FILTRATION SYSTEMS

CROSS-REFERENCE TO RELATED APPLICATIONS

[001] The present application claims priority to U.S. Provisional Patent Application Serial No. 61/311,646 filed on March 8, 2010, the contents of which is incorporated herein by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

[002] Field of the Invention

[003] A retrofit adaptor used for replacing conventional filtration units with more efficient cross-flow filtration units in existing filtration systems.

[004] Related Technology

[005] There are several presently marketed stacked filter systems, commercially available from Millipore Corporation (Bedford, Mass.), such as the Prostak® cross-flow filter. Solid- containing influent liquid is fed at one side of the plate from a central location into a transversely extending feed distribution conduit, which is provided with openings at spaced- apart intervals along the length of the conduit for egress of the solids-containing liquid. At the opposite side of the adjacent plates, the flow channel is similarly constructed with a liquid collection conduit having openings along its length to collect the solids-depleted liquid and discharge same from a central outlet communicating with the collection conduit.

[006] A major problem which has been encountered in cross-flow filters of the above- described type is that the liquid flow distribution, as for example reflected by the volumetric liquid flow rate or the liquid superficial velocity, is highly non-uniform in the transverse direction of the flow channel. Such maldistribution of the solid-containing liquid is a result of the fact that (1) the influent liquid is introduced into the feed distribution conduit at a central location, and (2) the cross sectional area of the liquid inlet is smaller than the sum of the inlet cross sectional areas of the cross flow subchannels.

[007] Due to the pressure drop in the transverse direction, from the medial inlet port of filter plate assembly to the extremities of the feed distribution conduit, the local longitudinal flow (cross-flow) of liquid from the inlet side to the outlet side of the stacked plates, at progressively farther transverse distances from the central liquid inlet port, is progressively reduced in correspondence to the pressure drop experienced as the liquid is directed transversely to the outer extremities of the distribution conduit.

[008] As a result, there is preferential channeling of the liquid at the central part of the flow channel from the inlet side to the outlet side thereof, and concomitant under-utilization of the peripheral areas of the filter. The available filter surface therefore is partially utilized in cross flow and partially in dead end filtration. When the solids in the central portion have been built up to a point requiring backwashing or cleaning of the filter, only that portion of the filter utilized in cross flow can be cleaned. The peripheral areas of the filter sheet remain fouled and cause carryover of fouled material from one batch process to the next.

[009] Pellicon.® by Millipore is another type of stacked plate cross-flow filter which has been commercialized and employs a transversely extending liquid distribution conduit with spaced-apart openings therein to introduce solids-containing liquid into the flow channel between adjacent stacked plates. However, instead of a central inlet port to flow the solids- containing liquid to such conduit, the liquid is axially fed into the conduit from a feed line connected to a transverse extremity of the conduit. This feed arrangement results in a progressive diminution of the liquid pressure at increasing transverse distances in the feed end of the distribution conduit, which in turn results in progressively transversely decreased cross-flow rates of liquid in the flow channel.

[0010] Although the dual serpentine flow path arrangement described above provides a somewhat better distribution of liquid flow across the area extent of the filter paper element, the sharp turns in the flow path at the extremities of the baffles create edge and entrance effects in the flow streams which produce substantial dead space and bypassing therein. As a result of such anomalous flow phenomena, the filtration efficiency of the baffled serpentine flow arrangement is significantly reduced.

[0011] In order to convert existing inefficient filtration systems to a more efficient system, it has been necessary in the past, to replace the entire system. Consequently, it is highly desirable to provide adaptive means to replace the above discussed inefficient filters in the respective systems with a filter unit that provide superior mass transfer efficiency.

SUMMARY OF THE INVENTION

[0012] This invention is directed to a retrofit kit which permits filters described in U.S. Pat. No. 5,049,268, U.S. Pat. No. 5,868,930, U.S. Pat. No 7,544,296, U.S. Provisional Application No. 61/264,799 and other filters described hereinbelow to replace inefficient filters in existing filtration systems.

[0013] The retrofit adaptor kit provides for replacing conventional filter units with a desirable cross-flow filter unit, wherein the cross-flow filter unit preferably comprises retentate sheets with retentate elongated channels positioned in the middle section of the sheet and in parallel positioning with permeate openings positioned on both sides of the retentate elongated channels, and permeate sheets and filter sheets with permeate openings positioned corresponding to placement in the retentate sheet. Preferably, the cross-flow filter unit comprises at least one sequence of retentate sheet, filter sheet, permeate sheet, filter sheet, and retentate sheet, wherein the retentate sheet comprises a multiplicity of elongated opening positioned along the longitudinal axis of the retentate sheet and permeate opening positioned parallel and on each side of the retentate openings, and wherein the filter and permeate sheets include permeate openings aligned with permeate opening in the retentate sheet and retentate openings aligned with opposing ends of the retentate openings of the retentate sheet.

[0014] In one aspect, the present invention provides for a retrofit adaptor kit comprising a pair of rectangular or square base members wherein each base plate member comprises a first face side and a second face side, a first end and second end side positioned along the longitudinal axis of the base member, perpendicular to the first and second face sides; and a third end and fourth end side positioned normal to the first end and second end side, wherein the first face side is in contact with a cross-flow filter unit and the first face side comprises two open fluid channels, including a permeate channel and a retentate channel, wherein the permeate channel is positioned within and along the longitudinal axis of the first face side of the base member positioned near the first or second side end side and in fluid communication with permeate opening of a filter unit and the retentate channel is positioned within the first face side of the base member and normal to the permeate channel and in fluid communicate with retentate opening of the filter unit, wherein the third end side comprises a permeate port in fluid communication with the base member permeate channel and the third or fourth end side comprises a retentate port in fluid communication with the base member retentate channel.

[0015] Preferably, the base members further comprise at least one U-shaped slot positioned on each of the third and fourth end sides for accepting an alignment pin for positive positioning of the adaptor kit between clamping holders or used for holding a clamping bolt, and wherein the first face side of two base members are positioned relative to each other to provide for fluid movement though the filter.

[0016] Notably, the permeate port and retentate port can both be positioned on one end, such as the third end side or the permeate port and retentate port can be positioned on the third end side and fourth end so that both ends have a port.

[0017] It should be noted that the retentate and permeate open channels in the base members may be referred to as U-shaped channels but in fact can be any geometric shape as long as they are open to the first face side of the base member and able to move the flow of fluids into and from the cross-flow filter unit from one base member to another base member.

[0018] In the alternative the two base members, may be clamped together by holders used in existing filtration systems. When using an existing holder there may be a need for adjustment in the holder for proper alignment of ports. In such a situation, a saddle may be necessary for such alignment and wherein the base member contacts the saddle or connected thereto. [0019] Preferably, the base members are fabricated from a rigid material with structural integrity including a polymeric material and the end ports are fitted with stainless steel or polymeric male or female fittings for connecting to filtration systems available from Pall, Novasep, GE, Satorius, Millipore and other commercially available filtration units.

BRIEF DESCRIPTION OF THE FIGURES

[0020] Figures 1A and B show photos of a base member alone and positioned with an OPTISEP 3000 filtration unit available from Smartflow Technologies, Inc, Cary, NC used as an example noting that other similar filtration units available from Smartflow may be interchangeable, and wherein the permeate port is located on one end side and the retentate port located on the opposite end side.

[0021] Figures 2 A shows a saddle for proper alignment of the retrofit adaptor; B show a combination of two base members adapted with two saddles holding the respective base members for proper alignment in an existing filtration holder, wherein the permeate port and retentate port are positioned on the same end side of a base member; C and D show the retrofit adaptor positioned in a conventional filtration unit.

[0022] Figure 3 shows photos of two base members clamped with stainless steel holders with an OPTISEP 3000 filter positioned therebetween.

[0023] Figure 4 shows a single use disposable system wherein the filter is disposable and the base member could also be fabricated as disposable.

[0024] Figure 5 shows a unit, either disposable or nondisposable, wherein the base members are positioned to provide for a series-flow configuration.

[0025] Figure 6 shows the first face of the base member 10 wherein both the retentate channel and permeate channels are shown. [0026] Figure 7 shows one end of the base member and showing a retentate port and permeate port in fluid communicate with the retentate channel and permeate channel, respectively.

[0027] Figure 8 shows examples of applicable permeate and retentate sheets used in one embodiment of a stack filter cassette and for use with two base members of the present invention.

[0028] Figure 9 shows a combination of the two base members and positioning of the filter stack therebetween.

[0029] Figure 10 shows a separation plate to direct the retentate flow used in the series-flow configuration of Figure 5.

[0030] Figure 11 shows the components of a preferred cross-flow filtration cassette for use with the retrofit adaptor in conventional filtration units.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention includes the use of a cross-flow filter unit in an adaption setup for use with existing filtration systems.

[0032] "Cross-flow filter" refers herein to a type of filter module or filter cassette that comprises a porous filter element across a surface of which the liquid medium to be filtered is flowed in a tangential flow fashion, for permeation through the filter element of selected component(s) of the liquid medium. In a cross-flow filter, the shear force exerted on the filter element (separation membrane surface) by the flow of the liquid medium serves to oppose accumulation of solids on the surface of the filter element. Cross-flow filters include filtration, microfiltration, ultrafiltration, nanofiltration and reverse osmosis filter systems. The cross-flow filter may comprise a multiplicity of filter sheets (filtration membranes) in an operative stacked arrangement, e.g., wherein filter sheets alternate with permeate and retentate sheets, and as a liquid to be filtered flows across the filter sheets, impermeate species, e.g. solids or high-molecular-weight species of diameter larger than the filter sheet's pore size, are retained and enter the retentate flow, and the liquid along with any permeate species diffuse through the filter sheet and enter the permeate flow. In the practice of the present invention, cross-flow filter modules and cross-flow filter cassettes useful for such filtration are commercially available from Smartflow Technologies , Inc. (Cary, North Carolina) including U.S. Pat. No. 5,049,268, U.S. Pat. No. 5,868,930, U.S. Pat. No 7,544,296, U.S. Provisional Application No. 61/264,799, the contents of which are incorporated by reference herein for all purposes.

[0033] The filter unit may be employed in stacked arrays to form a stacked cassette filter assembly in which the base sequence of retentate sheet (R), filter sheet (F), permeate sheet (P), filter sheet (F), and retentate sheet (R) may be repeated in the sequence of sheets in a filter assembly. Thus, the filter cassette of a desired total mass transfer area is readily formed from a stack of the repetitive sequences. In all repetitive sequences, except for a single unit sequence, the following relationship is observed: where X is the number of filter sheets, 0.5X-1 is the number of interior retentate sheets, and 0.5X is the number of permeate sheets, with two outer retentate sheets being provided at the outer extremities of the stacked sheet array.

[0034] The filter sheets, and the retentate and permeate sheets employed therewith, may be formed of any suitable materials of construction, including, for example, polymers, such as polypropylene, polyethylene, polysulfone, polyethersulfone, polyetherimide, polyimide, polyvinylchloride, polyester, etc.; nylon, silicone, urethane, regenerated cellulose, polycarbonate, cellulose acetate, cellulose triacetate, cellulose nitrate, mixed esters of cellulose, etc.; ceramics, e.g., oxides of silicon, zirconium, and/or aluminum; metals such as stainless steel; polymeric fluorocarbons such as polytetrafluoroethylene; and compatible alloys, mixtures and composites of such materials.

[0035] Preferably, the filter sheets and the retentate and permeate sheets are made of materials which are adapted to accommodate high temperatures and chemical sterilants, so that the interior surfaces of the filter may be steam sterilized and/or chemically sanitized for regeneration and reuse, as "steam-in-place" and/or "sterilizable in situ" structures, respectively. Steam sterilization typically may be carried out at temperatures on the order of from about 121°C to about 130°C, at steam pressures of 15-30 psi, and at a sterilization exposure time typically on the order of from about 15 minutes to about 2 hours, or even longer. Alternatively, the entire cassette structure may be formed of materials which render the cassette article disposable in character.

[0036] Thus, the cross-flow filtration unit comprises a multilaminate array, as shown in Figure 11, of sheet members of generally rectangular and generally planar shape with main top and bottom surfaces, wherein the sheet members include in sequence in the array a first retentate sheet, a first filter sheet, a permeate sheet, and second filter sheet, and a second retentate sheet, wherein each of the filter and permeate sheet members in the array has at least one inlet basin opening 45 at one end thereof, and at least one outlet basin opening 47 at an opposite end thereof, with at least one permeate passage opening 46 at longitudinal side margin portions of the sheet members; each of the first and second retentate sheets having at least one channel opening 44 therein, wherein each channel opening extends longitudinally between the inlet and outlet basin openings of the sheets in the array and is open through the entire thickness of the retentate sheet, and with each of the first and second retentate sheets being bonded to an adjacent filter sheet about peripheral end and side portions thereof, with their basin openings and permeate passage openings 46 in register with one another, and arranged to permit flow of filtrate through the channel openings of the retentate sheet 44 between the inlet 45 and outlet basin 47 openings to permit flow through the filter sheet to the permeate sheet and then on to the permeate passage openings.

[0037] According to one embodiment of the present invention, a cross-flow filtration module with uniform geometry is utilized for conducting the membrane separation. The phrase "uniform geometry" is defined herein as the geometric structure of a cross-flow filtration module, characterized by at least one permeate flow passage, at least one inlet, at least one outlet, and multiple fluid-flow sub-channels that are of substantially equal length between the inlet and the outlet.

[0038] In another embodiment of the present invention, cross-flow filtration modules with sub-channels that are equidistant to the inlet and outlet of said modules are employed for membrane separation. Moreover, such cross-flow filtration modules are characterized by optimal channel height, optimal transmembrane pressure, optimal membrane pore size and pore structure, optimal membrane chemistry, etc., which characteristics are selected in order to achieve the best combination of product quality and production yield.

[0039] For example, shear at the surface of the membrane is critical in minimizing gel layer formation, but excessive shear is deleterious in the following three key aspects: (1) excessive shear increases energy consumption, (2) excessive shear interferes with diffusion at the membrane surface, upon which the separation process directly depends, (3) excessive shear can deprive certain compounds of their bioactivities. It therefore is desirable to maintain shear within an optimal range.

[0040] Furthermore, it is possible to optimize the separate processes with cross-flow filtration modules of variable channel velocities but of uniform channel heights, given the fact that most commercial cross-flow modules are only available in a single channel height.

[0041] The transmembrane pressure (TMP) of the cross-flow filtration membrane can also be optimized after the appropriate tangential velocity has been determined. Transmembrane pressure is calculated as TMP = (inlet pressure + outlet pressure)/2 - permeate pressure. The purpose of optimizing the transmembrane pressure is to achieve maximum permeate flow rate. The normal relationship between transmembrane pressure and permeate flow rate can be best represented by a bell curve. Increases in transmembrane pressure cause increases in the permeate rate, until a maximum is reached, and after which any further increases in transmembrane pressure result in decreases in the permeate rate. It is therefore important to optimize the transmembrane pressure so that the maximum permeate flow rate can be obtained.

[0042] The adaptor of the present invention serves four purposes; retrofit, single use in filtrations units, single use stand-alone with compression plates, and single use series flow.

[0043] Retrofit Adaptor Enables SmartFlow's standard OPTISEP 3000 TFF module(s) to be used in cassette holders such as are offered by Pall, Novasep, GE, Sartorius, Millipore and other commercially available units. The polymeric adaptors provide the wetted process flow path. The stainless holder serves to locate and compress the adaptors/module(s) assembly.

[0044] Single Use - Disposable

The same or similar adaptors, in conjunction with bolted and/or hydraulic stainless compression plates also function as a single use module holder. The stainless compression plates are not wetted, and all fluid pathways are contained in the module(s) and adaptor plates; which are discardable after use.

[0045] Single Use - Disposable (in 3000 holder)

The same or similar device is able to be utilized as a disposable filter when using a standard OPTISEP 3000 holder to provide compression. In this configuration the porting and fluid paths of the stainless 3000 holder are still present but not used, all wetted port and pathways are contained in the module(s) and adaptor(s).

[0046] Adaptor in series-flow configuration

The use of two fixed base member plates, (one inverted as discussed below and shown in Figure 5) will enable the adaptor to be used in series flow operation. As configured, series flow allows the same membrane area to be driven with half the pump capacity as would be required in standard parallel configuration. Additionally, series flow configuration enables a lower hold up volume to be established due to all ports being located in closer proximity to each other, thus overall closer loop piping.

[0047] Referring now to Figure 1, there is shown a base member 10 in photo A, wherein the permeate port 14 and retentate port 12 are on opposite ends of the base member. Slots 18 are positioned for receiving an aligning pin for positioning of the base members in a holder or in the alternative may be used for positioning of bolts as shown in Figure 2D. Photo IB shows the placement of a preferred cross flow filtration unit 16, with components as shown in Figure 11 , wherein permeate channels and retentate channels align with the corresponding channels in the base member. Figure 1A shows an inside view of the base member wherein the permeate U-shaped channel 22 is visible and positioned along the longitudinal axis of the based member and in fluid communication with permeate port 14. The retentate channel 20 is positioned normal to the permeate channel and in fluid communication with retentate port 12. The adapter comprising two base members 10 enable the flow path through the filter cassette 16 to be retained (equal channel length). Viewing Figure 1A in relation to Figure 8, it should be noted that permeate channel 22 is in fluid communication with permeate flow channels 46 as shown in Figure 8. Retentate channel 20 of Figure 1 A is in fluid communication with retentate flow channels 44 and openings 45 of Figure 8.

[0048] The base members may be fabricated from any polymeric material such as polysulfone, polycarbonate; cellulose, combinations thereof and other fluid impermeable materials including biodegradable materials for a single use disposable option. Fabrication may include extruding polymeric material into a die form, cooling and removal from the die form. The material needs sufficient rigidity to maintain the structural integrity under the pressure of clamping into holders of conventional filtration systems. The retentate and permeate ports may include Tri-Clamp fittings ranging from ½" to 1 ½".

[0049] Figure 2A shows a saddle 24 that can be used for alignment of the adaptor in a Pall system wherein the two saddle feet 26 sit on the guide rails of the Pall holder system. The center hole 28 can be used to attach and locate the adaptor. Slot 30 provides for alignment of and placement of sliders 32 used in further alignment of the two base members in the holder. Figure 2B shows the set up of the adapter wherein two base members 10 are used and positioned on two saddles 24. The adaptor can use competitor's existing holder without any modification and can include 1-25 square feet of standard OPTISEP 3000, from Smartflow Technologies, modules or any of the other modules available from SmartFlow having the appropriately aligned permeate and retentate flow channels. The installation and use can include horizontal (Millipore) or side (Pall) placement of the adaptor unit as shown in Figure 2 C and D.

[0050] Figure 3 shows another embodiment of the present invention wherein the adapter is used wherein no saddle is needed and the holder is used for compression only. The clearance slots for alignment/end bolts are not utilized and instead utilizes standard alignment pins to locate the adaptor in the holder.

[0051] Figure 4 shows an embodiment used for single use with the option of disposing of the filter and base members after a single use. In the described embodiment, no saddle is required but instead the base members 10 and at least one filter cassette 16 are compressed between compression plates 34, wherein the compression plates may be fabricated from stainless steel, ceramic, polymer or any applicable material that provides the structural integrity required for clamping and holding the base members. The embodiment functions as a non-wetted clamp system that can be aligned and/or secured with bolts 32. The slots 18 are used for alignment pins 40 and the addition of handles 36 makes for ease of installation and positioning. Installation and use is possible in horizontal (Millipore), side (Pall) or standard vertical configurations (Smartflow).

[0052] Figure 5 shows the adaptor with two base members 10 configured in series-flow configuration. All ports are positioned on the same end of the adaptor set, and alignment pins 40 in alignment slots 18 positively positions the adaptor in the compression plates. Notably, this embodiment comprises two filters cassette 16 with a plate 48 positioned therebetween. Plate 48 as clearly shown in Figure 10 provides for the series flow of the retentate into first retentate port 12, through retentate channel 20, through the cross-flow filtration unit 16, comprising the components as shown in Figure 11 , and then movement through the retentate channels 47 (as shown in Figure 10 and located on the opposite end of the filter units relative to the flow of the retentate into and out of the retentate ports) for entry into second filter 16 and exiting out of retentate channel 20 and second retentate port 12. This provides for a limited loop and a small filtration unit provides for extended surface area for movement of fluid and the separation of the permeate from the retentate. [0053] Figures 6 shows the base member 10 with permeate channel 22 that is in fluid communication with fluid port 21 open to the end side of the base member. In this embodiment the retentate channel 20 is in fluid communication with fluid port 19. In this embodiment both fluid ports 19 and 21 are located on the same side of the end plate. Notably, in some embodiments the fluid ports can be located on opposite ends of the base member.

[0054] Figure 7 shows the end side of base member shown in Figure 6, wherein fluid ports 19 and 20 are visible and bolt recesses 17 are shown.

[0055] Figure 8 shows examples of applicable permeate and retentate sheets used in the preferred cross-flow filter cassette wherein the permeate openings 46 are parallel to the retentate channels in the retentate sheet 44.

[0056] Figure 9 shows a combination of the two base members and positioning of the cross- flow filter stack 16 therebetween. This figure provides for an understanding of the flow of retentate as it enters through retentate port 12, retentate channel 20, retentate channels 44 and in fluid communication with filter cassette 16 and existing at the opposite end of entry. Any permeate removed from the filtering system moves into permeate channels 22 and removed via fluid moving through permeate ports 14.

[0057] Figure 10 shows the plate used in the series-flow configuration of Figure 5 and positioned between two cross-flow filters 16, wherein flow into the first filter is diverted by plate 48 and moved along the longitudinal length of the plate 48 until is passes through the channels 47 and then into the second filter for movement therethrough and existing out of second filter.

[0058] Figure 11 shows the components of cross-flow filtration cassette 16, as previously described hereinabove.