WO2000030739A1

WO2000030739A1 - Catalyzed particulate oxidizer for reducing particulate emissions from a diesel engine and method

Info

Publication number: WO2000030739A1
Application number: PCT/US1999/027779
Authority: WO
Inventors: James M. Valentine
Original assignee: Clean Diesel Technologies, Inc.
Priority date: 1998-11-24
Filing date: 1999-11-23
Publication date: 2000-06-02
Also published as: HK1042266A1; AU1632900A; EP1163043A1; CN1328481A; EP1163043A4; CA2349846A1; JP2002530578A

Abstract

Operation of a diesel engine with low particulate emissions is achieved through the use of a catalyzed particulate oxidizer (14) designed to cause a large number of impacts of particulates with catalyzed surfaces. The catalyzed particulate oxidizer (14) can be precatalyzed or uncatalyzed initially, but catalyzed during use by a catalyst fed prior to or after combustion in the engine. Preferably, the fuel will contain a catalytic additive (29), such as diphenyl cyclooctadiene platinum (II) or platinum acetylacetonate and/or a fuel soluble organo-metallic compound of cerium, iron, copper or manganese. Alternatively, the platinum group metal or other catalytic compound can be added to the exhaust or combustion air. The catalyzed particulate oxidizer has a plurality of parallel plates having catalyzed undulating surfaces provided to create a large number of contact points for the particulates in the exhaust gas.

Description

DESCRIPTION

CATALYZED PARTICULATE OXIDIZER

FOR REDUCING PARTICULATE EMISSIONS

FROM A DIESEL ENGINE AND METHOD

Technical Field

The invention relates to methods that permit a diesel engine to operate efficiently with low particulate emissions.

Particulate emissions, e.g., PM 10 and PM 2.5, particularly from diesel engines, are considered health risks by a growing number of regulatory and health organizations. A number of technologies exist for controlling NO_* and to control diesel particulates. However, to date there is no technology available to reduce diesel particulate emissions to less than 0.1 g/bhp-Hr while also controlling NO_* and not creating servicing and reliability problems or requiring ultra-low sulfur (less than 50 ppm) fuel.

Background Art

Diesel engines provide advantages in fuel economy and are favored for this reason. However, there is a tradeoff between economy on the one hand, which favors complete combustion, and emissions of NO_x/ produced in large quantities under these conditions. Moreover, there is a tradeoff between NO_* and particulates and hydrocarbon (HC) emissions. There is no known technology that is available to take full advantage of diesel economy without suffering α penalty in terms of increased particulate and/or NO_x emissions.

When primary measures (actions that affect the combustion process itself) are taken to reduce NO_x in diesel engines, fuel economy is usually reduced and particulate emissions are increased, On the other hand, combustion conditions selected to reduce pollution from particulates and obtain good fuel economy, tend to increase NO_x.

Among the current strategies to lower NO_* emissions, exhaust gas recirculation (EGR) seems to be a good candidate, but with it, increases in particulates - in addition to fuel economy - will be major technical challenges. Injection timing retard (ITR), like EGR, can also be used to reduce NO_x but results in increased fuel consumption and increases particulate emissions.

The use of particulate traps for diesel engines has become common due to an inherent trade-off between NO_x and particulates - when actions are taken to reduce one, the other increases. Conceptually, the use of a trap could permit NO_x to be reduced to a great extent by techniques such as exhaust gas recirculation, engine timing adjustments, or other known technologies. However, the capture of particulates in a trap can be a problem due to loss in engine efficiency when the pressure drop across the trap becomes too high. Moreover, trap regeneration by burning the particulates can cause physical damage to the trap and requires the use of catalyst coatings, fuel additives or supplemental heaters to assist regeneration. Low sulfur fuel is also required for most catalyzed systems.

Pressure drops across pass-through catalytic oxidizers are much lower, but these devices are less effective at particulate removal. Also, these devices work best when the particulates are relatively wet with fluid hydrocarbons and do not work as effectively with dryer particulates of the type produced by engines operating with exhaust gas recirculation (EGR) employed for NO_x reduction. Generally, they reduce only the soluble organic fraction (SOF) fraction and are, therefore, limited to only 10 to 50% reductions.

A hybrid type of mechanism has be disclosed in PCT publication WO 97/232268, to Van Hardeveld, et al. That device is catalyzed to enable the particulates trapped to burn, but employs what is termed a turbulent flow precipitator to knock the particulates out of the exhaust stream for capture, collection and burning. This would tend to increase pressure drop much as the particulate filter. However, as with catalyzed traps, the burning cannot occur at low temperatures. When ignition of the particulates does occur, it can cause structural damage to the apparatus. The problems can be most severe where the engine is operated for long periods at low load.

Another problem with all precatalyzed devices, including traps and pass through oxidizers, is that they tend to lose activity too rapidly in the presence of sulfur. This will continue to be a problem for diesel engines far into the future because diesel fuel contains significant sulfur. In U. S. Patent No. 5,501 ,714, Valentine and Peter-Hoblyn disclose that the problem can be corrected for pass-through catalytic oxidizers, but this does not solve the basic problems with that technology already noted. And, in PCT publication WO 97/04045, Peter-Hoblyn, Valentine, Sprague and Epperly disclose that platinum alone or with cerium, copper or iron fuel additives could significantly reduce the balance point of a particulate trap. However, low- load conditions may still not be high enough to control back pressure and prevent excessive heat during regeneration. Also, Jelles, Makkee, Moulijn, Acres and Peter-Hoblyn reported at 22^nd CIMAC Congress in Copenhagen, Tuesday, May 19, 1998, that platinum/cerium fuel additives in combination with a catalyzed ceramic filter removed high levels of soot at lower temperatures than catalyzed filters or additives alone. Even with the enhanced performance of this system at low temperatures, the filter still suffers from inherently high back pressure and did not oxidize at temperatures below about 350°C.

Current technology does not provide an adequate solution to the problem of diesel particulates, especially for engines operated under conditions necessary to minimize NO_x emissions. Oxidizers are not effective at removing particulates because they principally reduce the SOF; and while traps are effective at collecting particulates the are troubled with inherent regeneration and durability problems and high back pressures.

Disclosure of Invention

It is an object of the invention to provide a method and apparatus, which provide significant particulate reductions.

It is an object of the invention to provide a method and apparatus, which provide significant, long-term particulate reductions and do so with a minimum of maintenance.

It is another object of the invention to provide a method and apparatus that enable optimizing operation of a diesel for reducing particulates, e.g., to less than 0.1 g/bhp-Hr, while dealing with NO_x reduction through use of engine changes such as EGR and ITR.

It is another object of the invention to provide a method and apparatus for enabling simultaneous reduction of particulates and NO_x from a diesei engine. It is another object of the invention to provide a method and apparatus that eliminate the poor removal efficiency normally associated with pass-through catalytic oxidizers.

It is another object of the invention to provide a method and apparatus that eliminate the fuel economy penalty normally associated with a diesel particulate trap.

It is yet another, and more specific object of the invention to provide a method and apparatus, which provide significant, long-term particulate reductions, e.g., to less than 0, 1 g/bhp-Hr, while simultaneously dealing with NO_x reduction through the use of exhaust gas recirculation and/or ITR.

These and other objects are achieved by the present invention, which provides an improved method and apparatus for operating a diesel engine with low particulate emissions.

The method of the invention comprises: equipping a diesel engine with a catalyzed particulate oxidizer having an inlet, an outlet, an enlarged central chamber and a plurality of parallel plates within the chamber, the plates having catalyzed, undulating surfaces provided to create large number of points of contact for particulates in exhaust; operating the diesei engine under conditions that create an exhaust containing particulates; and passing the exhaust through the catalyzed particulate oxidizer.

The catalyzed particulate oxidizer is also claimed.

Preferably, the fuel will contain a fuel-soluble organo-platinum group metal compound, e.g., comprising a platinum group metal selected from the group consisting of platinum, palladium, rhodium and mixtures of two or more of these. In an alternative embodiment, an effective platinum group metal compound can be added to the exhaust gases before the trap or combustion air. In an alternative, cerium, iron, copper, manganese or combinations of any of these with platinum can be used to reduce engine out particulate loading, including both the soluble and carbon soot fractions of the soot prior to the oxidizer. The resulting metal activated soot will also promote enhanced oxidation when it contacts the catalyzed surfaces.

In another preferred aspect of the invention, the engine is operated with exhaust gas recirculation and/or injection timing retard.

Description of the Drawings

The invention will be better understood and its advantages will be more apparent when the following detailed description is read in light of the accompanying drawings, wherein;

Figure 1 is a schematic representation of a diesel engine with an exhaust system including a catalyzed particulate oxidizer in accord with the invention;

Figure 2 is a schematic representation of a catalyzed particulate oxidizer in accord with the invention;

Figure 3 is an enlarged, cut-away schematic representation of a portion of a catalyzed particulate oxidizer in accord with the invention; and

Figure 4 is a schematic representation of a diesel engine operating with exhaust gas recirculation and an exhaust system including a catalyzed particulate oxidizer in accord with the invention.

Detailed Description of a Preferred Embodiment

The term "Diesel engine" is meant to include all compression-ignition engines, for both mobile (including marine) and stationary power plants and of the two-stroke per cycle, four-stroke per cycle and rotary types. The term "hydrocarbon fuel" is meant to include all of those liquid and gaseous fuels prepared from "distillate fuels" or "petroleum". The term "distillate fuel" means all of those products prepared by the distillation of petroleum or petroleum fractions and residues. The term " petroleum" is meant in its usual sense to include all of those materials regardless of source normally included within the meaning of the term, including hydrocarbon materials, regardless of viscosity, that are recovered from fossil fuels.

The term "diesel fuel" includes "distillate fuels" including diesel fuels meeting the ASTM definition for diesel fuels or others even though they are not wholly comprised of distillates and can comprise alcohols, ethers, organo-nitro compounds and the like (e.g., methanol, ethanol, diethyl ether, methyl ethyl ether, nitromethane). Also contemplated, are emulsions and liquid fuels derived from vegetable or mineral sources such as corn, alfalfa, shale, and coal. These fuels may also contain other additives known to those skilled in the art, including dyes, cetane improvers, anti-oxidants such as 2,6-di-tertiary-butyl-4-methylphenol, corrosion inhibitors, rust inhibitors such as alkylated succinic acids and anhydrides, bacteriostatic agents, gum inhibitors, metal deactivators, upper cylinder lubricants, antiicing agents and the like.

Reference to Figure 1 shows a diesel engine 10 fed fuel from a tank 11. The fuel is preferably catalyzed with a platinum group metal compound or one or more other catalyst compounds, such as cerium, iron or manganese. These latter material can be used alone or with a platinum group metal catalyst.

Exhaust from the engine will pass through exhaust pipe 12, carrying catalytic metals released from the fuel additive catalyst compositions of cerium, and preferably also platinum, to a catalyzed particulate oxidizer (CPO) 14. The CPO can be catalyzed either as installed or by building up a catalyst deposit by operating the engine with a platinum group metal fuel additive.

The CPO of the invention is schematically shown in longitudinal cross- section in Figure 2, The CPO 14 is shown as having an inlet 16, an outlet 18 and an enlarged central chamber 20. Within the chamber 20 are a plurality of essentially parallel plates 22 with catalyzed, undulating surfaces provided to create large number of points of contact for particulates in exhaust which enters at 16 and exits at 18. The plates will preferably be made of a ceramic, a silica-alumina composition such as cordierite, silicon carbide, glass or metal fibers, porous glass or metal substrates, or the like, or a suitable metal such as alloys of the type used in automotive exhaust systems. Among the suitable catalysts, are those known to be useful for catalyzing traps and pass-through catalytic oxidizers. Prominent among these are platinum group metals such as platinum, palladium and rhodium. The oxidizer may or may not be precoated with an alumina washcoat to provide high surface area prior to catalyzing. It is an advantage of the invention that the washcoat is not required.

Reference to Figure 3 schematically shows a section of a CPO enlarged to illustrate the dynamics of the process. Channels 24 are formed between individual plates 22. The channels are sufficiently wide to permit the exhaust gases to pass through with minimal pressure drop. The exact configuration of the channels will vary depending on many design and manufacturing variables. The peaks 26 and the valleys 28 formed in the sheets cause the gases to change direction frequently, The particulates, even though small, have a mass that causes them to impact the walls of the channels formed by the plates while the gases easily turn following the undulations in the plates. The particulates are not collected, but are oxidized at least partially by frequent impact with catalyzed surfaces of the plates 22. The undulations in the drawings are seen to be of chevron shape, but other suitable shapes, including sinusoidal, flat-topped chevrons, and the like can also be employed. In some embodiments, it will be desired to install the plates in sections along the length of the chamber. For example, the plates could be assembled into 2 to 5 sections, each filling the cross section of the chamber, but extending only a portion of its length. In this case, the sections would be separated by a space of preferably less than 5 inches, e.g, 0.25 to 3 inches.

As noted above, the fuel will preferably also contain a fuel-soluble organo-platinum group metal compound, e.g., of platinum, palladium or rhodium. Among these are platinum group metal compounds selected from the group consisting of platinum acetylacetonate and compounds having the general formula XPtRιR₂ wherein X is a ligand containing at least one unsaturated carbon-to-carbon bond with an olefinic, acetylenic or aromatic pi bond configuration and i and R₂ are, independently, benzyl, phenyl, nitrobenzyl or alkyl having 1 to 10 carbons, e.g., diphenyl cyclooctadiene platinum(ll).

Suitable platinum group metal compounds are disclosed for example in prior U.S. Patent Nos. 4,892,562 and 4,891 ,050 to Bowers and Sprague, 5,034,020 to Epperly and Sprague, 5,215,652 to Epperly, Sprague, Kelso and Bowers, and 5,266,083 to Peter-Hoblyn, Epperly, Kelso and Sprague, WO 90/07561 to Epperly, Sprague, Kelso and Bowers, and U. S. Patent Application Serial No. 08/597,517, filed January 31 , 1996, by Peter-Hoblyn, Valentine and Sprague, hereby incorporated by reference. Where the application permits, a blend of these compounds can be used with one or more other platinum group metal compounds such as soaps, acetyl acetonates, alcoholates, β-diketonates, and sulfonates, e.g., of the type which will be described in more detail below. The platinum group metal compound suitable for use as a fuel or gas- borne additive and/or other catalyst additive material, can be added in any manner effective for its intended purpose, such as by adding it to the fuel in bulk storage, to the fuel in a tank associated with the engine, or by continuous or intermittent addition, such as by a suitable metering device, e.g., 27 from tank 29 in Figure 1 , into: the fuel line leading to the engine or the fuel return line from the engine, or in the form of a vapor, gas or aerosol into the air intake, the exhaust gases before the CPO, exhaust gases after the CPO but before recirculation to the engine, or a mixing chamber or equivalent means wherein the exhaust gases are mixed with incoming air.

When employed, platinum group metal catalyst compositions are preferably employed at concentrations of less than 1 part by weight of platinum group metal per million parts by volume fuel (ppm). When used for the purpose of catalyzing an uncatalyzed CPO (or one that has become inactive), it is possible to higher doses, e.g., from 1 to 25 (or greater) ppm, to effect a rapid deposit of catalyst in the CPO. For the purposes of this description, all "parts per million" figures are on a weight to volume basis, i.e., grams/million cubic centimeters (which can also be expressed as milligrams/liter), and percentages are given by weight, unless otherwise indicated. Auxiliary catalysts (named so because they are preferably used with a platinum group metal composition, but can be used without such) are employed at levels effective for their intended purpose, preferably at levels of from 1 to 200 ppm of the fuel utilized, e.g., 5 to 60 ppm.

Among the auxiliary catalytic materials are organometallic salts of manganese, magnesium, calcium, iron, copper, cerium, sodium, lithium and potassium, which can be employed at suitable levels, e.g., from about 1 to about 100 ppm and preferably 20 to 60 ppm of the catalyst metal in combination with the platinum group metal catalyst in diesel fuels. Among these are the alcoholates, sulfonates, beta-diketonates and soaps, e.g., selected from the group consisting of steαrαtes, pαlmitαtes, lαurαtes, tαllαtes, nαpthαnαtes, other fatty acid soaps, and mixtures of two or more of these, of copper, calcium, magnesium, manganese, iron, cerium, sodium, lithium and potassium compounds as are known as fuel soluble and useful fuel additives.

Among preferred cerium compounds are: cerium III acetylacetonate, and various cerium soaps such as cerium III napthanate, cerium octoate, cerium stearate, cerium neodecanoate, and the like. Many cerium compounds are trivalent compounds meeting the formula: Ce(OOCR)₃, wherein R = hydrocarbon, preferably C₂ to C₂₂, and including aliphatic, alicyclic, aryl and alkyiaryl. The dosage level will be at a level of from about 1 to 100 ppm cerium per million parts of fuel (mg per liter), and preferably in the range of from about 5 to 30 ppm, preferably less than 20 ppm. This level can be reduced significantly over what is currently employed in the art by using the cerium in combination with a platinum-catalyzed particulate trap. Reference can be made to the aforementioned WO 97/04045 for a detailed listing, incorporated herein by reference, of other representative auxiliary catalyst compositions.

Reference to Figure 4 shows, schematically, a diesel engine 10 operating with exhaust gas recirculation and an exhaust system including a catalyzed particulate oxidizer 14 in accord with the invention. During EGR operation, combustion air from intake 13 (at high or low pressure, heated or cooled) and exhaust gases from line 32 (separated from the main exhaust gas stream 34) are mixed and fed to one or more cylinders of engine 10 (e.g., either diesei or lean-bum gasoline). The proportion of exhaust gases recirculated to the engine for forming a combustion air mixture will be effective to lower the production of NO_x by the engine utilizing the combustion air mixture as compared to combustion air not containing exhaust gases. Typically, from about 0 to about 30% can be recirculated. The combustion air mixture is typically compressed prior to introduction into engine cylinder(s) wherein it is further compressed, causing heating. The appropriate fuel is injected into the cylinders following compression. The fuel is then combusted with the combustion air mixture to produce exhaust gases that are discharged through exhaust stream 34. The cycle just described is repeated continuously as the engine continues to run in the EGR mode. EGR lowers the combustion temperature and oxygen to the combustion chamber and reduces the amount of NO_x produced, but as has been observed, it increases production of particulates and unburned hydrocarbons - again, the compromise between NO_x and complete combustion.

Downstream of exhaust stream 34 is a CPO unitl4. The CPO is effective within a temperature window of from about 150 to about 650° C, depending on the catalyst. During engine operation giving rise to these temperatures, the exhaust temperature is maintained at the temperatures most preferred for the CPO. At these temperatures, NO_x conversion by EGR is practical, and the EGR system is therefore operated. At other times, ITR can be used alone or in conjunction with EGR to reduce NO_x.

Figure 4 also illustrates a control system of a type useful to maintain the proper operation of EGR and CPO units. The controller 36 can, if desired, measure any of a number of parameters to assure optimum NO_x reduction and particulate oxidation. The temperature of the exhaust (sensor means 38) is one parameter of importance. Engine load is another key parameter (sensor means 40), and this or like factor can be monitored to determine the amount of NO_x being generated and the need for NO_x-reduction by EGR or engine timing changes (hot shown). The sensing means provided for sensing operating parameters indicative of conditions effective for NO_x reduction, sense the appropriate operating parameter and generate an operation signal representative thereof. The controller 36 provides control means for comparing one or more operation signals to appropriate reference value(s) and determines if NO_x reduction can be effectively operated. The controller then generates appropriate control signals representative of the result of the comparison. Means^'are provided to be responsive to the control signals for operating the EGR unit (and/or engine timing changes), as called for by the controller. Figure 1 shows, as representative of these latter means, valve 42.

The EGR unit and/or engine timing adjustments can be controlled, in response to a feed-forward controller in response to a number of measured parameters, including: engine load as represented by various mechanical or electronic measures such as fuel flow, tack or pulse width, engine speed, intake air temperature; barometric pressure; intake air humidity; exhaust gas temperature and/or other parameters effective for particular engines. In addition, to the extent that sensors are available, trim or feed back control can be provided based on residual gas species following the CPO, e.g., the level of NO_x, HC or CO. If desired, feedback control can be employed to trim the system in response to specific gas species, or any other measurable engine or exhaust gas property.

The above description is for the purpose of teaching the person of ordinary skill in the art how to practice the present invention, and it is not intended to detail all of those obvious modifications and variations of it which will become apparent to the skilled worker upon reading this description. It is intended, however, that all such modifications and variations be included within the scope of the present invention which is defined by the following claims.

Claims

1. A method for operating a diesel engine with low particulate emissions, comprising: equipping a diesel engine with a catalyzed particulate oxidizer having an inlet, an outlet, an enlarged central chamber and a plurality of parallel plates within the chamber, the plates having catalyzed, undulating surfaces provided to create large number of points of contact for particulates in exhaust; operating the diesel engine by burning fuel under conditions that create an exhaust containing particulates; and passing the exhaust through the catalyzed particulate oxidizer.

2. A method according to claim 1 , wherein the fuel contains a fuel-soluble organo-platinum group metal compound.

3. A method according to claim 1 , wherein the fuel contains a fuel-soluble organo-metallic compound of cerium, iron, copper or manganese.

4. A method according to claim 1 , wherein the fuel contains a fuel-soluble organo-platinum group metal compound and contains a fuel-soluble organo-metallic compound of cerium, iron, copper or manganese.

5. A method according to claim 2, wherein the fuel-soluble organo-platinum group metal compound is one selected from the group consisting of platinum, palladium or rhodium acetylacetonate and compounds having the general formula XPtR,R₂ wherein X is a ligand containing at least one unsaturated carbon-to-cdrbon bond with an olefinic, acetylenic or aromatic pi bond configuration and Ri and R₂ are, independently, benzyl, phenyl, nitrobenzyl or αlkyl having 1 to 10 carbons, e.g., diphenyl cyclooctadiene platinum(ll).

6. A method according to claim 1 wherein, a platinum compound is added to the exhaust or combustion air.

7. A method according to claim 1 wherein, the catalyzed particulate oxidizer is precatalyzed with platinum.

8. A method according to claim 1 wherein, the catalyzed particulate oxidizer is catalyzed by deposition of a platinum group metal from an additive blended with the fuel.

9. A method according to claim 1 wherein, the engine is operated with exhaust gas recirculation to reduce NO_x.

10. A method according to claim 1 wherein, the engine is operated with engine timing retard to reduce NO_x.

1 1. A method according to claim 1 wherein, the engine is operated with exhaust gas recirculation and/or engine timing retard to reduce NO_x.

12. A catalyzed particulate oxidizer having an inlet, an outlet, an enlarged central chamber and a plurality of parallel plates within the chamber, the plates having catalyzed, undulating surfaces provided to create large number of points of contact for particulates in exhaust.