U.S. patent application number 10/301421 was filed with the patent office on 2004-05-27 for method for reducing the lightoff temperature of a catalyst.
Invention is credited to Carter, Robert N., Lyubovsky, Maxim.
Application Number | 20040098969 10/301421 |
Document ID | / |
Family ID | 32324538 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040098969 |
Kind Code |
A1 |
Lyubovsky, Maxim ; et
al. |
May 27, 2004 |
Method for reducing the lightoff temperature of a catalyst
Abstract
A method to reduce the lightoff temperature of a catalyst. In
the method, the working fluid (the fuel and oxidant to be reacted
in the presence of the catalyst) is supplemented with a starter
fluid at least until the lightoff temperature of the catalyst is
reached. Preferably, the amount of starter fuel added is
sufficiently small such that a reaction of the starter fuel and
oxidant in the presence of the catalyst does not have a sufficient
heat release to raise the temperature of the catalyst to the
lightoff temperature.
Inventors: |
Lyubovsky, Maxim; (North
Haven, CT) ; Carter, Robert N.; (Honeoye Falls,
NY) |
Correspondence
Address: |
McCormick, Paulding & Huber
City Place II
185 Asylum Street
Hartford
CT
06103-3402
US
|
Family ID: |
32324538 |
Appl. No.: |
10/301421 |
Filed: |
November 21, 2002 |
Current U.S.
Class: |
60/284 ; 60/286;
60/300 |
Current CPC
Class: |
F01N 3/2006 20130101;
F01N 2430/00 20130101; B01J 8/0214 20130101; F01N 2430/04 20130101;
B01J 8/0278 20130101; B01J 23/63 20130101; B01J 2208/00716
20130101; F01N 3/30 20130101 |
Class at
Publication: |
060/284 ;
060/300; 060/286 |
International
Class: |
F01N 003/00; F01N
003/10 |
Claims
What we claim is:
1. A method for reducing a baseline lightoff temperature of a
catalyst intended to support an exothermic reaction between
constituents of a working fluid, the method comprising the steps
of: supplementing the working fluid with a starter fuel prior to
associating the working fluid with the catalyst, the working fluid
in association with the starter fluid in the presence of the
catalyst defining a supplemented lightoff temperature less than the
baseline lightoff temperature.
2. The method of claim 1 wherein the working fluid comprises fuel
and oxidant in fuel rich proportions.
3. The method of claim 1 wherein the working fluid comprises fuel
and oxidant, and the catalyst in cooperation with the starter fuel
and oxidant is capable of generating a heat of reaction, the heat
of reaction being insufficient to raise the catalyst to the
baseline lightoff temperature.
4. The method of claim 1 including the further step of
discontinuing the starter fuel after the catalyst lights off.
5. The method of claim 1 wherein the working fluid comprises fuel
and oxidant and the fuel has a reactivity, and the starter fuel has
a reactivity, and the working fluid fuel reactivity is less than
the starter fuel reactivity.
Description
FIELD OF THE INVENTION
[0001] The present invention is generally directed to a method for
the operation of a catalytic reactor, and, more specifically, to a
method for reducing the lightoff temperature of a catalyst within
the catalytic reactor.
BACKGROUND OF THE INVENTION
[0002] Catalytic reactors are well known devices for supporting
many chemical reactions, such as exothermic oxidative reactions.
However, in order for a catalytic reactor to support an exothermic
oxidative reaction at a desired rate, a catalyst, which is in a
catalyst bed, in the reactor needs to reach threshold temperature,
commonly referred to as lightoff temperature. Upon reaching the
lightoff temperature, the chemical reaction proceeds at the desired
rate generally at a temperature substantially higher than the
lightoff temperature.
[0003] Several methods for raising the temperature of the catalyst
to the lightoff temperature are known in the art. Common methods of
preheating the catalyst to the lightoff temperature include;
passing an auxiliary fluid, such as air, that has been heated
through the catalytic bed; resistive heating of a substrate on
which the catalyst is positioned, e.g. passing an electrical
current through the substrate; or preheating with a homogenous
flame. The working fluid, e.g., fuel and oxidant in an oxidation
reactor, may also be pre-heated to raise the temperature of the
catalyst to the lightoff temperature. All these methods require
auxiliary systems such as heaters, burners, or electric power
sources adding to the cost and complexity of the system.
[0004] Efforts to lower the lightoff temperature of a catalyst to
minimize the rise in temperature required to lightoff the catalyst
have been concentrated on engineering various aspects of the
catalyst. One such engineering effort has focused on catalyst
structure. For example where the catalyst is positioned on a
substrate, high area washcoats have been used in conjunction with
the catalyst to increase catalyst surface area and dispersion.
While achieving reduced catalyst lightoff temperatures, this
technique tends to reduce the durability of the catalyst.
[0005] Other methods that do not lowered lightoff temperature can
be used to lightoff a catalyst. In one such method, a starter
fuel/oxidant mixture is used to raise the temperature of the
catalyst to the lightoff temperature. After the lightoff
temperature is achieved, the starter fuel/oxidant mixture is
gradually replaced with an operational fuel/oxidant mixture. This
substitution strategy requires storage of multiple fuel types,
storage of significant amounts of a starter fuel, and precise flow
control during the switching process to avoid catalyst or catalytic
reactor damage.
[0006] Based on the foregoing it is the general object of the
present invention to overcome or improve upon the problems and
drawbacks of the prior art.
SUMMARY OF THE INVENTION
[0007] A catalyst supports an exothermic reaction between
constituents of a working fluid. Based on the working fluid, the
catalyst has a baseline lightoff temperature it must achieve before
the exothermic reaction proceeds at a desired rate. In the method
of the present invention, the working fluid is supplemented with a
starter fuel prior to associating the working fluid with the
catalyst. The working fluid in association with the starter fluid
in the presence of the catalyst defines a supplemented lightoff
temperature that is less than the baseline lightoff temperature. As
a result, the temperature rise required to lightoff the catalyst is
reduced. As an option, the start fuel may be discontinued after the
supplemented lightoff temperature is reached.
[0008] The precise starter fuel is application dependent. For
example, each working fluid, which has fuel and oxidant components,
interacts differently with a catalyst, or catalysts, within a
catalytic reactor. As a result, the selection of a starter fuel
depends on the interaction characteristics of the working fluid,
starter fuel and the catalyst(s).
[0009] The amount of starter fuel added to the working fluid need
not be significant. Preferably, the amount added is not sufficient
in and of itself to interact with the catalyst(s) within the
catalytic reactor to raise the catalyst(s) to a temperature at or
above the lightoff temperature. It, however, is preferred that the
starter fuel be more reactive than the fuel, or fuels, within the
working fluid as to the catalyst, or catalysts, within the
catalytic reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1. is a graph illustrating the relationship between
lightoff temperature and operational temperature of a catalyst.
[0011] FIG. 2 depicts a cross-sectional view of a catalytic reactor
in which the method disclosed herein might be employed.
DETAILED DESCRIPTION OF THE INVENTION
[0012] In exothermic oxidative reactors, a catalyst therein lights
off when the catalyst temperature rises dramatically from an
initial catalyst temperature to an operational temperature. FIG. 1
shows this relationship. The auxiliary heating profile, denoted by
reference number 10, shows the temperature of the catalyst as a
function of the heat applied thereto. As depicted in FIG. 1, the
catalyst is heated from, for example, ambient conditions to a
lightoff temperature, say T.sub.1. Upon reaching the lightoff
temperature T.sub.1, the catalyst temperature jumps nearly
instantaneously from the lightoff temperature to a considerably
higher operational temperature designated A.
[0013] In FIG. 1, it has been assumed that the catalyst temperature
results directly from the auxiliary heat applied to the catalyst.
This assumption is based on the further assumption that if the
working fluid is flowing over the catalyst before the catalyst is
at the lightoff temperature, the exothermic reactions occurring in
the presence of the catalyst are minimal. Thus for all practical
purposes, these reactions do not significantly increase the
temperature of the catalyst. In the event the exothermic reactions
are more than minimal, the catalyst temperature before lightoff
will be equal to the sum of the catalyst temperature resulting form
the auxiliary heat applied thereto and the temperature rise
resulting from the exothermic reactions. Therefore, the auxiliary
heating profile 10 will have to be adjusted accordingly.
[0014] In the present method, the working fluid is supplemented
with a starter fluid. As a result, the lightoff temperature of the
catalyst is reduced. Referring to FIG. 1, the baseline lightoff
temperature, i.e., the catalyst temperature that is required to
lightoff the catalyst if only the working fluid is considered,
denoted T.sub.1 is reduced to a supplemented lightoff temperature
denoted T.sub.2. As a result of the addition of the starter fluid,
the auxiliary heating required for the catalyst is similarly
reduced.
[0015] As the operational temperature of the catalyst is a function
of lightoff temperature of the catalyst, the operational
temperature of the catalyst is reduced from point A to point B when
the lightoff temperature is reduced from the baseline lightoff
temperature T.sub.1 to the supplemented lightoff temperature
T.sub.2. After lightoff, the temperature increase of the catalyst
above the lightoff temperature results from the exothermic
reactions between the components of the working fluid. Thus, the
operational temperature of the catalyst after lightoff is
approximately equal to the sum of lightoff temperature and the
temperature rise due to the exothermic reactions. Thus, a reduction
in catalyst lightoff temperature equates to a similar reduction in
catalyst operational temperature. As a result, points A and B are
on a line designated 12 that is generally parallel to the auxiliary
heating profile 10.
[0016] The amount of starter fuel required is minimal as compared
to the amount of fuel in the working fluid. Preferably, the heat
release of the starter fuel when reacted with oxidant in the
working fluid in the presence of the catalyst is sufficiently low
that it is incapable in and of itself of raising the initial
catalyst temperature of the catalyst to the baseline lightoff
temperature T.sub.1. While the method reduces the lightoff
temperature, it is still anticipated that some auxiliary heating of
the catalyst may still be required. This auxiliary heating could be
by conventional methods known to those skilled in the art.
[0017] The method of the present invention is shown in conjunction
with a fixed geometric catalytic reactor suitable for performing
the method. As shown in FIG. 2, the catalytic reactor, generally
denoted by the reference number 50, is comprised of housing 52. The
housing 52 defines a chamber 54, an entrance 56, and an exit 58. A
plurality of conduits 60, each having a first opening 62, a second
opening 64, and an exterior surface 66, penetrate the housing 52.
The penetration is such that a portion of each conduit 60 is
positioned within the chamber 54 with the first opening 62 outside
the chamber 54 and the second opening 64 inside the chamber. A
catalyst 68 is positioned on a portion of an exterior surface 66 of
at least one conduit 60 within the chamber 54 between the first
opening 62 and the second opening 64.
[0018] In this fixed geometry catalytic reactor, a mixture, working
fluid, with or without starter fuel, 70 enters through the entrance
56 and flows toward the exit 58. Additional air 72 flows into the
entrances 62 of the conduits 60 passing through the conduits and
exiting through the conduit exits 64. The mixture 70 contacts the
additional oxidant 72 as the additional oxidant exits into the
chamber 54. Mixing of the mixture 70 and additional oxidant 72
begins almost immediately.
EXAMPLE 1
[0019] The method was employed with a catalytic reactor similar to
that depicted in FIG. 2 using methane and oxygen, as a constituent
of air, as the working fluid. The catalytic reactor had a platinum
catalyst supported on a La-stabilized .gamma.-alumina washcoat. The
average flow rate of the working fluid with starter fluid, if
present, was about 50 ft/sec. The working fluid with starter fluid,
if present, had an initial temperature of about 200.degree. C.
Auxiliary heating of the catalyst was accomplished by preheating
the working fluid. The tests were conducted at a pressure of 1 atm.
The results are as follows:
[0020] Starter Fuel--Propane (LPG)
[0021] Fuel/Air Equivalence Ratio* --3.0 (working fluid plus
starter fuel)
[0022] *the actual fuel/oxidant ratio divided by the stoichiometric
fuel/oxidant ratio based on a complete combustion reaction.
1 vol. % to fuel within 0 2.1 4.4 10 40 working fluid Lightoff
Temp. Before - 386 306 287 <200 <200 Degrees C. After -
393
[0023] Starter Fuel--Hydrogen
[0024] Fuel/Air Equivalence Ratio--3.0 (working fluid only)
2 vol. % to fuel 0 3.8 4.6 5.4 6.2 6.9 7.7 within working fluid
Lightoff Temp. Before - 406 374 345 327 303 276 <200 Degrees C.
After -- 396
[0025] Starter Fuel--Hydrogen Sulfide
[0026] Fuel/Air Equivalence Ratio --3.0 (working fluid only)
3 vol. % to fuel within working fluid 0 0.001 0.003 0.01 Lightoff
Temp. Before - 412 344 310 318 Degrees C. After - 383
[0027] The before and after temperatures provided under the
condition of zero starter fuel indicate the minor hysteresis
effects associated with the operation of catalytic reactors. Based
on the above data, it is clear that the lightoff temperature for
the catalyst was reduced in all cases with a minor addition of a
starter fuel to the working fluid.
EXAMPLE 2
[0028] Same conditions as Example 1, except a rhodium catalyst was
used instead of a platinum catalyst. The results are as
follows:
[0029] Starter Fuel--Propane (LPG)
[0030] Fuel/Air Equivalence Ratio--3.0 (working fluid plus starter
fuel)
4 vol. % to fuel within working fluid 0 4.4 10 40 Lightoff Temp.
Before - 415 408 396 387 Degrees C. After - 420
[0031] Starter Fuel--Hydrogen
[0032] Fuel/Air Equivalence Ratio --3.0 (working fluid only)
5 vol. % to fuel within 0 3.8 11.1 15.4 18.2 working fluid Lightoff
Temp. Before - 413 394 336 <200 <200 Degrees C. After -
391
[0033] Starter Fuel--Hydrogen Sulfide
[0034] Fuel/Air Equivalence Ratio--3.0 (working fluid only)
6 vol. % to fuel within working fluid 0 0.001 0.003 0.01 Lightoff
Temp. Before - 402 430 455 473 Degrees C. After - 410
[0035] As shown in the data above, H.sub.2 reduced the lightoff
temperature over a rhodium catalyst, but propane did not. Hydrogen
sulfide, on the other hand, increased the lightoff temperature.
This illustrates that the starter fuel is dependent upon the
catalyst.
[0036] Although the present invention has been described in
considerable detail with reference to certain preferred versions
thereof, other versions are possible. Therefore, the spirit and
scope of the invention should not be limited to the description of
the preferred versions contained herein.
* * * * *