WO2002005934A2

WO2002005934A2 - Membrane packets, methods for making membrane packets, and membrane packet assemblies

Info

Publication number: WO2002005934A2
Application number: PCT/US2001/017497
Authority: WO
Inventors: Stephen A. Geibel; Gerard P. Henricksen
Original assignee: Pall Corporation; Fendya, Thomas, J.
Priority date: 2000-05-31
Filing date: 2001-05-31
Publication date: 2002-01-24
Also published as: AU2001275042A1; WO2002005934A3

Abstract

A membrane packet and method of making a membrane packet comprising a plurality of porous membranes, each porous membrane having a first region and a second thinner region, wherein the plurality of porous membranes are stacked, the first regions of the porous membrane being axially aligned and the second regions of the porous membranes being axially aligned, and wherein the second regions of the porous membranes are compressed and comprise a compression bond maintaining the stack of porous membranes as an integral unit.

Description

MEMBRANE PACKETS, METHODS FOR MAKING MEMBRANE PACKETS, AND MEMBRANE PACKET ASSEMBLIES

This application claims priority based on United States Provisional

Application No. 60/208,062 which was filed on May 31, 2000 and is incorporated by reference.

Technical Field The invention relates to membrane packets, methods for making membrane packets and membrane packet assemblies and, in particular, to packets, methods, and assemblies of porous membranes useful in processes such as filtration, adsorptive separation, affinity separation, ionic exchange separation and chromatography.

Background of the Invention

Many processes involve the use of porous membranes which are stacked on one another and sealed in a housing having an inlet and an outlet. For example, in filtration, a fluid (e.g., a gas, a liquid, or a mixture of gas and liquid) containing an undesirable substance (e.g., particulate matter) may be directed into the inlet of the housing and through the stack of porous membranes, which traps the particulate matter within the stack of porous membranes. The filtered fluid then exists the housing through the outlet. In adsorptive separation or affinity separation, a fluid containing a substance (e.g., a protein) may be directed into the inlet of the housing and through the stack of porous membranes, where the protein attaches to the porous membranes, either chemically and/or physically. The fluid then exists the housing through the outlet with none of, or a lower concentration of, the protein. Conventional stacks of porous membranes have several disadvantages.

For example, if the stack is configured as a stack of loose membranes not bound to one another, it is difficult to effectively seal the peripheral edge of the stack of membranes. Further, the user must manipulate this stack of loose membranes, which increases in difficulty as the number of porous membranes increases and as the size of the porous membranes decreases. This difficulty ' in handling loose membranes is exacerbated by static charges on the porous membranes which can cause the membranes to repel each other and fly apart and stick to the user's fingers. These disadvantages can be overcome by potting the peripheral edge of the stack of porous membranes, e.g., encasing the peripheral edge in a potting compound such as urethane. While this approach is effective, it is expensive, prohibitably expensive for small membrane packets which might be used, for example, for testing purposes. Alternatively, the edge of the stack of porous membranes can be potted with a molten thermoplastic or it can be heat sealed by applying heat and melting the face of the edge. However, many porous membranes are very sensitive to heat and can be damaged, e.g., denatured, by the application of a molten thermoplastic or the direct application of heat.

Summary of the Invention The invention overcomes many of the problems associated with conventional membrane packets, methods for making membrane packets, and membrane packet assemblies.

In accordance with one aspect of the invention, a membrane packet comprises a plurality of porous membranes. Each porous membrane has a first region and a second thinner region. The porous membranes are stacked with the first regions of the porous membranes being axially aligned and the second regions of the porous membranes being axially aligned. The second regions of the porous membranes are compressed and comprise a compression bond maintaining the stack of porous membranes as an integral unit. In accordance with another aspect of the invention, a method of making a membrane packet comprises stacking a plurality of porous membranes, including axially aligning first regions of the porous membranes and axially aligning second regions of the porous membranes. The method further comprises compressing the second regions of the porous membranes to form a compression bond which maintains the plurality of porous membrane as an integral unit.

In accordance with another aspect of the invention, a membrane packet comprises a plurality of porous membranes, each porous membrane having a first region and a second thinner region. The membrane packet further comprises one or more spacers. The porous membrane and the spacers are stacked with the first regions of the porous membranes being axially aligned and the spacers and the second regions of the porous membrane being axially aligned. The second regions of the porous membranes are compressed and the compressed second regions and the spacers comprise a compression bond maintaining the stack of porous membrane as an integral unit.

In accordance with another aspect of the invention, a method for making a membrane packet comprises stacking plurality of porous membranes and one or more spacers, including axially aligning first regions of the porous membranes and axially aligning the spacers and second regions of the porous membranes. The method further comprises compressing the second regions of the porous membranes and forming a compression bond which maintains the plurality of porous membranes as an integral unit.

Brief Description of the Drawings

Figure 1 is an oblique view of a membrane packet. Figure 2 is a cross-sectional view of the membrane packet of Figure 1. Figure 3 is a stack of porous membranes.

Figure 4 is a cross-sectional view of the stack of porous membranes of Figure 3.

Figure 5 is a cross-sectional view of a membrane packet and opposed dies.

Figure 5 a is a cross-sectional view of the swaging profile of a die. Figure 6 is a cross-sectional view of a membrane packet assembly. Figure 7 is a cross-sectional view of another membrane packet assembly.

Figure 8 is a cross-sectional view of a stack of porous membranes and porous spacers.

Figure 9 is a cross-sectional view of another membrane packet. Figure 10 is a cross-sectional view of a stack of porous membranes and solid spacers.

Figure 11 is a cross-sectional view of another membrane packet. Figure 12 is a cross-sectional view of another membrane packet. Figure 13 is a cross-sectional view of another membrane packet assembly.

Detailed Description of Embodiments

An example of a membrane packet 100 embodying the present invention is shown in Figures 1 and 2. The membrane packet 100 generally comprises a stack of porous membranes 101. A wide variety of porous membranes may be used with the invention. For example, the porous membrane may comprise a metallic material, such as stainless steel, a ceramic material, such as glass fiber, or a natural fiber material. In many preferred embodiments, the porous membrane comprises a polymeric material, such as polyethersulfone, polysulfone, polystyrene, polypropylene, polyamide (e.g., nylon), PVDF, PTFE, polyethylene, polyimide, cellulose, cellulose acetate, nitrocellulose, and regenerated cellulose. The porous membrane may also comprise a composite including, for example, a polymeric porous membrane and chromatography resins, ceramics, porous glass, silica, polymer beads, catalysts, and adsorbents such as activated carbon or carbon fibers, either deposited within the porous membrane or captured between porous membranes of the membrane packet. Each porous membrane preferably has the form of a porous sheet, e.g., either a single layer or multiplayer sheet, such as a porous metal sheet, a fibrous (including filamentous) nonwoven or woven sheet, or a porous supported or unsupported film. In many preferred embodiments, the porous membrane comprises a high voids volume, porous polymeric film. The porous membrane may have any suitable pore structure or pore rating, including a microporous pore rating in the range from about O.lμ to about 20μ, e.g., in the range from about O.lμ to about lOμ, preferably from about O.lμ to about 5μ more preferably from about 0.3μ to about 1.5μ, and even more preferably from about 0.4μ to about 0.9μ. Further, the porous membrane may naturally function as, or may be modified in any suitable manner to function as, a filter medium, an affinity membrane, an adsorptive membrane, an ionic exchange membrane, or a charged membrane and may be useful in a myriad of processes, including filtration and other separation processes, such as affinity separations, adsorptive separations, ionic exchange separations, charge-based separations, and chromatographic techniques. Examples of suitable porous membranes are disclosed in International Application No. PCT/USOO/04746, which designated the United States and is incorporated by reference.

The stack may include layers in addition to the porous membranes 101, e.g., drainage layers, support layers, bonding layers, and/or spacing layers. The additional layers may be co-extensive with the porous membranes or may extend along only a portion of the porous membranes. However, in many preferred embodiments, the stack is formed only of porous membranes 101 and no additional layers. In any of the embodiment, the porous membranes 101 may be identical to one another or they may differ from one another.

Each porous membrane 101 preferably includes a first region 102 and a second region 103. Each first region 102 may comprise the functional portion of the porous membrane 101, i.e., the portion of the porous membrane that is involved in the filtration or separation process. The first regions 102 are preferably axially aligned with one another in the stack.

The second regions 103 of the porous membranes 101 are also preferably axially aligned with one another in the stack. Each second region 103 preferably lies continuously along the periphery of the first region 102 but may lie discontinuously along the periphery of the first region or may be formed within the interior of the first region. Further, after compression each second region 103 is thinner than the first region 102, the second regions 103 being compressed to form a compression bond that maintains the stack of porous membranes 101 as an integral unit. The compressed second regions 103 are preferably substantially impermeable, i.e., the second regions 103 are substantially solidified or have permeability substantially less than the permeability of the first regions 102, for example, by a factor of about 10 or more, preferably about 100 or more. Consequently, the compressed second regions 103 of the porous membranes 101 may serve both to form the compression bond and to form a peripheral seal that prevents fluid from passing laterally outwardly from the first regions 102 of the porous membranes 101 of the membrane packet 100.

The membrane packet 100 may be made in a variety of ways. In a preferred embodiment, the plurality of porous membranes 101 may be stacked with the first regions 102 axially aligned and the second regions 103 axially aligned. One or more additional layers may be included in the stack, but in many preferred embodiments the stack preferably consists of only the porous membranes 101. The porous membranes 102 are then compressed or densified, preferably axially compressed, at the second regions 103 to form a compression bond that maintains the porous membranes 101 as an integral unit.

The porous membranes 101 may be laid over one another to form the stack, as shown in Figures 3 and 4. In several preferred embodiments, there are no additional layers and at least one side or both sides of each porous membrane 101 lie next to an immediately adjacent porous membrane 101. Alternatively, one or more additional layers may be interposed in the stack between each porous membrane or between regular or irregular groups of the porous membranes.

The stack of porous membranes may comprise a stack of large sheets and several membrane packets may be formed from the stack. Alternatively, the stack of porous membranes may comprise a stack of disks, rectangles, hexagons, or any other regular or irregular shape, and a single membrane packet may be formed from the stack. In any event, the number of porous membranes included in the stack may vary depending on such factors as the thickness, void volume, and elasticity of the porous membrane and the physical and/or chemical sensitivity of the porous membrane. For many preferred embodiments, the stack may have from about 2 to about 50 porous membranes, more preferably from about 2 to about 30, and even more preferably from about 3 to about 20, e.g., 10-20, porous membranes. The stack of porous membranes 101 may be rolled or otherwise pre- compressed slightly, for example, to eliminate any air pockets between the porous membranes 101. The stack of porous membranes 101 is then compressed or densified at the second regions to form the compression bond. For example, the stack may be axially compressed or densified by a die, such as a swaging die. Preferably, the stack of porous membranes 101 is axially compressed or densified at the second regions 103 between first and second opposed swaging dies 104, 105, as shown in Figure 5. The swaging dies 104, 105 are preferably identical, although they may differ, and each has a swaging profile 106, 107 which contacts the stack of porous membranes 101. The first and second dies 104, 105 are moved relatively toward one another, squeezing, crushing, and densifying the second regions 103 of the porous membranes 101 between the opposed swaging profiles 106, 107.

The movement of the dies 104, 105 may be halted, for example, at a predetermined distance separating the dies 104, 105 or at a predetermined pressure corresponding to the formation of a compression bond which maintains the stack of porous membranes 101 as an integral unit. While not being bound by any particular theory of operation, the compression bond may principally be a mechanical interlock at the surfaces of adjacent second regions 103 of the porous membranes 101. For example, as the second regions 103 are densified between the swaging profiles 106, 107, portions of adjacent second regions 103 may move or extrude into one another at the surfaces of the second regions 103, forming a mechanical interlock which holds the adjacent porous membranes 101 to one another. This compression bond is particularly effective after the porous membranes 101 have been compressed and before they are wetted by any fluid. The predetermined distance or pressure may also correspond to the collapse of the porous membrane, and/or any additional layer, to a. substantially solidified state, beyond which radial extrusion of the solidified material may occur to the possible detriment of the membrane packet.

The predetermined distance and/or pressure at which the relative movement of the dies 104, 105 is halted may also correspond to the formation of a seal at the periphery of the membrane packet 100. As the second regions 103 are crushed between the dies 104, 105, the second regions are preferably rendered substantially impermeable, i.e., the pore structure of each second region 103 is crushed to render the second region 103 substantially solidified or to render a permeability in the second region 103 which is substantially less than the permeability in the first region 102, for example, by a factor of about 10 or more, preferably about 100 or more. Because the second regions 103 are substantially impermeable and because the surfaces of adjacent layers of the second regions 103 are tightly pressed against one another or co-mingled, fluid passing through the first regions 102 of the membrane packet 101 is prevented from moving laterally outwardly from the first regions 102 through the second regions 103, effectively sealing the membrane packet 100. The compression parameters, such as the predetermined distance and pressure and the swaging profile of the die, may vary depending on such factors as the number of porous membranes, the thickness and void volume of the porous membranes, and the type of material forming the porous membranes, e.g., the base material of the porous membranes and/or the coating material on the porous membranes. For example, the predetermined distance or pressure may be arranged to provide a height at the second regions 103 of the membrane packet 100 on the order of the solids volume fraction (i.e., one minus the voids volume fraction) of the porous membrane 101 times the thickness of the porous membrane 101 times the number of porous membranes 101 in the membrane packet 100. At this height, the second regions 103 may provide both an effective compression bond and seal.

The swaging profiles are preferably configured to prevent the porous membranes 101 from breaking or weakening sufficiently to cause premature failure, especially at the interface or transitional region between the first regions 102 and the second regions 103. The swaging profile preferably has a shape or contour which minimizes stress concentrations at the interface between the first regions 102 and the second regions 103 as the porous membrane 101 are being crushed between the dies 104, 105. For example, as shown in Figure 5 a, the swaging profile may comprise a taper, a radius, and a flat. The taper (e.g., θ) preferably begins at the inner diameter and tapers to the radius which, in turn, curves to the flat which extends to the outer diameter. The degree of the taper and the size of the radius may vary depending on the factors previously described. The swaging profile, especially the radius, may be a smooth, polished surface to reduce abrasion of the porous membranes. Further, while the dies 104, 105 shown in Figure 5 are hollow, they may alternatively be solid and contoured to support the first regions 102 as well as the second regions 103 during swaging. The compression parameters may be determined empirically for any given stack of porous membranes in accordance with a desired compression bond and a desired seal.

For many preferred embodiments, the compression bond is the sole bond maintaining the membrane packet 100 as an integral unit. The compression bond is formed quickly, uniformly, and inexpensively, holds effectively, and avoids the introduction of extraneous materials that may leech into any fluids directed through the membrane packet 100. However, a variety of supplemental bonds may be applied to the membrane packet 100, for example, at the second regions 103. For example, a thermal bond may be applied to the second regions 103 during or after compression of the second regions 103. Heat may be applied to form a supplemental thermal bond and/or to relax the porous membranes 101 at the interface between the first regions

102 and the second 103 during compression. The heat may be introduced in a variety of ways, for example, by heating the dies, by radiant heating, by sonic heating, or as a weld. Other supplemental bonds include an adhesive bond, e.g., by providing an adhesive layer between one or more of the second regions 103 of the porous membranes 101, and solvent bond, e.g., by introducing and removing a solvent in the second regions 103 which bonds adj acent porous membranes 101.

Once bonded, the stack of porous membranes may be cut to form the final shape of the membrane packet 100. Cutting may involve merely trimming the peripheral edges of the membrane packet or it may involve stamping one or more membrane packets from a stack of large membrane sheets. The membrane packets may be stamped in any of the previously described shapes, including circular or rectangular. In some embodiments, a punch may be employed with the swaging dies 104, 105 shown in Figure 5. In a preferred embodiment, the punch may cut the compressed second regions

103 of the membrane packet 100 along the outer diameter of the swaging dies 104, 105. The punch may be part of the swaging dies or may be a second stage of the swaging tooling.

Example

Sixteen layers of a generally circular, porous polyethersulfone film identifiable by the trade designation SUPOR of Pall Corporation were stacked one on another. Each porous film had a generally uniform thickness of about 0.005 inch. The sixteen layers were swaged between opposed identical swaging dies. Each swaging die was hollow and had an inner diameter at the swaging profile of about 14 mm and an outer diameter of about 18 mm. The swaging profile tapers at about 30° from vertical from the inner diameter to a radius of about 1 mm that curves to a flat that extends to the outer diameter of the die.

The peripheral region of the stack of porous films was compressed between the swaging dies to collapse the peripheral region to a height of about 0.020 inch. No external heat, adhesive, or solvent was applied during or after the swaging process. The swaging dies were then separated and the membrane packet was removed from the dies.

The first regions of the membrane packet had a diameter of about 14 mm and an unrestrained thickness of about 0.10 inch due to some pillowing of the porous membranes in the first regions. The second regions of the membrane packet comprise a peripheral band around the first regions having a width of about 2 mm and a thickness of about 0.020 inch. The compressed second regions of the membrane formed a compression bond which held the porous films of the membrane packet as an integral unit and an effective seal at the peripheral edge of the membrane packet.

Membrane packets embodying the invention may be used in a wide variety of housings. For example, the membrane packets are particular useful in reusable housings for conducting tests, e.g., tests to assess one or more characteristics of the porous membranes, including performance capabilities such as porosity rating and clean flow versus pressure drop, retention capabilities such as bacterial or viral retention, filtration capacity such as particulate capture versus fouling rate, and separation capability and efficiency such as substance contents upstream versus downstream. The test results may be used to predict performance of the larger production scale membranes systems.

One example of a membrane packet assembly 120 is shown in Figure 6. The membrane packet assembly 120 preferably comprises a reusable housing apparatus 121 having an inlet 122 and an outlet 123. The housing apparatus 121 may comprise first and second removable sections, e.g., an inlet section 124 and an outlet section 125, and the membrane packet 100 may be disposed between the removable sections 124, 125 in the fluid flow path defined by the housing apparatus 121 between the inlet 122 and the outlet 123. The membrane packet assembly 120 may further include a porous support 126 disposed in the housing apparatus 121 downstream of the membrane packet 100. The membrane support 126 is operatively associated with the membrane packet 100 to react pressure drop loads through the membrane packet 100. Consequently, the porous support 126 may comprise a wide variety of porous materials, such as a porous metal or polymeric mesh, which have sufficient structural integrity to support the membrane packet 100. The membrane support 126 is preferably much more permeable than the porous membranes of the membrane packet 100, providing a much smaller resistance to flow through the membrane packet assembly 120 than the membrane packet 100. Alternatively or additionally, the membrane packet assembly may include a support, such as a channeled structure or a grid structure, which is separate from or, preferably, integral with the housing apparatus and which supports the downstream side of the membrane packet. The membrane packet assembly 120 further includes a sealing mechanism to prevent fluid from bypassing the membrane packet 100. For example, where the membrane packet 100 is formed of relatively high temperature polymeric porous membranes, which tend to be relatively brittle due to the compression caused by swaging, the sealing mechanism may comprise a resilient seal 127, such as an o-ring. The o-ring may be disposed between the compressed second regions 103 of the membrane packet 100 and the housing apparatus 121, for example, between the second regions 103 and the inlet section 124, e.g., in a manner which prevents bypass around the membrane packet 100 and leakage from between the housing sections 124, 125. For membrane packets comprising relatively low temperature thermoplastic porous membranes, which remain relatively deformable after swaging, the sealing mechanism may comprise a knife edge or crushing edge associated with one or both of the inlet section 124 and the outlet section 125 of the housing apparatus 121. The knife-edge or crushing edge may be embedded in the second regions 103 of the membrane packet 100 to effect the seal against bypass of the membrane packet 100 or leakage from the housing apparatus 121.

The membrane packet assembly 121 shown in Figure 6 is particular useful for conducting tests, e.g., for assessing the membrane packet 100. For example, a first membrane packet 100 having a first type of porous membrane may be inserted in the housing apparatus 121 and sealed within the housing apparatus 121 by the resilient seal 127. A fluid may then be directed through the housing apparatus 121, i.e., into the inlet 122, through the membrane packet 100 and the porous support 126, and out the outlet 123. The flow of fluid may then be interrupted and the first membrane packet 100 may be removed. The porous membranes of the first membrane packet 100 may then be analyzed and/or the influent and effluent fluids may be analyzed for differential characteristics. A second membrane packet 100 having a different type of porous membrane may then be installed in the housing apparatus 121 and sealed in the housing apparatus 121 by the resilient seal 127. The flow of fluid may then be re-established through the housing apparatus 121, i.e., into the inlet 122, through the second membrane packet 100 and the porous support 126, and out the outlet 123. The flow of fluid may then be again interrupted and the second membrane packet 100 may be removed from the reusable housing apparatus 121. The porous membranes of the second membrane packet 100 may then be analyzed and/or the influent and effluent fluids may be analyzed for differential characteristics. The results of the analysis may determine which of the porous membranes of the membrane packets provide the best performance.

While a membrane packet assembly comprising a reusable housing apparatus has many advantages, the invention is not limited to a reusable housing apparatus. A wide variety of housing apparatuses are suitable, including a housing apparatus that is completely molded in place around the membrane packet, for example, an injection molded thermoplastic housing. This membrane packet assembly may be particularly useful as a disposable, single use membrane packet assembly.

While the membrane packets illustrated in the previous figures principally comprise porous membranes, the invention is not limited to these membrane packets. Further examples of membrane packets 200, 300 are shown in Figures 7 and 9. In each example, the membrane packet 200, 300 comprises a plurality of porous membranes 201, 301 which are stacked over one another with the first regions 202, 302 of the porous membranes 201, 301 axially aligned and the second regions 202, 303 of the porous membrane 201, 301 axially aligned. Each porous membrane 201, 301 may be similar or identical to any of the porous membranes previously described. However, the membrane packet 200, 200 includes layers in addition to the porous membranes 201, 301. For example, each membrane packet 200, 300 further includes spacer layers 209, 309.

For a membrane packet including only or mostly porous membranes ^• such as porous films, the preferred height of the second regions after compression may be on the order of the porous membrane solid volume fraction (e.g., as a percentage) times the original pre-compressed stack height. Further, the ability of the porous membrane to form a compression bond is affected by factors such as the degree of mechanical interlocking of adjacent porous membranes and the surface porosity or roughness of the porous membranes. Consequently, the difference between the height of the membrane packet at the second regions and the height of the membrane packet at first regions increases with an increasing number of porous membranes in the stack. The greater is this difference in heights, the more the porous membranes must elongate in the interface between the first regions and the second regions, i.e., at the swaging profile. Consequently, the number of porous membranes in the stack may be determined by the ability of the porous membrane to conform to the swaging profile without being damaged, e.g., broken or weakened sufficiently to cause premature failure.

In the embodiment shown in Figures 7-10, spacers 209, 309 are interposed between the porous membranes 201, 301, allowing the number of porous membranes 201, 301 in the membrane packet 200, 300 to be greatly increased without forming an elongated swaging profile at the interface between the first regions 202, 302 and the second regions 203, 303.

As shown in Figure 8, porous spacers 209 are interposed between each of the porous membranes 201. Alternatively, the porous spacers may be disposed between regular or irregular groups of porous membranes. Further, as shown in Figure 8, the porous spacers 209 are preferably not coextensive with the porous membranes 201. Rather, the porous spacers 209 preferably extend only along the second regions 203 of the porous membranes 201. The thickness and distribution of porous spacers 209 in the stack depends, for example, on the solids volume of the porous spacers 209 and the solids volume of the porous membrane 201. Preferably, the porous spacers 209 are distributed within the stack such that after compression between the dies, the height of the membrane packet 200 at the second regions 203 is similar to the height of the membrane packet 200 at the first regions 201 and none of the porous membranes 201 are unduly elongated at the interface between the first regions 202 and the second regions 203. Further, the porous spacers 209, as well as the second regions 203 of the porous membranes 201, are densified sufficiently to be substantially impenneable. As the solid volume of the spacer layer increases, the height of the precompressed spacer layer may be decreased to offset the reduced height reduction during compression. As the solid volume percentage approaches 100%, the spacer 309 may comprise a solid material as shown in Figures 9 and 10. Again, the solid spacers 309 preferably extend only along the second regions 303 of the porous membranes 301. Further, the number and distribution of solid spacers 309 is arranged to provide a membrane packet 300 having a height at the second regions 303 of the porous membrane 301 similar to the height at the first regions 302 and none of the porous membranes 301 are unduly elongated at the interface between the first regions 302 and the second regions 303. The solid spacer layers 309 preferably have a sufficient surface roughness to ensure an adequate compression bond when the stack is compressed between the swaging dies. A supplemental thermal, adhesive, or a solvent bond may be provided, for example, between one or both surfaces of each solid spacer layer 309 and the adjacent second region 303 of the porous medium 301.

The membrane packets 200, 300 may be made in a variety of ways, including those previously described with respect to the membrane packet 100 shown in Figures 1 and 2. For example, a plurality of porous membranes 201, 301 and spacers 209, 309 may be stacked with the first regions 202, 302 axially aligned and the second regions 203, 303 and the spacers 209, 309 axially aligned. One or more additional layers may be included in the stack, but in many preferred embodiments the stack preferably consists of only the porous membranes 201, 301 and the spacers 209, 309. The stack is then compressed or densified, preferably axially compressed, at the second regions 203, 303 to form a compression bond which maintains the plurality of porous membranes 201, 301 and spacers 209, 309 as an integral unit. The stack may also be compressed or densified at the second regions 203, 303 to effect a seal at the outer periphery of the membrane packets 200, 300. For example, the stack of porous membranes 201, 301 and spacers 209,

309 may be axially compressed or densified by a die or, preferably, between a pair of opposed dies similar to the dies 104, 105 shown in Figure 5. The compression parameters, including the predetermined distance and pressure and the swaging profile of the dies, may be determined according to the factors previously described and additionally the thickness, voids volume, and material of the spacers 209, 309. Further, the inner edge of the porous spacer 209 and, especially, the solid spacer 309 may be contoured to complement the swaging profile of the dies and to prevent the porous membranes 201, 301 from breaking or weakening at the interface or transition region between the first regions 202, 302 and the second regions 203, 303. Further, providing a contour at the inner edge of the spacers 209, 309 minimizes or eliminates any voids or gaps which may form, e.g., in the interface or transition region, between the porous membranes 201, 301 and spacers 209, 309 after compression. The contour at the inner edge of the spacers 209, 309 may vary. However, in many preferred embodiments the contour comprises a rounded or bullet-shaped configuration, as shown, for example, in Figures 9 and 10.

For many preferred embodiments, the compression bond is the sole bond maintaining the membrane packet 200, 300 as an integral unit. However, a variety of supplemental bonds, including thermal, adhesive, and solvent bonds, may be applied as previously described. For example, one or more supplemental bonds maybe applied between the second regions 203, 303 of the porous membranes 201, 301 and the spacers 209, 309.

Once bonded, the stack of porous membranes 201, 301 and spacers 209, 309 may be cut to form the final shape of the membrane packet 200, 300. For example, as previously described, the membrane packets may be trimmed, punched, or stamped.

While the invention has been described and illustrated with reference to several embodiments, the invention is not limited to these embodiments. Many variations and/or modifications would be obvious to those of ordinary skill in the art in light of the foregoing teachings. For example, a membrane packet may comprise a plurality of porous layers. Some of these porous layers may include both compressed or densified regions and uncompressed regions while others may include uncompressed regions but not any compressed or densified regions. The membrane packet may consists only of porous membranes or may comprise porous membranes and additional layers such as drainage layers, bonding layers, or spacer layers. The plurality of porous layers is stacked with the uncompressed regions axially aligned and the compressed regions axially aligned, the compressed regions forming a compression bond which maintains the membrane packet as an integral unit. One example of a membrane packet 400 having a plurality of porous layers is shown in Figure 11. The outer porous layers 401a, 401b preferably include both uncompressed regions 402 and compressed regions 403. The inner porous layers 401c preferably comprise only uncompressed regions 402. The inner porous layers 401 c preferably consist only of porous membranes but may, alternatively, comprise porous membranes and additional layers. The outer porous layers 401a, 401b may comprise porous membranes or may comprise porous cover layers which do not function as porous membranes. The membrane packet 400 may be made in a manner analogous to those previously described. For example, the porous layers 401a, 401b, 401c may be stacked with the uncompressed regions 402 axially aligned and the regions to be compressed 403, e.g., the lateral regions, axially aligned. The stack may then be compressed, for example, between opposed dies similar to those shown in Figure 5. The lateral regions 403 of the outer porous layers 401a, 401b are then compressed to form the compression bond and, preferably, to effect a seal in the compressed regions 403 and in the interface or transition region between the uncompressed regions 402 and the compressed regions 403 that prevents bypass of the uncompressed regions 402. While in the illustrated embodiment only the outer porous layers 401a, 401b include regions 403 to be compressed, the invention is not limited to this embodiment. For example, one or more of the inner porous layers may include lateral regions that are axially aligned and compressed with the lateral regions 403 of the outer porous layers 401a, 401b to form the compression bond. The compression bond may be the sole bond maintaining packet as an integral unit or supplemental bonds, such as thermal, adhesive, or solvent bonds, may be provided.

Many of the previous embodiments comprise a plurality of porous membranes. Commercially available porous membranes are usually thin because the parameters of thin membranes, e.g., uniformity of thickness and pore structure, are more easily controlled. Further, thin membranes are more easily and effective modified, e.g., coated or otherwise surface modified. However, the invention is not limited to a membrane packet comprising a plurality of porous membranes, such as a plurality of thin porous membranes. For example, a membrane packet embodying the present invention may consist of a single thick porous membrane or two or more thick porous membranes. In one embodiment, shown in Figure 12, a single porous membrane 501 comprising a thick fibrous depth filter medium, such as an HDC medium, may be made into a membrane packet 500. The porous membrane 501 has a thickness of about 1/16 inch or more and may be modified, e.g., surface modified, in a variety of ways as previously disclosed. The porous membrane 501 of the membrane packet 500 includes an uncompressed region 502 and a compressed region 503 which preferably extends around the periphery of the uncompressed region 502. The compressed region 503, which may be compressed in a manner analogous to any of those previously described, preferably is substantially impermeable and effects a seal preventing bypass or lateral leakage from the uncompressed region 502.

Modifications and variations of the membrane packet assembly would also be apparent to those of ordinary skill in the art in light of the foregoing teachings. For example, as shown in Figure 13, a membrane packet assembly 600 embodying the invention may include a housing apparatus 601 having an inlet 602 and an outlet 603 and a plurality of membrane packets 604 stacked within the housing apparatus 601 in the flow path between the inlet 602 and the outlet 603 in any suitable manner. For example, the housing apparatus 601 may comprise two reusable sections, an inlet section 610 and an outlet section 611, and several membrane packets 604 may be stacked within the bousing apparatus 601, for example, directly upon one another. A membrane porous support 612 may be disposed between the stack of membrane packets 604 and the outlet 603. A membrane support may also be disposed between one or more adjacent membrane packets. The membrane packet assembly 600 further includes a seal mechanism, such as a plurality of o-ring seals 613 disposed between the compressed regions 614 of the membrane packets 604 and the housing apparatus 601, to prevent bypass around the membrane packets 604 and leakage from the housing apparatus 601. The membrane packet assembly functions in manner similar to that previously described with regard to the membrane packet assembly 120 shown in Figure 6. However, the number of porous membranes and membrane packets may be greatly increased. Each porous membrane, or each membrane packet, may be identical to one another or they may differ from one another.

Claims

1. A membrane packet comprising a plurality of porous membranes, each porous membrane having a first region and a second thinner region, wherein the plurality of porous membranes are stacked, the first regions of the porous membrane being axially aligned and the second regions of the porous membranes being axially aligned, and wherein the second regions of the porous membranes are compressed and comprise a compression bond maintaining the stack of porous membranes as an integral unit.

2. The membrane packet of claim 1 wherein the stack of porous membranes comprises from about 2 to about 30 porous membranes.

3. The membrane packet of any preceding claim wherein one or more of the porous membranes comprise a porous polymeric film.

4. The membrane packet of any preceding claim wherein one or more of the porous membranes comprise an adsorptive, affinity, ionic exchange or chromatographic membrane.

5. The membrane packet of any preceding claim wherein the second region of each porous membrane comprises a peripheral region.

6. The membrane packet of any preceding claim wherein each porous < membrane is generally circular.

7. The membrane packet of any preceding claim wherein the stack of porous membranes includes first and second adjacent porous membranes, the second region of the first porous membrane being compression bonded to the second region of the second porous membrane.

8. The membrane packet of any preceding claim wherein the stack consists only of the plurality of the porous membranes.

9. The membrane packet of any of claims 1-7 further comprising one or more layers interposed with the plurality of porous membranes.

10. The membrane packet of any preceding claim wherein the compression bond is the sole bond maintaining the stack of porous membranes as an integral unit.

11. The membrane packet of any of claims 1-9 further comprising a thermal, adhesive, or solvent bond supplementing the compression bond.

12. A membrane packet assembly comprising: a housing apparatus having an inlet and an outlet and a membrane packet as claimed in any preceding claim cooperatively arranged with the housing apparatus between the inlet and the outlet.

13. The membrane packet assembly of claim 12 further comprising a support disposed downstream of the membrane packet and arranged to support the membrane packet within the housing apparatus.

14. The membrane packet assembly of claim 12 or 13 further comprising a sealing mechanism operatively associated with the housing apparatus and the membrane packet.

15. A method of using a membrane packet comprising: directing a flow of fluid through a reusable housing apparatus having an inlet and an outlet, including directing the fluid through a first membrane packet as claimed in any of claims 1-11; interrupting the fluid flow; replacing the first membrane packet with a second membrane packet; and re-establishing the fluid flow through the second membrane packet.

16. A method of making a membrane packet comprising: stacking a plurality of porous membranes, including axially aligning first regions of the porous membranes and axially aligning second regions of the porous membranes; and compressing the second regions of the porous membranes to form a compression bond which maintains the plurality of porous membranes as an integral unit.

17. The method of claim 16 wherein stacking a plurality of porous membranes comprises stacking from about 2 to about 30 porous membranes.

18. The method of claim 16 or 17 wherein stacking the porous membranes comprises stacking one or more adsorptive, affinity, ionic exchange or chromatographic membranes.

19. The method of any of claims 16-18 wherein compressing the second regions of the porous membranes comprises compressing regions peripheral to the first regions of the porous membranes.

20. The method of any of claims 1649 wherein compressing the second regions of the porous membranes includes compression bonding the second region of a first porous membrane and the second region of a second adjacent porous membrane.

21. The method of any of claims 16-20 wherein stacking a plurality of porous membranes consists of stacking only porous membranes on one another.

22. The method of any of claims 16-20 wherein stacking the porous membranes comprises stacking one or more layers with the plurality of porous membranes.

23. The method of any of claims 16-22 wherein compressing the second regions of the porous membranes comprises swaging the second regions with at least one die.

24. The method of claim 23 wherein swaging the second regions of the porous membrane comprises swaging the second regions of the porous membranes between first and second opposing dies.

25. The method of any of claims 16-24 further comprising cutting the plurality of porous membranes .

26. The method of claim 25 wherein cutting the porous membrane comprises punching the integral unit from a die.

27. The method of any of claims 16-26 wherein compressing the second regions of the porous membranes to form a compression bond comprises forming a compression bond as the sole bond which maintains the stack of porous membranes as an integral unit.

28. The method of any of claims 16-26 further comprising forming a thermal, adhesive or solvent bond operatively associated with the second regions of the porous membranes to supplement the compression bond.

29. A membrane packet comprising a plurality of porous membranes, each porous membrane having a first region and a second thinner region, and one or more spacers, wherein the porous membranes and the spacers are stacked, the first regions of the porous membranes being axially aligned and the spacers in the second regions of the porous membranes being axially aligned, and wherein the second regions of the porous membranes are compressed and comprise a compression bond maintaining the stack of porous membranes and spacers as an integral unit.

30. The membrane packet of claim 29 wherein the spacer comprises a porous spacer.

31. The membrane packet of claim 29 wherein the spacer comprises a solid spacer.

32. A method of making a membrane packet comprising: stacking a plurality of porous membranes and one or more spacers, including axially aligning first regions of the porous membranes and axially aligning the spacers and second regions of the porous membranes; and compressing the second regions of the porous membranes to form a compression bond which maintains the plurality of porous membranes and spacers as an integral unit.

33. A membrane packet comprising any one or more of the novel features disclosed in the specification and/or drawings or comprising any patentable combination of the features disclosed in the specification and/or drawings.

34. A method of making a membrane packet comprising any one or more of the novel features disclosed in the specification and/or drawings or comprising any patentable combination of features disclosed in the specification and/or drawings.