SPIRAL WOUND FILTRATION DEVICE AND METHODS OF MANUFACTURE

Abstract

A spiral wound membrane module, comprising a perforated core having an axially extending internal bore; at least one membrane packet comprising a folded membrane sheet defining a first outer face, a first inner face, a second outer face and a second inner face, the fold of the folded membrane sheet being a leading end of the membrane packet; a feed sheet positioned between the first and second inner faces so as to be sandwiched by the folded membrane sheet; a first permeate screen adjacent the first outer face of the membrane sheet defining a first permeate channel; a second permeate screen adjacent the second outer face of the membrane sheet defining a second permeate channel; and a fluid impermeable support coupled to the leading edge of the membrane packet. Also disclosed is a method of manufacturing the spiral wound membrane module.

Claims

1. A method of forming a filter module, comprising providing at least one membrane sheet, at least one feed screen and at least one permeate sheet; folding said at least one membrane sheet along its length to form a leaf with two halves integrally formed together; positioning said at least one feed screen between said two halves to form a membrane packet having a membrane packet fold; positioning an impermeable support at the location of said membrane packet fold to form a leading edge of said membrane packet; and spirally winding said membrane packet and said at least one permeate sheet about a core, the position of said impermeable support avoiding the formation of a void region in front of said leading edge of said membrane packet.

2. The method of claim 1, wherein said impermeable support is wedge-shaped.

3. The method of claim 1, wherein said module is cylindrical in cross-section and has an outer surface of cured adhesive.

4. The method of claim 1, comprising providing a plurality of membrane packets, each having a leading edge and a fluid impermeable support coupled to each respective leading edge.

5. The method of claim 1, wherein said at least one membrane sheet includes a first membrane sheet and a second membrane sheet, said at least one feed screen includes a first feed screen and a second feed screen, and said at least one permeate sheet includes a first permeate sheet and a second permeate sheet, wherein a first permeate channel is defined between said first membrane sheet and said first permeate sheet and a second permeate channel is defined between said second membrane sheet and said second permeate sheet; the method further comprising potting said filter module by positioning the filter module into sealing relation with a mold cavity; introducing an adhesive into said mold cavity; applying a vacuum to said mold cavity; whereby said vacuum drives said adhesive into said first and second permeate channels; and allowing said adhesive to cure.

6. A method of filtering product through a spiral wound membrane module having an end face, the module comprising: a perforated core having an axially extending internal bore; at least one membrane packet comprising a folded membrane sheet defining a first outer face, a first inner face, a second outer face and a second inner face, the fold of said folded membrane sheet being a leading edge of said membrane packet; a feed screen positioned between said first and second inner faces so as to be sandwiched by the folded membrane sheet; a first permeate sheet adjacent said first outer face of said membrane sheet defining a first permeate channel; a second permeate sheet adjacent said second outer face of said membrane sheet defining a second permeate channel; and a fluid impermeable support coupled to said leading edge of said membrane packet and occupying a void between said leading edge and said first and second permeate sheets; the method comprising: introducing said product at said end face under pressure, causing said product to flow axially through the feed screens, and then flow tangentially across said membrane sheet with a portion flowing through the membranes sheet where it reaches said first permeate channel defined between said first outer face of said membrane sheet and said first permeate sheet.

7. The method of claim 6, further comprising removing from said module permeate that flows to the perforated core.

8. The method of claim 6, wherein said impermeable support is wedge-shaped.

9. A membrane packet for a spiral wound membrane module, the membrane packet comprising, in an unwound condition, a folded membrane sheet defining a first outer face, a first inner face, a second outer face and a second inner face, the fold of said folded membrane sheet being a leading edge of said membrane packet, and a feed sheet positioned between said first and second inner faces so as to be sandwiched by the folded membrane sheet; a first permeate screen adjacent said first outer face of said membrane sheet defining a first permeate channel; a second permeate screen adjacent said second outer face of said membrane sheet defining a second permeate channel; and a wedge-shaped fluid impermeable support coupled to said leading edge of said membrane packet and made of a compressible material.

10. The membrane packet of claim 9, further comprising a perforated core having axially extending internal bore, wherein when said membrane packet is wound on said perforated core, the wedge-shaped fluid impermeable support occupies the region where a void would otherwise form upon winding said membrane packet on said perforated core, said support conforming to the shape of the void.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG. 1 is a photograph showing a wedge-shaped void formed between a membrane and a feed screen of a spiral wound filtration device in accordance with the prior art;

[0020] FIG. 2 is a photograph showing a support inserted in the void formed between a membrane and permeate screen, and between a membrane and a feed screen, of a spiral wound filtration device in accordance with certain embodiments;

[0021] FIG. 3 is a cross-sectional view of a support in accordance with certain embodiments;

[0022] FIG. 4 is a diagrammatic illustration of a support and membrane packet during a winding operation;

[0023] FIG. 5 is a cross-sectional view of a potting mold in accordance with certain embodiments;

[0024] FIG. 6 is a photograph of a top view of a spiral wound membrane module in accordance with certain embodiments;

[0025] FIG. 7 is a photograph of a module with a feed screen having a border in accordance with certain embodiments;

[0026] FIG. 8 is a photograph of a feed screen with four borders in accordance with certain embodiments.

DETAILED DESCRIPTION

[0027] A more complete understanding of the components, processes and devices disclosed herein can be obtained by reference to the accompanying drawings. The figures are merely schematic representations based on convenience and the ease of demonstrating the present disclosure, and is, therefore, not intended to define or limit the scope of the exemplary embodiments.

[0028] Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.

[0029] The singular forms a, an, and the include plural referents unless the context clearly dictates otherwise.

[0030] As used in the specification, various devices and parts may be described as comprising other components. The terms comprise(s), include(s), has, can, having, contain(s), and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional components.

[0031] In certain embodiments, the filtration device is a filtration module having a fluid inlet, a fluid outlet spaced from the fluid inlet, a permeate outlet, a central core having a plurality of openings and an axially extending bore along its entire length, one or more membrane packets, in each of which is sandwiched a feed sheet or screen which may be a polyolefin sheet such as polypropylene, and one or more permeate sheets such as one or more polyester screens that may be epoxy impregnated to provide it with sufficient strength to withstand the typical operating pressures encountered during use. The feed screen provides space for the flow of feed between the opposing membranes that sandwich it. The permeate sheets provide fluid pathways for permeate flow to the perforated core. The membrane packet or packets and permeate sheet or sheets are wound in a spiral configuration about the core. The membrane within each membrane packet may be a single layered or multilayered membrane, and may be used for filtration of unwanted materials including contaminants such as infectious organisms and viruses, as well as environmental toxins and pollutants that could be removed by size exclusion and chemical or physical adsorption of the combination thereof. The membrane may be comprised of any suitable material, including, but not limited to polyether sulfone, polyamide, e.g., Nylon, cellulose, polytetrafluoroethylene, polysulfone, polyester, polyvinylidene fluoride, polypropylene, a fluorocarbon, e.g. poly (tetrafluoroethylene-co-perfluoro (alkyl vinyl ether)), poly carbonate, polyethylene, glass fiber, polycarbonate, ceramic, and metals. It may be a microfiltration, ultrafiltration or reverse osmosis membrane. Ultrafiltration membranes are particularly preferred.

[0032] One suitable spiral wound filtration device is the Pellicon capsule commercially available from MilliporeSigma. The Pellicon capsule is a single use, single pass tangential flow filtration device that uses Ultracel composite, solvent-resistant membranes and is suitable for bioprocessing of antibody-drug conjugates and monoclonal antibodies. Those skilled in the art will appreciate that other spiral wound devices are also suitable, including re-usable and/or multiple pass tangential flow devices.

[0033] Typically, a spiral wound device is manufactured by winding one or more packets made up of a folded membrane and feed screen sandwiched by the folded membrane, and one or more permeate sheets, into the device around a perforated core or mandrel. In some embodiments, one full circumferential wrap of a permeate sheet may be first wound around the core to provide an adequate fluid pathway for permeate fluid to travel to the openings in the core. Since the membrane packet is generally thicker than the other materials, the winding operation of the membrane packet creates a wedge-shaped void region in front of the leading edge 5 of the membrane packet as it winds over itself, as can be seen in FIG. 1.

[0034] More specifically, FIG. 1 illustrates the folded over leading edge 5 of a membrane 10 with a feed screen 12 sandwiched by the folded over membrane 10. The folded over membrane 10 with a feed screen sandwiched within the fold comprises a membrane packet 14. As the membrane packet 14 is wound over itself, void region 15 forms as seen just to the left of the membrane packet leading edge 5, and this void region 15 is typically generally wedge-shaped. To eliminate this void region 15, it has been conventionally filled with excess adhesive to seal it, which is a tedious manual process and not always successful. For example, the subsequent compression of the winding tension, and nip forces, can cause the adhesive to be squeezed out of the space, again creating a void region and possibly deforming the areas around it. This creates a bypass region for fluid flow and reduces product yield and overall performance of the device.

[0035] In accordance with certain embodiments, a support 20 is coupled to the leading edge 5 of the membrane packet so that upon winding of the packet, the support 20 occupies the space where the void region 15 would otherwise form, as shown in FIGS. 2 and 4. The size and shape of the support 20 can be determined based on prior experience of the size and shape of the void region 15 formed during a typical winding operation for a given size filter module. Support 20 can be coupled to the leading edge 5 using adhesive means, ultrasonic welding means, heat welding means, ultra-violet glue means or any other suitable means.

[0036] FIG. 3 illustrates a preferred embodiment of the support 20, where a wedge-shaped support 20 is shown. Upon winding of the membrane packet 14, the support 20 will occupy the region where a void region 15 would normally form, and a fluid bypass region is minimized or avoided, as the membrane 10 is forced to remain in contact with the feed screen 12.

[0037] In addition, in accordance with certain embodiments as set forth below, during the potting process the device is submerged in adhesive, and a vacuum is pulled on the permeate fluid flow channel. If the void 15 is present, adhesive migrates into the permeate fluid flow channel, causing blockage of the channel. The support 20 thus also functions to mitigate or eliminate such adhesive migration, and reduces the amount of adhesive necessary to seal the area. This also results in a more uniform permeate channel seam near the core or mandrel 12 and ultimately a more uniform membrane area within each spiral wound filtration module.

[0038] In certain embodiments, the support 20 is attached to the leading edge 5 of the membrane packet 14, such as at seam locations, with a suitable adhesive (e.g., an epoxy or polyurethane). Where multiple membrane packets 14 are wound on a single core, e.g., in a multi-leaf assembly, each membrane packet 14 may have a support 20 attached to its leading edge 5. For example, FIG. 6 illustrates a four-leaf assembly, and consequently there are four supports 20 visible radially outwardly from the central perforated core 12.

[0039] In some embodiments, the support 20 is wedge-shaped to match the anticipated void that forms in the absence of the support 20. In some embodiments, the thicker end 21 of the support 20 is 0.031 inches thick, and tapers to the thin edge 22 of the support 20 which is 0.003 inches thick, although those skilled in the art will appreciate that the size is not critical, since the support 20 is compressible and will conform to the shape of the void. The thin edge 22 may have corners that are radiused or rounded to eliminate sharp edges that could tear the materials that it comes into contact with. The thicker end 21 of the support 20 may be fixed to the leading end 5 of the membrane packet with a suitable adhesive. In certain embodiments, the support 20 is elongated and extends the entire length of the membrane packet 14, as best seen in FIG. 8. In other embodiments, individual supports 20 may be positioned at only the opposite faces of the membrane packet 14 to block adhesive intrusion into the permeate channel, and not extend the entire length of the membrane packet 14. In certain embodiments, the support 20 is made of a solid, fluid impervious material not deleterious to the filtration operation to be carried out with the module, and capable of providing an adequate seal for vacuum seals on the mold used to introduce adhesive, as discussed in greater detail below. Suitable materials include thermoplastic elastomers, such as Pebax 5533 SA01 Med Pantone 298C. Preferably the material has sufficient flexibility to conform to the shape of the core 12.

[0040] Once the support 20 is fixed to the leading edge 5 of the membrane packet 15, the membrane packet 15 may be tightly wound under tension about the core 12 together with the permeate screen 16 (FIG. 4) and adhesive to form a spirally wound assembly. As the support 20 is wound in, it becomes sandwiched on either side by the permeate screen 14, which holds the support 20 in place until adhesive is applied to fix it in position. Because the leading edge 5 of the membrane packet 14 is supported by the support 20, the membrane 10 stays in contact with the feed screen 12 and is prevented from collapsing during a nip roller step, which removes the adhesive from the area and leads to a deleterious fluid bypass.

[0041] However, binding the assembly with adhesive during winding is somewhat variable, and is prone to gap formation which can lead to device failure.

[0042] Accordingly, in accordance with certain embodiments, the assembly can be bonded together with the use of a driving force such as a vacuum, or some pressure differential, to distribute the generally low-viscosity adhesive into the permeate sheet 14 uniformly to create a robust and uniform seam without the variability that results with manually made seams. In order to prevent potting adhesive form entering the feed channel during the potting process, a fluid impermeable feed screen border may be used as shown in FIG. 7. The feed screen border also prevents any feed flow from reaching any membrane outside of the border. This effect defines the effective membrane area, greatly reducing membrane area variability. Applying a feed screen border on the leading and trailing edge restricts the flow to membrane area only inside these edges, and thus defines the active membrane length for each membrane packet, which also improves feed channel geometry and permeate channel geometry. In certain embodiments, at least three of the feed screen sides include fluid impermeable borders to prevent adhesive from entering feed channels during potting. In some embodiments, one of the fluid impermeable borders is on the feed face, one is on the retentate face, and one is one the open tail end of the membrane packet (which is part of the circumference). The feed and retentate borders are removed to activate the spiral for feed flow. The feed tail border may remain. In some embodiments all four of the sides of the feed screen include fluid impermeable borders (FIG. 8) during potting, and again the feed and retentate borders are removed to activate the spiral for feed flow. Adhesive in the feed channel could lead to catastrophic loss of feed channel flow, or loss of integrity in operation by delaminating the membrane e.g. as the membrane moves apart under feed pressurization.

[0043] Once the potting adhesive is applied and cured, the border on the spiral inlet and outlet faces can be removed such as by cutting it away to reopen the feed channel. A viscous polyurethane adhesive (or thermoplastic, silicone or thermoplastic elastomer) is suitable for forming the solid impermeable feed screen border. In certain embodiments, during dispensing of the border adhesive onto the feed screen to form the fluid impermeable border, a film such as a polyethylene film may be used as a backing layer for the feed screen. In some embodiments, a second layer of film, e.g., polyethylene film, is also applied to the top of the feed screen after all of the adhesive has been deposited around the perimeter, and the resulting feed screen sandwich is compressed to distribute the adhesive into the shape of the border.

[0044] FIG. 5 shows a suitable mold body 30 for potting a spirally wound assembly using vacuum as a driving force for distributing the adhesive. In certain embodiments, a dry would spiral assembly 25 is placed in the mold body 30 having an adhesive injection port 31 in fluid communication with an interior mold body cavity 32 in which the dry wound spiral assembly 25 is positioned. Preferably the adhesive injection port 31 is located at or near the bottom of the mold body 30, so that the adhesive flows upwardly upon the application of a driving force so that any entrapped air is removed during filling. In some embodiments, the perforated core 12 of the dry wound spiral assembly 25 is placed in sealing relation with a tapered, or O-ring interface 33 of the mold body 30. O-ring seals 36 or the like may be provided at the opposite end of the mold body 30 to ensure that the dry wound spiral assembly 25 is in sealing relation with the mold body 30, so that upon the application of vacuum, there are no leaks.

[0045] In some embodiments, a suitable potting adhesive, such as an epoxy or a polyurethane, is introduced into the injection port 31, and a vacuum is applied at the vacuum inlet 40 to drive the adhesive into the permeate screen creating all necessary device seams, and around the spiral assembly 25 to completely envelope the assembly 25. Suitable vacuum levels range from 1-15 in Hg from 1-300 seconds. Once the adhesive cures, the device is covered in an annular hard shell reinforced with permeate screen 35 (FIG. 6), which resists expansion under high pressure drop situations, for example up to 100 psig. Such expansion can open the feed channel geometry and lead to a reduction in device performance.

[0046] In some embodiments, the mold body 30 can be configured so that certain features are formed on the outer surface of the cured adhesive, such as an annular ring for receiving an O-ring in the event the formed spiral assembly is used as a stand-alone module, i.e., without any outer housing or pressure vessel. These features may also be machined.

[0047] In some embodiments, the mold can be a housing that forms part of the final product, such as a plastic housing inside of which the spiral wound filter is positioned.

[0048] The device is sterilizable such as by steam, ethylene oxide gas or radiation such as beta or gamma radiation.

[0049] While various aspects and embodiments have been disclosed herein, other aspects, embodiments, modifications and alterations will be apparent to those skilled in the art upon and understanding the preceding detailed description. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting. It is intended that the present disclosure be construed as including all such aspects, embodiments, modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.