U.S. patent application number 09/266330 was filed with the patent office on 2001-12-20 for activated carbon air filters.
This patent application is currently assigned to U.S. Philips Corporation. Invention is credited to GELDERLAND, SIGRID M R, MARRA, JOHANNES.
Application Number | 20010052224 09/266330 |
Document ID | / |
Family ID | 26313271 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010052224 |
Kind Code |
A1 |
GELDERLAND, SIGRID M R ; et
al. |
December 20, 2001 |
ACTIVATED CARBON AIR FILTERS
Abstract
An activated carbon air filter for use in room air cleaners and
the like comprises a corrugated paper structure formed of
substantially non-porous paper, preferably Kraft paper, whose
surface is coated with carbon by means for example of a dipping
process in which the structure is immersed in an aqueous slurry
containing carbon and a binder. Through use of a particular paper
thickness and channel dimensions, a highly efficient, low volume,
long lifetime air cleaning filter is obtained.
Inventors: |
GELDERLAND, SIGRID M R;
(WAALRE, NL) ; MARRA, JOHANNES; (EINDHOVEN,
NL) |
Correspondence
Address: |
ERNESTINE C BARTLETT
US PHILIPS CORPORATION
580 WHITE PLAINS ROAD
TARRYTOWN
NY
10591
|
Assignee: |
U.S. Philips Corporation
|
Family ID: |
26313271 |
Appl. No.: |
09/266330 |
Filed: |
March 11, 1999 |
Current U.S.
Class: |
55/521 |
Current CPC
Class: |
B01D 53/02 20130101;
B01D 2259/4508 20130101; B01D 2253/3425 20130101; B01D 2253/25
20130101; Y10S 55/05 20130101; B01D 2253/102 20130101; B01D
2257/106 20130101; B01D 39/18 20130101; B01D 2257/404 20130101;
B01D 2257/708 20130101 |
Class at
Publication: |
55/521 |
International
Class: |
B01D 046/52 |
Claims
1. An activated carbon air filter comprising a corrugated paper
structure carrying activated carbon, characterised in that the
paper comprises a substantially non-porous, organic fibre paper and
in that the activated carbon is provided as a coating on the paper
surface.
2. An air filter according to claim 1, characterised in that the
corrugated paper structure comprises a honeycomb structure having
air channels approximately 1 mm in diameter.
3. An air filter according to claim 2, characterised in that the
corrugated paper is of an E-flute construction having a cell height
between substantially 1.2 to 1.4 mm and a pitch of substantially 3
mm.
4. An air filter according to any one of claims 1 to 3,
characterised in that the filter comprises at least around 130
grams of active carbon per litre of filter volume.
5. An air filter according to any one of claims 1 to 4,
characterised in that the substantially non-porous paper comprises
Kraft paper.
6. An air filter according to claim 5, characterised in that the
paper has a density of approximately 49 gm/m.sup.2.
7. An air cleaning device comprising an activated carbon air filter
as claimed in any one of the preceding claims, and air moving means
for producing a flow of air through the air filter.
8. A method of making an activated carbon air filter comprising a
corrugated paper structure carrying activated carbon which method
comprises forming the corrugated paper structure from substantially
non-porous, organic fibre paper and thereafter applying the
activated carbon in the form of a coating on the surface of the
corrugated paper.
9. A method according to claim 8, characterised in that the paper
is coated using an aqueous slurry comprising carbon mixed with a
binder.
10. A method according to claim 9, characterised in that the binder
comprises a cellulose ether.
11. A method according to claim 9, characterised in that the
coating is applied by drawing the slurry up the channels defined by
the corrugations.
12. A method according to claim 11, characterised in that the paper
is wetted prior to drawing the slurry up the channels.
Description
[0001] This invention relates to air filters and methods of
manufacturing the same. In particular, the invention concerns
corrugated paper filter structures using activated carbon for
cleaning air.
[0002] Such active carbon filters are employed in air cleaning
equipment such as room air cleaners and other air filtration
devices in which, for example, air is passed over the filter by
means of an air moving device such as a fan whereby the active
carbon filter removes, inter alia, organic gases, radon, ozone and
N0.sub.2 from the air-flow through adsorption.
[0003] The performance of the filter is determined by the
gas-removal efficiency, the capacity and the pressure drop (air
resistance). The gas-removal efficiency is determined, along with
the absorption capacity, by the quantity of effective active
carbon, and, along with the pressure drop, also by the structure of
the filter.
[0004] An object of the present invention is to provide an
activated carbon air filter which has improved performance.
[0005] It is another object of the present invention to provide an
activated carbon air filter which provides a high gas-removal
efficiency and a high capacity combined with a low pressure drop
and a small volume.
[0006] The invention provides a carbon filter of corrugated paper
structure which is optimised in terms of its cost, the obtained
carbon weight per unit filter volume, the corrugation specifics of
the filter, the face area of the filter and the filter thickness,
the pressure drop across the carbon filter, the adhesion of the
carbon coating to the corrugated paper support medium, and which
can be utilised advantageously in an air cleaner wherein specific
boundary conditions exist with respect to the process conditions,
particularly air speed, pressure drop, filter volume, and one-pass
air cleaning performance.
[0007] According to one aspect of the present invention there is
provided an activated carbon air filter comprising a corrugated
paper structure carrying activated carbon, which is characterised
in that the paper comprises a substantially non-porous, organic
fibre paper and in that the activated carbon is provided as a
coating on the paper surface.
[0008] According to another aspect of the present invention there
is provided a method of making an activated carbon air filter
comprising a corrugated paper structure carrying activated carbon,
which method comprises forming the corrugated paper structure from
substantially non-porous, organic fibre paper and thereafter
applying the activated carbon in the form of a coating on the
surface of the corrugated paper.
[0009] Conventionally, activated carbon paper air filters comprise
an inorganic fibre, porous, paper which is impregnated with the
carbon, with the carbon particles dispersed in the voids between
the paper fibres, prior to the paper being corrugated and formed
into a honeycomb structure. Such filters tend to have a limited
carbon content, and typically the carbon loading is around 70
gms/litre of filter volume.
[0010] Through using a substantially non-porous paper and providing
the carbon as a coating on the surface of the paper, with the
carbon coating confined and adhering to the paper surface,
considerable improvement in the operational effectiveness of the
filter is obtained. In a preferred embodiment, the corrugated paper
is formed into a honeycomb structure having air channels
approximately 1 mm in diameter, preferably using an E-flute
construction having a cell height between 1.2 to 1.4 mm and a pitch
of substantially 3 mm, and with a carbon coating approximately 0.1
to 0.2 mm thick, then a carbon loading of approximately 130 gm of
carbon per litre of filter volume is achieved which dramatically
improves air cleaning performance. The channel size selection
results in filter functionality, particularly efficiency, lifetime,
pressure drop and filter volume, being optimised.
[0011] Preferably, the non-porous paper comprises Kraft paper,
desirably having a density of approximately 49 gm/m.sup.2. The
fibre density of such paper is sufficient to prevent carbon
particles of around 50 .mu.m or more diameter penetrating the
fibrous interior, thus ensuring that the carbon remains confined to
the paper surface to which it adheres. Kraft paper offers the
advantages of low cost, ease of paper corrugation before coating,
and low weight as well as providing desired properties for ensuring
adequate adherence of the carbon coating to its surface.
[0012] In a preferred method of making the air filter, the carbon
coating is applied using an aqueous slurry including a binder,
preferably carboxymethylcellulose, which provides consistency and
promotes good adhesion of the coating to the paper. The coating is
applied by partly immersing the corrugated paper structure in the
slurry, preferably with prior wetting of the paper, and drawing the
slurry up through the corrugation channels, for example using
capillary action or by sucking, and thereafter forcing the slurry
out, by air blowing or the like, and drying, thereby leaving a
homogeneous and dense carbon coating on the paper surface.
[0013] According to a further aspect of the present invention,
there is provided an air cleaning device comprising an activated
carbon air filter in accordance with the first aspect of the
invention and air moving means operable to produce a flow of air
through the air filter.
[0014] Embodiments of air filters and their methods of manufacture
in accordance with the present invention will now be described, by
way of example, with reference to the accompanying drawing, in
which:
[0015] FIG. 1 is a schematic perspective view of part of the
structure of one example embodiment of air filter; and
[0016] FIG. 2 shows schematically and highly simplified a
cross-section through an air cleaning device incorporating the air
filter.
[0017] Referring to FIG. 1, in this embodiment a support, generally
referenced at 10, having the structure of the eventual filter is
coated with carbon by means of a dipping process which involves
immersing the structure in an aqueous slurry containing carbon. The
support material is a strong paper structure consisting of several
alternately stacked flat and corrugated sheets, 12 and 14, of Kraft
paper which are glued together by means of a water-resistant glue.
Stacking of these sheets results in a honeycomb-like structure
having many mutually parallel channels. The paper thickness (d)
preferably ranges from 0.1 to 0.2 mm, and the channel diameter
ranges from 1.2 to 2 mm. Using a wet coating process, this
preformed paper structure is coated with an aqueous slurry of a
binder-containing active carbon powder in water. The particle size
of the powder is less than 150 .mu.m. The binder is a cellulose
ether, for example carboxymethyl-cellulose, methyl cellulose, or a
thermoplastic material, for example polyvinyl alcohol, which is
present in a quantity of at least 4% (m/m) relative to the quantity
of active carbon.
[0018] The coating process comprises the following steps.
Pre-wetting of the paper, for example by spraying, is desirable to
prevent the possibility of the slurry clotting during coating which
would otherwise result in channel blockages. The preformed paper
honeycomb structure is therefore water-humidified and then (partly)
arranged in the slurry, the channels being in the vertical
position. The slurry is then sucked upwards, for example, with the
aid of a slight vacuum, so that all channels are filled with the
slurry substantially uniformly. Following this, the slurry is
forced from the channels by application of an over-pressure
(compressed air) and air is blown through the channels to open the
channels. Thereafter, the carbon-coated paper structure is dried,
by blowing dry air through the channels, leaving a homogeneous and
dense activated carbon coating on the paper surfaces which is
smooth and non-powdery. The carbon loading in the corrugated paper
structure is determined by the thickness of the dried coating
which, in turn, is determined by the viscosity of the carbon
slurry. A high viscosity results in more slurry remaining in the
channels after drainage and a high viscosity is obtained by either
increasing the carbon fraction or by a high molecular weight
binder. A high carbon fraction in combination with the use of a low
molecular weight binder, e.g. carboxymethyl-cellulose, is preferred
because it results in greater carbon coating.
[0019] In this manner, a satisfactorily adhering active carbon
layer of 0.1-0.2 mm is applied to the paper channel walls. The
"one-pass-efficiency" for the removal of most organic gases with
such a filter is 90%.
[0020] The addition of a binder to the carbon slurry assists in
accomplishing sufficient internal consistency in the carbon coating
and ensures good carbon adhesion to the paper. The adsorption
capacity of the filter is slightly adversely affected by the
presence of the binders but is predominantly determined by the
adsorption capacity of the active carbon powder used. A binder
fraction of 4% is sufficient to obtain a good adhesion. A binder
fraction of 16% or more causes the adsorption capacity to decrease
substantially. The filter comprises about 130 to 150 grams of
active carbon per litre of filter volume. Thus, a 3.5 litre volume
can contain around 500 grams of carbon. The air meets little
resistance upon passing through the filter. For example, at an air
velocity v=1 m/s, the pressure drop across a filter having a length
L=40 mm is 40-45 N/m.sup.2.
[0021] The paper used is made from organic fibres and has a dense,
substantially non-porous, form. Kraft paper is particularly
preferred. This is a kind of paper made from cellulose fibres
according to the so-called Kraft process. Such paper tends to be
slightly hydrophobic, so wetting with water is resisted, and is
dense, though not-completely non-porous. However, its fibre density
is sufficient to prevent activated carbon particles of, say, 50
.mu.m or greater in diameter penetrating the fibrous interior of
the paper sheet. The coated carbon slurry thus remains confined
substantially to the surface of the paper to which it adheres.
[0022] Kraft paper offers the advantages of low cost, low weight,
and environmentally-friendly disposability. Further, it has an
inherent stiffness which is beneficial and can easily be corrugated
prior to coating and provides adequate adherence of the carbon
coating to its surface.
[0023] In a particularly preferred embodiment, bleached Kraft paper
having a weight of approximately 49 grams/m.sup.2 is utilised. This
is corrugated, prior to the carbon coating process, to a standard
E-flute, with a cell height (h) of 1.2 to 1.4 mm and a pitch (P)
between 3 mm and 3.2 mm. These parameters are important for
optimising the filter functionality with regard especially to
efficiency, lifetime, pressure drop and filter volume.
[0024] The corrugated paper can be rolled up, stacked, fan-folded
or otherwise assembled to produce the desired filter shape, such as
for example the structure shown in the drawing. The overall
thickness (L) of the filter structure in this embodiment is around
30 mm to 40 mm. Following the subsequent coating of the corrugated
paper walls using an activated carbon slurry and drying process as
described above, the air channels in the resulting carbon honeycomb
filter have a diameter close to 1 mm, with the amount of carbon
contained in the surface coating being around 130 grams/litre of
filter, which provides exceptional air cleaning performance.
[0025] Instead of coating the paper by a dipping process, it is
envisaged that a flow coating method may be used in which the
slurry is poured over the paper structure and then sucked or blown
through the channels.
[0026] In summary, therefore, there is disclosed an activated
carbon air filter for use in room air cleaners and the like which
comprises a corrugated paper structure formed of substantially
non-porous paper, preferably Kraft paper, whose surface is coated
with carbon by means for example of a dipping process in which the
structure is immersed in an aqueous slurry containing carbon and a
binder. Through use of a particular paper thickness and channel
dimensions, a highly efficient, low volume, long lifetime air
cleaning filter is obtained.
[0027] FIG. 2 shows schematically in cross-section and in
simplified form an air cleaning device using this air filter. The
filter, 10, is mounted in a housing 20, defining a passage for the
flow of air between an air inlet 21 and an air outlet 22, together
with an air moving device 24, such as an electrically driven fan,
which is operable to produce a flow of air, as indicated by the
arrow, from the inlet to the outlet and through the filter, the air
channels defined by the corrugations of the filter being aligned
with the air flow direction. Rather than being arranged to draw air
through the filter in this manner, the air moving device may of
course be arranged to blow air through the filter instead.
* * * * *