Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
1996-10-18
2001-07-10
Therkorn, Ernest G. (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S641000, C210S651000, C210S654000
Reexamination Certificate
active
06258276
ABSTRACT:
FIELD OF INVENTION
The present invention relates to certain novel membranes and the novel uses of certain membranes.
BACKGROUND OF THE INVENTION
Membranes are used, for instance, in separation processes as selective barriers that allow certain chemical species to pass, i.e., the permeate, while retaining other chemical species, i.e., the retentate. Membranes are used in many applications, for example as biosensors, heparinized surfaces, facilitated transport membranes utilizing crown ethers and other carriers, targeted drug delivery systems including membrane-bound antigens, catalyst-containing membranes, treated surfaces, sharpened resolution chromatographic packing materials, narrow band optical absorbers, and in various water treatments which involve removal of a solute or contaminant, for example, dialysis, electrodialysis, microfiltration, ultrafiltration, reverse osmosis, nanofiltration and in electrolysis and in fuel cells and batteries.
There are a large number of supports or substrates for membranes. Specific physical and chemical characteristics to be considered when selecting a substrate include: porosity, surface area, permeability, solvent resistance, chemical stability, hydrophilicity, flexibility and mechanical integrity. Other characteristics may be important in certain applications.
In Mika et al., J. Membr. Sci., 108 (1995) pp 37 to 56, there is described a procedure for modifying microporous polypropylene and polyethylene membranes wherein 4-vinylpyridine is in situ polymerized into the pores of the membrane.
SUMMARY OF THE INVENTION
We have found that, by cross-linking the membranes described by Mika et al. with a suitable cross-linking agent, such as divinylbenzene (DVB), thee are provided charged membranes comprising porous microfiltration substrate membranes whose pores have located therein a cross-linked polyelectrolyte or hydrogel anchored to the substrate polymer, which exhibit novel effects in a variety of membrane applications.
In particular, the membranes exhibit significant ion rejection properties, enabling water softening to be effected, particularly at ultra-low pressure, such as the pressure of tap water, by removing multivalent ions, such as calcium and magnesium, in preference to monovalent ions, such as sodium.
The membranes further exhibit electrochemical separator properties which make them suitable for a wide variety of applications, including electrodialysis, battery separators, fuel cell separators and electrochemical synthesis.
In addition, the membrane may be used for Donnan dialysis, diffusion dialysis and pervaporation.
Accordingly, in one aspect of the present invention, there is provided an improvement in a membrane separation process selected from the group consisting of pressure driven membrane separation, diffusion dialysis, Donnan dialysis, electrodialysis, electrochemical synthesis and pervaporation, 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.
The polyelectrolyte or hydrogel may be found 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 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 introduces to the in situ-formed polymer.
Alternatively, the polyelectrolyte or hydrogel may be formed in the pores of the 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 the in situ-forming polymer.
The properties of the cross-linked polyelectrolyte or hydrogel located in the pores of the substrate, by covalent bonding to or cross-linked around structural elements of the porous substrate may be modified for specific applications by selection of the appropriate degree of cross-linking.
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Mika, A New Class of Polyelectrolyte-filled Microfiltration Membranes, Journal of Membrane Science, 108 (1995) pp. 37-56.
Childs Ronald F.
Dickson James M.
Mika Alicja M.
McMaster University
Sim & McBurney
Therkorn Ernest G.
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