Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Patent
1998-03-10
2000-05-02
Langel, Wayne
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
4232391, 423392, 423393, 423403, C01B 2100, C01B 2138, C01B 2126
Patent
active
06056928&
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for removing nitrogen oxides such as NO, NO.sub.2 and N.sub.2 O from a gas stream containing same. Nitrogen oxides are formed as by-products in many processes in which HNO.sub.3 is used as oxidizing agent in liquid phase. Especially the conversion of alcohols, aldehydes and ketones, for example the conversion of cyclohexanol and cyclohexanone into adipic acid, of acetaldehyde into glyoxal or of glyoxal into glyoxylic acid, and also the production of nicotinic acid and hydroxylamines liberate for example appreciable amounts of N.sub.2 O as well as other nitrogen oxides.
In Science 251 (1991), 932, Tmiemens and Trogler show that N.sub.2 O has a certain destructive potential for the Earth's atmosphere. N.sub.2 O serves as the major stratospheric source of NO, which in turn has an essential influence on the depletion of ozone in the stratosphere. In addition, N.sub.2 O is considered a greenhouse gas whose global warming potential is said to be about 290 times greater than that of CO.sub.2.
Recent years have witnessed the publication of a multiplicity of patent and non-patent documents concerned with reducing the N.sub.2 O emissions due to anthropogenic sources.
A multiplicity of patents describe catalysts for reducing or decomposing N.sub.2 O, for example DE 43 01 470, DE 42 24 881, DE 41 28 629, WO93/15824, EP 625369, WO94/27709, U.S. Pat. No. 5,171,553.
U.S. Pat. No. 5,200,162 discloses that the exothermic reaction of the decomposition of N.sub.2 O into nitrogen and oxygen can lead to a multiplicity of process problems associated with high process temperatures. It describes a process for decomposing N.sub.2 O in a gas stream by contacting an N.sub.2 O-containing gas stream under N.sub.2 O decomposition conditions with a catalyst for decomposing N.sub.2 O into nitrogen and oxygen by first cooling part of the exit gas whose N.sub.2 O content is reduced and then recycling it into the N.sub.2 O decomposition zone. In the case of N.sub.2 O-containing waste gas streams containing additional NO.sub.x it is stated to be frequently very desirable to pretreat the gas stream to remove NO.sub.x upstream of the N.sub.2 O decomposition zone by selective reduction of NO.sub.x with ammonia in the presence of oxygen.
In Abatement of N.sub.2 O emissions produced in the adipic acid industry, Environmental Progress 13 (1994), No. 2, May, 134-137, Reimer, Slaten, Seapan, Lower and Tomlinson describe a boiler gas reburn system coupled with selective non-catalytic reduction (SNCR) for destroying N.sub.2 O. A flow diagram of the catalytic decomposition of N.sub.2 O shows an N.sub.2 O decomposition catalyst stage coupled with an NO.sub.x abatement SCR catalyst stage.
Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, volume A17, 1991, pages 293-339, describes the production of HNO.sub.3 by burning ammonia and absorbing the combustion products in water. Nonselective catalytic reduction (NSCR) and selective catalytic reduction (SCR) processes can be used for treating the waste gases from the HNO.sub.3 production process.
It is an object of the present invention to provide a process for removing nitrogen oxides from a gas stream containing same.
It is a further object of the present invention to provide a process for removing nitrogen oxides from a gas stream containing major quantities of N.sub.2 O as well as other nitrogen oxides.
It is a further object of the present invention to provide a process for removing nitrogen oxides from a gas stream containing same to produce nitric acid (HNO.sub.3).
It is a further object of the present invention to provide a process for removing nitrogen oxides from a gas stream containing same under simple conditions.
It is a further object of the present invention to provide an apparatus for the aforementioned processes.
We have found that these objects are achieved by the processes and apparatus claimed in the claims.
The term "nitrogen oxides" as used in the description and the claims designates the oxides of nitrogen, especially dinitrogen oxide
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Burger Gert
Fetzer Thomas
Otto Bernhard
Roth Emil
Ruppel Wilhelm
BASF - Aktiengesellschaft
Langel Wayne
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