High performance filters comprising inorganic fibers having inorganic fiber whiskers grown thereon

• US 6,390,304 B1
• Filed: 02/04/2000
• Issued: 05/21/2002
• Est. Priority Date: 06/02/1997
• Status: Expired due to Fees

• Current Assignee: HITCO Carbon Composites, Inc. (Sgl Carbon Se)
• Original Assignee: HITCO Carbon Composites, Inc. (Sgl Carbon Se)
• Inventors: Wilson, Doug, Mathur, Raj
• Primary Examiner(s): Drodge, Joseph W.
• Application Number:
  US09/498,460
• Time in Patent Office: 837 Days
• Field of Search: 210/439, 210/500.23, 210/491, 210/500.25, 210/500.26, 210/500.27, 210/502.1, 210/503, 210/505, 210/508, 210/509, 428/306.6, 428/307.3, 428/312.2, 428/312.6, 428/317.9, 428/318.4, 428/319.1, 428/408, 428/446, 428/698, 501/94, 501/95.1, 501/95.2, 501/95.3, 501/96, 501/97, 501/87, 501/88, 501/90, 502/224, 502/229, 502/326, 502/527.12, 555/23, 555/24
• US Class Current: 210/491
• CPC Class Codes: B01D 2239/0471 Surface coating material
• CPC Class Codes: B01D 2239/0609 Knitted
• CPC Class Codes: B01D 2239/0613 Woven
• CPC Class Codes: B01D 2239/064 The fibres being mixed
• 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 2239/10 Filtering material manufacturing
• CPC Class Codes: B01D 2239/1208 Porosity apparatus incorporating such gas filtering material B01D2275/30 - B01D2275/307
• CPC Class Codes: B01D 2239/1225 Fibre length
• CPC Class Codes: B01D 2239/1233 Fibre diameter
• CPC Class Codes: B01D 39/2017 the material being filamentary or fibrous
• CPC Class Codes: B01D 39/2055 Carbonaceous material solid sorbent compositions comprising free carbon B01J20/20
• CPC Class Codes: B01D 39/2065 the material being fibrous
• CPC Class Codes: B01D 39/2082 the material being filamentary or fibrous
• CPC Class Codes: C04B 2111/00793 as filters or diaphragms
• CPC Class Codes: C04B 2235/5224 Alumina or aluminates
• CPC Class Codes: C04B 2235/5228 Silica and alumina, including aluminosilicates, e.g. mullite
• CPC Class Codes: C04B 2235/524 Non-oxidic, e.g. borides, carbides, silicides or nitrides
• CPC Class Codes: C04B 2235/5244 Silicon carbide
• CPC Class Codes: C04B 2235/5248 Carbon, e.g. graphite
• CPC Class Codes: C04B 2235/5252 having a specific pre-form
• CPC Class Codes: C04B 2235/526 : characterised by the length of the fibers
• CPC Class Codes: C04B 2235/5264 : characterised by the diameter of the fibers
• CPC Class Codes: C04B 2235/5268 : Orientation of the fibers
• CPC Class Codes: C04B 2235/5276 : Whiskers, spindles, needles or pins
• CPC Class Codes: C04B 35/565 : based on silicon carbide
• CPC Class Codes: C04B 35/584 : based on silicon nitride
• CPC Class Codes: C04B 35/6265 : involving reduction or oxidation
• CPC Class Codes: C04B 35/6268 : characterised by the applied pressure or type of atmosphere, e.g. in vacuum, hydrogen or a specific oxygen pressure
• CPC Class Codes: C04B 35/62876 : with metals
• CPC Class Codes: C04B 35/80 : Fibres, filaments, whiskers, platelets, or the like
• CPC Class Codes: C04B 35/806 : The matrix of the ceramic products consisting of non-oxides only
• CPC Class Codes: C04B 35/82 : Asbestos; Glass; Fused silica
• CPC Class Codes: C04B 35/83 : Carbon fibres in a carbon matrix
• CPC Class Codes: C04B 41/009 : characterised by the material treated
• CPC Class Codes: C04B 41/455 : the coating or impregnating process including a chemical conversion or reaction
• CPC Class Codes: C04B 41/4596 : with fibrous materials or whiskers
• CPC Class Codes: C04B 41/5001 : with carbon or carbonisable materials
• CPC Class Codes: C04B 41/5053 : non-oxide ceramics carbon or carbonisable materials C04B41/5001
• CPC Class Codes: C04B 41/5144 : with a composition mainly composed of one or more of the metals of the iron group
• CPC Class Codes: C04B 41/81 : Coating or impregnation
• CPC Class Codes: Y10T 428/249955 : Void-containing component partially impregnated with adjacent component
• CPC Class Codes: Y10T 428/30 : Self-sustaining carbon mass or layer with impregnant or other layer

Abstract

A filter media system, which is capable of operating in the microfiltration regime, offers: low cost, durability, high temperature and chemical resistance, no particulation, mechanical strength, separation efficiency, and biocompatibility. The present invention provides a filter media system comprising a fibrous substrate of at least one of carbon and ceramic fibers, wherein an array of carbon or ceramic fiber whiskers have been grown onto the fibrous substrate, without prior densification of the fibrous substrate. A process for manufacturing a filter media system wherein a carbon fiber is treated with a solution of metal catalyst salt, heated in hydrogen at elevated temperatures to reduce the metal salt to metal, and whisker growth is initiated on the surfaces of the metal deposited carbon fibers by decomposition of low molecular weight hydrocarbon gas at elevated temperature is also provided.

Claims

1. A filter media system comprising a fibrous substrate of at least one of carbon or ceratic fibers wherein an array of carbon or ceramic fiber whiskers have been grown onto surfaces of the fibers comprising the fibrous substrate, wherein the filter media system has an interconnected porosity that is adapted to allow fluid to flow through the filter media system and a pore size distribution that is adapted to capture particles in the range of about 0.1 to about 100 microns.

2. The filter media system of claim 1 wherein said fibrous substrate has a level of total metal impurity below about 10 parts per million.

3. The filter media system of claim 1 wherein the fibers are selected from the group consisting of unidirectional array, woven cloth, fabric, felt, tow, chopped fabric, chopped tow, brushed fabric, and cut-pile fabric.

4. The filter media system of claim 1 wherein the ceramic fibers comprise at least one of silicon carbide, silicon nitride, aluminosilicate, silica, and glass.

5. The filter media system of claim 1 wherein the filter media system contains about 10% to about 90% fibers by weight and about 90% to about 10% matrix by weight based on the weight of the substrate.

6. The filter media system of claim 1 wherein the amount of fiber whiskers in the system ranges from about 5% to about 90% by weight of the total substrate and fiber whiskers.

7. The filter media system of claim 1 wherein the fiber whiskers are selected from the group consisting of carbon, silicon carbide, silicon nitride, titanium carbide, titanium nitride, and mixtures thereof.

8. The filter media system of claim 1 wherein the fiber whiskers are about 1 to about 25 microns in length.

9. The filter media system of claim 1 wherein the fiber whiskers have a range of about 5 to about 15 microns in length.

10. The filter media system of claim 1 wherein the fiber whiskers are about 0.1 to about 5 microns in diameter.

11. The filter media system of claim 1 wherein the whisker configuration is straight.

12. The filter media system of claim 1 wherein the whisker configuration is highly branched.

13. The filter media system of claim 1 wherein the carbon fibers comprise carbon fibers made from PAN, pitch, or rayon precursors.

14. The filter media system of claim 1 wherein the fiber whiskers are disposed in a selected location.

15. The filter media system of claim 1 wherein the fiber whiskers are intimately bonded to the fibrous substrate.

16. The filter media system of claim 1 wherein said system is highly permeable.

17. The filter media system of claim 1 wherein, in the microfiltration range, provides a pore size distribution sufficiently small to trap particles in the range of about 0.2 to about 2 microns.

18. The filter media system of claim 1 wherein the system is in the form of a structure selected from the group consisting of a plate, hollow tube, open cylinder, corrugated plate, and corrugated cylinder.

19. A filter module containing the filter media of claim 1.

20. The filter media system of claim 1 wherein the system is adapted for use in at least one of:

i) microfiltration,

ii) high purity filtration,

iii) selectively removing unwanted species in foodstuffs,

iv) selectively removing unwanted species in milk,

v) selectively removing unwanted species in fruit juices,

vi) selectively removing unwanted species in beer,

vii) for purifying blood,

viii) purifying chemically aggressive materials,

ix) for purifying acids,

x) for purifying alkalis,

xi) for purifying solvents,

xii) purifying organic chemicals,

xiii) purifying organic chemicals, and

xiv) removing particulate matter from air.

21. The filter media system of claim 1 wherein the system comprises carbon fibers and whiskers, and is capable of operating at temperatures of about 500°

C. in air and about 3000°

C. in a non-oxidizing atmosphere.

22. The filter media system of claim 1 wherein the system comprises ceramic fibers and whiskers, and is capable of operating at temperatures of up to about 2000°

C.

23. The filter media system of claim 1 wherein the system is highly durable.

24. The filter media system of claim 1 wherein the system has strength sufficient to resist loads imparted by fluctuating pressures.

25. The filter media system of claim 1, wherein the fiber whiskers are grown on the outside of the substrate.

26. The filter media system of claim 1, wherein the fiber whiskers are grown on the inside of the substrate.

27. The filter media system of claim 1 wherein the filter media comprises carbon fibers having carbon fiber whiskers grown thereon, and wherein at least one of the carbon fibers and carbon fiber whiskers comprise activated carbon.

28. The filter media system of claim 1 wherein the carbon fiber whiskers comprise activated carbon.

29. The filter media system of claim 28 comprising activated carbon fiber whiskers on a silica fiber substrate.

30. The filter media system of claim 28 comprising activated carbon fiber whiskers on a silica fiber substrate, adapted for electrostatic precipitation with the application of an electric field.

31. A process for manufacturing a filter media system comprising carbon fibers, wherein an array of carbon fiber whiskers have been grown onto said carbon fibers, comprising:

a) providing a plurality of carbon fibers;

b) treating the carbon fibers with a solution of metal catalyst salt;

c) heating the carbon fibers in hydrogen at elevated temperatures to reduce the metal salt to metal, said metal being deposited on said carbon fibers; and

d) initiating whisker growth on the surfaces of the metal deposited carbon fibers by decomposition of low molecular weight hydrocarbon gas at elevated temperature.

32. The process in claim 31 wherein the solution of metal catalyst salt is selected from the group consisting of nickel chloride and ferric chloride.

33. The process of claim 31 wherein the whisker growth is initiated on the surfaces of the catalyst deposited carbon fibers by decomposition of a gas selected from the group consisting of ethanes methane, and propane.

34. The process of claim 31 wherein the fiber whiskers are grown on the surfaces of the carbon fibers using metal catalyzed chemical vapor deposition (CVD).

35. A process for manufacturing a filter media system comprising ceramic fibers, wherein an array of ceramic fiber whiskers have been grown onto the surfaces of said ceramic fibers, comprising:

a) providing a plurality of ceramic fibers;

b) treating the ceramic fibers with a solution of metal catalyst salt;

c) heating the ceramic fibers in hydrogen at elevated temperatures to reduce the metal salt to metal, said metal being coated on the ceramic fibers; and

d) initiating whisker growth on the surfaces of the metal coated ceramic fibers by subjecting the ceramic fibers to a whisker precursor.

36. The process of claim 35 wherein the precursor is selected from the group consisting of methylchlorosilane, alkylchlorosilane, polycarbosilane, and polycarbosilazane.

37. The process of claim 35 wherein the ceramic matrix is selected from the group consisting of silicon carbide and silicon nitride.

38. The process of claim 35 wherein the ceramic fibers are selected from the group consisting of silicon carbide, silicon nitride, aluminosilicate, silica, glass, and mixtures thereof.

39. The process of claim 35 wherein the fiber whiskers are selected from the group consisting of carbon, silicon carbide, silicon nitride, titanium carbide, titanium nitride, and mixtures thereof.