Reactions of Sulfur Dioxide with Ammonia
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環境 科 学 会 誌6(2):143-150(1993) 143 Reactions of Sulfur Dioxide with Ammonia Kouichi HIROTA*, Toshiaki NIINA**, Erry ANWAR*** Hideki NAMBA*, Okihiro TOKUNAGA* and Yoneho TABATA Abstract Reactions of SO2 with NH3 were studied at 45-105•Ž in gaseous mixture of NO, oxygen and nitrogen with and without water. The reactions proceed at reaction temperature lower than 65•Ž in the presence of 10% water and white powdery reaction products were uniformly deposited on the surface of a reactor and of a fiber filter. From the chemical analysis of the products dissolved in water, the main components of the products were considered to be ammonium sulfate, sulfite, hydrogen sulfate and hydrogen sulfite. The reactions may proceed in absorbed water on the surface of a reactor and a fiber filter. Key Words : sulfur dioxide, ammonia, reaction, reaction temperature, relative humid ity ably affected by gaseous components and reac 1. Introduction tion temperature. Irradiation with electron beam was proposed In this report, we studied on reactions of SO2 as an effective method for removing NOX and with NH3 in gaseous mixture of which compo SO2 in flue gases from industrial plants such as nents were colse to that of coal-fired flue gas to power stations, steel plants, etc. In this proc- clarify the characteristics of the reactions and ess, electron beam irradiation in the presence of to evaluate the contribution of the reactions in ammonia added causes conversions of NOX and SO2 removal in electron beam treatment of SO2 to aerosol of ammonium nitrate and sulfate coal-fired flue gas. which can be collected by an electrostatic 2. Experimental precipitator or by a bag filter1•`3). We found a part of SO2 was removed through reactions 2.1 Materials with NH3 without electron beam irradiation in Nitrogen, oxygen, carbon dioxide and 1 or this process, but the mechanism of this reaction 3% SO2,1 or 3% NH3 and 3000 ppm NO diluted was not clear. with nitrogen were used as purchased from the Studies on reactions of SO2 with NH3 have Nippon Sanso Company without further purifi been done in 1960's and 70's4•`10). These studies cation. Purities of all these gases and gaseous mainly focused on the aerosol formation at compounds were above 99.9%. around room temperature in the presence of a 2.2 Apparatus trace amount of water and the results of these Experiments were carried out using a flow studies showed that the reactions were remark experimental system shown in Fig. 1. A cylin - Received December 1, 1992 ; Accepted February 12, 1993 * Department of Radiation Research for Environment and Resources, Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-12, Japan. ** Department of Engineering, the University of Takai. *** Center for the Application of Isotope and Radiation, National Atomic Energy Agency , Indonesia. 144 HIROTA, NIINA, ANWAR, NAMRA, TOKUNAGA and TABATA Fig. 1 Apparatus drical reaction vessel made of Pyrex-glass of 33 The temperature of the line A was set to be 2- cm long and 8 cm diameter was placed in a 3•Ž higher than that of the water bath to pre- thermostatic oven. A sheet of fiber filter was vent condensation of water vapor in the line placed at down-stream position of the vessel to and the line B was heated to be 115•Ž not to collect powdery reaction products. The flow proceed reactions of SO2 with NH3 in the line. rates of nitrogen, oxygen, 1 or 3% SO2 and 3000 The measurement of SO2 concentration was ppm NO were individually controlled using done by an infra-red absorpion type SO2 detec each flow control valve and these gases were tor (Shimazdu : IRA 107). Before introducing passed into a mixing vessel of same size as the the sample gas into the detector, the sample gas reaction vessel through each pipe. All pipes of 1 1/min was led into a filter to remove which were used for connection between instru powdery products and then into an ammonia ment parts were made of Teflon. The mixing scrubber in which glass fiber soaked with con vessel was filled with a lot of glass-made cylin centrated phosphoric acid was set to remove drical rings of 25 mm long and 12 mm diameter NH3. and was placed just before the reaction vessel in 2.3 Procedure the oven. On the way to the mixing vessel The temperature of the oven was first set to from the flow control valve, nitrogen was be 105•Ž, and all gaseous components other introduced into water of which temperature than 1 or 3% NH3 were continuously fed into was controlled in a water bath (Eyela : Digital the reactor through the mixing vessel. When Uni Ace UA-100) to prepare water-saturated the indication of SO2 concentration was stable, nitrogen and the nitrogen was then led into the 1 or 3% NH3 was directly introduced into the mixing vessel through a heated pipe to mix with reactor where reactions of SO2 with NH3 were other gaseous components. On the other hand, initiated accompanying the change of the indi 1 or 3% NH3 was directly introduced into the cation of SO2 concentration. When the indica reactor, where NH3 reacted with SO2. Reac tion of SO2 concentration was stable at the tion temperature was detected by a thermocou temperature of the oven of 105•Ž, the tempera ple detector (CA) inserted into the reactor. ture of the oven was changed to 100•Ž. The The temperatures of line A and B in Fig. l were same procedure was done to get the stable controlled by each temperature controller. indication of SO2 concentration resulting from 145 Reactions of S02 with NH3 reactions with NH3 at every temperature from 105 to 45•Ž at 5•Ž intervals. Typical total flow rate of gaseous mixture was 101/min and typi cal reaction time of the gas in the reactor was 10 sec. 2.4 Analysis of products White powdery products deposited on the inner surface of the reactor were washed with distilled water of about 100 ml to dissolve. A part of the water solution was used for analysis of NH4+, SO32- and SO42- ions by an ion chromatograph (Toyo Soda Industry Co. Ltd. : HLC-601). The analytical conditions for these ions were as follows ; For SO42- and 5032-: column TSK gel IC-Anion PW Fig. 2 Effect of H2O on NH3-SO2 Reac tion (Toyo Soda Industry) Initial Concentration of Water ; eluent 10% acetonitrile 0% (•œ), 3% (•¤), 5% (•›), 7% flow rate of eluent 1.2 ml/min (••), 10% (• ), 15% (•ž), 20% column temperature 40•Ž (•¢) detector conductivity initial Concentrations ; SO2 (600 For NH4+: ppm), NH3 (1200 ppm), NO (225 column TSK gel IC-Cation ppm), 02 (10%) and N2 (Balance) (Toyo Soda Industry) eluent 2 mM HNO3 flow rate of eluent 1.2 ml/min column temperature 40•Ž detector conductivity 3. Results and Discussion When SO2 was mixed with NH3 in the gase ous mixture of NO, oxygen, water and nitrogen, SO2 concentration was decreased gradually accompanying the formation of white powdery products on the surface of the vessel and the filter at the temperature lower than a certain value. In this report, the degree of reactions of SO2 with NH3 was indicated by removal of SO2 (1-[SO2]/[SO2]o, where [SO2]o and [SO2] were SO2 concentrations before and after the reactions in gaseous mixture). Fig. 3 Relationship between Water Con 3.1 Dependency of reaction temperature centration and SO2 Removal on NH3-SO2 Reaction Dependency of reaction temperature on SO2 Reaction Temperature (•Ž) ; 45 removal in the gaseous mixture of 600 ppm SO2, (•›), 50 (• ), 55 (•ž), 60 (•¢), 65 1200 ppm NH3, 225 ppm NO, 10% oxygen and (•¤), 70 (••) nitrogen (balance) was shown in Fig. 2 for Initial Concentrations ; SO2 (600 various concentrations of water ranging from 0 ppm), NH3 (1200 ppm), NO (225 to 20%. It should be pointed out from the ppm), 03 (10%) and N2 (Balance) 146 HIROTA, MINA, ANWAR, MAMBA, TOKUNAGA and TABATA figure that no SO2 removal was observed with- out water. While in the presence of water, SO2 removal was observed at reaction temperature lower than a certain value and was increased almost linearly with lowering the temperature. The highest temperature at which SO2 removal was observed is hereinafter named as "the highest reaction temperature" in this report. "The highest reaction temperature" was lower with lowering concentration of water in gase ous mixture and was determined to be 71•Ž and 55•Ž at the water concentration of 20% and 3%, respectively. The figure 3 showed relationship between SO2 removal and water concentration at various reaction temperatures, which indicat ed clearly remarkable dependency of water concentration and reaction temperature on Fig. 5 Effect of SO2 Concentration on NH3-SO2 Reaction reactions of SO2 with NH3. 3.2 Dependency of reaction time Initial Concentration of NH3 ; 1200 ppm (•›) and 1600 ppm (• ) Effect of reaction time on reactions of SO2 Initial Concentrations ; NO (225 with NH3 was studied at the reaction tempera ppm), O2 (10%), H2O (10%) and ture of 50•Ž in the gaseous mixture of 600 ppm N2 (Balance). SO2, 1200 ppm NH3, 225 ppm NO, 5% water, Reaction Temperature; 50•Ž 10% oxygen and nitrogen (balance). The obtained relationship between reaction time and SO2 removal was shown in Fig. 4. SO2 removal rate (SO2 removal/sec) was calcu lated to be 5.4%/sec at the initial stage of the reactions and was gradually decreased with reaction time. The results suggest that the reactions are affected by concentrations of SO2 and/or NH3 in gaseous mixture.