WO2014039575A1 - Phase inversion membrane and method for manufacturing same using soluble fibers - Google Patents

Phase inversion membrane and method for manufacturing same using soluble fibers Download PDF

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Publication number
WO2014039575A1
WO2014039575A1 PCT/US2013/058087 US2013058087W WO2014039575A1 WO 2014039575 A1 WO2014039575 A1 WO 2014039575A1 US 2013058087 W US2013058087 W US 2013058087W WO 2014039575 A1 WO2014039575 A1 WO 2014039575A1
Authority
WO
WIPO (PCT)
Prior art keywords
fibers
type
backing
fabric
membrane
Prior art date
Application number
PCT/US2013/058087
Other languages
French (fr)
Inventor
John R. Herron
Original Assignee
Hydration Systems, Llc
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 Hydration Systems, Llc filed Critical Hydration Systems, Llc
Publication of WO2014039575A1 publication Critical patent/WO2014039575A1/en

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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
    • B01D69/10—Supported membranes; Membrane supports
    • B01D69/107—Organic support material
    • 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
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
    • B01D39/1692—Other shaped material, e.g. perforated or porous sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
    • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
    • B01D2239/0604—Arrangement of the fibres in the filtering material
    • B01D2239/0618—Non-woven
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2239/00—Aspects relating to filtering material for liquid or gaseous fluids
    • B01D2239/06—Filter cloth, e.g. knitted, woven non-woven; self-supported material
    • B01D2239/0604—Arrangement of the fibres in the filtering material
    • B01D2239/064—The fibres being mixed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/002—Forward osmosis or direct osmosis

Definitions

  • This invention relates to a support fabric for thin film composite membranes and asymmetric membranes for use in water filtration processes.
  • RO reverse osmosis
  • flat- sheet RO membrane production a thin, dense, nonwoven fabric (100 - 150 microns thick) has a polymer solution cast onto it, and the coated fabric is introduced into a coagulation bath where the solvent is removed and the membrane is formed.
  • the fabrics used in RO are relatively dense and highly calendered so that the coating solution does not penetrate the full thickness of the fabric before congealing. This provides a back layer of uncoated nonwoven fabric on the membrane which is required for adhesion of the membrane when it is formed into membrane elements.
  • the nonwoven fabrics are required in RO to provide mechanical strength and stability to the membrane. In comparison to the high pressure drops seen across the RO rejection layer, the density and impermeability of the nonwoven fabric backing layer contributes little to the system flow resistance. In other words, the use of a nonwoven fabric backing layer does not significantly impede flow in RO processes.
  • highly calendered nonwoven fabric backing layers do not work well in forward osmosis (FO) membrane processes.
  • FO membranes are formed by phase inversion in a manner similar to RO membranes.
  • FO process differs from RO in that, instead of a being a pressure driven process, FO is a diffusion based process. A consequence of the diffusion driving force in FO is that the diffusion resistance of the nonwoven fabric is a major impediment to the FO process. Dense fabrics which provide negligible resistance in RO may actually drop FO productivity by as much as a factor of 10.
  • the disclosed invention is a nonwoven fabric backing for membranes, and method for making same. More specifically, the nonwoven backing fabric is comprised of a combination of two types of fibers, wherein the first type are fibers that are substantially insoluble in the coagulation and annealing baths, and the second type of fibers are partially or substantially completely soluble in the annealing bath.
  • a membrane is produced by subjecting the backing fabric of the invention to phase inversion by casting a polymer solution onto the fabric to produce a coated fabric, introducing the coated fabric to a coagulation bath, and thereafter subjecting the coated fabric to annealing.
  • the resulting membrane possesses sufficient mechanical strength for the FO process while being thin, possesses an open structure to allow diffusion, and still provides an uncoated back surface for adhesion during the assembly of membrane elements.
  • the method involves producing a thin, highly-calendered dense, nonwoven backing fabric support material similar to those used in RO processes, but wherein a portion of the fibers in the fabric are composed of a material (e.g., plastic) that is at least partially soluble in the coagulation bath and/or annealing baths.
  • the nonwoven backing fabric support material is used as a support for a polymeric layer.
  • the nonwoven backing fabric is comprised of a combination of water insoluble and water soluble fibers.
  • the fibers of the first type are substantially insoluble in the coagulation and annealing baths.
  • the fibers of the second type are at least partially soluble in the coagulation bath and are substantially completely soluble in the annealing bath.
  • the fibers of the first type may be a blend of fibers with different diameters, lengths, and polymer type, but at least one constituent must have a melting point that is lower than the melting point of the fibers of the second type.
  • the membrane is produced by casting a polymer solution onto the nonwoven backing fabric to produce a coated fabric, introducing the coated fabric to a coagulation bath, and thereafter subjecting the coated fabric to annealing.
  • the substantially soluble fibers in the fabric dissolve at least partially in the coagulation and annealing baths, leaving a membrane comprising nonwoven backing fabric no longer containing the soluble fibers, wherein the fabric has a polymeric membrane coating.
  • first (insoluble) and second (soluble) fibers in the nonwoven fabric backing according to the invention may vary.
  • the nonwoven fabric backing could be made of about 40% to about 50% fibers that are soluble, or other proportions.
  • the nonwoven fabric backing according to the invention may be comprised of only one type of substantially soluble fiber and one type of substantially insoluble fiber.
  • type refers to the particular composition of the fiber.
  • the fabric backing may be comprised of two or more types of substantially soluble fibers and/or two or more types of substantially insoluble fibers.
  • Nonlimiting examples of appropriate materials fibers for the nonwoven fabric backing support are as follows.
  • the substantially insoluble (non-dissolving) fibers polyester, co-polyester, polypropylene, PET or PVA, and mixtures of the foregoing may be used.
  • water soluble PET or PVA may be used.
  • the first type of fibers is a mixture of PET fibers and either EVA or polypropylene, and the second type of fibers is PVA.

Abstract

The disclosed invention is a nonwoven fabric backing for membranes, and method for making same. More specifically, the nonwoven backing fabric is comprised of a combination of two types of fibers, wherein the first type are fibers that are substantially insoluble in the coagulation and annealing baths, and the second type of fibers are partially or substantially completely soluble in the annealing bath. A membrane is produced by subjecting the backing fabric of the invention to phase inversion, by casting a polymer solution onto the fabric to produce a coated fabric, introducing the coated fabric to a coagulation bath, and thereafter subjecting the coated fabric to annealing. The resulting membrane possesses sufficient mechanical strength for the FO process while being thin, possesses an open structure to allow diffusion, and still provides an uncoated back surface for adhesion during the assembly of membrane elements.

Description

PHASE INVERSION MEMBRANE
AND METHOD FOR MANUFACTURING SAME USING SOLUBLE FIBERS
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This PCT patent application claims priority to the pending provisional application serial number 61/697,656 filed on September 6, 2012 entitled "Phase Inversion Membrane and Method for Manufacturing Same Using Soluble Fibers," the entire disclosure of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a support fabric for thin film composite membranes and asymmetric membranes for use in water filtration processes.
BACKGROUND
[0003] Membranes formed by phase inversion of polymer solutions are widely used in water filtration. Essentially all reverse osmosis (RO) membranes are made using the process. In flat- sheet RO membrane production, a thin, dense, nonwoven fabric (100 - 150 microns thick) has a polymer solution cast onto it, and the coated fabric is introduced into a coagulation bath where the solvent is removed and the membrane is formed. The fabrics used in RO are relatively dense and highly calendered so that the coating solution does not penetrate the full thickness of the fabric before congealing. This provides a back layer of uncoated nonwoven fabric on the membrane which is required for adhesion of the membrane when it is formed into membrane elements.
[0004] The nonwoven fabrics are required in RO to provide mechanical strength and stability to the membrane. In comparison to the high pressure drops seen across the RO rejection layer, the density and impermeability of the nonwoven fabric backing layer contributes little to the system flow resistance. In other words, the use of a nonwoven fabric backing layer does not significantly impede flow in RO processes. [0005] In contrast, highly calendered nonwoven fabric backing layers do not work well in forward osmosis (FO) membrane processes. FO membranes are formed by phase inversion in a manner similar to RO membranes. However, the FO process differs from RO in that, instead of a being a pressure driven process, FO is a diffusion based process. A consequence of the diffusion driving force in FO is that the diffusion resistance of the nonwoven fabric is a major impediment to the FO process. Dense fabrics which provide negligible resistance in RO may actually drop FO productivity by as much as a factor of 10.
SUMMARY OF THE INVENTION
[0006] The disclosed invention is a nonwoven fabric backing for membranes, and method for making same. More specifically, the nonwoven backing fabric is comprised of a combination of two types of fibers, wherein the first type are fibers that are substantially insoluble in the coagulation and annealing baths, and the second type of fibers are partially or substantially completely soluble in the annealing bath. A membrane is produced by subjecting the backing fabric of the invention to phase inversion by casting a polymer solution onto the fabric to produce a coated fabric, introducing the coated fabric to a coagulation bath, and thereafter subjecting the coated fabric to annealing.
[0007] The resulting membrane possesses sufficient mechanical strength for the FO process while being thin, possesses an open structure to allow diffusion, and still provides an uncoated back surface for adhesion during the assembly of membrane elements.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The method involves producing a thin, highly-calendered dense, nonwoven backing fabric support material similar to those used in RO processes, but wherein a portion of the fibers in the fabric are composed of a material (e.g., plastic) that is at least partially soluble in the coagulation bath and/or annealing baths. The nonwoven backing fabric support material is used as a support for a polymeric layer.
[0009] The nonwoven backing fabric is comprised of a combination of water insoluble and water soluble fibers. The fibers of the first type are substantially insoluble in the coagulation and annealing baths. The fibers of the second type are at least partially soluble in the coagulation bath and are substantially completely soluble in the annealing bath.
[0010] The fibers of the first type may be a blend of fibers with different diameters, lengths, and polymer type, but at least one constituent must have a melting point that is lower than the melting point of the fibers of the second type.
[0011] The membrane is produced by casting a polymer solution onto the nonwoven backing fabric to produce a coated fabric, introducing the coated fabric to a coagulation bath, and thereafter subjecting the coated fabric to annealing. The substantially soluble fibers in the fabric dissolve at least partially in the coagulation and annealing baths, leaving a membrane comprising nonwoven backing fabric no longer containing the soluble fibers, wherein the fabric has a polymeric membrane coating.
[0012] The proportions of first (insoluble) and second (soluble) fibers in the nonwoven fabric backing according to the invention may vary. For example, the nonwoven fabric backing could be made of about 40% to about 50% fibers that are soluble, or other proportions.
[0013] The nonwoven fabric backing according to the invention may be comprised of only one type of substantially soluble fiber and one type of substantially insoluble fiber. The term "type" as used herein refers to the particular composition of the fiber. Alternatively, the fabric backing may be comprised of two or more types of substantially soluble fibers and/or two or more types of substantially insoluble fibers.
[0014] Nonlimiting examples of appropriate materials fibers for the nonwoven fabric backing support are as follows.
[0015] For the first type of fibers, i.e., the substantially insoluble (non-dissolving) fibers, polyester, co-polyester, polypropylene, PET or PVA, and mixtures of the foregoing may be used
[0016] For the second type of fibers, i.e., the substantially soluble fibers, water soluble PET or PVA may be used.
[0017] Other materials may also be used, provided that they have the solubility and melting point characteristics required to produce the backing described herein. [0018] In a preferred embodiment, the first type of fibers is a mixture of PET fibers and either EVA or polypropylene, and the second type of fibers is PVA.
[0019] When a polymer membrane is cast on this fabric, the polymer will not completely penetrate the fabric due to the high density of the fabric. As the cast polymer membrane travels through the coagulation and rinse baths, however, the soluble fibers in the fabric will dissolve and leave an open backing structure having an uncoated back. The uncoated backing is useful for adhering the membrane structure to other components in the membrane element.

Claims

1. A nonwoven backing for a membrane comprising fibers of a first type and fibers of a second type, wherein:
a) the fibers of the first type are substantially insoluble in water; and b) the fibers of the second type are substantially soluble in water.
2. The nonwoven backing of Claim 1 , wherein the fibers of the first type have a melting point that is lower than the melting point of the fibers of the second type.
3. The nonwoven backing of Claim 2, wherein the fibers of the first type are selected from the group consisting of polyester, co-polyester, polypropylene, PET or PVA, and mixtures thereof, and the fibers of the second type are selected from the group consisting of water soluble PET or PVA and mixtures thereof.
4. The nonwoven backing of Claim 3, wherein the fibers of the first type comprise PET and EVA or polypropylene, and the fibers of the second type comprise PVA.
5. A method for manufacturing a phase inversion membrane comprising the steps of: a) providing a porous nonwoven backing comprising fibers of a first type and fibers of a second type, wherein the fibers of the first type are substantially insoluble in water; and the fibers of the second type are substantially soluble in water;
b) casting a polymer solution onto the backing to form a coated backer; and c) introducing the coated backing to a coagulation bath to remove solvent remaining from the polymer solution, and subjecting the coated backing to an annealing bath, to produce a phase inversion membrane.
6. The method of Claim 5, wherein step (a) comprises providing a backing comprising:
a) fibers of the first type selected from the group consisting of polyester, co- polyester, polypropylene, PET or PVA, and mixtures thereof; and
b) fibers of the second type selected from the group consisting of water soluble PET or PVA and mixtures thereof.
PCT/US2013/058087 2012-09-06 2013-09-04 Phase inversion membrane and method for manufacturing same using soluble fibers WO2014039575A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201261697656P 2012-09-06 2012-09-06
US61/697,656 2012-09-06

Publications (1)

Publication Number Publication Date
WO2014039575A1 true WO2014039575A1 (en) 2014-03-13

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Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1148382A (en) * 1965-02-23 1969-04-10 Rasmussen O B Split films of polymer material
US3950255A (en) * 1973-11-09 1976-04-13 Daicel Ltd. Supported semi-permeable membranes
US3992495A (en) * 1973-09-07 1976-11-16 Sumitomo Chemical Company, Limited Method of manufacturing a semipermeable membrane from a water-soluble polymeric resin
US4046843A (en) * 1974-09-05 1977-09-06 Sumitomo Chemical Company, Limited Process for preparing membranes for separation of substances
US4933083A (en) * 1985-04-15 1990-06-12 Hoechst Celanese Corp. Polybenzimidazole thin film composite membranes
US5567510A (en) * 1994-12-30 1996-10-22 Minnesota Mining And Manufacturing Company Dispersible compositions and articles and method of disposal for such compositions and articles
US20080017569A1 (en) * 2006-05-09 2008-01-24 Ramsey Thomas H Porous composite membrane materials and applications thereof
US20080143014A1 (en) * 2006-12-18 2008-06-19 Man-Wing Tang Asymmetric Gas Separation Membranes with Superior Capabilities for Gas Separation
US20100221983A1 (en) * 2009-01-05 2010-09-02 Innopad, Inc. Multi-layered chemical-mechanical planarization pad

Patent Citations (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1148382A (en) * 1965-02-23 1969-04-10 Rasmussen O B Split films of polymer material
US3992495A (en) * 1973-09-07 1976-11-16 Sumitomo Chemical Company, Limited Method of manufacturing a semipermeable membrane from a water-soluble polymeric resin
US3950255A (en) * 1973-11-09 1976-04-13 Daicel Ltd. Supported semi-permeable membranes
US4046843A (en) * 1974-09-05 1977-09-06 Sumitomo Chemical Company, Limited Process for preparing membranes for separation of substances
US4933083A (en) * 1985-04-15 1990-06-12 Hoechst Celanese Corp. Polybenzimidazole thin film composite membranes
US5567510A (en) * 1994-12-30 1996-10-22 Minnesota Mining And Manufacturing Company Dispersible compositions and articles and method of disposal for such compositions and articles
US20080017569A1 (en) * 2006-05-09 2008-01-24 Ramsey Thomas H Porous composite membrane materials and applications thereof
US20080143014A1 (en) * 2006-12-18 2008-06-19 Man-Wing Tang Asymmetric Gas Separation Membranes with Superior Capabilities for Gas Separation
US20100221983A1 (en) * 2009-01-05 2010-09-02 Innopad, Inc. Multi-layered chemical-mechanical planarization pad

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