Emissions control system and method

An exhaust gas emissions control system lowers cold-start hydrocarbon emissions by using heat exchange structure to lower the temperature of exhaust gas prior to the exhaust gas passing through a hydrocarbon adsorbent and using the extracted heat to heat a catalytic converter to its light-off temperature. In some embodiments, multi-component hydrocarbon adsorbers effective under different operating conditions further reduce cold-start hydrocarbon emissions.

FIELD OF THE INVENTION 
This invention relates to a vehicular emissions control system which 
incorporates a catalytic converter and an adsorber to control hydrocarbon 
emissions. More particularly, the invention relates to control system 
designs incorporating a heat exchanger to improve the combined performance 
of a hydrocarbon adsorber and a catalytic converter. 
BACKGROUND OF THE INVENTION 
Modern vehicular emissions control systems typically employ a catalytic 
converter to reduce hydrocarbon emissions. The catalytic converter 
contains a catalyst which converts unburned exhaust hydrocarbons to less 
environmentally detrimental exhaust gases. 
Unfortunately, modern catalytic converters only operate after reaching 
temperatures in excess of about 300 degrees Centigrade. For this reason, a 
substantial portion of hydrocarbon emissions occur during the first few 
minutes of cold-start engine operation before the converter reaches its 
minimum effective operating temperature, otherwise known as the converter 
"light-off" temperature. Because the first few minutes of operation is an 
integral part of automotive emissions tests, and because over 60% of the 
measured hydrocarbons are emitted during the cold-start period of the 
test, reducing cold-start hydrocarbon emissions is of critical importance. 
Recent tightening of emissions requirements to limit emissions of certain 
hydrocarbon compounds such as benzene has further underscored the need for 
reduced cold-start hydrocarbon emissions. 
To reduce cold-start hydrocarbon emissions, emissions control designers 
have proposed routing exhaust gases through hydrocarbon adsorbers such as 
charcoal for a short period of time following an engine cold-start. For 
example, Templin, U.S. Pat. No. 3,645,098 teaches the use of an exhaust 
gas valve downstream of a catalytic converter for directing unconverted 
cold-start hydrocarbons onto a charcoal adsorber. As adsorber temperature 
increases, hydrocarbons initially adsorbed during the cold-start period 
are released from the adsorber and recirculated into the engine or exhaust 
manifold. Once the catalytic converter reaches its light-off temperature, 
the exhaust gas valve routes exhaust gas directly from the catalytic 
converter to the tailpipe. 
While Templin's system might reduce hydrocarbon emissions below the levels 
emitted from similar systems lacking an adsorber, his system is not 
preferred because the system requires an exhaust gas valve to operate 
reliably under the severe chemical and temperature conditions present in 
the exhaust gas stream and because the physical adsorbance efficiency of 
his absorber is likely to decrease significantly with increasing exhaust 
gas temperature. 
To overcome the disadvantages of systems like Templin's, other designers 
have turned to multi-adsorber systems. In these systems, exhaust gas flow 
is directed first to a low temperature adsorber chamber. As system 
temperature increases, flow is directed around the low temperature 
adsorber chamber to a second adsorber chamber containing an adsorber 
useful in a temperature range above that of the low temperature adsorber 
and below the catalytic converter light-off temperature. One example of 
such a system is disclosed in Minami, U.S. Pat. No. 4,985,210. 
Minami discloses a system in which cold-start exhaust gas initially flows 
serially through a charcoal adsorber chamber, a Y-zeolite or mordenite 
adsorber chamber and a catalytic converter. When exhaust gas temperature 
reaches a predetermined level, an exhaust gas valve operates to route 
exhaust gas around the charcoal adsorber and directly into the second 
adsorption chamber containing the mordenite or zeolite. Because the second 
adsorber is believed to provide some additional hydrocarbon hold-up at 
temperatures exceeding the upper useful temperature of the charcoal 
adsorber, emissions may be reduced from the levels emitted from systems 
like Templin's. Unfortunately, like Templin's, Minami's system also 
employs an exhaust gas valve which must function reliably under the harsh 
physical and chemical conditions found in exhaust gas streams. 
Additionally, because exhaust gas passes directly into Minami's adsorbers, 
heat is lost in the adsorbers, thereby delaying catalytic converter 
light-off. 
To avoid the reliability problems inherent in valved emissions systems, 
other designers have turned to non-valved designs combining an adsorber 
and a catalytic converter in a single unit. One such example is disclosed 
in U.S. Pat. No. 3,067,002 to Reid. Reid discloses an exhaust gas 
emissions control system in which a plurality of catalyst-containing 
channels are interspersed with a plurality of manifolded open ducts within 
a housing. As exhaust gas passes through the open ducts, the gas 
indirectly heats the catalyst contained in the catalyst beds prior to the 
exhaust gas entering the beds. Reid states that an adsorbent such as a 
natural or synthetic zeolite can be incorporated into a portion of each 
catalyst bed. 
While Reid's design might reduce the time before catalytic converter 
light-off, the design appears to preclude the use of heat-damageable 
adsorbers such as charcoal because exhaust gas must continually pass 
through the adsorber at all times while the engine is running. More 
significantly, Reid's physical arrangement of interspersed heat transfer 
ducts, adsorbent and catalyst within a single envelope appears to limit 
the potential temperature difference between adsorber and catalyst, 
thereby limiting the potential effectiveness of his system. 
What is needed is a mechanically simple, valveless exhaust gas emissions 
control system that employs one or more adsorbents to reduce hydrocarbon 
emissions over at least a substantial portion of the time period between 
an engine cold-start and catalytic converter light-off. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide an improved emissions control 
system for reducing cold-start hydrocarbon emissions. 
It is another object of the invention to provide a valveless exhaust gas 
emissions control system offering improved cold-start emissions control. 
It is yet another object of the invention to provide an emissions control 
system in which heat is removed from the exhaust gas and transferred to a 
catalytic converter prior to the exhaust gas passing through a hydrocarbon 
adsorber. 
It is still another object of the invention to provide an improved 
hydrocarbon adsorbent for use in exhaust gas emissions control systems. 
Other objects of the invention will become apparent as disclosed herein. 
The foregoing objects can be accomplished by providing an emissions control 
system for treating engine exhaust gas comprising adsorber means for 
trapping hydrocarbons present in the exhaust gas following a cold engine 
start, catalytic converter means operatively connected to the adsorber 
means downstream of the adsorber means for catalytically reacting 
hydrocarbons present in the exhaust gas and heat exchange means 
operatively connected to the adsorber means upstream of the adsorber means 
for transferring exhaust gas heat from the exhaust gas to the catalytic 
converter means, thereby warming the catalytic converter and lowering the 
exhaust gas temperature prior to the exhaust gas entering the adsorber 
means. 
The invention employs heat exchange techniques to improve the combined 
performance of hydrocarbon-adsorbing and catalytic conversion emissions 
control systems components. In each embodiment, heat transferred from the 
exhaust gas raises the temperature of the system's catalytic conversion 
component before the cooled exhaust gas contacts the system's 
hydrocarbon-adsorbing component. 
Removing heat from the exhaust gas prior to passing the gas through the 
system's hydrocarbon adsorber increases hydrocarbon hold-up time because 
the adsorber is more effective at lower temperatures. Furthermore, because 
the removed heat is used to warm the catalytic converter, the catalytic 
converter lights off sooner than it would if the exhaust gas heat was not 
transferred to it. These effects combine to substantially reduce 
hydrocarbon emissions during the time period immediately following a cold 
engine start. 
In each case, and in contrast to systems such as those disclosed by Reid, 
the temperature differential between the hydrocarbon-adsorbing component 
and the catalytic conversion component is maximized by physically 
separating the adsorbing component from the converting component, thereby 
synergistically enhancing the performance of both components. In some 
embodiments, adsorbers effective under different emissions system 
operating conditions or temperature ranges are combined to provide 
improved adsorber performance to further minimize cold-start hydrocarbon 
emissions.

DETAILED DESCRIPTION OF THE INVENTION 
Each of the emissions control systems discussed below uses heat transfer 
techniques in conjunction with a catalytic converter component and a 
hydrocarbon-adsorbing component to lower cold-start hydrocarbon emissions. 
While the adsorbents, catalysts and heat exchanger designs discussed below 
are exemplary of those useful in the invention, it will be apparent to 
those skilled in the art that other configurations employing different 
catalysts, heat exchange structures or hydrocarbon adsorbers can be 
constructed without departing from the scope of the invention. 
FIG. 1 is a simplified cross-sectional view of one embodiment of an 
emissions control system 20 in accordance with the present invention. 
System 20 includes a catalytic converter 22 filled with a conventional 
automotive exhaust gas catalyst 24. Catalyst 24 typically will be an 
inorganic oxide support impregnated with a combination of noble metals 
such as platinum, palladium and rhodium. Such a combination of noble 
metals is useful for catalytically oxidizing exhaust gas hydrocarbons and 
carbon monoxide and for reducing the amount of harmful oxides of nitrogen 
(NO.sub.x) released to the environment. While catalyst 24 is illustrated 
in the common pellet form, the physical form of catalyst 24 is not 
critical. 
Converter 22 preferably includes a plurality of open-ended heat exchange 
ducts 26 running through converter 22 between and in contact with pellets 
24. A converter jacket 28 surrounds converter 22 and includes an exhaust 
gas inlet tube 30 for admitting engine exhaust into jacket 28 and a jacket 
internal baffle 31 for preventing entering exhaust gas from passing around 
rather than through ducts 26. 
An exhaust gas outlet tube 32 is connected between jacket 28 and an inlet 
end 34 of an adsorber chamber 36 filled with a hydrocarbon adsorber 38 as 
discussed herein. An exhaust gas recirculation pipe 40 connects an outlet 
end 42 of adsorber chamber 36 to an inlet end 44 of catalytic converter 
22. An exhaust gas discharge pipe 46 provides an outlet for gases 
discharged from a discharge end 48 of catalytic converter 22. 
During operation, exhaust gas enters jacket 28 through inlet tube 30, loses 
heat to converter 22, and exits jacket 28 through outlet tube 32. The heat 
given up by the exhaust gas helps to bring converter 22 to its light-off 
temperature and causes exhaust gas exiting outlet tube 32 to be at a lower 
temperature than would be the case in the absence of the heat transfer to 
converter 22. Cooled exhaust gas from outlet tube 32 enters adsorber 38, 
causing uncombusted hydrocarbons to remain trapped on adsorbent 38 until 
adsorbent 38's temperature rises to a temperature sufficient to desorb the 
hydrocarbons from adsorbent 38. Until the desorption temperature is 
reached, uncombusted hydrocarbons are collected and remain trapped within 
chamber 36 while the hydrocarbon-depleted exhaust gas is discharged 
through pipe 40, converter 22 and pipe 46. 
After the desorption temperature has been reached, hydrocarbons are 
desorbed from adsorbent 38 and are catalytically oxidized in converter 22 
if converter 22 has reached its light-off temperature. Because exhaust gas 
is cooled prior to entering chamber 36, adsorbent 38 requires a longer 
time to reach its desorption temperature. If desired, exhaust gas entering 
outlet pipe 32 and adsorbent 38 can be cooled further by providing 
heat-sink structure such as optional fins 50 on the outer surfaces of pipe 
32 and/or chamber 38. Furthermore, because the heat removed from the 
exhaust gas heats converter 22, converter 22 reaches its light-off 
temperature quickly. The foregoing effects combine to significantly reduce 
hydrocarbon emissions during the cold-start period. Finally, because 
chamber 36 is physically separate from converter 22, the temperature 
differential between converter 22 and adsorbent 38 is maximized, further 
enhancing the effectiveness of system 20. 
FIG. 2 schematically illustrates another embodiment of an emissions system 
52 in accordance with the present invention. In system 52, exhaust gas 
passes through tube bundles (not visible) in stand alone air-to-air heat 
exchanger 54 prior to flowing into an adsorber 56. Heat given up from the 
exhaust gas to heat exchanger 54 reheats previously cooled gas exiting 
adsorber 56 which passes over the tube bundles in heat exchanger 54 on its 
way to catalytic converter 58. The physical separation of heat exchanger 
54, adsorber 56 and converter 58 helps to maintain adsorber 56 below its 
desorption temperature while causing converter 58 to heat up and light-off 
at the earliest possible time. 
The embodiment shown in FIG. 2 can reduce exhaust gas temperatures by up to 
about 200 degrees Centigrade under typical exhaust gas conditions. To 
obtain this result, heat exchanger 54 should have a tube area of about 9 
square feet. It is preferred that exchanger 54 be constructed from a 
corrosion resistant material such as 316 grade stainless steel. Other heat 
exchange devices such as plate-type exchangers also are suitable for use 
as exchanger 54. Useful data for constructing suitable heat exchangers can 
be found in standard engineering treatises such as the 5th Edition of 
Perry and Chilton's Chemical Engineer's Handbook which are known to those 
skilled in the art of heat exchanger design. 
FIG. 3 schematically illustrates an emissions system 60 somewhat similar in 
design to that shown in FIG. 2. System 60 employs a catalytic converter 62 
having an integral heat exchange structure incorporated therein. Exhaust 
gas flows through heat exchange channels 64 in converter 62, through an 
adsorber 66, and back through manifolded catalytically-active channels 68. 
The perpendicular flow of exhaust gas through channels 64 heats 
catalytically-active channels 68 and lowers the exhaust gas temperature 
before the exhaust gas reaches adsorber 66. 
A suitable structure for catalytic converter 62 can be produced by using 
monolithic ceramic catalyst support technology similar to that discussed 
in conjunction with FIGS. 7-9. FIG. 4 illustrates a simple configuration 
of such a device. A manifolded monolithic catalytically-active heat 
exchanger 70 includes alternating, perpendicular rows of heat exchange 
ducts 72 and catalytically-active ducts 74. Exhaust gas enters one end of 
heat exchange ducts 72 through heat exchanger inlet manifold 76, exits the 
opposite end of ducts 72, is collected by heat exchanger outlet manifold 
78 and passes on to adsorber 66 (see FIG. 3). Exhaust gas returning from 
adsorber 66 passes through a catalytic converter inlet manifold 80, 
through catalytically-active ducts 74, and is collected and exhausted from 
exchanger 70 through catalytic converter outlet manifold 82. 
Exchanger 70 can be formed by cementing together alternating, perpendicular 
rows of catalytically-active and non-active extruded ceramic ducts as 
discussed below. Alternatively, similarly shaped metallic or 
ceramic-coated metallic structures may be produced and joined together by 
cementing or welding as appropriate. Catalytically-active rows 74 can be 
produced by washcoating catalyst onto the inner surface of each active 
duct. If desired, ducts 72 and 74 can run parallel, with the flows through 
channels 72 and 74 running countercurrent to one another. In this case, 
the cementing together of alternating rows of catalytically-active and 
non-active channels can be avoided by washcoating a single extruded 
structure having every other row of channels plugged at each end prior to 
the washcoating process. Additional constructional details for monolithic, 
catalytically-active heat exchangers are discussed below in conjunction 
with FIGS. 7-9. As used hereafter, the term "monolith" means a unitary 
structure having a plurality of generally symmetric ducts useful for 
carrying or containing catalyst or hydrocarbon-adsorbing materials. 
FIGS. 5 and 6 illustrate another emissions systems configuration useful for 
practicing the invention. Turning first to FIG. 5, an emissions control 
system 84 includes a catalytic converter 86 concentrically located within 
a system housing 88. Exhaust gas enters converter 86 through an inlet tube 
90 at a front end 92 of housing 88, flows through a plurality of 
manifolded heat exchange ducts 94 within converter 88 and is discharged 
into a rear end 96 of housing 88. Exhaust gas then flows toward front end 
92 of housing 88 through an adsorbent 98, reverses flow and flows through 
a catalytically-active region 100 of converter 88 and out an exhaust pipe 
102. 
FIG. 6 is a cross section of system 84 taken along line 6--6 of FIG. 5. As 
can be seen be comparing FIGS. 5 and 6, manifolded heat exchange ducts 94 
run longitudinally through converter 86 within catalytically-active region 
100. Gas passing through ducts 94 heats catalyst 100, thereby lowering the 
exhaust gas temperature before the gas flows through adsorbent 98. 
Catalysts and adsorbents suitable for use in the embodiments discussed in 
conjunction with FIGS. 1-6 generally include pelletized, extruded or 
supported forms well-known in the art, although these designs also are 
well-suited to the application of ceramic or metallic monolithic supports 
bearing washcoated or homogeneously-mixed catalyst or adsorber as 
discussed below. Tubing and metallic components should be constructed from 
a corrosion resistant metal and may include additional heat-sink structure 
such as disclosed in conjunction with FIG. 1 to further lower the 
temperature of exhaust gas entering the hydrocarbon-adsorbing portion of 
the system. 
FIGS. 7-9 illustrate still another embodiment of the invention. FIG. 7 is 
an exploded perspective view of a monolithic catalytically-active heat 
exchanger emissions control system 1 1 4 which incorporates an adsorbent 
for reducing cold-start hydrocarbon emissions. Principal components of 
system 114 include an inlet manifold 116, an outlet manifold 118, a 
monolithic catalytically-active heat exchanger 120 comprising a first 
monolith portion 122 having a plurality of catalyst-coated heat exchange 
channels 124, a second monolith portion 126 having a plurality of 
adsorber-coated channels 128, a system housing 130 for enclosing monolith 
120, and a bottom plate 132 for reversing exhaust gas flow as explained 
herein. 
During operation of system 114, exhaust gas enters inlet manifold 116 
through an exhaust gas inlet tube 134 and passes through a plurality of 
outlet manifold apertures 136 and into heat exchange channels 124. As will 
be discussed in detail in conjunction with FIGS. 8 and 9, apertures 136 
allow the exhaust gas to enter every other row of channels 124. Gas passes 
through channels 124, losing heat to the channel walls, and passes through 
adsorber-coated channels 128 toward bottom plate 132. Plate 132 includes a 
surface 138 located away from the lower ends of channels 128. Surface 138 
allows gas to escape from the alternate rows of channels 128 and enter the 
adjacent rows of channels 128'. The exhaust gas passes upwardly through 
channels 124' which are covered over at their upper ends by outlet 
manifold 118. Gas exiting the upper ends of channels 124' is collected by 
outlet manifold 118 and discharged through an outlet manifold discharge 
tube 140. 
First monolithic portion 122 functions as a combination heat exchanger and 
catalytic converter in a manner similar to catalytically-active heat 
exchanger 70 shown in FIG. 4. During the cold-start period, 
catalytically-active channels 124 and 124' are heated as exhaust gas 
passes through them. As before, the heat lost to channels 124 and 124' 
causes catalyst contained within these channels to reach its light-off 
temperature rapidly and lowers the temperature of the exhaust gas before 
the gas reaches adsorber-coated channels 128 and 128' in second monolith 
portion 126. As system 114 heats up, hydrocarbons initially adsorbed onto 
channels 128 and 128' are desorbed from these channels and pass through 
catalytically-active channels 124'. Preferably, both channels 124 and 124' 
contain catalyst, thereby maximizing the amount of catalytic surface area 
available for a given volume of monolith. 
Because monolith 120 includes physically separated catalytically-active and 
hydrocarbon-adsorbing zones, a useful temperature differential between 
catalyst and adsorbent is more easily attained than in a converter having 
alternating catalytically-active and hydrocarbon-adsorbing regions. 
Additional mechanical details of outlet manifold 118 and bottom plate 132 
are best explained in conjunction with FIGS. 8 and 9. Referring first to 
FIG. 8, exhaust gas entering inlet manifold 116 enters alternate channels 
of first monolith portion 122 by passing through apertures 136 in outlet 
manifold 118. The exhaust gas then passes downwardly first through 
channels 124 and then through adsorber-coated channels 128 in second 
monolith portion 126. As the exhaust gas exits the lower ends of channels 
128, the gas strikes plate 132 and then travels upwardly first through 
channels 128' and then through channels 124'. As gas exits the upper ends 
of channels 124', it enters a plurality of open-bottomed horizontally 
directed channels 142 which route exhaust gas into outlet manifold 
discharge tube 140 (see FIGS. 7 and 9). As can be seen in FIG. 8, the 
closed tops of channels 142 provide the structure that blocks gas flow 
from inlet manifold 116 into channels 124'. 
Turning now to FIG. 9, upwardly moving gas exiting channels 124' is 
collected in open-bottomed duct 142 and directed out discharge tube 140. 
It is preferred that the cross sectional area of duct 142 increase toward 
discharge tube 140 to provide for a fairly constant gas velocity as the 
cumulative volume of gas discharged from channels 124' increases in that 
direction. 
The number and relative size of the monolith channels illustrated in FIGS. 
7-9 has been simplified to explain the operation of the invention. An 
operative number of channels for system 114 is about up 60 by 60 channels 
with a channel density of about 100 channels per square inch. Channel wall 
thickness should be about 0.017 inches while the distance between channel 
walls should be about 0.083 inches. The length of monolith portions 122 
and 126 can be about 8 and 4 inches, respectively, with the catalyst and 
adsorber loadings discussed below. 
The width of outlet channel apertures 136 generally should correspond to 
the width of channels 124 but can be narrowed to provide a 0.05 thick 
aperture wall. The thicker wall lends mechanical strength to manifold 118 
and makes aligning manifold 118 with monolith 120 less critical. The width 
of horizontal ducts 142 can also be about 0.05 inches and should taper 
upwards to a height of about 0.25 inches where ducts 142 empty into 
discharge tube 140. 
Metallic components of system 114 such as manifolds 116 and 118, housing 
130 and bottom plate 132 preferably are constructed from a corrosion 
resistant material such as 316 stainless steel. Tubing such as exhaust gas 
inlet tube 134 and that forming a part of outlet manifold discharge tube 
140 should be formed from welded stainless steel tubing. Welds used to 
fabricate components such as discharge tube 140 should be as small as 
possible to minimize the effects of warping. 
System 114 is assembled by first fastening monolith 120 within housing 130 
to form a single unit. Outlet manifold 118 is then carefully placed over 
the exposed upper end of monolith 120 so that apertures 136 are in 
registry with channels 124. If desired, alignment grooves may be cut in or 
alignment stops fastened to the underside of manifold 118 to ensure that 
manifold 118 remains in registry with channels 124 during assembly. 
Sighting ports in inlet manifold 116 are also useful for this purpose. 
Bottom plate 132 and inlet manifold 118 are attached over opposite ends of 
the monolithic unit and manifold 118 by screws 144, spring washers 146 and 
nuts 148 as shown in FIGS. 7 and 8. Screws 144, washers 146 and nuts 148 
preferably are formed from a corrosion resistant stainless steel. Spring 
washers 146 should provide for about 0.05 inches of thermal expansion at 
each end of screws 144 to prevent damage to monolith 120 that would 
otherwise be caused by thermal expansion of monolith 120 under operating 
conditions. Mechanical devices other than springs that provide for the 
appropriate degree of thermal expansion can also be used. 
Hydrocarbon adsorbents suitable for depositing on monolith 120 as well as 
in other embodiments of the invention include Union Carbide ultrastable Y 
sieves such as LZY-72 and LZY-82 and siliceous adsorbents such as 
silicalite. Most adsorbers containing microporous structures less than 
about 20 Angstroms in diameter such as natural and synthetic zeolites are 
also suitable. While activated carbon is an excellent adsorber, its use in 
this application is not preferred as it can be damaged by sustained 
exposure to high temperature exhaust gas. For this reason, activated 
carbon should not be used except where the exhaust gas constituents will 
not oxidize the carbon significantly and where adsorber operating 
temperature is sufficiently low to ensure continued operability of a 
carbon adsorber. 
A hydrocarbon-adsorbing material useful in system 114 is a mixed zeolytic 
adsorber deposited on an extruded cordierite monolith at a concentration 
of about 40 weight percent of the support weight. This type of adsorber 
can be commercially prepared in accordance with the U.S. patents 
incorporated by reference herein. Alternatively, a similarly-sized 
adsorber module could be used in place of the cordierite monolith. In this 
case, an equivalent amount of adsorber in the form of extrudates or 
monolithic elements can be packed in the module. In this packed 
embodiment, exhaust gas flows through the packed adsorber while reversing 
direction toward ducts 124'. 
The effectiveness of adsorbents used in system 114, as well as in systems 
like those previously described, can be enhanced by combining two or more 
adsorbers which are effective in different temperature ranges or for 
different exhaust gas mixtures. The suitability of various adsorbents for 
combination can be determined in the following manner. 
EXAMPLE 
An adsorbent test reactor was constructed from a 2 inch length of 3/8 inch 
inner diameter glass tubing. The frontal cross section of a 220 square 
centimeter ceramic monolith such as those discussed in conjunction with 
FIGS. 7-9 was ratioed to the 0.7 square centimeter cross sectional area of 
the test reactor to determine that a test flow of about 3 liters per 
minute could be used to simulate the typical 25 cubic foot per minute flow 
from an automobile exhaust. The typical 3 gram per minute hydrocarbon 
emission rate of an average engine was correspondingly scaled to determine 
that the simulated hydrocarbon emission rate should be about 0.01 grams 
per minute. 
Approximately two grams of adsorbent were placed in the test reactor. In 
the cases of the LZY-72 and -82 adsorbents, the adsorbents were formed 
onto monolithic ceramic test pieces by the Corning Co. of Corning, N.Y. 
The USY sieve catalyst tested was a highly dealuminated USY sieve 
extrudate made from Grade 760 adsorbent obtained from the Conteka Co. and 
which included a 20 percent alumina binder. Adsorbent grade silicalite was 
obtained from the Union Carbide Co. and tested both as a 42% silicalite 
washcoat on a cordierite monolith and as an extrudate. Activated carbon in 
a granular form was obtained from the Cenco Co. 
A water-saturated nitrogen flow of about 3 liters per minute was 
established through the test reactor. Adsorbent performance was then 
tested by injecting a toluene adsorbate at a constant partial pressure and 
measuring the percent toluene breakthrough at the bed outlet with a flame 
ionization detector. Relative adsorber performance was evaluated by 
comparing the times for 25, 50 and 100 percent toluene breakthrough at 25 
degrees Centigrade. These experiments were repeated at 100, 150, 200 and 
250 degrees Centigrade. The results of the experiments are summarized in 
Table 1. PG,14 
TABLE I 
______________________________________ 
Tem- 
per- Time Required to Reach 
ature 
% Breakthrough (mins.) 
Adsorbent 
Form .degree.C. 
.sup.t 25 
.sup.t 50 
.sup.t 100 
______________________________________ 
LZY-72 Monolith 25 1.0 1.4 1.6 
LZY-82 Monolith.sup.1 
25 0.3 0.8 1.5 
LZY-82 Monolith.sup.2 
25 0.3 0.8 1.3 
USY Sieve 
Extrudate 25 5.2 10.5 17.5 
Silicalite 
Extrudate 25 2.7 5.5 11.4 
Silicalite 
Monolith 25 0.2 0.7 2.7 
Carbon Granules 25 &gt;60 &gt;60 &gt;60 
LZY-72 Monolith 100 13.0 17.7 26.0 
LZY-82 Monolith.sup.1 
100 9.2 14.0 19.8 
LZY-82 Monolith.sup.2 
100 10.1 18.9 27.4 
USY Sieve 
Extrudate 100 1.2 3.5 7.5 
Silicalite 
Extrudate 100 1.1 2.5 6.5 
Silicalite 
Monolith 100 0.8 2.8 4.3 
Carbon Granules 100 39.9 48.5 55.6 
LZY-72 Monolith 150 7.0 10.7 15.7 
LZY-82 Monolith.sup.1 
150 0.8 3.8 7.7 
LZY-82 Monolith.sup.2 
150 0.5 5.0 8.8 
USY Sieve 
Extrudate 150 0.5 1.0 2.0 
Silicalite 
Extrudate 150 0.8 1.6 3.2 
Silicalite 
Monolith 150 0.2 0.5 0.8 
Carbon Granules 150 18.7 24.4 30.0 
LZY-72 Monolith 200 2.2 4.6 8.0 
LZY-82 Monolith.sup.1 
200 0.2 0.3 0.5 
LZY-82 Monolith.sup.2 
200 0.3 0.4 0.6 
USY Sieve 
Extrudate 200 0.1 0.5 2.0 
Silicalite 
Extrudate 200 1.0 1.8 4.1 
Silicalite 
Monolith 200 0.5 0.7 2.1 
Carbon Granules 200 5.6 9.8 15.1 
LZY-72 Monolith 250 0.5 0.8 1.3 
Carbon Granules 250 2.1 4.2 7.8 
______________________________________ 
.sup.1 (9% silica binder) 
.sup.2 (25% alumina binder) 
The 25% breakthrough times summarized in Table 1 show that LZY-72, a 
hydrophilic adsorber, provides superior toluene adsorption at temperatures 
of about 1500.degree. C. and greater. On the other hand, hydrophobic 
absorbers such as silicalite and dealuminated USY sieve outperformed 
LZY-72 at 25 degrees Centigrade and offered comparable performance up to 
at least 100 degrees Centigrade. 
The results suggest that an improved hydrocarbon adsorber can be produced 
by mixing two adsorbers effective at different temperatures. For this 
reason, it is believed that a dual component adsorbent comprising part 
LZY-72 and part silicalite or dealuminated USY sieve adsorbent will offer 
improved hydrocarbon hold-up in emissions control systems. It is also 
believed that the use of a mixture of hydrophobic and hydrophilic 
adsorbents may provide superior adsorber performance over the range of 
conditions encountered between cold-start and catalyst light-off because 
the hydrophobic adsorbers are not effected by the relatively high 
concentrations of water vapor present in the low temperature gas exhausted 
immediately after engine start-up. As used hereafter, an "effective" 
adsorber is defined as an adsorber having a 25% breakthrough time of 
greater than one minute at a given temperature under the experimental 
conditions disclosed above. 
It also should be noted that if granularized carbon is selected for use as 
an adsorbent, it may be in either a hydrophilic and hydrophobic form. 
Hydrophobic forms of carbon can be prepared by heat treating hydrophilic 
forms of carbon to remove the hydrophilic groups on and near the surface 
of the carbon granules. 
A catalytically-active structure useful in monolith 120 is a cordierite 
monolithic support structure washcoated with up to about 40 weight percent 
of an exhaust gas catalyst of the type previously discussed. Such a 
structure can be purchased or prepared by procedures like those taught in 
the U.S. patents incorporated by reference herein. 
Monolithic support structures suitable for use in exhaust gas treatment 
systems are well known in the art. Ceramic batch materials useful for 
forming ceramic monolithic catalyst and adsorbent supports include 
cordierite, mullite, alumina, lithium aluminosilicates, zirconia, 
feldspars, quartz, fused silica, kaolin clay, aluminum titanate, 
silicates, spinels and mixtures thereof. The desired shape of the 
monolithic support can be obtained by extruding the ceramic batch material 
through an extrusion die to form honeycombed, square or other geometry 
channels. The extruded batch material should be sintered by firing the 
material to a temperature typically between about 800 and 1500 degrees 
Centigrade. 
Metallic monolithic supports may also be used in the invention. For 
example, a monolith having a plurality of ducts may be formed by rolling a 
fan-folded sheet around itself and welding the sheet of metal as required 
to retain the desired shape. Metals and welding points should be chosen to 
minimize the effects of thermal expansion. 
Catalysts and adsorbents may be deposited on or in monolithic supports by 
wash-coating a previously-prepared support or by mixing the catalyst or 
adsorbent into the ceramic batch material prior to extrusion if the 
catalyst or adsorbent can survive the extrusion and sintering processes. 
Techniques useful for producing catalytically-active or 
adsorber-containing ceramic materials can be found in U.S. Pat. Nos. 
4,888,317 and 4,657,880. Techniques for producing monolithic ceramic 
support media can be found in U.S. Pat. Nos. 5,039,644, 4,877,766, 
4,631,268, 4,631,269, 4,637,995, 3,885,976 and 3,790,653. Techniques for 
wash-coating monolithic supports are well known in the art and examples 
can be found in U.S. Pat. No. 4,532,228. The foregoing U.S. patents are 
each hereby incorporated by reference. 
Monolith 120 can be produced by dipping first portion 122 into a catalyst 
solution to a depth equal to the length of first portion 122. Portion 126 
can be similarly prepared by turning the support structure upside down and 
dipping it into an adsorbent washcoat solution to a depth equal to the 
length of second portion 126. If certain channels are desired to remain 
free of catalyst or adsorbant, these channels should be plugged prior to 
dipping the monolith into the washcoat solution. While it is preferred 
that monolith 120 be prepared from a single extruded support, portions 122 
and 126 may be prepared as separate monoliths and cemented together if 
ceramic or welded or otherwise joined if the support is metallic. 
The use of heat exchanging components such as those discussed above also 
enables the use of alternative gas treatment regimes in which the 
different components of a multifunction catalyst can be preferentially 
distributed throughout different regions of the system. For example, an 
embodiment similar to the one shown in FIGS. 7-9 could be operated with a 
NO.sub.x -reducing catalyst such as those that contain rhodium, ruthenium 
or similar metals in channels 124 ahead of adsorber portion 126 and a 
platinum or standard three-way catalyst in channels 124' after adsorber 
portion 126. In this case, the engine could be operated with a rich 
air/fuel mixture which will provide a reductive environment in the 
channels 124 which will enhance NO.sub.x reduction. Supplemental oxygen 
should be provided after the hydrocarbon-adsorbing portion of the system 
to ensure effective catalytic conversion of hydrocarbons and carbon 
monoxide. This also facilitates the use of hydrocarbon adsorbers which 
might otherwise be damaged or rendered ineffective by continued exposure 
to oxygen. 
It should be noted that the improved adsorber performance derived from the 
use of heat exchange techniques and improved adsorbent combinations in 
accordance with the present invention may require adjustment of other 
emissions control equipment. Such a change is likely to be required 
because the improved hydrocarbon adsorber performance delays the time at 
which the initial burst of adsorbed hydrocarbons is released to the 
catalytic converter. This in turn may require changes such as providing 
extra combustion air during the time the desorbed hydrocarbons reach the 
catalytically-active portion of the emissions system. 
The emissions control systems just described are representative of the many 
variations and modifications of the invention which will be apparent to 
those skilled in the emissions systems art after studying the examples 
disclosed herein. Therefore, the invention is not intended to be limited 
by these examples. For example, the use of other adsorbers, catalysts and 
heat exchanger configurations is contemplated, and the scope of the 
invention is intended to be limited only by the following claims.