Microporous membranes and uses thereof

Abstract

Charged membranes comprise a porous substrate and a cross-linked polyelectrolyte or hydrogel located in the pores of the substrate and are useful in a variety of membrane separation processes including pressure driven membrane separation, diffusion dialysis. Donnan dialysis, electrodialysis, electrochemical synthesis and pervaporation.

What we claim is:  
     
         1 . In a membrane separation process which is pervaporation or selected from the group consisting of pressure driven membrane separation, diffusion dialysis, Donnan dialysis, electrodialysis and electrochemical synthesis effecting ionic selectivity, the improvement which comprises employing a charged membrane comprising a porous substrate and a cross-linked polyelectrolyte or hydrogel located in the pores of the substrate.  
     
     
         2 . The process of  claim 1  wherein said membrane comprises a microporous substrate and about 20 to about 400 wt % weight of microporous substrate of a cross-linked in-situ polymerized polyelectrolyte or hydrogel located in the pores of the substrate and cross-linked by up to about 30 wt % of the polymerized monomers in the polyelectrolyte or hydrogel.  
     
     
         3 . The process of  claim 1  wherein said membrane separation process comprises a pressure-driven membrane separation to effect preferential removal of multivalent cations from an aqueous medium containing monovalent cations and multivalent cations.  
     
     
         4 . The process of  claim 2  wherein, in said microporous membrane, the quantity of in-situ polymerized polyelectrolyte or hydrogel is about 30 to about 200 wt % and the amount of cross-linking monomer is up to about 10 wt % of the in-situ polymerized monomers.  
     
     
         5 . The process of  claim 4  wherein the quantity of in-situ polymerized polyelectrolyte or hydrogel is about 45 to about 100 wt % and the amount of cross-linking monomers is about 0.25 to about 5 wt %.  
     
     
         6 . The process of  claim 2  which is effected at a pressure of 70 psig (500 kPa) or less.  
     
     
         7 . The process of  claim 6  wherein said membrane comprises a microporous substrate in the pores of which is in situ polymerized from about 45 to about 100 wt % of the substrate of vinylpyridine which is cross-linked with from about 0.25 to about 5 wt % of total monomers by divinylbenzene.  
     
     
         8 . The process of  claim 7  wherein amine groups in the polyelectrolyte are quaternized.  
     
     
         9 . The process of  claim 1  wherein said membrane separation process comprises electrodialysis, diffusion dialysis or Donnan dialysis and wherein, in said microporous membrane, the quantity of in-situ polymerized polyelectrolyte or hydrogel is about 50 to about 250 wt % and the amount of cross-linking monomers is from about 0.25 to about 30 wt % of the in-situ polymerized monomers.  
     
     
         10 . The process of  claim 9  wherein the quantity of in-situ polymerized polyelectrolyte or hydrogel is about 150 to about 250 wt % and the amount of cross-linking monomers is about 15 to about 25 wt %.  
     
     
         11 . The process of  claim 1  wherein said membrane separation process comprises electrodialysis, diffusion dialysis or Donnan Dialysis and wherein said microporous membrane comprises a microporous substrate having about 150 to about 250 wt % of the substrate of a cross-linked polyelectrolyte or hydrogel located in the pores of the substrate, said polyelectrolyte or hydrogel being polymerized 4-vinylpyridine which is cross-linked with about 15 to about 25 wt % of total polymerized monomers in said polyelectrolyte or hydrogel, by divinylbenzene and exhibiting a low electrical resistance and a low water permeability.  
     
     
         12 . The process of  claim 1  wherein the polyelectrolyte or hydrogel is formed in the pores of the substrate by in situ polymerization of a monomer or a mixture of monomers with a cross-linking agent, the monomer or at least one of the monomers of the monomer mixture being selected from those monomers which contain a functional group that provides an ion-exchange site and those which contain a group which is susceptible to a reaction by which such functional groups are subsequently introduced to in situ-formed polymer.  
     
     
         13 . The process of  claim 1  wherein the polyelectrolyte or hydrogel is formed in the pores of substrate by, first, in situ polymerization of a monomer or a mixture of monomers, the monomer or at least one of the monomers of the monomer mixture being selected from those monomers which contain a functional group that provides an ion-exchange site and those which contain a group which is susceptible to a chemical reaction by which such functional groups are subsequently introduced to the in situ-formed polymer, and, subsequently, cross-linking in situ-formed polymer.  
     
     
         14 . The process of  claim 1  wherein the polyelectrolyte is a copolymer of vinylpyridine and a monomer selected from divinylbenzene and divinylpyridine.  
     
     
         15 . The process of  claim 13  wherein the polyelectrolyte is polyvinylpyridine cross-linked with a dialkylating reagent after in situ polymerization.  
     
     
         16 . The process of  claim 15  wherein said dialkylating agent is 1,3-dibromopropane or α, α′dibromo-ρ-xylene.  
     
     
         17 . The process of  claim 14  wherein the polyvinylpyridine is quaternized with an alkyl or aryl substituted alkyl halide or sulphate.  
     
     
         18 . The process of  claim 1  wherein the polyelectrolyte is selected from the group consisting of (1) copolymers of vinylbenzyl chloride and divinylbenzene and the ion-exchange functional groups are introduced by reaction with a tertiary amine; (2) copolymers of styrene and divinylbenzene and the ion-exchange functional groups are introduced by sulfonation; (3) copolymers of acrylic acid and divinylbenzene; (4) copolymers of methacrylic acid and divinylbenzene; (5) copolymers of acrylic acid and a diacrylate; or (6) copolymers of methacrylic acid and a diacrylate.  
     
     
         19 . The process of  claim 1  wherein the substrate is a microporous polyolefin substrate.  
     
     
         20 . The process of  claim 19  wherein the polyolefin is polypropylene or polyethylene.  
     
     
         21 . The process of  claim 1  wherein the properties of the bound polyelectrolyte or hydrogel are modified for a specific membrane and separation process by selection of the degree and type of cross-linking of the polyelectrolyte or hydrogel.  
     
     
         22 . A charged membrane comprising a microporous polypropylene or polyethylene substrate and about 45 to about 100 wt % of a cross-linked polyelectrolyte or hydrogel located in the porous of the substrate, said cross-linked polyelectrolyte or hydrogel being polymerized 4-vinylpyridine which is cross-linked with from about 0.25 to about 5 wt % of total polymerized monomers in said polyelectrolyte by divinylbenzene.  
     
     
         23 . The charged membrane of  claim 22  wherein amine groups in said polyelectrolyte or hydrogel are quaternized by reaction with a quaternizing agent.  
     
     
         24 . The charged membrane of  claim 23  wherein said quaternizing agent is an alkyl or arylalkyl halide or a sulphate.  
     
     
         25 . The charged membrane of  claim 24  wherein said quaternizing agent is dimethyl sulphate.  
     
     
         26 . A charged membrane comprising a microporous polypropylene or polyethylene substrate and a cross-linked polyelectrolyte or hydrogel located in the pores thereof which is further cross-linked by reaction with a cross-linking agent.  
     
     
         27 . The charged membrane of  claim 26  wherein said cross-linking agent is 1,3-dibromopropane or α, α′dibromo-ρ-xylene.  
     
     
         28 . The charged membrane of  claim 26  wherein said cross-linked polyelectrolyte or hydrogel is a copolymer of vinylpyridine and a monomer selected from divinylbenzene and divinylpyridine.  
     
     
         29 . The charged membrane of  claim 28  wherein amine groups in said polyelectrolyte or hydrogel are quaternized.  
     
     
         30 . The charged membrane of  claim 29  wherein said amine groups are quaternized by reaction with dimethylsulphate.  
     
     
         31 . A charged membrane comprising a microporous polypropylene or polyethylene substrate and about 150 to about 250 wt % of the substrate of a cross-linked polyelectrolyte or hydrogel located in the pores of the substrate, said polyelectrolyte or hydrogel being polymerized 4-vinylpyridine which is cross-linked with about 15 to about 25 wt % of total polymerized monomers in said polyelectrolyte or hydrogel, by divinylbenzene and exhibiting a low electrical resistance and a low water permeability.  
     
     
         32 . The charged membrane of  claim 31  wherein said cross-linked polyelectrolyte or hydrogen is a copolymer of vinylpyridine and a monomer selected from divinylbenzene and divinylpyridine.  
     
     
         33 . The charged membrane of  claim 31  wherein said polymerized 4-vinylpyridine is quanternized.  
     
     
         34 . The charged membrane of  claim 33  wherein said polymerized 4-vinylpyridine is quanternized with dimethylsulphate.  
     
     
         35 . The charged membrane which is suitable for water treatment applications and comprising a microporous substrate about 30 to about 200 wt % cross-linked by up to about 10 wt % of in-situ polymerized monomers in the polyelectrolyte or hydrogel.  
     
     
         36 . A charged membrane of  claim 35  wherein the quantity of in-situ polymerized polyelectrolyte or hydrogel is about 45 to about 100 wt % and the amount of cross-linking monomers is about 0.25 to about 5 wt %.  
     
     
         37 . A charged membrane which is suitable for electrodialysis, diffusion dialysis and Donnan dialysis applications comprising a microporous substrate and about 50 to about 250 wt % of microporous substrate of a cross-linked in-situ polymerized polyelectrolyte or hydrogel located in the pores of the substrate and cross-linked by from about 0.25 to about 30 wt % of in-situ polymerized monomers in the polyelectrolyte or hydrogel.  
     
     
         38 . The charged membrane of  claim 37  wherein the quantity of in-situ polymerized polyelectrolyte or hydrogel is about 150 to about 250 wt % and the amount of cross-linking monomers is about 15 to about 25 wt %.