U.S. patent application number 10/477961 was filed with the patent office on 2004-11-18 for compositions for reducing atmosheric oxidising pollutants.
Invention is credited to Morgan, Christopher.
Application Number | 20040226699 10/477961 |
Document ID | / |
Family ID | 9914595 |
Filed Date | 2004-11-18 |
United States Patent
Application |
20040226699 |
Kind Code |
A1 |
Morgan, Christopher |
November 18, 2004 |
Compositions for reducing atmosheric oxidising pollutants
Abstract
A composition for reducing atmospheric oxidizing pollutants
comprising a reducing agent comprising: at least one transition
element and/or one or more compounds including at least one
transition element wherein the standard electrode potential of the
redox reaction including the transition element and an ionic
species of the transition element or between the ionic species of
the transition element present in the or each compound and a
further ionic species of the transition element is less than +1.0
volt; a precious metal-free trap material capable of trapping at
least one atmospheric reducing pollutant, whereby the at least one
atmospheric oxidizing pollutant is reduced by a combination of the
trap material and at least one trapped atmospheric reducing
pollutant, which at least one trapped atmospheric reducing
pollutant is consequently oxidized; or a manganese-based catalyst,
preferably MnO.sub.2 or a derivative thereof including
cryptomelane, and a water soluble binder.
Inventors: |
Morgan, Christopher;
(Royston, GB) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
9914595 |
Appl. No.: |
10/477961 |
Filed: |
June 28, 2004 |
PCT Filed: |
May 15, 2002 |
PCT NO: |
PCT/GB02/02141 |
Current U.S.
Class: |
165/134.1 ;
165/905; 29/890.03 |
Current CPC
Class: |
B01J 23/80 20130101;
Y10T 29/4935 20150115; B01J 23/83 20130101; B01D 53/9454 20130101;
B01J 37/0246 20130101; B01D 2259/4558 20130101; B01J 37/0232
20130101; B01J 23/34 20130101; Y02T 10/12 20130101; B01D 53/74
20130101; B01D 53/8675 20130101; Y02A 50/20 20180101; B01D 53/885
20130101 |
Class at
Publication: |
165/134.1 ;
165/905; 029/890.03 |
International
Class: |
F28F 019/00; B21D
053/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2001 |
GB |
0111733.2 |
Claims
1. A heat exchanger comprising an atmosphere-contacting surface
coated with a composition for reducing atmospheric oxidising
pollutants, which composition comprises a reducing agent comprising
a manganese-based catalyst and a water soluble binder.
2. A heat exchanger according to claim 1, wherein the
manganese-based catalyst is MnO.sub.2 or a derivative thereof.
3. A heat exchanger according to claim 2, wherein the MnO.sub.2
derivative is cryptomelane.
4. A heat exchanger according to claim 1, wherein the water-soluble
binder is a cellulosic binder.
5. A heat exchanger according to claim 4, wherein the cellulosic
binder is selected from the group consisting of an ether ester and
semi-synthetic cellulosic binder.
6. A heat exchanger according to claim 1, wherein the water soluble
binder is a vinyl or acrylic binder.
7. A heat exchanger according to claim 1, wherein the
manganese-based catalyst is supported on a high surface area oxide
selected from the group consisting of alumina, ceria, silica,
titania, zirconia and a mixed oxide of any two or more thereof.
8. A heat exchanger according to claim 1, wherein the composition
further comprises particles of a transition metal for improving the
thermal conductivity of the composition.
9. A heat exchanger according to claim 1, wherein the surface
comprises aluminium or an aluminium alloy.
10. A heat exchanger according to claim 1, wherein the heat
exchanger is a radiator and/or a condenser.
11. A method of making a heat exchanger comprising an
atmosphere-contacting surface coated with a composition for
reducing atmospheric oxidising pollutants, which composition
comprises a reducing agent comprising a manganese-based catalyst
and a water soluble binder, which method comprises the steps of
coating the surface with the composition and heating the coated
surface for a sufficient time to cure the composition, wherein the
heating step consists of heating the coated surface to
.ltoreq.90.degree. C.
12. A heat exchanger according to claim 4, wherein the cellulosic
binder is hydroxypropyl- or methylcellulose.
13. A heat exchanger according to claim 1, wherein the water
soluble binder is polyvinyl alcohol or ammonium
polymethacrylate.
14. A heat exchanger according to claim 8, wherein the transition
metal is silver or copper.
15. A heat exchanger according to claim 10, wherein the radiator
and/or a condenser is part of a motor vehicle.
Description
[0001] The present invention relates to compositions for reducing
atmospheric oxidising pollutants, such as ozone (O.sub.3) and
nitrogen dioxide (NO.sub.2), and in particular to compositions for
coating surfaces for contacting the atmosphere.
[0002] By "atmospheric oxidising pollutant" herein, we mean an
atmospheric pollutant that has the potential to oxidise other
atmospheric pollutants in a redox reaction. Examples of atmospheric
oxidising pollutants include O.sub.3, NO.sub.2, dinitrogen
tertroxide (N.sub.2O.sub.4) and sulfur trioxide (SO.sub.3).
[0003] Ground-level O.sub.3, a component of smog, is created from
the reaction of nitrogen oxides (NOx) and hydrocarbons (HC), from
vehicle and industrial emissions. Aldehydes, organic species having
a relatively high Maximum Incremental Reactivity adjustment factor
(MIR) also known as carter factors (as defined by "Californian
Non-methane organic gases test procedures", The California
Environmental Protection Agency Air Resource Board dated Aug. 5,
1999), are also produced. Part of this reaction is catalysed by
sunlight and can be represented by two equations:
O.sub.2+RCH.sub.2CH.sub.3+NO.fwdarw.RCH.sub.2CHO+NO.sub.2; and
(i)
NO.sub.2+O.sub.2.fwdarw..sup.hvO.sub.3+NO. (ii)
[0004] Smog can cause asthma and respiratory ailments and is a
particular problem in the southern California basin, Los Angeles
and Houston, Tex. in the USA.
[0005] In WO 96/22146, Engelhard describes the concept of coating
an atmosphere-contacting surface of a vehicle with a composition
for treating one or more atmospheric pollutant, such as O.sub.3
alone, O.sub.3 and carbon monoxide (CO) or O.sub.3, CO and HC. The
surface is preferably that of a heat exchanger, such as a radiator
or air conditioner condenser, located within the vehicle's engine
compartment. As the vehicle is propelled through the atmosphere,
pollutants suspended in the atmosphere contact the composition and,
depending on the formulation of the composition, it catalyses the
reduction of the atmospheric oxidising pollutant O.sub.3 to oxygen,
and/or the oxidation of the atmospheric reducing pollutant carbon
monoxide to carbon dioxide and/or of HC to water and carbon
dioxide.
[0006] Engelhard markets a vehicle radiator having a catalytic
coating for reducing O.sub.3 under the trade name PremAir.RTM..
Details of PremAir.RTM. can also be found on Engelhard's website at
www.Engelhard.com/premair. It is also described in its WO 96/22146.
We understand that the active material on the marketed radiators is
a manganese-based component, cryptomelane
(KMn.sub.8O.sub.16.xH.sub.2O, structurally related to
.alpha.-MnO.sub.2). Coated radiators have been fitted on certain
Volvo production passenger vehicles, e.g. the S80 luxury sedan in
USA and throughout Europe.
[0007] Catalytically coated heat exchangers are also used for
treating aeroplane cabin air and for reducing O.sub.3 emissions
from computer printers, photocopiers etc.
[0008] Modern heat exchangers for use in vehicles are made from
aluminium or aluminium alloys and are manufactured by companies
such as Visteon, Delphi and Valeo. Heat exchangers for non-vehicle
applications can also be made from aluminium or aluminium alloys.
Hereinafter "aluminium" will be used to refer to aluminium and
alloys of aluminium.
[0009] Aluminium is a relatively reactive metal. For example, it is
known that when aluminium is exposed to atmospheric oxygen it
develops a surface coating of oxide. Accordingly, when an aluminium
heat exchanger is coated with a catalytic coating, such as the
cryptomelane-based composition used in Engelhard's Premair system,
it is important that the composition does not react with the
aluminium substrate. If the catalytic coating does react with
and/or promote the corrosion of the aluminium substrate, this can
drastically reduce the working life of the heat exchanger. In
vehicle applications, heat exchangers are exposed to conditions
which can promote metallic corrosion including moist air, salt
and/or grit.
[0010] To test the ability of vehicle components to withstand
corrosion, there have been devised certain standard laboratory
cyclic salt spray corrosion tests termed "SWAAT" (e.g. ASTM G-85 A3
adapted from ASTM B117). Engelhard has been at pains to point out
in its Society of Automotive Engineers (SAE) presentations (see SAE
982728 and 1999-01-3677) that the application of its catalytic
coatings does not affect the resistance to corrosion of an
aluminium radiator core and fully assembled radiators as tested by
SWAAT. Furthermore, it has performed its own laboratory galvanic
corrosion tests to show that brazed joints to the aluminium core
are not prone to corrosion (see the SAE papers mentioned above). In
the SWAAT test no leaks were detected following up to 1700 hours of
the cyclic salt spraying of both Engelhard's coated aluminium
radiator and a control un-coated aluminium radiator; independent
tests concluded that, in the galvanic corrosion tests, no adverse
galvanic corrosion effects would be expected from application of
the reducing agent coating on aluminium radiators as shown by
galvanic current measurements.
[0011] However, we believe that, in practice, the aluminium vehicle
radiators including the PremAir.RTM. manganese-based catalytic
coatings are indeed more susceptible to corrosion following
prolonged use as compared with non-coated radiators. Without
wishing to be bound by theory, we believe that this is because
under acidic conditions, the oxidation potential of Mn.sup.4+ (the
redox state of manganese in MnO.sub.2) and Mn.sup.2+ as measured by
the standard electrode potential is relatively high being +1.1406
volt. Increased corrosivity of a catalytic coating will have an
economic impact on the vehicle manufacturer or its customer, in
that the radiator will need to be replaced earlier than for an
un-coated radiator, either within warranty or at the cost of the
vehicle owner. Alternatively, or additionally, components of the
composition including the catalytic material may contribute to the
increased corrosion experienced in PremAir.RTM. coated
radiators.
[0012] In our co-pending British patent application of the same
filing date entitled "Agents for reducing atmospheric oxidising
pollutants", the contents of which are incorporated herein by
reference, we describe a number of alternative precious metal-free
agents for reducing atmospheric oxidising pollutants such as
O.sub.3 to those described by Engelhard in WO 96/22146 that show
similar or higher activity for O.sub.3 reduction than Engelhard's
manganese-based catalysts, e.g. cryptomelane, at the same ambient
temperature. We believe that our alternative reducing agents are
less likely to cause corrosion to an aluminium substrate in SWAAT
and Engelhard's galvanic corrosion tests when compared with
Engelhard's manganese-based compositions because the standard
electrode potential of the redox reaction including the transition
element and an ionic species of the transition element or between
the ionic species of the transition element present in the or each
compound and a further ionic species of the transition element is
less than +1.0 volt.
[0013] In our co-pending British patent application of the same
filing date entitled "Method of treating atmospheric pollutants",
the contents of which are incorporated herein by reference, we
describe how a precious-metal free trap material including at least
one trapped atmospheric reducing pollutant, such as a hydrocarbon,
can reduce at least one atmospheric oxidising pollutant
Consequently, the at least one trapped atmospheric reducing
pollutant itself is oxidised. One application for our observation
is in treating atmospheric O.sub.3 and hydrocarbons contacted by a
vehicle by coating an atmosphere contacting surface such as a
radiator with a composition including the trap material. Non-mobile
applications are equally viable, as is explained in the above
specification.
[0014] Modem radiators comprise a radiator core typically of
aluminium, which core including fins or plates extending from the
outer surface of a housing or conduit for carrying a fluid to be
cooled. To this core is fitted one or more plastic tanks which
carry the fluid to and from the radiator core. In the process for
manufacturing PremAir.RTM. coated radiators, it is understood that
the temperatures required to cure the catalyst composition applied
to the radiator core are sufficient to heat damage plastic tanks.
Accordingly, in the process used in practice, the coated radiator
cores are prepared in a separate step before the plastic tanks are
fitted thereto.
[0015] It would be a considerable advantage in the manufacture of
coated heat exchangers to be able to cure the reducing agent
composition at temperatures below which plastic components, such as
plastic tanks for radiators, suffer heat damage. For example, this
would avoid a number of steps of the manufacturing process used by
Engelhard in making PremAir.RTM. coated radiators, thus saving
energy in the curing process and making the process as a whole more
time and cost efficient.
[0016] As will be appreciated by the person skilled in the art, the
formulation of a composition suitable for application of a reducing
agent to a surface is complex. In addition to the active reducing
agent component, the formulation can include one or more binder
(including thermosetting or thermoplastic polymeric binders),
stabiliser, age resistor, dispersant, plasticiser, flow improver,
water resistance agent or adhesion improvement agent. The binder
provides cohesion to the composition. Furthermore, it provides
adhesion of the "wet" composition to a substrate following
application, and once cured, it provides adhesion and mechanical
robustness to the coating to prevent it flaking after prolonged
thermal cycling, and the ability to withstand knocks and bumps.
[0017] Among the factors that the skilled formulator will consider
in formulating a composition including a reducing agent for
coating, e.g. an aluminium alloy radiator, are the solvent medium
and its compatibility with the other components and how the
composition is to be used. For example, how does the composition
handle, flow or mix? Will the composition separate or settle on
standing? Does the formulation diminish the activity of the
reducing agent, for example by preventing air accessing the
component, by chemical reaction with the solvent or any other
component in the formulation or does the curing process thermally
deactivate the reducing agent? Is the composition suitable for the
chosen mode of application, e.g. spray coating, electrostatic spray
coating or screen-printing? Does the cured formulation have the
required physical properties?
[0018] It can be seen, therefore, that the problem of developing a
composition that cures at lower temperatures cannot be solved
merely by exchanging the solvent of a known composition for one
with a lower boiling point.
[0019] In WO 96/22146 Engelhard describe a number of polymeric
binder components for use in the catalyst compositions described
therein. The preferred polymers and copolymer binders are vinyl
acrylic polymers and ethylene vinyl acetate copolymers. Cellulosic
polymers are also mentioned but none of the Examples exemplify a
composition including a cellulosic binder.
[0020] We have now found that, very surprisingly, water soluble
binders are particularly suited to compositions for coating
atmosphere contacting surfaces, which compositions include, as an
active component, the precious metal-free reducing agents described
in our co-pending British patent application of the same filing
date entitled "Agents for reducing atmospheric oxidising
pollutants", the trap materials per se described in our co-pending
British patent application of the same filing date entitled "Method
of treating atmospheric pollutants" or the catalysts described in
WO 96/22146, particularly manganese-based catalysts such as
MnO.sub.2 and derivatives thereof, particularly cryptomelane. This
observation provides a number of very useful advantages.
[0021] By "atmospheric reducing pollutant" herein, and as described
in our co-pending British patent application of the same filing
date entitled "Method of treating atmospheric pollutants", we mean
an atmospheric pollutant that has the potential to reduce other
atmospheric pollutants in a redox reaction. Non-limiting examples
of atmospheric reducing pollutants are hydrocarbons including
aliphatic hydrocarbons, e.g. alkanes, and cyclic hydrocarbons;
paraffins; olefins, alkenes and alkynes; dialkenes including
conjugated unsaturated hydrocarbons; carboxylic, peroxy or sulfonic
acids; partially oxygenated hydrocarbons including aldehydes,
conjugated aldehydes, ketones, ethers, alcohols and esters; amides;
ammonium compounds; aromatic hydrocarbons and cycloparaffins; any
of the above including one or more nitrogen-, sulfur-, oxygen- or
phosphorus-atoms; CO; sulphur dioxide and soot or particulate
matter components exhausted from, e.g. a power plant (as defined
hereinbelow).
[0022] According to one aspect, the invention provides a
composition for reducing atmospheric oxidising pollutants, which
composition comprises a reducing agent comprising: at least one
transition element and/or one or more compounds including at least
one transition element wherein the standard electrode potential of
the redox reaction including the transition element and an ionic
species of the transition element or between the ionic species of
the transition element present in the or each compound and a
further ionic species of the transition element is less than +1.0
volt; a precious metal-free trap material capable of trapping at
least one atmospheric reducing pollutant, whereby the at least one
atmospheric oxidising pollutant is reduced by a combination of the
trap material and at least one trapped atmospheric reducing
pollutant, which at least one trapped atmospheric reducing
pollutant is consequently oxidised; or a manganese-based catalyst,
preferably MnO.sub.2 or a derivative thereof including
cryptomelane, and a water soluble binder.
[0023] Whilst the trap material per se embodiment of the present
invention substantially does not decompose O.sub.3, for the
purposes of the present specification it is embraced within the
meaning of "reducing agent". See also our co-pending British patent
application for further details.
[0024] An important advantage of the present invention is that the
composition can be cured at relatively low temperatures, e.g.
.ltoreq.90.degree. C., compared with compositions including
Engelhard's preferred binders. In particular, this feature enables
the preparation of a radiator core fitted with its plastic tanks in
a continuous process, i.e. without having first to prepare a coated
core and then fit the plastic tanks thereto. In contrast with
compositions requiring higher curing temperatures, the coated
radiator core must be prepared before assembling the tanks to
prevent heat damage of the tanks during curing. Thus, not only is
there an economic advantage in that the energy required to cure the
composition is reduced, but the process of radiator manufacture is
simplified.
[0025] The composition according to the invention can be applied to
a surface with known technology such as by spraying using a
compressed air spray gun, by an electrostatic application process
or using a screen printing process. Furthermore, the cured
composition has acceptable physical properties as displayed by
scrape, wipe, ultrasonic and SWAAT tests. In particular, no
deterioration was seen following thermal cycling and the cured
composition does not hydrate when contacted with aqueous media or
flake or chip.
[0026] In one preferred embodiment, the water-soluble binder is a
cellulosic binder. The cellulosic binder can be an ether or ester
or semi-synthetic cellulosic binder, but is preferably
hydroxypropyl- or methylellulose.
[0027] In another preferred embodiment, the water-soluble binder is
a vinyl or acrylic binder, preferably polyvinyl alcohol or ammonium
polymethacrylate.
[0028] Preferably, the transition element is copper, iron or zinc
or a mixture of any two or more thereof. The or each compound
including one or more transition element can be any suitable
compound such as an oxide, carbonate, nitrate or hydroxide, but is
preferably an oxide. In some circumstances, it is preferable to
reduce the transition element in a transition element-including
compound if in the reduced form the reducing agent is more active
in its intended use. Compounds including transition elements prior
to reduction can be referred to as `precursor`. For example, in a
preferred embodiment the reducing agent is CuO/ZnO/Al.sub.2O.sub.3
is the precursor and the active form of the reducing agent is
obtained by reducing the CuO to give Cu/ZnO//Al.sub.2O.sub.3. The
reduced form of a transition element can be stabilised with
suitable stabilisers as appropriate.
[0029] If supported, the transition element or transition element
compound is preferably supported on a high surface area oxide
selected from alumina, ceria, silica, titania, zirconia, a mixture
or a mixed oxide of any two or more thereof.
[0030] According to preferred embodiments, the active form of the
reducing agent is copper (II) oxide per se, a mixture of reduced
copper (a) oxide and zinc oxide on an alumina support or iron oxide
on a mixed alumina/ceria support.
[0031] Methods of manufacturing copper (II) oxide, copper (II)
oxide and zinc oxide on Al.sub.2O.sub.3 or iron oxide on a mixed
alumina/ceria support are known to a person skilled in the art or
can be deduced by reasonable experimentation, e.g. by
co-precipitation of the or each transition element component and/or
support. For example, in a CuO/ZnO//Al.sub.2O.sub.3 reducing agent
the Cu and Zn can be co-precipitated and the already formed
Al.sub.2O.sub.3 added thereto. Specific details of the
manufacturing processes will not be given here.
[0032] The CuO/ZnO//Al.sub.2O.sub.3 reducing agent composition can
be any suitable for the intended e.g. CuO30:ZnO60:Al.sub.2O.sub.3
10 or CuO60:ZnO30:Al.sub.2O.sub.3 10. Commercially available forms
of these compositions are available from ICI as ICI 52-1 and ICI
51-2 respectively. Commercially available CuO/ZnO//Al.sub.2O.sub.3
is sold as pellets, which can be ground to the required particle
size.
[0033] Preferred precious metal-free trap materials include high
surface area inorganic species such as zeolites, other molecular
sieves, crystalline silicates, crystalline silicate-containing
species, aluminas, silicas, (optionally amorphous)
aluminosilicates, layered clays and aluminium phosphates. Where the
trap material is zeolite, we prefer beta-zeolite or zeolite Y and
most preferably ZSM-5, optionally metal-substituted, so long as the
metal substituted zeolite does not decompose O.sub.3 per se, e.g.
the zeolite is not transition metal substituted.
[0034] According to a further aspect, the invention provides a
method of making an atmosphere-contacting surface according to the
invention comprising the steps of coating the surface with the
composition and heating the coated surface to .ltoreq.90.degree. C.
for a sufficient time to cure the composition.
[0035] In a preferred embodiment, the atmosphere-contacting surface
is associated with a means for causing movement of the surface
relative to the atmosphere.
[0036] In a preferred embodiment the means for causing movement of
the surface relative to the atmosphere is a power plant. The power
plant can be an engine fuelled by gasoline, diesel, liquid
petroleum gas, natural gas, methanol, ethanol, methane or a mixture
of any two or more thereof, an electric cell, a solar cell or a
hydrocarbon or hydrogen-powered fuel cell.
[0037] Preferably the atmosphere-contacting surface is on or in a
vehicle, and the movement-causing means is a power plant as
described above. The vehicle can be a car, van, truck, bus, lorry,
aeroplane, boat, ship, airship or train, for example. A
particularly preferred application is for use in heavy-duty diesel
vehicles, i.e. vans, trucks, buses or lorries, as defined by the
relevant European legislation.
[0038] The atmosphere-contacting surface can be any suitable
surface that encounters and contacts the atmosphere, most
preferably, at relatively large flow rates as the vehicle moves
through the atmosphere. The support surface is preferably located
at or towards the front end of the vehicle so that air will contact
the surface as the vehicle is propelled through it. Suitable
support locations are fan blades, wind deflectors, wing mirror
backs or radiator grills and the like. Alternative locations for
supporting the reducing agent are given in WO 96/22146 and are
incorporated herein by reference.
[0039] In a most preferred embodiment the apparatus comprises a
heat exchange device such as a radiator, an air conditioner
condenser, an air charge cooler (intercooler or aftercooler), an
engine oil cooler, a transmission oil cooler or a power steering
oil cooler. This feature has the advantage that the heat exchange
device reaches above ambient temperatures, such as up to
140.degree. C., e.g. 40.degree. C. to 110.degree. C., at which, for
example, O.sub.3 reduction can occur more favourably. A further
advantage of using heat exchangers as the support surface for the
or each reducing agent composition is that in order to transfer
heat efficiently they have a relatively large surface area
comprising fins or plates extending from the outer surface of a
housing or conduit for carrying a fluid to be cooled. A higher
surface area support surface provides for a greater level of
contact between the each reducing agent composition and the
atmosphere.
[0040] By "ambient" herein we mean the temperature and conditions,
e.g. humidity, of the atmosphere.
[0041] In a particularly preferred embodiment, the apparatus
comprises a radiator and/or air conditioning condenser which is
housed within a compartment of a vehicle also including the power
plant, e.g. an air-cooled engine. This provides the advantage that
the radiator and/or condenser is exposed to ambient atmospheric air
as the vehicle is propelled through the atmosphere whilst being
protected by the radiator grill from damage by particulates, e.g.
grit or stones, and from the impact of flies. For mid- and
rear-engine vehicles, air intakes and conduits can be arranged to
carry atmospheric air to and from the supported reducing agent. A
further advantage of locating the radiator and/or condenser in the
engine compartment is that exposure to corrosion-causing agents
such as moist air, salt and/or grit is reduced and hence so too is
the rate of any corrosion. Whilst the radiator and/or condenser can
be formed of any material, it is usually a metal or an alloy. Most
preferably, the heat exchanger is aluminium or an alloy containing
aluminium.
[0042] Where the atmosphere-contacting surface is of a heat
exchanger, it is important that the composition coating the surface
does not reduce the effectiveness of the substrate to transfer
heat. Accordingly, in one preferred feature, the composition of the
invention can include particles of a transition metal, preferably
silver or copper, for improving the thermal conductivity of the
composition.
[0043] Another advantage of using a heat exchanger, such as a
radiator, as the support surface for the reducing agent is that the
radiator is releasably attached to a vehicle, typically in the
engine compartment of the vehicle. This enables coated radiators
and other heat exchangers to be retrofitted to the vehicle, e.g.
during normal servicing of the vehicle, thereby to improve the
pollutant treating ability of the vehicle.
[0044] Alternatively the apparatus can be non-mobile, and the
surface is associated with the movement-causing means to provide
the required relative movement between the surface and the
atmosphere. For example, the surface can be one or more blades for
causing movement of air. In one embodiment the blades are fan
blades for cooling a stationary power plant such as for powering an
air conditioning unit or advertising hoarding. In another
embodiment the blade is a fan or turbine blade for drawing air into
the air conditioning system of a building.
[0045] In addition to, or instead of, the support surface being on
a fan or turbine blade, the surface can be the internal surfaces of
pipes, tubes or other conduits for carrying atmospheric air, e.g.
in an air conditioning system for a vehicle or a building and
condenser elements in air conditioning units provided that the
movement of the air is caused by a movement causing means.
[0046] That the reducing agents for use in the present invention
are at least as active for reducing O.sub.3 as Engelhard's
Premair.RTM. manganese-based components is shown in Example 4
below, where a 20 mm thick aluminium radiator coated with a
composition including our mixture of "reduced" copper (II) oxide
and zinc oxide on an alumina support gave a % O.sub.3 conversion of
94% whereas the commercially available 40 mm thick Premair.RTM.
aluminium radiator including cryptomelane had a % O.sub.3
conversion of 100%. From Example 1 we know that O.sub.3 conversion
activity improves significantly if the reducing agent loading is
doubled. Therefore, if our coating were applied on a 40 mm thick
unit at the same mass per unit volume, we would expect the O.sub.3
conversion to improve from 94%, probably to 100%.
[0047] In order that the invention may be more fully understood,
the invention will now be described by reference to the following
illustrative Examples and by reference to the accompanying
drawings, in which:
[0048] FIG. 1 is a bar chart showing the % O.sub.3 conversion for
various candidate reducing agents;
[0049] FIG. 2 is a bar chart showing the effect on % O.sub.3
conversion of increasing CuO content on the O.sub.3 conversion of
CuO/ZnO//Al.sub.2O.sub.3; and
[0050] FIG. 3 is a bar chart comparing the % O.sub.3 conversion of
a composition including a mixture of copper (II) oxide and zinc
oxide on an alumina support and a hydroxypropyl cellulose binder
with a bare radiator and a Premair.RTM. radiator.
EXAMPLE 1
[0051] To screen candidate O.sub.3 reducing agents at room
temperature, a test rig comprising an upstream O.sub.3 generator, a
stainless steel tube including metal mesh to pack a reactor bed
material therebetween and a downstream O.sub.3 detector was set up
in a fume cupboard. O.sub.3 was generated and mixed with air before
passing through the reactor bed containing powder or pellet
samples. The exhaust gas from the reactor bed was passed through
the O.sub.3 detector (measured in 5 ppm units) before being vented.
An inlet O.sub.3 concentration of 200 ppm at a space velocity
(GHSV) of .about.1000/hr was used. Whilst higher space velocities
would be observed at, e.g. the surface of a radiator, and
atmospheric O.sub.3 concentrations are present in the parts per
billion range, the results were useful to compare directly the
potential of each material tested to reduce O.sub.3.
[0052] The following materials were tested: H--Y zeolite (Si:Al
ratio 200:1)--1" powder bed; a ceria-zirconia mixed oxide 1" powder
(ceria-zirconia mixed oxide is an oxygen storage component used in
three way catalyst compositions); iron oxide on a ceria support
(hereinafter "Fe reducing agent")--1" pellet bed;
Cu/ZnO//Al.sub.2O.sub.3--1" pellet bed; Cu/ZnO//Al.sub.2O.sub.3--1"
powder bed; and Cu/ZnO//Al.sub.2O.sub.3 on a ceramic monolith.
[0053] FIG. 1 shows the results of a comparison of the O.sub.3
decomposition activity of these materials tested in the rig
described above at room temperature. No O.sub.3 conversion was
observed for the empty system or over a bare metallic or ceramic
substrate. Zeolite and ceria-zirconia were also found to have no
O.sub.3 decomposition activity. The best material tested was
Cu/ZnO//Al.sub.2O.sub.3; this gave approximately 70% conversion
over a 1" bed of pellets, compared to 45% for a 1" bed of Fe
reducing agent. Cu/ZnO//Al.sub.2O.sub.3 coated onto a ceramic
monolith. As expected, the form of the reducing agent material was
important--after grinding the Cu/ZnO//Al.sub.2O.sub.3 pellets into
a fine powder, the O.sub.3 conversion increased to 100%.
[0054] It was also confirmed that the O.sub.3 conversion is
dependent on the reducing agent loading. For
Cu/ZnO//Al.sub.2O.sub.3 powder, as the loading increased from 0.5
to 1 g the O.sub.3 conversion increased from 48 to 63%. At higher
loadings 100% conversion was achieved. A similar trend was observed
for the Fe reducing agent; doubling the reactor bed depth from 1"
to 2" increased the O.sub.3 conversion from 45 to 100%, while
reducing the bed depth to 1/2" reduced the O.sub.3 conversion to
25%.
EXAMPLE 2
[0055] To test whether the O.sub.3 conversion of our best candidate
O.sub.3 reducing agent Cu/ZnO//Al.sub.2O.sub.3 can be improved by
including copper (II) oxide, a series of materials were prepared by
mixing Cu/ZnO//Al.sub.2O.sub.3 and copper (II) oxide at ratios of
100:0, 75:25, 50:50, 25:75 and 0:100 by mass. The O.sub.3
conversion was measured using the rig and procedure described in
Example 1 above for 0.5 g of each powder and the results are shown
in FIG. 2. They clearly show that adding copper oxide increases the
O.sub.3 conversion from 48% for the undoped material to .about.62%
for material with .gtoreq.50% copper oxide.
EXAMPLE 3
[0056] There is now described a composition including the
Cu/ZnO//Al.sub.2O.sub.3 reducing agent component for application to
e.g. an aluminium alloy radiator substrate.
[0057] Cu/ZnO//Al.sub.2O.sub.3 was mixed with an aqueous solution
of hydroxypropyl cellulose binder, Klucel.TM., to a concentration
of 10% wt/wt. The coating was applied to each side of a Visteon
aluminium alloy radiator of 20 mm thickness using a compressed air
spray gun and then cured at or below 90.degree. C.
EXAMPLE 4
[0058] There is now described a composition including a beta
zeolite trap component for application to an aluminium radiator
substrate. Beta zeolite was mixed with an aqueous solution of
hydroxypropyl cellulose binder, Klucel.TM., to a concentration of
10% wt/wt. The coating was applied to each side of a Visteon
aluminium radiator of 20 mm thickness using a compressed air spray
gun and then cured at up to 90.degree. C.
EXAMPLE 5
[0059] This Example is designed to compare the O.sub.3 conversion
activity of our Cu/ZnO//Al.sub.2O.sub.3 reducing agent with that of
Engelhard's Premair.RTM. catalyst.
[0060] A Ford Mondeo radiator manufactured by Visteon was supplied
for coating. This radiator, consisting of uncoated aluminium foil,
has a face area of 16".times.10" and a thickness of 20 mm. The unit
was coated with a washcoat including the Cu/ZnO//Al.sub.2O.sub.3
and a 10% wt/wt aqueous solution of a hydroxypropyl cellulose
binder (trade name "Klucel") described in Example 3 above using a
compressed air spray gun. Two layers were applied to each side,
loading of 68 g or 0.54 g/in.sup.3. After drying, the radiator was
found to have a thick, dark brown coating of approximately 20 mm
total thickness which had acceptable adhesion and resisted most
physical abrasion.
[0061] The activity of the coated radiator was tested and compared
to a bare aluminium alloy radiator and an Engelhard Premair coated
aluminium alloy radiator. Activity testing was carried out in a
similar manner to the material screening described in Example 1
above, with the powder bed reactor modified so that it clamped onto
either side of the radiator. The results can be seen in FIG. 3. 94%
O.sub.3 conversion was obtained over the Cu/ZnO//Al.sub.2O.sub.3
coated aluminium radiator; this compared favourably with the 100%
conversion obtained over the Premair.RTM. radiator. The thickness
of the Premair.RTM. radiator was approximately 40 mm, twice that of
the radiator coated with our Cu/ZnO//Al.sub.2O.sub.3 composition.
No conversion was obtained from a bare radiator.
* * * * *
References