EP0156837A1 - Membrane pour osmose inverse et son procede de fabrication - Google Patents

Membrane pour osmose inverse et son procede de fabrication

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Publication number
EP0156837A1
EP0156837A1 EP19840903388 EP84903388A EP0156837A1 EP 0156837 A1 EP0156837 A1 EP 0156837A1 EP 19840903388 EP19840903388 EP 19840903388 EP 84903388 A EP84903388 A EP 84903388A EP 0156837 A1 EP0156837 A1 EP 0156837A1
Authority
EP
European Patent Office
Prior art keywords
layer
hydrogel
support
polymer
membrane
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19840903388
Other languages
German (de)
English (en)
Inventor
Wolfgang J. Wrasidlo
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Brunswick Corp
Original Assignee
Brunswick Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Brunswick Corp filed Critical Brunswick Corp
Publication of EP0156837A1 publication Critical patent/EP0156837A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction

Definitions

  • This invention pertains to new and improved membranes which are primarily useful in the treatment of water by reverse osmosis but which are also capable of other uses.
  • the invention also pertains to the process of making such membranes.
  • a reverse osmosis membrane should have certain desirable features. It should be comparatively easy and inexpensive to make. In addition, a satisfactory membrane of this type should be capable of withstanding the usual handling and storing prior to and during installation in a reverse osmosis apparatus without physical damage or deterioration. Within such an apparatus a reverse osmosis membrane must present as low a resistance to the movement or flow of water from one side or surface of the membrane to the other as reasonably possible. Normally, the membrane must be capable of passing a significant quantity of water per unit time. In addition, • the membrane should be capable of withstanding the pressure normally applied to the treated water and the pressure differential across the membrane without detrimental affect on the flow characteristics of the membrane.
  • a satisfactory reverse osmosis membrane must also not be affected by biodegradation and/or chemical reaction under the conditions or circumstances of use.
  • the overall economics of a satisfactory reverse osmosis membrane require that', for some uses, the membrane be relatively satisfactory in removing contaminants, such as sodium chloride, from water, but in most applications, such membranes need not have to remove substantially all of such a contaminant from water. Water having a limited salt content may be tolerated and used, for example, by many plants and animals.
  • a more specific object of the present invention is to provide new and improved reverse osmosis membranes.
  • Another object of the present invention is to provide reverse osmosis membranes which are comparatively easy and inexpensive to manufacture and which are not apt to be damaged as a result of the normal handling and storage prior to and during their installation.
  • Still another object of the present invention is to provide reverse osmosis membranes which exhibit comparatively limited resistance to the movement or flow of water and which are capable of withstanding the pressures normally encountered during use.
  • Yet another object of this invention is to provide reverse osmosis membranes which are not damaged by either biodegradation or chemical reaction in the usual or normal conditions or circumstances of their use.
  • An additional object of this invention is to provide a process for making these reverse osmosis membranes.
  • the present invention provides, in one aspect, a reverse osmosis membrane which comprises an active layer and a physical support.
  • the active layer consists essentially of a continuous non-porous uniform film of an organic film-forming polymer which is substantially inert in the presence of
  • OMPI ⁇ IPO ' ' oxidizing agent having a sufficient oxidizing potential to serve as a sterilizing agent.
  • the film has a thickness of from about 50 to about 1500 Angstroms.
  • a preferred active layer is cellulose triacetate.
  • the physical support for the active layer comprises a highly asymmetric polymeric membrane which contains a skin and a porous substructure.
  • the skin contains pores which have an average pore diameter of from about 0.005 to about 3.0 microns.
  • the substructure comprises a reticulated structure which contains pores having an average pore diameter of from about 10 to about 20,000 times as large as the average pore diameter of the pores of the skin.
  • This asymmetric support has a bulk porosity greater than about 70%.
  • a preferred physical support for the support layer is polyvinylidene fluoride.
  • the reverse osmosis membrane of the present invention preferably utilizes as a support for the active layer an asymmetric layer or member of a relatively rigid or stiff character in which the porosity increases in accordance with the distance from a specific surface of the support layer or membrane.
  • This surface of the support holds and is preferably bonded to a hydrogel layer serving several functions. It physically supports the active layer and in addition it serves to facilitate movement of water from the entire surface of the active layer to the pores in the support layer. This latter function is beneficial in increasing the flow through the entire membrane.
  • This invention is also intended to provide a new and improved process for the manufacture of the reverse osmosis membranes described hereinabove. More specifically, it is intended to provide a process as hereinafter indicated which may be easily and conveniently carried out at a comparatively low cost and which is especially desirable because of the physical characteristics of reverse osmosis membranes as are produced by this process.
  • This process comprises a) applying to the surface of the porous support a water-containing solution of prepolymer chains capable of reacting so as to form an active layer, and b) concurrently reducing the solvent content of this solution and reacting the prepolymer chains so as to form the active layer.
  • the viscosity of the solution, the time and manner of contact of the solution with the surface, and the rate and conditions of the solvent removal are such that the active layer is formed on the surface of the support without penetration of the active layer into the pores of the support to an extent sufficient to detrimentally affect the ability of water to flow through the support.
  • the active layer is located on the hydro ⁇ gel layer after the hydrogel layer is formed.
  • the hydrogel layer reacts with the support as it is created so as to be cross-linked with the support.
  • the active layer is preferably cross-linked to the hydrogel layer as it is formed.
  • reverse osmosis membrane 10 in accordance with this invention which includes porous support 12 having surface 14 supporting hydrogel layer 16.
  • This layer 16 has further surface 18 remote from support 12 which in turn carries and physically supports active layer 20.
  • numeral 14 may be considered as designating the surface of layer 16 adjacent to support 12.
  • numeral 18 may be considered as designating the surface of layer 20 adjacent layer 16.
  • Support 12 may be referred to as a support layer or member. Support 12 may be reinforced by another support (not shown) if this is desirable for
  • support 12 may be any porous member physically capable of supporting layers 16 and 20.
  • support 12 may consist of a layer or sheet of paper, a layer or sheet of a felted, woven, knitted fabric or a layer or sheet of a perforated material. It will, of course, be recognized that such layers or sheets are known and are capable of being utilized for mechanical filtration purposes.
  • support 12 should preferably provide a minimum resistance to fluid flow from surface 14 to another surface 22 to support 12. Within limits it is.possible to reduce the resistance to fluid flow through support 12 by increasing the number of pores within support 12 and by increasing the relative sizes or dimensions of these pores. When carried to an extreme, however, expedients of this type are self-defeating since to be effective as a support, support 12 must have sufficient mass to hold layer 16 and 20 so that they are not likely to become physically damaged.
  • the pores in support 12 must be relatively small in order to minimize the chance of damage to layers 16 and 20 when membrane 10 is subjected to a fluid pressure differential. Also, in order to minimize resistance to fluid flow these pores should be as "short" as possible. However, the lengths
  • support 12 preferably has a physical character as indicated diagrammatically in the drawing.
  • This support 12 is an asymmetric support in which surface 14 is essentially a film permeated by a multitude of small holes or pores 26.
  • the material within support 12 is "arranged" in a manner somewhat suggestive of the manner in which arches are utilized in many churches and similar buildings so that surface 24 of support 12 is essentially of an open character and only is intersected by sufficient material in post or pillar-like form so that support 12 can adequately serve its function. Between surfaces 14 and 24 both the material content and the porosity of support 12 vary with distance.
  • Pores 26 should preferably cover from about 10 to about 30 percent of the area of surface 14 and for from about 70 to about 95 percent of the surface area of surface 22 to be open.
  • the preferred support 12 used with the present invention may be described as an asymmetric layer, film or membrane containing on one surface from about 10 to about 30 percent open area and, on the other surface, from about 70 to about 95 percent open area. The amount of open area gradually changes in accordance with the distance between these two surfaces.
  • Pores 26 on surface 14 should be sufficiently small so that there is no tendency of layers 16 and 20 to collapse into or rupture adjacent to these pores during the use of membrane 10. On the other hand, if pores 26 are too small they tend to impede flow through support 12. Accordingly, it is preferred that holes or pores 26 in surface 14 should be at least about 0.05 microns in diameter and should be no greater than about 0.5 microns in diameter. This maximum dimension is related to the characteristics and dimensions of layers 16 and 20 and may be varied somewhat in accordance with the changes in these layers 16 and 20 permissible within the scope of the present invention. The minimum figure is based upon flow control considerations which are substantially unrelated to the character of layers 16 and 20.
  • a preferred support 12 in accordance with the present invention may also be varied between comparatively wide limits. Regardless of whether or not support 12 is asymmetric in character as indicated in the preceding discussion, it must contain sufficient mass so as to be capable of physically supporting layers 16 and 20 so that these layers will not be damaged during use of membrane
  • the amount of material required to attain a desired reinforcement may be readily determined by routine experimentation and will vary somewhat depending upon whether or not an auxiliary support (not shown) is used with support 12 and depending upon the properties of the material within support 12.
  • An integral asymmetric support 12 is best formed of an appropriate relatively "stiff" polymer, preferably a polymer
  • support 12 be at least about 40 microns thick when used with an auxiliary support (not shown) which is capable of mechanically supporting support 12. When no such auxiliary support is used, it is preferred that support 12 be at least about 100 microns thick. If support 12 is substantially thinner than indicated, it may rupture due to the presence of a fluid pressure differential during use of membrane 10. Normally, support 12 should not be more than about 20 microns thicker than either of these values since it would then present undesirable resistance to fluid flow.
  • Support 12 is preferably formed from a conventional or known polysulfone, polya ide, or polyvinylidene fluoride although other polymers may also be used. Such polymers are relatively rigid and stiff and may be easily formed into supports corresponding to the preferred support 12. Further, such materials may be reacted so as to be cross-linked with hydrogel layer 16 as hereinafter described.
  • a particularly preferred physical support is made of polyvinylidene fluoride.
  • the support for the reverse osmosis membranes of the present invention is also preferably highly asymmetric as disclosed in applicant's Serial No. 290,927, filed August 11, 1981, and entitled "IMPROVED ANISOTROPIC MEMBRANES AND PROCESS THEREFOR", the disclosure of which is hereby incorporated by reference.
  • Hydrogel layer 16 is a gel or gel system which may be based upon an inorganic material such as alumina or silica.
  • hydrogels of the present invention are based upon water swollen random coils of polymer chains which are water loving in the sense that they tend to take up water so that there is some water “bound” in the polymer coils and some "free” or unbound water between the swollen polymer chains.
  • hydrocolloids or hydrocolloid-like polymers The polymers which are utilized to form such hydrogels are sometimes referred to as hydrocolloids or hydrocolloid- like polymers.
  • Polyacrylic polymers, diaminobutane polymers and compounds such as alginic acid, guar gum and the like are commonly referred to as hydrocolloids or hydrocolloid-like polymers.
  • the molecular weight of a polymer or compound used to form a hydrogel utilized in layer 16 is important. If the polymer chains were too large, the viscosity of a solution containing such polymer chains would become so great as to make it difficult to utilize this solution in manufacturing layer 16. Furthermore, if these chains were too large, the process of manufacturing layer 16 would be unnecessarily complicated due to shear degradation. On the other hand, if the molecular weight of these chains were too low, hydrogel layer 16 would penetrate or clog pores 26 of support 12 to an extent sufficient to detrimentally affect fluid flow through pores 26 as a result of the formation of layer 16 upon layer 12.
  • hydrogel layer 16 may be made using at least one polymer which contains vinyl groups since such polymers may be readily cross-linked through the formation of covalent links as the hydrogel is formed, and since such polymers form gels or gel systems which are effective in conveying or conducting water.
  • polymers containing hydroxyl groups which may be cross-linked by ester groups or containing carboxylic acid
  • Hydrogel layer 16 has two functions: (1) it physically holds or supports layer 20 at or along surface 18, and (2) it serves to distribute water flow from layer 20 to pores 26 of support 12. In order for layer 16 to adequately serve its purpose of distributing water, the hydrogel system within this layer 16 should not be significantly affected by any temperature changes normally encountered in shipping and handling of completed membrane 10. Further, layer 12 should be capable of conveying or transporting water effectively at any normally encountered water temperature. Accordingly, layer 16 preferably should consist essentially of a thermally irreversible gel system.
  • hydrogel layer 16 may best be explained by indicating what would happen if layer 20 was located directly against surface 14 of support 12. If this were the case those portions of layer 20 directly adjacent to pores 26 would receive fluid from layer 20 while those portions of layer 20 in contact with surface 14 between pores 26 would be blocked off by the material at surface 14 so as to be unavailable for reverse osmosis purposes.
  • Hydrogel layer 16 prevents this blocking effect because of the ability of a hydrogel to transmit or convey water. Hydrogel layer 16 is used with the present invention to conduct water from all portions of layer 20 in contact with surface 18 to pores 26 in surface 14. Thus this hydrogel layer 16 avoids what may be referred to as "dead spots" along
  • hydrogel layer 16 For hydrogel layer 16 to carry out this distributive function effectively, it must be sufficiently thick to distribute or conduct fluid from layer 20 to pores 26. It must also be sufficiently thick so as to be continuous or non-porous so as to completely support layer 20. On the other hand, layer 16 should not be so thick as to provide any substantial or excessive resistance to liquid flow from layer 20 to support 12 other than such resistance as is inherently necessary in distributing liquid from all portions of surface 18 to pores 26. Layer 16 should preferable be about as thick as the average distance between pores 26.
  • layer 16 should have a dry thickness of from about 0.1 to about 5 microns. If layer 16 is substantially thinner than about 0.1 micron, there is some danger that it will be of a discontinuous character and it probably will not be thick enough to adequately transport and convey water. If, on the other hand, layer 16 is substantially thicker than 5 microns, more hydrogel will be present than is needed to perform the hydrogel functions, and the excess hydrogel will tend to interfere with water flow. Hydrogel layer 16 has a dry thickness of preferably from about 2 to about 3 microns since such a hydrogel layer adequately performs its intended functions and is normally free of any defects such as discontinuities.
  • hydrogel layer 16 Since the polymer chains in a hydrogel tend to swell in the presence of water or water and another appropriate solvent, the "wet" thickness of hydrogel layer 16 is greater than its dry thickness. This fact should be noted since on occasion reverse osmosis membrane 10 may be supplied with hydrogel layer 16 substantially depleted of liquid.
  • the amount of swelling is dependent upon the specific polymer used in creating hydrogel layer 16.
  • a polymer must be capable of taking up an amount of water equal to at least 150 percent of the weight of the polymer present when layer 16 is at ambient pressure and temperature if the hydrogel is to be able to convey water at a desirable rate.
  • the amount of water within layer 16 is at least 15 times the weight of polymer present under the noted conditions for the water to have a desired degree of mobility within layer 16. If layer 16 contains an amount of water substantially in excess of about 200 times the weight of the polymer under the noted conditions, hydrogel layer 16 will not normally possess the physical properties necessary for it to perform the functions discussed hereinabove.
  • hydrogel layer 16 Several other considerations should be noted in connection with hydrogel layer 16.
  • the polymer chosen for use in the formation of the hydrogel should be such that the hydrogel is not significantly affected by pressures such as will normally be encountered during use of membrane 10.
  • the gel type structure formed will not be broken down or damaged at such pressures.
  • the pressure applied to membrane 10 during use may affect layer 16. In general, the greater the pressure applied to
  • SUBSTITUTE SHEET membrane 10 the greater the extent to which hydrogel layer 16 will tend to be compacted. The more layer 16 is compacted the greater the resistance of layer 16 to water flow through it and the greater the chance that some minor amount of water may be expressed from layer 16.
  • Active layer 20 is critical to the operation of reverse osmosis membrane 10 because it is this layer which normally completely performs the actual separation achieved in any reverse osmosis procedure.
  • layer 20 In order to achieve this separation with water, layer 20 must be hydrophilic so as to be capable of dissolving the water and thus segregate the dissolved water from other materials in the solution being purified which will not go into soltution to any significant extent in the polymer in active layer 20.
  • the active layer should be capable of absorbing generally at least about 2, typically from about 2 to about 20, and preferably from about 5 to about 15 percent by weight water on the basis of its own dry weight.
  • layer 20 the greater the degree of water absorption by layer 20 the better since the easier it would be for water to move through this layer and, hence, the greater the flow which may be achieved through membrane 10.
  • salt penetration into layer 20 tends to increase with an increase in water absorption. If layer 20 absorbs beyond about 20 percent by weight of water on the basis of its own weight, layer 20 will tend not to be as selective as normally desired in achieving purification. If an amount of water
  • SUBSTITUTE SHEET ⁇ J A substantially less than about 2 percent by weight of the dry polymer is absorbed by layer 20 during use of membrane 10, flow through membrane 10 is so limited as to make it unsuitable for most normal uses.
  • layer 20 The ability of layer 20 to absorb water should be considered in connection with another factor.
  • layer 20 may be generally from about 50°A to about 1500°A thick. Preferred results are achieved, however, when layer 20 is from about 200°A to about 500°A thick.
  • membrane 10 Unless water to be purified using membrane 10 has been previously treated to kill any and all microorganisms, layer 20 will be exposed to those microorganisms. Since polymers of a hydrophilic, water dissolving water character normally are either susceptible to attack as a result of growth of microorganisms on such polymers or susceptible to clogging as a result of microorganisms growing on the surface of such polymers, it is disadvantageous to use membrane 10 with water which has not been treated to kill microorganisms present within such water.
  • TITUTE SHEET many different ways in order to kill microorganisms, as a practical matter there is only one way which is normally economic for killing microorganisms in water.
  • This method involves treating water with an oxidizing agent having an oxidation potential sufficient to serve as a sterilizing agent for the water.
  • Chlorine is the most commonly utilized sterilizing agent although ozone, and to a lesser extent other agents, such as iodine and various chlorine containing compounds, may also be used. Since such oxidizing or sterilizing agents must normally be used, the polymer utilized in layer 20 should be substantially inert in the presence of an oxidizing agent having an oxidation potential sufficient to serve as a sterilizing agent.
  • the polymer utilized in layer 20 should also be substantially inert in the presence of any enzyme which may be reasonably expected to be found within the water.
  • layer 20 serves essentially as a barrier which isolates both the material in hydrogel layer 16 and the material in support 12 from any oxidizing agent and any enzyme present within the water. Even if some of the oxidizing agent or some enzyme within the water being treated
  • SUBSTITUT should contact layer 16 or support 12, the chance of such contact causing any damage which would significantly detrimentally affect the operation of membrane 10 is quite limited. Even if layer 16 or support 12 should become damaged as a result of contact with such an oxidizing agent or enzyme, this will not normally affect the operation of membrane 10 since it is layer 20, not layer 16 or support 12, which accomplishes the salt separation which is the purpose of this membrane.
  • Epoxy, pheonolic, partially hydrolyzed polyvinyl ester polymer or polymer system, and cellulose triacetate are preferred for use in layer 20 since such polymers are generally adequately resistant to oxidation and to enzyme attack, are sufficiently hydrophilic to be used in separating water, and may be applied to layer 16 without damaging it while membrane 10 is manufactured.
  • not all polymers of these classes are useful for layer 20.
  • the desired degree of inertness in layer 20 results from the selection of a precise structural formula of the polymer or polymer system used in creating layer 20. Furthermore, the suitability of a particular polymer for use in layer 20 may generally be determined on the basis of routine testing in order to determine if such a polymer
  • OMPI WIPO ⁇ ?N A T possesses the various desirable characteristics indicated hereinabove.
  • Epoxy, phenolic and partially hydrolyzed polyvinyl ester polymers, and cellulose triacetate, are normally desired for use in layer 20 but even these polymers may not be desirable if they contain various reactive groups which may be chemically attacked by an oxidizing agent or enzyme.
  • any polymer useful in layer 20 should contain ester, vinyl or tertiary amide cross-links in the polymer.
  • any useful polymer of the epoxy type should have exposed carboxylic acid groups.
  • any epoxy, phenolic, partially hydrolyzed polyvinyl ester, or cellulose triacetate should only contain hydroxyl groups which are spaced or remote from electron donor or electrophilic groups and any halogen or other hydroxyl groups present in the polymer chain.
  • the epoxy resins useful in the this invention may be formed by cross-linking prepolymer chains having terminal hydroxyl groups with tetrafunctional carboxylic acids and anhydrides to produce polymers containing ester cross- linkages and exposed carboxylic acid groups.
  • phenolic polymers may be obtained by cross-linking conventional commercially available resol and novolak or phenoxy resins with difunctional acid anhydrides such as maleic, phthallic and various similar difunctional anhydrides.
  • the partially hydrolyzed polyvinyl esters useful in this invention may be produced by partially hydrolyzing polymers,
  • OMP such as polyvinyl acetate or butyrate resins
  • a polyvinyl ester which is from about 10 to about 50% hydrolyzed is satisfactory for use in this invention. If such a polymer is hydrolyzed to an extent substantially greater than about 50% it will not exhibit the desired degree of salt rejection. If it is hydrolyzed substantially less than about 10%, it will not exhibit the desired ability to absorb water. Whenever the expression "partially hydrolyzed polyvinyl ester" is used in this specification or claims, it designates a polymer which has been hydrolyzed in an amount as noted.
  • the preferred polymer for use as the active layer is cellulose triacetate because for its resistance to chlorine, favorable water permeability, and very high salt retention.
  • the cellulose triacetate is applied to the support preferably by dip coating the support in a very dilute (from about 0.1 to about 0.7% by weight) solution of cellulose triacetate in chloroform.
  • the support may be submerged within the solution of cellulose triacetate via a roller submerged within the solution.
  • pol inylidene fluoride is the preferred support because it is compatible with the chloroform solvent and also because it otherwise functions as a useful support.
  • the reverse osmosis membranes of the present invention may be manufactured in a number of different, somewhat
  • ⁇ NA related manners When this membrane uses a conventional or known support as support 12, one must first locate layer 16 upon support 12 and then subsequently located layer 20 on layer 16. Because layers 16 and 20 are quite thin they cannot normally be separately manufactured and then deposited in place at a reasonable cost, but must be formed in situ. Thus, layer 16 must be formed upon layer 12 and then in turn layer 20 must be formed upon layer 16. By utilizing entropic segregation as indicated hereinbelow, these layers 16 and 20 may be concurrently produced.
  • layers 16 and 20 may be created utilizing known or conventional techniques for creating comparatively thin continuous films or coatings.
  • layer 16 and 20 may be- formed by preparing appropriate solvent solutions and then depositing these solutions by known or conventional roller, transfer, brush, wick or dip coating techniques. Any such deposition of solution must, of course, be followed by solvent removal, either by air drying or by heating at a temperature sufficiently low as to avoid polymer damage but sufficiently high as to cause some cross-linking between polymer chains.
  • support 12, layer 16 and layer 20 are all preferably cross-linked so as to achieve a type of chemical bond at each of surfaces 14 and 18.
  • Such cross-linking may be achieved by utilizing appropriate polymers or polymer systems capable of cross-linking.
  • support 12 preferably consists essentially of a polysulfone, polyamide, or polyvinylidene fluoride having a particular type of asymmetric physical structure.
  • This support 12 may be manufactured by forming a solution of the polymer and then casting this solution onto an imporous transfer sheet such as, for example, a stainless steel belt to a desired thickness capable of resulting in the production of a support 12 having a particular desired thickness. Thereafter, the exposed surface of the film located on the imporous sheet may be quenched in water, preferably deionized or distilled water, at ambient temperatures. The support may then be removed from the transfer sheet. This results in the production of support 12 having a preferred physical structure as indicated hereinabove. Preferably support 12 is then washed several times with deionized or distilled water to remove any vestiges of the solvent employed in preparing the polymer solution.
  • Support 12 produced in this manner may or may not contain reactive groups capable of cross-linking with the polymer or polymer system used in a hydrogel layer 16.
  • the surface of the support may be treated to modify the polymer in order to place reactive groups on the surface of the polymer.
  • a polymer such as a polysulfone
  • a hydrogen peroxide solution under such conditions as to modify the surface of the polysulfone so that the surface contains sufficient hydroxyl groups to effectively cross-link to or with subsequently created hydrogel layer 16.
  • Other treatments designed to accomplish the same type of objective may also be used.
  • the surface of a polysulfone support may be treated with a very dilute solution of chlorosulfonic acid for a brief period to produce the sulfonic acid groups capable of forming cross-links.
  • hydrogel layer 16 care should be taken in preparing hydrogel layer 16 in order to substantially avoid the penetration of hydrogel 16 within pores 26 in surface 14 of support 12. This penetration is substantially avoided or minimized preferably by applying an extremely dilute solution of a hydrogel forming polymer of a molecular weight as indicated hereinabove and then removing solvent under such conditions that there is minimal penetration of the solution within pores 26. In general, the higher the viscosity of the solution the less chance of penetration.
  • hydrogel forming polymer within such a solution is swollen by the solvent or solvent systems used to as great an extent as reasonably possible and the solvent solution of the hydrogel polymer coils is quite dilute, several important benefits are achieved.
  • One such benefit is that the solution of the hydrogel polymer coils may be readily handled as a liquid so as to be readily applied by techniques discussed hereinabove.
  • Another benefit is that the swollen polymer coils within the solution are large enough that the solution is sufficiently viscous so that it will not readily penetrate pores 26 within surface 12 and thus not clog or block these pores.
  • Surface 14 of support 12 may be considered more or less as a common filter in filtering solids out of a liquid by tending to hold back swollen polymer coils on surface 14 so that such coils will constitute layer 16 as solvent is removed.
  • a viscosity controlling agent which is sufficiently inert so as not be affect the operation of layer 16 or which will be expelled from layer 16 during its final stages of formation and readily removed during rinsing.
  • a common high molecular weight polyethylene glycol having wax-like characteristics may be used in the amount of 2 or 3% by weight of the total weight of the polymer or polymer system in hydrogel layer 16 so as to increase the viscosity of the hydrogel polymer solution.
  • the use of such a viscosity controlling agent is preferred in
  • the solvent or solvent system may contain very minor amounts of wetting agents which will tend to promote uniform spreading of the hydrogel forming solution.
  • the solvent or solvent system employed in producing hydrogel layer 16 should be of such a nature as to avoid any sort of "action" with respect to support 12. Thus, for example, that solvent or solvent system is preferred which does not significantly tend to swell any polymer within support 12. If the solvent or solvent system tends to dissolve or significantly swell the polymer in support 12, there is danger that the desired porosity within support 12 may be detrimentally affected and this, in turn, would detrimentally affect the flow characteristics of membrane 10.
  • the solvent or solvent system should consist of water or a mixture of water with a lower aliphatic alcohol (C* j _ to Cg inclusive) such as, for example, isopropyl alcohol.
  • a lower aliphatic alcohol such as, for example, isopropyl alcohol.
  • the water is, of course, required in order to form a hyrdogel. Both it and the lower aliphatic alcohol may readily be removed from layer 16 as it is being formed.
  • the solution used in forming hydrogel layer 16 may be prepared by first dissolving in a solvent the particular polymer or polymers which preferably contain a least two reactive sites capable of being used in forming covalent cross-links at each of their ends.
  • a hydrogel forming polymer is formed which has a desired stability against weakening of the solution by heat—i.e., there is produced a thermally irreversible gel.
  • hydrogel polymers The presence of reactive sites on the hydrogel polymers is also beneficial for other reasons. Because of the dilution of the solution needed to form hydrogel layer 16, there is usually adequate reactive sites on the hydrogel polymers for two different types of cross-linking to occur. When support 12 contains these reactive sites, these reactive sites form covalent bonds with the reactive sites in the hydrogel polymer material of layer 16 during deposition and solvent removal.
  • hydrogel forming polymer or polymers so that not all functional sites capable of cross-linking are reacted prior to the creation of the final active layer 20.
  • active layer 20 reasonably corresponds to the procedure previously described in connection with the formation of layer 16. This procedure involves forming a solution, depositing the solution, and then removing the solvent from the solution as well as the other details set forth hereinabove.
  • a solvent or solvent system as previously described in connection with the creation of layer 16 which consists of water, a lower aliphatic alcohol (C, to Cg inclusive), or a mixture of the two. Because such a solvent or solvent system is the same as that used in the formation of hydrogel layer 16, there is substantially no chance of damage to the hydrogel layer 16 as a result of the use of this solvent or solvent system.
  • This solvent or solvent system is utilized in connection with layer 16 because it does tend to dissolve or swell the preferred polymer used in forming support 12. If support 12
  • SUBSTITUTE SHEET is resistant to the solvent, however, it may be used in forming layer 20 provided it also does not damage layer 16.
  • chloroform may be used if support 12 is made of a polyester or polyamide.
  • the polymers which are capable of being used in forming layer 20 tend to be relatively difficult to dissolve in the solvent or solvent system. This is particularly the case when the molecular weights of such polymers are as high as is normally desired in connection with layer 20 and when the polymers are epoxy or phenolic.
  • the solution used in forming layer 20 consisting of an epoxy or phenolic polymer will also contain prepolymer chains of comparatively low molecular weight which have to be further reacted with one another to form active layer 20 having the ultimate physical properties.
  • the solution employed will, because of the solubility problem noted, normally contain prepolymer chains having (1) terminal hydroxyl groups which are sufficiently short so as to readily dissolve in the solvent or solvent system and (2) tetrafunctional carboxylic acid anhydrides of a similar solubility. As previously indicated, for a phenolic layer 20 such chains may be novolak or phenoxy resins.
  • a phenolic resin it is normally considered necessary to incorporate within the solution a comparatively small, but effective, amount of a hardener and/or a catalyst in accordance with conventional practice. These materials are necessary in promoting the desired actions in forming the final active polymer within a comparatively limited time period at a comparatively moderate temperature.
  • Suitable curing agents or hardeners are various divalent acids and divalent acid anhydrides such as maleic, phthallic and other similar acids which are conventionally used for this purpose.
  • Conventional catalysts such as boron trifluoride, various quaternary phosphonium alkyl or aryl compounds, benzoyltrimethylammonium iodide, zinc stearate, N,N-diethanolamine and the like may be conveniently utilized.
  • the curing agents, catalyst, and prepolymer chains used to form a phenolic layer 20 must, of course, be selected with reference to their solubility in the particular solvent or solvent system employed.
  • the solution used in forming an epoxy or phenolic layer 20 is preferably sufficiently dilute so that there is substantially no chance of the prepolymer chains present in the solution reacting until the solvent content of the solution is reduced as, for example, by evaporation during
  • the precise amount of solvent or solvent mixture needed may be determined by routine experimentation. An excess over the amount needed is preferably employed so as to avoid any possibility of an undesired reaction.
  • membrane 10 having separate hydrogel layer 16 and separate active layer 20 concurrently by making use of entropic segregation.
  • a solution is prepared utilizing a solvent or a solvent system such as is used in connection with the separate preparation of either of these layers.
  • This solution should contain both swollen hydrogel polymer coils and various specific "ingredients" as identified hereinabove for the production of active layer 20.
  • Such a solution should be applied to support 12 and then heated at a temperature sufficient to volatilize the solvent present and to cause appropriate reactions leading to the formation of active layer 20 and hydrogel layer 16.
  • Such heating conditions should normally be sufficiently effective to cause any cross-linking which is possible between the functional groups of the polymer forming ingredients.
  • the solution utilized should be applied to support 12 in any conventional manner known to those skilled in this art.
  • layers 16 and 20 When the solution is heated, entropic segregation will take place to a significant extent. This segregation may be promoted by precise control of the heating used to remove the solvent and to cause reaction from the ingredients from within the solution applied to create layers 16 and 20.
  • layers 16 and 20 When layers 16 and 20 are produced in this manner, they are not as separate and distinct as when separately produced. To a significant extent, they are physically intermixed such that they are not readily separated.
  • layers 16 and 20 are produced in this manner, they are sufficiently effective in removing salt from salt water so as to provide water which is sufficiently salt free to be useful in many different non-critical applications where extreme water purity is not required. When extreme water purity is required, however, layers 16 and 20 should be separately produced.
  • Support 12 may be prepared by first preparing a solution of 11 parts polyarylsulfone in 14 parts methyl butanol and 75 parts dimethylformamide. This solution is cast at 30°C onto an inert, imporous transfer sheet such as, for example, a flexible belt coated with a polyethylene surface coating at a temperature of about 20°C to a wet thickness of about 400 microns. The film produced in this manner is then quenched in distilled water at a temperature of about 20°C for a period of about three minutes. Then the support is washed several times in distilled water and dried in air at about 160°C for two minutes.
  • an inert, imporous transfer sheet such as, for example, a flexible belt coated with a polyethylene surface coating at a temperature of about 20°C to a wet thickness of about 400 microns.
  • the film produced in this manner is then quenched in distilled water at a temperature of about 20°C for a period of about three minutes. Then the support is washed several
  • a previously prepared solution of 1 part polyacrylic acid polymer having an average molecular weight of about 1,000,000 in 99 parts distilled water at 20°C is coated on the surface of the support remote from the transfer sheet in a thickness as determined by experimentation to be adequate to form a hydrogel layer having a dry thickness of about two hundred microns.
  • the support including the wet film, is dried in a forced air oven at about 140°C for a period of about two minutes. Drying results in the production of a hydrogel layer corresponding to layer 16.
  • Active layer 20 is prepared by first preparing a solution of 0.4 parts epoxy resin having an average molecular weight of about 20,000 (Araldite 488), 0.1 parts prepolymer of phenol-formaldehyde, water borne phenolic hardener, 0.001 part boron tri-fluoroethanate catalyst, 49.2 parts water, and 50.0 parts methyl alcohol at 20°C. This solution is then placed on the hydrogel layer. An excess of this solution over the amount which automatically adheres to the hydrogel layer as a result of surface tension is applied to the hydrogel layer. The coated composite sheet is then held vertically for the time required for the latter coating to drain so as to establish its own surface thickness. As soon as this occurs, the composite, including the solution, is baked in air at 120°C for five minutes to remove solvent and to cure the active film. The completed membrane is then removed from the transfer sheet.
  • epoxy resin having an average molecular weight of about 20,000 (Araldite 488)
  • prepolymer of phenol-formaldehyde water
  • Example 1 The procedure of Example 1 is followed but instead of the inert, imporous transfer sheet of Example 1 there is used a continuous sheet of paper sold under the trademark "PELLON 6800".
  • Example 1 The procedure of Example 1 is varied so that the transfer sheet is removed from the support immediately following the air drying of the film which is converted into the support. Using this procedure, the support is not reinforced since a hydrocolloid layer and an active layer are produced on it.
  • Example 1 The procedure of Example 1 is varied in connection with the production of the active layer.
  • a solution containing one part of an A-stage or resol, one-step, ther osetting phenol-formaldehyde resin consisting primarily of partially condensed phenol alcohols in 99 parts water at room temperature is titrated to a pH of about 7 utilizing a 0.1N solution of sodium hydroxide.
  • This solution is applied to the hydrogel layer instead of the solution used to produce the active layer in Example 1.
  • the composite is air dried at 100°C for a period of 10 minutes to produce the final membrane. This membrane is then removed from the transfer sheet.
  • hydrogel layer 16 and active layer 12 are formed by using a solution consisting of 1.8 parts of acrylic acid, 0.2 parts of an epoxy resin having an average molecular weight of about 25,000 (Araldite 6010) and 98 parts of ethanol. The solution is filtered and allowed to stand at room temperature for a period of one hour.
  • the transfer sheet and the support holding the applied solution are heated in an oven in air at about 120°C for a period of about 10 minutes. This removes the solvent present and results in entropic segregation to the extent that the hydrocolloid layer and the active layer produced are reasonably separate and distinct from one another, although there is still an intermingling of these layers at the interface between them.
  • Example 6 The procedure of Example 1 is varied by providing an additional step. This step concerns the treatment of the dry support prior to the application of the polyacrylic acid solution.
  • the exposed surface of the support is treated with a solution containing 30 parts hydrogen peroxide, 0.02 parts of a conventional surfactant (FSN) and 69.98 parts water to which there has been added an amount of ferrous sulfate which is such that the solution contains 5 parts per million of ferrous sulfate.
  • FSN conventional surfactant
  • This solution is applied to the surface of the support at a temperature of 85°C and is held in contact with this surface for a period of 10 minutes. Thereafter, the treated support is washed several times in distilled water and then air dried at 120°C for a period of five minutes.
  • the support treated in this manner contains hydroxyl groups which react with the polyacrylic acid during the subsequent step of Example 1 so as to form covalent cross-links.
  • Example 7 The procedure of Example 1 is varied by providing an additional step which corresponds closely to the additional step set forth in Example 6. This additional step also concerns the treatment of the dry support prior to the application of the polyacrylic acid solution.
  • the exposed surface of the support is treated with a solution containing 0.1 parts of chlorosulfonic acid in 99.9 parts of hexane at room temperature for a period of about 20 seconds. Reaction is indicated by the formation of hydrogen chloride gas. This reaction produces sulfonic acid groups on the support which cross-link with polyalkylamine (Dow, Tydex 12) added during the subsequent step of Example 1 so as to form covalent cross-links.
  • Example 8 The procedure of Example 1 is varied by utilizing a solution of a polyacrylic acid derivative polymer or prepolymer segments having a molecular weight of about 500,000 and having two vinyl groups attached to each polymer chain instead of the polyacrylic polymer specified in Example 1. All other details are as specified in Example 1.
  • Example 9 The procedure of Example 1 is varied so as to produce as membrane using a different active layer than is specified in Example 1.
  • This alternate active layer uses a hydrolyzed polyvinyl acetate which is prepared by: (1) treating a commercial polyvinyl acetate polymer with a solution of 10 parts sodium hydroxied in 90 parts water at ambient temperature until about 50% of the polymer is hydrolyzed; (2) precipitating the hydrolyzed polymer from the solution with ethanol; (3) separating this polymer by filtration; (4) neutralizing the separated polymer with hydrochloric acid; and (5) washing and drying the polymer.
  • This polymer is used by forming a solution containing 0.5 parts of it in 99.5 parts acetone and 0.025 parts pyromellitic anhydride.
  • the solution is spread on a hydrogel layer as specified in Example 1 to a thickness which will produce an active layer of a desired thickness after drying. It is then allowed to air dry.
  • the final membrane is produced by heating in air at 120°C for 10 minutes.
  • a preferred support is prepared by first dissolving 15 grams of polyvinylidene fluoride in 85 milliliters of dimeth lformamide by stirring over a period of about 12 hours. This solution is then cast onto an inert, imporous transfer sheet which is a flexible belt with a polyethylene surface coating at 20°C using a knife with a gap of 15 mils. The film produced in this manner is then quenched in distilled water at about 20°C for a period of about 5 minutes. . The support produced as a result of these steps is then washed several times in distilled water and then dried in air at about 100°C for a period of ten minutes.
  • a previously prepared solution of 1 part polyacrylic acid having an average molecular weight of about 1,000,000 in 99 parts distilled water at 20°C is coated on the surface of the support remote from the transfer sheet to a wet thickness which will ultimately result in a dry thickness of about two microns.
  • the support including the wet film, is dried in a forced air oven at about 140°C for a period of about two minutes. This drying results in the production of a hydrogel layer corresponding to layer 16.
  • Active layer 20 is prepared by applying a 0.3% cellulose triacetate solution in chloroform to the polyvinylidene support by means of a polyurethane foam coating wick.
  • the support stains with crystal violet dye but the thin film component does not produce a dye stain which illustrates the fact that the thin film is continuous.
  • the membrane is used to purify water containing sodium chloride.
  • the sodium chloride rejection is 89%.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

Membrane pour osmose inverse (10) présentant des caractéristiques physiques améliorées, particulièrement utile dans la purification de l'eau. Cette membrane comprend une couche active mince (20) composée d'un polymère filmogène, de préférence du triacétate de cellulose, pouvant se dissoudre dans une quantité limitée d'eau. La couche active est utilisée en combinaison avec un support poreux (12), de préférence du fluorure de polyvinylidène. Cette couche active est disposée sur une couche d'hydrogel (16) facilitant le mouvement de l'eau qui s'éloigne de la couche active généralement en direction des pores dans le support. Le support utilisé est une couche ou membrane asymétrique dans laquelle la porosité va en s'accroissant lorsque l'on s'éloigne de la couche d'hydrogel. La membrane complète peut être produite en utilisant des solutions de solvant qui sont appliquées successivement sur la couche ou membrane de support et à partir desquelles on extrait le solvant.
EP19840903388 1983-08-26 1984-08-27 Membrane pour osmose inverse et son procede de fabrication Withdrawn EP0156837A1 (fr)

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US52681183A 1983-08-26 1983-08-26
US526811 1983-08-26

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Publication number Priority date Publication date Assignee Title
EP0470377B1 (fr) * 1990-07-09 1995-05-24 Dainippon Ink And Chemicals, Inc. Membrane et appareil de contact gaz-liquide et procédé de préparation d'un liquide contenant un gaz dissous
US5254143A (en) * 1990-07-09 1993-10-19 Dainippon Ink And Chemical, Inc. Diaphragm for gas-liquid contact, gas-liquid contact apparatus and process for producing liquid containing gas dissolved therein
WO2007007343A2 (fr) * 2005-07-14 2007-01-18 Ben Gurion University Of The Negev Research And Development Authority Membranes composites et procedes de preparation de celles-ci
WO2017069990A1 (fr) * 2015-10-22 2017-04-27 Uop Llc Membranes à revêtement à double couche pour séparations de gaz
CN110449047B (zh) * 2019-07-11 2022-09-27 南京工业大学 一种面向沼液纯化的高通量正电纳滤膜及其制备方法

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US3556305A (en) * 1968-03-28 1971-01-19 Amicon Corp Composite membrane and process for making same
US3750735A (en) * 1970-06-16 1973-08-07 Monsanto Co Removal of water from liquid mixtures containing formaldehyde using a porous polymeric membrane
GB1391973A (en) * 1971-09-07 1975-04-23 Aqua Chem Inc Polyvinyl acetal membrane
US4161446A (en) * 1977-11-23 1979-07-17 Coillet Dudley W Process for the treatment of ground water
US4387024A (en) * 1979-12-13 1983-06-07 Toray Industries, Inc. High performance semipermeable composite membrane and process for producing the same

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See references of WO8500985A1 *

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WO1985000985A1 (fr) 1985-03-14

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