Abstract
The present invention relates to a spiral wound membrane element designs wherein the membrane sheet is fabricated with selective flux and rejection characteristics that can then be modified using various intensities and wavelengths of energy such as UV or the visible spectrum to optimize characteristics of the membrane sheet such as flux or rejection, and that can be utilized to optimally bond photopolymer spacers either above the active surface of the membrane sheet, or below the active surface.
Claims
1. A method of producing a membrane comprising: (a) providing a permeable support layer sheet; (b) disposing a polymer coating on a first surface of the permeable support layer sheet, where the polymer coating has one or more properties that can be varied by exposure to light; (c) supplying light to the polymer coating at wavelengths and intensities to produce a membrane having flux and rejection properties desired for use in a spiral wound filtration element.
2. The method of claim 1, wherein step (c) comprises directing light toward the permeable support layer sheet from the side of the first surface, such that the light reaches the polymer coating before reaching the permeable support layer sheet.
3. The method of claim 1, wherein step (c) comprises directing light toward the permeable support layer sheet from opposite the side of the first surface, such that the light reaches the polymer coating after transiting the permeable support layer sheet.
4. The method of claim 1, wherein step (c) comprises providing a source of light at a fixed location, and moving the permeable support layer sheet relative to the source of light.
5. The method of claim 1, wherein step (c) comprises providing a source of light at a location that is moveable relative to the permeable support layer sheet, and moving the source of light relative to the permeable support layer sheet.
6. The method of claim 1, wherein step (c) comprises supplying light having intensity, wavelength, or both, that vary with region of the membrane.
7. The method of claim 6, wherein the polymer coating has a thickness, and wherein step (c) comprises supplying light having intensity, wavelength, or both, that vary responsive to the thickness of the polymer coating.
8. The method of claim 6, wherein step (c) comprises supplying light having intensity, wavelength, or both, that is constant across a first dimension of the membrane and vary along a second dimension of the membrane.
9. The method of claim 6, wherein the membrane sheet has a thickness, and wherein step (c) comprises supplying light having intensity, wavelength, or both, that vary responsive to the thickness of the membrane sheet.
10. The method of claim 6, wherein step (c) comprises supplying light such that the flux of the membrane has a first value near a first end or side of the membrane and a second value near a second, opposite, end or side of the membrane, wherein the second value is greater than the first value.
11. The method of claim 10, wherein the flux of the membrane varies smoothly from the first value to the second value between the first and second ends or sides.
12. The method of claim 6, wherein step (c) comprises supplying light such that the rejection of the membrane has a first value near a first end or side of the membrane and a second value near a second end or side of the membrane, opposite the first end or side of the membrane, wherein the second value is greater than the first value.
13. The method of claim 10, wherein the rejection of the membrane varies smoothly from the first value to the second value between the first and second ends or sides.
14. (canceled)
15. The method of claim 1, wherein the light comprises ultraviolet light.
16. A membrane for use in a spiral wound filtration element, having a flux or rejection that has a first value near a first end or side of the membrane and a second value near a second, opposite, end or side of the membrane, wherein the second value is greater than the first value.
17. The membrane of claim 16, wherein the flux or rejection of the membrane varies smoothly from the first value to the second value between the first and second ends or sides.
18. The membrane of claim 16, having a flux that has a first flux value near a first end or side of the membrane and a second flux value near a second, opposite, end or side of the membrane, wherein the second flux value is greater than the first flux value; and having a rejection that has a first rejection value near a first end or side of the membrane and a second rejection value near a second, opposite, end or side of the membrane, wherein the second rejection value is greater than the first rejection value.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0007] FIG. 1 is a view of a conventional spiral wound membrane element prior to rolling.
[0008] FIG. 2 is a view of a membrane sheet with a UV light above the active surface of the membrane with the membrane sheet moving across the fixed position of the UV light.
[0009] FIG. 3 is a view of a membrane sheet with a UV light below the active surface of the membrane with the membrane sheet moving across the fixed position of the UV light.
[0010] FIG. 4 is a view of a membrane sheet with a UV light below the active surface of the membrane with the UV light moving relative to the fixed position of the membrane sheet.
[0011] FIG. 5 is a view of a membrane sheet with a UV light below the active surface of the membrane with printed patterns on the active surface of the membrane sheet.
[0012] FIG. 6 is a view of a membrane sheet with the intensity of UV light changing linearly along the length of the membrane sheet.
[0013] FIG. 7 is a view of a membrane sheet with the intensity of UV light changing variably along the length of the membrane sheet corresponding with the thickness of the material in the membrane sheet such that the UV intensity at the top of the membrane sheet is at the desirable value along the length of the membrane sheet.
MODES FOR CARRYING OUT THE INVENTION AND INDUSTRIAL APPLICABILITY
[0014] FIG. 1 is a schematic illustration of elements of a conventional spiral wound membrane element 10. Permeate collection tube 12 comprises holes 14 in collection tube 12 where permeate fluid is collected from permeate feed spacer 22. In fabrication, membrane sheets 24 and 28 comprises one sheet that is folded at center line 30. Membrane sheets 24 and 28 are typically comprised of a permeable support layer, for example polysulfone or polysulfone over polyethylene, and an active polymer membrane layer bonded or cast on to the support layer. Active polymer membrane surface 24 is adjacent to feed spacer mesh 26 and non-active support layer 28 is adjacent to permeate carrier 22. Feed solution 16 enters between active polymer membrane surfaces 24 and flows through the open spaces in feed spacer mesh 26. As feed solution 16 flows through feed spacer mesh 26, total dissolved solids (TDS) ions are rejected at active polymer membrane surfaces 24 and molecules of permeate fluid, for instance water molecules, pass through active polymer membrane surfaces 24 and enter permeable permeate carrier 22. As feed solution 16 passes along active polymer membrane surface 24, the concentration of TDS ions increases due to the loss of permeate fluid in bulk feed solution 16, and thereby exits the reject end of active polymer membrane sheet 24 as reject solution 18 with a higher TDS than feed solution 16. Permeate fluid in permeate carrier 22 flows from distal end 34 of permeate carrier 22 in the direction of center tube 12 where the permeate fluid enters center tube 12 through center tube entrance holes 14 and exits center tube 12 as permeate solution 20. To avoid contamination of the permeate fluid with feed solution 16, active polymer membrane surfaces 24 are sealed with adhesive along adhesive line 32 through permeate carrier 22 thereby creating a sealed membrane envelope where the only exit path for permeate solution 20 is through center tube 12.
[0015] In an example embodiment of the present invention shown in FIG. 2, the characteristics of the active membrane surface on membrane sheet 42 can be formulated to create a desired flux and rejection of salt at the membrane surface. UV light can be exposed to the active membrane surface to change or optimize the flux and rejection performance of the active membrane layer. Wavelengths such as visible light can also be utilized. UV light source 44 is positioned above membrane sheet 42. Membrane sheet 42 is drawn along fixed UV source 44. The rate of motion of membrane sheet 42 can be varied as well as the intensity of UV source 44 to achieve the desired flux and rejection values for a specific application.
[0016] In an example embodiment of the present invention shown in FIG. 3, UV light source 44 is placed below membrane sheet 42 and membrane sheet 42 has some transparency to UV or visible light. Membrane sheet 42 is drawn along fixed UV source 44. The rate of motion of membrane sheet 42 can be varied as well as the intensity of UV source 44 to achieve the desired flux and rejection values for a specific application. The treatment parameters used can depend on membrane characteristics such as amine loadings, polymer coatings, and cleaning protocols; and on desired performance characteristics. The desired properties of the membrane can include rejection (the amount or percentage of sale rejected at the membrane surface) and flux (the amount of fluid passing through the membrane surface in a given area of membrane surface). Rejection and flux can depend on the active surface after treatment. Those skilled in the art are familiar with the various dependencies involved and can select treatment parameters based on the specific membrane in use and the desired properties for the application.
[0017] In an example embodiment of the present invention shown in FIG. 4, UV light source 44 is placed below membrane sheet 42 and membrane sheet 42 has some transparency to UV or visible light. UV source 44 is drawn along membrane sheet 42. The rate of motion of UV source 44 can be varied as well as the intensity of UV source 44 to achieve the desired flux and rejection values for a specific application.
[0018] In an example embodiment of the present invention shown in FIG. 5, feed spacers 43 can be applied on the active surface of membrane sheet 42 to create a fluid feed channel for the flow of feed solution across the surface of membrane sheet 42. Spacers can also be applied on the bottom side of membrane sheet 42 such that feed spaces are created on the active surface of membrane sheet 42 by virtue of applying pressure in the feed space and embossing membrane sheet 42 over the spacers when pressure is applied to the feed solution. With the appropriate energy intensity of UV light applied by UV light source 44, photopolymer spacers can be hardened, and at the same time the flux and rejection characteristics of the membrane can be modified. Feed spacers 43 can be applied by direct printing of photopolymer on the membrane sheet, by offset printing, by screed printing, by gravure printing, or other techniques that may apply the spacing material to membrane sheet 42.
[0019] In an example embodiment of the present invention shown in FIG. 6, the intensity of UV source 44 can be varied along either or both of the linear or transverse directions of membrane sheet 42 to vary the flux and rejection characteristics of the membrane sheet at any location on membrane sheet 42. For example, as feed solution flows along the surface of membrane sheet 42 salt ions are rejected and the concentration of salt at the membrane surface will increase. It can be desirable to have increased flux or improved rejection characteristics at these areas of membrane sheet 42 to improve the overall performance of the membrane element or system. These performance characteristics can be advantageous for conventional membrane elements, and for membrane elements with feed flow along the long length of the membrane sheet in order to improve recovery (ratio of permeate to feed solution) in elements such as those manufactured by Pentair Corporation under the name GRO, or for membrane systems such as pressure retarded osmosis or forward osmosis.
[0020] In an example embodiment of the present invention shown in FIG. 7, membrane sheet 42 can have thickness or translucence variations 46 in the construction of membrane sheet 42. These variations can be compensated for by changing the wavelength or energy intensity of UV source 44 as membrane sheet 42 passes along UV source 44, or as UV source 44 passes along membrane sheet 42, depending on construction of the UV exposure apparatus. The energy intensity can be varied longitudinally, laterally, or both, across the surface of membrane sheet 42. The energy intensity can be optimized for solidifying the photopolymer spacers, or for optimizing the flux or rejection characteristics of membrane sheet 42, or combinations thereof.
[0021] The present invention has been described in connection with various example embodiments. It will be understood that the above descriptions are merely illustrative of the applications of the principles of the present invention, the scope of which is to be determined by the claims viewed in light of the specification. Other variants and modifications of the invention will be apparent to those skilled in the art.
