I n d . Eng. Chem. Res. 1994,33,3125-3130
3125
Kinetics of Wet Air Oxidation of Glyoxalic Acid and Oxalic Acid Rajesh V. Shende and Vijaykumar V. Mahajani' Department of Chemical Technology, University of Bombay, Matunga, Bombay 400 029,India
Oxidation of lower molecular weight monobasic and dibasic acids such as formic acid, acetic acid, glyoxalic acid, and oxalic acid is often the rate-controlling step during wet air oxidation (WAO) of a n aqueous waste stream exhibiting very high chemical oxygen demand (COD). The kinetics of WAO of glyoxalic acid and oxalic acid was studied in absence and presence of a cupric sulfate catalyst in the temperature range of 120-245 "C and oxygen partial pressure of 0.3451.380 MPa. The wet oxidation of oxalic acid was found to required more severe conditions as compared to glyoxalic acid. The reaction mechanism and kinetic model have been discussed.
Introduction Wet oxidation is found to be a very attractive and useful technique for treatment of effluent streams exhibiting high biological oxygen demand (BOD) and chemical oxygen demand (COD) (Randall and Knopp, 1980). When the source of oxygen is air, it is also referred to as wet air oxidation. Many times the terms wet oxidation and wet air oxidation are used to mean the same thing. In the following text we have used the terminology wet air oxidation (WAO)even though oxygen was used in place of air. The WAO process is becoming increasingly popular among environmental engineers for treating industrial waste in order to meet discharge standards. Many organic compounds undergoining WAO gradually degrade to low molecular weight compounds and, finally, to highly refractory lower carboxylic acids. Devlin and Harris (1984) have studied wet air oxidation of phenol and listed various oxidation products. These include monobasic and dibasic acids, such as acetic acid, formic acid, glyoxalic acid, oxalic acid, etc. These acids are quite stable and invariably develop a resistance to further oxidation, which results in finite COD and BOD at the end of wet air oxidation. The finite residual COD and BOD thus left may not meet the discharge standards that are becoming more and more stringent day by day. Therefore, more severe oxidation conditions are required for complete oxidation. However, the severity of the process can be reduced by using catalysts. The lower molecular weight acids being difficult to oxidize, their oxidation to COa and HzO often becomes the rate-controlling step in overall COD reduction process to meet discharge standards using WAO technique. To have a thorough insight into the process and for better understanding of suitable reactor design, knowledge of kinetics of WAO of low molecular weight acids is desired. In the present study, kinetics of WAO of oxalic acid and glyoxalic acid have been reported since they were discovered as the wet oxidation products of phenolics. Gould et al. (1976) and Li et al. (1979) have studied oxidation of oxalic acid and glyoxalic acid in presence of ozone. However, they have not commented about interconversions of glyoxal, glyoxalic acid, and oxalic acid. Imamura et al. (1982) have studied oxidation of oxalic acid in the temperature range of 112-160 "C. In case of noncatalytic oxidation, 27% reduction in total organic carbon (TOC)was observed at 140 "C in just 20 min. While in catalytic oxidation using Co/Bi [5/11 complex oxide catalyst, about 32% TOC removal was
* Author to whom correspondence should be addressed. 0888-5885/94/2633-3125$04.50l0
observed at 140 "C. However, 90% TOC reduction was achieved at 160 "C. Moreover, they have observed that C o B i [5/11 oxide catalyst is remarkably active for the oxidation of all refractory lower molecular weight acids. Li et al. (1991) reported WAO of oxalic acid in the temperature range of 227-310 "C. The reaction was found to be first order with respect to substrate and 0.31 with respect to oxygen. The activation energy was found to be 31.9 kcaVgmo1. In the present investigation we have focused our attention to the use of CuSO4 as a homogeneous catalyst for wet air oxidation of both the acids to reduce severity of WAO process. The residual copper catalyst in the form of "Cu" ions can be removed from the aqueous stream by ion exchange technique so as to meet the discharge standards with respect to copper as well.
Materials and Analytical and Experimental Procedures Materials. Oxalic acid used was of Analytical Reagent grade obtained from S. D. Fine Chemicals, Bombay (India). Glyoxalic acid as 50% solution in water was obtained from MERCK-Schuchardt. Cupric sulfate was of Analytical Reagent grade, and it was used as a catalyst. The chemicals used for COD analysis were of Analytical Reagent grade. Oxygen from a cylinder with minimum purity of 99.5% was used for oxidation. Analytical Procedures. Chemical Oxygen Demand. The samples obtained during wet air oxidation were analyzed for COD using the standard dichromate reflux method (Snell, 1967). Infrared (IR) Spectroscopy and Gas Chromatography (GC). In order to detect formic acid as an intermediate formed, if at all, during wet air oxidation, some typical samples were subjected to IR and GC analysis (GC instrument used, Chemito-3865, Toshniwal Instruments India Ltd.; IR instrument used, Perkin Elmer -270-30 spectrophotometer). Oxalic acid as an intermediate formed during wet air oxidation of glyoxalic acid was analyzed qualitatively by IR spectroscopy. Experimental Procedure. The oxidation was carried out in a 2-L SS 316 autoclave equipped with a six bladed turbine agitator having a variable-speed arrangement. The gas inlet, release valve, cooling water feed line, pressure gauge, and safety port were situated on the top of the experimental setup as shown in Figure 1. The sample line and a thermocouple were well immersed in the reaction mixture. The autoclave was charged with a known concentration of glyoxalic/oxalic acid. In case of noncatalytic WAO, the reaction mixture was heated to the desired 0 1994 American Chemical Society
3126 Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994
T
where A = glyoxalic acid, B = oxalic acid, and C = CO:! and HzO. The above reactions can also be presented as CHOCOOH
+ 0, -2C0, + H,O kl
CHOCOOH + '/,O, STATION
HOOCCOOH Figure 1. Schematic diagram of the experimental rig. Labeling is as follows: CW, cooling water; CY, gas cylinder; E2, sample condenser; GS, gas spargerkquid sampling device; H, electric heater; PI, presure indicator; R, reaction vesseVautoclave; S, sample; SI, speed indicator; RD,rupture disc; T, thermowell; TIC, temperature indicator and controller.
temperature. Once the temperature attained the sample was withdrawn. This time was taken as "zero" time for a reaction. The reaction temperature was controlled using a temperature controller. Oxygen was then sparged in the vessel to predetermined pressure level. During sampling the oxygen pressure was maintained in order to keep the system at constant pressure. Samples were withdrawn periodically and analyzed for COD. In the case of the catalytic wet air oxidation the same procedure was followed except that the catalyst was first mixed in the substrate and the reaction mixture was then charged in the autoclave.
Results and Discussion Wet air oxidation is a heterogeneous gas-liquid reaction, and consists of the following steps taking place in series at macroscopic level: transfer of oxygen from bulk of gas phase to gas-liquid interface (gas phase mass transfer); instantaneous saturation of interface with respect to solute gas, 0 2 , in this case; transfer of the dissolved oxygen from gas-liquid interface to the bulk of liquid (liquid phase mass transfer); chemical reaction in the liquid phase. The gas side resistance was estimated to be negligible in the range of operating temperatures used for oxidation studies in the present investigation. This is due to the very high diffusivity of oxygen in the gas phase and its low solubility in water. The liquid side mass transfer resistance was completely eliminated by studying the rates of oxidation a t impeller speed of 14 rps. Preliminary calculations based on oxygen consumption indicated that the reaction was not sufficiently fast enough to take place in gas-liquid diffusion film (Doraiswamy and Sharma, 1984). Thus it was ensured that the reaction was kinetically controlled .under the experimental conditions employed. Due to the very low concentrations of substrate used, the oxygen solubility was considered to be that in water and was estimated from the data published by Crammer (1980). Kinetics of Wet Air Oxidation of Glyoxalic Acid The destruction of glyoxalic acid (i.e. reduction in COD) to harmless products can be represented as a complex reaction A-C
+ '/,O,
k2
k3
HOOCCOOH 2C0,
+ H,O
(2) (3)
(4)
The destruction of organics (i.e. reduction in COD) via wet oxidation techniques are known to be free radical reactions (Li et al. (1991); Tufano (1993)):
0,
+ H,O RH + HO' R' + 0, ROO' + RH 0'
-
0' + 0'
-.HO' -.R'
+ HO'
+ H,O
-.ROO' -.R'
+ ROOH
(5)
(6) (7) (8)
(9)
where RH = organic substrate resulting in COD. The reaction continues until C02 and HzO are formed. From the envinmental process engineer's point of view, the concentration of any reactant or intermediate is not important but their combined presence resulting in COD is important. The engineer is mainly concerned with monitoring COD of the stream. Although we have observed that oxalic acid alone can not be destroyed below 200 "C (under the conditions discussed later), the presence of glyoxalic acid may trigger free radical attack on oxalic acid and thus initiating its destruction. Therefore the mathematical model cannot be formulated on the basis of the assumption that oxalic acid will not be destroyed in presence of glyxoalic acid below 200 "C. We need to check this hypothesis independently. Since we are interested from environmental point of view in monitoring COD, results are presented in term of COD destruction globally and not with respect to individual components namely glyoxalic acid and oxalic acid. Figure 2 exhibits variation in COD with respect to time a t various temperatures. The results can be analyzed as shown in the following: The destruction of (COD) can be represented as d(C0D) - r = k, exp[g][CODl" [O,]" (10) dt For a given temperature and oxygen partial pressure we have pseudo-m-th order expression as d(C0D) - &(COD)" dt
(11)
The data presented can be well fitted to m = 1,for given temperature and time. Thus d(C0D) - &(COD) dt and hence
k
0
}-I
(COD), In (COD), = ht
(12)
Ind. Eng. Chem. Res., Vol. 33,No. 12,1994 3127 ' 0 0 2 ' 3.00
~
00
, O O E t
0
F
I
\ I
a
5000
' 1 ,
'
1 0 0' 0' 0
L 8 1 1
' ' 1 '51 0' 0 0 ' '
20000
'
TIME (sec)
~
~
'
TIME
~
'
~
~
~
(sec)
Figure 2. Effect of temperature and oxygen partial pressure on COD reduction (noncatalyticoxidation of glyoxalic acid). Symbols represent the following: (0) 150 "C, 0.690 MPa; (A) 175, 0.345; 175, 1.380; (+) 200, 0.690. (0)175, 0.690; (a)
oxidation. Symbols represent the following: (0) 150 "C, 0.690 MPa; (0) 175,0.345;(opensix-pointstar) 175,0.690;( x ) 175,1.380; (A) 200, 0.690.
The variation in & with respect to temperature and oxygen concentration can then yield E-th energy of activation and n-th order with respect to oxygen. It is interesting to note that we have observed the destruction of COD with respect to time being a two-step process namely the first step of fast reduction followed by slower destruction. From the process point of view the knowledge of both the steps is important. For example the higher initial rates could be misleading at a later stage, for the global rate constant is also different for the second slow step. This is mainly due to various free radical reactions taking place as discussed above. Tufano (1993)has analyzed phenol oxidation in water at high temperature and also observed that the reaction exhibited first-order behavior with respect to phenol. The order with respect to oxygen can vary between 0 and 1 depending upon which is the rate-controlling step in reactions 5-9. Thus we can justify our assumption of order with respect to substrate to be unity and indeed it correlates data well in two zones. The catalyst accelerates all the reactions and its role can be quantified by way of following expression:
The first step corresponds t o glyoxalic acid partly decomposing into CO2 and H20, and simultaneously, part of the glyoxalic acid oxidizing to oxalic acid. The second slow step reflects the higher resistance provided by oxalic acid for further oxidation. As temperature increases, more acid gets converted almost instantaneously into oxalic acid. (Oxalic acid was observed as one of the degradation product in IR analysis.) Since oxalic acid is fairly stable over the temperature range of oxidation of glyoxalic acid, it eventually leads to the slow step of oxidation. The energy of activation based on reduction in COD for both the steps was found to be 12.8 and 27.9 kcal/(g mol), respectively. The effect of oxygen partial pressure was studied over the range of 0.345-1.380 MPa, a t the temperature of 175 "C. The order with respect t o oxygen was found to be 0.926and 0.207,for the first fast and the slow step, respectively. In all the cases the data was correlated as outlined earlier (eq 12). On the basis of our experimental findings, the global rate equation for noncatalytic wet air oxidation of glyoxalic acid is given by
d(C0D) - r = K O exp[~][CODl[021n~catalystlP dt (13)
---
The data can be analyzed in similar manner as discussed in the case of noncatalytic reaction. The kinetics of noncatalytic oxidation was carried out in the temperature range of 150-200 "C and oxygen partial pressure range of 0.345-1.173 MPa (system total pressure 1.19-2.29 MPa). Interestingly, the oxidation reaction was found to be a two-step reaction. The oxidation followed first-order kinetics with respect to COD content in both the steps, as shown in Figure 3.It can be seen that COD reduction is initially very fast, and then it slowed down. A high percentage of COD reduction can be achieved by increasing the reaction time. It was observed that about 46% COD reduction was obtained at 150 "C and 0.69 MPa oxygen partial pressure in 5 h. However, 93% reduction was achieved within 1.5 h, at 200 "C and 0.69 MPa oxygen partial pressure. The observed two-step kinetic behavior can be explained as follows:
Figure 3. First-order kinetics plot of noncatalytic glyoxalic acid
for fast step
r1 = (1.453 x lo5)exp[-6441.14][~0~]1.0[0,]0.926 (14) for slow step
Catalytic oxidation of glyoxalic acid using cupric sulfate was studied in the temperature range of 135160 "C and oxygen partial pressure range of 0.3451.173 MPa. For the catalyst loading of 1.2525 x kmol/m3, the first-order kinetic plot is shown in Figure 4. The kinetics of catalytic oxidation was also found to be first order with two distinct steps as indicated in noncatalytic oxidation. A slow step indicated greater resistance provided by oxalic acid for further oxidation. (Oxalic acid was detected in IR analysis.) No traces of formic acid were observed in IR analysis as well as in
'
~
~
3128 Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994 4.00
t -E/R = 1 1 4 3 8 . 7
00
0.001
50
00
t 50
00
000
2.00
Figure 4. First-order kinetics plot of catalytic oxidation of glyoxalic acid. Symbols represent the following: (0)135 "C,0.690 km01/m3; (0) 150,0.345,1.252 x ( x ) 150, MPa, 1.252 x 0.690, 1.252 x (D)150, 0.690, 3.319 x loT4;(crossed dot) 150, 0.690, 5.020 x lW3; (A) 150, 1.173, 1.252 x ( 0 )160, 0.690, 1.252 x
gas chromatographic analysis of oxidized samples of glyoxalic acid. Activation energy for the fast and the slow step was found to be 22.7 and 28.2 kcal/(g mol), respectively. These values confirm the absence of mass transfer resistance. A plot of In K versus 1/T for both noncatalytic and catalytic oxidation is shown in Figure 5. The order with respect t o oxygen was found to be almost "zero" for the second step. The effect of catalyst was studied over the range of 3.319 x to 5.020 x km01/m3catalyst loading at 150 "C, using 0.69 MPa oxygen partial pressure. The order with respect to catalyst for the two steps was found to be 0.714 and 0.908, respectively. Kinetic data for the catalytic wet air oxidation of glyoxalic acid can be correlated by the following expressions: for first step
2.20
2. 40
2. 60
1/T x 1 0 '
TIME (sec)
Figure 5. Plot of 1/T versus In k (for catalytic and noncatalytic oxidation). Symbols represent the following: (0) first step (noncatalytic), (A) second step (noncatalytic), (+) fist step (catalytic), (D)second step (catalytic). Table 1. Range of COD Values for Validity of the Rate Expressions rl to r4
02 partial T, "C pressure, MPa 150 175 175 175 200
0.69 0.345 0.69 1.38 0.69
135 150 150 150 150 150 160
0.69 0.69 0.69 0.69 0.345 1.173 0.69
catalyst concentration km01/m3
1.2525 x 3.319 x 1.2525 x 5.020 x 1.2525 x 1.2525 x 1.2525 x
COD range, mgiL rl
r2
1052-626 1052-637 1052-435 1049-425 1041-325
626-568 637-434 435-369 425-347 325-74
r3
r4 366-320 350-304 373-253 462-218 365-247 377-242 410-84
1050-366 1050-350 1050-373 1048-462 1051-365 1051-377 1050-410
required. The reaction was found to be first-order kinetics with respect to substrate (in terms of COD) as shown in Figure 6. A COD reduction of 30% was achieved at 245 "C in 5 h, which clearly indicates [0,1°~614~CuS0410~714 (16) stability of oxalic acid. The activation energy was found to be 30.9 kcal/(g mol) which also indicates the absence for second step of mass transfer resistance. The effect of oxygen partial pressure was studied in the range of 0.690-1.035 MPa, r4 = (7.534 x lo1') ~ X ~ [ - ~ ~ ~ ~ * ~ x~ ] [ C O DatI 225 ' ~ "C temperature. The order with respect to oxygen was found to be 0.321. The global rate equation [o,]o~05[cuso4]o~908 (17) for noncatalytic WAO of oxalic acid based on our experimental findings is as follows: The range of COD over which kinetic expressions (eqs 14-17) are valid is exhibited in Table 1. In the case of noncatalytic oxidation of glyoxalic acid, more than 93% COD reduction was obtained a t 200 "C and 0.69 MPa oxygen partial pressure in 1.5 h. HowIn the case of oxalic acid oxidation using molecular ever, similar reduction was obtained using 1.2525 x oxygen, formic acid was not observed as a degradation lop3kmoVm3 catalyst loading a t 160 "C in 5 h. product in GC analysis as well as in IR studies. Thus, it can be safely concluded that oxalic acid is directly Kinetics of Wet Air Oxidation of Oxalic Acid being converted into carbon dioxide and water during The noncatalytic wet air oxidation of oxalic acid was the experimental conditions employed in the present carried out in the temperature range of 225-245 "C and investigation. oxygen partial pressure of 0.690-1.035 MPa. Since, The catalytic WAO of oxalic acid was carried out using oxalic acid was found to be more stable as compared to CuSO4 as a catalyst in the temperature range of 120glyoxalic acid, more severe reaction conditions were to 6.2687 150 "C and catalyst loading of 3.1506 x
Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994 3129
1
0. 5 O t
-7,
-7. 0. 40
-8. 0 . 30
-0.
,y
CI
-9. 0.20
-9. 0 . 10
-9.
0.00
0
5000
:
10000
16000
5
3
.
20000
0
1
-
1/T
TIHE ( s e c )
Figure 6. First-order kinetics plot of noncatalytic oxidation of oxalic acid. Symbols represent the following: (0) 225 "C, 0.345 MPa; (A)225,0.690;(W) 225,1.035;(crossed dot) 235,0.690;( 0 ) 245,0.690.
I. 00 1
.
2
0
80
60
40
20
00
0
5000
10000
TIME
15000
20000
( s e c )
Figure 7. First-order kinetics plot of catalytic oxidation of oxalic acid. Symbols represent the following: (circled triangle) 120 "C, 0.690 MPa, 4.684 x km01/m3; (8)130,0.690,4.684 x ( x ) 140,0.345,4.684 x (open six-point star) 140,0.690,4.684 x (W) 140,1.380, 4.684 x (0)140,0.690, 3.150 x ( 0 )140,0.690,6.268x x 10-3 kmol/m3. The first-order kinetic plot for catalytic WAO of oxalic acid in the above range of operating conditions is shown in Figure 7. It was observed that the reduction in COD was not significant above the catalyst loading of 6.2687 x kmoVm3, at 140 "C. About 96% COD reduction was achieved in 1 h at 150 "C and 0.69 MPa oxygen partial pressure. Since oxalic acid is more stable as compared to glyoxalic acid and requires severe oxidation conditions, which can be reduced significantly by using cupric sulfate as a catalyst, copper catalyst on reacting with oxalic acid in equivalent molar proportions, formed copper oxalate. We have observed fine solid particles ranging from 0.357 to 0.714 pm (analyzed on a Horiba particle size distribution analyzer Copa-700,Japan) of copper oxalate in the sample collected at around 30 "C. We postulate that the copper oxalate thus generated undergoes oxidation and produces copper oxide and carbon dioxide. Copper
x 10'
Figure 8. Plot of In k versus 1/T(noncatalytic and catalytic oxidation of oxalic acid). Symbols represent the following: (0) noncatalytic; (+) catalytic.
oxide in turn reacts with oxalic acid and copper oxalate is generated. IR analysis showed a clear indication of oxalate formation and its oxidation. Thus, oxidation of oxalic acid in the presence of cupric sulfate is governed by two ~ basic reactions viz. formation of copper oxalate and its oxidation. Copper oxalate is formed during oxidation which is insoluble in water at room temperature. While determining the COD, samples were well mixed and a uniform suspension was used for refluxing. The exact solubility of copper oxalate is not known under reaction conditions and hence global rate expression is presented to ease the process design. Under these conditions speed of agitation has no effect on the rate of reaction and therefore gas-liquid and liquidsolid mass transfer effects were deemed to be absent. The reaction kinetics presented here is for an overall system. The overall activation energy was found to be 19.1 kcal/(g mol). A plot of In k versus 1/T for both noncatalytic and catalytic oxidation is shown in Figure 8. The effect of oxygen partial pressure was studied in the range of 0.69-1.38 MPa. The order with respect to oxygen was found to be 0.146. The effect of catalyst concentration was studied in the range of 3.1506 x to 6.2687 x lop3km01/m3 catalyst loading, at 140 "C. The order with respect to catalyst was found to be 0.283. The global rate expression for catalytic wet air oxidation of oxalic acid is as follows: r6
= (7.169 x
lo6) exp[-9616.37 T ][COD]'.' x [0210.146[ cuso,lo~283 (19)
It is possible to theoretically model the reactions as outlined by Li et al. (1991). However, we strongly feel that the rate constant k3 for oxalic acid decomposing to COz could not be considered from that derived from the experiments on oxalic acid as a starting material. Considering complexity of the reactions, the presence of the glyoxalic acid is likely to have influence on k3 also. Recently, Mishra et al. (1994)have observed that during wet air oxidation of diethanolamine and morpholine, the rate of oxidation is significantly higher in a mixture of both when compared to individual rates. Therefore the applicability of such modeling is difficult to comprehend.
3130 Ind. Eng. Chem. Res., Vol. 33, No. 12, 1994
It is possible to detoxi6 the waste stream with respect to copper by conventional well-known techniques such as ion exchange or precipitation as insoluble sulfide salt. Conclusions Cupric sulfate was found to be a very effective catalyst in destroying glyoxalic and oxalic acid. The oxidation of glyoxalic acid (noncatalytic and catalytic) was found to obey first-order kinetics with respect to substrate (in terms of COD) with two distinct steps. The second slow step indicates higher resistance provided by oxalic acid for further oxidation. Wet air oxidation of oxalic acid was found to obey first-order kinetics with respect to substrate and it was found to be oxidized directly into carbon dioxide and water. Acknowledgment Mr. R. V. Shende is grateful to University Grants Commission, India, for the financial support. Nomenclature COD = chemical oxygen demand, mg/L BOD = biochemical oxygen demand, mgL TOC = total organic carbon E = energy of activation, cal/(g mol) m = order with respect to COD n = order with respect to oxygen p = order with respect to catalyst R = gas constant, kcal/(g mol K) k, = pre exponential factor (unit dependent on n and p ) T = temperature, K t = time, s [COD], = initial COD, mg/L [CODlt = COD ( m a ) at time “t”(s)
= reaction rate constant, for reaction 2 k z = reaction rate constant, for reaction 3 123 = reaction rate constant, for reaction 4
kl
Literature Cited Crammer, S. D. The Solubility of Oxygen in Brines from 0 to 300 “C. Znd. Eng. Chem. Process Des. Dev. 1980,19,300-305. Devlin, H. R.;Harris, I. J. Mechanism of the oxidation of Aqueous Phenol With Dissolved Oxygen. Znd. Eng. Chem. Fundam. 1984,23,387-390. Doraiswamy, L. K.; Sharma, M. M. Heterogeneous Reactions; Analysis, Examples and Reactor Design; John Wiley and Sons: New York, 1984;Vol. 2. Gould, J. P.; Weber, W. J., Jr. Oxidation of Phenols by Ozone. J. Water Pollut. Control Fed. 1976,48 (l),47-60. Imamura, S.;Kinunaka, H.; Kawabata, N. The Wet Oxidation of Organic Compounds Catalyzed by Co-Bi Complex Oxides. Bull. Chem. Soc. Jpn. 1982,55,3679-3680. Li, K. Y.; Kuo, C. H.; Weeks, J. A Kinetic Study of Ozone-Phenol Reaction in Aqueous Solutions. AIChE J . 1979,25,583. Li, L.;Chen, P.; Gloyna, E. F. Generalized Kinetic Model For Wet Oxidation of Organic Compounds. NChE J . 1991,37,16871697. Mishra, V. S.; Joshi, J. B.; Mahajani, V. V. Kinetics of Wet Air Oxidation of Diethanolamine and Morpholine. Water Res. 1994, 28, 1601. Randall, T. L.; Knopp, P. V. Detoxification of Specific Organic Substances by Wet Oxidation. J . Water Pollut. Control Fed. 1980,52,2117-2129. Snell, F. D.; Ettre, L. S. Encyclopedia of Industrial Chemical Analysis; John Wiley and Sons; New York, 1967;Vol. 17. Tufano, V. A Multi-Step Kinetic Model for Phenol Oxidation in High Pressure Water. Chem. Eng. Technol. 1993,16,186-190. Received for review November 29, 1993 Revised manuscript received July 13,1994 Accepted August 24, 1994@
Abstract published in Advance ACS Abstracts, October 15, 1994. @
