(19)
`
`(12)
`
`Europaisches Patentamt
`European Patent Office
`een des brevets
`Office europeen des brevets
`
`EUROPEAN PATENT APPLICATION
`
`£ P 0 7 9 1 3 8 3 A 1
`
`(43) Date of publication:
`27.08.1997 Bulletin 1997/35
`
`(21) Application number: 97301285.9
`
`(22) Date of filing: 26.02.1997
`
`(84) Designated Contracting States:
`DE FR GB IT SE
`
`(30) Priority: 26.02.1996 J P 65389/96
`
`(71) Applicant: JAPAN GORE-TEX, INC.
`Setagaya-ku Tokyo-To 156 (JP)
`
`(72) Inventors:
`• Hamasaki, Sadakatsu
`Okayama-Shi, Okayama-Ken 709-08 (JP)
`
`(54)
`
`An assembly for deaeration of liquids
`
`(51) Intel e B01D 19/00
`
`• Kobayashi, Masayuki
`Okayama-Shi, Okayama-ken 701-11 (JP)
`
`(74) Representative: McCallum, William Potter et al
`Cruikshank & Fairweather
`19 Royal Exchange Square
`Glasgow G1 3AE Scotland (GB)
`
`A deaeration assembly for removal of air or oth-
`(57)
`er gases dissolved in a liquid. The assembly includes a
`deaeration element having a gas-channel-forming com-
`ponent enclosed and sealed within an envelope formed
`of a nonporous fluoropolymer film. The assembly also
`incudes a liquid-channel- forming component which can
`be positioned on the outside of the element, or can be
`
`enclosed with the gas-channel-forming component
`within the element. The assembly can be formed in spi-
`ral-wound or folded configurations for installation in a
`deaeration module or apparatus. The deaeration as-
`sembly is useful for removal of gases dissolved in chem-
`ically aggressive liquids, high-purity liquids, and other
`special liquids.
`
`CO
`00
`CO
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`O)
`Is-
`o
`a .
`LU
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`Printed by Jouve, 75001 PARIS (FR)
`
`GE-1031.001
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`

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`1
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`EP 0 791 383 A1
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`2
`
`Description
`
`deaerated.
`According to a first aspect of the present invention,
`there is provided a deaeration assembly for removal of
`a gas from a liquid comprising:
`
`(a) a deaeration element having a gas-channel-
`forming component enclosed and sealed within an
`envelope formed of a non-porous fluoropolymer
`film, said envelope having inward-facing and out-
`ward-facing surfaces and at least one port leading
`from the inside to the outside of said envelope for
`passage of gases permeating into the element to a
`location external to the assembly; and
`(b) a liquid-channel-forming component contiguous
`with at least one outward-facing surface of said
`fluoropolymer film envelope.
`
`In use liquid to be deaerated is passed over the out-
`ward-facing surface of the element at a pressure higher
`than the pressure inside the element. The gas channels
`formed by the gas-channel-forming component provide
`pathways through the inside of the envelope for gases
`which have permeated from the liquid through the film
`forming the envelope, to the port. The port provides a
`means for transfer of gases to a location external to the
`apparatus. The liquid-channel-forming component pro-
`vides pathways for liquid to pass over and to contact the
`outward-facing surface of the element. When the ele-
`ment is formed into a spiral or folded structure, the liquid-
`channel-forming component also serves as a spacer be-
`tween adjacent layers of the element.
`According to a further aspect of the present inven-
`tion, there is provided a deaeration assembly for remov-
`al of a gas from a liquid comprising a deaeration element
`having a gas-channel-forming component and a liquid-
`channel-forming component enclosed and sealed within
`an envelope formed of a non-porous fluoropolymer film,
`said envelope having inward-facing and outward-facing
`surfaces and at least one port leading from the inside to
`the outside of said envelope for passage of gases per-
`meating into the element to a location external to the
`assembly;
`
`wherein said liquid-channel-forming component is
`contiguous with at least one inward-facing surface
`of said fluoropolymer film envelope, and
`wherein the region of said fluoropolymer film enve-
`lope in contact with said liquid-channel-forming
`component conforms to the channel-forming con-
`tours of the liquid-channel-forming component to
`form liquid channels in said outward-facing surface.
`
`The present invention also involves a deaeration el-
`ement for use in a deaeration assembly in accordance
`with the invention.
`Embodiments of the present invention will now be
`described, by way of example, with reference to the ac-
`companying drawings, in which:-
`
`s
`
`30
`
`The present invention relates to apparatus for de-
`aeration of liquids, more particularly, to an assembly for
`removing a gas that is dissolved in a liquid.
`That corrosive, oxidative, reactive, and contaminat-
`ing properties harmful to certain products and equip-
`ment is associated with air or other gases dissolved in
`liquid is well known. To reduce or minimize these harm-
`ful effects are among many reasons why it is sometimes 10
`desirable to remove air and/or other gases dissolved in
`a liquid.
`Known apparatus for performing such deaeration or
`degassing operations are modules which use a porous
`polymeric membrane material through which the dis- 15
`solved gas can permeate as the means for removing the
`gas from the liquid. Typically, in this type of apparatus,
`deaeration is accomplished by having one side of the
`membrane contact the liquid to be deaerated, and on
`the other side of the membrane provide a gas channel, 20
`usually under reduced pressure, to draw away the gas
`permeating through the membrane. Such systems are
`quite effective in deaerating water of normal purity.
`However, a problem with the above-mentioned de-
`aeration apparatus in which a porous polymeric mem- 25
`brane material is used is that, when the liquid to be de-
`aerated is a solvent, a liquid fat or oil, or an aqueous
`liquid that contains a surfactant, the liquid tends to wet
`the membrane material and penetrate through the
`pores, thus precluding deaeration.
`In an effort to solve this problem, there have been
`proposals for a deaeration apparatus that makes use of
`a non-porous membrane material, for example, one ob-
`tained by coating the surface of a porous polymeric sup-
`port membrane with a silicone resin, or other polymer 35
`resin through which gases can permeate at acceptable
`rates. While this apparatus does indeed allow deaera-
`tion to be performed when the liquid to be deaerated is
`a relatively mild solvent, liquid fat or oil, or aqueous liq-
`uid that contains a surfactant, they are not successfully 40
`used when the liquid to be deaerated is of exceptionally
`high purity or is chemically aggressive. For example, liq-
`uids such as the deionized water required for semicon-
`ductor processing, or special liquids such as photoresist
`liquids or developing fluids used in the manufacture of 45
`semiconductor products. Such liquid tend to leach sub-
`stances from the separation membranes which then
`contaminate the liquids; or the liquids may cause the
`membranes to degrade and fail.
`It is an object of the present invention to obviate or
`mitigate at least one of these disadvantages. This may
`be achieved by providing an assembly for use in a de-
`aeration apparatus with which such special high purity
`and aggressive liquids can be deaerated.
`The deaeration assembly for use in a deaeration 55
`may resist attack by high purity or aggressive liquids,
`and may minimize leaching of materials from the assem-
`bly which could harmfully contaminate the liquid to be
`
`so
`
`2
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`GE-1031.002
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`Figure 1 is a cross-sectional view of the element
`containing a gas-channel-forming component en-
`closed by an envelope having an unreinforced edge
`seal;
`Figure 2 is a partial cross-sectional view of the ele-
`ment with an envelope having a reinforced edge
`seal;
`Figure 3 is a cross-sectional view of a gas-channel-
`forming component;
`Figure 4 is a cross-sectional view of a deaeration
`element containing a gas-channel-forming compo-
`nent;
`Figure 5 is a cross-sectional view of an example of
`a connection between a gas removal tube and the
`envelope at a port in the envelope;
`Figure 6 shows a spirally-wound element with a liq-
`interposed be-
`uid-channel-forming component
`tween adjacent outer surfaces of the element;
`Figure 7 shows a folded element with a liquid-chan-
`nel-forming component interposed between adja-
`cent outer surface of the element;
`Figure 8 is a cross-section view of a module con-
`taining an embodiment of the assembly of the in-
`vention;
`Figure 9 is a partial cross-sectional and perspective
`view of a deaeration element in which both the gas-
`channel-forming component and liquid-channel-
`forming component are contained within the enve-
`lope;
`Figure 10 is a partial cross-sectional view of adja-
`cent element layers of another deaeration element
`in which both the gas-channel-forming component
`and liquid-channel-forming component are con-
`tained within the envelope.
`
`With reference to the figures, the invention will be
`described in detail. To facilitate understanding, the same
`numerical identifiers for elements common to the figures
`will be used through the figures.
`The term "non-porous" is used herein simply to de-
`scribe a material which is essentially free of pores or
`voids, and which is a barrier to bulk flow of liquids or
`gases.
`While a material may be non-porous, it may still be
`"permeable" to liquids or gases. The term "permeable",
`(and correspondingly "impermeable"), or a variation
`thereof, is used herein to describe the property of a ma-
`terial to transport (or not transport) a particular species,
`such as gas or water-vapor, through the material. The
`term describes the overall property of mass transfer by
`diffusion at a molecular level, and in no way implies any
`particular scientific mechanism by which this occurs.
`In Figure 1 is shown a cross-section of a deaeration
`element 1 which includes an envelope 4 made of a sin-
`gle sheet of non-porous fluoropolymer film. The enve-
`lope encloses a porous gas-channel-forming material 2
`on each side of which is laminated a porous polymeric
`membrane 3. The overlapping edges of the fluoropoly-
`
`5
`
`10
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`30
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`35
`
`mer film envelope 4 are sealed at an edge region 5
`which extends along the length and across the ends of
`the deaeration element 1 .
`Non-porous fluoropolymer films are used to make
`the envelope 4 of the deaeration element 1 due to their
`well known chemical inertness, i.e., they are highly re-
`sistant to attack by aggressive chemicals, solvents, oils,
`and high purity water or other aqueous liquids, and
`thereby minimize contamination of liquids in contact with
`them. Many fluoropolymers can be used so long as non-
`porous films made of them have sufficient chemical re-
`sistance to the liquids to which they will be exposed and
`are sufficiently permeable by the gases dissolved or en-
`trained in the liquids. Preferably, the fluoropolymers are
`is melt-processible thermoplastic fluoropolymers such as
`tetrafluoroethylene-hexafluoropropylene
`copolymer
`(FEP), tetrafluoroethylene-(perfluoroalkyl) vinyl ether
`copolymer (PFA), amorphous fluoropolymers, such as
`TEFLON AF® amorphous fluoropolymer, and the like.
`20 Such fluoropolymers are well know in the art and are
`readily available in sheet and film form from a number
`of suppliers.
`The thickness of the non-porous fluoropolymer film
`influences properties such as gas permeation rate,
`25 strength, processability, durability in use, etc., and may
`necessitate some compromise or trade-offs between
`desired properties. The film used to make the envelope
`4 should be in the range 5 to 1 00 micrometers thick, and
`preferably in the range 1 0 to 40 micrometers thick. If the
`film is less than about 5 micrometers thick, it will be dif-
`ficult to handle and will lack pressure resistance and du-
`rability in use. On the other hand, if the film is thicker
`than about 100 micrometers, gas permeation rates
`through the film may be too low to be useful.
`There are no particular limitations on the length and
`width dimensions of the envelope 4 except as dictated
`by deaeration performance desired and availability of
`materials. Typically, the envelope 4 should be in the
`range 10 to 100 centimeters wide and in the range 2 to
`40 20 meters long. As the element 1 is typically operated
`at a pressure differential between the outside and inside
`of the element, the inside being at a lower pressure,
`there are some practical limitations imposed due to
`pressure drop across the element walls or through the
`interior of the element. If the envelope is too long, it will
`be difficult to maintain the desired pressure differential
`across the walls of the element over its full length. On
`the other hand, if the envelope is too short there may
`not be sufficient surface area available to achieve the
`so desired gas permeation rate. Nevertheless, even with
`these considerations, there is considerable flexibility in
`choosing suitable length and width dimensions for the
`envelope 4.
`The non-porous fluoropolymer film envelope 4 can
`55 be made from a single sheet as shown in Figure 1, or
`can be made using two sheets of non-porous fluoropol-
`ymer film, in which case the seal region 5 extends
`around the entire periphery of the element. Alternatively,
`
`45
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`EP 0 791 383 A1
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`thin-walled tubes of a melt-processible thermoplastic
`fluoropolymer can be extruded or blow-molded and flat-
`tened to form the envelope 4. In this case, only the ends
`will have a seal region 5. Sealing the open edges of an
`envelope 4 made of a melt-processible thermoplastic
`fluoropolymer film can be readily accomplished by ap-
`plication of heat and pressure at seal regions 5 where
`the film overlaps the porous gas-channel-forming com-
`ponent 2. Many heat sealing methods are known in the
`art and can be used.
`An alternative seal region 15 is illustrated in Figure
`2. In this configuration reinforcing strips 6 of porous pol-
`ytetrafluoroethylene (PTFE) film are placed on the out-
`ward-facing surfaces of the envelope 4 at the seal region
`1 5 prior to heat sealing. When heat sealing is performed
`some of the melt-processible fluoropolymer film pene-
`trates into the porous PTFE film and the strength and
`reliability of the seal are enhanced. The porous PTFE
`film also serves as an excellent release material which
`prevents contact between melted thermoplastic fluor-
`opolymer and equipment surfaces applying heat and
`pressure to the seal region 15. Preferably, the porous
`PTFE film is porous expanded polytetrafluoroethylene
`film.
`The interior of the deaeration element 1 contains a
`gas-channel-forming component 2 which provides path-
`ways through the inside of the element for gases which
`have permeated from the liquid through the film forming
`the envelope 4, to at least one port through the film en-
`velope 4 which is connected to means for transfer of
`gases to a location external to the apparatus. The gas-
`channel-forming component must be able to withstand
`the compressive forces exerted on it, be compatible with
`the gases to be removed from the liquid, and, within
`these limitations, have a structure as open or porous as
`possible so as to minimize the pressure drop through
`the interior of the element 1 . Preferably the gas-channel-
`forming component 2 is made of a synthetic polymer,
`although other materials can also be used. Suitable pol-
`ymeric material and forms are known in the art and are
`available commercially. Suitable materials include poly-
`mers such as polyolefins, polyesters, nylons, poly-
`urethanes, polycarbonates, polystyrenes, polyvinyl
`chloride, polyvinylidene chloride, and the like; or fluor-
`opolymers such as PTFE, FEP, PFA, polyvinylfluoride,
`polyvinylidene fluoride, and the like. Suitable forms in-
`clude nonwoven fabric, knit fabric, woven fabric or
`mesh, open-cell foams, porous membranes, and the
`like. The thickness of the gas-channel-forming compo-
`nent 2 is preferably in the range of about 0.3 millimeters
`to about 2 millimeters, and should have length and width
`dimensions somewhat less, about 2 millimeters to about
`10 millimeters less, than the length and width dimen-
`sions of the envelope 4 in order to provide sufficient area
`to form the seal region 5.
`It can be desirable to laminate a porous membrane
`3 to both sides of the gas-channel-forming component
`2, to form a subassembly as shown in Figure 3; or to
`
`one side of the gas-channel-forming component 2, as
`shown in Figure 4, where the subassembly is shown po-
`sitioned in the fluoropolymer envelope 4 of the element
`1 . The porous membrane 3 provides support to the non-
`5 porous fluoropolymer film forming the envelope 4 and
`helps to more uniformly distribute the compressive load
`on the gas-channel-forming component 2 encountered
`during operation. By providing such support to the fluor-
`opolymer film, a thinner film can be used to form the en-
`10 velope 4, thereby increasing the gas permeation rate
`from the liquid outside the element to the gas channels
`inside the element. Preferably the porous membrane 3
`is also made of a synthetic polymer and its selection is
`subject to the same constraints listed above for the gas-
`'s channel-forming component. Most preferred are porous
`membranes of polytetrafluoroethylene.
`Porous polytetrafluoroethylene sheet or film suita-
`ble for use in the invention can be made by processes
`known in the art, for example, by stretching or drawing
`20 processes, by papermaking processes, by processes in
`which filler materials are incorporated with the PTFE
`resin and which are subsequently removed to leave a
`porous structure, or by powder sintering processes.
`Preferably the porous polytetrafluoroethylene mem-
`25
`25 brane is porous expanded polytetrafluoroethylene film
`having a structure of interconnected nodes and fibrils,
`as described in U.S. Patent Nos. 3,953,566 and
`4,187,390 which describe the preferred material and
`processes for making them.
`The porous membrane should have a pore volume
`in the range of about 30 to 95 percent, a nominal pore
`size in the range of about 0.1 to 100 micrometers, and
`be about 5 to about 100 micrometers thick.
`Lamination of the porous membrane 3 to the gas-
`35
`35 channel-forming component 2 can be done using con-
`ventional methods and equipment, for example, by ad-
`hesive bonding. The adhesive can be applied to the sur-
`face to be bonded of either layer, and should be applied
`in a non-continuous pattern. A non-continuous pattern
`40 of adhesive is used herein to indicate a layer of adhesive
`40
`which is applied to a surface so as to not form a non-
`porous continuous film. For example, a layer applied to
`a surface as a pattern of discrete dots, a porous non-
`woven web or mesh, or the like.
`The adhesive may be selected from many known in
`the art. The adhesive can be a thermoplastic, thermo-
`setting, or reaction curing type, in liquid or solid form,
`selected from the classes including, but not limited to,
`polyamides, polyacrylamides, polyesters, polyolefins,
`so polyurethanes, and the like. The adhesive should be ap-
`50
`plied so that it forms a porous (non-continuous) gas-per-
`meable layer which minimizes resistance to air flow
`while adhering the porous membrane 3 to the gas-chan-
`nel-forming component 2. Preferably, the adhesive is
`55 applied so as to cover about 30 percent or less of the
`surface. Suitable application means include gravure
`printing, spray coating, powder coating, interposing a
`non-woven web of adhesive, and the like.
`
`30
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`Lamination of the porous membrane 3 to the gas-
`channel-forming component 2 can be also be done us-
`ing conventional heat-fusing methods and equipment,
`for example, by application of heat and pressure in the
`nip between rolls, or by a heated platen press.
`One or more ports, or openings, are provided in the
`element 1 for passage of gases out of the element.
`Transfer means, preferably a tube of the same melt-
`processible thermoplastic fluoropolymer used to form
`the envelope 4, for removal of gases from inside the el-
`ement to a location external to the module or apparatus
`in which the element 1 is positioned is connected to the
`port by any convenient method. The outside diameter
`of the tube should be about 4 millimeters to about 10
`millimeters, and the wall thickness about 0.5 millimeters
`to about 1 millimeter. By way of example only, one such
`connection is illustrated in Figure 5.
`In Figure 5 is shown a section of one wall of the
`melt-processible thermoplastic fluoropolymer film enve-
`lope 4 in which an opening 22 leading to the inside of
`the element has been made. An end of a tube 23, pref-
`erably of the same fluoropolymer as the envelope, is po-
`sitioned around the opening 22. A fluoropolymer ring 27
`and porous PTFE film 26 are pressed into place around
`the end of the tube 23 so that, when finally positioned,
`the film forming the envelope 4 and the PTFE film 26
`overlap the end of the tube 23, and the edge of the ring
`27 is approximately even with the end of the tube 23.
`The portion of the envelope 4 overlapping the end of the
`tube 23 is heat sealed to the end of the tube by applica-
`tion of a heated plate (not shown) to the PTFE film por-
`tion overlapping the end of the tube, and a strong air-
`tight seal is formed. The fluoropolymer ring 25 serves
`as a strain relief for the connection and also prevents
`distortion or contraction of the envelope film during the
`heat sealing step. The porous PTFE film 26 serves to
`reinforce the seal region and serves as a release mate-
`rial to prevent melted fluoropolymer from sticking to the
`heated plate.
`To most efficiently use the element, it may be posi-
`tioned in a module or apparatus in a spiral-wound con-
`figuration, as shown in Figure 6; or in a folded configu-
`ration, as shown in Figure 7. In such configurations a
`space between adjacent element layers must be provid-
`ed to permit the liquid to be deaerated to contact the
`outer surface of the element and to permit the liquid to
`flow through the module. This space can be provided by
`interposing a liquid-channel-forming component 12 be-
`tween adjacent layers of the element 1 , as shown in Fig-
`ures 6 and 7. The void size and distance between ele-
`ment layers provided by the liquid-channel-forming
`component 12 should be in the range 50 to 1000 mi-
`crometers, preferably in the range 100 to 400 microm-
`eters. If the spacing is larger than 1000 micrometers,
`deaeration performance will suffer as the diffusion dis-
`tance for the gas through the liquid will become too
`great. If the spacing is less than 50 micrometers, the
`pressure drop of the liquid through the liquid-channel-
`
`15
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`25
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`30
`
`forming component may become too high. The length
`of the liquid-channel-forming compnonent should be
`roughly the same as the length of the deaeration ele-
`ment. The width of the liquid-channel-forming compo-
`5 nent should be at least as wide as the deaeration ele-
`ment, and may be somewhat wider (about 1-2 centim-
`eters) so as to extend beyond and protect the longitudi-
`nal edges of the fluoropolymer film envelope.
`As with the gas-channel-forming component de-
`10 scribed earlier, suitable materials include polymers such
`as polyolefins, polyesters, nylons, polyurethanes, poly-
`carbonates, polystyrenes, polyvinyl chloride, polyvinyli-
`dene chloride, and the like, or fluoropolymers such as
`PTFE, FEP, PFA, polyvinylfluoride, polyvinylidene fluo-
`ride, and the like, in forms such as nonwoven fabric, knit
`fabric, woven fabric or mesh, and the like. In systems in
`which chemically aggressive and high purity liquids, or
`special liquids in which contamination must be mini-
`mized, it is preferred that the liquid-channel-forming
`20 component be made of a fluoropolymer such as PTFE,
`PFA, FEP.
`A cross-sectional view of a deaeration apparatus or
`module containing a spiral-wound assembly of the in-
`vention is shown in Figure 8. The module 41 has a cy-
`lindrical casing body 41 a, and end caps 41 b at each end.
`A spirally-wound element 1 , with a liquid-channel-form-
`ing component 12 interposed between adjacent layers
`of the element, is disposed in the casing body. A gas
`removal tube 23 is connected to the element 1 and exits
`the module through a fitting in an end cap 41 b. An inlet
`opening 46 for a liquid to be deaerated, and a vent open-
`ing 48 for removal of air during initial filling of the module
`with the liquid, are provided in one end cap. In the op-
`posing end cap is an outlet opening 47 for liquid which
`35 has been deaerated. At each end of the spiral-wound
`assembly is a porous spacer element 49 which serves
`both to space the assembly within the module and pro-
`vides passages for liquid. The module shown is a con-
`ventional type, well known in the art, as are the materials
`40 and constructions methods to make it, which are select-
`ed according to the fluids and operating conditions
`which will be encountered in the projected end-use.
`Again, in systems in which chemically aggressive and
`high purity liquids, or special liquids in which contami-
`45 nation must be minimized, it is preferred that the module
`be made of a fluoropolymer such as PTFE, PFA or FEP,
`or the liquid-wetted surfaces be lined with a fluoropoly-
`mer.
`After the module is initially filled with a liquid to be
`so deaerated, and trapped air exhausted through the vent
`opening 48, liquid flow through the liquid-channel-form-
`ing component is begun and the interior of the element
`1 is operated at a pressure lower than the pressure of
`the liquid flowing over the outer surface of the element,
`for example, by drawing a vacuum through the gas re-
`moval tube 23. Gas dissolved in the liquid, driven by the
`pressure differential between the liquid and the interior
`of the element, diffuses out of the liquid and permeates
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`forming component to generally conform to the high
`spots and depressions of the woven material to form
`corresponding high spots and depressions in the out-
`ward-facing surface to form channels 65 for passage of
`liquids over the outward-facing surface of the element
`61.
`
`In this embodiment of the assembly of the invention
`a liquid-channel-forming component external to the el-
`ement is not needed which significantly reduces the risk
`10 of contamination of the liquids, reduces material costs,
`and simplifies manufacture of the assembly.
`
`Example 1
`
`through the fluoropolymer film forming the envelope of
`the element, passes through the gas channels formed
`inside the element to the gas removal tube, and thence
`out of the module. At the same time, the dissolved gas
`concentration in the liquid becomes progressively lower
`as the liquid flows over and past the surface of the de-
`aeration element.
`The deaeration assembly of the invention accom-
`plishes the efficient removal of gases dissolved not only
`in ordinary liquids such as water or aqueous solutions,
`but also in chemically aggressive, high purity, and other
`special liquids, while contributing virtually no contami-
`nants to the liquids.
`Referring to Figures 9 and 1 0, another embodiment
`of the deaeration assembly of the invention is shown.
`The second embodiment differs from the embodiment
`described hereinabove in that [i] both the liquid-channel-
`forming component and gas-channel-forming compo-
`nent are enclosed within the fluoropolymer film forming
`the envelope of the element, [ii] the liquid-channel-form-
`ing component is contiguous with at least one inward-
`facing surface of the fluoropolymer film, [iii] the fluor-
`opolymer film conforms to the contours of the liquid-
`channel-forming component thereby creating channels
`along the outward-facing surface of the fluoropolymer
`film, and [iv] the liquid-channel-forming component does
`not come in contact with the liquid to be deaerated. In
`other respects, the second embodiment is the same as
`the embodiment described earlier.
`Figure 9 shows an element 51 consisting of a gas-
`channel-forming subassembly 52 of a porous mem-
`brane laminated to each side of a gas-channel-forming
`component (as depicted in Figure 3), and a liquid-chan-
`nel-forming component 53 of a porous ribbed material,
`each component contiguous with an inward-facing sur-
`face of an envelope 54 of a non-porous fluoropolymer
`film. The ribbed material of the liquid-channel-forming
`component can be, for example, a knitted ribbed fabric
`of synthetic polymer fibers. In operation, the pressure
`differential between the outside and the inside of the el-
`ement