Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
1993-11-19
2001-01-09
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S171000, C422S177000, C422S180000
Reexamination Certificate
active
06171556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the treatment of an engine exhaust gas stream, and more specifically to a method and apparatus for treating an engine exhaust gas stream containing pollutants including unburned hydrocarbons.
2. The Related Art
Molecular sieves, including zeolites, have been found to be useful for adsorbing harmful components such as hydrocarbons from gaseous streams containing these and other pollutants. For example, U.S. Pat. No. 4,985,210 is directed to an exhaust gas purifying apparatus for an automobile employing a three-way catalyst with either a Y-type zeolite or a mordenite used in a hydrocarbon trap upstream of the three-way catalyst. In the embodiment of
FIG. 2
of U.S. Pat. No. 4,985,210, a bed of activated carbon is disposed upstream of an adsorbent zone. A solenoid-operated valve mechanism serves to direct the exhaust gas stream either through or around the activated carbon bed, depending on the temperature of the exhaust gas stream, and then through the adsorbent zone and the three-way catalyst.
U.S. Pat. No. 5,051,244 is directed to a process for treating an engine exhaust gas stream in which the gas stream is directed through a molecular sieve in an adsorbent zone during the cold-start phase of engine operation. When the hydrocarbons begin to desorb, the adsorbent zone is by-passed until the catalyst is at its operating temperature, at which point the gas stream is again flowed through the adsorbent zone to desorb hydrocarbons and carry them to the catalyst zone. A paper by M. Heimrich, L. Smith and J. Kotowski entitled
Cold
-
Start Hydrocarbon Collection for Advanced Exhaust Emission Control
, SAE Publication Number 920847, discloses an apparatus which functions in a manner similar to that of U.S. Pat. No. 5,051,244.
U.S. Pat. No. 5,125,231 to Patil et al, dated Jun. 30, 1992, discloses an engine exhaust system for reducing hydrocarbon emissions, including the use of Beta zeolites as hydrocarbon adsorbents (see column 5, lines 63 through column 6, line 14). Zeolites having a silica/alumina ratio in the range of 70/1 to 200/1 are preferred adsorbents (see column 6, lines 7-11). The apparatus includes by-pass lines and valves to direct exhaust gases from a first converter directly to a second converter during cold-start operation and when the first converter reaches its lightoff temperature, to either by-pass the second converter or recycle effluent from it to the first converter (see e.g., column 10, lines 10-28).
U.S. Pat. No. 5,158,753 discloses an exhaust gas purifying device comprising: a catalyst device installed in the exhaust gas path of an internal combustion engine for treating the exhaust gas of the engine; an adsorbing device installed in the exhaust gas path between the catalyst device and the internal combustion engine, for treating the exhaust gas of the engine. One embodiment includes a heat exchanger for performing heat transfer between the exhaust gas flowing from the internal combustion engine to the adsorbing device and the exhaust gas flowing from the adsorbing device to the catalyst device. Alternatively, the catalyst device includes a catalyst secured in the low-temperature-side gas flow path of a heat exchanger, and the exhaust gas flowing from the internal combustion engine to the adsorbing device is allowed to flow to the high-temperature-side gas flow path of the heat exchanger.
SUMMARY OF THE INVENTION
The present invention relates to an apparatus and method for treating engine exhaust gases employing an apparatus having a first and a second catalyst zone and an adsorbent zone between them, wherein the first and second catalyst zones are in heat transfer relation to one another. Heat transfer from the first catalyst zone to the second catalyst zone helps to bring the second catalyst therein more quickly to its effective operating temperature, and the adsorbent zone reduces the quantity of hydrocarbons discharged to the atmosphere by adsorbing them until the second catalyst is at a temperature at which it can more effectively convert at least some of the hydrocarbons to innocuous substances.
Specifically, the present invention provides a method of treating an engine exhaust gas stream containing hydrocarbons and other pollutants at least during a cold-start period of operation. The method comprises the steps of (a) flowing the exhaust gas stream through a first catalyst zone having therein a first catalyst effective at least for the conversion of some of the pollutants to innocuous products; (b) flowing the effluent of the first catalyst zone through an adsorbent zone comprising an adsorbent effective to temporarily adsorb at least some hydrocarbons remaining in the gas stream; and (c) flowing the effluent of the adsorbent zone through a second catalyst zone comprising a second catalyst effective at least for the conversion of at least some of the hydrocarbons to innocuous products. In the process of the invention, heat is transferred from the first catalyst zone to the second catalyst zone, to improve the efficacy of the second catalyst zone at least during the cold-start period of engine operation.
According to one aspect of the present invention, the exhaust gas stream may be flowed through an indirect heat exchange means which may comprise a crossflow monolith having a first plurality of passages defining a first flow path through the monolith and disposed in heat exchange relationship with a second plurality of passages defining a second flow path through the monolith which is segregated from the first flow path. The first catalyst zone and the second catalyst zone may be disposed in the respective first and second flow paths of the crossflow monolith. The first catalyst may comprise an oxidation catalyst, and the method may comprise oxidizing carbon monoxide to carbon dioxide in the first catalyst zone.
Another aspect of the invention provides that a third catalyst zone may comprise a third catalyst effective for the oxidation of hydrocarbons and be disposed between the first and second catalyst zones, and the method may comprise flowing the exhaust gas stream through the third catalyst zone.
Another aspect of the invention provides that the adsorbent material may comprise a molecular sieve material, for example, a molecular sieve material selected from the group consisting of faujasite, chabazite, silicalite, zeolite X, zeolite Y, ultrastable zeolite Y, offretite, and Beta zeolites. In particular, ion-exchanged Beta zeolites may be used, such as Fe/Beta zeolite, or preferably, H/Beta zeolite. The zeolites, preferably Beta zeolites may have a silica/alumina molar ratio of from at least about 25/1, preferably at least about 50/1, with useful ranges of from about 25/1 to 1000/1, 50/1 to 500/1 as well as about 25/1 to 300/1 for example, from about 100/1 to 250/1, or alternatively from about 35/1 to 180/1. Other useful and preferred silica to alumina molar ratios for zeolites are at least 200/1 with more preferred ratios of from about 200/1 to about 1000/1, and Beta zeolite ratio ranges preferably from about 200/1 to about 600/1. Most preferably, the adsorbent material is a low zeolite having a relative Bronsted acidity, as defined below, of less than 1.0, preferably less than 0.5, more preferably less than 0.25, yet more preferably less than 0.1 and most preferably less than 0.05.
Preferred zeolites, include ZSM, Y and Beta zeolites, with Beta zeolites particularly preferred. The preferred zeolites are treated to reduce the number of acid sites. This can be accomplished by leaching the zeolite with an organic or inorganic acid. The zeolite alternatively or additionally can be steam treated with steam at from 350 to 900° C. with the steam temperature increasing at from 100 to 600° C. degrees per hour. Steam treatment has been found to reduce the relative Bronsted acidity, and result in an increase the durability of the zeolite when used in hydrocarbon adsorption applications in exhaust gas streams.
The present invention includes adsorbent compositions comprising zeolit
Burk Patrick Lee
Dettling Joseph Charles
Heck Ronald Marshall
Hochmuth John Karl
Steger John Joseph
Engelhard Corporation
Negin Richard A.
Tran Hien
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