U.S. patent application number 09/164874 was filed with the patent office on 2002-02-07 for catalytic plasma reduction of nox.
Invention is credited to BALMER, MARI LOU, BARLOW, STEPHAN E., KIM, ANTHONY Y., ORLANDO, THOMAS M., TONKYN, RUSSELL G..
Application Number | 20020014071 09/164874 |
Document ID | / |
Family ID | 22596459 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014071 |
Kind Code |
A1 |
BALMER, MARI LOU ; et
al. |
February 7, 2002 |
CATALYTIC PLASMA REDUCTION OF NOX
Abstract
The present invention is based upon the discovery that
microporous catalysts, especially zeolites in the class of metallic
Faujasites, Linde Type A (LTA) and combinations thereof having a
pore size greater than 3 angstroms in combination with a plasma are
capable of catalyzing conversion of NO.sub.x to N.sub.2 in a real
or actual exhaust stream without any gas phase additive.
Inventors: |
BALMER, MARI LOU; (WEST
RICHLAND, WA) ; KIM, ANTHONY Y.; (SEATTLE, WA)
; TONKYN, RUSSELL G.; (KENNEWICK, WA) ; BARLOW,
STEPHAN E.; (RICHLAND, WA) ; ORLANDO, THOMAS M.;
(KENNEWICK, WA) |
Correspondence
Address: |
PAUL W ZIMMERMAN
INTELLECTUAL PROPERTY SERVICES
BATTELLE MEMORIAL INSTITUTE
P O BOX 999
RICHLAND
WA
99352
|
Family ID: |
22596459 |
Appl. No.: |
09/164874 |
Filed: |
October 1, 1998 |
Current U.S.
Class: |
60/273 ;
60/275 |
Current CPC
Class: |
B01D 53/32 20130101;
F01N 2570/14 20130101; B01D 53/9431 20130101; B01D 2255/2025
20130101; B01D 2255/2027 20130101; F01N 3/0892 20130101; Y02A 50/20
20180101; B01D 2255/2045 20130101; Y02A 50/2344 20180101; B01D
53/8628 20130101; B01D 53/8631 20130101; B01D 53/9422 20130101;
B01D 2255/50 20130101 |
Class at
Publication: |
60/273 ;
60/275 |
International
Class: |
F01N 003/00 |
Goverment Interests
[0001] This invention was made with Government support under
Contract DE-AC0676RLO1830 awarded by the U.S. Department of Energy.
The Government has certain rights in the invention.
Claims
We claim:
1. A method of catalytic plasma conversion of at least one nitrogen
oxide from an exhaust gas stream containing said at least one
nitrogen oxide to a nitrogen gas, comprising the steps of: (a)
providing a vessel with an inlet and an outlet, the vessel having a
zeolite catalyst selected from the group of metallic Faujasite,
Linde Type A and combinations thereof therein together with
electrodes for creating a plasma, said zeolite catalyst containing
a metal in an exchange site; (b) passing said exhaust gas stream
into the inlet through said vessel and contacting said exhaust gas
stream with said catalyst and said plasma thereby converting said
at least one nitrogen oxide to said nitrogen gas, forming a
nitrogen oxide reduced exhaust gas stream; and (c) flowing said
nitrogen oxide reduced exhaust stream through the outlet.
2. The method as recited in claim 1, wherein said metallic
Faujasite has a structure selected from the group of zeolite X,
zeolite Y and combinations thereof.
3. The method as recited in claim 2, wherein said metal is selected
from the group of alkali, alkali earth, transition metal and
combinations thereof.
4. The method as recited in claim 1, wherein said zeolite catalyst
contains metal atoms from about 5% to about 100% of available
sites.
5. The method as recited in claim 1, wherein said zeolite catalyst
has a pore size of greater than 3 angstrom units.
6. The method as recited in claim 5, wherein said metallic
Faujasite has a pore size of at least 6 angstrom units.
7. The method as recited in claim 1, wherein said metal in said
Linde Type A is a cation selected from the group consisting of Li,
Na, Ca and combinations thereof.
8. The method as recited in claim 1, wherein said exhaust gas is at
a temperature of at least 100.degree. C.
9. The method as recited in claim 1, wherein said zeolite catalyst
has a metal selected from the group consisting of Na, Cs, Ca, Co,
Ag, Ni, and K.
10. The method as recited in claim 1, wherein said electrodes are
arranged in a tube array.
11. An apparatus for catalytic plasma conversion of at least one
nitrogen oxide from an exhaust gas stream containing said at least
one nitrogen oxide to a nitrogen gas, comprising: (a) a vessel with
an inlet and an outlet; (b) the vessel having therein a zeolite
microporous catalyst selected from the group of metallic Faujasite,
Linde Type A and combinations thereof; together with (c) electrodes
for creating a plasma; wherein (d) said exhaust gas stream passes
into the inlet through said vessel and contacts said exhaust gas
stream with said catalyst and said plasma, thereby converting said
at least one nitrogen oxide to said nitrogen gas, forming a
nitrogen oxide reduced exhaust gas stream, and said nitrogen oxide
reduced exhaust stream passing through the outlet.
12. The apparatus as recited in claim 11, wherein said metallic
Faujasite has a structure selected from the group of zeolite X,
zeolite Y and combinations thereof.
13. The apparatus as recited in claim 12, wherein said metallic
Faujasite has a metal selected from the group of alkali, alkali
earth, transition metal and combinations thereof.
14. The apparatus as recited in claim 11, wherein said zeolite
catalyst contains metal atoms from about 5% to about 100% of
available sites.
15. The apparatus as recited in claim 11, wherein said zeolite
catalyst has a pore size greater than 3 angstrom units.
16. The apparatus as recited in claim 15, wherein said metallic
Faujasite has a pore size of at least 6 angstrom units.
17. The apparatus as recited in claim 11, wherein said electrodes
are arranged in a tube array.
18. The apparatus as recited in claim 11, wherein said zeolite
microporous catalyst has a metal selected from the group consisting
of Na, Cs, Ca, Co, Ag, Ni, and K.
19. A method of converting at least one nitrogen oxide to nitrogen
gas, comprising the steps of: (a) providing a vessel with an inlet
and an outlet, the vessel having a microporous catalyst of a
titanosilicate with a free aperture of at least 3.5 angstroms, said
free aperture defined by a base porous material impregnated with a
cation selected from the group consisting of alkaline earth,
alkali, transition, and combinations thereof therein together with
electrodes for creating a plasma; (b) passing said exhaust gas
stream into the inlet through said vessel and contacting said
exhaust gas stream with said catalyst and said plasma thereby
converting said at least one nitrogen oxide to a nitrogen gas,
forming a nitrogen oxide reduced exhaust gas stream; and (c)
flowing said nitrogen oxide reduced exhaust stream through the
outlet.
20. The method as recited in claim 19, wherein said cation is
selected from the group consisting of Li, Na, K, Cs and
combinations thereof.
21. The method as recited in claim 19, wherein said electrodes are
arranged in a tube array.
22. A method of catalytic plasma conversion of at least one
nitrogen oxide from an exhaust gas stream containing said at least
one nitrogen oxide to a nitrogen gas, wherein at an optimum
temperature from about 150.degree. C. to about 180.degree. C.,
NO.sub.x reduction is greater than 52%, comprising the steps of:
(a) providing a vessel with an inlet and an outlet, the vessel
having a zeolite catalyst selected from the group of metallic
Faujasite, Linde Type A and combinations thereof therein together
with electrodes for creating a plasma, said zeolite catalyst
containing a metal in an exchange site; (b) passing said exhaust
gas stream into the inlet through said vessel and contacting said
exhaust gas stream with said catalyst and said plasma thereby
converting said at least one nitrogen oxide to said nitrogen gas,
forming a nitrogen oxide reduced exhaust gas stream; and (c)
flowing said nitrogen oxide reduced exhaust stream through the
outlet.
23. The method as recited in claim 22 wherein said zeolite has a
free aperture from 3 angstroms to 7 angstroms.
24. The method as recited in claim 22, wherein said zeolite
catalyst has a metal selected from the group consisting of Na, Cs,
Ca, Co, Ag, Ni, and K.
25. The method as recited in claim 24 wherein said zeolite has a
free aperture from 3 angstroms to 7 angstroms.
26. The method as recited in claim 22, wherein said electrodes are
arranged in a tube array.
Description
FIELD OF THE INVENTION
[0002] The present invention relates to catalytic plasma reduction
of nitrogen oxide (NO.sub.x). More specifically, the present
invention relates to selection of a microporous catalyst to obtain
conversion of the nitrogen oxide to nitrogen gas without external
addition of any gas phase additive.
[0003] As used herein, the phrase and similar phrases to "without
external addition of any gas phase additive" refers to the absence
of any non-exhaust input.
[0004] As used herein, the term "pore size" is the network ring
opening size in the absence of a charge compensating cation or a
"bare" material.
[0005] As used herein, the term "free aperture" is the size of an
opening through the pore after a cation has been inserted into the
pore of the bare material.
BACKGROUND OF THE INVENTION
[0006] Combustion exhaust theoretically should be simply carbon
dioxide and water vapor. However, because most fuels are complex
compounds, and because the source of oxidant is the atmosphere with
about 21 vol. % nitrogen, combustion exhaust generally contains
unburned hydrocarbons and one or more versions of nitrogen oxide
(NO.sub.x) converted from the nitrogen. Even a methane or hydrogen
fuel source can have unburned fuel and produce nitrogen oxide.
[0007] There has been much effort expended to obtain both the
greatest possible energy from a fuel and achieve a clean exhaust
free of hydrocarbons and nitrogen oxide. One approach toward
achieving clean exhaust has been plasma assisted catalytic
reduction operated downstream of the combustion chamber.
[0008] An example of this approach is U.S. Pat. No. 5,711,147 to
Vogtlin et al. wherein a non-thermal plasma gas is combined with
.gamma.-Al.sub.2O.sub.3 catalyst and a stream of added hydrocarbon
to achieve an 80% reduction of NO.sub.x. A disadvantage of this
method is the added hydrocarbon defeating the goal of maximizing
energy extraction from the fuel.
[0009] The U.S. Pat. No. 5,715,677 to Wallman et al. achieves an
unspecified reduction of nitrogen oxide (NO.sub.x) from diesel
exhaust by collecting particulate and NO.sub.x onto an adsorbent
bed with bead size from 5-10 mm then exposing the adsorbent bed to
plasma. Materials for the adsorbent bed included metal oxides,
dolomite, zeolites of ZSM-5, Cu-ZSM-5, and H-mordenite, and
perovskites. A disadvantage of this method is the semi-batch or
non-continuous mode of operation requiring separate adsorption and
plasma exposure steps.
[0010] The U.S. Pat. No. 5,746,984 to Hoard is directed to treating
cold-start emissions by adsorbing the cold start emissions on a
storage device then desorbing them as the exhaust temperature
increases followed by destroying the desorbed cold start emissions
in a non-thermal plasma. A honeycomb monolith is prepared to
receive a coating of an adsorbing material as the storage device.
Adsorbing materials are recited as oxides of copper, barium and
lanthanum, and CuZSM-5 zeolite. Hoard reports that operation of the
plasma reactor consumes no more than about 2% of engine energy
consumption.
[0011] However, it has been shown in Analysis of Plasma-Catalysis
for Diesel NOX Remediation, J Hoard, M L Balmer, Diesel Engine
Emissions Reduction Workshop Proceedings, 1998 that in the case of
Cu-ZSM-5 placed either in the plasma or downstream of (after) the
plasma, converts the gas phase species back to NO.sub.x, an
undesirable product. Thus, Hoard's report of 2% consumption is not
for complete conversion of NO.sub.x to N.sub.2.
[0012] The U.S. Pat. No. 5,458,748 to Breault et al. show NO.sub.x
conversion as a function of applied voltage for the plasma, with
conversion up to about 98%. However, no catalyst other than plasma
is used and the products of conversion include HNO.sub.3 which is
corrosive unless removed. In addition it has been shown by B M
Pentrante, W J Pitz, M C Hsaio, B T Merritt, and G E Vogtlin, in
the Proceedings for the 1997 Diesel Engine Emissions Reduction
Workshop that in the absence of a catalyst, the plasma chemistry
primarily converts NO to NO.sub.2 with some NO.sub.x disappearing
to unmeasured products NO.sub.x species converted in the plasma are
converted back to NO.
[0013] U.S. Pat. No. 5,609,736 to Yamamoto describes a vessel
formed of opposing conductive plates and opposing dielectric plates
between the opposing conductive plates. The volume of the vessel is
filled with beads having a catalytic coating thereon. Catalytic
coatings specified are oxidation catalysts of noble metals and
metallic oxides. Removal of carbon tetrachloride is reported.
Nitrogen oxide conversion is mentioned but not quantitatively
reported.
[0014] UK patent application GB 2,274,412 A describes a chamber
filled with pellets held between screens that act as electrodes and
showing removal of toluene from a gas stream. The pellets are Pb or
Ba niobate, titanate or zirconate. Nitrogen oxide removal is not
quantified.
[0015] Japanese Kokai JP 6-269635 describes a plasma exhaust gas
processing apparatus and absorbent apparatus connected in order. No
catalyst is used. The conversion product NO.sub.2 is absorbed in
the absorbent apparatus. A disadvantage of this technique is the
need to regenerate the absorbent apparatus.
[0016] The German Offenlegungsschrift DE 195 10 804 A1 discusses
combining an exhaust gas stream with a reduction agent that is made
into a plasma and contacted with a catalyst. The reduction agent is
a nitrogen compound, for example nitrogen, ammodia, hydrazine or
cyanuric acid or is aliphatic or olefin hydrocarbon or hydrogen.
The catalyst may be zeolites doped with elements of the platinum
group, copper group, or iron group, oxides doped with elements of
the platinum-, aluminum-, titanium- or lanthanide groups or their
mixtures, mixed oxides of wolfram, chrome, or vanadium. NO.sub.x
reduction is not quantified. A disadvantage of this process is the
addition of a reduction agent.
[0017] The paper PLASMA-ASSISTED HETEROGENOUS CATALYSIS FOR
NO.sub.x REDUCTION IN LEAN-BURN ENGINE EXHAUST, B M Penetrante, M C
Hsiao, B T Merritt, G E Vogtlin, Proceedings of the 1997 Diesel
Engine Emissions Reduction Workshop discusses the advantage of
using plasma in combination with "a new class of catalysts that are
potentially more durable, more active, more selective and more
sulfur tolerant". Because the inventors of U.S. Pat. No. 5,711,147
(discussed above) are included as authors of this paper, and the
paper was published after the patent application was filed, it is
hypothesized that the "new class of catalysts" includes gamma
alumina mentioned in the patent and possibly other catalyst
materials mentioned in the literature. FIG. 4(b) of the paper shows
maximum conversion of NO.sub.x to N.sub.2 of 77% at about 25 J/L
energy density in real diesel exhaust. It is assumed that the added
hydrocarbon mentioned in the patent is also used to obtain the data
in the paper although an added hydrocarbon is not specifically
mentioned in the paper.
[0018] The abstract of the paper CATALYST ASSISTED REACTION BY
USING NON-THERMAL PLASMA ON NITRIC OXIDES REMOVAL, K Shimizu, T
Oda, 1997, identifies Na-ZSM-5 as an effective catalyst in
combination with non-thermal plasma for NO.sub.x removal. FIG. 4 of
the paper shows a maximum removal rate of less than 55% for input
power up to 30 W.
[0019] Japanese patent application Hei 6-106025, K lsogai et al.
discusses a plasma reactor with catalyst material for decomposition
of NO.sub.x. Catalyst material is metal oxide, and zeolites of
H-ZSM-5, H-Y, H-Mordenite, Na-ZSM-5, and Cu-ZSM-5. Decomposition
rate is not shown. The ineffectiveness of Cu-ZSM-5 because of
reconversion to NO was mentioned above.
[0020] Japanese patent application Hei 6-15143 K Isogai discusses a
plasma reactor with a photocatalytic dielectric material. The
photocatalytic dielectric material may be TiO.sub.2, ZnO,
SrTiO.sub.2, and ZnS. Nitrogen oxide destruction is not
quantified.
[0021] As may be seen from the review of prior art literature
provided herein, the energy efficiency of NO.sub.x conversion is
often not reported and when it is reported, it is difficult to
compare because of different bases of quantification. The
destruction rate of NOX decreases logarithmically with energy
density as shown in Tonkyn (Vehicle Exhaust Treatment Using
Electrical Discharge methods, "Tonkyn, Barlow, Balmer, Orlando,
Hoard, and Goulette, SAE Paper 971716, May 1997), specifically
[NO]=[NO].sub.o*e.sup.-E/.beta.
[NO.sub.x]=[NO.sub.x].sub.f+([NO.sub.x].sub.o-[NO.sub.x].sub.f)*
e.sup.-E/.beta.
[0022] where .beta. (or beta parameter) is the first order decay
parameter in Joules/standard liter, [NO.sub.x].sub.o is the initial
NOx concentration and [NO.sub.x].sub.f is the final NO.sub.x
concentration. The beta parameter is therefore a quantitative
measure of energy consumption of the conversion of NO.sub.x to
N.sub.2. In general, a low beta value indicates that the energy
efficiency is high, or alternatively, that the amount of energy
expended to achieve the maximum NO.sub.x destruction is relatively
low. The overall NO.sub.x destruction efficiency is affected by
both the type of plasma reactor and the type of catalyst. Other
measures of conversion efficiency include percent of total fuel
consumption, and percent destruction for a given power (Watts).
[0023] Although much attention and work has been done to clean up
combustion gas exhaust streams, there is still a need in the art
for an apparatus and method that is capable of converting NO.sub.x
to N.sub.2 in a real or actual exhaust stream without any gas phase
additive and with greater energy efficiency.
SUMMARY OF THE INVENTION
[0024] The present invention is based upon the discovery that
microporous materials having a free aperture greater than 3
angstroms in combination with a plasma are capable of catalyzing
conversion of NO.sub.x to N.sub.2 in a real or actual exhaust
stream without any gas phase additive.
[0025] It is an object of the present invention to provide a method
of NO.sub.x conversion to N.sub.2 using a plasma in the presence of
a microporous catalyst.
[0026] It is a particular advantage of the present invention that
the optimum performance is achieved at temperatures and gas
compositions typically found in the exhaust of light duty
vehicles.
[0027] The subject matter of the present invention is particularly
pointed out and distinctly claimed in the concluding portion of
this specification. However, both the organization and method of
operation, together with further advantages and objects thereof,
may best be understood by reference to the following description
taken in connection with accompanying drawings wherein like
reference characters refer to like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a cross section of a single stage apparatus of the
present invention.
[0029] FIG. 2A is a cross section of a two-stage apparatus of the
present invention.
[0030] FIG. 2B is a cutaway of a tube array reactor encased in a
metallic housing.
[0031] FIG. 2C is a cutaway of an alternate tube array reactor.
[0032] FIG. 3 is a single stage NO.sub.x conversion graph for
Z-Y-Na.
[0033] FIG. 4 is a single stage NO.sub.x conversion graph for
Z-Y-K.
[0034] FIG. 5 is a single stage NO.sub.x conversion graph for
Z-Y-Cs.
[0035] FIG. 6 is a single stage NO.sub.x conversion graph for
Z-Y-Ga.
[0036] FIG. 7 is a single stage NO.sub.x conversion graph for
Z-Y-Co.
[0037] FIG. 8 is a single stage NO.sub.x conversion graph for
Z-Y-Ag.
[0038] FIG. 9 is a single stage NO.sub.x conversion graph for
Z-Y-Ni.
[0039] FIG. 10 is a single stage NO.sub.x conversion graph for
Z-X-Na.
[0040] FIG. 11 is a two-stage NO.sub.x conversion graph for
Z-Y-Na.
[0041] FIG. 12 is a double single stage NO.sub.x conversion graph
for Z-Y-Na.
[0042] FIG. 13 is a single stage NO.sub.x conversion graph for
LTA-K.
[0043] FIG. 14 is a single stage NO.sub.x conversion graph for
LTA-Na.
[0044] FIG. 15 is a single stage NO.sub.x conversion graph for
LTA-Ca.
[0045] FIG. 16 is a single stage NO.sub.x conversion graph for
ETS-10.
DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0046] The present invention shown in FIG. 1 includes a method and
an apparatus for catalytic plasma removal of at least one nitrogen
oxide from an exhaust gas stream 100 containing the at least one
nitrogen oxide by converting the at least one nitrogen oxide to a
nitrogen gas (N.sub.2). The method and apparatus rely upon a vessel
102 with an inlet 104 and an outlet 106, the vessel 102 having a
microporous catalyst 108 therein together with electrodes 110 for
creating a plasma. The exhaust gas stream 100 is passed into the
inlet 104 through the vessel 102 and contacted with the microporous
catalyst 108 and the plasma thereby converting the at least one
nitrogen oxide to a nitrogen gas, forming a nitrogen oxide reduced
exhaust gas stream 112, and flowing the nitrogen oxide reduced
exhaust stream 112 through the outlet 106. If the dielectric
constant of the microporous catalyst 108 is not sufficient to
prevent arcing between the electrodes 110, a dielectric barrier 114
may be added. If the microporous catalyst 108 is not self
supporting, a support frit 116 may be used. The microporous
catalyst 108 may be supported in a binder including but not limited
to attapulgite clay, alumina and combinations thereof. It is
important that the binder permit gas (hydrocarbon and NO.sub.x)
access to the microporous catalyst 108.
[0047] The vessel 102 may have separate chambers as shown in FIG.
2A, a plasma chamber 200 and a catalyst chamber 202.
[0048] Alternatively, two vessels 102 having microporous catalyst
108 therein may be placed in series (not shown) as a double single
stage configuration, or a double two-stage configuration.
[0049] The plasma chamber may comprise a packed bed reactor or a
tube array reactor. Packed bed reactors suffer from electrical
current flow across the particles of the packed bed and higher
pressure drop through the packed bed which contribute to higher
energy requirements than are needed with tube array reactors. The
tube array is the preferred reactor for the plasma chamber due to
its lower energy requirement and higher efficiency design resulting
from factors such as a higher transfer of electrical energy into
the plasma and the openness of the tube array design which
facilitates a lower pressure drop across the tube array. A tube
array reactor 250 encased in a metallic housing 252 is shown in
FIG. 2B. Dielectric tubes 254 are metalized on the inside 256 and
electrified by fused contacts 258 to a high voltage power source
(not shown). In this tube array design, the exhaust gas stream
enters the chamber inlet 260 and flows in a transverse direction
across the dielectric tubes before exiting the chamber outlet 262.
In an alternate configuration shown in FIG. 2C, taken from U.S.
Pat. No. 5,458,748, the exhaust gas stream enters the chamber inlet
260 and flows through the tubes 254 in a parallel direction with
the tubes 254.
[0050] A preferred microporous catalyst is a zeolite in the class
of metallic Faujasites, Linde Type A (LTA) and combinations
thereof. The microporous catalyst may have all pores as microporous
(pore size of 15 angstroms or less) or may have mixed micropores
(15 angstroms or less) and mesopores (greater than 15
angstroms).
[0051] The metallic Faujasite must be crystalline and has a
structure selected from the group of zeolite X, zeolite Y and
combinations thereof. Microporous material composition includes but
is not limited to aluminosilicate and titanosilicate. Other network
site cations include iron, gallium, germanium and combinations
thereof. The metal in the exchange site of metallic Faujasite may
be alkali, including but not limited to Mg, Li, Na, K, Rb, Cs,
alkali earth, including but not limited to Ca, Sr, Ba, transition
metals including but not limited to Sc, Y, Ti, Zr, Hf, V, Nb, Ta,
Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Os, Co, Rh, Ir, Ni, Pd,
Pt, Cu, Ag, Au, rare earths and combinations thereof. Rare earths
include but are not limited to Ce and Sm. The amount of metal atoms
in the metallic Faujasite may range from about 5% to about 100% of
available sites for metal atoms. The metallic Faujasite has a
micropore size of at least 6 angstrom units. Generally, zeolite Y
has a pore size of about 7 angstroms and zeolite X has a pore size
of about 10 angstroms. Metallic Faujasite in or after plasma
converts more than 55% of NO.sub.x to N.sub.2 for certain cations
at a temperature of about 180.degree. C. The optimum temperature is
from about 150.degree. C. to about 250.degree. C. This is an
advantage because diesel exhaust from a light duty vehicle is
typically near 150.degree. C. to 200.degree. C.
[0052] Free aperture size greater than 3.5 angstrom units permits
flow of unburned hydrocarbon into the pores of the metallic
Faujasite during conversion with at least one benefit of preventing
the formation of nitric acid. Free aperture size greater than 6
angstrom units is preferred.
[0053] The catalyst structure may be a perforated or porous
monlith, beads, powder or combination thereof.
[0054] Zeolites of Linde Type A (LTA) are characterized by pore
sizes on the order of 4 angstroms. Small cations, including but not
limited to Li, Na, Ca and combinations thereof permit NO.sub.x
conversion to N.sub.2. Large cations, for example K, fill the pore
preventing entrance of unburned hydrocarbons and substantially
reduce conversion to the point of inoperability.
[0055] Other microporous materials with structures different from
Faujasite or Type A including titanosilicate (ETS-10) templated
mesoporous materials with micropores have been found useful for
NO.sub.x conversion to N.sub.2.
EXPERIMENTAL APPARATUS AND METHOD FOR EXAMPLES
[0056] Simulated exhaust gas streams were obtained from gas tanks
with mass flow controllers. The exhaust gas test conditions were
100.degree. C. to 300.degree. C. in a lean mix of O.sub.2 (2-8 vol.
%), CO.sub.2 (.ltoreq.7 vol. %), H.sub.2O (2-10 vol. %), CO (<1
vol. %), hydrocarbon (25-3100 ppm (as propylene or nonene, etc.)),
and NO (10-500 ppm) at a space velocity of 2,000-45,000 hr.sup.-1.
Two catalyst configurations were used, either a single stage of a
packed bed of catalyst material in the plasma region or two-stages
of a plasma region followed by a packed bed of the catalyst
material (FIG. 2).
[0057] NO and NO.sub.x were monitored with a chemiluminescent
NO.sub.x detector with differences attributed to NO.sub.2. End
products of CO.sub.2 and N.sub.2 were monitored with a mass
spectrometer and gas chromatograph.
Example 1
[0058] Catalysts known in the prior art were used to measure
NO.sub.x conversion with plasma. The amount of CO.sub.2 was less
than 4 vol. %. The catalyst was in the form of a bead or pellet
with particles held with a binder. Table E1-1 shows the catalysts
and conversion results.
1TABLE E1-1 Prior Art Catalyst Performance Catalyst Stages Temp
(.degree. C.) Beta % NO.sub.x H-ZSM-5 <10 Na-ZSM-5 1 200 52
Cu-ZSM-5.sup.A 1 150 42 Cu-ZSM-5 1 200 41 Cu-ZSM-5 1 180 15
Cu-ZSM-5 1 250 36 Na-ZSM-5 1 200 52 H-Z-Y 2 200/300 6.5 0-67.sup.B
H-Z-Y 1 200 --.sup.C H-Mordenite 1 180 33 20 Al.sub.2O.sub.3 1 180
20 Auto Beads 1 180 21 (PGM, Al.sub.2O.sub.3, CeO.sub.2)
.sup.ANO.sub.x conversion excludes thermal NO.sub.x reduction for
Temp >200 C. .sup.BConversion high at onset is close to 67%,
however rapid degradation of activity observed after several hours.
In general, protonated zeolites adsorbed large amounts of
hydrocarbon then failed by deactivation or conduction. .sup.CSample
adsorbs large amounts of hydrocarbon and possibly NOX, the reactor
(plasma) fails due to conduction.
Example 2
[0059] Metallic Faujasites according to the present invention were
used for NO.sub.x conversion. The Z-X materials were obtained from
Aldrich Chemical Milwaukee, Wis. Zeolite Y (Z-X materials) with a
Na as the exchange cation was obtained from Zeolyst International
Valley Forge, Pa. To obtain zeolite Y with other cations, an ion
exchange or solution impregnation technique was used on the Zeolyst
material. Pellets were made from powders using either a gamma
alumina binder or an attapulgite clay binder and 500.degree. C.
heat treatment.
[0060] The Z-Y with sodium was tested on a monolith honeycomb. The
others were in the form of a bead or pellet secured with a binder.
The single stage, conditions typically were: Temp. 180.degree. C.,
space velocity 12,000 hr.sup.-1 (4 L/min), O.sub.2 (8 vol. %),
CO.sub.2 (7 vol. %), H.sub.2O (7 vol. %), CO (0.0 vol. %),
hydrocarbon (C.sub.3H.sub.6 525 ppm, C.sub.3H.sub.8 75 ppm), and NO
(250 ppm). In addition, there was argon (9,000 ppm) and hydrogen
(130 ppm). For 2-stage experiments, the conditions were similar
with water content reduced to 2 vol. %, NO reduced to 150 ppm, and
hydrocarbon levels reduced to C.sub.3H.sub.6 400 ppm.
[0061] Results are shown in Table E2-1 and FIGS. 3-12. The Z-Y with
sodium was tested on a monolith honeycomb as well as in pellet and
bead form. The others were in the form of a bead or pellet secured
with a binder.
[0062] FIGS. 3-10 are for single stage operation with various
cations. Single stage operation achieves 36-88% conversion with
beta parameters ranging from 20-78 J/L. For Ag zeolite Y, which
converts 73% of NOx at 50 J/L, or 3.3 Watts, or an equivalent of
approximately 5% of the vehicle fuel would be used to reduce
NO.sub.x to N.sub.2.
[0063] For two-stage operation using Z-Y-Na, 29-81% conversions are
obtained for the beta parameter ranging from about 2 to 13 (fuel
equivalent range from about 0.7% to about 4%). In FIG. 9 the beta
parameter is 5 for a catalyst in the two stage configuration that
achieves 81% NO.sub.x destruction at 20J/L, or 0.35 Watts, or 0.002
J/gram NO.sub.x, or an equivalent of approximately 2% of the
vehicle fuel would be used to reduce NO.sub.x to N.sub.2 nitrogen
(a Ford Taurus was used to calculate fuel equivalent). For
comparison, current catalytic converter systems need to operate at
stoichiometric air/fuel ratios which results in a reduction of fuel
efficiencies of about 6%.
2TABLE E2-1 NO.sub.x conversion with Faujasite Free Temp % Nox
.beta. Reactor Material Aperture (.ANG.) Si:Al % H.sub.2O Cation
(.degree. C.) Reduced NO/NO.sub.x Type.sup.H Stages Z-Y 7.4 5 8 Na
100 36 --/46 PB 1 Z-Y 7.4 5 8 Na 180 67-77 51/57.sup.A PB 1 Z-Y 7.4
5 8 Na 300 40 --/37 PB 1 Z-Y 7.4 5 8 K 180 75 35/43 PB 1 Z-Y 7.4 5
8 Cs 180 80 32/40.sup.B PB 1 Z-Y 7.4 5 8 Ca 180 55 24/47 PB 1 Z-Y
7.4 5 8 Ga 180 50 31/36.sup.C PB 1 Z-Y 7.4 5 8 Co 180 76
24/20.sup.D PB 1 Z-Y 7.4 5 8 Mn 180 18 --/48 PB 1 Z-Y 7.4 5 8 Ag
180 88 23/34.sup.E PB 1 Z-Y 7.4 5 8 Ni 180 74 17/22.sup.F PB 1 Z-Y
7.4 5 8 Fe 180 37 67/40 PB 1 Z-Y 7.4 5 8 Ce 200 43 --/78 PB 1 Z-X
9-10 5.6 8 Na 180 36 33/20.sup.G PB 1 Z-Y 7.4 5 2 Na 180 65 4.5 TAR
2 Z-Y 7.4 5 2 Na 180 81 5/5 TAR 2 Z-Y 7.4 5 2 K 150 67 10/9 TAR 2
Z-Y 7.4 5 2 K 225 50 6/10 TAR 2 Z-Y 7.4 5 2 Ce 180 33 --/5.5 TAR 2
Z-X 9-10 5.6 2 Na 180/164! 70 13/9.6 TAR 2 Z-X 9-10 5.6 2 Na
180/224! 63 3.6/3.6 TAR 2 Z-X 9-10 5.6 2 Na 180/303! 29 2/1.6 TAR 2
Z-Y 9-10 5.6 8 Na 180 36 6/6 TAR 2 .times. 2 --No Data !Reactor
temperature different from the catalyst temperature .sup.AFIG. 3
.sup.BFIG. 5 .sup.CFIG. 6 .sup.DFIG. 7 .sup.EFIG. 8 .sup.FFIG. 9
.sup.GFIG. 10 .sup.HPB is packed bed and TAR is tube array
reactor.
[0064] For a double single stage operation with Z-Y-Na with a
conversion of 36%, FIG. 12 shows a beta parameter of about 6 which
are about the same as a two-stage configuration.
Example 3
[0065] An experiment was conducted to demonstrate the effect of
free aperture on the present invention. The catalyst was zeolite
LTA with a Si:Al ratio of 1:1 in pellet form. For the single stage,
conditions were Temp. 180.degree. C., space velocity 12,000
hr.sup.-1 (4 L/min), O.sub.2 (8 vol. %), CO.sub.2 (7 vol. %),
H.sub.2O (7 vol. %), CO (0.0 vol. %), hydrocarbon (C.sub.3H.sub.6
525 ppm, C.sub.3H.sub.8 75 ppm), and NO (250 ppm). In addition,
there was argon (9,000 ppm) and hydrogen (130 ppm). Results are
shown in Table E3-1.
3TABLE E3-1 NO.sub.x conversion with Various Free Aperture Free
Aperture Temp % Nox .beta. Cation (.ANG.) (.degree. C.) % H.sub.2O
Stages Reduced NO.sub.x K 3 180 8 1 4 10.sup.A Na 4 180 8 1 4
NA.sup.B Ca 5 180 2 1 50 30.sup.C K 3 226 2 2 7 -- Na 4 221 2 2 23
-- Ca 5 219 2 2 57 35 .sup.AFIG. 11 .sup.BFIG. 12 .sup.CFIG. 13
[0066] Results are further shown in FIGS. 13-15 for single stage
conversion showing both NO and NO.sub.x conversion. FIG. 13 is for
zeolite LTA with potassium (K), FIG. 14 is for zeolite LTA with
sodium (Na), and FIG. 15 is for zeolite LTA with calcium (Ca). For
conversion rates from 4-57%, the beta parameter ranges from 10 to
30 respectively.
Example 4
[0067] An experiment was conducted to demonstrate titanosilicate as
a catalyst for NO.sub.x conversion to N.sub.2. Catalyst beads were
synthesized from the titanosilicate ETS-10 powder (obtained from
Engelhard corporation, Iselin, N.J.) using an attalpulgite clay or
alumina binder. The free aperture of this catalyst was oval shaped
with opening of 4.9.ANG..times.7.6.ANG.. The titanosilicate
catalyst in a single-stage configuration with 8% water, at
180.degree. C. achieved 47% NO.sub.x conversion with a beta
parameter of 39 (FIG. 16).
[0068] While a preferred embodiment of the present invention has
been shown and described, it will be apparent to those skilled in
the art that many changes and modifications may be made without
departing from the invention in its broader aspects. The appended
claims are therefore intended to cover all such changes and
modifications as fall within the true spirit and scope of the
invention.
* * * * *