US2942932A - Process of oxidizing carbon monoxide and hydrocarbon in exhaust gases - Google Patents

Description

June 28, 1960 L. P. ELLIOTT PROCESS OF OXIDIZING CARBON MONOXIDE AND HYDROCARBON IN EXHAUST GASES Filed April 1, 1957 LAVERNE P. ELLIOTT United States Patent PROCESS OF OXIDIZING CARBON MONOXIDE AND HYDROCARBON IN EXHAUST GASES Laverne P. Elliott, Berkeley, Calif., assignor to California Research Corporation, San Francisco, Calif., a

corporation of Delaware Filed Apr. 1, 1957, Ser. No. 649,775

4 Claims. (Cl. 23-2) This invention relates to an improved exhaust system for internal combustion engines whereby the discharge of carbon monoxide and of non-combusted and partially combusted products to the atmosphere is prevented or minimized throughout the complete operating cycle of the engine.

When fuels burn in an automotive engine, combustion is relatively incomplete and a considerable portion thereof is'discharged in the unburned or partially burned condition. Various means have been proposed heretofore for ameliorating this situation, such means generally involving passing the exhaust gases through a bed of oxidation catalyst in the exhaust line. For example, U.S. Patent No. 1,400,959 proposes the use of granulated coke, powdered charcoal and alumina in finely divided form, the catalyst mass being used as a resistance heater by passing electric current from an external source through the mass to raise the same to operating temperatures. U.S. Patent No. 1,903,803 proposes the use of alloy of lead, manganese and copper having an oxidized surface as an oxidation catalyst, while U.S. Patent No. 2,025,140 teaches; the use of heavy metal manganites for the same purpose. However, except for the electric heating of Patent No. 1,400,959 wherein the catalyst mass might possibly be brought up to operating temperatures prior to starting the engine,-none of the said processes contemplate the full combustion of exhaust products during periods of start-up when the engine is cold and the exhaust temperature is too low for an oxidation catalyst to be effective.

Accordingly, it is an object of the present invention to provide an eficient means, including a catalytic oxidation zone, for freeing exhaust gases ofcarbon monoxide and of various hydrocarbon components, whether saturated, unsaturated, or partially oxygenated, and which is efficient not only when the engine is in a steady state of operation delivering exhaust gases at high temperatures, but also when the engine is starting and the exhaust gases are too cold to be reactive in the presence of conventional oxidizing catalysts.

Gasoline engines normally run rich, that is, with airfuel ratios too low for complete combustion of the fuel. Accordingly, if full combustion of the exhaust products is to be effected, oxygen must be supplied to the exhaust. This oxygen or air deficiency varies greatly with different operating conditions. Thus, during normal or cruising conditions, approximately 1 to 4% of the fuel supplied to the engine is discharged unburned. This amount increases to from about 2 to 8% while the engine is idling,

and may be as large as during starti-up or under decelerating conditions. While it would be possible to continuously supply the exhaust line with an excess of air large enough to efiect complete combustion during periods of normal as well as abnormal (i.e., start-up or deceleration) operation, such procedure would be inefficient and uneconomical inasmuch as the periods of maximum air demand are relatively brief and occur during 2,942,932 Patented June 28, 1960 only a small proportion of the total operating cycle. Further, the use of unnecessarily large amounts of ex traneous air during periods of normal operation would so lower the temperature of any oxidizing catalyst employed as to make the same ineffective for the intended purpose.

It is therefore a further object of the present invention to provide a means' of oxidizing undesired components of exhaust gases which minimizes the use of extraneous air.

The foregoing and other objects of the present invention are attained by the provision of a dual exhaustcontacting system whereby, during at least the cold, startup period of the engine, the exhaust -is first passed through an adsorbent contained in an adsorbing zone and thereafter through an oxidizing catalyst contained in a conversion zone, said catalyst preferably being one of the type having an oxygen reservoir, as hereinafter described. During the said start-up period, the various undesired exhaust gas components are adsorbed by the charcoal or other equivalent medium employed. Thereafter, as the engine warms up, the hotter exhaust gases gradually desorbv said components while simultaneously bringing the catalyst to effective operating temperatures. In this way, not only is release of undesirable gases prevented when the oxidizing catalyst is cold and ineffective, but

also such gases are released to the catalyst gradually so that by spreading peak air demand from this source is avoided. After the exhaust gas reaches full operating temperature, the adsorbent is in regenerated condition, and ready for a subsequent cold start-up period of usage. As shown hereinbelow, means may be provided for cutting the adsorption chamber out of service after the engine has thus reached operation temperatures.

The adsorbent employed in the adsorption chamber may comprise any material such as, for example, activated charcoal, silica gel, or high surface area activated alumina, which has good adsorption characteristics and is stable over relatively long operating periods even when repeatedly exposed to high temperature exhaust gases. Such material, however, need not be capable of maintaining this activity under the more extreme temperature conditions imposed by the exhaust gases, since, as noted above, the adsorption chamber may be cut out of the exhaust gas path after the engine warms from the period of start-up operation.

The catalyst employed inthe oxidation chamber should be one of high surface area and which is characterized by good activity even after repeated exposure over relatively long operating periods, to the high temperatures of exhaust gases. Representative catalysts, which are generally supported on a'base material of high surface area such as activated alumina or the like, comprise the various acid oxides of metals in groups V through VIII of the periodic table, together with the salts of said 0xides, preferably alkali and alkaline earth metal salts thereof. 'In general, those catalysts wherein the metal is present in the higher valence states of those possible, are the most effective for the purpose of the present invention. Exemplary catalysts are M00 W0 V0 V205, .Ta O ,'NaMn0 Na MnO K2MI104, Ca(MnO Ba(MnO 2, Na2MDO4, K2M004, NH2WO4, K2WO4, Na VO Na CrO Na cr o CaOrO, and K Cr- O In general, the oxidation catalyst is present in an amount of from about 2 to 30%, based on the overall weight of the catalyst and its support.

A particularly useful oxidation catalyst was obtained by impregnating an activated alumina of high surface area with potassium dichromate. This catalyst is somewhat active at about 700 F., and is fully active at about 900 F., as heated by the exhaust gases. In the absence completely burn the exhaust gas components, the catalyst becomm reduced to'K CrO and thus contributes a substantial amount of oxygen to the combustion process. By thus furnishing a reservoir of oxygen during periods of abnormal engine operation, as under decelerating conditions, it is possible to effect full combustion of exhaust components while supplying less excess air to the exhaust stream than would otherwise be required. This feature also characterizes many others of the catalysts enumerated above. Thereafter, as normal engine operation is resumed, with an exhaust stream relatively rich in free oxygen, the catalyst reverts to the K Cr O- state, thereby resuming the dual function of an etfective oxidation-cata lyst and an oxygen reservoir. 7

In the following description of the invention, reference is made to the accompanying drawing, in which Fig. 1 is a diagrammatical illustration of a system suitable to carry out the invention; and V Fig. 2 is an illustration of another embodiment of the invention. A 7

Referring to Fig. 1 of the drawing, exhaust gases enter the system from the exhaust manifold of an internal combustion engine through line-10. Line 10 discharges into a chamber 11 which contains adsorbent material such as activated charcoal, silica gel or alumina. When the exhaust gases are relatively cool, for example when starting or just after starting the engine, the adsorption chamber 11 is effective in adsorbing and holding back carbon monoxide and hydrocarbons in the exhaust gas which would'otherwise be discharged to the atmosphere unoxidized because the oxidizing catalyst in chamber 16 is not yet at operating temperature. When the exhaust gas in line 10 reaches full operating temperature (e.g., 8001,200 F.) the adsorbent in chamber 1 1 has lost its adsorptive capacity and becomes regenerated for use in the next cold starting operation. While the adsorbent is warming up, the retained materials are gradually disengaged, and flow downstream to the oxidizer 1 6.

The exhaust gases flow from adsorbent chamber 11 a through line 12 and thence through an eductor 13. The

purpose of eductor i3 is to introduce and admix through line 14 a quantity of air into the exhaust gases. The

an amount of oxygen equal to about 125 to 150% of that stoichiometrically required to burn completelythe average amount of carbon monoxide and hydrocarbons contained in the exhaust gas. 0

The mixture of air and-exhaust gases flows from eductor 13 through line 15 to the catalytic oxidation chamber 16 provided with, for example, a catalyst consisting et inch, high surface area alumina pellets'impreg mated with suflicient potassium dichromate'solution to give a finished (dried and calcined) catalyst containing 14% by weight K cr O- about 10 to 25 pounds ofcata lyst being'adequate for an average automobile engine.

, quantity of air so introduced is proportioned to provide 4 tioned that the exhaust gas flow is through line 24, adsorption chamber 25, line 26, oxidizer 30, and thence through line 31, to the atmosphere. Thus, during the period of operationwhen the adsorption chamber 25 is efiective, oxidation chamber 30 is being brought up to operating temperatures. When a predetermined exhaust gas temperature in line 20 (cg, 800 F.) has been reached, valve 21 is positioned by 'the temperature sensitive control device 22 so that flow is now from line 29 into line 23, and the adsorption chamber 25 is cut ofi from contact with exhaust gas, the cut-off temperature being selected so that the adsorbent in chamber 25 is left in regenerated condition. The hot exhaust gas in line 23 flows through eductor-.27 where air is introduced through line 28 in quantity as discussed above for eductor 13 in Fig. 1. The mixture of air and exhaust gas then flows through line 29 into oxidation chamber 30. Combustion products are discharged. to the atmosphere through line 31. The adsorbent material and oxidizing catalyst in chambers 25 and 30 are respectively as described for chambers 11 and 16 in the discussion of Fig.

labove.

When the catalyst or the adsorbent medium employed herein give evidence of wearing out, it is contemplated that the same may readily be replaced. This may conveniently be accomplished by providing each of the materials in the form of a cartridge, which can be removed for inspection and/or replacement at will.

I claim:

l. A process for oxidizing carbon monoxide and bydrocarbons contained in exhaust gases that progressively increase in temperature from below about 800 Fpto about 1200 P. which comprises passing said gases at a temperature up to about 800 F. into an adsorption zone containing an adsorbent to adsorb said carbonmonoxide and hydrocarbons, passing the resultingtreated exhaust gases into an oxidation zone containing an oxidation catalyst to preheat said catalyst, Withdrawing the treated exhaust gases from said oxidation zone, discontinuing thepassage of the exhaunt gases to said adsorption zone when the temperature of said gases is about 800 F., passing said exhaust gases at a tcrnperatureof from about 800 to about 1200" Rte an eduction zone, contacting the exhaust gases with a separate oxygen-containing gas in said eduction zone, passing the resulting gaseous mixture from saideduction zone to said oxidation zone, and withdrawing an oxidized gaseous stream from said oxidation zone. p v

2. The process'of claim 1 wherein the adsorbent is activated charcoal. i 7 3. The process of claim 1 wherein oxidation catalyst comprises from about 2 to 30% by Weight potassium dichromate supported 'on activated alumina. 7

4. The process of claim 1 wherein the oxygen-containing gas contains oxygen-in an amountequal'to about to 'of thatstoichiometrically required to .burn completely the average amount of carbon monoxide and hydrocarbons contained in said exhaust gas.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. A PROCESS FOR OXIDIZING CARBON MONOXIDE AND HYDROCARBONS CONTAINED IN EXHAUST GASES THAT PROGESSIVELY INCREASE IN TEMPERATURE FROM BELOW ABOUT 800*F. TO ABOUT 1200*F. WHICH COMPRISES PASSING SAID GASES AT A TEMPERATURE UP TO ABOUT 800*F. INTO AN ADSORPTION ZONE CONTAINING AN ASBORBENT TO ADSORB SAID CARBON MONOXIDE AND HYDROCARBONS, PASSING THE RESULTING TREATED EXHAUST GASES INTO AN OXIDATION ZONE CONTAINING AN OXIDATION CATALYST TO PREHEAT SAID CATALYST, WITHDRAWING THE TREATED EXHAUST GASES FROM SAID OXIDATION ZONE, DISCONTINUING THE PASSAGE OF THE EXHAUST GASES TO SAID ABSORPTION ZONE WHEN THE TEMPERATURE OF SAID GASES IS ABOUT 800*F., PASSING SAID EXHAUST GASES AT A TEMPERATURE OF FROM ABOUT 8000* TO ABOUT 1200*F. TO AN EDUCATION ZONE, CONTACTING THE EXHAUST GASES WITH A SEPARATE OXYGEN-CONTAINING GAS IN SAID EDUCATION ZONE, PASSING THE RESULTING GASEOUS MIXTURE FROM SAID EDUCATION ZONE TO SAID OXIDATION ZONE, AND WITHDRAWING AN OXIDIZED GASEOUS STREAM FROM SAID OXIDATION ZONE.

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