WO2006044712A1

WO2006044712A1 - Separation elements and methods of making separation elements

Info

Publication number: WO2006044712A1
Application number: PCT/US2005/037105
Authority: WO
Inventors: Thomas Fendya; Mark Hurwitz; Carolyn Shapiro; Robert Spearing
Original assignee: Pall Corporation
Priority date: 2004-10-14
Filing date: 2005-10-14
Publication date: 2006-04-27

Abstract

Separation elements (10) and methods for making separation elements include permeable polymeric membranes (12) which are thermally bonded to polymeric structural members (14). The separation elements (10) may be used to purify, segregate, and/or concentrate a variety of fluids and/or fluid components.

Description

SEPARATION ELEMENTS AND METHODS OF MAKING SEPARATION

ELEMENTS

This application claims the benefits of priority based on United States Provisional Application no. 60/618,145 which was filed on October 14, 2004, and is incorporated by reference.

DISCLOSURE OF THE INVENTION

The present invention relates to separation elements and methods of making separation elements and in particular to separation elements including permeable membranes thermally bonded to mesh layers. The separation elements may be used to purify, segregate, and/or concentrate a variety of fluids and/or fluid components.

In accordance with one aspect of the invention, a separation element comprises a mesh layer and a permeable polymeric membrane. The mesh layer includes no more than one polymeric component which has a softening temperature and an active region which has a plurality of bonding sites.. The permeable polymeric, membrane has a pore structure which permits fluid to flow through the membrane. The permeable polymeric membrane also has a softening temperature which is higher than the softening temperature of the polymeric component of the mesh layer. The permeable polymeric membrane is thermally bonded to the mesh layer at the bonding sites, the single polymeric component at the bonding sites being resolidified in contact with the permeable polymeric membrane without substantially collapsing the pore structure of the permeable polymeric membrane in the active region.

In accordance with another aspect of the invention, a method of making a separation element comprises registering a permeable polymeric membrane and a mesh layer which includes a single polymeric component. The permeable polymeric membrane has a pore structure which permits fluid to flow through the membrane and overlies an active region of the mesh layer which has a plurality of bonding sites. The method also comprises heating the bonding sites of the mesh layer to a temperature.at . or above the softening temperature of the mesh layer, including at least softening the single polymeric component at the bonding sites. The method further comprises applying pressure to the permeable polymeric membrane and the mesh layer in the vicinity of the bonding sites to thermally bond the permeable polymeric membrane to the mesh layer, including resolidifying the single polymeric component at the bonding sites in contact with the permeable polymeric membrane without substantially collapsing the pore structure of the permeable polymeric membrane in the active region. In accordance with another aspect of the invention, a separation element comprises a mesh layer and a permeable polymeric membrane. The mesh layer includes two or more polymeric components and a first one of the polymeric components has a softening temperature greater than or equal to the softening temperatures of all other components. The mesh layer also includes an active region which has a plurality of bonding sites. The permeable polymeric membrane has a pore structure which permits fluid to flow through the membrane and a softening temperature which is higher than the softening temperature of the first polymeric component of the mesh layer. The permeable polymeric membrane is thermally bonded to the mesh layer at the bonding sites, the polymeric components at the bonding sites being resolidified in contact with the permeable polymeric membrane without substantially collapsing the pore structure of the membrane in the active region.

In accordance with another aspect of the invention, a method of making a separation element comprises registering a permeable polymeric membrane and a mesh layer which includes two or more polymeric components. The permeable polymeric membrane has a pore structure which permits fluid to flow through the membrane and overlies an active region of the mesh layer which has a plurality of bonding sites. The method also comprises heating the bonding sites of the mesh layer to a temperature at or above the highest softening temperature of all polymeric components in the mesh layer, including at least softening the polymeric components at the bonding sites. The method further comprises applying pressure to the permeable polymeric membrane and the mesh layer in the vicinity of the bonding sites to thermally bond the permeable membrane to the mesh layer, including resolidifying the polymeric components at the bonding sites in contact with the permeable polymeric membrane without substantially collapsing the pore structure of the membrane in the active region.

Separation elements and methods of making separation elements embodying the present invention offer many advantages. For example, the permeable polymeric membranes are securely bonded to the mesh layers, enabling them to withstand forces that would otherwise tear them apart, e.g., forces encountered during cross-flow fluid treatment and backwashing processes. The bonding sites of the mesh layer are exposed to a heat source that is hotter than the softening temperature of the sole polymeric component of the mesh layer or than the highest softening temperature of the plurality of polymeric components of the mesh layer. Consequently, all or substantially all of the bonding sites may become at least soft and may even be capable of flowing. Thus, a large number of the bonding sites can participate in bonding the permeable polymeric membrane to the mesh layer once they contact the permeable membrane. This results in a highly secure bond. Yet the thermal bond, while secure, does not result in a substantial collapse of the pore structure of the membrane, which allows the membrane to remain highly permeable even after it is thermally bonded to the mesh layer. Further, separation elements and methods embodying the invention avoid the introduction of contaminants into the fluid streams passing through them. For example, there are no bonding agents, such as adhesives or solvents, which may leach contaminants into the fluid streams.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is an exploded end view of a separation element. Figure 2 is a cross-sectional view of the thermally bonded separation element of Figure 1. - - -

Figure 3 is an exploded end view of another separation element. Figure 4 is a cross-sectional view of a separation module.

DESCRIPTION OF EMBODIMENTS

While many different separation elements may embody the invention, in one example, illustrated in Figure 1, a separation element 10 comprises at least one permeable polymeric membrane 12, e.g., first and second permeable polymeric membranes 12, thermally bonded to a mesh layer 14. The permeable polymeric membranes 12 may be thermally bonded to the mesh layer 14 at a plurality of bonding sites 16 in an active region 18 of the mesh layer 14. Bonding sites may include points or regions of contact between the mesh layer 14 and the permeable polymeric membranes 12. Fluid to be treated by the separation element 10 may be directed through the permeable membranes 12 toward the mesh layer 14, with permeate being received by the mesh layer 14. Alternatively, fluid to be treated by the separation element 10 may be directed along the mesh layer 14 with permeate passing through the permeable membranes 12 away from the mesh layer 14. The active region 18 of the mesh layer 14 may comprise a region which receives permeate from the permeable membranes 12 or which directs fluid to be treated through the permeable membranes 12. The active region 18 comprises many or all of the bonding sites 16.

While the mesh layer 14 may comprise a variety of materials, for many embodiments, the mesh layer 14 includes no more than one principal polymeric component. The sole polymeric component of the mesh layer 14 has a softening temperature, and the permeable polymeric membranes 12 have softening temperatures which are higher than the softening temperature of the sole polymeric component of the mesh layer 14. The softening temperature may be described as the temperature sufficient to at least partially soften a polymer so that the polymer can plastically deform or viscously flow. The difference between the softening temperatures of the mesh layer 14 and the permeable membranes 12 is preferably enough to facilitate exposing both the mesh layer 14 and the membranes 12 to a heat source and softening the mesh layer 14 without softening the membranes 12. For example, for some embodiments, there may be a difference of up to about 10°C or more between the softening temperatures of the permeable membranes 12 and the mesh layer 14. Exemplary polymeric components for the mesh layer include, but are not limited to, polypropylene, polyester, polystyrene, polycarbonate, polyethylene, polysulfone, polyethersulfone, polyimide, polyetherimide polyamide, polyvinylchloride (PVC), polyvinylidene fluoride (PVDF), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), poly-ether-ether ketone (PEEK), polyacrylonitrile (PAN), and polytetrafluoroethylene (PTFE). The mesh layer may also include other secondary components, including, for example, one or more additives or fillers, such as fiberglass. A preferred mesh layer, in some embodiments, may comprise a polypropylene mesh.

In the illustrated embodiment, the mesh layer 14 may comprise an extruded mesh including a first set of parallel strands 20 in one plane fixed atop a second set of parallel strands 22 in another plane. The first set of strands 20 may extend at any suitable angle, e.g., 90°, to the second set of strands 22. The strands in a set may be spaced any suitable distance from one another, e.g., may have any desired strand count, and may have any suitable diameter. A wide variety of other meshes may be used, including woven meshes and expanded meshes.

The permeable polymeric membranes may comprise any of numerous separation media, and the first and second membranes may be identical or different. In many embodiments, the first and second permeable membranes are identical. The permeable membranes may have any pore structure which permits fluid to flow through the membrane. The pore structure may be any arrangement of pores, passages or other openings which extend through the membrane or interconnect with one another within the membrane to permit fluid flow between opposite surfaces of the membrane and which effect the separation of one or more components from the. . fluid. The pore structure may be defined by a variety of removal ratings. Membranes may include microporous membranes (e.g., membranes generally having removal ratings of from about 0.1 μm to about 100 μm or more), ultrafiltration membranes (e.g., membranes generally having removal ratings of less than about 0.1 μm), nanofiltration membranes (e.g., membranes generally having removal ratings of from about 10 A to about 100 A), and reverse osmosis membranes (e.g., membranes generally having removal ratings of less than about 10 A). Exemplary separation media include porous, permeable or semipermeable polymeric films or woven or non- woven sheets of polymeric fibers. For many embodiments, the permeable membranes may comprise a porous or permeable polymeric film.

The membranes may be prepared from a variety of polymeric materials including any of the polymeric materials identified above with respect to the mesh layer, as well as cellulose and/or cellulose derivatives, and may be formed in any of numerous processes, including any casting, extruding, expanding, weaving, fiber lay- down or fiber weaving process. The permeable membranes may comprise one or more polymeric components forming the structural matrix of the membrane, and may include additional non-polymeric components as well. Further, the membranes may be treated in any of numerous ways to impart one or more of various characteristics to the membranes. For example, the membranes may be surface treated to affect the wettability of the membrane or to affect the capture characteristics of the membrane.

The permeable polymeric membranes may comprise an unsupported or a supported membrane. An unsupported membrane may include a separation region which has the pore structure of the membrane. A supported membrane may include a separation region and a support region on and/or within which the separation region may be supported. The separation region and support region of the membrane may comprise identical or different materials. The separation region may include the pore structure of the membrane and the support region may comprise a fibrous woven or nonwoven web. In embodiments including an unsupported membrane or a supported membrane, the mesh layer may be thermally bonded to the separation region, e.g., to the surface of or within the pore structure. For many embodiments, all of the polymeric components forming the structural matrix of the membrane, i.e. the separation region, may have softening temperatures which are higher than the softening temperature of the sole polymeric component of the mesh layer.

Consequently, the sole polymeric component of the mesh layer may be softened without softening the separation region of the permeable polymeric membrane. Since the separation region of the permeable membrane is not softened, the thermally bonded membrane may not include any resolidified polymeric components from the separation region. The softening temperature of the polymeric component(s) of the support region of the membrane may be greater than, equal to or even less than the softening temperature of the polymeric components of the separation region.

Many different permeable polymeric membranes and polymeric mesh layers may be paired with one another to allow softening the polymeric component of the mesh layer without softening the permeable membrane. Examples of some of the more preferred pairs include:

1) a cast, supported polyethersulfone membrane (polypropylene nonwoven support) and a polypropylene mesh layer;

2) a cast, unsupported polyvinylidene fluoride membrane and a polypropylene mesh layer;

3) a cast, unsupported polyethersulfone membrane and a polysulfone mesh layer.

The permeable polymeric membranes 12 are thermally bonded to the bonding sites 16 in the active region 18 of the mesh layer 14. The bonding sites may be configured in a variety of ways. For example, the bonding sites may comprise a plurality of discrete points or areas along one or both surfaces of the mesh layer. In the illustrated embodiment, the bonding sites 16 may comprise long, thin regions extending along the outer surfaces of each set of strands 20, 22. However, in some embodiments, the bonding sites may extend for less than the entire length of the strands, e.g., the bonding sites may comprise discrete points or areas spaced along the length of the strands.

As best seen in Figure 2, one permeable polymeric membrane 12 may be thermally bonded to the bonding sites 16 along the first set of parallel strands 20 of a mesh layer 14 and the other permeable membrane 12 may be thermally bonded to the bonding sites 16 along the second set of parallel strands 22 of the mesh layer 14. The polymeric component of the mesh layer 14 at the bonding sites 16 is resolidified in contact with the permeable membranes 12, e.g., at an interface region 24 between the separation region of the permeable membrane 12 and each bonding site 16, to thermally bond the permeable polymeric membrane 12, i.e., the separation region, to the mesh layer 14. The interface region 24 may comprise a mass of resolidified polymeric material, e.g., from the bonding site 16, in contact with a surface 25 of the permeable membrane 12, e.g., the surface of the separation region and the pore structure, and/or the interface region 24 may comprise a mass of resolidified polymeric material extending into the separation region of the membrane 12 beyond the surface 25, e.g., into the interstices of the membrane 12 slightly beyond the surface 25. For example, softened polymeric material from the bonding site may move through any support region of the permeable membrane, into contact with the surface and/or the interstices of the separation region and the pore structure and resolidify. In some embodiments, the interface region 24 may include some resolidified polymeric material from other than the bonding site, e.g., from the support region of the permeable membrane. However, the interface region 24 preferably does not include any resolidified polymeric membrane matrix material, e.g., from the separation region of the permeable membrane. Although the polymeric component at the bonding sites 16 is resolidified in contact with the permeable membrane, the pore structure of the permeable membrane may be occluded only at the interface region 24. In most embodiments, the pore structure of the permeable membrane 12 in the region 26 beyond the interface region 24, i.e. between the interface region 24 and the opposite surface of the membrane 12, is neither occluded nor collapsed. In some embodiments, the pore structure of the permeable membrane 12 in the region 26 above the interface region 24 may be modified, e.g., slightly compressed, but the region 26 remains largely permeable. Thus, the thermally bonded permeable polymeric membranes 12 remain highly permeable in the active region 18. For example, as illustrated by the arrows indicating flow in Figure 2, fluid may flow freely through the membrane 12, e.g., from one surface to an opposite surface, in areas 28 spaced from the bonding sites 16. In other areas 29 adjacent the bonding sites 16, fluid may flow freely through the surface of the permeable polymeric membrane 12 and laterally through the membrane 12 away from the bonding sites 16.

In some embodiments, the separation element 10 may include additional layers. For example, in the embodiment illustrated in Figure 3, at least one intermediate layer 30 may be disposed between the permeable polymeric membrane 12 and the mesh layer 14. Although the embodiment illustrated in Figure 3 includes only a single permeable polymeric membrane 12 and a single intermediate layer 30 on one side of the mesh layer 14, the separation element may include multiple intermediate layers on one side of the mesh layer and/or a second permeable polymeric membrane, with or without one or more intermediate layers on the other side of the mesh layer. The intermediate layer may have a variety of functions and configurations. For example, for many embodiments, the intermediate layer may comprise a reinforcing layer, a fluid distribution layer, and/or a cushioning layer and may be in the form of a mass of fibers or woven or nonwoven fibrous sheets or meshes. Any of a variety of materials may be utilized, including polymeric and fiberglass materials. The polymeric component or components comprising the intermediate layer may have a variety of softening temperatures, for example, softening temperatures greater than, equal to or even less than the softening temperature of the mesh layer. In some embodiments, the intermediate layer may comprise a polyetheretherketone mesh.

While many different methods for making a separation element may embody the present invention, one exemplary method may comprise registering at least one permeable polymeric membrane and a mesh layer. For example, the permeable polymeric membrane and mesh layer are preferably registered, e.g., aligned, so that the permeable polymeric membrane overlies an active region of the mesh layer. In many embodiments, registering the permeable polymeric membrane and the mesh layer may include positioning the permeable polymeric membrane adjacent to a surface of the mesh layer in the active region. In some embodiments, registering the permeable polymeric membrane may include registering two permeable polymeric membranes with opposite sides of a mesh layer, e.g., simultaneously or sequentially. For example, a first permeable membrane may be positioned adjacent to one surface of the mesh layer in the active region and a second permeable membrane may be positioned adjacent to an opposite surface of the mesh layer in the active region. The permeable membrane or membranes may be placed in direct contact with the mesh layer or may be slightly spaced from the mesh layer. In other embodiments, registering the permeable polymeric membrane and the mesh layer may include positioning the permeable polymeric membrane adjacent to a surface of at least one intermediate layer, the intermediate layer being positioned adjacent to a surface of the mesh layer in the active region.

The exemplary method may also comprise heating at least the mesh layer. For example, at least the bonding sites in the active region of the mesh layer may be heated. In some embodiments, bonding sites in active regions on both sides of the mesh layer may be heated, e.g., heated simultaneously or sequentially. Any suitable heating arrangement may be used, including, but not limited to, electrical resistance, induction, microwave, radio frequency, sonic, convection, and/or radiant heaters. For example, in many embodiments, the mesh layer may be heated by positioning a heated platen in proximity to, e.g., on or near, the surface of the mesh layer to which the permeable polymeric membrane will be bonded. The heating arrangement may be applied to the mesh layer before the permeable polymeric membrane is registered with the mesh layer. However, for many embodiments, the heating arrangement may be applied to the mesh layer after the permeable polymeric membrane and any intermediate layer are registered with mesh layer, hi many embodiments, a protective layer such as a non-stick polytetrafluoroethylene (PTFE) sheet may be located between the heated platen and mesh layer, e.g., between the heated platen and the permeable membrane. In some embodiments, a non-stick protective layer may comprise a PTFE coating on the platen. Energy from the heating arrangement may pass through the permeable membrane and any intervening layers, e.g., any protective layer and/or intermediate layer, to the mesh layer. Heating the mesh layer after the membrane and any intermediate layer are registered has several advantages. For example, the bonding sites don't lose heat while the permeable membrane and any intermediate layer are being registered with the mesh layer.

The heating arrangement may be arranged to heat at least the bonding sites of the mesh layer to a temperature which is at or above the softening temperature of the sole polymeric component of the mesh layer. Consequently, the polymeric component at a large majority, e.g., all or virtually all, of the bonding sites may become at least soft, e.g., plastically deformable, and may even be capable of flowing, e.g., viscously flowing. After bonding the permeable membrane and any intermediate layer to the mesh layer, the mesh layer preferably retains much of its drainage capability, both edgewise and straight through the mesh layer. Consequently, the heating arrangement preferably does not heat the mesh layer to the extent that the mesh layer grossly deforms, for example, where the strands of the mesh layer entirely melt or merge into one another. Further, where the mesh layer is heated after the permeable polymeric membrane and any intermediate layer are registered with the mesh layer, the heating arrangement may be arranged to heat the mesh layer through the polymeric membrane and the intermediate layer without collapsing the pore structure of the membrane. For example, the heating arrangement may be arranged to heat the bonding sites of the mesh layer to a temperature which is at or above the softening temperature of the polymeric component of the mesh layer and to heat the permeable polymeric membrane to a temperature which is below the higher softening temperatures of the polymeric components of the permeable membrane, i.e., the polymeric components of the separation region. The heating arrangement may heat any intermediate layer or any support region of the permeable membrane, to a temperature below, equal to or even higher than the softening temperature of any polymeric component of the intermediate layer or support region. Consequently, in many embodiments, the polymeric component of the mesh layer is softened, the polymeric components of any intermediate layer or support region may or may not be softened, but the matrix, e.g., the separation region of the permeable membranes, is not softened. The amount of energy supplied by the heating arrangement, e.g., its temperature; the amount of time that the heating arrangement heats the mesh layer, e.g., directly or through the permeable membrane, and any intermediate layer; and the proximity of the heating arrangement to the mesh layer, the permeable membrane and any intermediate layer to appropriately heat the bonding sites, are bonding process parameters which depend on factors such as the structure, composition, and characteristics of the permeable membrane, the mesh layer and any intermediate layer, including, for example, the softening temperatures, the thicknesses and the insulative qualities of one or more of these elements. These parameters may be determined empirically for each combination of permeable membrane, mesh layer, and any intermediate layer. As a general guide, in most embodiments, the heating arrangement may be heated to at least the softening temperature of the sole polymeric component of the mesh layer. In some embodiments, due to the insulative quality of any intervening layers, e.g., any protective layer and/or intermediate layer present between the heating arrangement and the bonding sites, the heating arrangement may be heated to temperatures greater than the softening temperatures of the sole polymeric component of the mesh layer. In some embodiments, due to the presence of any insulating intervening layers between the heating arrangement and the permeable membrane, the heating arrangement may be heated to as high as or higher than the softening temperature of the polymeric components of the separation region of the permeable membrane without softening the permeable membrane. The exemplary method may also comprise applying pressure to the permeable polymeric membrane and/or the mesh layer to press the heated bonding sites of the mesh layer against the permeable membrane, e.g., the separation region of the permeable membrane. In embodiments including permeable membranes on opposite sides of the mesh layer, the heated bonding sites on both sides of the mesh layer may be pressed against the adjacent permeable membranes. The pressure may be applied in the vicinity of the bonding sites by various mechanisms, including, for example, rollers; spring-biased, pneumatic, screw-driven or hydraulic plates; or weights. The pressure may be applied directly to the permeable membrane and/or the mesh layer, with or without any intermediate layer, or indirectly. For example a protective layer, such as a non-stick polytetrafluoroethylene (PTFE) sheet, may be located between the permeable membrane and the pressure mechanism. As another example, an elastomeric sheet may be placed along the surface of the mesh layer opposite the surface to which the permeable membrane will be bonded. The elastomeric sheet may compensate for any unevenness in the bonding surface of the mesh layer when the permeable membrane and the mesh layer, with or without any intermediate layer, are pressed together. Further, the pressure may be applied while the heating arrangement heats the bonding sites of the mesh layer and/or after the heating arrangement heats the bonding sites of the mesh layer. In some embodiments, the pressure may be applied, at least in part, by the heating arrangement. For example, a heated platen may soften the bonding sites of the mesh layer and simultaneously press the permeable membrane against the mesh layer, which may rest on a heated or unheated base, with or without any compensation means, e.g., with or without an elastomeric sheet. When the permeable membrane is pressed against the heated bonding sites in the active region of the mesh layer, with or without any intervening layer, the softened polymeric component of each bonding site is pressed into contact with at least the surface of the permeable membrane, i.e., the surface of the separation region, at an interface region. For example, the softened polymeric component of the bonding sites may plastically deform, or even flow, through any intermediate layer and through any support region of the permeable membrane into contact with the surface of the separation region of the permeable membrane, at the interface regions. In some embodiments, one or more interface regions may extend into the permeable membrane, i.e., into the interstices of the support region and even into the separation region. The softened polymeric component of the bonding site may penetrate beyond the surface of the separation region and into the membrane matrix pore structure. For example, the polymeric component of the bonding site may penetrate into less than about 50% or less than about 25% or less than about 10% or less than about 5% of the thickness of the permeable membrane. In many embodiments, the softened polymeric component may also plastically deform in a lateral direction, e.g., the polymeric component may spread outwardly away from the bonding site to increase the area of the interface region. Less penetration into the thickness of the permeable membrane and less lateral spread are both preferred because they result in less occlusion of the pore structure and greater permeability of the membrane around the interface region.

To further enhance the permeability of the membrane above the interface region, the permeable membrane is pressed against the heated bonding sites in the active region of the mesh layer without significantly crushing or collapsing the pore structure of the membrane above the interface regions. Although the pore structure above the interface regions may, or may not, be altered by the application of pressure, as well as heat, the membrane remains permeable above the interface regions because the pore structure is not significantly crushed or collapsed. The amount of pressure and the amount of time the pressure is applied to appropriately press the permeable membrane and the mesh layer together are bonding process parameters which depend on factors such as the structure, composition, and characteristics of the permeable membrane, the mesh layer, and any intermediate layer, including, for example, the compressive yield strength of the permeable membrane. These parameters may be determined empirically for each combination of permeable membrane, mesh layer, and any intermediate layer. The exemplary method may also comprise resolidifying the softened polymeric component of the bonding sites, on one or both sides of the mesh layer, in the interface regions, thereby thermally bonding the permeable membrane(s), e.g., the separation region of the permeable membrane(s), to the mesh layer, with or without any intermediate layer. The softened polymeric component of the bonding sites may be resolidified by cooling the softened polymeric component in contact with, e.g., on and/or within, the separation region of the permeable membrane. For example, the heating arrangement may be removed or it may cease supplying heating energy, allowing the temperature of the mesh layer to fall below the softening temperature of the polymeric component and return to ambient temperature. Alternatively, the combination of the permeable membrane, the mesh layer, and any intermediate layer may be actively cooled, for example, by directing a cooling fluid through the base on which the mesh layer rests. As the softened polymeric material at the bonding sites in the interface regions cools and resolidifies, the permeable membrane, the mesh layer and any intermediate layer may continue to be pressed against one another to maintain contact between the permeable membrane and the bonding sites of the mesh layer and thereby enhance the thermal bond.

Methods for making separation elements, and the separation elements themselves, provide a permeable membrane, the separation region of which is thermally bonded to a mesh layer, and, in the active region, the membrane remains highly permeable while being securely fixed to the mesh layer. The membrane may be bonded to the mesh layer without crushing or collapsing the pore structure above the interface region at each bonding site. This increases fluid flow in the active region through the membrane in either direction because more of the membrane is available for fluid flow. For example, fluid may enter the surface of the membrane above the interface regions at the bonding sites and flow edgewise or laterally through the uncollapsed pore structure, exiting the opposite surface of the membrane at the unoccluded portions of the membrane between the interface regions. Yet, the highly permeable membrane is securely fixed to the mesh layer. Because all of the polymeric material at the bonding sites may be softened and then resolidified in contact with the permeable membrane including the separation region, all of the bonding sites, and the entire area of each bonding site, are available to participate in the thermal bond. This results in a tight, secure thermal bond between the permeable membrane and the mesh layer which, for example, may be capable of withstanding repeated reverse flows, i.e., flow from the mesh layer through the permeable membrane, of liquid and/or gas. For example, the separation element may be repeatedly cleaned by directing liquid and/or gas in a reverse direction through the permeable membrane or repeatedly subjected to Starling flow without ripping the permeable membrane away from the mesh layer.

While methods for making separation elements and the separation elements themselves may have a highly permeable membrane in the active region of the mesh layer, outside of the active region the permeable membrane may be bonded to the mesh layer very differently. For example, at the periphery of the active region, the membrane and the mesh layer may be bonded to one another and/or other structural elements in a manner which seals the separation element at the periphery. In some embodiments, sufficient heat and/or pressure may be applied to the membrane and/or the mesh layer outside of the active region to completely crush or collapse the pore structure of the membrane and/or to obliterate the openings in the mesh layer and thereby seal the periphery. In other embodiments, sealants or adhesives may be applied to the membrane or the mesh layer outside of the active region to completely occlude the pore structure of the membrane and/or the openings in the mesh layer and thereby seal the periphery. However, within the active region the permeable membrane remains highly permeable and securely thermally bonded to the mesh layer. In some embodiments, one or more separation elements may be combined with a feed inlet arrangement and a permeate outlet arrangement to form a separation module. Fluid to be treated by the separation element(s) may enter the module through the feed inlet arrangement and flow to one or more separation elements. Feed fluid may flow along feed passages and fluid passing from the feed passages through the permeable polymeric membranes, e.g., permeate, may flow along permeate passages to the permeate outlet arrangement to be removed from the module. In some embodiments, the module may be adapted for cross-flow separation and a portion of the fluid, e.g., retentate, may exit the module through a retentate outlet arrangement without passing through a permeable polymeric membrane. The separation module may be variously configured in a wide variety of structures and geometries. One of a myriad of examples of a separation module 100 including a plurality of stacked separation elements 10 is illustrated in Figure 4. While the illustrated separation module 100 comprises rectangular separation elements 10, the separation module 100 may have a variety of other geometric configurations, e.g., circular separation elements. A separation module may also include any suitable number of separation elements, for example two, three, four, five, or even more, e.g., up to 10 or more or 20 or more, which may be stacked between opposite end plates 121 and edge plates (not shown). Separation modules embodying the invention may include a multitude of flow paths, e.g., feed, permeate, and retentate flow paths, through the module. The flow paths may have a variety of configurations in order to efficiently distribute fluid throughout the module, for example, to efficiently distribute feed fluid to the separation elements and remove permeate and retentate from the separation elements. The separation module may introduce feed fluid to, remove permeate from, and remove retentate from any suitable location on the module.

The separation module may include a feed inlet arrangement having any of a myriad of configurations. For example, the feed inlet arrangement may introduce fluid at an edge region of the module or at a top or bottom portion of the module. The feed inlet arrangement may direct feed fluid to flow along any suitable path, e.g., along a feed passage having any suitable configuration, from the feed inlet arrangement to the separation elements. In the illustrated embodiment, an exemplary feed inlet arrangement 120 may comprise a manifold 122 which is located at an edge region of the separation module 100 and which may introduce feed fluid at a lengthwise end of the module 100. In the illustrated embodiment, feed fluid may flow along feed passages 124 comprising open channels, meshes or channeled plates stacked between the separation elements 10. In the active region of each separation element 10, permeate passes through the permeable polymeric membranes 12 facing the feed passages 124 to permeate passages 126 comprising the mesh layers 14 of the separation elements 10. Alternatively, the mesh layers of the separation element may comprise the feed channels and the permeate passages may comprise open channels, meshes or channeled plates. The feed passages may be sealed from the permeate passages in many different ways, including for example, by sealants, adhesives or heat sealing at a lengthwise end of the passage. The permeate outlet arrangement may have any of a multitude of configurations. In the illustrated embodiment, the permeate outlet arrangement 130 may comprise a permeate channel 132 axially extending through the separation module 100 and spaced from the feed inlet arrangement 120. The permeate channel 132 may comprise one or more holes or other passages extending through the stack of separation elements 10 and feed passages 124. The permeate channel 132 may be - sealed from the feed passages 124 in many different ways, including for example, by grommets, gaskets, sealants or adhesives which surround the permeate channel 132 in the feed passages 124. Permeate may be removed from the permeate channel 132 at the top or bottom of the separation module 100 or at any intermediate position. In some embodiments the permeate outlet arrangement may comprise a manifold located at an edge region of the separation module.

In embodiments adapted for cross-flow filtration, a retentate outlet arrangement may remove retentate from the separation module. The retentate outlet arrangement may have any of numerous configurations. For example, in the embodiment illustrated in Figure 4, the retentate outlet arrangement 140 may comprise a manifold 142 located at an edge region of the module 100, opposite the feed inlet arrangement 120. In other embodiments, the retentate outlet arrangement may have other configurations, for example, an axial channel extending through the separation module.

While various aspects of the invention have previously been described and illustrated in the Figures, the invention is not limited to these embodiments. For example, separation elements embodying the invention may comprise a mesh layer which is similar to the mesh layers previously described but has more than one polymeric component. In these embodiments, the plurality of polymeric components in the mesh layer include a first polymeric component having a softening temperature which is greater than or equal to the softening temperature of all other polymeric components in the mesh layer but which is less than the softening temperature of the polymeric components forming the separation regions of the permeable polymeric membranes to be bonded to the mesh layer. Separation elements which include a mesh layer having a plurality of polymeric components may be made by methods similar to those previously described. Thus, the mesh layer may be exposed to a - heating arrangement and all of the polymeric components at the bonding sites of the mesh layer may be at least softened. Heating the mesh layer then includes at least softening all of the polymeric material at all or substantially all of the bonding sites. The softened polymeric components may plastically deform or even flow into contact with the permeable polymeric membrane, e.g., the separation region, and resolidify in the interface regions to thermally bond the mesh layer to the separation regions of the permeable membranes, as previously described. Since all of the polymeric components at the bonding sites are softened and then resolidified in contact with the permeable membrane, substantially all of the bonding sites, as well as substantially the entire area of each bonding site, are available to participate in the thermal bond. This results in a tight, secure thermal bond between the permeable membrane and the mesh layer. The thermal bond, while highly secure, does not substantially collapse or occlude the pore structure of the membrane, allowing the membrane to remain highly permeable even after it is thermally bonded to the mesh layer.

The plurality of polymeric components may comprise a variety of polymeric materials, including any of those polymeric materials described with respect to the single polymeric component mesh layer. The plurality of polymeric components in the mesh layer may be included in a variety of proportions and configurations. For example, an extruded mesh layer including two or more polymeric components may have different strands comprising different polymeric components and/or any one strand may include multiple polymeric components arranged in a wide variety of ways. For example, each polymeric component may be arranged in a discrete region of the strand. Preferably, the amounts and configuration of the polymeric components are such that heating the mesh layer to at or above the softening temperature of the first polymeric component, e.g., to at or above the softening temperature of the polymeric component having the highest softening temperature, does not grossly deform the mesh layer.

This invention is also not limited to the previously described methods of making a separation element. In some embodiments, the permeable polymeric membrane may be thermally bonded to a mesh layer to which one or more intermediate layers have previously been thermally bonded. For example, registering at least one permeable polymeric membrane may include positioning the membrane adjacent an intermediate layer which is thermally bonded to the bonding sites of a mesh layer in the active region. The intermediate layer may be bonded to the mesh layer by methods similar to those previously described for thermally bonding a permeable membrane to the mesh layer. However, the interface regions may penetrate entirely through the intermediate layer. For example, the intermediate layer may be registered with the mesh layer, e.g. aligned, so that the intermediate layer overlies the bonding sites in the active region of the mesh layer. The mesh layer including the bonding sites may be heated, e.g. before or after registering the intermediate layer with the mesh layer, to a temperature at or above the softening temperature of the polymeric component or components of the mesh layer. Pressure may then be applied to press the softened polymeric component or components of the bonding sites into contact with the intermediate layer and the softened polymeric component may be resolidified in the interface regions in contact with, e.g. on or within, the intermediate layer.

The permeable polymeric membrane may then be thermally bonded to the mesh layer including the intermediate layer substantially as previously described. For example, the permeable polymeric membrane may be registered with the active region of the mesh layer, and the bonding sites of the mesh layer may be heated again to a temperature at or above the softening temperature of the polymeric component or components of the mesh layer. Pressure may then be applied to press the permeable membrane, intermediate layer, and mesh layer and to force the softened bonding sites through the bonded intermediate layer and into contact with the permeable polymeric membrane, i.e. the separation region. The softened polymeric component of the bonding sites may then be resolidified in contact with, e.g. on and/or within, the permeable membrane to thermally bond the permeable polymeric membrane to the mesh layer.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Claims

CLAIMS:

1. A separation element comprising: a mesh layer including no more than one polymeric component, having a softening temperature and an active region having a plurality of bonding sites, and a permeable polymeric membrane having a pore structure which permits fluid to flow through the membrane, wherein the permeable polymeric membrane has a softening temperature higher than the softening temperature of the polymeric component and wherein the permeable polymeric membrane is thermally bonded to the mesh layer at the bonding sites, the single polymeric component at the bonding sites being resolidified in contact with the permeable polymeric membrane without substantially collapsing the pore structure of the membrane in the active region.

2. The separation element according to claim 1 wherein the mesh layer includes first and second sides, each side having an active region and a plurality of bonding sites, and a first permeable polymeric membrane thermally bonded to the bonding sites on the first side of the mesh layer and a second permeable polymeric membrane thermally bonded to the bonding sites on the second side of the mesh layer, the single polymeric component at the bonding sites on the first and second sides of the mesh layer being resolidified in contact with the first and second permeable polymeric membranes, respectively, without substantially collapsing the pore structure of the membranes in the active region.

3. The separation element according to claim 1 wherein the permeable polymeric membrane includes a separation region and a support region and the mesh layer is thermally bonded to the separation region.

4. The separation element according to claim 1 wherein the polymeric component of the mesh layer comprises polypropylene and the permeable polymeric membrane comprises a polyethersulfone membrane.

5. The separation element according to claim 1 wherein the polymeric component of the mesh layer comprises polypropylene and the permeable polymeric membrane comprises a polyvinylidene fluoride membrane.

6. The separation element according to claim 1 wherein the polymeric component of the mesh layer comprises polysulfone and the permeable polymeric membrane comprises a polyethersulfone membrane.

7. The separation element according to claim 1 wherein the polymeric component of the mesh layer comprises polypropylene and the permeable polymeric membrane comprises a nylon membrane.

8. The separation element according to any of the above claims wherein the permeable polymeric membrane includes no resolidified membrane matrix material.

9. The separation element according to any of the above further comprising one or more intermediate layers disposed between the permeable polymeric membrane and the mesh layer.

10. A method of making a separation element comprising: registering a permeable polymeric membrane and a mesh layer including a single polymeric component, wherein the permeable polymeric membrane has a pore structure which permits fluid to flow through the membrane and overlies an active region of the mesh layer having a plurality of bonding sites; heating the bonding sites of the mesh layer to a temperature at or above the softening temperature of the polymeric component, including at least softening the single polymeric component at the bonding sites; and applying pressure to the permeable polymeric membrane and the mesh layer in the vicinity of the bonding sites, including resolidifying the single polymeric component at the bonding sites in contact with the permeable polymeric membrane, to thermally bond the permeable polymeric membrane to the mesh layer, without substantially collapsing the pore structure of the membrane in the active region.

11. The method according to claim 10 wherein the bonding sites of the mesh layer are heated after registering the permeable polymeric membrane and the mesh layer and the permeable polymeric membrane is heated to a temperature below the softening temperature of the membrane.

12. The method according to claim 10 wherein resolidifying the single polymeric component at the bonding sites in contact with the permeable polymeric membrane comprises resolidifying the component in contact with a separation region of the membrane.

13. The method according to claim 10 including registering a first permeable polymeric membrane with a first side of a mesh layer where the first permeable membrane overlies an active region of the first side of the mesh layer having a plurality of bonding sites and registering a second permeable polymeric membrane with a second side of a mesh layer, where the second permeable membrane overlies an active region of the second side of the mesh layer having a plurality of bonding sites, heating the bonding sites on the first and second sides mesh layer to a temperature at or above the softening temperature of the polymeric component, including at least softening the polymeric component at the bonding sites on the first and second sides of the mesh layer, and applying pressure to the permeable polymeric membranes and the mesh layer in the vicinity of the bonding sites, including resolidifying the single polymeric component at the bonding sites on the first and second sides of the mesh layer in contact with the first and second membranes, respectively, without substantially collapsing the pore structure of the membranes in the active region.

14. A separation element comprising: a mesh layer including two or more polymeric components, wherein a first one of the polymeric components has a softening temperature greater than or equal to the softening temperatures of all other components, the mesh layer further including an active region which has a plurality of bonding sites; and a permeable polymeric membrane having a pore structure which permits fluid to flow through the membrane and a softening temperature which is higher than the softening temperature of the first polymeric component of the mesh layer, wherein the permeable polymeric membrane is thermally bonded to the mesh layer at the bonding sites, the polymeric components at the bonding sites being resolidified in contact with the permeable polymeric membrane without substantially collapsing the pore structure of the membrane in the active region.

15. The separation element according to claim 14 wherein the mesh layer includes first and second sides, each side having an active region and a plurality of bonding sites, and a first permeable polymeric membrane thermally bonded to the bonding sites on the first side of the mesh layer and a second permeable polymeric membrane thermally bonded to the bonding sites on the second side of the mesh layer, the polymeric components at the bonding sites on the first and second sides of the mesh layer being resolidified in contact with the first and second permeable polymeric - membranes, respectively, without substantially collapsing the pore structure of the membranes in the active region.

16. The separation element according to claim 14 wherein the permeable membrane includes a separation region and a support region and the mesh layer is thermally bonded to the separation region.

17. The separation element according to claim 14 wherein the first polymeric component of the mesh layer comprises polypropylene and the permeable polymeric membrane comprises a polyethersulfone membrane.

18. The separation element according to claim 14 wherein the first polymeric component of the mesh layer comprises polypropylene and the permeable polymeric membrane comprises a polyvinylidene fluoride membrane.

19. The separation element according to claim 14 wherein the first polymeric component of the mesh layer comprises polysulfone and the permeable polymeric membrane comprises a polyethersulfone membrane.

20. The separation element according to any of claims 14-19 wherein the permeable polymeric membrane includes no resolidified membrane matrix material.

21. The separation element according any one of claims 14-20 further comprising one or more intermediate layers disposed between the permeable polymeric membrane and the mesh layer.

22. A method of making a separation element comprising: registering a permeable polymeric membrane and a mesh layer which includes two or more polymeric components, wherein the permeable polymeric membrane has a pore structure which permits fluid to flow through the membrane and overlies an active region of the mesh layer which has a plurality of bonding sites; heating the bonding sites of the mesh layer to a temperature at or above the highest softening temperature of all the polymeric components in the mesh layer, including at least softening the polymeric components at the bonding sites; and applying pressure to the permeable polymeric membrane and the mesh . layer to thermally bond the permeable polymeric membrane to the mesh layer, including resolidifying the polymeric components at the bonding sites in contact with the permeable polymeric membrane without substantially collapsing the pore structure of the membrane in the active region.

23. The method according to claim 22 wherein the bonding sites of the mesh layer are heated after registering the permeable polymeric membrane and the mesh layer and the permeable polymeric membrane is heated to a temperature below the softening temperature of the membrane.

24. The method according to claim 22 wherein resolidifying the single polymeric component at the bonding sites in contact with the permeable polymeric membrane comprises resolidifying the component in contact with a separation region of the membrane.

25. The method according to claim 22 including registering a first permeable polymeric membrane with a first side of a mesh layer where the first permeable membrane overlies an active region of the first side of the mesh layer having a plurality of bonding sites and registering a second permeable polymeric membrane with a second side of a mesh layer, where the second permeable membrane overlies an active region of the second side of the mesh layer having a plurality of bonding sites, heating the bonding sites on the first and second sides mesh layer to a temperature at or above the highest softening temperature of all the polymeric components in the mesh layer, including at least softening the polymeric components at the bonding sites on the first and second sides of the mesh layer, and applying pressure to the permeable polymeric membranes and the mesh layer in the vicinity of the bonding sites, including resolidifying the polymeric components at the bonding sites on the first and second sides of the mesh layer in contact with the first and second membranes, respectively, without substantially collapsing the pore structure of the membranes in the active region.