Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
  • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion
  • F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
  • B01D53/86—Catalytic processes
  • B01D53/90—Injecting reactants
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—Removing only nitrogen compounds
  • B01D53/9409—Nitrogen oxides
  • B01D53/9413—Processes characterised by a specific catalyst
  • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9495—Controlling the catalytic process
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
  • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2251/00—Reactants
  • B01D2251/20—Reductants
  • B01D2251/208—Hydrocarbons
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/10—Noble metals or compounds thereof
  • B01D2255/104—Silver
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/209—Other metals
  • B01D2255/2092—Aluminium
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
  • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
  • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• This invention relates to a method of reducing coking of AgZAl 2 O 3 hydrocarbon selective catalytic reduction (HC-SCR) catalysts in a lean burn engine exhaust gas stream.
• HC-SCR hydrocarbon selective catalytic reduction
• HC-SCRs are sometimes also referred to in the literature as non-selective catalytic reduction (NSCR) catalysts, lean NO x catalysts (LNC), lean NO x reduction catalysts, "DeNO x catalysts” and NO x occluding catalysts.
• NCR non-selective catalytic reduction
• LNC lean NO x catalysts
• DeNO x catalysts lean NO x reduction catalysts
• NO occluding catalysts NO occluding catalysts.
• hydrocarbons react with nitrogen oxides (NO x ), rather than oxygen (O 2 ), to form nitrogen (N 2 ), carbon dioxide (CO 2 ) and water (H 2 O) according to Reaction (1):
• HC-SCR catalysts used to selectively promote the desired reaction (1) are PfAl 2 O 3 , Cu exchanged ZSM-5 and Ag/Al 2 O 3 .
• Ag/Al 2 O 3 catalysts operate at higher temperatures and over a broad temperature range, and have recently shown promise in vehicle testing (Klingstedt et al., Topics in Catalysis, 30/31, 2004, 27 and Lindfors et al., Topics in Catalysis, 28, 2004, 185, the entire contents of which are incorporated herein by reference).
• All of these catalysts exhibit high activity for the selective reduction of NO x by hydrocarbons, including long chain alkane and diesel fuel, but each type of catalyst suffers from some form of limitation in use.
• PfAl 2 O 3 catalysts display lower NO x conversion and lower selectivity towards nitrogen; N 2 O (conversion >60%) is a basic product. Additionally, the HC-SCR activity window of PfAl 2 O 3 catalysts is limited to low temperatures (about 150 - 250 0 C).
• Cu/ZSM-5 catalysts can suffer from thermal deactivation due to copper sintering and dealumination of the zeolite.
• AgZAl 2 O 3 catalysts are tolerant to hydrothermal ageing, but can suffer from chemical deactivation caused by coking or sulphation.
• Coking is not a significant factor in the activity of any HC-SCR catalyst at higher temperatures since above approximately 400 °C any carbon present will be burnt to form CO 2 thereby leaving the catalyst surface available for reactions to take place thereon. As such it is important to differentiate between the absolute activity of any particular HC-SCR catalyst, and the reduction in activity that coking may result in. An increase in the absolute activity of any particular HC-SCR catalyst will not necessarily be the result of a concomitant reduction in coking.
• the invention provides a method of reducing coking over a AgZAl 2 O 3 hydrocarbon selective catalytic reduction (HC-SCR) catalyst in an exhaust stream of a lean burn internal combustion engine, which exhaust stream comprising hydrocarbon and NO x , which method comprising controlling the hydrocarbon to molar NO x ratio of the exhaust stream so as to be less than or equal to
• HC-SCR hydrocarbon selective catalytic reduction
• the temperature of the exhaust stream relevant to this invention is the temperature of the exhaust stream as it impacts the HC-SCR catalyst.
• the hydrocarbon has a relatively low aromatics species content, e.g. comprising from O to 10% aromatics.
• the HQNO x is controlled so as to be between 0.5 and 2.0 when the exhaust gas temperature is less than or equal to 300 0 C and between 4.5 and 7.0 when the exhaust gas temperature is greater than or equal to 425 0 C.
• the hydrocarbon species has a relatively high aromatics species content, e.g. comprising from 10 to 40% aromatics.
• the HC:NO X is controlled so as to be between 1.0 and 2.0 when the exhaust gas temperature is less than or equal to 300 0 C and between 4.5 and 5.0 when the exhaust gas temperature is greater than or equal to 425 0 C.
• Aromatics as defined herein include, but are not limited to, the following species: toluene, ethylbenzene, xylenes, polaromatics, 1-methylnaphthalene, n- pentylbenzene, biphenyl, 1-butylnaphthalene, n-nonylbenzene, 2-octylnaphthalene and n-tetradecylbenzene.
• Controlling the HC:NO X ratio of the exhaust stream can be achieved by either varying the amount of hydrocarbon present in response to the amount OfNO x present, or by varying the amount of NO x present in response to the amount of hydrocarbon present. This can be achieved by monitoring the levels of NOx or hydrocarbon present in the exhaust stream, or predicting the levels OfNO x or hydrocarbon present in the exhaust stream. Such levels may be predicted by referring to the NO x or hydrocarbon levels known to be present during certain engine conditions.
• the hydrocarbon for use in the present invention may be injected into the engine exhaust stream upstream of the HC-SCR catalyst, or it may be produced by cracking engine fuel.
• Engine fuel may be cracked in the cylinder of the engine or in the exhaust gas stream.
• PCT/GB2006/002595 incorporated herein by reference.
• Exhaust Gas Recirculation or fuel combustion techniques such as HCCI during a relevant portion of the engine speed/load map, may be used to alter the supply OfNO x to the HC-SCR catalyst.
• Suitable engine fuels include those that have relatively high aromatics hydrocarbon species content such as diesel (including US06, an Ultra Low Sulphur Diesel-ULSD for implementation in 2007) and gasoline, and those that have relatively low aromatics hydrocarbon species content such as FT-GTL (Fischer-Tropsch gas to liquids) and biodiesel.
• diesel including US06, an Ultra Low Sulphur Diesel-ULSD for implementation in 2007
• gasoline and those that have relatively low aromatics hydrocarbon species content
• FT-GTL Fischer-Tropsch gas to liquids
• the exhaust gas stream also comprises hydrogen.
• hydrogen can have an advantageous effect on HC-SCR activity at relatively low levels, e.g. less than 1000 ppm, optionally less than or equal to 600 ppm. Whilst it is possible to increase hydrogen content in an exhaust gas by combusting hydrocarbon fuel, e.g. injected into the exhaust gas upstream of the HC-SCR, or by engine calibration, such an increase in hydrogen is generally accompanied by an increase in hydrocarbon as well. In a particular embodiment, relatively low levels of hydrogen can be introduced into the exhaust gas without simultaneously increasing hydrocarbon content of the exhaust gas by contacting a reforming catalyst with hydrocarbon.
• this invention provides an exhaust system for a lean burn engine, which system comprising a Ag/Al 2 O 3 HC-SCR catalyst and means, when in use, for controlling the HQNO x ratio of the exhaust gas so as to be less than or equal to 2.0 when the exhaust stream temperature is less than or equal to 300 0 C, between 2.0 and 4.5 when the exhaust stream temperature is from 300 0 C to 425 0 C, and 4.5 or greater when the exhaust stream temperature is greater than or equal to 425 0 C.
• the HQNO x can be controlled by adjusting the HC concentration in the exhaust gas, by adjusting the NO x concentration in the exhaust gas, or both.
• the exhaust system comprises means, when in use, for controlling the supply of the hydrocarbon. Such means can comprise means for injecting hydrocarbon into exhaust gas upstream of the HC-SCR catalyst or for adjusting the timing of fuel injection into one or more engine cylinders.
• the exhaust system comprises means, when in use, for controlling the supply of NO x .
• NO x control means can comprise Exhaust Gas Recirculation or fuel combustion techniques such as HCCI during a relevant portion of the engine speed/load map. In either of these two embodiments, the control means may include a pre-programmed electronic control unit.
• the exhaust system comprises means for increasing the amount of hydrogen present in the exhaust gas stream.
• means for increasing the amount of hydrogen present in the exhaust gas stream can include a fuel reformer, based on platinum group metals or nickel (see Trimm et al., Catalysis
• the hydrocarbon species may be injected into the engine exhaust gas stream upstream of the HC-SCR catalyst, or it may be produced by cracking engine fuel, thereby to produce shorter chain hydrocarbons. If the hydrocarbon species is produced by cracking engine fuel, this cracking may be done in the combustion cylinder of the engine or in the exhaust gas stream. Therefore the exhaust system may comprise means for injecting hydrocarbon species into the exhaust gas stream or means for cracking engine fuel in either the combustion cylinder of the engine or in the exhaust gas stream.
• the invention provides a lean burn internal combustion engine including an exhaust system according to the invention, and a vehicle or stationary power source including such a lean burn engine.
• Figure 1 shows how NO x conversion activity at 250 0 C varies with time for different fuels
• Figure 2 shows how the steady state NO x conversion activity varies with temperature for both GTL and US06 fuels at hydrocarbon to NO x ratios of 2.5 and 4.5;
• Figure 3 shows how NO x conversion activity at 300 0 C varies with time for both GTL and US06 fuels at hydrocarbon to NO x ratios of 2.5 and 4.5;
• Figure 4 shows how the steady state NO x conversion activity varies with temperature for both GTL and US06 fuels at optimised hydrocarbon to NO x ratios
• Figure 5 shows how the steady state NO x conversion activity of US06 fuel (at optimised hydrocarbon to NO x ratios) varies with temperature with either 300 ppm or 600 ppm H 2 present in the gaseous mixture.
• Figure 6 shows how the steady state NO x conversion activity of US06 fuel (at optimised hydrocarbon to NO x ratios) varies with temperature with 300 ppm H 2 present in the gaseous mixture at low levels OfNO x .
• the HC-SCR activity of the catalysts was measured by flowing diesel type fuels (US06 or GTL) in a gaseous mixture (NO 500ppm, hydrocarbon (Cl equivalent) 2250ppm, CO 240ppm, O 2 12%, H 2 O 5%, CO 2 4.6%, balance N 2 at a total flow rate of 3 L/min) over 0.6 g of catalyst.
• NO x conversions were typically measured after 10 mins at constant catalyst inlet temperature starting from 200 °C and increasing the temperature in 50 °C intervals to 500 °C. We refer to this as steady-state NO x conversion.
• Figure 1 shows the steady state NO x concentration for hydrocarbon to NO x ratio of 4.5 for n-octane, n-decane, n-dodecane, GTL and US06 at 250 0 C as a function of time.
• Octane and decane show poor NO x conversion whilst dodecane shows good initial activity although its high reactivity, relative to GTL and US06, also promotes coke deposition therefore leading to a rapid decrease in reactivity.
• the steady state NO x conversion activity for 2 wt% AgZAl 2 O 3 of Example 1 was measured for hydrocarbon to NO x ratios of 2.5 and 4.5 using GTL and US06 fuel as the source of the hydrocarbon species.
• Figure 2 shows that the NO x conversion activity is generally higher for GTL than for US06 and that NO x conversion is more effective using the lower HQNO x at lower temperatures.
• the difference in performance between GTL and US06 may be partly due to the higher cetane number of GTL relative to US06, see Table 1. Additionally, we believe the improvement in NO x conversion is due to deactivation through coking occuring at temperatures of less than 400 0 C (the 50% distillation temperature of both fuels is approx. 300 0 C, see Table 1) and less hydrocarbon species being present results in less coking. However, at higher temperatures the higher HQNO x is more effective for NO x conversion.
• Figure 3 shows the steady state NO x concentration for hydrocarbon to NO x ratios of 2.5 and 4.5 for GTL and US06 at 300 0 C as a function of time.
• Figure 4 shows the NO x conversion activity for optimised hydrocarbon to NO x ratios for US06 and GTL fuels.
• optimised we mean that the HQNO x was increased, in accordance with the invention, as the temperature of the exhaust stream increased.
• the variable ratios for the two sources of hydrocarbon are also given, see right hand axis.
• Figure 5 shows significant improvements in the HC-SCR catalyst activity results from the addition of H 2 with the activity window broadening towards lower temperatures, even at low levels of H 2 addition.
• the 300 ppm H 2 test from Example 5 was repeated using a gas mixture containing 200 ppm NO x , and with the amount of US06 present adjusted to maintain optimised hydrocarbon to NO x ratios.
• Figure 6 shows that the HC-SCR catalyst is highly effective at low levels Of NO x , as well as at higher levels OfNO x .

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Environmental & Geological Engineering (AREA)
• Health & Medical Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Biomedical Technology (AREA)
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• Toxicology (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Exhaust Gas After Treatment (AREA)

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• 2005
  • 2005-11-14 GB GBGB0523135.2A patent/GB0523135D0/en not_active Ceased
• 2006
  • 2006-11-09 WO PCT/GB2006/050376 patent/WO2007054740A1/en not_active Ceased
  • 2006-11-09 KR KR1020087011360A patent/KR20080077112A/ko not_active Withdrawn
  • 2006-11-09 US US12/084,997 patent/US8387367B2/en not_active Expired - Fee Related
  • 2006-11-09 EP EP06808740A patent/EP1948351A1/en not_active Withdrawn
  • 2006-11-09 CN CNA2006800425005A patent/CN101309742A/zh active Pending
  • 2006-11-09 AU AU2006313538A patent/AU2006313538A1/en not_active Abandoned
  • 2006-11-09 JP JP2008540702A patent/JP4938021B2/ja not_active Expired - Fee Related

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