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. 3.3 Effect of initial concentration of SO2

Effect of initial concentration of SO2 (300-

1800 ppm) on SO2 removal was studied for

initial concentrations of NH3 of 1200 and 1600

ppm in the gaseous mixture of SO2, NH3, 225

ppm NO, 10% water, 10% oxygen and nitrogen

(balance) at the reaction temperature of 50•Ž.

As shown in Fig. 5, SO2 removal was decreased

markedly with increasing initial concentration

of SO2 from 400 to 1200 ppm and gradually with

the concentration above 1200 ppm for both Fig. 4 Relationship between Reaction initial NH3 concentrations of 1600 and 1800 Time and SO2 Removal ppm. The SO2 removal was larger for initial Initial Concentrations ; SO2 (600 NH3 concentration of 1800 ppm than for that of ppm), NH3 (1200 ppm), NO (225 1600 ppm over the whole range of initial concen ppm), 03 (10%), CO2 (12.5%), H2 0 (5%) and N2 (Balance). tration of SO2.

Reaction Temperature ; 50•Ž Reactions of SO2 with NH3 147

3.4 Reaction products In the experiments mentioned in the previous paragraphs 3-1 to 3-3, white powdery products were uniformly deposited on the surface of the reactor and the fiber filter. To determine the chemical components, the reaction products were washed with distilled water and the water solution was analyzed by a high pressure liquid chromatography (HPLC) for ammonium ion (NH4+), sulfite ion (5032-) and sulfate ion (SO42-). The analysis of SO42- and 5032- was made twice for each sample. The first analy sis was performed just after washing the reac tion products with distilled water and the sec ond was done 24 hours after the washing. When the water solution was analyzed just Fig. 6 Liquid Chromatogram of Water after washing the reaction products, two peaks Solution were observed on the chromatogram and one of Initial Concentrations ; NH3 (1200 them disappeared on the chromatogram ppm), SO2 (600 ppm), NO (225 obtained 24 hours after the washing, as shown ppm), 02 (10%), H2O (10%), N2 in Fig. 6. It was confirmed by the experiments (Balance) with the water solutions of Na2SO3 and (NH4) 2

SO4 that the peak 1 and 2 in the figure were [NH4+] / [SO42-] in the water solutions just identified to be SO32- and 5042- respectively after the washing and 24 hours after the wash- and the peak 1 was completely disappeared 24 ing were summarized in Table 1 for various hours after dissolving Na2SO3 accompanying initial concentrations of SO2 and NH3. All the the increasing of the height of the peak 2. obtained ratios except for the sample of the

From the fact, it can be considered that the initial concentration of 1200 ppm NH3 and 300 water solution of the reaction products contains ppm SO2 were less than 2. Hartley et al.4)

SO42- and 5032- ions just after washing the reported that (NH4) 2SO4 was the main product reaction products. Existing S032- ions are of reactions of SO2 with NH3 at 23•Ž in the completely oxidized to SO42- ions in the water gaseous mixture of oxygen, water and nitrogen solution in 24 hours after the washing and and the product was formed through precursors resulting ratio of [NH4+] / [SO42-] in the solu such as NH3SO2 and (NH3) 2502. Considering tion becomes smaller 24 hours after washing the results obtained by Hartly et al., the experi than just after the washing. Ratios of mental fact that ratios of [NH4+] / [SO42-] in

Table 1. The Obtained Ratios of [NH4+] / [SO42-] in Water Solutions

* ; obtained by analysis just after the washing ** ; obtained by analysis 24 hours after the washing

Initial Concentrations ; SO2 (1600-400 ppm), NH3 (16000 or 1200 ppm), NO (225 ppm), 02 (10%), H2O (10%) and N3 (Balance) Reaction temperature ; 50•Ž 148 HIROTA, NIINA, ANWAR, NAMBA, TOKUNAGA and TABATA the sample solutions are less than 2 with excep tion for the sample solution of 1200 ppm NH3 and 300 ppm SO2 initial concentration indicates that the reaction products contain not only (NH4)2SO4 and (NH4)2S03 but also NH4HSO4 and NH4HSO3. 3.5 Effect of material of reactor Effect of material of reactor on reactions of SO2 with NH3 was examined with a glass-made reactor and a stainless steel reactor of the same size under the same reaction conditions. The results were shown in Fig. 7. With the stain- less steel reactor, "the highest reaction temper ature" was lower than that with the glass-made reactor. This indicates that reactions of SO2 with NH3 are affected by material of reactor and proceed more on the surface of the glass- Fig. 7 Effect of Reactor Material on made reactor than on that of the stainless steel NH3-S03 Reaction Material of Reactor ; Glass (•›) reactor. and Stainless Steel (• ) 3.6 Reaction mechanism Inital Concentrations ; SO2 (600 When gaseous mixture of SO2, NH3, NO, ppm), NH3 (1200 ppm), NO (225 oxygen and nitrogen with water was irradiated ppm), O2 (10%), H2O (10%) and in the glass-made reactor with light from a He- N3 (Balance) Ne laser (NEC : GLG5260) at the temperature at which the reactions proceeded and reaction observations that reactions of SO2 with NH3 products deposited on the surface of the reac doesn't take place in the gas-phase, but on the tor, scattering of the laser beam caused by surface of the reactor and the filter. Yager et aerosol was not observed in the gas-phase in al.1" obtained relationship between relative the reactor. In this case, the products formed humidity and the number of molecular layer of through reactions of SO2 with NH3 were uni water absorbed on glass and found that a formly deposited on the surface of the reactor molecular layer of water was formed at the and the filter. It may be confirmed from the relative humidity of about 50% and the mole-

"Highest Reaction Temperature" ; the highest temperature at which reactions of SO 2 with NH3 occur "Lowest Relative Humidity" ; the lowest relative humidity at which reactions of SO 2 with NH3 occur Initial Concentrations ; SO2 (600 ppm), NH3 (1200 ppm), NO (225 ppm), O2 (10%), H2O (3- 20%) and N2 (Balance) 149 Reactions of SO2 with NH3

Fig. 8 Reaction Mechanism cules of the water layer increased with relative 4. Conclusions humidity. In our experiments, the reactions did not occur without water and "the highest Reactions of SO2 with NH3 were studied in reaction temperature" was lower with lowering the gaseous mixture of 400-1800 ppm SO2, 1200 the concentration of water in gaseous mixture, or 1600 ppm NH3, 225 ppm NO, 10% oxygen as mentioned in the paragraph 3-1. Table 2 and nitrogen with and without water up to the showed "the highest reaction temperature" and concentration of 20% to clarify the characteris "the lowest relative humidity" for various tics of the reactions and its contribution to water concentrations ranging from 3 to 20%, removal of SO2 in the electron beam irradiation (where "the lowest relative humidity" was process for purification of flue gas. Following defined to be the lowest relative humidity at conclusions were drawn ; which reactions of SO, with NH3 were obser (1) the reactions proceed at reaction tempera ved in gaseous mixture). As can be seen in the ture lower than 65•Ž in the gaseous mixture table, "the lowest relative humidity" was obser with 10% water, ved to be higher with higher water concentra (2) the reactions proceed more with lowering tion. From the observations of Yager et al. reaction temperature and with increasing con and our experimental results, it can be consid- centration of water, ered that reactions of SO2 with NH3 take place (3) ammonium sulfate and sulfite, and ammo in water layer formed on the surface of the nium hydrogensulfate and hydrogensulfite are reactor and the filter as shown in Fig. 8. When considered to be main components of the reac reaction temperature becomes lower than a tion products, certain value and relative humidity becomes (4) the reactions may proceed in water higher than a certain value, water layer is for- absorbed on the surface of a reactor and a fiber med on the surface of the reactor and the filter. filter,

Then SO2 and NH3 are dissolved into the layer (5) It was confirmed by this experiments that as HS03-, SO32- and NH4+ ions. Some HSO3- some SO2 is removed through reactions with and SO32- ions are then oxidized to be HSO4- NH3 at the place of which temperature is lower and SO42- ions respectively in the presence of than 65•Ž in the electron beam irradiation proc- oxygen in the water layer. And these ions of ess for purification of flue gas. HSO3-, SO32-, HSO4- and SO42- may react with References NH4+ions to produce NH4HSO3, (NH4)2SO3, (NH4)2SO4 and NH4HSO4. 1) Tokunaga, O., H. Namba and N. Suzuki (1985) Enhancement of removal of SO2 and NOx by 150 HIROTA, NIINA, ANWAR, NAMBA, TOKUNAGA and TABATA

powdery materials in radiation treatment of phrosulphite prepared by gas-phase reactions. exhaust gases. Int. J. Appl. Radiat. Isot., 36, J. Chem. Soc., (A), 2461-2466. 807-812. 7) Scott, W. D. and D. Lamb (1970) Two solid 2) Namba, H., Y. Aoki, O. Tokunaga, R. Suzuki compounds which decompose into a common and S. Aoki (1988) Experimental evidence of vapor. Anhydrous reactions of ammonia and N2 formation from NO in simulated coal-fired sulfur dioxide. J. Amer. Chem. Soc., 92, 3943- flue gas by electron beam irradiation. Chem. 3946. Lett., 1465-1468. 8) Kiang, C. S., D. Stauffer and V. A. Mohnen 3) Namba, H., O. Tokunaga, R. Suzuki and S. (1973) Possibilites for atmospheric aerosol for Aoki (1990) Material balance of nitrogen and mation involving NH3. Nature Phys. Sci., 244, sulfur components in simulated flue gas treated 53-54. by an electron beam. Appl. Radiat. Isot., 41, 9) Carabine, M. D., E. L. Maddock and A. D. 569-573. Moore (1971) Particle size distributions in 4) Hartley, E. M. and M. J. Matteson (1975) aerosols formed from gaseous reaction. Nature Sulfur dioxide reaction with ammonia in Phys. Sci., 231, 18-19. humid air. Ind. Eng. Chem. Fundam., 14, 67-72. 10) Arrowsmith, A., A. B. Hedley and J. M. Beer 5) Landreth, R., R. G. de Pena, and J. Heicklen (1973) Particle formation from NH3- SO2- (1975) Thermodynamics of the reaction of H20- Air gas phase reactions. Nature Phys. ammonia and sulfur dioxide in the presence of Sci., 244, 104-105. water vapor. J. Phys. Chem., 79, 1785-1788. 11) Yager, W. A. and S. O. Morgan (1931) Surface 6) Scargill, D. (1971) Dissociation constants of leakage of pyrex glass. J. Phys. Chem., 35, 2026- anhydrous ammonium sulphite and ammonium 2042.

二酸 化 イオ ウ とア ンモ ニア の反応

広 田 耕 一・*・新 名 俊 明**・ エ リ ー ア ン ワ ー***・

南 波 秀 樹*・ 徳 永 興 公*・ 田 畑 米 穂**

(*日 本 原 子 力 研 究 所(高 崎 研 究 所)環 境 資 源 利 用 研 究 部,〒370-12群 馬 県 高 崎 市 綿 貫 町1233, **東 海 大 学 工 学 部,***イ ン ドネ シ ア 原 子 力 エ ネ ル ギ ー 庁)

摘 要

反 応 温 度 範 囲45～105℃,水 分 の 有 無 の 条 件 下 で,NO,酸 素 及 び 窒 素 の 混 合 ガ ス 中 の SO2とNH3の 反 応 に つ い て研 究 を行 な っ た。 この 反 応 は,水 分 存 在 下 で 反 応 温 度65℃ 以 下 に於 い て 起 り,こ の 反 応 に よ る 白 い 生 成 物 は反 応 容 器 及 び フ ィ ル タ ー 表 面 に 均一 に 付 着 し た。 こ の 生 成 物 を水 に溶 か して 分 析 し た 結 果,生 成 物 の 主 成 分 は硫 酸 ア ン モ ニ ウ ム,亜 硫 酸 ア ン モ ニ ウ ム,硫 酸 水 素 ア ン モ ニ ウ ム 及 び 亜 硫 酸 水 素 ア ンモ ニ ウム で あ る と考 え られ る。 こ の 反 応 は反 応 容 器 及 び フ ィル タ ー の表 面 に 吸 着 し た水 層 中 で 起 る と考 え られ る 。

キ ー ワ ー ド:二 酸 化 イ オ ウ,ア ン モ ニ ア,反 応,反 応 温 度,相 対 湿 度