pre-wetting agent; (b) casting the porous substrate / support layer on the permeate carrier by a phase inversion method; (c) forming the enhanced flat sheet membrane by forming a selective layer / active layer on the porous substrate / support layer by (i) the phase inversion method during the formation of the porous substrate / support layer or (ii) the interfacial polymerization method.

[0251] In various embodiments, the backing layer used in traditional membranes is omitted, which results in a reduction (thinning) in the overall thickness of the spiral wound leaf pack, and thus more of the enhanced flat sheet membranes of the present invention can be loaded into the spiral wound membrane module. The omission of the backing layer also simplifies the manufacturing process.

[0252] In various embodiments, the permeate carrier can be a hydrophilic or hydrophobic warp knitted mesh fabric.

[0253] In various embodiments, the pre-wetting agent used herein can be a liquid containing a surfactant solution.

[0254] Although the present invention has been particularly shown and described with reference to specific embodiments, those skilled in the art should understand that various changes in form and detail may be made without departing from the spirit and scope of the present invention as defined by the appended claims. Therefore, the scope of the present invention is defined by the appended claims, and all changes that fall within the meaning and scope of the equivalents of the claims should be covered.

Claims

1. An enhanced flat sheet membrane, the enhanced flat sheet membrane being operable to withstand vacuum pressure and high pressure up to 1500 psi, wherein the enhanced flat sheet membrane comprises: A polymer membrane; A permeate carrier that enhances the polymer membrane and has channels for guiding the permeate flow, wherein the permeate carrier includes filaments that form a network with pore sizes of 300 microns or greater, and the filaments define permeate channels configured to guide the permeate flow in a certain direction; wherein the polymer membrane binds the permeate carrier therein, And the channel portion of the permeate carrier is exposed on the surface of the polymer membrane; And the enhanced flat sheet membrane further comprises a pre-wetting agent coated on the permeate carrier, wherein the pre-wetting agent comprises a component different from the polymer membrane.

2. The enhanced flat sheet membrane according to claim 1, wherein, The network includes a woven network, a non-woven network or a warp-knitted network, and wherein the network is formed of: cellulose, polyester, polypropylene, acrylic acid, sulfonated polysulfone, polysulfone, polyethersulfone, polyimide, polyamide, polybenzimidazole, polyacrylonitrile, polyarylsulfone, poly(vinyl butyral), polyetherimide, derivatives thereof or combinations thereof.

3. The enhanced flat sheet membrane according to claim 2, wherein, The pore size of the network ranges from 300 μm to 5000 μm.

4. The enhanced flat sheet membrane according to any one of claims 1 to 3, wherein, The polymer membrane has a porous base layer, wherein: (i) An active rejection layer is formed on the porous base layer; and (ii) The permeate carrier is incorporated into the porous base layer; Wherein the porous base layer includes cellulose, polyester, polypropylene, acrylic acid, sulfonated polysulfone, polysulfone, polyethersulfone, polyimide, polyamide, polybenzimidazole, polyacrylonitrile, polyarylsulfone, poly(vinyl butyral), polyetherimide, derivatives thereof or combinations thereof.

5. The enhanced flat sheet membrane according to claim 4, wherein, The active rejection layer includes polyamide, polyamine, polyamide-imide, polyol, polyphenol, derivatives thereof or combinations thereof.

6. The enhanced flat sheet membrane according to any one of claims 1 to 3, wherein, The thickness of the enhanced flat sheet membrane ranges from 20 μm to 300 μm.

7. The enhanced flat sheet membrane according to any one of claims 1 to 3, wherein, The enhanced flat sheet membrane is operable to withstand pressures from 1.5×10 -11 psi to 1500 psi.

8. The enhanced flat sheet membrane according to any one of claims 1 to 3, wherein, The enhanced flat sheet membrane is operable for microfiltration, ultrafiltration, nanofiltration, reverse osmosis, pressure retarded osmosis, forward osmosis, pervaporation, membrane distillation and / or gas separation.

9. A method for manufacturing an enhanced flat sheet membrane, the enhanced flat sheet membrane being operable to withstand vacuum pressure and high pressure up to 1500 psi, wherein the enhanced flat sheet membrane comprises: A polymer membrane; A permeate carrier that enhances the polymer membrane and has channels for guiding the permeate flow, wherein the permeate carrier includes filaments that form a network with pore sizes of 300 microns or greater, and the filaments define permeate channels configured to guide the permeate flow in a certain direction; Wherein the polymer membrane incorporates the permeate carrier therein, and the channel portion of the permeate carrier is exposed on the surface of the polymer membrane, wherein the method comprises: Contacting the permeate carrier with a pre-wetting agent; Casting the polymer solution onto the permeate carrier in a direction that prevents the polymer solution from oozing out through the pores of the permeate carrier; and Forming the polymer membrane from the polymer solution, and the permeate carrier is incorporated into the polymer membrane, Wherein the pre-wetting agent comprises a component different from the polymer solution.

10. The method according to claim 9, wherein, Contacting the permeate carrier with the pre-wetting agent includes: dispensing the pre-wetting agent onto the permeate carrier at a flow rate of 10 mL / min to 10 L / min, wherein dispensing the pre-wetting agent onto the permeate carrier is carried out by spraying, atomizing, pouring, sponge coating, slot die deposition, roll coating, nip roll coating, drop coating or immersion.

11. The method according to claim 9, wherein, The pre-wetting agent includes the component as a liquid or an aerosol, wherein the liquid or aerosol comprises: an anionic surfactant, wherein the anionic surfactant includes a detergent, a fatty acid, a foaming agent or a dispersant; or a non-ionic surfactant, wherein the non-ionic surfactant includes an alcohol, an ester, a phenol, an ether or an amide; or a cationic surfactant, wherein the cationic surfactant includes a salt solution, wherein the salt solution includes an organic solvent or an inorganic solvent, wherein the organic solvent includes N-methyl-2-pyrrolidone, dimethylformamide, hexane or a combination thereof, wherein the inorganic solvent includes water; or a combination thereof.

12. The method according to any one of claims 9 to 11, further comprising removing excess pre-wetting agent from the permeate carrier.

13. The method according to any one of claims 9 to 11, further comprising dissolving a polymer in an organic solvent to form the polymer solution for casting onto the permeate carrier, wherein the organic solvent includes 1-methyl-2-pyrrolidone, dimethylacetamide, dimethylformamide or a combination thereof.

14. The method according to claim 13, wherein, The concentration of the polymer in the organic solvent ranges from 5 wt% to 50 wt%.

15. The method according to any one of claims 9 to 11, wherein, The viscosity of the polymer solution ranges from 100 cps to 100000 cps.

16. The method according to any one of claims 9 to 11, wherein Forming the polymer membrane includes coagulating the polymer solution by phase inversion in the presence of a non-solvent.

17. The method according to claim 16, wherein, Coagulating the polymer solution by phase inversion includes casting the polymer solution onto the permeate carrier and immersing the polymer solution and the permeate carrier in the non-solvent, wherein the polymer solution and the permeate carrier are arranged such that the polymer solution faces any direction in the non-solvent.

18. The method according to claim 16, wherein, Forming the polymer membrane includes coagulating the polymer solution by phase inversion at a temperature of -10 °C to 150 °C.

19. The method according to any one of claims 9 to 11, further comprising subjecting the polymer membrane to interfacial polymerization or chemical crosslinking to form an active rejection layer.

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