GB2458994A - The use of urea in catalytic production of hydrogen - Google Patents

The use of urea in catalytic production of hydrogen Download PDF

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Publication number
GB2458994A
GB2458994A GB0806603A GB0806603A GB2458994A GB 2458994 A GB2458994 A GB 2458994A GB 0806603 A GB0806603 A GB 0806603A GB 0806603 A GB0806603 A GB 0806603A GB 2458994 A GB2458994 A GB 2458994A
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Prior art keywords
urea
hydrogen
catalytic
nox
unit
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GB0806603D0 (en
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Martyn Vincent Twigg
Ian Carmichael Wishart
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Johnson Matthey PLC
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Johnson Matthey PLC
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    • 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
    • B01D53/46—Removing components of defined structure
    • B01D53/72—Organic compounds not provided for in groups B01D53/48 - B01D53/70, e.g. hydrocarbons
    • 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
    • B01D53/9431—Processes characterised by a specific device
    • 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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/323—Catalytic reaction of gaseous or liquid organic compounds other than hydrocarbons with gasifying agents
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/323—Catalytic reaction of gaseous or liquid organic compounds other than hydrocarbons with gasifying agents
    • C01B3/326—Catalytic reaction of gaseous or liquid organic compounds other than hydrocarbons with gasifying agents characterised by the catalyst
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/48—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents followed by reaction of water vapour with carbon monoxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/202—Hydrogen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0233—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a steam reforming step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0283—Processes for making hydrogen or synthesis gas containing a CO-shift step, i.e. a water gas shift step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0435—Catalytic purification
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/04—Integrated processes for the production of hydrogen or synthesis gas containing a purification step for the hydrogen or the synthesis gas
    • C01B2203/0465—Composition of the impurity
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/08—Methods of heating or cooling
    • C01B2203/0805—Methods of heating the process for making hydrogen or synthesis gas
    • C01B2203/085—Methods of heating the process for making hydrogen or synthesis gas by electric heating
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/12—Feeding the process for making hydrogen or synthesis gas
    • C01B2203/1205—Composition of the feed
    • C01B2203/1211—Organic compounds or organic mixtures used in the process for making hydrogen or synthesis gas

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

Abstract

A method of generating hydrogen, such as on a vehicle, is disclosed which comprises passing urea over a catalyst, such as a nickel-containing catalyst. Also disclosed is an NOx control system for combustion exhausts, especially for vehicles and more especially but not exclusively for light duty diesel vehicles, which has a urea storage tank, urea dosing means and a control unit associated therewith, and a SCR catalyst unit, a NOx absorber unit or a combination thereof: wherein the urea tank is connected to a catalytic unit capable of converting urea into hydrogen, and means for supplying the hydrogen formed to the SCR catalyst unit and/or the NOx absorber unit. Further disclosed is a catalytic reactor having a flow-through monolith having a plurality of cells some of which have a resistance heating wire with a catalytic surface.

Description

IMPROVEMENTS IN EMISSION CONTROL
The present invention concerns improvements in emission control, more especially it is concerned with the control of emissions from internal combustion engines such as in vehicles.
Ammonia selective catalytic reduction (SCR) is well established for controlling NOx emissions into the atmosphere from power and chemical plants, and more recently from the exhaust gas of vehicles with lean-burn internal combustion engines, and especially compression ignition ("diesel") engines.
Certain disadvantages are associated with the use of ammonia. Mixtures of ammonia and air can be explosive. Ammonia is also a highly irritating caustic gas that is inconvenient to store on a vehicle so it is often derived from a precursor, usually urea, that is stored in the form of an aqueous solution. The reactions involved are hydrolysis of the urea to ammonia which then selectively reduces NOx to dinitrogen.
The overall SCR process can be summarised by the Reactions (1) -(3), and a range of catalysts can be used for the SCR process. The most well known are based on vanadium, and more recently catalysts containing zeolites have been used. It is possible to use a separate catalyst for the hydrolysis reaction, and these are also usually based on metal oxides.
2(NH2) 2CO + 2H2O -4NH3 (1) 4N0 + 4NH3 + 02 -4N2 + 6H2O (2) 2NO2 + 4NH3 + 02 -3N2 + 6H2O (3) In practice reaction of NO2 with ammonia is slower than that of NO, and we discovered that mixtures of the two oxides of nitrogen react more rapidly that the single compounds alone.
The emission control engineer also has available, for use as the NOx control means, NOx absorbers, sometimes called NOx absorber catalysts. These are now well known in the art.
Urea itself, (NH2)2C0, is a stable crystalline solid (melting point 132.7°C) and it offers advantages of being easily transported and stored. Furthermore, it is cheap and readily available; some 100 million tons/year are manufactured from the exothermic reaction of ammonia and by-product CO2 for use as a fertiliser.
USP 6,871,471 discloses an emission control system for an internal combustion engine, in which urea is converted into ammonia, part of which is passed, as the reductant, to an SCR catalyst, and part of which is converted to hydrogen. The hydrogen is fed to a fuel cell and electricity storage unit. A link between the hydrogen supply and the SCR catalyst is contemplated. However, it is plain that this system had not been constructed or operated at the time of filing the patent, and at the present time, the system is not in commercial use.
During experimental work on the catalytic hydrolysis of aqueous urea solutions in connection with one of our previous developments on this subject (see EP 1,054,722) we used hot nickellchromium wire to heat the gas stream containing fine droplets of an aqueous urea solution. The yield of ammonia was surprisingly less than that obtained with other heating devices, and we thought another product might be being formed. Analysis of the product gases confirmed that considerable quantities of hydrogen were being produced.
The equipment used is illustrated conceptually in Figure 1, and Figure 2 shows pulses of hydrogen-containing gas produced when urea solution was periodically sprayed onto the hot nickel/chromium wire. Typically the wire temperature was between 450 and 700°C, achieved by applying 12 to 24 volts across the heater wire and a current flow of 2 to 4 amps.
It appears the possibility of using urea as a direct source of H2 has not been previously considered, although it appears to be very convenient. The process involved may be represented by Reaction (4), the steam reforming of urea. This has the advantage an additional 50% of H2 is theoretically derived from water. This is particularly convenient when the source of urea is an aqueous solution of urea.
(NH2)2C0 + H2O -3H2 + N2 + CO2 (4) The steam reforming of urea is facile, it is only mildly endothermic (AH° = +63.92 kJ/mol) compared to the more common steam reforming of hydrocarbons (for methane AH° = +206 J/mol), and above 727°C the potential by-product CH4 is not even thermodynamically feasible. Reaction (4) is an equilibrium that is coupled with the water gas shift Reaction (5). Even without excess water thermodynamic calculations show the H2 content of the gas produced is 52% with the co-products being N2 (24%), CO (20%) and CO2 (0.05%). Excess water will drive the reaction to forming more H2, more CO2 and less CO. That is, excess water will drive the water gas shift reaction over to the right hand side, Reaction (5).
CO + H20 -H2 + CO2 (5) Any ammonia that might be present will be cracked to H2 and N2 over a nickel containing surface, Reaction (6), at operational temperatures. This means of producing hydrogen, being such a facile reaction, could be used with considerable advantage on vehicles, especially diesel-powered vehicles, requiring low temperature exhaust gas NOx control.
2NH3 -3142 + N2 (6) Low temperature NOx control on diesel powered vehicles, and especially on cars, is critical. SCR systems are not active until about 200°C, and although NOx-traps can absorb NOx at low temperatures they cannot be regenerated effectively with CO or hydrocarbons at temperatures below say 3 00°C. The exhaust gas temperature of a diesel car is typically about 150°C for most of the European Test Cycle, only reaching about 300°C in the final high speed part of the test. Thus, for most practical operating conditions, it has been extremely difficult to provide adequate NOx control by exhaust gas aftertreatment devices.
Reactions with H2 are facile and can take place at very low temperatures. For example, NOx SCR with H2 over platinum takes place at room temperature. Similarly, and perhaps more importantly, NOx-traps, that can absorb NOx at low temperatures, can be regenerated with hydrogen at low temperatures.
SCR on vehicles is expected to increase dramatically in order to meet upcoming emission regulations, and urea will be carried on vehicles as the source of the reductant.
We propose to use urea steam reforming as a convenient source of on-board hydrogen, and use it during low temperature "cold start" conditions of diesel engines.
The favoured system comprising a urea based hydrogen generator coupled with a NOx-trapping system that is regenerated by hydrogen from the former unit. Reactions of the newer zeolite SCR catalysts have yet to be tested with hydrogen.
The present invention provides a method of generating hydrogen, especially on a vehicle, comprising passing urea over a catalyst, especially a nickel-containing catalyst. Conventional experimentation is able to identify other suitable catalysts and is able to optimise the catalyst for any particular application.
Although in this description, we are particularly concerned with the provision of hydrogen to NOx control systems on a vehicle, the present invention should not be regarded as limited thereto, and the hydrogen generated directly from urea can form a useful fuel or reactant for many uses. In particular, the use of urea as a hydrogen source for fuel cells appears to offer several advantages over the use of methanol, which has significant toxicity issues.
The present invention also provides an improved NOx control system, especially for vehicles and more especially but not exclusively for light duty diesel vehicles, having a urea storage tank, urea dosing means and a control unit associated therewith, and a SCR catalyst unit, a NOx absorber unit or a combination thereof, wherein the urea tank is connected to a catalytic unit capable of converting urea into hydrogen, and means for supplying the hydrogen formed to the SCR catalyst unit and/or the NOx absorber unit.
The conventional engine electronic control unit can desirably include another function, that of controlling the generation of hydrogen as taught herein, and distributing and dosing it to the appropriate component(s) of the exhaust aftertreatment system. The ECU may limit the hydrogen generation and distributing and dosing to cold start and low temperature sections of the engine operating cycle, or may provide a steady-state or graduated hydrogen dosage throughout the engine operation.
The above improved NOx control system may form part of a more complex emission control system, which may in particular include particulate removal. EP 1054722 (Johnson Matthey et al) teaches an improved SCR system which has become known as the SCRT� system. The present invention may be used in combination with an SCRT� system.
Particulate removal may be achieved especially by filtering. Filters in common use are often catalysed to reduce particulate combustion temperatures. Mostly, those filter types known as wall flow filters, are used as well as more unconventional filters including types of static mixer and like relatively open constructions, in which particulate is retained for an adequate residence time to effect reaction of the particulate.
In one embodiment, the filter is preceded by an oxidation catalyst. The oxidation catalyst may be coated on the filter, either uniformly or as a "stripe" or more concentrated oxidation catalyst deposit on the upstream section of the filter.
The present invention offers many possibilities of improving overall effectiveness of a three-way or four-way catalytic vehicle exhaust aftertreatment system. Thus, the NOx removal component(s) may precede the filter, the point of injection of the reductant or the reductant and hydrogen may be upstream of the filter or directly into the filter.
Particular systems to be considered are a catalytic filter or catalyst followed by a filter followed by either or both of an SCR catalyst and a NOx absorber, in which hydrogen as the sole reductant or forming part of the reductant together with ammonia, is injected into or upstream of the filter. The skilled person will be able to devise very many ways of meeting future emission regulations using the present invention.
Where hydrocarbon fuel is used as reductant in an emission control system, for example with NOx absorbers, or in order to raise the temperature of a filter in order to effect removal of particulate, there is often a fuel penalty of a few percent. The present invention may avoid or reduce this fuel penalty. Hydrogen produced according to the present invention can assist light-off of three-way catalysts used in gasoline engines.
The present invention has the potential to provide a more efficient emission control system, especially on start-up or in low temperature parts of the operating cycle. The hydrogen may be supplied to more than one component within the system. Because of the improved overall efficiency, the size of catalytic components, and associated weight penalty, can be reduced, with consequent reductions in overall system cost.
In the experimental work forming the basis for the invention, a honeycomb monolith reactor having a Ni/Cr heating wire located in at least some, preferably the majority, of the cells. One embodiment of the reactor is illustrated in the photograph which is Figure 3. Such a reactor appears to be novel and to have advantageous properties when used to catalytic endothermic reactions. Accordingly, the invention also provides a catalytic reactor having a flow-through monolith having a plurality of cells, wherein each of at least a proportion of the cells has a resistance heating wire located therein, and the resistance heating wire has a catalytic surface. The resistance heating wire may be entirely composed of a catalytic metal, such as Ni/Cr alloy or Pt, or may have a core carrying a catalytic coating.

Claims (10)

  1. CLAIMS1. A method of generating hydrogen, especially on a vehicle, comprising passing urea over a catalyst, especially a nickel-containing catalyst.
  2. 2. The use of urea as a feedstock in the catalytic production of hydrogen.
  3. 3. The use of urea and water vapour as a feedstock in the catalytic production of hydrogen.
  4. 4. The use of hydrogen produced from urea as a fuel for a fuel cell.
  5. 5. The use of hydrogen produced from urea as a reductant for NOx in combustion exhausts.
  6. 6. An improved NOx control system for combustion exhausts, especially for vehicles and more especially but not exclusively for light duty diesel vehicles, having a urea storage tank, urea dosing means and a control unit associated therewith, and a SCR catalyst unit, a NOx absorber unit or a combination thereof, wherein the urea tank is connected to a catalytic unit capable of converting urea into hydrogen, and means for supplying the hydrogen formed to the SCR catalyst unit and/or the NOx absorber unit.
  7. 7. An improved NOx control system according to claim 6, in combination with filter means capable of reducing particulate in the exhaust.
  8. 8. The use of hydrogen produced by the catalytic reaction of urea and water vapour in an exhaust gas aftertreatment system.
  9. 9. The use according to claim 6, during cold start and/or during low temperature sections of the engine operating cycle.
  10. 10. A catalytic reactor having a flow-through monolith having a plurality of cells, wherein each of at least a proportion of the cells has a resistance heating wire located therein, and the resistance heating wire has a catalytic surface.
GB0806603A 2008-04-11 2008-04-11 The use of urea in catalytic production of hydrogen Withdrawn GB2458994A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT202000002764A1 (en) * 2020-02-12 2021-08-12 Ecospray Tech Srl DEVICE AND METHOD FOR THE SELECTIVE ABATEMENT OR REDUCTION OF NOX NITROGEN OXIDES IN GAS OR FUMES FROM COMBUSTION IN PARTICULAR GAS OR FUMES GENERATED BY THE ACTIVITY OF AN INTERNAL COMBUSTION ENGINE

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030219371A1 (en) * 2002-04-15 2003-11-27 Amendola Steven C. Urea based composition and system for same
US6871491B2 (en) * 2002-05-03 2005-03-29 Robert Bosch Gmbh Combustion system having an emission control device

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030219371A1 (en) * 2002-04-15 2003-11-27 Amendola Steven C. Urea based composition and system for same
US6871491B2 (en) * 2002-05-03 2005-03-29 Robert Bosch Gmbh Combustion system having an emission control device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IT202000002764A1 (en) * 2020-02-12 2021-08-12 Ecospray Tech Srl DEVICE AND METHOD FOR THE SELECTIVE ABATEMENT OR REDUCTION OF NOX NITROGEN OXIDES IN GAS OR FUMES FROM COMBUSTION IN PARTICULAR GAS OR FUMES GENERATED BY THE ACTIVITY OF AN INTERNAL COMBUSTION ENGINE
WO2021161210A1 (en) * 2020-02-12 2021-08-19 Ecospray Technologies S.R.L. Device and method for the abatement or selective reduction of nitrogen oxides nox in combustion gas or fumes, in particular in gas or fumes generated by the activity of an internal combustion engine

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