Ind. Eng. Chem. Res. 1988,27, 1235-1241 1235

Friday, D. K.; LeVan, M. D. AZChE J. 1982,28,86. Friday, D. K.; LeVan, M. D. AZChE J. 1984, 30,679. Gelbin, D.; Bunke, G.; Wolff, H. J.; Neimass, J. Chem. Eng. Sci.

Grevillot, G.; Tondeur, D.; Dodds, J. A. J. Chromatogr. 1974, 102,

Helfferich, F.; Klein, G. Multicomponent Chromatography; Marcel

Hindmarsh, A. C. ACM-SIGNUM Newsletter 1980, 15(4), 10. James, D. H.; Phillips, C. S. G. J. Chem. SOC. 1954, 1954, 1066. Kumar, R.; Dissinger, G. R. Znd. Eng. Chem. Process Des. Dev. 1986,

25, 456. LeVan, M. D.; McAvoy, R. L., Jr.; Davis, M. M.; Dolan, W. B. In

Fundamentals of Adsorption; Liapis, A. I., Ed.; Engineering Foundation: New York, 1987, pp 349-358.

1983,38, 1993.

421.

Dekker: New York, 1970; pp 105-272.

Pan, C. Y.; Basmadjian, D. Chem. Eng. Sci. 1971, 26, 45.

Rhee, H. K.; Amundson, N. R. Chem. Eng. J. 1970, 1,241. Rhee, H. K.; Amundson, N. R. AZChE J. 1982, 28, 423. Rhee, H. K.; Aris, R.; Aumndson, N. R. Phil. Trans. R. SOC. 1970,

A267, 419. Rhee, H.-K.; Aris, R.; Amundson, N. R. First-Order Partial Differ-

ential Equations with Applications. Vol. I . Single Equations; Prentice-Hall: Englewood Cliffs, NJ, 1986.

Rhee, H. K.; Heerdt, E. D.; Amundson, N. R. Chem. Eng. J . 1972, 3, 22.

Richardson, L. F. Phil. Trans. R. SOC. 1927, 226, 199. Ruthven, D. M. AZChE J. 1978,24, 540. Ruthven, D. M. Principles of Adsorption and Adsorption Processes;

Wiley-Interscience: New York, 1984.

Received for review August 12, 1987 Accepted February 22, 1988

Absorption Characteristics of Sulfur Dioxide in Water in the Presence of a Corona Discharge

Niraj Vasishtha and Arun V. Someshwar* Department of Chemical Engineering, University of New Hampshire, Durham, New Hampshire 03824

The absorption characteristics of sulfur dioxide into a stagnant body of distilled water are investigated in the presence of point-plane ionic discharges in a closed chamber a t 30 f 0.1 "C. SO2 removal is seen to be enhanced when the liquid surface is subjected to the discharge, with the bulk of the enhancement resulting in acidic deposition within the chamber. Gas-phase oxidation of SO2 in the absence of liquid water is seen to be minimal. The effects of varying the discharge intensity and polarity and gas oxygen content on the observed absorption rate enhancements are reported.

The removal of sulfur dioxide from effluent gases emanating from coal-fired electric-generating plants in ways that are efficient and inexpensive continues to be a problem of paramount concern. Existing flue gas desul- furization (FGD) technologies make use of expensive scrubbers with alkaline reagents as the principal scrubbing medium. Extreme levels of corrosion caused by these reagents have necessitated the use of expensive corro- sion-resistant scrubber materials, resulting in high capital costs. The problem of waste disposal of the alkaline sludge is an additional unwelcome factor. In recent years, several researchers (Koppang, 1977; Pilat and Raemhild, 1977; Marks, 1970) have observed that when liquid water is sprayed from electrified nozzles its SO2 absorption capacity increases dramatically. While the experimental evidence presented by these authors points clearly in the direction of an advanced technique for SO2 removal, the precise nature of these charge-induced effects is as yet unclear. Considering that spray dryers using liquid reagents are still the dominant FGD method of operation, a further eluci- dation of the fundamental underlying parameters is im- perative.

Background Previous work related to enhanced, charge-induced, SOz

absorption can be grouped into three categories. The first category comprises mainly pilot-plant studies in which a liquid absorbent was sprayed from nozzles maintained at a high electric potential into a flowing gas stream con- taining SOz. Koppang (1977) and Pilat and Raemhild (1977), while working primarily with particulate emission control, found that charged liquid water droplets issuing from electrified nozzles were capable of removing sub- stantial amounts of SO2, far exceeding even that attrib- utable to saturation. Marks (1970) provides further ex- perimental evidence of the superior absorption capabilities of charged aerosols for certain noxious gaseous species.

0888-5885/88/2627-1235$01.50/0

The second category of researchers was primarily in- terested in accounting for possible enhancements in mass-transfer rates of SO2 absorption into liquid absor- bents. Uchigasaki et al. (1967) conducted a detailed lab- oratory study looking into the absorption of SOz (among other gases) into water and 1 N NaOH in a wetted wall column and in the presence of a wire-cylinder electric discharge. The SOz concentrations studied in this work were typically over 2 mol % or 20000 ppm, which far exceeds the levels commonly found in effluent gases from coal-fired power plants (typically 0 to 3000 ppm). This study was conducted under various conditions of discharge density, polarity, and SO2 and Oz content in the gas stream. On the basis of their results, the authors have suggested that the enhanced removal of SOz in a short-contact-time apparatus was due primarily to a vast improvement in the overall mass-transfer coefficient in the presence of the discharge. However, they also seem to indicate that the enhancement of the transfer coefficient is a strong function of the gas Oz content (being negligible in the absence of 0,) and that the discharge leads to partial oxidation of the SOz with the resulting HzS04 being detected in both the exiting gas and liquid phases. Uchigasaki and Endo (1969) and Asano and Uchigasaki (1970) have also reported on significantly enhanced absorption rates of SOz into other alkaline solutions such as N,N-dimethylamine and aqueous Ca(OH), solution. Sheldstad et al. (1974) have also cor- roborated the observations of increased absorption rates of SO2 into water and several other alkaline reagents in the presence of a wire-cylinder discharge identical with the one used by Uchigasaki et al. (1967). They concluded that the largest effect of the corona occurs in those liquids which give the highest absorption rate without corona (primarily the most alkaline liquids).

Carleson and Berg (1983) investigated the absorption of pure SO2 into water droplets formed by electrified nozzles in an attempt to observe any enhanced mass-

0 1988 American Chemical Society

1236 Ind. Eng. Chem. Res., Vol. 27, No. 7,1988

transfer rates resulting from surface-charge-induced in- ternal Circulation. Working in an oxygen-free atmosphere, they failed to detect any improvements in the coefficients due to the surface charge densities alone. What im- provements they did observe they attributed to the re- duced drop diameter (and hence increased surface area per unit mass) of the charged droplets issuing from electrified nozzles and increased velocities of these droplets while traversing in an externally applied electric field. Matteson and Giardina (1974) also looked into the absorption rates of SOz (750-4000 ppm) into growing droplets of electrically charged water. They concluded that the presence of the electrical charges provided for additional sites for SOz adsorption, which then increased the overall rate of ab- sorption during the initial stages of drop formation.

A third category of researchers have focused on the gas-phase oxidation of SOz in the presence of electric discharges. Matteson et al. (1972) have conducted a de- tailed study of the gas-phase oxidation of SOz (500-3000 ppm) in a humid, air mixture subjected to an electrical discharge. They were able to demonstrate that when the flowing, humid, air stream was subjected to a wire-cylinder discharge significant fractions of the SOz content were converted to an acid mist over a residence time of the order of minutes. They have also reported on various other observations such as the disappearance of ozone normally produced in the discharge in direct proportion to the SO2 removed, the role of gas oxygen content, and the apparent order of the SO2 oxidation reaction. Several other re- searchers have looked into the feasibility of using electrical discharges for the oxidation and subsequent removal of SOz (Palumbo and Fraas, 1971; Moyes and Smith, 1965; Glockler and Lind, 1939) from air. The general consensus is that discharge-induced gas-phase SOz oxidation is fea- sible, but the practicality of utilizing such a technique for the treatment of waste gases is in serious doubt. The need for an absorbing media such as water or other dilute al- kaline solutions therefore becomes imperative for desul- furization on a practical scale.

Present Work In the present work, the results obtained from the ab-

sorption of SOz into a stagnant body of distilled water, with the latter subjected to point corona discharges, are pres- ented. The corona discharge was produced at the tips of four needle points placed directly above the water surface. The SOz absorption was conducted in a closed chamber, with the initial gas-phase SOz content usually around 1600 ppm. Both negative and positive corona discharges were tested and the effects of varying the corona current density observed. The role of Oz content in the gas stream was also briefly studied. In the bulk of the experiments, gas- phase SOz concentration profiles (with time) during ab- sorption into a body of 30 cm3 of distilled water were generated, both with and without the imposed discharge. Several runs were also conducted specifically to account for the material balance of the initial input of SOz into the system at the end of a run. In order to estimate the role played solely by discharge-induced, gas-phase SO2 oxida- tion, tests were also conducted in the absence of a body of liquid water and for various levels of humidity in the closed chamber.

Experimental Section Figure 1 gives a schematic representation of the ex-

perimental setup. The absorption chamber consisted of a Pyrex dessicator (with an internal gas volume of about 6.24 L) which was fitted with a PVC top and maintained

Figure 1. Schematic representation of the experimental setup: (1) glass absorption chamber, (2) high-voltage electrode, (3) ground electrode, (4) Teflon tray with liquid sample, (5) corona needle electrode, (6) hypodermic needle, (7) circulation pump, (8) syringe pump, (9) pressure gauge, (10) electrometer, (11) high-voltage supply, (12) nitrogen, (13) temperature-controlled air bath, (14) septum, (15) temperature controller, (16) to liquid analysis, (17) to vacuum pump, and (18) to atmosphere.

in a temperature-controlled air furnace at 30 f 0.1 "C. A high-voltage supply (Spellman RHSR 25PN60) provided between 6 and 7 kV of potential to four stainless steel needle points in order to initiate the corona discharge. The discharge current was measured by a Keithley electrometer (Model 617). A syringe pump was used to deliver 30 cm3 of distilled water through a blunted hypodermic needle (22 gauge, stainless steel) into a Teflon tray placed directly beneath the needle points. A circulation pump was used to keep the gas mixture in the chamber fairly well mixed. A septum fitted to the chamber top allowed for the in- jection of pure SOz samples into the chamber and the extraction of well-mixed samples of the chamber gas at selected time intervals.

The experiments were conducted in three distinct con- figurations. These are depicted in Figure 2. In the type I configuration, no liquid body of water was present within the chamber. The discharge was created between the needle points and a grounded metal plate, and the effects of the discharge on the SOz concentration profile with time were recorded for several chamber humidity conditions. In the type I1 configuration, 30 cm3 of distilled water was placed in the Teflon tray. However, the tray was placed below the grounded metal plate, with the result that al- though liquid water was present in the chamber the ionic discharge traversed from the points to the plate without impinging on the water surface. In the type I11 configu- ration, the water was placed directly in the path of the discharge in between the points and the grounded metal plate, with the water itself being grounded. In this latter configuration, the water may be expected to have been significantly charged, although the measurement of this charge with the discharge being active has not been fea- sible. Also, a significant water mist is created by the bombardment of the ions on the water surface, generally leading to a displacement of about 3% of the water in the tray. On the basis of the power dissipated by the discharge and the circulation of the gases in the chamber, temper- ature rises in both the liquid water and the gases are ex- pected to be minimal.

Procedure. Prior to the start of a run, the chamber was evacuated over extended periods of time (several hours) after which room air was allowed to fill the chamber to a pressure slightly above atmospheric. Once temperature

Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988 1237

\ 2

‘ 2 4

I Figure 2. Electrode configuration types: (a, top) type I, (b, middle) type 11, (c, bottom) type 111; (1) high-voltage electrode, (2) ground electrode, (3) corona needle, (4) Teflon tray with liquid sample.

equilibrium had been achieved, a sample of pure SOz (generated separately) was injected into the chamber, the circulation pump turned on, and the experiment begun. At intervals of nearly every 20 min samples of the gas were extracted from the chamber and analyzed for their SO2 content. For type I1 and type I11 experiments, after about 50-min duration, distilled water was fed through the hy- podermic needle into the Teflon tray. For the “with discharge” runs, a t about t = 90 min the corona discharge was initiated and maintained at the required discharge intensity for the remainder of the experiment. At the end of a run (typically about 3-h duration), the liquid sample was analyzed for both dissolved SO2 and SO2 oxidized to

To conduct the liquid-side analysis, the water sample was siphoned out due to the slight positive pressure maintained in the system. This water was then split into two streams, one of which was fed directly into an analysis flask containing an iodine solution for iodometric analysis of the absorbed SO2 content. The other stream was fed to a similar flask which was subjected to vacuum (to ex- tract any dissolved SOz) and then titrated with a 0.01 N NaOH solution to determine the acid content of the water.

The gas-side measurement consisted of a dilution system capable of accurately diluting concentrated 5-mL gas samples (0-2000 ppm) extracted from the chamber with nitrogen down to levels measurable by a Thermoelectron (Model 43A) ambient, pulsed, flouroscent, SO2 analyzer. The purity of the SO2 samples injected at the beginning of each experiment was periodically checked on a gas chromatograph fitted with a Poropak QS column.

Typically, the above analyses provided the profile of gas-phase SO2 concentration with time and the sulfur content in the liquid phase at the end of a particular run. These profiles provided a qualitative picture of the roles of discharge current density, polarity, and gas Oz content

HzSOk

on the SOz absorption. They also indicated the extents to which gas-phase oxidation of the SO2 was taking place. To obtain a more quantitative picture of how the SOz distributed itself a t the end of a discharge application, a set of consecutive runs was conducted as above, each for a period of about 3 h, with the discharge being active for half this duration. From the material balance calculations, which included the categories of dissolved and oxidized SO2 in the liquid phase and SO2 remaining in the gas phase, it became apparent that significant portions of the SOz were unaccounted for during the discharge runs. Owing to repeated observations of significant mist for- mation in the chamber when the discharge was active and acidic corrosion of the chamber metallic parts, a second set of runs was then conducted with an additional analysis performed for possible acidic deposition on the glass chamber walls. Distilled water was used to rinse the glass walls of the chamber at the end of a run and the washings tested for acidity. Acidic depositions on the metallic electrode components and the Teflon circulation tubing were not tested for.

Results Type I Experiments. As previously mentioned, in the

absence of any liquid water within the chamber, these experiments were conducted to verify whether the point corona discharges utilized here were by themselves capable of oxidizing the SO2. Parts A, B, and C of Figure 3 rep- resent the SO2 concentration profiles with time for three levels of relative humidity, viz., (a) about 30%, (b) 4570, and (c) 63%, with and without a negative corona discharge (i = -50 PA). To obtain the desired humidity, air, hu- midified by a water bubbler, was fed into the chamber for over an hour and vented out through a humidity sensor (EG&G, Model 911). The feed was then discontinued and the humid air within the chamber circulated with the pump. The results for the type I runs seem to indicate that in the present case, wherein only small fractions of chamber gas (estimated to be less than 1%) are subjected to point discharges, the oxidation of SO2 to SO3 is indeed rather negligible. The gradual dip in the profiles with time, especially a t the higher humidities, may be attributed to the corrosion reactions on the various metallic components within the chamber. In spite of using type 316 stainless steel components as far as possible, the severe corrosive effects of moist, SOz-laden air could not be avoided.

Type I1 Experiments. In these runs, 30 cm3 of liquid water was placed below the grounded metal plate, with the result that the discharge did not impinge upon the water surface. Tests for the level of charging of the water at the end of the experiment confiimed the lack of any significant charging in this configuration. Although not measured (as humidity sensor was sensitive to acidic gaseous streams), the chamber humidity in these runs is expected to have been close to saturation for the bulk of the discharge ap- plication. Figure 4 represents the SO2 profiles generated with and without the ionic discharge for a current intensity of -50 FA. It is evident from this figure that even at extremely high levels of humidity SO2 oxidation reactions are negligible in the present configuration, in apparent contradiction to the findings of several investigators.

Figure 5 shows typical SO2 absorption profiles obtained for a 30-cm3 body of water placed within the chamber, in the absence of any discharge. These profiles, which were found to be quite reproducible, will be depicted as a “no- field” solid curve in later figures. The continued decline of the SO2 profile even after over 2 h of gas-liquid contact time may be attributed to primarily two factors, viz.; (a) the ongoing SO2 liquid-phase oxidation in the 02-rich en-

1238 Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988 ryrm-p-m

_______ 2000.0

1000.0

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Figure 3. (A, top) Dry chamber experiment [R.H. - 30%]. (B, middle) Humid chamber [R.H. 43.4-47.2%]. (C, bottom) Humid chamber [R.H. - 65%].

vironment, and (b) the corrosion reactions on the various metallic parts.

Type I11 Experiments. As shown in Figure 2, in the type I11 runs, the water was placed directly in the path of the discharge, with the water itself being grounded. Fig- ures 6, 7, and 8 show the SO2 profiles for negative dis- charges of i = -25, -50, and -75 MA, respectively. These runs were conducted with the gas phase comprised of air (0, content of 21%). The significant increase in the SO2 removal rate once the corona is initiated definitely points to some additional removal mechanisms being brought into play. Figure 9 provides a summary of the negative dis- charge effects a t various current densities.

200(1.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , , . . , . . . . , . . , . , , . , , ( , . , .

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Figure 4. Sulfur dioxide removal in type I1 corona discharge.

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Figure 6. Type I11 corona discharge [i = -25 PA].

Figures 10 and 11 show the absorption profiles for positive discharges of +25 and +50 MA, respectively. The lower solid curves in these figures correspond to the profiles for the negative discharge runs shown earlier. For similar current densities, both positive and negative discharges seem to yield similar results.

Finally, Figure 12 represents a brief investigation into the role of O2 in these type I11 runs. The profile corre- sponding to bottled N2 (containing <0.1% 0,) clearly represents a reduction in the discharge-induced effect. Increasing the O2 content to about 4.2% seems to enhance the SO2 removal rate.

Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988 1239

1 2 3 4 5 6 7 8 9

10

0 0 0

-25 -25 -50 -50 -75 -75 -75

183 184 183 179 181 185 181 186 181 187

39.75 35.95 36.48 28.32 29.61 23.93 24.91 20.10 20.21 17.90

Table I. SO2 Material Balance for Type I11 Runs liquid phase gas phase

total, % SOz, % unaccounted, % run i, PA time, min dissolved, % oxidized, %

11.87 51.62 54.89 -6.51 11.14 11.85 21.19 20.77 22.40 22.20 23.86 23.40 24.85

47.09 48.33 49.51 50.38 46.33 47.11 43.96 43.61 42.75

55.85 53.69 37.69 38.82 27.75 28.86 24.58 22.39 26.14

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Figure 8. Type I11 corona discharge [ i = -75 PA].

Runs To Determine Material Balance of the Sulfur Dioxide. As mentioned earlier, a series of experiments were conducted simultaneously with the specific intent of accounting for the initial input of SO2 at the end of about 3 h. The first set of such runs included three categories, viz., (i) dissolved SOz, (ii) oxidized SOz in the liquid, and, (iii) the remaining gas-phase SOz. Table I provides a summary of these calculations. From this table, it can be seen that in the presence of the electrical discharges sig- nificant fractions of the SOz input were found to be unaccounted for, with the unaccounted fractions increasing with increasing current densities. The percentage of SOz in the liquid that is oxidized nearly doubles in the presence of the discharge. However, surprisingly enough, the total SOz in the liquid phase does not change all that signifi- cantly.

Based on the repeated observations of significant mist formation in these runs, it was suspected that the unac-

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1240 Ind. Eng. Chem. Res., Vol. 27, No. 7, 1988

Table 11. SO2 Material Balance Including Chamber Washings ~ ~ ~ ~ ~ ~ ~ ~ _ _ _ _ ~ ~~~

liquid phase gas phase run i. uA time. min dissolved, 70 oxidized, 70 total lia, 70 SO,, 70 washings, 70 unaccounted, 70 13 -50 122 3.16 44.79 14 -50 126 3.80 46.88 15 -50 125 5.80 40.89 16 -50 12.8 3.38 40.45 17 -50 127 3.90 38.13 11 0 123 30.34 9.65 12 0 124 31.53 10.79

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Figure 12. Effect of % oxygen in air on type I11 runs.

counted SO2 was most likely in the form of SO2 acidified to H2S04 and deposited on the various internal surfaces of the absorption chamber and circulation tubing. A second set of runs was therefore conducted to include in the analysis a category for acidified SO2 in chamber washings. The glass walls of the chamber were washed down with water at the end of a run, and the washings were tested for acidity. Acidic deposits on other metallic com- ponents within the chamber and on the circulation tubing were not analyzed for due to the cumbersome procedure that this would have entailed. Table I1 provides the ma- terial balance with this new category included. In com- paring the numbers in Table I with those in Table 11, a note of caution is in order. The runs represented in Table I1 correspond to a gas circulation rate several times higher than the one used for those in Table I (about 0.5 L/min). This was due to a decision to replace all the l/*-in. tubing by ‘I4-in. tubing. Also, due to the higher circulation rates, the discharge was applied for only about a half hour, with the discharge initiated as before at about t = 90 min. The results in Table I1 clearly show that the bulk, if not all, of the unaccounted SO2 observed in Table I is in the form of acidic deposits on the chamber insides. The near total oxidation of the liquid-phase SO2 in runs corresponding to the discharge application is a direct result of the sig- nificantly higher gas circulation rate.

Discussion and Conclusions The goals of this study are 2-fold. In the first phase,

the results of which are presented here, the intent is to understand the role of discharges, and/or the intensely charged liquid interfaces resulting from the impingement of these discharges, on the conversion and subsequent removal of SO2 in gas mixtures, especially over relatively large residence times. The phenomena attendant with purely the transport rate of SO2 are not the object of this paper. The second phase of this study, which is presently ongoing, will look into the various factors that govern the enhancement in the rate of SOz absorption in short-con-

47.95 18.90 22.89 10.26 50.48 20.70 27.58 1.24 46.69 19.42 15.83 18.06 43.83 17.64 28.10 11.93

39.99 54.75 0.92 4.34 42.32 52.11 2.07 3.50

42.03 19.16 24.03 14.78

tact-time apparatus and across liquid interfaces charged either by being issued through electrified nozzles or by being subjected to a corona discharge.

The results presented here provide some interesting elucidation on the characteristics of SO2 absorption in the presence of electric charges (or discharges). The conclu- sions from the type I experiments point to the absence of any gas-phase oxidation mechanisms in the present elec- trode geometry. This is in seeming contradiction with the results of several researchers (Matteson et al., 1972; Pa- lumbo and Fraas, 1971) who have observed that significant SOz oxidation to SO3 could take place when a humid air stream is subjected to an electric discharge. The apparent discrepancy could be due to two reasons. The first con- cerns the fact that a very small fraction of the gas volume (<l%) is subjected to the discharge in the present ex- periments, as compared to nearly all of the gas in the above works. The second reason could be found in an interesting invention patented by Hoenig (1987). Here, the author demonstrates how when a partially saturated humid air stream flowing through a pipe is subjected to a corona discharge this results in condensation of the water vapor into microdroplets. The charged droplets are then driven to the ground electrode. Such a phenomenon is likely due to a redistribution of the water vapor concentration profiles when a humid stream is subjected to an ionic discharge (Someshwar and Peshori, 1987). This could account for the droplet formation so clearly observed in the work of Matteson et al. (1972). While the type I runs showed no signs of droplet formation (presumably due to the first reason), the type I11 runs always produced a significant mist within the chamber. This was due to the direct impingement of the discharge on the water surface. Thus, it would seem that for the removal of SO2 in a humid air stream the prior formation of water microdroplets, sig- nificantly charged by virtue of being in the path of the discharge, is quite essential. Furthermore, as the total mist formation in the present runs accounted for no more than about 3% of the initial water content in the tray, and hence less than about 2% of the total initial SO2 (see total SOz in liquid phase, Table 11), the fact that significantly higher amounts were detected in the washings points to another important observation, viz., that the bulk of the SO2 ox- idation was occurring on the charged droplet interface with the resulting SO3 combining readily with water vapor to yield the acidic deposition.

Matteson et al. (1972) have observed that the rate of oxidation of SO2 is about equal to the rate of disappearance of the ozone that would otherwise accumulate in the ab- sence of SOz. This result could not be confirmed here due to the difficulty of measuring ozone contents in extracted samples of 5 mL. However, with regard to the observation made by the above authors that the order of the SOz ox- idation reaction was close to zero, the results presented here seem to substantiate this. In Figures 6-9 the dif- ference in the slopes of the “with discharge” and “no-field“ SO2 profiles gives the rate of removal (ppm S02/minute) solely due to the discharge. This rate is fairly constant,

Ind. Eng. Chem. Res., Vol. 27, No. 7 , 1988 1241

Carleson, T. E.; Berg, J. C. Chem. Eng. Sci. 1983, 31, 871. Glockler, G.; Lind, S. C. “The Electrochemistry of Gases and Other

Hoenig, S. A. U.S. Patent 4670026, 1987. Koppang, R. R. Proceedings of the Workshop held at the Center for

Continuing Education, University of Notre Dame, Notre Dame, IN, April 20-22, 1977.

Dielectrics; Wiley: New York, 1939; sec. 8.16.

Marks, A. M. U.S. Patent 3 503 704 1970. Matteson, M. J.; Giardina, P. J. Enuiron. Sci. Technol. 8(1), 55. Matteson, M. J.; Stringer, H. L.; Busbee, W. L. Enuiron. Sci. Tech-

Moyes, A. J.; Smith, C. R. Chem. Eng. 1965, CE163. Palumbo, F. J.; Fraas, F. J. Air Pollut. Contr. Assoc. 1971,21(3), 143. Pilat, M.; Raemhild, G. A. Conference on Particulate Collection

Problems in the use of Electrostatic Precipitators in the Metal- lurgical Industry, Denver, 1977.

Shelstad, K. A.; Castle, G. S. P.; Kipp, E. B. AIChE Symp. Ser. 1974, 70(137), 88.

Someshwar, A. V.; Peshori, D. L. Chem. Eng. Commun. 1987,50,331. Uchigasaki, K. A.; Endo, K. Tohoku Daigaku Hisuiyoeki Kagaku

Uchigasaki, K. A.; Sugawara, M.; Takamatsu, T. J. Chem. Eng. Jpn.

nol. 1972, 6(10), 895.

Kenkyusho Hokoku 1969,29(1), 73.

1967, 31, 878.

irrespective of the chamber SOz content, and is only de- pendent on the intensity of the discharge. The precise implications of this are at present unclear, but it no doubt has an important bearing on the scheme of charge-induced oxidation reaction mechanisms.

Finally, the direct role of O2 is once again confirmed in this work, as is the conclusion that the nature of the po- larity of the discharge is immaterial with regard to the oxidation reaction. Also, it seems apparent that besides a charged liquid interface the presence of gaseous species produced in a discharge (such as O3 or atomic 0) is es- sential for the SOz oxidation reaction. However, this has to be verified by careful studies of the SO2-OZ reaction in a discharge-free gas phase and over a charged liquid in- terface, with the level of charge being comparable to that achieved by a discharge impingement.

Acknowledgment Financial support for this work provided by the National

Science Foundation Grant CBT-8505650 is gratefully ac- knowledged.

Literature Cited Asano, K.; Uchigasaki, K. Tohoku Daigaku Hisuiyoeki Kagaku

Kenkyusho Hokoku 1970,20(1), 43.

Received for review September 14, 1987 Revised manuscript received February 23, 1988

Accepted March 7, 1988