U.S. patent application number 09/956915 was filed with the patent office on 2002-02-28 for gas filter, process for producing a gas filter and use of this gas filter.
This patent application is currently assigned to Creavis Gesellschaft Fuer Technologie. Invention is credited to Hoerpel, Gerhard, Hying, Christian, Penth, Bernd.
Application Number | 20020023419 09/956915 |
Document ID | / |
Family ID | 27512604 |
Filed Date | 2002-02-28 |
United States Patent
Application |
20020023419 |
Kind Code |
A1 |
Penth, Bernd ; et
al. |
February 28, 2002 |
Gas filter, process for producing a gas filter and use of this gas
filter
Abstract
A gas filter, a process for producing a gas filter and the use
of the gas filter are claimed. The filtration of gases, in
particular of gases which are contaminated by solids, e.g.
automobile exhaust gases, is difficult since the solids which have
been filtered out block the filter over the course of time. The gas
filter of the invention can be used over relatively long periods of
time since it is regenerable. The improvement achieved by the
invention compared to conventional gas filters is that the filter
comprises a composite material which can be heated in a simple
manner by application of a voltage to the electrically conductive
support material of the composite material and thermally
decomposable substances Which can block the filter can be
decomposed. The filter of the invention can be used wherever gases
which are contaminated by thermally decomposable solids have to be
cleaned.
Inventors: |
Penth, Bernd; (Lebach,
DE) ; Hoerpel, Gerhard; (Nottuln, DE) ; Hying,
Christian; (Rhede, DE) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Creavis Gesellschaft Fuer
Technologie
Marl
DE
|
Family ID: |
27512604 |
Appl. No.: |
09/956915 |
Filed: |
September 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09956915 |
Sep 21, 2001 |
|
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09308222 |
Jul 26, 1999 |
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09308222 |
Jul 26, 1999 |
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PCT/EP98/05946 |
Sep 18, 1998 |
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Current U.S.
Class: |
55/523 ; 210/490;
210/510.1 |
Current CPC
Class: |
B01D 2325/02 20130101;
B01J 35/06 20130101; B01D 69/141 20130101; B01D 71/024 20130101;
B01D 67/0093 20130101; Y10T 428/249957 20150401; B01D 46/4263
20130101; B01D 2265/06 20130101; B01J 37/033 20130101; B01D 67/0072
20130101; B01J 37/0225 20130101; B01D 46/0056 20130101; B01D 46/71
20220101; B01J 37/0215 20130101; B01D 67/0041 20130101; B01D 53/228
20130101; B01D 46/521 20130101; B01D 67/0048 20130101; B01D 71/028
20130101; B01D 67/0069 20130101; B01D 46/24 20130101; B01D 46/48
20130101; Y10S 55/10 20130101; B01D 53/32 20130101; B01D 53/8675
20130101; B01D 53/885 20130101; B01D 2323/08 20130101; B01D 71/02
20130101 |
Class at
Publication: |
55/523 ; 210/490;
210/510.1 |
International
Class: |
B01D 039/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 20, 1997 |
DE |
197 41 498.2 |
Mar 18, 1998 |
DE |
198 11 708.6 |
Mar 19, 1998 |
DE |
198 12 035.4 |
May 8, 1998 |
DE |
198 20 580.5 |
Jun 3, 1998 |
DE |
198 24 666.8 |
Claims
1. A regenerable gas filter for filtering gases which comprises a
composite material based on at least one open-structured and
material-permeable support and having on at least one side of the
support and in the interior of the support at least one inorganic
component which comprises essentially at least one compound of a
metal, a semimetal or a mixed metal with at least one element of
main groups III to VII.
2. A regenerable gas filter which comprises a composite material
which is obtainable by application of a suspension which comprises
at least one inorganic component comprising compound of at least
one metal, a semimetal or a mixed metal with at least one element
of main groups III to -VII and a sol to an open-structured and
material-permeable support and by subsequent heating at least once
during which the suspension comprising at least one inorganic
component is solidified on or in or on and in the support.
3. A gas filter as claimed in at least one of claims 1 and 2,
wherein the composite material or the gas filter is permeable to
gases, solids or liquids.
4. A gas filter as claimed in at least one of claims 1 to 3,
wherein the open-structured and material-permeable support has
intermediate spaces having a size of from 0.02 to 500 .mu.m.
5. A gas filter as claimed in at least one of claims 1 to 4,
wherein the support comprises at least one material selected from
the group consisting of carbon, metals, alloys, glass, ceramics,
minerals, plastics, amorphous substances, natural products,
composite materials or at least one combination of these
materials.
6. A gas filter as claimed in at least one of claims 1 to 5,
wherein the support comprises at least woven, felted or ceramically
bound fibers or at least sintered spheres or particles.
7. A gas filter as claimed in at least one of claims 1 to 6,
wherein the support comprises at least one at least partially
electrically conductive material.
8. A gas filter as claimed in at least one of claims 1 to 7,
wherein the support is perforated.
9. A gas filter as claimed in at least one of claims 1 to 8,
wherein the material-permeable support has been made
material-permeable by laser treatment or ion beam treatment.
10. A gas filter as claimed in at least one of claims 1 to 9,
wherein the support comprises fibers of at least one material
selected from the group consisting of carbon, metals, alloys,
ceramics, glass, plastics, composite materials, minerals or fibers
of at least one combination of these materials.
11. A gas filter as claimed in at least one of claims 1 to 10,
wherein the support comprises woven fibers of metal or alloys.
12. A gas filter as claimed in at least one of claims 1 to 11,
wherein the support comprises at least one woven steel mesh.
13. A gas filter as claimed in at least one of claims 1 to 12,
wherein the support comprises at least one woven mesh having a mesh
opening of from 5 to 500 .mu.m.
14. A gas filter as claimed in at least one of claims 1 to 13,
wherein the support comprises at least one expanded metal having a
mesh opening of from 5 to 500 .mu.m.
15. A gas filter as claimed in at least one of claims 1 to 14,
wherein the support comprises a sintered metal, a sintered glass or
a metal nonwoven having a pore width of from 0.1 to 500 .mu.m.
16. A gas filter as claimed in at least one of claims 1 to 15,
wherein the support comprises at least aluminum, silicon, cobalt,
manganese, zinc, vanadium, molybdenum, indium, lead, bismuth,
silver, gold, nickel, copper, iron, titanium, platinum, stainless
steel, steel or brass or an alloy of these materials or a material
coated with Au, Ag, Pb, Ti, Ni, Cr, Pt, Pd, Rh, Ru and/or Ti.
17. A gas filter as claimed in at least one of claims 1 to 16,
wherein the inorganic component comprising at least one compound of
at least one metal, semimetal or mixed metal with at least one
element of main groups III to VII or at least one mixture of these
compounds comprises at least one compound of the transition
elements and of main groups III to VII or at least one compound of
the transition elements and at least one compound of main groups
III to VII, with the compounds having a particle size of from 0.01
to 25 .mu.m.
18. A gas filter as claimed in at least one of claims 1 to 17,
wherein the inorganic component comprising a compound of at least
one metal, at least one semimetal or at least one mixed metal with
at least one element of main groups III to VII or a mixture of
these compounds comprises at least one compound of an element of
transition groups III to VIII or at least one element of main
groups III to V with at least one of the elements Te, Se, S, 0, Sb,
As, P, N, Ge, Si, C, Sa, Al or B or at least one compound of an
element of transition groups III to VIII and at least one element
of main groups III to V with at least one of the elements Te, Se,
S, 0, Sb, As, P, N, Ge, Si, C, Ga, Al or B or a mixture of these
compounds.
19. A gas filter as claimed in at least one of claims 1 to 18,
wherein the inorganic component comprises at least one compound of
at least one of the elements C, Y, Ti, Zr, V, Cr. Mo, W, Fe, Co, B,
Al, In, Tl, Si, Ge, Sn, Pb, Sb or Bi with at least one of the
elements Te, Se, S, O, Sb, As, P, N, C or Ga or at least one of
these elements.
20. A gas filter as claimed in at least one of claims 1 to 19,
wherein the inorganic component comprises aluminosilicates,
aluminum phosphates, zeolites or partially: exchanged zeolites.
21. A gas filter as claimed in at least one of claims 1 to 20,
wherein the inorganic component comprises amorphous microporous
mixed oxides which may contain up to 20% of non-hydrolyzable
organic compounds.
22. A gas filter as claimed in at least one of claims 1 to 21,
wherein the inorganic component comprises at least aluminum oxide
or titanium oxide.
23. A gas filter as claimed in at least one of claims 1 to 22,
wherein the composite material comprises at least two particle size
fractions of at least one inorganic component.
24. A gas filter as claimed in claim 23, wherein the particle size
fractions in the composite material have a particle size ratio of
from 1:1 to 1:100.
25. A gas filter as claimed in at least one of claims 23 and 24,
wherein the composite material has a ratio of amounts of the
particle size fractions of from 0.01:1 to 1:0.01.
26. A gas filter as claimed in at least one of claim 1 to 25,
wherein the composite material comprises particle size fractions
having an average particle size of from 0.3 to 3 .mu.m.
27. A gas filter as claimed in at least one of claims 1 to 26,
wherein the material permeability of the composite material can be
limited to particles having a particular maximum size by means of
the particle size of the inorganic component used.
28. A gas filter as claimed in at least one of claims 1 to 27,
wherein the composite material has pores which are permeable to
particles having a maximum size of from 0.1 to 0.5 .mu.m.
29. A gas filter as claimed in at least one of claims 1 to 28,
wherein the composite material is bendable.
30. A gas filter as claimed in claim 29, wherein the composite
material can be bent to a radius of down to 2 .mu.m.
31. A gas filter as claimed in at least one of claims 1 to 30,
wherein the gas filter has the composite material rolled into a
suitable container having at least one gas inlet and at least one
gas outlet, with the composite material being arranged so that the
gas to be filtered must, after entering the gas filter, pass at
least once through the composite material before it can leave the
gas filter via the gas outlet.
32. A gas filter as claimed in at least one of claims 1 to 31,
wherein thermally decomposable solids or liquids which have been
filtered from a filtered gas and block the pores of the composite
material are removed from the gas filter by baking the gas filter
by application of a voltage to the support of the composite
material.
33. A gas filter as claimed in at least one of claims 1 to 32,
wherein the gas inlet and the gas outlet are provided with a flow-
or pressure-measuring device by means of which the pressure or the
amount of gas entering and leaving the filter is measured and when
a preset difference between the measured values, which represents a
measure of the blocking of the composite material, is reached, the
baking of the gas filter is commenced.
34. A gas filter as claimed in at least one of claims 1 to 33,
wherein the composite material comprises at least one catalytically
active component.
35. A gas filter as claimed in claim 34, wherein the composite
material comprises, as catalytically active component, at least one
inorganic material, at least one metal or at least one
organometallic compound which has catalytically active centers on
its surface.
36. A gas filter as claimed in claim 34, wherein the composite
material comprises, as catalytic component, a zeolite, silicalite
or an amorphous microporous mixed oxide.
37. A gas filter as claimed in claim 34, wherein the composite
material comprises, as catalytically active component, at least one
oxide of at least one of the elements Mo, Sn, Zn, V, Mn, Fe, Co,
Ni, As, Sb, Pb, Bi, Ru, Re, or, W, Nb, Hf, La, Ce, Gd, Ga, In, Tl,
Ag, Cu, Li, K, Na, Be, Mg, Ca, Sr and Ba.
38. A gas filter as claimed in claim 34, wherein the composite
material comprises at least titanium suboxide as catalytically
active component.
39. A gas filter as claimed in claim 34, wherein the composite
material comprises, as catalytically active component, at least one
metal compound selected from among the compounds of the metals Pt,
Rh, Ru, Ir, Au, Ag, Os, Re, Cu, Ni, Pd and Co.
40. A gas filter as claimed in claim 34, wherein the composite
material comprises, as catalytically active component, at least one
metal selected from among the metals Pt, Rh, Ru, Ce, Ir, Au, Ag,
Os, Re, Cu, Ni, Pd and Co.
41. A process for producing a gas filter as claimed in any of
claims 1 to 40, which comprises producing a material-permeable
composite material by applying, in and on at least one
open-structured and material-permeable support, at least one
suspension which comprises at least one inorganic component
comprising at least one compound of at least one metal, a semimetal
or a mixed metal with at least one of the elements of main groups
III to VII and a sol and by solidifying the suspension on or in or
on and in the support material by subsequent heating at least
once.
42. The process as claimed in claim 41, wherein the suspension is
applied on and in or else on or in the support by printing,
pressing-on, pressing-in, rolling-on, doctor blade coating,
painting-on, dipping, spraying or casting.
43. The process as claimed in at least one of claims 41 and 42,
wherein an open-structured and material-permeable support
comprising a material selected from the group consisting of carbon,
metals, minerals, ceramic, composite materials or at least one
combination of these materials is used.
44. The process as claimed in at least one of claims 41 to 43,
wherein the support comprises at least one material which is at
least partially electrically conductive.
45. The process as claimed in at least one of claims 41 to 44,
wherein a woven stainless steel mesh is used as support.
46. The process as claimed in at least one of claims 41 to 45,
wherein the suspension which comprises at least one inorganic
component and at least one metal oxide sol, at least one semimetal
oxide sol or at least one mixed metal oxide sol or a mixture of
these sols is produced by suspending at least one inorganic
component in at least one of these sols.
47 The process as claimed in at least one of claims 41 to 46,
wherein the suspension comprises at least one catalytically active
component.
48. The process as claimed in at least one of claims 41 to 47,
wherein the sols are obtained by hydrolyzing at least one metal
compound, a mixed metal compound or at least one semimetal compound
using a liquid, a gas or a solid.
49. The process as claimed in claim 48, wherein the liquid, gas or
solid used for hydrolyzing the metal compound is water, water
vapor, ice, alcohol or an acid or a combination of these
compounds.
50. The process as claimed In at least one of claims 48 and 9,
wherein the compound to be hydrolyzed is added prior to the
hydrolysis to alcohol or an acid or a combination of these alcohol
or an acid or a combination of these liquids.
51. The process as claimed in at least one of claims 48 to 50,
wherein at least one metal nitrate, a metal chloride, a metal
carbonate, a metal alkoxide compound or at least one semimetal
alkoxide compound is hydrolyzed.
52. The process as claimed in claim 51, wherein at least one metal
alkoxide compound or at least one semimetal alkoxide compound
selected from among the alkoxide compounds of the elements Ti, Zr,
Al, Si, Sn, Ce and Y or a metal nitrate, a metal chloride or a
metal carbonate selected from among the metal salts of the elements
Ti, Zr, Al, Si, Sn, Ce and Y is hydrolyzed.
53. The process as claimed in claim 52, wherein a titanium alkoxide
compound is hydrolyzed.
54. The process as claimed in at least one of claims 41 to 53,
wherein the hydrolysis of the compounds to be hydrolyzed is carried
out using at least half the molar ratio of water, based on the
hydrolyzable group of the hydrolyzable compound.
55. The process as claimed in at least one of claims 41 to 54,
wherein the hydrolyzed compound is treated with at least one
organic or inorganic acid.
56. The process as claimed in claim 55, wherein the organic or
inorganic acid has a concentration of from 10 to 60%.
57. The process as claimed in at least one of claims 55 and 56,
wherein the hydrolyzed compound is treated with at least one
mineral acid selected from the group consisting of nitric acid,
sulfuric acid, perchloric acid and hydrochloric acid or a
combination of these acids.
58. The process as claimed in at least one of claims 41 to 57,
wherein a titanium dioxide sol acidified with mineral acid is used
as sol.
59. The process as claimed in at least one claims 41 to 58, wherein
at least one inorganic component having a particle size of from 1
to 10,000 nm is suspended in a sol.
60. The process as claimed in claim 59, wherein an inorganic
component comprising at least one compound selected from among
metal compounds, semimetal compounds, mixed metal compounds and
metal mixed compounds with at least one of the elements of main
groups III to VII, or at least one mixture of these compounds, is
suspended.
61. The process as claimed in at least one of claims 59 and 60,
wherein an inorganic component comprising at least one compound
from among the oxides of the transition elements or the elements of
main groups III to V is suspended.
62. The process as claimed in claim 61, wherein the oxides are
selected from among the oxides of the elements Sc, Y, Ti, Zr, V,
Nb, Cr, Mo, W, Mn, Fe, Co, B, Al, In, Tl, Si, Ge, Sn, Pb and
Bi.
63. The process as claimed in at least one of claims 41 to 62,
wherein at least one inorganic component used is aluminum oxide
having a particle size of from 0.3 to 3 .mu.m.
64. The process as claimed in at least one of claims 41 to 63,
wherein at least one catalytically active component is incorporated
into the composite material.
65. The process as claimed in at least one of claims 41 to 64,
wherein at least one catalytically active component is added to the
sol.
66. The process as claimed in at least one of claims 41 to 65,
herein at least one catalytically active component having a
particle size of from 1 to 10,000 nm is suspended in a sol.
67. The process as claimed in at least one of claims 65 and 66,
wherein at least one catalytically active component comprises at
least one compound selected from among metal compounds, semimetal
compounds, mixed metal compounds and metal mixed compounds with at
least one of the elements of main groups III to VII or organic
compounds or at least one mixture of these compounds.
68. The process as claimed in at least one of claims 41 to 67,
wherein at least one noble metal, a noble metal compound or a
zeolite is incorporated as catalytic component into the composite
material.
69. The process as claimed in at least one of claims 41 to 68,
wherein at least one catalytically active component comprises at
least one compound selected from the group consisting of zeolite,
silicalite or amorphous mixed oxide.
70. The process as claimed in at least one of claims 41 to 69,
wherein the proportion by mass of the suspended components
corresponds to from 0.1 to 500 times the hydrolyzed compound
used.
71. The process as claimed in at least one of claims 41 to 70,
wherein the suspension present on and in or else on or in the
support is solidified by heating the composite at least once at
from 50 to 1000.degree. C.
72. The process as claimed in claim 71, wherein the composite is
subjected to a temperature of from 50 to 100.degree. C. for from 10
minutes to 5 hours.
73. The process as claimed in claim 71, wherein the composite is
subjected to a temperature of from 100 to 800.degree. C. for from 1
second to 10 minutes.
74. The process as claimed in at least one of claims 71 to 73,
wherein heating is carried out by means of heated air, hot air,
infrared radiation, microwave radiation or electrically generated
heat.
75. The process as claimed in at least one of claims 71 to 73,
wherein heating is carried out using the support material as
electrical resistance heating element.
76. The process as claimed in at least one of claims 41 to 75,
wherein the solidification of the suspension is achieved by
applying the suspension on and in a preheated support.
77. The process as claimed in at least one of claims 41 to 76,
wherein at least one support is unwound from a roll, passed at a
speed of from 1 to 50 m/h through at least one apparatus which
applies the suspension on or in or on and in the support and at
least one further apparatus which makes possible the solidification
of the suspension on or in or on and in the support by heating and
the composite material produced in this way is wound up on a second
roll.
78. The process as claimed in at least one of claims 41 to 77,
wherein an unsintered ceramic or inorganic layer is applied to a
support and is strengthened by heating.
79. The process as claimed in at least one of claims 41 to 78,
wherein the dried and strengthened composite material impregnated
with a solution comprising at least one metal salt, the composite
material which has been treated in this way is dried by heating and
the metal salt which is present in and on or else in or on the
composite material is reduced to metal.
80. The process as claimed in at least one of claims 41 to 79,
wherein a metal salt which is present in the composite material is
reduced to metal by treating the composite material with a reducing
agent.
81. The process as claimed in claim 50, wherein the reducing agent
used is a borohydride.
82. The process as claimed in at least one of claims 41 to 81,
wherein a metal salt which is present in or on or else in and on
the composite material is reduced to metal by using the composite
material as electrode in an electrolysis.
83. The process as claimed in at least one of claims 41 to 82,
wherein a material-permeable composite material is introduced into
a container having at least two openings.
84. The process as claimed in claim 83, wherein the composite
material is introduced into folded or rolled form in the
container.
85. The process as claimed in at least one of claims 41 to 84,
wherein the composite material is fixed in the container so that a
gas flowing through the filter has to pass through the composite
material at least once.
86. The process as claimed in claim 8, wherein the composite
material is fixed in the container by welding, soldering or
adhesive bonding.
87. The process as claimed in at least one of claims 41 to 86,
wherein the support in the composite material is connected to at
least one power lead.
88. The use of a gas filter as claimed in at least one of claims 1
to 40 for cleaning waste or feed gases.
89. The use of a gas filter as claimed in at least one of claims 1
to 40, for cleaning waste gases from power stations.
90. The use of a gas filter as claimed in at least one of claims 1
to 40 for cleaning the exhaust gases of vehicles driven by internal
combustion engines.
91. The use of a gas filter as claimed in at least one of claims 1
to 40 for cleaning the exhaust gases of vehicles driven by diesel
engines.
Description
[0001] A gas filter, a process for producing a gas filter and use
of this gas filter are claimed.
[0002] Air pollution is known to present a serious problem in many
parts of the world. Depending on composition, the pollution can
lead to health problems among the human population. Furthermore,
the air pollution results in not inconsiderable economic loss. The
air pollution can be in the form of gases or of liquids dispersed
very finely in the air or in the form of tiny solid particles
present in the air. The solid particles which may be present in the
air and have been and are classified as carcinogenic include soot,
especially soot (particulates) which gets into the air via the
exhaust gases of diesel vehicles.
[0003] In many nations, regulations to regulate the maximum
permissible emission of particulates from motor vehicles have been
put in force.
[0004] Various methods and apparatus have already been developed
for treating solids-containing gases.
[0005] U.S. Pat. No. 4,872,889 and U.S. Pat. No. 4,948,403 claim
ceramic filter systems which are able to filter soot or solid
particles from the exhaust gases of diesel-powered vehicles.
[0006] A problem with these methods and apparatus is that the solid
particles block the filter relatively quickly and the filters thus
have to be replaced or regenerated at short intervals.
[0007] To regenerate blocked filters, there have been proposals for
methods which burn the solids blocking the pores of the filter in
motor vehicles by additional combustion of fuel. The disadvantage
of these methods is that regeneration leads to an increased fuel
consumption. In addition, the deep action of this method is only
weak, so that blockages caused by particles in the filter cannot be
remedied.
[0008] More recently, methods and apparatus which remove
filtered-out solids from the filter by heating to 600.degree. C.
have been developed.
[0009] According to DE 3800723, additional heating wires are used
for heating the filter.
[0010] EP 075372 uses heating elements comprising wire, expanded
metal or perforated foils for heating the filter.
[0011] GB 2193656 teaches a method and an apparatus which make use
of wires between which a current flows when a conductive bridge of
deposited soot forms.
[0012] U.S. Pat. No. 5,202,548 describes a filter which can be
baked out by application of a voltage since it is equipped with
electrically conductive honeycomb structures. U.S. Pat. No.
5,246,672 teaches the use of woven wire meshes and U.S. Pat. No.
5,254,840 teaches the use of a combination metallic and ceramic
honeycombs.
[0013] The filter materials used in the abovementioned methods or
apparatus have relatively small surface areas and thus either a low
filter action or, when she pores are made smaller to increase the
filter action, a small gas throughput. If the surface area is large
due to the use of porous materials, the pores become blocked very
quickly. Filtering relatively large amounts of gas requires the use
of large, relatively cumbersome gas filters which restricts the
possible uses of such gas filters.
[0014] It is therefore an object of the present invention to find
an economical process for producing a gas filter which, despite a
small size, is able to filter large amounts of gas and which can be
regenerated in a simple manner.
[0015] It has surprisingly been found that a gas filter which
comprises a material-permeable composite material based on at least
one open-structured and material-permeable support and having on at
least one side of the support and in the interior of the support at
least one inorganic component which comprises essentially at least
one compound of a metal, a semimetal or a mixed metal with at least
one element of main groups III to VII is able, even when small in
size, to filter large amounts of gas and can be regenerated in a
simple manner.
[0016] The present invention accordingly provides a regenerable gas
filter for filtering gases which comprises a composite material
based on at least one openstructured and material-permeable support
and having on at least one side of the support and in the interior
of the support at least one inorganic component which comprises
essentially at least one compound of a metal, a semimetal or a
mixed metal with at least one element of main groups III to
VII.
[0017] The present invention likewise provides a regenerable gas
filter which comprises a composite material which is obtainable by
application of a suspension which comprises at least one inorganic
component comprising a compound of at least one metal, a semimetal
or a mixed metal with at least one element of main groups III to
VII and a sol to an open-structured and materialpermeable support
and by subsequent heating at least once during which the suspension
comprising at least one inorganic component is solidified on or in
or on and in the support. The present invention also provides a
process for producing a gas filter as claimed in any of claims 1 to
40, which comprises producing a material-permeable composite
material by applying, in and on at least one open-structured and
material-permeable support, at least one suspension Which comprises
at least one inorganic component comprising at least one compound
of at least one metal, a semimetal or a mixed metal with at least
one of the elements of main groups III to VII and a sol and by
solidifying the suspension on or in or on and in the support
material by subsequent heating at least once.
[0018] The present invention likewise provides for the use of a gas
filter as claimed in any of claims 1 to 40 for cleaning waste or
feed gases.
[0019] For the purposes of the present invention, materialpermeable
means that materials which have this property are permeable to at
least a gas, a liquid or a solid. The permeability is dependent on
the size of the pores, mesh openings or holes which these materials
have.
[0020] The gas filter of the invention can be it used for the
filtration of any waste and feed gases from which, for example,
solid particles are to be removed. The gases to be filtered can
also comprise vapor or droplets of liquid. The advantage of the gas
filter of the invention is that, as a result of the use of an
electrically conductive support material in the composite material,
the latter can be baked out in a simple manner by application of a
voltage and thus be regenerated. If the composite material
comprises catalytically active materials, this heating only has to
be carried out once if the decomposition of the thermally
decomposable liquid droplets or solid particles is, in the case of
a sufficiently hot filter, catalyzed by the catalytically active
materials and thus proceeds swiftly. As a result, advantageously, a
virtually constant amount of gas can pass through the filter since
blocking of the filter by materials which are not thermally
decomposable increases only very slowly.
[0021] A further advantage of the gas filter of the invention is
that the novel composite material or gas filter can, due to the
fact that it is bendable, be rolled or folded and the filter-active
surface area of the filter can be very large in a small volume.
[0022] The gas filter of the invention is described below by way of
example without being restricted thereby.
[0023] The regenerable gas filter of the invention for the
filtration of gases comprises at least one composite material based
on at least one open-structured and material-permeable support and
having on at least one surface of the support and in the interior
of the support at least one inorganic component which comprises
essentially at least one compound of a metal, a semimetal or a
mixed metal with at least one element of main groups III to VII.
For the purposes of the present invention, interior of a support
means, for example, hollow spaces or pores in a support. According
to the invention, the regenerable gas filter comprises a composite
material which is obtained by application of a suspension which
comprises at least one inorganic component comprising a compound of
at least one metal, a semimetal or a mixed metal with at least one
element of main groups III to VII and a sol to an open-structured
and material-permeable support and by heating at least once during
which the suspension comprising at least one inorganic component is
solidified on or in or else on and in the support.
[0024] According to the invention, the composite material or gas
filter can be permeable to gases, solids or liquids, in particular
to particles having a size of from 0.5 nm to 10 .mu.m.
[0025] A support having intermediate spaces having a size of from
50 to 500 .mu.m can advantageously be present in the composite
material of the gas filter. This support can comprise woven or
felted fibers, expanded metal or sintered metal. The support
preferably comprises at least one at least partially electrically
conductive material.
[0026] The intermediate spaces can be pores, mesh openings, holes,
crystal lattice interstices or voids. The support can comprise at
least one material selected from the group consisting of carbon,
metals, alloys, glass, ceramics, minerals, plastics, amorphous
substances, natural products, composite materials or at least one
combination of these materials. The supports which can comprise the
abovementioned materials can have been modified by a chemical,
thermal or mechanical treatment method or a combination of
treatment methods. Preferably, the composite material comprises a
support comprising at least one metal, a natural fiber or a plastic
which has been modified by at least one mechanical forming
technique or treatment method, e.g. drawing, swaging, fulling,
rolling, stretching or forging. Very particularly preferably, the
composite material comprises at least one support comprising at
least woven, bonded, felted or ceramically bound fibers or at least
sintered or bonded shaped bodies, spheres or particles. In a
further, preferred embodiment, a perforated support can be used.
Material-permeable supports can also be ones which become or have
been made material-permeable by laser treatment or ion beam
treatment.
[0027] It can be advantageous for the support to comprise fibers of
at least one material selected from the group consisting of carbon,
metals, alloys, ceramics, glass, minerals, plastics, amorphous
substances, composite materials and natural products or fibers of
at least one combination of these materials, e.g. asbestos, glass
fibers, rock wool fibers, carbon fibers, metal wires, steel wires,
polyamide fibers, coconut fibers or coated fibers. Preference is
given to using supports which comprise at least woven fibers of
metal or alloys. Wires can also serve as metal fibers. The
composite material very particularly preferably comprises a support
comprising at least one woven mesh of steel or stainless steel,
e.g. woven meshes produced from steel wires, steel fibers,
stainless steel wires or stainless steel fibers by weaving, which
preferably has a mesh opening of from 5 to 500 .mu.m, particularly
preferably mesh openings of from 50 to 500 .mu.m and very
particularly preferably mesh openings of from 70 to 120 .mu.m.
[0028] The support of the composite material can, however, also
comprise at least one expanded metal having a pore size of from 5
to 500 .mu.m. According to the invention, the support can also
comprise at least one granular, sintered metal, a sintered glass or
a metal nonwoven having a pore width of from 0.1 .mu.m to 500
.mu.m, preferably from 3 to 60 .mu.m.
[0029] According to the invention, the composite material
preferably comprises a support comprising at least aluminum,
silicon, cobalt, manganese, zinc, vanadium, molybdenum, indium,
lead, bismuth, silver, gold, nickel, copper, iron, titanium,
platinum, stainless steel, steel, brass, an alloy of these
materials or a material coated with Au, Ag, Pb, Ti, Ni, Cr, Pt, Pd,
Rh, Ru and/or Ti.
[0030] The inorganic component present in the composite material or
gas filter can comprise at least one compound of at least one
metal, semimetal or mixed metal with at least one element of main
groups III to VII of the Periodic Table or at least one mixture of
these compounds. Here, the compounds of the metals, semi-metals or
mixed metals can comprise at least elements of the transition
series and main groups III to V or at least elements of the
transition series or main groups III to V, with these compounds
having a particle size of from 0.001 to 25 .mu.m. The inorganic
component preferably comprises at least one compound of an element
of main groups III to VIII or at least one element of main groups
III to V with at least one of the elements Te, Se, S, O, Sb, As, P,
N, Ge, Si, C, Ga, Al or B or at least one compound of an element of
main groups III to VIII and at least one element of main groups III
to V with at least one of the elements Te, Se, S, 0, Sb, As, P, N,
Ge, Si, C, Ga, Al or B or a mixture of these compounds.
Particularly preferably, the inorganic component comprises at least
one compound of at least one of the elements Sc, Y, Ti, Zr, V, Nb,
Cr, Mo, W, Mn, Fe, Co, B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb or Bi
with at least one of the elements Te, Se, S, O, Sb, As, P, N, C,
Si, Ge or Ga, e.g. TiO.sub.1, Al.sub.1 O.sub.3,ZrO, Y.sub.2O.sub.3,
BC, SiC, Fe.sub.3O.sub.2, SiN, SiP, nitrides, sulfates, phosphides,
silicides, spinels or yttrium-aluminum garnet or one of these
abovementioned elements itself. The inorganic component can also
comprise aluminosilicates, aluminum phosphates, zeolites or
partially exchanged zeolites such as ZSM-5, Na-ZSM-5 or Fe-ZSM-5 or
amorphous microporous mixed oxides which may contain up to 20% of
non-hydrolyzable organic compounds, e.g. vanadium oxide-silicon
oxide glass or aluminum oxidesilicon oxide-methylsilicon
sesquioxide glasses.
[0031] Preferably at least one inorganic component is present as a
particle size fraction having a particle size of from 1 to 250 nm
or having a particle size of from 260 to 10,000 nm.
[0032] It can be advantageous for the composite material to
comprise at least two particle size fractions of at least one
inorganic component. The particle size ratio of the particle size
fractions in the composite material is from 1:1 to 1:10,000,
preferably from 1:1 to 1:100. The composite material particularly
preferably comprises at least one particle size fraction having an
average particle size of from 0.3 to 3 .mu.m. The ratio of the
amounts of the particle size fractions in the composite material is
preferably from 0.01:1 to 1:0.01.
[0033] The material permeability of the composite material can be
limited to particles having a particular maximum size by means of
the particle size of the inorganic component used. It can be
advantageous for the composite material to have pores which are
permeable to particles having a maximum size of from 0.1 to 10
.mu.m, particularly preferably a maximum size of from 0.2 to 1.5
.mu.m.
[0034] The suspension which comprises at least one inorganic
component and by means of which the composite material of the
invention can be obtained can comprise at least one liquid selected
from the group consisting of water, alcohol and acid or a
combination of these liquids.
[0035] In a further particular embodiment of the gas filter of the
invention, the composite material comprises at least one
catalytically active component. The catalytically active component
can be identical when the inorganic component. This applies
particularly when the inorganic component has catalytically active
centers on the surface.
[0036] The catalytically active component present in the composite
material is preferably at least one inorganic material, at least
one metal or at least one organometallic compound which has
catalytically active centers on its surface. The catalytic
component present in the composite material is particularly
preferably a zeolite such as ZSM-5, Fe-ZSM-5, silicalite or an
amorphous microporous mixed oxide as described, for example, in DE
195 45 042 and/or DE 195 e.g. vanadium oxide-silicon oxide glass or
aluminum oxidesilicon oxide-methylsilicon sesquioxide glasses.
[0037] The composite material can, however, also comprise at least
one oxide of at least one of the elements Mo, Sn, Zn, V, Mn, Fe,
Co, Ni, As, Sb, Pb, Bi, Ru, Re, Cr, W, Nb, Hf, La, Ce, Gd, Ga, In,
Tl, Ag, Cu, Li, K, Na, Be, Mg, Ca, Sr and Ba as catalytically
active component.
[0038] In a particular embodiment of the material-permeable
composite material, this comprises at least titanium suboxide as
catalytically active component.
[0039] It can likewise be advantageous for the composite material
to comprise, as catalytically active component, at least one metal
compound selected from among the compounds of the metals Pt, Rh,
Ru, Ir, Au, Ag, Os, Re, Cu, Ni, Pd and Co, or at least one metal
selected from among the metals Pt, Rh, Ru, Ir, Au, Ag, Os, Re, Cu,
Ni, Pd and Co.
[0040] Particularly preferred catalytic components are, for
example, noble metals, noble metal compounds or materials coated
with noble metal particles. The addition of the catalytically
active component makes it possible to achieve a situation where the
filter becomes blocked more slowly after heating once due to
catalytic decomposition of thermally decomposable solids or
liquids, since only particles which cannot be destroyed thermally
block the filter. This particular embodiment enables the operating
life of the filter of the invention to be increased
considerably.
[0041] In a particularly preferred embodiment of the gas filter or
composite material of the invention, this can be made bendable
without destruction of the inorganic component solidified in the
interior of the support and on the support. The composite material
of the invention is preferably able to be bent to a smallest radius
down to 1 mm.
[0042] Preferably, the composite material in the gas filter is
rolled or folded in a suitable container having at least one gas
inlet and at least one gas outlet, with the composite material
being arranged so that the gas to be filtered has to pass, after
entering the gas filter, at least once through the composite
material before it can leave the gas filter via the gas outlet.
[0043] In one variant of the gas filter of the invention, thermally
decomposable or sublimable or vaporizable solids or liquids which
have been filtered from a filtered gas and block the pores of the
composite material, e.g. soot or hydrocarbon particles, can be
removed from the gas filter by baking out the gas filter by
application of a voltage to the support of the composite material.
Depending on the selected support material, preferably a support
material having a low electrical resistance, the filter can be
heated using a low voltage as is customary, for example, in motor
vehicles, e.g. 12 or 24 V. It can be advantageous for the gas inlet
and the gas outlet to be provided with a flow- or
pressure-measuring device by means of which the pressure or the
amount of the gas entering and leaving the filter is measured and
for the heating of the gas filter to be commenced on reaching a
preset difference between the measured values, which represents a
measure of the blocking of the composite material.
[0044] The process of the invention for producing the gas filter of
the invention is described below, without being restricted
thereto.
[0045] The gas filter of the invention can be produced by producing
a material-permeable composite material by applying, in and/or on
at least one open-structured and material-permeable support, at
least one suspension which comprises at least one inorganic
component comprising at least one compound of at least one metal, a
semimetal or a mixed metal With at least one of the elements of
main groups III to VII and a sol and by solidifying the suspension
on or in or on and in the support material by subsequent heating at
least once.
[0046] When carrying out the process of the invention, it can be
advantageous to apply the suspension on and in or else on or in at
least one support by printing, pressing-on, pressing-in,
rolling-on, doctor blade coating, painting-on, dipping, spraying or
casting.
[0047] The open-structured and material-permeable support can
comprise a material selected from the group consisting of carbon,
metals, alloys, ceramics, glass, minerals, plastics, amorphous
substances, natural products, composite materials or at least one
combination of these materials. The preferred support is a woven
stainless steel or steel mesh.
[0048] The suspension used, which comprises at least one inorganic
component and at least one metal oxide sol, at least one semimetal
oxide sol or at least one mixed metal oxide sol or a mixture of
these sols, can be produced by suspending at least one inorganic
component in at least one of these sols. It can be advantageous for
the suspension to comprise at least one catalytically active
component. The catalytically active component can be identical to
the inorganic component.
[0049] The sols are obtained by hydrolyzing at least one metal
compound, at least one semimetal compound or at least one mixed
metal compound using a liquid, a gas or a solid. It can be
advantageous for the liquid used for hydrolyzing the compound to be
hydrolyzed to be water, alcohol or an acid or a combination of
these liquids or the solid used to be ice or the gas used to be
water vapor. It can likewise be advantageous for the compound to be
hydrolyzed to be added prior to the hydrolysis to at least one
alcohol or at least one acid or a combination of these liquids. As
compound to be hydrolyzed, preference is given to hydrolyzing at
least one metal nitrate, a metal chloride, a metal carbonate, a
metal alkoxide compound or at least one semimetal alkoxide
compound, particularly preferably at least one metal alkoxide
compound, a metal nitrate, a metal chloride, a metal carbonate or
at least one semimetal alkoxide compound selected from among the
compounds of the elements Ti, Zr, Al, Si, Sn, Ce and Y or the
lanthanides and actinides, e.g. zirconium alkoxide, silicon
alkoxide or titanium alkoxide compounds, e.g. titanium
isopropoxide, silicon alkoxides, zirconium alkoxides, or a metal
nitrate such as sirconium nitrate.
[0050] It can be advantageous to carry out the hydrolysis of the
compounds to be hydrolyzed using at least half the molar ratio of
water, water vapor or ice, based on the hydrolyzable group, of the
hydrolyzable compound.
[0051] The hydrolyzed compound can be peptized by treatment with at
least one organic or inorganic acid, preferably a 10-60 strength
organic or inorganic acid, particularly preferably a mineral acid
selected from the group consisting of sulfuric acid, hydrochloric
acid, perchloric acid, phosphoric acid and nitric acid and mixtures
of these acids.
[0052] It is possible to use not only sols which have been prepared
as described above but also commercial sols such as titanium
nitrate sol, zirconium nitrate sol or silica sol. It can be
advantageous if at least one inorganic component having a particle
size of from 1 to 10,000 nm is suspended in at least one sol.
Preferably, an inorganic component comprising at least one compound
selected from among metal compounds, semimetal compounds, mixed
metal compounds and metal mixed compounds with at least one of the
elements of main groups III to VI, or at least one mixture of these
compounds, is suspended. Particularly preferably, at least one
inorganic component comprising at least one compound selected from
among the oxides of the transition elements or the elements of main
groups III to V, preferably oxides selected from among the oxides
of the elements Sc, Y, Ti, Zr, Nb, Ce, V, Cr, Mo, W, Mn, Fe, Co, B,
Al, In, Tl, Si, Ge, Sn, Pb and Bi, for example Y.sub.2O.sub.3, ZrO,
Fe.sub.1O.sub.3, Fe.sub.2O.sub.3, SiO, Al.sub.2O.sub.3, is
suspended.
[0053] The proportion by mass of the suspended component is
preferably from 0.1 to 500 times that of the hydrolyzed compound
used.
[0054] In a particular variant, the sol used is preferably titanium
dioxide sol acidified with mineral acid and/or the inorganic
component used is preferably aluminum oxide having a particle size
of from 0.3 to 3 .mu.m.
[0055] It can be advantageous for at least one catalytically active
component, e.g. a noble metal or a noble metal compound, to be
added to the sol and to be incorporated into the gas filter or the
composite material. It can likewise be advantageous for at least
one catalytically active component having a particle size of from 1
to 10,000 nm to be suspended in a sol. Preferably, at least one
catalytically active component comprising at least one compound
selected from among metal compounds, semimetal compounds, mixed
metal compounds and metal mixed compounds with at least one of the
elements of main groups III to VII or organic compounds, or at
least one mixture of these compounds, is suspended. Particularly
preferably, at least one catalytically active component comprising
at least one compound selected from among aluminosilicates,
aluminum phosphates, zeolites or partially exchanged zeolites, e.g.
ZSM-5, Na-ZSM-5 or Fe-ZSM-5, and amorphous microporous mixed oxides
which may contain up to 20 of non-hydrolyzable organic compounds,
e.g. vanadium oxide-silicon oxide glass or aluminum oxide-silicon
oxide-methylsilicon sesquioxide glasses, is suspended.
[0056] The proportion by mass of the suspended components is
preferably from 0.1 to 500 times that of the hydrolyzed compound
used.
[0057] Appropriate selection of the particle size of the suspended
compounds as a function of the size of the pores, holes or
intermediate spaces of the openstructured material-permeable
support, but also the layer thickness of the composite material of
the invention and the sol-solvent-metal oxide ratio, enable the
freedom from cracks of the gas filter of the invention or the
composite material to be optimized.
[0058] When using a woven mesh having a mesh opening of, for
example, 100 .mu.m, it is possible to increase the freedom from
cracks by using, preferably, suspensions which comprise a suspended
compound having a particle size of at least 0.7 .mu.m. In general,
the ratio of particle size to mesh opening or pores should be from
1:1000 to 50:100. The composite material of the invention
preferably has a thickness of from 5 to 1000 .mu.m, particularly
preferably from 50 to 150 .mu.m. The suspension comprising sol and
compounds to be suspended preferably has a weight ratio of sol to
compounds to be suspended of from 0.1:100 to 100:0.1, preferably
from 0.1:10 to 10:0.1.
[0059] According to the invention, the suspension present on or in
or else on and in the support can be solidified by heating the
composite at from 50 to 1000.degree. C. In a particular variant,
the composite is subjected to a temperature of from 50 to
100.degree. C. for from 10 minutes to 5 hours. In a further
particular variant, the composite is subjected to a temperature of
from 100 to 800.degree. C. for from 1 second to 10 minutes.
[0060] The composite can be heated by means of heated air, hot air,
infrared radiation, microwave radiation or electrically generated
heat. In a particular embodiment of the process of the invention,
it can be advantageous for heating to be carried out using the
support material as electric resistance heating element. For this
purpose, the support can be connected via at least two contacts to
a power source. Depending on-the power of the power source, the
voltage which is applied and the intrinsic resistance of the
electrically conductive support, the support heats up when the
power is switched on and the suspension present in and on the
support can be solidified thereby.
[0061] In a further, preferred embodiment of the process of the
invention, solidification of the suspension can be achieved by the
suspension being applied on or in or else on and in a preheated
support and thus being solidified directly after application. In a
further, particular embodiment of the process of the invention, it
can be advantageous for at least one support to be unwound from a
roll, passed at a speed of from 1 m/h to 1 m/s through at least one
apparatus which applies the suspension on or in or on and in the
support and at least one further apparatus which makes possible the
solidification of the suspension on or in or on and in the support
by heating and the composite material thus produced is wound up on
a second roll. This makes it possible to produce the gas filter of
the invention or the composite material by a continuous
process.
[0062] In a further, particular embodiment of the process of the
invention it can be advantageous to apply a ceramic or inorganic
layer to a support which may be a composite material or a composite
material produced by the process of the invention. This can be
carried out, for example, by laminating a green (unsintered)
ceramic layer or an inorganic layer which is, for example, present
on an auxiliary film onto the support or by treating the composite
material with a further suspension as described above. This
composite can be strengthened by heating, e.g. by means of infrared
radiation or a furnace.
[0063] The green ceramic layer used preferably comprises
nanocrystalline powder of at least one semimetal oxide or metal
oxide such as aluminum oxide, titanium dioxide or zirconium
dioxide. The green layer can also comprise an organic binder.
[0064] The use of a green ceramic layer makes it readily possible
to provide the composite material of the invention with an
additional ceramic layer which, depending on the size of the
nanocrystalline powder used, restricts the material permeability of
the composite material produced in this way to very small
particles.
[0065] The green layer preferably comprises nanocrystalline powder
having a particle size of from 1 to 1000 nm. If nanccrystalline
powder having particle sizes of from 1 to 1 nm is used, the
composite material of the invention to which an additional ceramic
layer has been applied has a material permeability for particles
having a size which corresponds to that of the particle size of the
powder used. If nanocrystalline powder having a size above 10 nm is
used, the ceramic layer is permeable to particles which are half
the size of the particles of the nanocrystalline powder used.
[0066] The application according to the invention of at least one
further inorganic layer or ceramic layer gives a composite material
of the invention which has a pore gradient. In addition, multiple
application of a layer makes it possible to produce composite
materials having a particular pore size using even those supports
whose pore size or mesh opening is not suitable for producing a gas
filter or composite material having the required pore size. This
may be the case, for example, when a gas filter or composite
material having a core size of 0.25 .mu.m is to be produced using a
support having a mesh opening of above 300 .mu.m. To obtain such a
gas filter or composite material, it can be advantageous to first
apply to the support at least one suspension which is suitable for
treating supports having a mesh opening of 300 .mu.m and to
solidify this suspension after application. The composite material
obtained in this way can then be used as a support having a lower
mesh opening or pore size. It is possible to apply to this support,
for example, a further suspension which comprises, for example, a
compound having a particle size of 0.5 .mu.m.
[0067] The crack insensitivity of composite materials having large
mesh openings or pore sizes can also be improved by applying
suspensions which comprise at least two suspended compounds to the
support. As compounds to be suspended, preference is given to using
compounds which have a particle size ratio of from 1:1 to 1:10,
particularly preferably from 1:1. to 1:2.5. The proportion by
weight of the particle size fraction hating the smaller particle
size should not exceed a portion of at most 50%, preferably 20% and
very particularly preferably 10%, of the total weight of the
particle size fractions used.
[0068] Despite the application of an additional ceramic layer or
inorganic layer, which may comprise catalytically active
components, to the support, the composite material of the invention
can be bendable.
[0069] The gas filter of the invention or the composite material
can also be produced by laying a support, which may, for example,
be a composite material or another suitable support material, onto
a second support which may consist of the same material as the
first support or a different material or of two supports having a
different material permeability or porosity. A spacer, a drainage
material or another material suitable for conducting away
materials, e.g. a composite fabric, can be laid between the two
support materials. The edges of the two supports are joined
together, for example by soldering, welding or adhesive bonding.
Adhesive bonding can be carried out using commercial adhesives or
adhesive tape. The suspension can be applied in the manner
described above to the composite support prepared in this way.
[0070] In a particularly preferred embodiment, the superposed
supports between which at least one spacer, a drainage material or
the like may be arranged can be rolled up before or after,
preferably after, the joining of the edges of the supports. The
spacing between two composite supports which become juxtaposed on
rolling-up can be influenced by use of thick or thin adhesive tapes
for joining the edges of the supports. A suspension as described
above can be applied to such rolled-up composite supports by, for
example, dipping into a suspension. The composite support can be
freed of excess suspension by means of compressed air after
dipping. The suspension applied to the composite support can be
solidified as described above. A gas filter or composite material
produced in this way can be used as gas filter in a rolled module.
In a further particular embodiment of the process of the invention,
the composite support mentioned can also be produced by unrolling
two supports and, if provided, at least one spacer from individual
rolls and then laying them on top of one another. The edges of the
supports can again be joined by soldering, welding, adhesive
bonding or by other suitable methods of joining flat bodies. The
suspension can then be applied to the composite support produced in
this way. The application of the suspension can be carried out, for
example, by spraying or painting the composite support with the
suspension or by conveying the composite support through a bath in
which the suspension is present. The applied suspension is
solidified by one of the abovementioned methods. The composite
material produced in this way can be wound onto a roll. A further
suspension of a further inorganic layer can be applied to and/or
introduced into such a material by repeated application and
solidification. The use of different suspensions enables the
material properties to be set as desired or according to the
intended use. Not only further suspensions but also unsintered
ceramic and/or inorganic layers which are obtainable by
laminating-on as described above can be applied to this composite
material. This embodiment of the process of the invention can be
carried out continuously or batchwise, preferably continuously. A
composite material produced in this way can be used as gas filter
in a flat module.
[0071] The support in the gas filter or composite material can,
depending on the support material used, be removed again so as to
form a ceramic material which no longer contains any support
material. If the support material used is, for example, a natural
material such as a cotton nonwoven, this can be removed from the
composite material by oxidation in a suitable reactor. If a metal,
e.g. iron, has been used as support material, this support can be
dissolved out of the composite material by treating the composite
material with acids, preferably with concentrated hydrochloric
acid. If the support material additionally comprised zeolite, flat
zeolite bodies can be produced in this way.
[0072] It can be advantageous to use the composite material as
support for the production of a gas filter or composite material
according to the invention. In a particular embodiment of the
process of the invention, it is possible, after solidification of
the suspension or ceramic or inorganic layer on and/or in the
support material, to treat the dried and strengthened gas filter or
composite material with a solution comprising at least one metal
compound, preferably a metal salt such as RhCl.sub.3. The treatment
can comprise, for example, spraying, painting or rolling the
solution comprising a metal compound onto the composite material
or, for example, dipping the composite material into a solution
comprising a metal compound. The gas filter or composite material
which has been treated in this way is dried by heating. Heating can
be carried out as indicated above. The metal compound which is
present in and on or in or on the composite material after
application and drying of the solution is reduced to the metal. It
can be advantageous to reduce a metal compound present in and/or on
the composite material to the metal using a reducing agent,
preferably a borohydride, very particularly preferably
NaBEt.sub.3H, LiBEt.sub.3H, NaBMe.sub.3H or KBPrH.
[0073] It can likewise he advantageous to reduce a metal compound
present on or in or else on and in the composite material to the
metal by using the composite material as electrode in an
electrolysis.
[0074] Catalytically active metals can also be applied in and/or on
the gas filter or composite material by using a composite material
without a catalytically active component as electrode in the
electrolysis of a solution comprising a noble metal salt. Here, it
is necessary for the composite material to comprise at least TiO as
an inorganic component and at least one partially electrically
conductive support. On application of a voltage of, for example,
from 2 to 3 volt, the composite material becomes electrically
conductive due to formation of titanium suboxide, which is
electrically conductive. As a result of the electrolysis,
catalytically active noble metal, preferably in the form of very
fine particles, deposits in and/or on the composite material or gas
filter.
[0075] This makes it possible to produce gas filters which comprise
metals and/or noble metals as catalytic components.
[0076] It is also possible to use the gas filter or composite
material of the invention as support for producing a gas filter
according to the invention.
[0077] In a particular variant for producing the gas filter of the
invention, at least one material-permeate composite material is
introduced, preferably rolled or folded, into a container having at
least two openings.
[0078] The composite material is preferable fixed in the container,
preferably by welding, soldering or adhesive bonding, so-that a gas
flowing through the filter has to pass through the composite
material at least once. The support in the composite material of
the gas filter is preferable connected to at least one power
lead.
[0079] It can be advantageous to combine preferred embodiments of
the process of the invention with at least one further preferred
embodiment of the process of the invention. It may likewise be
advantageous to combine preferred embodiments of the gas filter of
the invention with at least one further preferred embodiment of the
gas filter of the invention. With knowledge of the present
invention, a person skilled in the art will be able to see further
embodiments of the process of the invention, the gas filter of the
invention and/or further possible uses of the process of the
invention or the gas filter of the invention. The gas filter of the
invention can be used for cleaning gases, in particular waste gases
or feed gases, and very particularly preferably gases containing at
least one solid.
[0080] The gas filters of the invention are preferable used for
cleaning waste gases from power stations or for cleaning the
exhaust gases from vehicles driven by internal combustion engines.
The gas filter of the invention is very particularly preferably
used for cleaning the exhaust gases from vehicles driven by diesel
engines.
[0081] The following examples describe the process of the invention
for producing a gas filter according to the invention, without the
process being restricted to these examples.
EXAMPLE 1
[0082] A suspension comprising 25 g of zirconium isopropoxide was
hydrolyzed with 20 g of water. The resulting precipitate was
subsequently treated with about 40 g of 25% strength nitric acid
and, after the precipitate had dissolved completely, 60 g of
aluminum oxide Al6SG from Alcca) were added. This suspension as
stirred until all agglomerates had completely dissolved and was
applied in a thickness of 60 .mu.m to a square-weave mesh of
stainless steel having a mesh opening of 0 .mu.m. This composite
was exposed to air at 450.degree. C. for 3 seconds and was dried
and solidified in this way.
[0083] The composite material obtained in this way was used for gas
filtration. The present composite material is suitable, when
installed in a gas filter, for filtering exhaust gases from diesel
engines, since solid particles having a size of upward from 0.25
.mu.m are selectively retained. The solid particles having a size
of greater than 0.25 .mu.m which are filtered out gradually block
the filter during use. Application of a voltage to the support of
the composite material enables the filter or the composite material
to be heated so that particles able to be destroyed thermally can
be removed from the filter by means of oxidation reactions.
EXAMPLE 2
[0084] A Pt/Rh catalyst is incorporated on and in a composite
material as produced and described in Example 1. For this purpose,
a suspension comprising a zirconium oxide sol which had been
prepared by hydrolyzing 25 g of zirconium isopropoxide with 20 g of
water and subsequently treating the resulting precipitate with 410
g of 25 strength nitric acid and contained he Pt/Rh catalyst in a
concentration of 1 was applied on and in the composite material as
support. Solidification of the suspension by heating the composite
by means of air at 450.degree. C. for 3 seconds gave a composite
material which is suitable for use as or in a gas filter.
[0085] This gas filter, too, is very useful for the filtration of
gases containing solid particles. The solid particles having a size
of greater than 0.25 .mu.m which are filtered out gradually block
the filter during use. Application of a voltage to the support of
the composite material enables the filter or the composite material
to be heated so that particles able to be destroyed thermally can
be removed from the filter.
[0086] When the filter has reached a suitable process temperature
at which the oxidatively decomposable solids can be destroyed
catalytically by oxidation reactions owing to the presence of the
Pt/Rh catalyst, the solids which have been filtered cut are
continually destroyed by oxidation, resulting in considerably
reduced blockage of the gas filter. In this embodiment of the gas
filter of the invention, energy does not have to be consumed
continually for regeneration of the filter, but it is sufficient
for the gas filter to be heated at least once during the start-up
or running-up phase. Once the reaction in and on the filter is
proceeding, the energy liberated in the destruction of the solid
particles generates the high temperatures necessary for
regeneration of the filter.
* * * * *