LIQUID FILTRATION MEDIA

• US 20110042316A1
• Filed: 11/05/2010
• Published: 02/24/2011
• Est. Priority Date: 03/06/2007
• Status: Active Grant

• Current Assignee: DuPont Safety & Construction, Inc. (DuPont de Nemours, Inc.)
• Original Assignee: E. I. du Pont de Nemours and Company (Corteva, Inc.)
• Inventors: Chen, Guanghui, Gommeren, Henricus Jacobus Cornelis, Knorr, Lawrence Mark
• Granted Patent: US 9,180,393 B2
• Time in Patent Office: Days
• US Class Current: 210/650
• CPC Class Codes: B01D 2239/025 comprising nanofibres apparatus incorporating such gas filtering material see B01D46/546
• CPC Class Codes: B01D 2239/065 More than one layer present in the filtering material apparatus incorporating such gas filtering material B01D2275/10
• CPC Class Codes: B01D 2239/0668 The layers being joined by heat or melt-bonding
• CPC Class Codes: B01D 2239/0681 The layers being joined by gluing
• CPC Class Codes: B01D 2311/04 Specific process operations in the feed stream; Feed pretreatment
• CPC Class Codes: B01D 2311/2649 Filtration
• CPC Class Codes: B01D 2323/39 Electrospinning
• CPC Class Codes: B01D 2325/40 Fibre reinforced membranes
• CPC Class Codes: B01D 39/1623 of synthetic origin
• CPC Class Codes: B01D 39/1692 Other shaped material, e.g. perforated or porous sheets
• CPC Class Codes: B01D 61/147 Microfiltration
• CPC Class Codes: B01D 61/16 Feed pretreatment
• CPC Class Codes: B01D 61/18 Apparatus therefor
• CPC Class Codes: B01D 69/12 Composite membranes; Ultra-thin membranes
• CPC Class Codes: B01D 69/1213 Laminated layers
• CPC Class Codes: B01D 71/36 Polytetrafluoroethene
• CPC Class Codes: B01D 71/56 Polyamides, e.g. polyester-amides
• CPC Class Codes: D04H 1/42 characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
• CPC Class Codes: D04H 1/4374 using different kinds of webs, e.g. by layering webs
• CPC Class Codes: D04H 1/43838 Ultrafine fibres, e.g. microfibres

Abstract

A liquid filter with a composite medium that has a nanoweb adjacent to and optionally bonded to a microporous membrane. The membrane is characterized by an LRV value of 3.7 at a rated particle size, and the nanoweb has a fractional filtration efficiency of greater than 0.1 at the rated particle size of the membrane. The nanoweb also has a thickness efficiency ratio of greater than 0.0002 at that efficiency. The nanoweb acts to provide depth filtration to the membrane, prefilters particles and extends the lifetime of the membrane.

Claims

1. A filter system for filtering particles from liquid comprising at least one nanoweb layer of polymeric nanofibers upstream of, and in fluid contact with, a microfiltration membrane, wherein the nanoweb layer has a filtration efficiency rating of at least 10% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, and a thickness efficiency ratio of greater than about 0.0002, and wherein the pressure drop across the nanoweb is less than or equal to 60% of that across the filter system for a given fluid flow rate.

2. The filter system of claim 1 in which the microfiltration membrane is rated at less than 5 microns.

3. The filter system of claim 2 in which the microfiltration membrane is rated at less than 2 microns.

4. The filter system of claim 3 in which the microfiltration membrane is rated at less than 1.2 microns.

5. The filter system of claim 1 in which the nanoweb layer has a filtration efficiency rating of at least 30% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, and a thickness efficiency ratio of greater than about 0.0005.

6. The filter system of claim 1 in which the nanoweb layer has a filtration efficiency rating of at least 50% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, and a thickness efficiency ratio of greater than about 0.001.

7. The filter system of claim 1 in which the nanoweb layer has a filtration efficiency rating of at least 80% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, and a thickness efficiency ratio of greater than about 0.002.

8. The filter system of claim 1 in which the nanoweb layer has a filtration efficiency rating of at least 90% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, and a thickness efficiency ratio of greater than about 0.003.

9. The filter system of claim 1 in which the nanoweb layer has a filtration efficiency rating of at least 95% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, and a thickness efficiency ratio of greater than about 0.004.

10. The filter system of claim 1 in which the membrane comprises a polymeric material selected from the group consisting of expanded polytetrafluoroethylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polycarbonate, polyamide, polyacrylonitrile, polyethylene, polypropylene, polyester, cellulose acetate, cellulose nitrate, mixed cellulose ester, and blends and combinations thereof.

11. The filter system of claim 1 in which the nanoweb has a thickness of less than about 300 μ

m.

12. The filter system of claim 1 in which the nanoweb has a thickness of less than about 150 μ

m.

13. The filter system of claim 1 in which the nanoweb and the membrane are adjacent to each other.

14. The filter system of claim 13 in which the nanoweb and the membrane are bonded over at least a fraction of their surfaces.

15. The filter system of claim 14 in which the membrane and the nanoweb are bonded by a means selected from the group consisting of thermal lamination, point bonding, ultrasonic bonding, and adhesive bonding.

16. (canceled)

17. (canceled)

18. A composite liquid filtration medium comprising at least one nanoweb layer of polymeric nanofibers adjacent to and in a face to face relationship with a microfiltration membrane, wherein the nanoweb layer has a filtration efficiency rating of at least 95% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, a thickness efficiency ratio of greater than about 0.01, and wherein the pressure drop across the nanoweb is less than or equal to 60% of that across the composite liquid filtration medium for a given fluid flow rate, and wherein the nanoweb layer is positioned upstream of the microfiltration membrane.

19. A filter system for filtering particles from liquid comprising at least one nanoweb layer of polymeric nanofibers upstream of, and in fluid contact with, a microfiltration membrane, wherein the nanoweb layer has;

a mean flow pore size of less than or about fives times that of the membrane,

a bubble point pore size of less than or about 7.5 times than that of the membrane, and

a thickness less than or equal to about twice the thickness of the membrane.

20. The filter system of claim 19 in which the microfiltration membrane is rated at less than 5 microns.

21. The filter system of claim 20 in which the microfiltration membrane is rated at less than 2 microns.

22. The filter system of claim 21 in which the microfiltration membrane is rated at less than 1.2 microns.

23. The filter system of claim 19 in which the nanoweb layer has;

a mean flow pore size of less than or about three times that of the membrane, and

a bubble point pore size of less than or about 4.5 times than that of the membrane.

24. The filter system of claim 19 in which the nanoweb layer has;

a mean flow pore size of less than or about two times that of the membrane, and

a bubble point pore size of less than or about three times than that of the membrane.

25. The filter system of claim 19 in which the membrane comprises a polymeric material selected from the group consisting of expanded polytetrafluoroethylene, polysulfone, polyethersulfone, polyvinylidene fluoride, polycarbonate, polyamide, polyacrylonitrile, polyethylene, polypropylene, polyester, cellulose acetate, cellulose nitrate, mixed cellulose ester, and blends and combinations thereof.

26. The filter system of claim 19 in which the nanoweb has a thickness of less than about 300 μ

m.

27. The filter system of claim 19 in which the nanoweb has a thickness of less than about 150 μ

m.

28. The filter system of claim 19 in which the nanoweb and the membrane are adjacent to each other.

29. The filter system of claim 28 in which the nanoweb and the membrane are bonded over at least a fraction of their surfaces.

30. The filter system of claim 29 in which the membrane and the nanoweb are bonded by a means selected from the group consisting of thermal lamination, point bonding, ultrasonic bonding, and adhesive bonding.

36. The method of claim 26 in which the nanoweb layer and the membrane layer are adjacent to each other.

31. (canceled)

32. (canceled)

33. A method for filtering particles from a liquid comprising the steps of passing the liquid through a nanoweb layer, followed by a membrane layer in fluid contact with the nanoweb layer, in which the nanoweb layer has a filtration efficiency rating of at least 10% for a particle size at which the membrane is rated with an LRV of 3.7 or greater, and a thickness efficiency ratio of greater than about 0.0002, and wherein the pressure drop across the nanoweb is less than or equal to 60% of that across the composite liquid filtration medium for a given fluid flow rate, and the nanoweb layer is positioned upstream of the microfiltration membrane.

34. The method of claim 33 in which the nanoweb layer and the membrane layer are adjacent to each other.

35. A method for filtering particles from a liquid comprising the steps of passing the liquid through a nanoweb layer, followed by a membrane layer, wherein the nanoweb layer has;

a mean flow pore size of less than or about fives times that of the membrane,

a bubble point pore size of less than or about 7.5 times than that of the membrane, and

a thickness less than or equal to about twice the thickness of the membrane,

and the nanoweb layer is positioned upstream of the microfiltration membrane.