Light curing for membrane performance

Abstract

To optimize characteristics of a flat membrane such as permeate flux or salt rejection of a spiral wound membrane element.SOLUTION: The present invention relates to a spiral wound membrane element designs. Therein a flat membrane sheet is fabricated with selective permeate flux and salt rejection characteristics that can then be modified using various intensities and wavelengths of energy such as UV or a visible spectrum to optimize characteristics of the flat membrane such as permeate flux or salt rejection, and that can be utilized to optimally bond photopolymer spacers either above an active surface of the flat membrane, or below the active surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Technical Field The present invention relates to a membrane system used for separating fluid components, particularly a spiral membrane element.

Background Art

[0002] Background Art Spiral membrane filtration elements are known in the art and typically include a laminated structure called a leaf, which consists of a flat membrane sealed on three sides to or around a permeable permeate carrier. The permeable permeate carrier extends beyond the envelope-shaped membrane at one end and surrounds the central tube, and the central tube creates a path perpendicular to the axis of the central tube for discharging the permeate out of the end of the central tube through holes in the central tube. The laminated structure spirally surrounds the central tube and is spaced apart from itself by a permeable supply-side spacer so that the raw solution flows axially through the element from the supply-side end to the reject end of the spiral element. Conventionally, the supply-side spacer is used to allow the raw water to flow, a portion of which flows through the membrane into the spiral element, and the reject water can exit the element axially with respect to the element configuration, parallel to the central tube. Spiral membrane elements may utilize one leaf or may include multiple leaves spirally wound around the central tube. In some configurations, the leaf is relatively square, meaning that the width of the leaf is relatively close to the width of the leaf. This typically applies to elements with standard diameters such as 2.5", 4", 8", and 16" and a common length of 40". In other configurations, particularly for smaller spiral membrane elements with lengths shorter than 40", such as those used in residential or commercial applications for lighting, the leaf of the membrane has a dimension perpendicular to the central tube that is longer than the dimension horizontal to the central tube, which is the typical axis along which crossflow occurs. In some cases, the length of the leaf in such a configuration is three times or more the width of the leaf. It is rare for an element to be manufactured with a configuration where the length of the leaf is significantly smaller than the width of the leaf.

[0003] Improved versions of the design of spiral elements are disclosed in U.S. Patent No. 6,632,357 to Barger et al., U.S. Patent No. 7,311,831 to Bradford et al., and Australian Patent (No. 2014223490) and Japanese Patent (No. 6499089) entitled “Improved Spiral Wound Element Construction” by Roderick et al., which use islands or protrusions deposited on the inner or outer surface of the membrane or directly embossed instead of conventional supply-side spacers. Typically, the fluid supply flow is perpendicular to the central tube of the spiral element. During manufacture, after the element is spirally wound, the envelope-shaped flat membrane is pasted and then cut, and then the supply-side edge of the envelope-shaped membrane presents a flat surface to the flow of raw water. Provisional Patent Application No. 62849952 entitled “Entrance Features in Spiral Wound Elements” by Beckman, et al. describes a tapered leading edge of the envelope-shaped flat membrane. PCT Patent Application No. PCT / US2018 / 016318 entitled “Graded Spacers for Filtration Wound Elements” by Roderick, et al. describes the features of a supply-side spacer having a variable height over the length of the supply-side space and the permeate carrier space. U.S. Patent Application No. PCT / US17 / 62425 entitled “Flow Directing Devices for Spiral Wound Elements” by Herrington, et al. describes a telescoping prevention device incorporating a rotating vane that helps wash away the supply end of the spiral element with fluid flow and avoid the collision of particle obstacles in the raw water stream with the end of the envelope-shaped membrane.

[0004] In the manufacture of printed spacers rather than mesh spacers, various adhesives are used to fabricate supply-side space components, which are bonded to the active surface of the flat membrane. In other applications, the supply-side space components are attached to the inert surface of the flat membrane. In many of these cases, the adhesive applied to the membrane to create the supply-side space contains a photopolymer, which cures rapidly when ultraviolet (UV) energy is applied to the photopolymer material, thus curing rapidly and taking on a set physical shape. Depending on the composition of the polymer membrane surface, the characteristics of the permeate flux and the desalination rate characteristics of the active polymer coating may change upon UV exposure. In some cases, UV exposure can be detrimental to the permeate flux and desalination rate. In other cases, UV energy can improve the permeate flux characteristics by increasing the permeate flux or by improving the desalination rate. In this case, the desalination rate of the flat membrane can be increased, and as a result, a higher quality production fluid, i.e., one with fewer salt ions, can be produced, thus improving the efficiency of the membrane.

Summary of the Invention

Means for Solving the Problems

[0005] Disclosure of the Invention Understanding of the present invention can be facilitated by the content of U.S. Patent No. 6,632,357 to Barger et al., U.S. Patent No. 7,311,831 to Bradford et al., and Australian Patent (No. 2014223490) and Japanese Patent (No. 6499089) entitled “Improved Spiral Wound Element Construction” to Roderick et al., each of which is incorporated herein by reference.

[0006] Many design parameters of the helical element affect the performance of the element. Fluid flow characteristics such as flow velocity, flow path shape, and the geometry of the supply side spacer affect residence time, shear, and turbulence, which in turn affect performance characteristics such as the membrane permeate flux, salt rejection rate, and recovery rate of the membrane system. The "recovery rate" of a helical filtration element is defined as the ratio of the permeate flow rate to the raw water flow rate within the membrane element. The typical single element recovery rate of currently used reverse osmosis elements ranges from 10% to 30%, which means that 70 - 90% of the raw water exits the element in the reject stream. For example, in a household reverse osmosis system, it can be more economical, environmentally, and morally sound to reduce the reject stream so that the water discarded into the sewer is less compared to the water produced for drinking (i.e., the permeate). During the production and casting of the polymer layer in flat membrane manufacturing, the permeate flux and salt rejection rate of the membrane can be adjusted by the polymer formulation composition during production. For example, the permeate flux can be dramatically increased by adjusting the chemical formulation composition. Similarly, the salt rejection rate of the membrane can also be adjusted. In some cases, for example, it is possible to affect both the permeate flux and the salt rejection rate such that the permeate flux increases and the salt rejection rate decreases. When these conditions exist in the finished flat membrane, the salt rejection rate can be improved without sacrificing the permeate flux by exposing the flat membrane to UV light. The UV light can be applied either on or under the active surface of the membrane. The UV light can also be scanned along the length (or width) of the flat membrane, the flat membrane can be pulled along a fixed position of the UV light source, or a combination thereof. The UV light can also be varied along or across the length of the flat membrane, thereby varying the salt rejection rate along or across the flat membrane to make it easier to obtain a permeate of more uniform quality. The casting of the membrane is not always a uniform process, and there may be variations in the thickness of the polymer coating on the membrane substrate. When the thickness of the active coating of the flat membrane varies, the intensity of the UV light can be changed to ensure that the desired proper permeate flux and salt rejection rate are achieved at any point on the flat membrane and reach the desired values.Similarly, the intensity of the UV light can be varied to ensure that an appropriate amount of UV energy is imparted to the photosensitive polymer used as a spacer on the flat film, and the spacer is applied either on or below the membrane active surface. Different wavelengths of energy can also be used, including but not limited to visible and UV wavelengths.

Brief Description of the Drawings

[0007] Brief Description of the Drawings

Figure 1

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Figure 6

Figure 7

Modes for Carrying Out the Invention

[0008] Embodiments of the Present Invention and Industrial Application Fields Figure 1 is a schematic view of the elements of a conventional spiral membrane element 10. The permeate collecting pipe 12 includes holes 14 in the collecting pipe 12 where the permeate is recovered from the permeate supply side spacer 22. During manufacturing, the flat membranes 24 and 28 include a single sheet folded about a center line 30. The flat membranes 24 and 28 typically consist of a permeable support layer, such as polysulfone or polysulfone on polyethylene, and an active polymer membrane layer bonded or cast on top of the support layer. The active polymer membrane surface 24 is adjacent to the supply side spacer mesh 26, and the inert support layer 28 is adjacent to the permeate carrier 22. The raw water 16 enters between the active polymer membrane surfaces 24 and flows through the open spaces within the supply side spacer mesh 26. As the raw water 16 flows through the supply side spacer mesh 26, the total dissolved solids (TDS) ions are blocked at the active polymer membrane surface, and the molecules of the permeating fluid, such as water molecules, pass through the active polymer membrane surface 24 and enter the permeable permeate carrier 22. As the raw water 16 moves along the active polymer membrane surface 24, the TDS ion concentration increases in the bulk raw water 16 due to the loss of the permeating fluid, and thereby exits as reject water 18 having a higher TDS than the raw water 16 from the reject end of the active polymer flat membrane 24. The permeating fluid within the permeate carrier 22 flows from the tip 34 of the permeate carrier 22 towards the central pipe 12, where the permeating fluid enters the central pipe 12 through the central pipe inlet hole 14 and exits the central pipe 12 as permeate water 20. To avoid contamination of the permeating fluid with the raw water 16, the active polymer membrane surface 24 is sealed with an adhesive along the adhesive line 32 through the permeate carrier 22, thereby creating a sealed envelope-shaped membrane where the only exit path for the permeate water 20 there is through the central pipe 12.

[0009] In an exemplary embodiment of the present invention shown in Figure 2, the active membrane surface on the flat membrane 42 can be formulated to obtain a desired permeate flux and desalination rate at the membrane surface. The active membrane layer's permeate flux and desalination rate performance can be altered or optimized by irradiating the active membrane surface with UV light. Wavelengths such as visible light can also be used. The UV light source 44 is positioned above the flat membrane 42. The flat membrane 42 is pulled along the fixed UV light source 44. In addition to the moving speed of the flat membrane 42, the intensity of the UV source 44 can also be varied to achieve the desired permeate flux and desalination rate values for individual applications.

[0010] In an exemplary embodiment of the present invention shown in FIG. 3, the UV light source 44 is installed below the flat membrane 42, and the flat membrane 42 has a certain degree of permeability to UV or visible light. The flat membrane 42 is pulled along the fixed UV source 44. In addition to the moving speed of the flat membrane 42, the intensity of the UV source 44 can also be changed to achieve the desired values of the permeation flux and the desalination rate for individual applications. The processing parameters used may depend on membrane properties such as amine loading, polymer coating, and cleaning protocols, as well as the desired performance characteristics. The desired properties of the membrane can include the desalination rate (the amount or percentage of salt blocked at the membrane surface) and the permeation flux (the amount of fluid passing through the membrane surface at a certain surface area of the membrane surface). The desalination rate and the permeation flux may depend on the active surface after treatment. Those skilled in the art are familiar with the various dependencies involved and can select the processing parameters based on the specific membrane and its application in use and the desired characteristics.

[0011] In an exemplary embodiment of the present invention shown in FIG. 4, the UV light source 44 is installed under the flat membrane 42, and the flat membrane 42 has a certain degree of permeability to UV or visible light. The UV source 44 is pulled along the flat membrane 42. In addition to the moving speed of the UV source 44, the intensity of the UV source 44 can be changed to achieve the values of the permeation flux and the desalination rate desired for individual applications.

[0012] In an exemplary embodiment of the present invention shown in FIG. 5, the supply side 43 can be applied onto the active surface of the flat membrane 42 to create a fluid supply path for the flow of raw water across the surface of the flat membrane 42. The spacer can also be applied to the bottom surface of the flat membrane 42, and the supply side space is created on the active surface of the flat membrane 42 by applying pressure within the supply side space such that when the pressure is applied to the raw water, the flat membrane 42 is pressed onto the spacer to create unevenness. With an appropriate energy intensity of the UV light irradiated by the UV light source 44, the photopolymer spacer can be cured, and at the same time, the permeate flux and desalination rate characteristics of the membrane can be changed. The supply side spacer 43 can be applied by directly printing a photopolymer onto the flat membrane by offset printing, screen printing, gravure printing, or other techniques by which a spacing material can be applied to the flat membrane 42.

[0013] In an exemplary embodiment of the present invention shown in FIG. 6, by varying the intensity of the UV source 44 along either or both the linear or transverse direction of the flat membrane 42, the permeate flux and desalination rate characteristics of the flat membrane at any position on the flat membrane 42 can also be changed. For example, when the raw water flows along the surface of the flat membrane 42, the salt ions are blocked, and the concentration of salt at the membrane surface increases. It may be desirable to have increased permeate flux or improved desalination rate characteristics in these regions of the flat membrane 42 to enhance the overall performance of the membrane element or system. These performance characteristics can be advantageous for conventional membrane elements and for membrane elements having a supply flow along the long length of the flat membrane, such as those manufactured by Pentair Corporation under the name GRO, for example, to improve the recovery rate (the ratio of permeate to raw water) of the element, or for membrane systems such as osmotic power generation or forward osmosis.

[0014] In an exemplary embodiment of the present invention shown in FIG. 7, the flat film 42 may have thickness or translucency variations 46 in the configuration of the flat film 42. These variations can be compensated by changing the wavelength or energy intensity of the UV source 44 when the flat film 42 moves along the UV source 44 or when the UV source 44 moves along the flat film 42, depending on the configuration of the UV exposure apparatus. The energy intensity can be changed longitudinally, laterally, or both across the surface of the flat film 42. The energy intensity can be optimized to solidify the photopolymer spacer, or to optimize the permeation flow rate or desalination rate characteristics of the flat film 42, or both.

[0015] The present invention has been described in connection with various exemplary embodiments. It should be understood that the above description is merely illustrative of the application of the principles of the present invention as defined by the claims to be read in light of the specification. Other variations and modifications of the present invention will be apparent to those skilled in the art.

Claims

1. A method for producing a membrane, comprising the steps of: (a) providing a permeable support layer sheet; (b) disposing a polymer coating on a first surface of the permeable support sheet, the polymer coating having one or more properties that can be altered by exposure to light; (c) applying light to the polymer coating at a wavelength and intensity to produce a membrane having desirable flux and salt rejection characteristics for use in a spiral wound filtration element; The method includes:

2. 2. The method of claim 1, wherein step (c) includes directing light from the side of the first surface toward the transmissive support sheet such that the light reaches the polymer coating before reaching the transmissive support sheet.

3. 2. The method of claim 1, wherein step (c) comprises directing light toward the transmissive support sheet from a side opposite the first surface such that the light reaches the polymer coating after passing through the transmissive support sheet.

4. The method of claim 1 , wherein step (c) comprises providing a light source at a fixed position and moving the transmissive support sheet relative to the light source.

5. The method of claim 1 , wherein step (c) comprises providing a light source at a location movable relative to the transmissive support sheet; and moving the light source relative to the transmissive support sheet.

6. The method of claim 1 , wherein step (c) comprises providing light having an intensity, wavelength, or both that varies across regions of the film.

7. 7. The method of claim 6, wherein the polymer coating has a thickness, and step (c) comprises providing light having an intensity, a wavelength, or both that varies with the thickness of the polymer coating.

8. 7. The method of claim 6, wherein step (c) comprises providing light having an intensity, wavelength, or both that is constant in a first dimension of the film and that varies along a second dimension of the film.

9. 7. The method of claim 6, wherein the flat film has a thickness, and step (c) comprises providing light having an intensity, a wavelength, or both that varies with the thickness of the flat film.

10. 7. The method of claim 6, wherein step (c) comprises providing light such that the permeate flux through the membrane has a first value near a first end or face of the membrane and a second value near a second, opposite end or face of the membrane, the second value being greater than the first value.

11. 11. The method of claim 10, wherein the permeate flux of the membrane changes smoothly from the first value to the second value between the first and second ends or faces.

12. 7. The method of claim 6, wherein step (c) comprises providing light such that the salt rejection of the membrane has a first value near a first end or face of the membrane and a second value near a second end or face of the membrane opposite the first end or face of the membrane, the second value being greater than the first value.

13. 11. The method of claim 10, wherein the salt rejection of the membrane transitions smoothly from the first value to the second value between the first and second ends or faces.

14. A method for producing a membrane, comprising the steps of: (a) providing a flat membrane; (b) disposing one or more spacing features on a first surface of the flat film, the spacing features comprising a material having one or more properties that can be changed by exposure to light; (c) providing the spacing feature with light of a wavelength and intensity to produce a spacing feature having desired characteristics; The method includes:

15. The method of any one of claims 1 to 14, wherein the light comprises ultraviolet light.

16. 1. A membrane for use in a spiral wound filtration element, the membrane having a permeate flux or salt rejection having a first value near a first end or face of the membrane and a second value near a second, opposite end or face of the membrane.

17. 17. The membrane of claim 16, wherein the permeate flux or salt rejection of the membrane changes smoothly from the first value to the second value between the first and second ends or faces.

18. 17. The membrane of claim 16, having a permeate flux having a first permeate flux value near a first end or face of the membrane and a second permeate flux value near a second, opposite end or face of the membrane, the second permeate flux value being greater than the first permeate flux value; and having a salt rejection having a first salt rejection value near a first end or face of the membrane and a second salt rejection value near a second, opposite end or face of the membrane, the second salt rejection value being greater than the first salt rejection value.

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