Classifications

• • 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
  • B01D53/54—Nitrogen compounds
  • B01D53/56—Nitrogen oxides
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/064—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof containing iron group metals, noble metals or copper
  • B01J29/072—Iron group metals or copper
• • 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
  • B01D53/8621—Removing nitrogen compounds
  • B01D53/8625—Nitrogen oxides
  • B01D53/8628—Processes characterised by a specific catalyst
• • 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
  • B01D53/8621—Removing nitrogen compounds
  • B01D53/8625—Nitrogen oxides
  • B01D53/8631—Processes characterised by a specific device
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/20—Metals or compounds thereof
  • B01D2255/207—Transition metals
  • B01D2255/20738—Iron
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/50—Zeolites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2255/00—Catalysts
  • B01D2255/50—Zeolites
  • B01D2255/504—ZSM 5 zeolites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/402—Dinitrogen oxide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2257/00—Components to be removed
  • B01D2257/40—Nitrogen compounds
  • B01D2257/404—Nitrogen oxides other than dinitrogen oxide
• • 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
  • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

• NO and N0 2 have long been known as compounds with ecotoxic relevance (acid rain, smog formation) and worldwide limits for their maximum permissible emissions have been set, in recent years nitrous oxide has also become a focus of environmental protection this to a not inconsiderable extent for the depletion of stratospheric ozone and for
• Processes for the reduction of NO x are also based on zeolite catalysts and are carried out using a wide variety of reducing agents.
• iron-containing zeolites in particular seem to be of interest for practical use.
• US Pat. No. 4,571,329 claims a process for reducing NO x in a gas which consists of at least 50% of NO 2 by means of ammonia in the presence of an Fe zeolite. The ratio of NH3 to N0 2 is at least 1.3. According to the method described here, NO x -containing gases are to be reduced with ammonia without the formation of N 2 0 as a by-product.
• No. 5,451,387 describes a process for the selective catalytic reduction of NO x with NH 3 over iron-exchanged zeolites, which works at temperatures around 400.degree.
• Fe and Cu zeolite catalysts again appear to be particularly suitable which either bring about a pure decomposition of the N 2 0 into N 2 and 0 2 (US Pat. No. 5,171,553) or also for the catalytic reduction of the N 2 0 Help of NH 3 or
• JP-A-07 060 126 describes a process for the reduction of N 2 0 with NH 3 in the presence of iron-containing zeolites of the pentasil type at temperatures of 450 ° C.
• the N 2 0 breakdown that can be achieved with this process is 71%.
• a one-step process ie the use of a single catalyst for reducing both NOx and N 2 O, is particularly desirable.
• the reduction of NO x with ammonia can take place in the presence of Fe zeolites at temperatures below 400 ° C, however, as mentioned, temperatures> 500 ° C are generally required for the N 2 0 reduction.
• Temperatures means more energy consumption, but above all because the zeolite catalysts used are not stable to aging under these conditions in the presence of water vapor.
• JP-A-09 000 884 claims the simultaneous use of ammonia and hydrocarbons.
• the hydrocarbons selectively reduce the N 2 0 contained in the exhaust gas, while the NO x reduction is brought about by the added ammonia. The whole
• the object of the present invention is to provide a simple but economical process, in which if possible only one catalyst is used, which delivers good conversions both for the NOx and for the N 2 O decomposition distinguishes a minimal consumption of reducing agent and in which no further ecologically questionable by-products are generated.
• the present invention relates to a method for reducing the content of NO x and
• N 2 0 in process gases and exhaust gases the process being carried out in the presence of a catalyst, preferably a single catalyst which essentially comprises one or more iron-laden zeolites, and the gas containing N 2 0 and NO x for removing N 2 0 in a first step in a reaction zone I at a temperature ⁇ 500 ° C is passed over the catalyst and the resulting gas stream is passed in a second step in a reaction zone II over the iron-zeolite catalyst, the gas stream a portion NH 3 is added, sufficient to reduce the NO x (see Figure 1).
• a catalyst preferably a single catalyst which essentially comprises one or more iron-laden zeolites
• NO x as an activating agent accelerates the N 2 0 breakdown in the presence of iron-containing zeolites.
• NO does not co-catalyze the N 2 0 decomposition.
• the method according to the invention makes it possible to carry out both the decomposition of N 2 O and the reduction of NO x at a uniformly low operating temperature, which was not possible until now with the methods described in the prior art.
• N 2 0 is degraded in accordance with the above reaction equations in the presence of NO x even at temperatures at which decomposition of N 2 0 without NO x would not take place at all.
• the N 2 0 content in the process according to the invention is in the range from 0 to 200 ppm, preferably in the range from 0 to 100 ppm, in particular in the range from 0 to 50 ppm.
• the invention relates to a device for reducing the content of NO x and N 2 0 in process gases and exhaust gases, comprising at least one catalyst bed comprising a catalyst which essentially contains one or more iron-laden zeolites and two reaction zones, the The first zone (reaction zone I) is used for the decomposition of N 2 0 and NO x is reduced in the second zone (reaction zone II) and there is a device for introducing NH 3 gas between the first and second zones (cf. Figures 1 and 2).
• the design of the catalyst bed is freely configurable in the sense of the invention. For example, it can take the form of a tubular reactor or a radial basket reactor. A spatial separation of the reaction zones, as shown in Fig. 2, also corresponds to the meaning of the invention.
• Catalysts used according to the invention essentially contain, preferably> 50% by weight, in particular> 70% by weight, of one or more zeolites loaded with iron.
• zeolites loaded with iron preferably> 50% by weight, in particular> 70% by weight
• another zeolite containing iron such as an iron-containing zeolite of the MFI or MOR type can be contained in the catalyst used according to the invention.
• the catalyst used according to the invention can contain further additives known to the person skilled in the art, such as, for example, binders.
• Catalysts used according to the invention are preferably based on zeolites into which iron has been introduced by a solid-state ion exchange. Usually one starts with the commercially available ammonium zeolites (eg NH -ZSM-5) and the corresponding iron salts (eg FeS0 x 7 H 2 0) and mixes them mechanically in a ball mill at room temperature. (Turek et al .; Appl. Catal. 184, (1999) 249-256; EP-A-0 955 080). Reference is hereby expressly made to these references. The catalyst powders obtained are then added to the air in a chamber furnace
• the iron-containing zeolites are washed intensively in distilled water and dried after filtering off the zeolite. Finally, the iron-containing zeolites obtained in this way are mixed with the appropriate binders and mixed and, for example, extruded into cylindrical catalyst bodies. All binders commonly used are suitable as binders, the most common being aluminum silicates such as e.g. Kaolin.
• the zeolites that can be used are loaded with iron.
• the iron content can be up to 25%, based on the mass of zeolite, but preferably 0.1 to 10%.
• the iron-loaded zeolites of the MFI, BEA, FER, MOR and / or MEL type are preferably contained in the catalyst. Precise information about the structure or structure of these zeolites are in the Atlas of Zeolite Structure Types, Elsevier, 4th revised edition 1996, given explicit reference is made to the.
• Zeolites preferred according to the invention are of the MFI (Pentasil) or MOR (Mordenite) type. Zeolites of the Fe-ZSM-5 type are particularly preferred.
• reaction zone I and reaction zone II can be spatially connected to one another, as shown in FIG. 1, so that the gas loaded with nitrogen oxides is continuously passed over the catalyst, or they may be spatially separated from one another, as can be seen in FIG. 2.
• iron-containing zeolites are used in reaction zones I and II. This can be different catalysts in the respective zones or preferably the same catalyst.
• the temperature of reaction zone I in which the laughing gas is broken down is ⁇ 500 ° C., preferably in the range from 350 to 500 ° C.
• the temperature of reaction zone II preferably corresponds to that of reaction zone I.
• the process according to the invention is generally carried out at a pressure in the range from 1 to 50 bar, preferably 1 to 25 bar.
• the NH 3 gas is fed in between reaction zone I and II, ie behind reaction zone I and upstream of reaction zone II, by means of a suitable device, such as, for example, a corresponding pressure valve or appropriately designed nozzles.
• the gas loaded with nitrogen oxides is usually at a space velocity of 2 to 200,000 h "1 , preferably 5,000 to 100,000 h " 1 based on the added catalyst volume of both reaction zones passed over the catalyst.
• the water content of the reaction gas is preferably in the range of ⁇ 25% by volume, in particular in the range of ⁇ 15% by volume.
• a low water content is generally preferred.
• a high water content plays a subordinate role for the NO x reduction in reaction zone II, since high NOx degradation rates are achieved here even at relatively low temperatures.
• reaction zone I a relatively low water concentration is generally preferred since a very high water content would require high operating temperatures (e.g.> 500 ° C). Depending on the type of zeolite used and the operating time, this could be the hydrothermal one
• the process according to the invention makes it possible to decompose N 2 0 and NO x at temperatures ⁇ 500 ° C., preferably ⁇ 450 ° C. to N 2 , 0 2 and H 2 0, without the formation of ecologically unsafe by-products, such as toxic carbon monoxide, which in turn removes them should be.
• the reducing agent NH3 is used for Reduction of NO x consumed, but not or only insignificantly for the decomposition of N 2 0.
• a ZSM-5 type zeolite loaded with iron was used as the catalyst.
• the Fe-ZSM-5 catalyst was produced by solid ion exchange, starting from a commercially available zeolite in ammonium form (ALSI-PENTA, SM27). Detailed information on the preparation can be found in: M. Rauscher, K. Kesore, R. Mönnig, W. Schwieger, A. Tißler, T. Turek: Preparation of highly active Fe-ZSM-5 catalyst through solid State ion exchange for the catalytic decomposition of N 2 0. in Appl. Catal. 184 (1999) 249-256.
• the catalyst powders were calcined in air at 823K for 6h, washed and dried at 383K overnight. After the addition of appropriate binders, extrusion into cylindrical catalyst bodies followed, which were broken down into granules with a grain size of 1-2 mm.

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• Environmental & Geological Engineering (AREA)
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• General Chemical & Material Sciences (AREA)
• Oil, Petroleum & Natural Gas (AREA)
• Organic Chemistry (AREA)
• Materials Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Catalysts (AREA)
• Exhaust Gas Treatment By Means Of Catalyst (AREA)

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  • 2000-01-14 DE DE10001539A patent/DE10001539B4/de not_active Expired - Lifetime
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