60/136,758, which was filed on May 28,1999.

TECHNICAL FIELD OF THE INVENTION The present invention relates to separation elements, methods, and systems for purifying fluids, e. g., aqueous liquids such as aqueous liquids containing oil and/or particulate matter, and to methods for making separation elements.

BACKGROUND OF THE INVENTION In a variety of situations, an aqueous liquid may pick up oil, known as"tramp oil", and/or particulate matter as it flows within a system. For example, aqueous machine coolants or aqueous wash liquids may pick up oil and/or particulate matter from machine parts. It is desirable to treat these aqueous liquids by passing the liquid through a separation element, such as a coalescer element or a filter element, to remove the oil and/or particulate matter so that the coolant or other liquid may be reused or disposed of according to appropriate standards. However, many traditional separation elements tend to foul quickly when separating particulate matter and oil, particularly when higher levels of oil are present. In addition, because the oil may penetrate the surface and become embedded deep within the separation element, such traditional separation elements are very difficult to clean. For example, these traditional separation elements effectively resist cleaning by backwash or blowback once oil and particulate matter have become embedded in them. Consequently, the service life of many traditional separation elements in an oily environment has been unduly limited.

SUMMARY OF THE INVENTION One aspect of the present invention provides a separation element which is arranged to be incorporated in a system wherein a fluid containing particulate matter and/or oil is passed in one direction through the separation element and a cleaning fluid is passed in an opposite direction through the separation element, the separation element comprising an oleophobically treated porous separation medium.

Another aspect of the present invention provides a method of purifying a fluid, e. g., liquid, gas or a mixture of liquid and gas, containing particulate matter and/or oil.

The fluid, including the particulate matter and/or oil, is passed in one direction through an oleophobically treated porous medium. Then, a cleaning fluid is passed in the opposite direction through the oleophobically treated porous medium to remove the particulate matter and/or oil from the oleophobically treated porous medium.

Another aspect of the present invention provides a method of purifying an aqueous liquid containing particulate matter and oil. The aqueous liquid, including the particulate matter and the oil, is passed through a microporous, oleophobically treated filter medium, and particulate matter and oil are retained by the oleophobically treated filter medium.

Another aspect of the present invention provides a method of oleophobically treating a separation element to be used in separating particulate matter and/or oil from a fluid containing the particulate matter and/or oil. An oleophobic agent is directed in one direction through the separation element and then the oleophobic agent is directed in the opposite direction through the separation element.

Another aspect of the present invention provides an oleophobically treated separation element for purifying a fluid containing particulate matter and/or oil. The separation element comprises a microporous separation medium, the separation element being oleophobically treated so that the oleophobicity throughout the separation medium is substantially uniform.

Another aspect of the present invention provides a system for purifying an aqueous liquid containing particulate matter and oil. The system comprises a housing, at least one fluid inlet and at least one fluid outlet in the housing, and at least one separation element including a microporous, oleophobically treated separation medium. The microporous, oleophobically treated separation medium has an upstream surface communicating with the inlet and a downstream surface communicating with the outlet. The separation medium is disposed in the housing to remove particulate matter and oil from an aqueous liquid directed through the inlet and between the upstream and downstream surfaces of the separation medium. The system also includes a backwashing arrangement coupled with the housing to backflush fluid through the separation element from the downstream surface of the separation medium to the upstream surface of the separation medium.

Utilizing a separation element, such as a coolescer element or a filter element, that has been oleophobically treated provides for better separation of oil and particulate matter from a fluid, such as a gas or a liquid, containing particulate matter and oil than separation elements which have not been oleophobicity treated, particularly when the fluid to be purified contains high levels of tramp oil. It is also remarkable that separation elements which are oleophobically treated to provide for a uniform oleophobicity throughout the separation element foul significantly less quickly and clean significantly better than conventional separation elements. In some embodiments of the invention, a substantially uniform oleophobicity may be obtained throughout an entire separation element by directing an oleophobic agent through the separation element in opposite directions, e. g. from outside-in and inside-out through the separation element, preferably under a pressure differential.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a schematic drawing of a separation system according to the present invention showing a first step in a separation process according to the present invention.

Figure 2 is a schematic drawing of a separation system of the invention showing a second step in the separation process.

Figure 3 is a schematic drawing of a separation system of the present invention showing the a step of the separation process.

Figure 4 is a schematic drawing illustrating a separation system of the invention showing a backflush step according to the invention.

DETAILED DESCRIPTION Separation elements, methods, and systems embodying the present invention may be used to purify a wide variety of fluids, including gases, liquids and mixtures of gases and liquids, such as fluids containing particulate matter and/or oil; for example, an aqueous liquid containing particulate matter and oil, as an immiscible phase suspended in the aqueous liquid. The separation elements embodying the invention are oleophobically treated and may include a separation pack and various hardware components used to support the separation pack in a particular configuration.

The separation pack perferably includes a separation medium, such as a filter medium or a coalescer medium. The separation pack may further include one or more drainage media, such as an upstream drainage medium and/or a downstream drainage medium respectively positioned upstream and/or downstream of the separation medium. The separation pack, which preferably has a hollow cylindrical shape, may be configured in a variety of ways. For example, it may comprise a fibrous mass.

Alternatively, it may comprise one or more layers of a helically wrapped separation medium and/or one or more drainage media, for example, as disclosed, in U. S. Patent No. 5,290,446, incorporated herein by reference in its entirety. Alternatively, it may be formed by melt-blowing fibers on a rotating core, as disclosed, for example, in U. S. Patent Nos. 4,726,901 and 5,846,438, both incorporated herein by reference in their entireties. One example of a helically wrapped separation element or a melt- blown separation element is available from Pall Corporation under the trade designation PROSEP. The separation pack may also comprise a pleated configuration, such as a straight radially extending pleat design. Another suitable configuration is a non-radially extending pleat design, as disclosed, for example, in U. S. Patent No. 5,543,047, incorporated herein by reference in its entirety. One type of non-radially pleated separation element is available from Pall Corporation under the trade designation SEPTRA.

Various types of separation media may be used with the present invention.

The separation media may include a wide variety of materials capable of forming a porous structure suitable for treating liquids, including porous metal media, porous ceramic media, porous glass fiber media, and/or porous polymeric media. The separation media may include fibrous media, such as a mass of fibers, fibrous mats, woven or non-woven fibrous sheets, and fibrous depth filters made by a variety of means, including melt blowing, Fourdrinier deposition, or air laying. In addition, the separation media may include a porous film or membrane.

Preferred media for a pleated separation element, for example, an element having a non-radial pleat configuration, include polyolefins, such as polyethylene, polypropylene, polymethylpentene; aramid; and fluoropolymers. Preferred media for fibrous deposits include polypropylene, TPX, polyester, and nylon. In a separation element with helically wrapped layer (s) of separation media, aramid and fluoropolymers, such as a HalarX ethylene chlorotrifluoroethylene copolymer, are preferred media.

The porous separation media of the present invention are not restricted to any particular pore sizes or structures. Where the separation medium comprises a filter medium, microporous and ultraporous filter media are preferred. The porous filter media preferably have removal ratings in the range from about 1 p or less to about 2001l or more, more preferably in the range from about 10 to about 90u.

The separation pack may also contain one or more additional layers such as an upstream drainage medium, a downstream drainage medium, and/or a cushioning layer. The upstream and downstream drainage media are disposed upstream and downstream of the upstream and downstream surfaces of the separation medium, respectively. The upstream and downstream drainage media can be made of any materials having suitable edgewise flow characteristics, e. g., suitable resistance to fluid flow through the layer in a direction parallel to its surface. The edgewise flow resistance of each drainage medium is preferably arranged to provide an even distribution of fluid along the surface of the separation medium. The drainage media may be in the form of a mesh or screen or a woven or non-woven porous sheet.

A cushioning layer may be disposed between the separation medium and one or both of the drainage media. The cushioning layer helps prevent abrasion of the separation medium due to rubbing contact with the drainage media during pressure fluctuations of the fluid system in which the filter is installed. The cushioning layer is preferably made of a material smoother than the drainage media and having a higher resistance to abrasion than the separation medium. For example, a suitable cushioning layer may be a polymeric non-woven fabric.

The separation element may also include an outer cage or wrap and a centrally disposed core for greater structural integrity and to reduce stresses on the separation pack during separation and backflush operations. The core serves to support the inner periphery of the separation pack against forces in the radially inward direction and also helps to give the separation element axial strength and rigidity against bending.

However, depending upon the forces acting on the separation element during separation, it may be possible to omit the core.

The cage may be disposed about the exterior of the separation pack. The cage serves to protect the separation pack during handling and to support the separation pack against forces in the radially outward direction. A wrap member may be used instead of, or in addition to, a cage to resist radially outward forces. The wrap may be made of any material which is compatible with the liquid being treated. Examples of

suitable materials for the wrap member include a metal mesh, such as a stainless steel mesh, and polymeric materials, such as a polymeric mesh or sheet. Preferred is a high tension mesh made of a polymeric material, such as a long chain polyethylene.

Methods of attaching the wrap member to the separation pack are described in U. S.

Pat. No. 5,543,047.

The separation element may have one or more closures, including end caps such as open end caps, blind end caps, and joiner caps, bonded to the separation pack.

At least one of the end caps may be provided with an aperture to allow flow of treated or untreated liquid along the interior of the separation element. The end caps may be fashioned from any suitably impervious material, such as a metallic, ceramic, or polymeric material, which is compatible with the liquid being treated. Conventional techniques may be used to attach the end caps to the separation pack, such as by use of an epoxy, by polycapping (as taught, for example, in U. S. Pat. No. 4,154,688), or by spin welding.

Separation elements embodying the invention are preferably treated with an oleophobic treatment solution so that the surface energy of at least the separation medium, and preferably the other components of the separation element, is lower than the surface tension of the oil to be removed from an aqueous solution containing particulate matter and oil. In this way, oil and/or particulate matter may be retained by the separation medium while aqueous liquid passes through the separation medium.

By"oleophobic"it is meant that the separation medium has a critical surface energy less than the surface tension of oil. Liquids with surface tensions lower than the critical surface energy of the separation medium tend to easily wet the separation medium. Liquids with surface tensions higher than the critical surface energy of the separation medium do not easily wet the separation medium.

The surface energy of the separation medium may, for example, be more specifically described as having a"critical wetting surface tension" (CWST). The CWST of a porous medium, in units of dynes/cm, is defined as the mean value of the surface tension of the liquid which is absorbed and that of a liquid of neighboring surface tension which is not absorbed, as disclosed, for example, in U. S. Patent No.

4,880,548. Preferably the CWST of the treated separation medium is in the range from about 18 dynes/cm or less to about 23 dynes/cm or more.

Preferably, the oleophobic treatment solution comprises an aqueous liquid and an oleophobic agent, which imparts the desired oleophobic properties to the separation element. The aqueous liquid may be deionized (DI) water and the preferred oleophobic agents include materials available from Minnesota Mining and Manufacturing Co. under the trade designations FX-259, FC-3375, FC-259, FC-808, FC-824, and FX-3569. The aqueous liquid and the oleophobic agent may be mixed in any suitable ratio. For example, about 8 parts of a suitable agent (by volume) may be mixed with about 100 parts of DI water to yield a preferred oleophobic treatment solution.

The separation element may be oleophobically treated to be able to separate oil from an aqueous liquid in a variety of ways. For example, one or more of the components of the separation element may be separately oleophobically treated, and then assembled to form the separation element. The oleophobic treatment solution may be placed in contact with one or more of the components of the element and the oleophobic agent may then be allowed to cure. Then, the components may be assembled to form the separation element. However, it is preferred that the separation element be completely assembled and then oleophobically treated as a unit.

The separation element, or components of the separation element, may be oleophobically treated by immersing the separation element in an oleophobic treatment solution containing an oleophobic agent. For example, the separation element may be immersed in the solution for a sufficient time to saturate the separation element. The time required to saturate the separation element may vary based on various factors, including the characteristics, such as thickness and pore structure, of the separation medium and the existence and characteristics of support/drainage media, core, cage or wrap and end caps. A wetting agent, such as isopropyl alcohol, may be used to aid the saturation of the separation element. After the oleophobic treatment solution has saturated the separation element, including the separation medium, the separation element may be removed from the solution and the oleophobic agent may be allowed to cure.

More preferably, the oleophobic treatment solution may be passed in one direction, e. g., inside-out or outside-in, through the separation element, including, for example, the outer wrap, the separation medium, and the drainage media, to saturate the separation element. The flow of solution may then be terminated and the oleophobic agent may then be allowed to cure. However, in accordance with one

aspect of the invention, after passing the oleophobic treatment solution in one direction, the solution may then be passed in the opposite direction through the separation element to even more completely saturate the separation element. Passing the solution back and forth in opposite directions through the separation element may be continued for as many cycles as desired to fully saturate the separation element with the oleophobic treatment solution. Preferably, the solution is passed through the separation element by a pressure differential across the element. For example, a vacuum may be drawn, or a higher pressure exerted, on one side of the separation element, forcing the solution through the separation element. Reversing the pressure differential reverses the direction of flow. During each half cycle, the solution may be directed through the separation element for a period of time which depends on the characteristics of the separation element. Preferably the period of time is in the range from about 0.5 minute or less to about 30 minutes or more. After the separation element has been fully saturated, the flow solution may be terminated and the oleophobic agent may then be allowed to cure.

By passing the oleophobic treatment solution through the separation element, especially back and forth through the separation element over one or more cycles, the components of the separation element may become more thoroughly saturated with the oleophobic treatment solution throughout the entire depth and breadth of each component. The flow of solution through the separation element drives the solution deep into and completely through the porous components, such as the outer wrap and the separation pack. Reversing the direction of flow ensures that any air pockets are driven from the porous components, allowing the oleophobic treatment solution to completely saturate all regions of the separation element. This is particularly advantageous for separation elements which include multiple wraps of a separation medium or separation and drainage media or which include pleated separation packs, especially non-radially pleated separation packs. These separation packs are thick; so passing the oleophobic treatment solution back and forth through the separation element best ensures that the separation pack is thoroughly saturated with the solution throughout the depth and breadth of the separation pack, as well as the outer wrap.

Once the oleophobic agent is cured, the components of the separation element, including, especially, the porous components such as the outer wrap, the drainage media, and the separation medium are highly oleophobic, preferably substantially

uniformly oleophobic, throughout the depth and/or breadth of each component, providing a far more effective and cleanable separation element.

Various alternative oleophobic treatment processes may also be used. For example, passing the oleophobic treatment solution through the separation element may be combined with immersing the separation element in the oleophobic treatment solution. Further, the oleophobic agent may be cured only once after the separation element has been saturated with the oleophobic treatment solution or multiple times throughout the saturation process.

After the separation element is fully contacted by the oleophobic treatment solution, the excess solution may be removed in any suitable manner. For example, the excess solution may be drained from the separation element. The separation element, coated with an oleophobic agent, may then be cured in any suitable manner.

For example, the separation element may be dried, by applying heat to the separation element. One method of drying the separation element includes drying the separation element in an oven, such as a fan-assisted oven, preferably in an inert atmosphere.

The temperature that the separation element may be exposed to may depend upon the maximum temperature that may be sustained by the oleophobic agent and the components of the separation element without damage. Preferred drying temperatures are in the range from about 75°C or less to about 82°C or more. The time required to cure the oleophobic agent depends on factors such as the characteristics of the separation element and the temperature used to dry the separation element. It is preferred that the separation element be cured for up to approximately 6 hours or more, more preferably, for about 4 hours.

EXAMPLE 1 A PROSEP filter element having a 1-inch outer diameter, a fibrous polypropylene filter medium, a perforated core, a long chain polyethylene mesh wrap surrounding the filter medium, and glass fiber filled polypropylene end caps is oleophobically treated. The untreated filter element may have a liquid service removal rating of 99% at 6 microns and 99.9% at 8 microns. The clean pressure drop in aqueous service may be 1.2 psi/gpm per 10 inch element at 70°F.

An oleophobic treatment solution is prepared by mixing an oleophobic agent obtained from Minnesota Mining and Manufacturing Company under the trade

designation FX 259 SCOTCHGARD Brand Fabric Protector, in concentration of 20 g/1 in deionized water. The concentration may be increased to 40 g/l.

The filter element is saturated with the oleophobic treatment solution, allowing sufficient time to wet out the entire filter element. After the filter element is wetted, the oleophobic treatment solution is then flowed for about 1 minute through the filter element from the outside-in by the application of a vacuum on one side of the filter element. The oleophobic treatment solution is then flowed for about 1 minute through the filter element in the opposite direction, i. e., inside-out, by application of a vacuum on the opposite side of the filter element. The filter element is then drained and cured by drying for 4 hours at 82°C in an oven.

The oleophobicity of the oleophobically treated filter element is tested by a Scotchgard full oil kit, available from Minnesota Mining and Manufacturing Company. The ratings provided by the test are from 1 to 8, with 1 indicating poor oleophobicity and 8 indicating high oleophobicity. The oleophobically treated filter element attains a rating of 7 or 8 across the entire depth of the filter element, including the wrap and the filter medium.

Another aspect of the present invention relates to regenerable, self-cleaning separation systems, such as a system for separating particulate matter and/or oil from fluids, e. g., aqueous liquids. An exemplary separation system separates particulate matter as well as oil from a liquid; so the system utilizes filter elements as the separation elements. However, for other separation systems, e. g., systems which separate a discontinuous phase and/or oil from a gas or liquid, the separation elements may, for example, comprise coalescer elements. Further, because the exemplary separation system separates particulate matter and/or oil from a liquid, the system preferably utilizes a backwash mechanism for cleaning the separation element.

However, for other separation systems, the system may utilize a blowback mechanism to clean the separation elements.

One example of a system embodying the present invention is illustrated schematically in Figures 1 to 4. The system, indicated generally by reference numeral 60, includes a housing 70 having at least one fluid inlet and at least one fluid outlet.

Preferably, the housing 70 includes a process liquid inlet 71 to introduce liquid being processed into a process liquid chamber 80. For example, the process inlet 71 may be located in a lower portion of the housing 70 and is associated with a flow control valve 72. A purified liquid outlet 77 allows for removal of purified liquid from a

purified liquid chamber 90. For example, the purified liquid outlet 77 may be located in an upper portion of the housing and associated with a flow control valve 78.

Various other components may be associated with the separation system. For example, a backwash mechanism including a backwash inlet 73 and associated valve 74 may be provided, e. g., combined with a vent conduit 75, which serves as a common conduit for both a vent 69 and the backwash liquid or assist gas. The vent conduit 75 and an associated valve 76 may be provided in the housing 70 for removal of air and other gases from the purified liquid chamber 90. A process fluid chamber vent 79 and an associated valve 82 may be provided in the housing 70 for removal of air and other gases from the process liquid chamber 80. A drain outlet 81, a drain conduit 83 and associated valve 88 may be provided in the bottom of the housing 70 in the process liquid chamber 80. A flush inlet 85 and an associated valve 84 may be separately formed in the bottom of the contaminated liquid chamber 80 or placed in fluid communication with the drain conduit 83, as illustrated in Figures 1 to 4. The separation system may also include additional valves, gauges, actuating mechanisms and control devices to effectively form a separation/backflushing operation described below.

In the embodiment illustrated in Figures 1 to 4, a tube sheet 100 serves as a support for the oleophobically treated filter elements 10 and as a fluid barrier to separate the process liquid chamber 80 from the purified fluid chamber 90. The oleophobically treated filter elements are preferably the helically wrapped elements, the melt-blown elements, or the non-radial pleated elements discussed above, although other filter elements may be used. Further, each of the filter elements is preferably oleophobically treated by any of the methods described above. The embodiment illustrated in Figures 1 to 4 includes a plurality of oleophobically treated filter elements arranged in parallel and secured downwardly depending from the tube sheet 100. A support plate (not shown) may extend across the housing to support the lower ends of the filter elements.

Another aspect of the invention relates to methods of separating particulate matter and/or oil from a fluid, e. g., a gas, a liquid or a mixture of gas and liquid.

Generally, the fluid, including the particulate matter and/or oil, is passed in one direction through an oleophobically treated porous medium. Recurrently, a cleaning fluid, e. g., a gas or a liquid or a mixture of gas and liquid, is passed preferably in the opposite direction through the oleophobically treated porous medium to remove

particulate matter and/or oil from the oleophobically treated porous medium. While a wide variety of fluids may be purified in accordance with the invention, the invention is particularly advantageous for removing particulate matter and oil from aqueous liquid mixtures containing particulate matter and oil, such as preferably machine coolants or washing liquids. The aqueous liquid mixture is contacted with an oleophobically treated separation medium to allow the aqueous phase to pass through the medium while particulate matter and oil are prevented from passing through the medium. Recurrently, the oleophobically treated separation elements may be cleaned, for example, by backwashing the elements.

One exemplary method may be described with reference to the regenerable separation system which is illustrated in Figures 1 to 4. As illustrated in Figure 1, process liquid, such as machine coolant or washing liquid, contaminated with oil and particulate matter, may be introduced through the process liquid inlet 71 to the process liquid chamber 80 of the housing 70 by opening the inlet valve 72. Air and other gases may be displaced from the process liquid chamber 80 via the vent 79 by opening the vent valve 82 to allow air or other gases or vapors contained in chamber 80 to escape through gas outlet vent 79, valve 82, vent conduit 87 and vent 69. As the contaminated process liquid fills the process liquid chamber 80 and approaches the tube sheet 100, most or all of the air contained in the process liquid chamber 80 may be discharged through the gas outlet vent 79, valve 82, vent tube 87 and vent 69.

Once the process liquid chamber 80 is filled with liquid and most or all of the air is displaced therefrom, the vent valve 82 may be closed.

As illustrated in Figure 2, liquid then passes into the oleophobically treated filter elements 10 through the oleophobically treated filter media and purified liquid emerges from the elements through the openings 101 of tube sheet 100 and passes into the purified liquid chamber 90. With the purified liquid outlet valve 78 closed and the vent valve 76 open, liquid fills the purified liquid chamber 90 and displaces air and any other gases or vapors present in the purified liquid chamber 90 through the outlet vent 69. When most or substantially all of the air is displaced from the purified liquid chamber 90, vent valve 76 may be closed. The vent cycles may be terminated by a liquid level switch (such as one of the capacitance-type switches) which senses the influent effluent at the proper level in the housing or related piping.

With the vent valves 76,82 and the backwash valve 74 closed and the process inlet valve 72 and the purified outlet valve 78 open, the filtration process may proceed

as illustrated in Figure 3. Contaminated process liquid flows through the process liquid inlet 71 into the process liquid chamber 80 and through the oleophobically treated filter elements 10, where the oil and particulate matter accumulate in or on the filter elements 10 as a cake. When the process liquid is an aqueous liquid, such as an aqueous machine coolant or washing solution, contaminated with oil and particulate matter, the helically wrapped filter elements, the melt-blown filter elements, and the non-radially pleated filter elements oleophobically treated as previously described have been found to be remarkably effective in removing both the oil and the particulate matter from the liquid without fouling unduly rapidly. From the filter elements 10 the purified liquid flows through the openings 101 in the tubesheet 100 into the purified liquid chamber 90 and out through the purified liquid outlet 77.

Filtration may proceed for a predetermined period of time or until the pressure drop across the filter elements rises to a predetermined level.

After filtration, the oleophobically treated filter elements 10 are preferably cleaned, for example, by backwashing or backflushing as illustrated in Figure 4. Any of several different backwashing techniques may be utilized. For example, the backflushing technique may comprise a gas-assisted backflush using the purified liquid in the purified liquid chamber 90 as the backwash liquid.

With the vent valves 76,82, the purified outlet valve 78 and the process inlet valve 72 closed, the backflush valve 74 may be opened, a high pressure gas, e. g., nitrogen or air, may be introduced into the purified liquid chamber 90. The drain valve 88 may be opened, either before, at the same time as, or after the backflush valve 74 is opened. Preferably, a rapidly opening drain valve and a large drain pipe are provided to create a hydraulic shock to the oleophobically treated filter elements causing the particulate cake on and/or within the filter elements to be more easily dislodged from the outer surface of and from within the oleophobically treated filter elements. With the drain valve open, the gas and purified liquid in the purified liquid chamber 90 are driven through the openings 101 in the tubesheet 100 into the interiors of the oleophobically treated filter elements 10 and outwardly through the filter elements 10, including the oleophobically treated filter media, flushing oil and particulate contaminants from the depth and outer surface of the filter elements 10.

Filter elements which are oleophobically treated as previously described have a high degree of oleophobicity throughout their depth and breadth. Consequently, the filter elements may be very effectively cleaned because the oil, as well as the particulate

matter, is easily flushed from all of the highly oleophobic regions of the filter elements, even deep within the filter media. The oil and particulate contaminants are then flushed from the housing through the drain pipe.

As shown in Figures 1 to 4, either the housing itself or the drain conduit 83 may be provided with a flush inlet. This is optionally provided in order that after a backwash cycle, the process liquid chamber 80 may be filled with another cleaning or flushing liquid and the material, including any particulate matter and oil, in process liquid chamber 80 may be flushed to the drain.

After cleaning the filter elements, the venting, filtration, and backwashing procedures may be repeated for as many cycles as desired.

Figures 1 to 4 illustrate one example of a regenerable, self-cleaning separation system. Although the single unit is highly efficient, purification of process liquid is intermittently halted during the backwash operation. To avoid such interruptions, two or more purification system units may be so arranged in parallel that when one unit stops the purification procedure in order to clean the oleophobically treated separation elements, the other unit (s) may be actuated and begin purifying contaminated fluid.

Use of such"duplex"systems employing two or more units permits continuous purification of fluid streams. An example of a duplex system is disclosed in United States Patent No. 5,628,916, which is incorporated by reference.

While the invention has been described in some detail by way of illustration and example, it should be understood that the invention is susceptible to various modifications and alternative forms, and is not restricted to the specific embodiments set forth. It should be understood that these specific embodiments are not intended to limit the invention but, on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.