Environ. Sci. Techno/. 1995, 29, 216-221
Kinetics of Acetic Acid Oxidation in Supercritical Water PHILLIP E . S A V A G E * A N D M I C H A E L A . SMITH Chemical Engineering Department, University of Michigan,
Ann Arbor, Michigan 48109-2136
Acetic acid was oxidized in supercritical water in batch microreactors at temperatures between 380 and 440 "C. The acetic acid concentrations ranged from 1.0 x to 5.2 x M, the oxygen to 7.1 x concentrations ranged from 5.7 x M, and the water density ranged from 6.7 to 25 M. Oxygen was always present in at least 3.5 times the stoichiometric amount required for complete oxidation. Analysis of the kinetics data showed that the global oxidation rate law was first order in acetic acid, 0.6 order in oxygen, and second order in water. The global rate constant has a pre-exponential factor M-2.6s-' and an activation energy of 73.6 of kcal/mol. This rate law also satisfactorily describes other sets of experimental data in the literature for the oxidation of acetic acid in supercritical water.
Introduction Supercritical water oxidation (SCWO) is a waste treatment technology being developed for the ultimate destruction of organic materials and especially organic compounds in aqueous waste streams. It is being explored for potential applications in treating mixed wastes ( I ) , military wastes (2),organic wastes generated during manned space missions (3),and a variety of industrial wastes (4). The technology involves the complete oxidation of organic compounds in an aqueous phase at conditions that exceed the critical point (T, = 374 "C, Pc = 218 atm) of water. Supercritical conditions are attractive because organic compounds, oxygen, and water can exist in a single, homogeneous fluid phase. Consequently, the rapid oxidation reactions can occur unfettered by the interphase transport limitations that occur at subcritical conditions where multiple phases exist. The development and rational design, optimization, control, and evaluation of any reactive process requires a knowledge of the governing reaction kinetics. Many research groups have recognized this need, and several SCWO kineticsstudies have been reported in the last several years. Global reaction rate laws are now available in the literature for the oxidation ofrepresentative pollutants such as phenol, chlorophenol, and pyridine in supercriticalwater (5-9). Savage et al. (10) discuss current work on SCWO kinetics in their review paper on reactions in supercritical fluids. Acetic acid is a common product from wet-air oxidation, and it is thought to be difficult to oxidize. In fact, Li et al. (11)proposed a simple but general reaction network for SCWO that identifies acetic acid as a key refractory intermediate that significantly influences the overall oxidation kinetics. Given this significance of acetic acid, it is not surprising that its behavior under SCWO conditions has received attention from several research groups (2,12-16) and that some kinetics data are available. Wightman (12) was the first to oxidize acetic acid at supercritical conditions, and he used high pressures of around 400 atm. He reported results from seven experiments and correlated these data with a global rate law that was first order in both acetic acid and oxygen. These reaction orders were assumed, however, and not determined experimentally. Nevertheless, until our work reported herein, Wightman's rate law had been the only one available for SCWO of acetic acid using 0 2 , and Li et al. (11) proposed its use in their reaction network. Gloyna and co-workers also oxidized acetic acid in supercritical water, but most of their work employed hydrogen peroxide or potassium permanganate as the oxidants (13-15). Lee (13), for example, reported a rate law for SCWO of acetic acid using H202 as the oxidant. Additionally, Lee et al. (14) and Chang et al. (15) did not measure the acetic acid concentration, but rather used the total organic carbon (TOC) reduction as the dependent variable in their work. Lee et al. (14) reported limited data for the SCWO of acetic acid with oxygen at 400, 450, and 500 "C. They briefly examined the effects of the oxygen * Corresponding author; FAX: (313) 763-0459; e-mail address:
[email protected].
216 ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 1,1995
0013-936X/95/0929-0216$09.00/0
@ 1994 American Chemical Society
concentration and the water density. They found that the TOC reduction increased as the oxygen concentration increased, but their data did not show a clear trend for the effect of the water density. Interestingly, Lee et al. (14) report that temperature had only a modest effect on the SCWO of acetic acid. The TOC reduction was 65% for reactions at both 450 and 500 "C and at otherwise identical conditions. The work of Lee et al. (14) and Chang et al. (15) provides some insight into the qualitative behavior of this system, but it does not provide a quantitative reaction rate law for SCWO of acetic acid with oxygen as the oxidant. Boock and Klein (16)reported initial oxidationrates and pseudo-first-order rate coefficients for six SCWO experiments with acetic acid. All of their experiments were accomplished at the same oxygen and water concentrations, so their data provide no information about the effects of these variables. The data reported by these authors show a large effect of the acetic acid concentration on the oxidation kinetics at 380 "C, but no statistically significant effect at 400 "C. If the trends in these limited data are correct, the global oxidation reaction is about 3.5 order in acetic acid at 380 "C, but first order at 400 "C. Boock and Klein also obtained an anomalouslylow activation energy. The authors pointed out that their quantitative kinetics results may have been influenced by the induction period of the autocatalytic oxidation reaction. Finally, Rice et al. (2) also oxidized acetic acid in supercritical water as part of a comparative study of the oxidative destruction of several different compounds. Their data did not permit development of a rate law for acetic acid. Their data were interesting, however, in that they showed that acetic acid reacted more rapidythan did other compounds they investigated (e.g., phenol). The authors pointed out, however, that disappearance of the reactant is only part of the story. One needs also to consider the rate of destruction of TOC to evaluate the technology fully and to determine which compounds are most difficult to treat by SCWO. The previous experimental investigations into acetic acid oxidation in supercritical water have provided some kinetics data and some information about qualitative trends, but they have not provided a quantitative global reaction rate law for this important compound. In this paper, we report the results ofkinetics experiments that allowed us to develop a quantitative rate law for SCWO of acetic acid using oxygen as the oxidant.
Experimental Section All chemicals used in this research were obtained commercially and used as received. The water was distilled and deionized prior to use in the experiments. The batch microreactors, which were fabricated from stainless steel Swagelok tube fittings, had an intemal volume of 2.0 cm3. The reactor comprised a318-in. port connector sealed with 318411. caps at both ends. In a few experiments we used a modified version of this reactor that had a 318in. cap at one end and a 318-in. to 1/8-in. reducing union at the opposite end. A short length of 1/8-in. 0.d. tubing connected the reactor body to a Whitey severe-service shutoff valve. A Swagelok quick-connect was attached to the other end of the valve. The matching end of the quickconnect was part of a gas distribution system used to load high-pressure oxygen into the reactor. A carefully measured volume of a previously prepared aqueous stock solution of acetic acid in a known concen-
tration was added to the reactor using a microliter syringe. The reactor was then sealed. The reactor headspace contained room air at ambient conditions in most experiments, but in a few experiments we loaded the reactors in an oxygen-filledglovebag so that the headspace contained pure oxygen rather than air. We also conducted a few experiments in which high-pressure oxygen was added to the reactor as described in the preceding paragraph. In all cases, the number of moles of oxygen present in the reactor was calculated using the ideal gas law. Since a single, homogeneousfluid phase exists at the supercritical reaction conditions employed, the amount of stock solution added to the reactor determines the water density and the initial concentration of acetic acid at reaction conditions. The loaded and sealed reactors were immersed in an isothermal fluidized sand bath preheated at the desired reaction temperature. We estimate the reactor heatup time to be 1-2 min based on experimentalmeasurements. After the desired batch holding time (typically 15 min) had elapsed, the reactors were removed from the sand bath and rapidly cooled to room temperature in a water bath. The cool reactors were then opened, and the reactor contents were recovered. The reactor contents were analyzed by high-performance liquid chromatography(HPLC). We used a Spectra-Physics instrument with UV detection at 210 nm for the routine quantitative analysis. The HPLC was equipped with a Supelcogel C610H organic acids column (30 cm x 7.8 mm i,d.), and a 0.1% H3P04 aqueous solution served as the mobile phase. A set of acetic acid solutions with known concentrations was run through the HPLC to establish a quantitative correlation between peak areas and acetic acid concentrationsand to verify that this correlation was linear over the range of concentrations of interest. The acetic acid conversion was calculated as 1 - [HOAcl/[HOAcl, where [HOAc]represents the acetic acid concentration after reaction and [HOAcl, is the initial concentration in the reactor. All experiments were repeated at least twice, and the average results were used in the kinetics analysis.
Results and Discussion In this section, we present experimental results from the SCWO of acetic acid and then use these results to determine the parameters in a global oxidation rate law. We also test the ability of the rate law to predict results reported in the literature for acetic acid oxidation in supercritical water. Kinetics of Acetic Acid Oxidation in SupercriticalWater. Four different sets of experiments were conducted to determine the parameters in the global power-law rate expression of eq 1:
(3
rate = A exp - [HOAcl"[O,lb~H,Olc
(1)
A and Ea are the Arrhenius pre-exponential factor and activation energy, respectively, and the quantities in brackets are concentrations. We determined the acetic acid reaction order from a set of experimentsinwhich the acetic acid concentration was varied and all other concentrations and the temperature were held constant. Likewise, we determined the oxygen reaction order from a set of experiments in which the oxygen concentration was varied and all other concentrations and the temperature were held constant. The water reaction order was determined from a set of experiments in which the water loading (density) VOL. 29, NO. 1, 1995 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
217
-7
n.
-"."
-7.21
-5.5/
-7.4j -7.6
5 -8.0 -8.2
-8.41
-8.6
-8.81 -10.0 -9.5 -9.0 -8.5 -8.0 -7.5 -7.0 -6.5 -6.0 In [HOAcl (moVliter) FIGURE 1. Effect of the acetic acid concentration on the kinetics of acetic acid oxidation in supercritical water. Reaction conditions were 400 "C, 15 min, [HzOI = 9.25 M, and [Ode = 0.007 M.
was varied. Although the effect of the water density on the reaction rate is being modeled by a power-law term in eq 1, it is important to recognize that we are not implying that the sole role of water is to serve as a reactant. Rather, the water density can also influence the global reaction rate by altering density-dependent properties ( 17) or by altering the rates of density-dependent elementary reactions (18). Finally, the Arrhenius parameters were determined from global rate constants obtained at different temperatures. The presentation of results that follows discusses the experimental results and the data analysis more fully. We conducted a set of experiments at seven different initial acetic acid concentrations and at 400 "C for a batch holding time (t) of 15 min. The water density at these reaction conditions was 9.25 M, and the oxygen concentration was 0.00715 M. The steam tables (19)give the system pressure as 250 bar at these reaction conditions. Using the steam tables to obtain an estimate of the system pressure is reasonable because the reaction mixture was always at least 99.4 mol % water. We calculated the conversion and then a pseudo-firstorder rate constant, k',for each experiment as -In(l - X ) t The pseudo-first-order rate constant in eq 2 is then related to the intrinsic rate constant, k, and the true reaction order, a, by the approximate relationship below
K=
k' = k[HOAcln~'[O,l~[H,Ol~
(3)
[HOAc] is the mean concentration of acetic acid in the reactor during the course of an experiment. Since the oxygen and water concentrations and the temperature were the same for all experiments in this set, the pseudo-firstorder rate constant will vary in these experiments only if the reaction order for acetic acid is not equal to unity. Moreover, the global reaction order for acetic acid can be estimated from the slope of a line fit through the experimental data for k vs [HOAc] on a log-log plot. Figure 1 displays the results of these experiments as a log-log plot of the pseudo-first-order rate constant cal218
ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29, NO. 1, 1995
-9.0 -6.0 -5.5 -5.0 -4.5 -4.0 -3.5 -3.0 -2.5 -5 In LO21 (moyliter)
,o
FIGURE 2. Effect of the oxygen concentration on the kinetics of acetic acid oxidation in supercritical water. Reaction conditions were 400 "C, 15 min., [HzOl = 9.25 M, and [HOAc10 = 0.001 M.
culated at each of the initial acetic acid concentrations. The run-to-runvariabilityinthese rate constants waswithin 425% of the mean values reported in Figure 1with the sole exception of the rate constants at the lowest acetic acid concentration. Here the range about the mean value reached 4~50%for a few experiments. The data in Figure 1 show some scatter, and a linear regression of the data reveals a modest upward trend. This trend indicates that the reaction is slightly greater than first order in acetic acid. The slope, m,of the line in Figure 1 is 0.08 & 0.09, where the stated uncertainty is the standard error of the estimate of the slope. The acetic acid reaction order, which is m 1, is thus 1.08 f 0.09. In recognition of the experimental and statistical uncertainty and to s i m p l e the remaining kinetics analysis, we will take the global reaction order for acetic acid to be equal to unity. The quantitative error in the approximation in eq 3 depends on the conversion and the true reaction order. The approximate relationship is most reliable when the true reaction order is close to unity and when the conversion is low. The appendix provides information that allows one to determine this error quantitatively. For the present data for SCWO of acetic acid, the conversions were between 23 and 32%,and the true reaction order was determined to be 1.08. Usingthese values,we find that the differencebetween the approximate solution we used (eq 3) and the exact analytical solution is only 0.14%. We next conducted aset of experiments at three different initial oxygen concentrations and at 400 "C for a batch holding time of 15 min. The water density at reaction conditions was 9.25 M, and the initial acetic acid concentration was 0.0010 M. The three different oxygen concentrations were obtained by filing the reactor headspace with room air, with pure oxygen at ambient conditions, and with pure oxygen at an elevated pressure (23psi). We then used the acetic acid conversions obtained in each experiment to calculate first-order rate constants for each run after eq 2. Figure 2 shows the effect of the initial oxygen concentration on the acetic acid oxidation kinetics. It is clear that higher oxygen concentrations give larger rate constants. Linear regression of the data in Figure 2 leads to a slope (oxygen
+
TABLE 1
Rate Constants for SCWO of Acetic Acid
-2.51
temp 4°C)
[HOAcl (M)
[Od
[HzOl
(M)
(M)
380 380 390 400 4OOa 420 430 440
0.0033 0.0042 0.0050 0.0050
0.023 0.029 0.032 0.035
25.0 16.7 12.0 9.3
0.0052 0.0011 0.0011
0.036 0.0075 0.0075
7.3 6.7 6.7
k (M-"s-')
95% Clb (YOof k)
6.5 x 2.1 x 3.8 x 1.4 x 1.0 10-4 3.5 x 8.0 x 1.5 x
16 43 19 20 12 11 10 16
no. of expts
8 6 16 9 30 5 6 3
'This rateconstant isa meanvaluedeterminedfrom theexperimental results reported in Figures 1-4. Confidence interval.
1.6
1.8 2.0 2.2 2.4 2.6 In [H201 (moVliter)
2.8
3.0
FIGURE 3. Effect of the water density on the kinetics of acetic acid oxidation in supercritical water. Reaction conditions were 400 "C, and 15 min.
reaction order) of 0.64 with a standard error of 0.17. This estimate of the oxygen reaction order is dependent on the value of the acetic acid reaction order. For example, if we take the acetic acid reaction order to be 1.17 (the upper bound from the result in Figure 1)rather than 1.0,we obtain an oxygen reaction order of 0.69 with a standard error of 0.20 from the present data. This difference in the estimated oxygen reaction orders is small, however, when compared with the uncertainties in the estimates. Given this uncertainty in the estimated oxygen reaction order, we will retain only one significant figure and take the global reaction order for oxygen to be 0.6. We determined the global reaction order for water by conducting aset of experimentsat 400 "C for a batch holding time of 15 min but with different water loadings. The water concentrations at reaction conditions ranged from 6.7 to 18.5 M. The oxygen concentration also varied in these experiments because the reactor headspace available for room air decreased as the water loading increased. We used the experimentally determined acetic acid conversions and the oxygen reaction order of 0.6 to calculate the apparent global rate constant K' as
IC'=
-ln(l - X )
= k[H,OIC
(4)
[0,10%
Figure 3 shows the variation of this rate constant with the water concentration on a log-log plot. The slope of the line that best describes these data provides the global reaction order for water. Linear regression of the data in Figure 3 leads to a slope of 2.0 with a standard error of 0.23. Thus, we take the water reaction order to be 2.0. Having determined the reaction orders in the global rate law for acetic acid oxidation in supercritical water, we next sought to express the rate constant in Arrhenius form. To accomplish this goal, we conducted sets of oxidation experiments at 380, 390, 400, 420, 430, and 440 "C. The experiments at 380, 390, 400, and 420 "C provided acetic acid conversions at at least five different batch holding times for otherwiseidentical reaction conditions. We used linear regression to determine the best value of the intrinsic
0.0013
0.0014
0.0015
0
16
l/Temp (K) FIGURE 4. Arrhenius plot for SCWO of acetic acid. Table 1 gives the reaction conditions.
reaction rate constant at each temperature. Table 1 provides the experimental results. The uncertainties (95% confidence intervals) in these rate constants exceeded f20% of the value reported for the rate constant in only one case. This exception is the rate constant determined at 380 "C and a 16.7 M water concentration, where the 95% confidence interval was f43% of the reported value. The experiments at 430 and 440 "Cprovided multiple measurements of the acetic acid conversion at identical reaction conditions that included a single batch holding time of 15 min. The mean conversion was used to calculate the rate constants given in Table 1. Again, the uncertainties in the rate constants were within &20% of the reported value. Figure 4 provides an Arrhenius plot of the kinetics data. Linear regression of the data in Figure 4 leads to an activation energy of 73.6 kcal/mol and a pre-exponential factor of 1019.8 M-2.6s-l. Combining the foregoing elements, we find that the rate law of eq 5 best describes our experimental data for acetic acid oxidation in supercritical water:
rate =
-73 600 e x p ( 7 )[HOAcl'~o[0,10~6[H,012~0 (5)
The concentrations are in mol/L, the activation energy is in cal/mol, and the rate is in mol L-' s-l. Comparison with Prevlous Work. As noted in the introduction to this paper, the literature does provide some VOL. 29, NO. 1, 1995 /ENVIRONMENTAL SCIENCE & TECHNOLOGY
219
conversion based on the disappearance of the acetic acid because acetic acid can be transformed to other organic intermediates before it is ultimately transformed to C02. Therefore, the rate constants calculated from the data of Lee et al. for TOC disappearance should be lower than the rate constants predicted by our rate law for acetic acid disappearance. Overall, we conclude that the kinetics predicted by the rate law in eq 5 are in good agreement with experimental data reported by others for the SCWO of acetic acid. Therefore, it appears that the rate law can be extrapolated to temperatures and water densities that are both higher and lower than those used to determine its parameters.
\
-141
B -16,'
~
~
,
,
,
I 1
.
"
'
Summary and Conclusions ~
0.0012 0.0013 0.0014 0.0015 0.0016 0.0017 l/Temp (K) FIGURE 5. Comparison of rate constants for SCWO of acetic acid calculated from rate law of eq 5 (solid line) from literature data [circles, Wightman (12); squares, Boock and Klein (16); unfilled triangles,Chang et al. (15);diamonds, Lee et al. (14);invertedtriangles, Rice etal. (dland from the present experimentaldata (filledtriangles).
previous reports of acetic acid oxidation in supercritical water. These reports provide some kinetics datawith which we can compare the rate law in eq 5. The data are typically reported in terms of a conversion achieved at a specific set of reaction conditions. We used these reported conversions to calculate the rate constant according to eq 6, which applies for reactions conducted in isothermal batch or plugflow reactors under conditions where the oxygen and water concentrations are essentially constant:
k=
-ln(l - X ) [0,1~1H2012~0t
Figure 5 is an Arrhenius plot that shows the rate constants calculated from literature data using our rate law as shown in eq 6. Table 2 gives the experimental conditions employed in these different studies. The solid line in Figure 5 gives rate constants calculated from our Arrhenius parameters. It is clear that the data of Rice et al. (Z), Wightman (12),and Chang et al. (15)are in good accord with the rate law of eq 5. The data of Boock and Klein (16) follow the rate law at low temperatures but remain well below the line at higher temperatures. Boock and Klein noted that their kinetics data were not consistent with other investigators. They suggested that the induction period, which often accompanies autoxidation reactions, may have affected the initial rates they reported and caused them to differ from other investigations. We also note that Boock and Klein used an oxygen concentration that was much higher than that used in any of the other studies. Perhaps this higher concentration has an effect on the reaction kinetics that is not captured in eq 5. The rate constants calculated from the data of Lee et al. (14) are also all lower than the values expected from the Arrhenius expression we obtained, but the agreement is better than that shown by the data of Boock and Klein. We note that Lee et al. did not analyze for acetic acid directly, but rather they used the total organic carbon content of the treated material to calculate the conversion. The conversion based on TOC reduction will always be less than the 220
ENVIRONMENTAL SCIENCE &TECHNOLOGY / VOL. 29. NO. 1, 1995
Acetic acid oxidation in supercritical water under the conditions employed in our experiments is first order in acetic acid, 0.6 order in oxygen, and second order in water. The activation energy is 73.6 kcallmol. This rate law gives a good correlation of our experimental results, and it also adequately describes several other sets of kinetics data in the literature obtained under different experimental conditions. ~
'
~
~
Acknowledgments Several undergraduate students at the University of Michigan (Kevin Buck, Michael Nielson, Spiro Vamvakas, and Jodi Murlick) conducted some of the acetic acid oxidation experiments. Sudhama Gopalan and Chris Martino provided advice and assistance with the experiments and the HPLC analyses. This project was supported by the National Science Foundation through Grant CTS-9015738 with its REU supplements and by the Department of Energy (DEFG22-92PC92536)and the Environmental Protection Agency (R817857-01-0).
Appendix: Comparison of Approximate Relation in Eq 2 and Exact Analytical Solution The differential equation that describes the disappearance of the reactant during a reaction in an isothermal, constantvolume batch reactor is dCldt = - k C (A.1) where C is the reactant concentration, k is the true rate constant, and a is the true reaction order. This differential equation can be solved exactly, and the analytical solution is
[
ln(1 - X) = 1 lnl-1-a ln(1 - X) = -kt
~~~~k~
for a t 1
fora= 1 (A.2) where X is the conversion and C, is the initial reactant concentration. When we calculate pseudo-first-order rate constants in eqs 2 and 3, we are implicitly assuming that C does not change much during the reaction so that dC-- -kC == -(keP-')C = -k'C
where
dt is the mean concentration, given as
(A.3)
Integrating the differential equation in eq A.3 with the
TABLE 2
Summary of Experimental Conditions for SCWO of Acetic Acid this work Wightman ( 70) Rice et at. (2) Lee et at. ( 72) Chang et al. ( 7 3 ) Boock and Klein ( 74)
temp ("C)
[Od (M)
[ H A (MI
[HOAcl (M)
380-440 338-445 441-532 400-500
0.0057-0.071 0.0068-0.0195 0.033-0.048 0.01-0.05 0.006-0.1 15 1.12
6.7-25 16.1-38.6 5.0-7.2 8.33,19.4 16.7 7.94
0.0001-0.0052 0.002-0.006 0.0075-0.011 0.005 0.005 0.00036-0.06
400
350-500
TABLE 3
Error (%) in Approximate Solution for Different Combinations of the Reaction Order (a) and Conversion (X) X
0.1 0.2 0.3 0.4 0.5 0.7
8
= 0.5
0.058 0.26 0.66 1.33 2.41 6.81
= 0.75
a = 1.5
a=2
0.032 0.14 0.36 0.74 1.34 3.83
-0.08 -0.363 -0.928 - 1 .go -3.50 - 10.6
-0.18 -0.83 -2.1 -4.4 -8.2 -26
8
average concentration taken to be constant then gives
calculations using eq A.8 for different reaction orders and conversions.
Notations A a b c Ea
k,K,V' M
PC R T
The purpose of this appendix is to identify the conditions required for this assumption to be a good one and to show that the experimental conditions employed in this research meet those criteria. We define the error in the approximate solution to be % error =
exact solution - approximate solution x 100 (A.6) exact solution Both the approximate (eq A.5) and exact (eq A.2) solutions are given above in a form where the right-hand side is equal to ln(1- X ) . Using the exact and approximate relations for ln(1 - X ) , we can write the error as % error =
x 100 (A.7) Using eq A.2 to eliminate the explicit appearance of kt in the error expression of eq A.7 and simplifymg eventually leads to
So the error in the approximation depends only on the conversion and the true reaction order. For the case of the data in Figure 1 for SCWO of acetic acid, the highest conversion was 32%, and the true reaction order was determined to be 1.08. Using these values in eqA.8 results in a 0.14% error in the approximate solution we employed. Table 3 provides the results of a few representative error
TC t X
Arrhenius pre-exponential factor global reaction order for acetic acid global reaction order for oxygen global reaction order for water activation energy global rate constants mol/L critical pressure gas constant temperature critical temperature batch holding time conversion
literature Cited (1) Dell'orco, P. C.; Foy, B. R.; Robinson, J. M.; Buelow, S . J. Hazard Waste Hazard Mater. 1993, 10, 221. (2) Rice, S. F.; Steeper, R. R.; LaJeunesse,C. A. Sandia Report SAND948203 UC-402. 1993. (3) Takahashi, Y.; Wydeven, T.; Koo, C. Adv. Space Res. 1989, 9,99. (4) Modell, M. In Standard Handbook ofHmrdous Waste Treatment and Disposal; Freeman, H. M., Ed.; McGraw-Hill: New York, 1989; pp 8.153-8.168. (5) Thornton, T. D.; Savage, P. E. AIChEJ. 1992, 38, 321. (6) Li, R.; Savage, P. E.; Szmukler, D. I. AIChE J. 1993, 39, 178. (7) Crain, N.; Tebbal, S.; Li, L.; Gloyna, E. F. Ind. Eng. Chem. Res. 1993, 32, 2259. (8) Tester, J. W.; Holgate, H. R.;Armellini,F. J.; Webley, P. A.; Killilea, W. R.; Hong, G. T.; Barner, H. E. In Emerging Technologies in Hazardous Waste Management IIb ACS Symposium Series 518; American Chemical Society: Washington, DC, 1993, pp 35-76. (9) Gopalan, S.; Savage, P. E. AIChEJ., in press. (101 Savage, P. E.; Gopalan, S.; Mizan, T. I.; Brock, E. E.; Martino, C. J. AIChE J., in press. (11) Li, L.; Chen, P.; Gloyna, E. F. AIChEJ. 1991, 37, 1687. (12) Wightman, T. J. M.S. Thesis, University of California at Berkeley, 1981. (13) Lee, D. Ph.D. Dissertation, University of Texas at Austin, 1990. (14) Lee, D.; Gloyna, E. F.; Li, L. J. Supercrit. Fluids 1990, 3, 249. (15) Chang, K.; Li, L.; Gloyna, E. F. J. Hazard Mater. 1993, 33, 51. (16) Boock, L. T.; Klein, M. T. Ind. Eng. Chem. Res. 1993, 32, 2464. (17) Savage, P. E.; Gopalan, S.; Li, R. In Chemical Oxidation; Eckenfelder, W. W., Bowers, A. R., Roth, J. A., Eds.; Technomic Publishing: Lancaster, PA, 1994; Vol. 3, pp 34-41. (18) Holgate, H. R.; Tester, J. W. J. Phys. Chem. 1994, 98, 800. (19) Haar, L.; Gallagher, J. S.; Kell, G. S. NBSINRC Steam Tables; Hemisphere Publishing: New York, 1984.
Received for review May 25, 1994. Revised manuscript received September 26, 1994. Accepted October 12, 1994.@
ES9403219 @
Abstract published inAdvanceACSAbstracts, November 15,1994.
VOL. 29, NO. 1, 1995 /ENVIRONMENTAL SCIENCE &TECHNOLOGY 1221
