United States Patent (19) 11, 3,927,177 Okabe et al. (45) Dec. 16, 1975 54 REMOVAL OF NITROGEN OXDES FROM 2,940,821 7/1960 Carus et al.......................... 423/599 GASEOUS MIXTURES USENG AOUEOUS 2,940,822 7/1960 Carus et al.......................... 423/599 ALKALINE MANGANATE OR 3,780, 158 121 1973 Welsh ................................... 423/49 PERMANGANATESOLUTIONS 3,780, 159 12/1973 Welsh ................................... 423149 (75) Inventors: Taijiro Okabe; Akitsugu Okuwaki, FOREIGN PATENTS OR APPLICATIONS both of Sendai; Shigetoshi 131,460 1919 United Kingdom................. 423/599 Nakabayashi, Shinminato, all of 219,461 1968 U.S.S.R............................... 423/239 Japan 226,568 1968 U.S.S.R............................... 423/239 (73) Assignees: Mitsubishi Kinzoku Kogyo Kabushiki Kaisha, Ote; Nippon Primary Examiner-Herbert T. Carter Chemical Industrial Co., Ltd., Assistant Examiner-Eugene T. Wheelock Tokyo, both of Japan Attorney, Agent, or Firm-Wenderoth, Lind & Ponack (22) Filed: Oct. 5, 1973 (21) Appl. No.: 403,974 57) ABSTRACT Nitrogen oxides in a gaseous mixture are removed 30 Foreign Application Priority Data therefrom by a removal method which comprises Oct. 6, 1972 Japan.............................. 47-100512 causing the gaseous mixture to contact an absorbent comprising a manganate or a permanganate or a man (52) U.S. Cl. ................ 423/235; 423/385; 423/395 ganese-containing substance, which forms a manga 51) Int. Cl’.......................................... C01B 21/00 nate or a permanganate at the time of use, oxidizing 58) Field of Search....... 4231235, 239, 49, 50, 385, manganese oxides formed at the treatment by the re 423/395, 599 duction of the manganate or permanganate with the nitrogen oxides, thereby to generate the oxy-acid salt 56 References Cited of manganese, and circulating the same. UNITED STATES PATENTS 4 Claims, 1 Drawing Figure 2,793, 112 5/1957 Mancke................................ 423150 U.S. Patent Dec. 16, 1975 3,927,177 3,927, 177 1 K.MnO, + 2NO, = 2KNO, MnO, (5) KMnO, + NO =KNO -- MnO + 4 O, (6) REMOVAL OF NITROGEN OXDES FROM KMnO, +3NO + 2KOH = 3KNO -- MnO, + HO (6)" GASEOUS MIXTURES USING AQUEOUS ALKALINE MANGANATE OR PERMANGANATE 5 (In an aqueous solution or in the presence of moisture.) SOLUTIONS In the case where the nitrogen oxide is only NO, BACKGROUND OF THE INVENTION there is no necessity of using the above mentioned This invention relates to a process for economically high-priced salts possessing oxidizing property in addi removing nitrogen oxides in gaseous mixtures through tion to alkalinity for removing only this NO, since NO, the use of manganates (V and VI valence salts of man 10 can be readily reacted and absorbed by contact with an ganese are known and the former may also be called alkaline compound. hypomanganate) or permanganates. The expression Accordingly, in the removal of nitrogen oxides, "(per)manganate' used herein means “a salt of oxy which is an object of this invention, on the basis of an acid of manganese'. absorption reaction as described above, the removal of The nitrogen oxides in gaseous mixtures discharged 15 NO only becomes a problem economically and techni from machines and facilities such as internal combus cally. As a method of carrying this out in an effective tion engines, chemical or metallurgical plants, power manner, we have previously conceived the use of alkali generation plants and buildings, gives rise to pollution (per)manganates, of the previous application. such as photochemical smog and is thereby a serious However, as long as the above-mentioned oxy-acid social problem. 20 salts of manganese are dependent on the present pro We have carried out continuous research, from the duction methods, they are of high price. In a method standpoint of eliminating pollution, on treatment of such as that, wherein new lots of these oxy-acid salts of gaseous mixtures containing these nitrogen oxides manganese are used each time in the treatment of gase (which, in actual practice, are principally NO and NO, ous mixtures containing nitrogen oxides, and the oxides and hereinafter referred to collectively as NO). As a 25 of manganese thus formed are discarded, the high cost result, we have discovered that (per)manganates, of the process materials gives rise to an increase in the which have a powerful oxidizing property, are very treatment cost. Furthermore, the discarding of the effective for this purpose as demonstrated in Japanese manganese oxides gives rise to new pollution. These Pat. application No. 17556/1972 (U.S. Pat. Applin. Ser. have been the principal difficulties restricting the use of No. 332,792). 30 (per)manganates. The reactions for absorbing NO and NO, through the Accordingly, it occurred to us that if it were possible use of (per)manganates, which are to be the basis of to oxidize and regenerate at low cost as (per)manga this invention, may be divided into the following three nates the manganese oxide (mostly in the form of man types. ganese dioxide) formed by the reduction of the (per)- 1. NO absorption reaction with a permanganate 35 manganates by the NO in the reactions of Eqs. (1) While this reaction is known with respect to aqueous through (6), it would be possible, by combining this solutions, we have previously disclosed in Japanese regeneration reaction with the above-mentioned NO. Patent Application No. 17556/1972 that an alkali absorption reactions, to provide a process for removing permanganate absorbs NO even in anhydrous NO, which is highly economical. With this possibility solid state. The absorption reaction of NO in the 40 and principle in view, we have carried out various stud case of potassium permanganate, for example, can ies on reactions for regenerating manganese oxides in be represented by the following Eq. (1) or (2), relation to No absorption reactions, and as a result, (2). have arrived at this invention. 45 KMnO, + NO = KNO -- MnO, (I) KMnO, + NO = KNO + MnO, + 4 O, (2) KMnO+ 3NO + 2KOH = 3KNO, + MnO, + HO (2) SUMMARY OF THE INVENTION (In an aqueous solution or in the presence of moisture.) 50 According to this invention, briefly summarized, 2. NO absorption reaction with a manganate there is provided a process for removal of nitrogen This reaction was made clear for the first time by us oxides in a gaseous mixture containing the same, char as mentioned hereinabove. In the case where acterized by the steps of causing the gaseous mixture potassium manganate (VI) is used as a manga containing a nitrogen oxide to contact an absorbent nate, the reaction can be represented by the 55 comprising a manganate or a permanganate, whereby following Eq. (3), (3)' or (4). the nitrogen oxide is converted into a nitrate or a nitrite KMnO, + 2NO -- O = 2KNOa - MnO, (3) and the manganate or permanganate is converted into (3)' . a manganese oxide, causing the manganese oxide to be (4) oxidized into a manganate or permanganate and circu KMnO, -2NO = 2KNO -- MnO, 60 lating the manganate or permanganate thus regener 3. NO, absorption reaction with a manganate or a ated to the absorption step. permanganate The nature, principle, and utility of the invention, as When potassium manganate (VI), for example, is well as further features thereof, will be apparent from used as a manganate, or potassium permanga the following detailed description beginning with a nate, for example, is used as a permanganate, the 65 consideratien, of general features of the invention and reaction can be represented by the following Eq. concluding with specific examples of practice consti (5) or (6), (6)'. tuting preferred embodiments of the invention. 3 3,927, 177 4 alkaline earth metal salts such as calcium salts, stron BRIEF DESCRIPTION OF THE DRAWING tium salts, and barium salts; Zinc salts and cadmium In the drawing: salts; and ammonium salts. Of these salts, the most FIG. 1 is a schematic flowsheet diagram indicating an representative are alkali metal salts, particularly So example of an absorption-regeneration system accord dium salts and potassium salts. ing to this invention in a state for producing nitrates as The oxides of nitrogen with which this invention is a by-product; and concerned are nitrogen monoxide (NO), dinitrogen FIG. 2 is a similar diagram indicating the system in a trioxide (NO), nitrogen dioxide (NO2), dinitrogen state for system of nitrates. pentoxide (NO), and nitrogen trioxide. Of these ox O ides, NO and NO are the most representative, and the DETAILED DESCRIPTION process of this invention is most effective with respect When the combination of the NO, absorption pro to NO and nitrogen oxide mixtures containing NO. cess step and the step for regeneration of manganese A gaseous mixture containing such oxides of nitrogen oxides is broadly divided, depending on the form of to be disposed of according to this invention has a utilization of the nitrates or nitrites formed as by-pro 5 composition containing nitrogen oxides of from trace ducts in the NO, absorption step, a system for produc to 100 mole percent, preferably from 30 to 50,000 ing nitrates as a by-product as indicated in FIG. 1 and parts per million (ppm) as NO or NO. The composi a nitrate decomposition system as indicated in FIG. 2 tion other than nitrogen oxides, within a gaseous mix result, for example, in the case of salt of an alkali metal. ture of this character, differs with the source of the The invention, however, is not limited to these two gaseous mixture, For example, in the exhaust gas of a systems. gasoline (petrol) engine, there are of the order of from The absorption step and the regeneration step in 100 to 3,000 ppm percent of NO, from 10 to 500 ppm, these nitrate by-product production sytem and nitrate SO, and about 12 mole percent of CO., and CO, hy decomposition system will now be considered in detail.