Envlron. Sci. Technol, 1987, 21, 266-272
Laxen for discussions. We also thank the staff of the Associated Octel Co., Ellesmere Port, U.K., for their discussions, practical assistance, interest, and encouragement. Registry No. Pb, 7439-92-1. Literature Cited (1) Wong, P. T. S.; Chau, Y. K.; Luxon, P. L. Nature (London) 1975,253, 263-264. (2) Thompson, J. A. J.; Crerar, J. A. Mar. Pollut. Bull. 1980, 11. 251-253. Rhode, S. F.; Weber, J. H. Environ. Technol. Lett. 1984, 5, 63-68. Harrison, R. M.; Laxen, D. P. H. Nature (London)1978, 275, 738-740. De Jonghe, W. R. A.; Adams, F. C. Talanta 1982, 29, 1057-1067. Harrison, R. M.; Laxen, D. P. H. Environ. Sci. Technol. 1978,12, 1384-1392. Chester, R.; Sharples,E. J.; Murphy, K.; Saydam, A. C.; Sanders, G. S. Mar. Chem. 1983,13, 57-72. Duce, R. A.; Arimoto, R.; Ray, B. J.; Unni, C. K.; Harder, P. J. J. Geophys. Res., C: Oceans Atmos. 1983, 88(9), 5321-5342. Lannefors, H.; Hanson, H. C.; Granat, L. Atmos. Environ. 1983, 17, 87-101. Patterson, C. C.; Settle, D.; Schank, B.; Burnett, M. In Marine Pollutant Transfer;Windom, H. L.; Duce, R. A., Ed.; Lexington Books: Lexington, MA, 1976. Harrison, R. M.; Radojevic, M.; Hewitt, C. N. Sci. Total Enuiron. 1985, 44, 235-244. Hewitt, C. N.; Harrison, R. M. Anal. Chim. Acta 1985,167, 227-287. Nielsen, T.; Egsgaard, H.; Larsen, E.; Schroll, G. Anal. Chim. Acta 1981, 124, 1-13.
(14) De Jonghe, W. R. A.; Chakraborti,D.; Adams, F. C. Environ. Sci. Technol. 1981, 15, 1217-1222. (15) Jiang, S.; Ma, C.; Ge, J.; Li, M.; Adams, F. C.; Winchester, J. W. Atmos. Environ. 1984, 28, 2553-2556. (16) Birch, J.; Harrison, R. M.; Laxen, D. P. H. Sci. Total Enuiron. 1980, 14, 31-42. (17) Sturges, W. Ph.D. Thesis, University of Lancaster, U.K., 1984. (18) Harrison, R. M.; Williams, C. R. Atmos. Environ. 1982, 16, 2669-2681. (19) Sykes, R. I.; Hatton, L. Atmos. Environ. 1976,10,925-934. (20) Smith, F. B.; Hunt, R. D. Atmos. Environ. 1978,12,461-477. (21) Hewitt, C. N.; Harrison, R. M. Proceedings o f the International Conference on Heavy Metals in the Environment, Athens, 1985; CEP Consultants: Edinburgh, 1985; pp 171-173. (22) Hewitt, C. N.; Harrison, R. M. Environ. Sci. Technol. 1986, 20, 797-802. (23) Hewitt, C. N.; Harrison, R. M. Atmos. Environ. 1985,19, 545-554. (24) Moore, H. E.; Poet, S. E.; Martell, E. A. Enuiron. Sci. Technol. 1976, 10, 586-591. (25) Junge, C. E. Air Chemistry and Radioactivity;Academic: New York, 1963. (26) Hewitt, C. N. Ph.D. Thesis, University of Lancaster, U.K., 1985. (27) Jarvie, A. W. P.; Markall, R. N.; Potter, H. R. Nature (London) 1985,255, 217-218. (28) Reisinger, K.; Stoeppler, M.; Nurnberg, H. W. Nature (London)1981,291, 228-229.
Received for review April 29, 1986. Accepted October 21, 1986. Financial support was provided by the Natural Environment Research Council, U.K., with assistance from The Associated Octel Co., Ltd., U.K.
Oxidative Degradation of Organic Acid Conjugated with Sulfite Oxidation in Flue Gas Desulfurization: Products, Kinetics, and Mechanism7 Y. Joseph Lee and Gary T. Rochelle" Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712
Organic acid degradation conjugated with sulfite oxidation has been studied under flue gas desulfurization (FGD) conditions. The oxidative degradation constantklz is defined as the ratio of organic acid degradation rate and sulfite oxidation rate times the ratio of the concentration of dissolved S(1V) and organic acid. It is not significantly affected by pH or dissolved oxygen in the absence of manganese or iron. However, itlz is increased by certain transition metals such as Fe, Co, and Ni and is decreased by Mn and halides. Lower dissolved S(IV)magnifies these effects. A free radical mechanism was proposed to describe the kinetics. Hydroxy and sulfonated carboxylic acids degrade approximately 3 times slower than saturated dicarboxylic acids, while maleic acid, an unsaturated dicarboxylic acid, degraded an order of magnitude faster. A wide spectrum of degradation products of adipic acid were found, including carounds, and hydrocarbons. H
Introduction
Currently, limestone slurry scrubbing is the dominant commercial technology for flue gas desulfurization (FGD). Presented at 189th National Meeting of the American Chemical Society, Miami Beach, March 1985. 286
Environ. Scl. Technol., Vol. 21, No. 3, 1987
The performance of limestone scrubbing is chemically limited by two pH extremes: (a) low pH near the gas/ liquid interface, which decreases the solubility and absorption rate of SO,; (b) high pH near the liquid/solid interface, which decreases the solubility and dissolution rate of limestone (1). Organic acids that buffer between pH 3.0 and pH 5.5 enhance SOz removal efficiency and limestone utilization at concentrations of 5-10 mM (2). Adipic acid was the first organic acid buffer additive successfully and generally applied to FGD processes up to commercial scale (3, 4). It has been replaced commercially by dibasic waste acid (DBA), a waste from adipic acid and cyclohexanone production, containing primarily adipic, glutaric, and succinic acids. DBA was found to be as effective as adipic acid (2, 3 ) . Other potential alternatives include hydroxy carboxylic acids and sulfonated carboxylic acids (4). They are of interest because of reduced volatility and potentially lower degradation rates. In addition to the expected loss of organic acid additive by entrainment of solution in waste solids, loss by chemical degradation and coprecipitation is also observed (2). Chemical degradation, which is conjugated with sulfite oxidation (5))is the most important mechanism of buffer loss under forced oxidation conditions (2, 3 ) . Assuming that both oxidation and degradation are free radical reactions proceeding by a common radical, Rochelle
0013-936X/87/0921-0266$01.50/0
0 1987 American Chemical Soclety
Table I. Steady-State Solution Composition in CaSOJ Slurry as a Function of pH: Closed Reactor, 55 "C, No Organic Acid pH
Fe, mM"
4.0 4.0 4.5 4.5 5.0 5.0 5.6 5.5
0.15 0.13 0.12 0.12 0.02 0.02 CO.01
