A Kinetic Model for Advanced Oxidation Processes of Aromatic

Ind. Eng. Chem. Res. 1999, 38, 4189-4199

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A Kinetic Model for Advanced Oxidation Processes of Aromatic Hydrocarbons in Water: Application to Phenanthrene and Nitrobenzene Fernando J. Beltra´ n,* Javier Rivas, Pedro M. A Ä lvarez, Miguel A. Alonso, and Benito Acedo Departamento de Ingenierıá Quı´mica y Energe´ tica, Universidad de Extremadura, 06071 Badajoz, Spain

A kinetic model for the advanced oxidation (ozonation alone, UV radiation alone, ozone plus hydrogen peroxide, ozone plus UV radiation, and UV radiation plus hydrogen peroxide) of aromatic hydrocarbons in water is proposed and tested with experimental results of the oxidation of nitrobenzene and phenanthrene, two aromatic hydrocarbons of different reactivity with ozone. The kinetic model leads to good results in the case that the compound treated reacts exclusively with ozone, that is, without the contribution of hydroxyl radical oxidation as in the case of phenanthrene oxidation. In this case, it is not necessary to account for intermediate reactions to have good predictions of experimental remaining concentrations of ozonation processes. On the contrary, when the aromatic hydrocarbon is mainly removed by hydroxyl radicals (case of nitrobenzene), mole balance equations of intermediates have to be included for the experimental concentrations to be reproduced. For so doing, the kinetic parameters, such as rate constants of reactions between ozone and hydroxyl radical with intermediates and their corresponding quantum yields at 254 nm, were also determined. The kinetic model, however, is unable to reproduce, with accuracy, the experimental results of the ozone-UV radiation oxidation system. Introduction As is known, many aromatic compounds, particularly, polynuclear aromatic hydrocarbons (PAHs) and nitroaromatic (NA) hydrocarbons, are classified as priority pollutants of water and their removal deserves special attention.1 In previous papers2-7 the suitability of ozonation and related chemical advanced oxidation processes (AOPs) for the removal from water of these aromatic hydrocarbons have been studied. These works mainly focused on the determination of quantum yields of direct photolysis and rate constants of the reactions between ozone and the hydroxyl radical with the aromatic compound. However, another important aspect to study is the kinetic modeling of these AOPs. Kinetic models of these processes can be useful tools both to simulate and to predict oxidation rates, the remaining pollutant concentration or oxidant doses to be applied. AOPs are characterized by the generation of hydroxyl radicals, species of high oxidizing power, that react on the matter present in water in an unselective way.8 So far, literature reports different researches aimed at the development and testing of kinetic models of processes such as ozonation, alone or combined with hydrogen peroxide or UV radiation,9-15 oxidation through hydrogen peroxide photolysis,16-18 or others like Fenton or electron beam processes.19-20 One of the common points of most of these works is the nature of compounds investigated. Thus, with some exceptions, most of the works dealt with organochlorine compounds of low molecular weight. These compounds, although water priority pollutants, did not lead to reacting intermedi* To whom correspondence should be addressed. Telephone: 34-924-289387. Fax: 34-924-271304. E-mail: fbeltran@ unex.es.

ates that could compete with the parent compound for the oxidant (ozone, hydroxyl radicals, UV light, etc.). The works of Glaze and Kang9,10 were one of the first to develop this subject, in this case, by studying the ozone combined with hydrogen peroxide oxidation of tetrachloroethylene based on a free radical mechanism. In some other works11,16 the kinetic model study was established once the water flow characteristics through the reactor were assessed by tracer experiments. In a few works, aromatic compounds and pesticides were also treated. Thus, a kinetic model for the ozonation of toluene was proposed by Yurteri and Gurol,11 although no free radical mechanism was given. Laplanche et al.13 studied the ozonation (with and without hydrogen peroxide) of atrazine and some of its metabolites in a bubble column. They assumed that the decomposition of ozone directly yields hydroxyl free radicals and they proposed an empirical function of pH, organic carbon of water, alkalinity, and ozone concentration for the concentration of hydroxyl free radicals. More recently, Kallas et al.14 presented oxidation rate data for PAHs’ removal from water based on a free radical mechanism. In this work, rate constants were obtained by fitting experimental results to the kinetic equations derived from the mechanism. However, in some cases, rate constants of ozone-PAHs reactions presented significant differences, depending on the chemical oxidation process used. Finally, other processes not treated in this work, Fenton-like processes19 or the electron beam process,20 have been the subject of study to propose a kinetic model also based on a free radical mechanism. In this work, a free radical and molecular mechanism is proposed to model the oxidation of aromatic compounds with ozone, hydrogen peroxide, and/or UV

10.1021/ie990189r CCC: $18.00 © 1999 American Chemical Society Published on Web 10/12/1999

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Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999

Table 1. Fluidodynamic Data of Reactors Used compounds PAHs (ref 2)

standard tank photochemical tanka standard tank photochemical tanka

NA (refs 6 and 7) a

kL, m s-1

reactor

kLa, s-1

10-4

10-2

2.5 × 4.6 × 10-5 2.4 × 10-4 4.6 × 10-5

3.5 × 3.5 × 10-3 3.8 × 10-2 3.9 × 10-3

β, %

V, L

Fg, L h-1

0.95 0.95 0.95 0.95

4.6 0.8 4.6 0.8

25 25 50 50

Intensity of incident radiation: 3.8 × 10-6 einstein L-1 s-1. Effective path of radiation through the photoreactor: 4.5 cm.7

Table 2. Reaction Mechanism for the O3/H2O2/UV System: Elementary Reactions, Reaction Rate Constants, and Quantum Yield Dataa reaction no.

reaction

rate constant or quantum yield

reaction no.

reaction

rate constant or quantum yield

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

O3 + OH- f •O2- + O2• O3 + HO2- f HO• + •O2- + O2 O3 + H2O + hv f 2HO• + O2 H2O2 + hv f 2HO• O3 + •O2- f •O3- + O2 HO3• f HO• + O2 O3 + HO• f HO4• HO4• f HO2• + O2 H2O2 + HO• f HO2• + H2O HO2- + HO• f HO2• +OHHO4• + HO2• f O3 + O2 + H2O •OH + HO• f H O 2 2 HO• + •O2- f OH- + O2 • • HO + HO3 f H2O2 + O2 HO3• + •O2- f OH- + 2O2 HO3• + HO3• f H2O2 + 2O2 HO4• + HO4• f H2O2 + 2O3 HO4• + HO3• f H2O2 + O2 + O3 HO4• + •OH f H2O2 + O3 HO4• + O2-• f OH- + O2 + O3

k1 ) 70 M-1 s-1 (ref 22) k2 ) 2.2 × 106 (ref 22) Φ3 ) 0.64 (ref 3) Φ4 ) 0.5 (ref 23) k5 ) 1.6 × 109 (ref 24) k6 ) 1.4 × 105 s-1 (ref 24) k7 ) 3.0 × 109 (ref 24) k8 ) 2.8 × 104 s-1 (ref 25) k9 ) 2.7 × 107 (ref 26) k10 ) 7.5 × 109 (ref 26) k11 ) 1010 (ref 25) k12 ) 5 × 109 (ref 25) k13 ) 1010 (ref 25) k14 ) 5 × 109 (ref 25) k15 ) 1010 (ref 25) k16 ) 5 × 109 (ref 25) k17 ) 5 × 109 (ref 25) k18 ) 5 × 109 (ref 25) k19 ) 5 × 109 (ref 25) k20 ) 1010 (ref 25)

21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

HCO3- + HO• f •CO3- + H2O CO32- + HO• f •CO3- + OHCO3- + O2-• f CO32- + O2 •CO - + O -• f CO 2- + O 3 3 3 3 •CO - + H O f HCO - + HO • 3 2 2 3 2 •CO - + HO - f CO 2- + HO • 3 2 3 2 • H3PO4 + HO f H2O + H2PO4• H2PO4- + HO• f OH- + H2PO4• HPO42- + HO• f OH- + HPO4-• HO2• a H+ + O2HO3• a H+ + O3H3PO4 a H+ + H2PO4H2PO4- a H+ + HPO4HPO4- a H+ + PO43H2CO3 a H+ + HCO3HCO3- a H+ + CO32H2O2 a HO2- + H+ M + zO3 f intermediates M + HO• f intermediates M + hv f intermediates

k21 ) 2 × 107 (ref 8) k22 ) 3.7 × 108 (ref 8) k23 ) 7.5 × 108 (ref 27) k24 ) 6 × 107 (ref 27) k25 ) 8 × 105 (ref 27) k29 ) 5.6 × 107 (ref 27) k27 ) 2.6 × 106 (ref 28) k28 ) 2.2 × 107 (ref 28) k29 ) 7.9 × 105 (ref 28) pK30 ) 4.8 (ref 22) pK31 ) 8.2 (ref 24) pK32 ) 2.2 (ref 29) pK33 ) 7.2 (ref 29) pK34 ) 12.3 (ref 29) pK35 ) 6.4 (ref 29) pK36 ) 10.4 (ref 29) pK37 ) 11.7 (ref 22) kd value in Table 3 kHOM value in Table 3 ΦM value in Table 3

a

Units of rate constants and quantum yields in M-1 s-1 and mol photon-1 unless indicated.

radiation. The model has been tested mainly to compare calculated results to those experimentally obtained during semibatch ozonations and advanced oxidation of nitrobenzene and phenanthrene2-7 in the slow kinetic regime of ozone absorption. Experimental Section Experimental data presented in this work was obtained in semibatch reacting systems as explained in previous papers2-7 where quantum yields and rate constant data of ozone and hydroxyl radical reactions with five aromatic compounds (nitrobenzene (NB), phenanthrene (PH), fluorene (F), 2,6-dinitrotoluene (DNT), and acenaphthene (A)) were determined. The main aromatics studied here are nitrobenzene (NB) and phenanthrene (PH), although fluorene (F) and 2,6dinitrotoluene (DNT) were also treated in some cases. In the case of acenaphthene (A) the kinetic model could not be applied because its ozonation developed in the moderate-fast kinetic regime of absorption at the conditions investigated. Reactor types, procedures, and analytical methods are given in these papers with detail.2-7 Table 1 gives the values of the reactor parameters and mass-transfer coefficients that were used in the kinetic model. Nonetheless, to improve the kinetic model, new experiments of single-ozonation, UV radiation, and oxidation reactions with hydrogen peroxide and UV radiation of 2-nitroresorcinol and muconic acid were also carried out. For these cases, reagents were obtained from Aldrich and used as received. Experimental procedures were similar to those published previously.2-7 Also, pulse tracer experiments21 were developed to confirm that the water phase of reactors was perfectly mixed.

Results and Discussion Reaction Mechanism. Advanced oxidation processes treated in this work are single and combined ozonation with hydrogen peroxide or UV radiation or the combination of the latter two to remove aromatic hydrocarbons from water. As indicated above, kinetic modeling of these processes has been studied separately with different compounds, specially low molecular organochlorine compounds. The reaction mechanisms of these processes differ in the free radical initiation reactions and direct reactions (ozone reactions and photochemical reactions), but most of the propagation and termination reactions coincide so that a full reaction mechanism for the four oxidation processes can theoretically be proposed. Table 2 presents what can be defined as a basic reaction mechanism of these processes. As can be seen from Table 2, reactions of intermediate compounds with ozone, free radicals, etc. have not yet been considered and will be discussed later. However, contrary to the oxidation of low molecular organochlorine compounds, reactions of intermediates can result fundamental to test the kinetic model of the oxidation of an aromatic compound in water, as shown below. The kinetic model was prepared from the mole balance of species presented: the aromatic compound, ozone (in gas and water phases), hydrogen peroxide, phosphate, and carbonate ions. In both reactors used tracer experiments confirmed that the water phase was perfectly mixed. For the gas phase the same flow characteristics were assumed to hold. The kinetic model was also based on the assumption that ozone reactions developed in the slow or very slow kinetic regime of absorption30 because in most practical cases the concentration of dissolved ozone was found during ozonation and concentrations of pollutants were

Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999 4191

very low. Equations of the kinetic model for semibatch ozonations, in reactors where the water and gas phases are perfectly mixed, are as follows: For ozone in water,

dCO3 dt

) NO3 + rO3

(1)

where rO3 is the disappearance rate of ozone in water due to different reactions (ozone photolysis, reactions with the aromatic compound, hydrogen peroxide, etc.) and NO3 the ozone mass-transfer rate from gas to water. For ozone in the gas phase,

dCO3g dt

)

(CO3gi - CO3g)Fg - [rUVO3g - NO3]βV (1-β)V

(2)

where rUVO3g is the ozone photolysis rate in this phase (see eq 16), Fg is the gas flow rate, CO3gi and CO3g are the ozone concentrations in the gas phase at the reactor inlet and outlet, respectively, β is the liquid holdup, and V is the reactor volume. For the aromatic hydrocarbon,

dCM ) rM dt

(3)

For hydrogen peroxide,

dCH2O2T dt

) rH2O2T

dCTPH ) rTPH dt

(5)

dCTBC ) rTBC dt

(6)

CO3gRT He

xkCMDO

3

kL

(8)

where CM is the concentration of any compound or free radical M that reacts with ozone, DO3 is the ozone diffusivity in water, k is the reaction rate constant, and kL is the individual liquid-phase mass-transfer coefficient. For the case of ozone reactions, rate constant data and Hatta numbers at the average experimental conditions2-7 used in this work are presented in Tables 2-5. As can be seen from Table 4, the Hatta numbers remain lower than 0.3, conditions for the reactions to be slow,30 except for reaction 38 (case of the ozone-acenaphthene reaction) and reactions 1 and 2 if the total hydrogen peroxide concentration and/or pH are higher than 10-3 M and 9, respectively. When the photochemical reactor is used, due to its lower liquid-phase mass-transfer coefficient value, reactions 5 and 7 can even be moderate for free radical concentrations higher than 10-11 M (not shown). Regarding reaction 3 of Table 2, the absorption of ozone accompanied by its direct photolysis, the rate constant, and hence the corresponding Hatta number depends on the presence of other absorbing compounds which affect the solution absorbance. The ozone photolysis rate can be expressed as follows:33

rUVO3 ) I0ΦO3FO3[(1 - exp(-µL)]

(9)

where I0, ΦO3, and L are the intensity of incident radiation, ozone quantum yield in water, and effective path of radiation through the photoreactor, respectively, and µ (absorbance solution) and FO3 (fraction of radiation that ozone absorbs) are defined as follows:

µ ) 2.303

∑iCi

(10)

and

where rTPH and rTBC are the net formation rates of total phosphate and bicarbonate ions in water, respectively. For a slow kinetic regime of ozone absorption, NO3 is defined as follows:

(

Ha )

(4)

where rM and rH2O2 are the hydrocarbon and total hydrogen peroxide net disappearance chemical reaction rates, respectively. For phosphate and bicarbonate ions,

NO3 ) kLa

with it,31 the Hatta number is defined as follows:30

)

- CO3

(7)

where kLa, R, and He are the volumetric mass-transfer coefficient, perfect gas law-costant, and Henry’s law constant, respectively, T is the absolute temperature, and CO3 is the concentration of ozone in the water. The kinetic model proposed in this work only holds for the cases of slow kinetic regime; that is, the oxidation rate is controlled by chemical reactions. Hence, the ozone absorption is constituted by two consecutive steps: diffusion of ozone through the film layer in the proximity of the gas-water interface and the chemical reactions in the bulk of water. Confirmation of the kinetic regime of ozone absorption for its reactions in water is checked by determining the corresponding Hatta number. Because ozone reactions are first-order with respect to both ozone and the compound that reacts

FO 3 )

2.303O3CO3 µ

(11)

i being the extinction coefficient (base 10) of any compound i that absorbs radiation. As shown in a previous paper,34 at the start of oxidation in the UV/O3 system, the ozone photolysis rate could be expressed by first-order kinetics where the rate constant value depended on the absorbance solution times the effective path of the photoreactor as follows:

For µL > 2: k)

I0ΦO3O3 MCM0

(12)

For µL < 0.4: k ) 2.303LI0ΦO3O3

(13)

However, in this work, eqs 12 or 13 only hold when M is nitrobenzene, 2,6-dinitrotoluene (µL > 2), or acenaphthene (µL < 0.4) (see Table 5). Fortunately, because the extinction coefficient of ozone at 254 nm is 3300 M-1 s-1,35 in the UV/O3 oxidation of fluorene or phenan-

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Table 3. Rate Constant Data, Extinction Coefficients, and Quantum Yields of Aromatics Studied NB DNT F PH A a

kd, M-1 s-1

kHOM, M-1 s-1

M, M-1 cm-1

ΦM (254 nm), mol photon-1

2.2 (ref 6) 5.7 (ref 6) 29 (ref 2) 2413 (ref 2) 1.1 × 105 (ref 2)

2.9 × (ref 7) 7.5 × 108 (ref 7) 9.9 × 109 (ref 4) 13.4 × 109 (ref 4) 8.8 × 109 (ref 4)

5564 (ref 7) 6643 (ref 7) 16654 (ref 3) 40540 (ref 3) 1333 (ref 3)

7.0 × 10-3 (ref 7) 2.2 × 10-2 (ref 7) 7.5 × 10-3 (ref 3) 6.9 × 10-3 (ref 3) 5.2 × 10-3 (ref 3)

za

compound

1 (ref 6) 1 (ref 6) 2 (ref 2) 1 (ref 2) 2 (ref 2)

109

Stoichiometric coefficient of reaction 38 of Table 2.

Table 4. Hatta Numbers of Reactions of Ozonea reaction no.b

species B OH-

1 1f 1g 2 2f 2g 2h 2i 3 5 7 38 38 38 38 38

CB, Mc 10-7

10-5 10-2 HO22 × 10-9 2 × 10-7 7 × 10-5 2 × 10-8 2 × 10-7 see results in Table 5 O2-• 10-11 HO• 10-11 NB 10-4 DNT 5 × 10-5 F 5 × 10-6 PH 2 × 10-6 A 2 × 10-5

Hattad

Hattae

10-4

4.4 × 4.4 × 10-3 0.14 10-2 0.1 2.0 3 × 10-2 0.11

2.4 × 10-3 2.4 × 10-2 0.75 5.9 × 10-2 0.59 10.8 0.19 0.59

2.1 × 10-2 2.8 × 102 2.4 × 10-3 2.8 × 10-3 1.9 × 10-3 1.1 × 10-2 0.24

0.11 0.16 1.3 × 10-2 1.5 × 10-2 1.1 × 10-2 6.2 × 10-2 1.32

a pH 7 and C -4 M unless indicated. Ozone diffusivity H2O2T ) 10 in water32 ) 1.7 × 10-9 m2 s-1. b Reaction number as in Table 2. c For aromatic hydrocarbons, concentrations correspond to average values used.2-7 d From eq 8 for the standard reactor. e From eq 8 for the photochemical reactor. f pH 9. g pH 12. h CH2O2T )10-3 M. i C -2 M. H2O2T )10

Table 5. Hatta Numbers of the Ozone Photolysis Reaction No. 3 hydrocarbonb

µL, M-1 c

k, s-1 d

Hattah

NB DNT F PH A

5.8 3.5 0.9 0.9 0.3

1.4 × 10-2 e 2.4 × 10-2 e 3.0 × 10-2 f 3.0 × 10-2 f 0.13g

0.11 0.14 0.16 0.16 0.32

a For the photochemical reactor. b Hydrocarbon present during ozone photolysis. c Concentration of hydrocarbon as in Table 4. d From eqs 12, 13 or 14 as indicated below. e From eq 12. f From eq 14. g From eq 13. h From eq 8.

threne, at the conditions applied, the absorbance solution µ can be approximated to 2.303MCM0, which indicates that the hydrocarbon is the main absorbing species (see Table 3 for M values) and the ozone photolysis rate also becomes a first-order kinetics, the rate constant being as follows:

k ) 2.303I0ΦO3

O3 [(1 - exp(-µL)] µ

(14)

As shown in Table 5, values of Hatta for reaction 3 when PAHs are present are near 0.3 (limiting value for the absorption regime to be moderate30). Table 6 gives chemical reaction rate equations corresponding to the reactions of Table 2 of ozone, the aromatic compound, hydrogen peroxide, phosphate ions, and bicarbonate ions. Reaction rate equations for free radicals, not shown, can easily be deduced from the reactions of Table 2. For these cases, net reaction rates were assumed to be zero according to the hypothesis of the stationary state. As far as the carbonate ion radical is concerned, it is known that this species also reacts

with the organics but the rate data of these reactions is only known for some cases34,35 and rate constant values are very much lower than those corresponding to reactions with a hydroxyl radical (reaction 39 of Table 2). Thus, in this work, carbonate radicals, formed from reactions 21 and 22 between carbonate ions and hydroxyl radicals, were assumed to only react with superoxide and ozonide ion radicals and hydrogen peroxide to regenerate the bicarbonate ion and the hydroperoxide ion radical (see reactions 23-26 in Table 2). Ozonation Alone. A Fortran program was prepared to solve differential equations (1)-(6) for the case of ozonation alone taking into account the equations of Table 6 and eq 7. The program uses the fourth-order Runge-Kutta method and the rate constant and parameter values given in Tables 1-3. In each iteration, concentrations of free radicals are first calculated by a trial and error procedure and then they are used to obtain the concentration of molecular species from the Runge-Kutta method. Figure 1 shows, as an example, the evolution of experimental and calculated concentrations of nitrobenzene with reaction time, corresponding to an ozonation reaction. As can be seen, the kinetic model overestimates the experimental results with very significant deviations. Similar results were obtained when simulating the ozonation of fluorene and 2,6dinitrotoluene. These three aromatics are characterized by their very low direct reactivity with ozone. Another important fact to note refers to the concentrations of ozone in water and in the gas leaving the reactor. Thus, as observed from Figures 2 and 3, calculated ozone concentrations are always higher than the experimental ones. On the other hand, for the case of phenanthrene, which reacts directly with ozone at a much higher rate (see rate constant in Table 3), although the kinetic regime is still slow (see Table 4), calculated concentrations were much closer to the experimental ones, as shown in Figure 4 as an example. Another PAH investigated,2-5 acenaphthene, that also reacts with ozone exclusively by a direct method, at the conditions studied, the kinetic model was not used because the kinetic regime of ozonation was moderate or fast (see Table 4 for Hatta numbers). Regarding the ozonation of fluorene, nitrobenzene, and 2,6-dinitrotoluene, at first sight, the results obtained (calculated concentrations much higher than the experimental ones) are surprising because reaction intermediates were not accounted for in the kinetic model. In the absence of intermediate reactions, at least theoretically, more ozone and hydroxyl radicals are available to react with the parent aromatic compound and a faster oxidation rate should be expected. This means that calculated concentrations of aromatics should have been lower than the experimental ones. Because direct reactions are not very important in the ozonation of these hydrocarbons (see Table 3 for rate constant values), it is evident that the mechanism lacks

Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999 4193 Table 6. Reaction Rate Equations of the Main Species of Advanced Oxidation Mechanism of Table 2a compound ozone in water aromatic compound total hydrogen peroxide total bicarbonate ion total phosphate ion a

equation of chemical rate, ri rO3 ) (k11C + 2k17C + k18C + k20CO2•-)CHO4• - k24CCO3•-CO2•- - (kdCM + k1COH- + k2CHO2- + k5CO2•- + k7CHO•)CO3 - rUVO3 rM ) -(zkdCO3 + kHOMCHO•)CM - rUVM rH2O2T ) (k12CHO• + k14CHO3•)CHO• + k16CHO3•2 + k17CHO4•2 - rUVH - [k9CHO• + k25CCO3•- + (k2CO3 + k10CHO• + k26CCO3•-) × 10(pH-11.7)](CH2O2T/(1 + 10(pH-11.7)) rTBC ) [k23CO2•- + k24CO3•- + k25CH2O2T/(1 + 10(pH-11.7)) + k26 × 10(pH-11.7)CH2O2T/(1 + 10(pH-11.7))]CCO3•- [(k21 + k22 × 10(pH-10.4)) × 10(pH-6.4)CTBC/(1 + 10(pH-6.4) + 10(2pH-16.8))]CHO• rPHT ) -(k27 + k28 × 10(pH-2.2) + k29 × 10(2pH-9.4))CPHT/(1 + 10(pH-2.2) + 10(2pH-9.4)) HO2•

HO4•

HO3•

For reaction rate of direct photolysis of ozone, rUVO3, aromatic compound, rUVM, and hydrogen peroxide, rUVH, see eq 9.

Figure 1. Verification of the kinetic model. Evolution of experimental and calculated dimensionless remaining concentrations of nitrobenzene with time during (1) ozonation and (2) O3/H2O2 oxidation. Symbols (experimental data) 0, ozonation alone; 9, O3/ H2O2 oxidation. Dotted curves: kinetic model without intermediate reactions. Solid curves: kinetic model with intermediate reactions. Conditions: (standard reactor) T ) 20 °C, pH 7, CTPH ) 10-3 M, and Fg ) 50 L h-1. For ozonation alone, the inlet ozone partial pressure is 264 Pa and CNB0 ) 7.98 × 10-5 M. For O3/H2O2 oxidation, the inlet ozone partial pressure is 304 Pa, CNB0 ) 1.52 × 10-4 M, and CH2O2T0 ) 1.75 × 10-4 M.

some free radical initiation reactions not accounted for in Table 1. Furthermore, some of these reactions should involve ozone as deduced from Figures 2 and 3 because the calculated concentrations should have been lower, that is, closer to the experimental ones. In an ozonation process, these reactions can likely be due to the presence of substances in water that promote the decomposition of ozone (i.e., Fe2+, humic substances, etc.) and/or to the action of intermediates that could react with ozone to yield organic peroxides or hydrogen peroxide.38-41 In this work, however, most experiments were carried out in pure water in the presence of phosphates to buffer the system or bicarbonate ions in some cases. Importance of Intermediates. According to the results obtained, the kinetic model predicts reasonably well the experimental results only in the case of phenanthrene that reacted exclusively with ozone through direct reaction. In other words, the kinetic model is valid on the basis of the mechanism of Table 2 when, in ozonation processes, free radical reactions contributions to the hydrocarbon oxidation rate is negligible (see Figure 4). On the contrary, when the

Figure 2. Verification of the kinetic model. Evolution of experimental and calculated concentration of dissolved ozone with time during ozonation. Symbols (experimental data): dotted curve, without intermediate reactions; solid curve, with intermediate reactions. Conditions: T ) 20 °C, pH 7, and CTPH ) 10-3 M. The inlet ozone partial pressure is 264 Pa, Fg ) 50 L h-1, and CNB0 ) 7.98 × 10-5 M (standard reactor).

aromatic hydrocarbon disappears through free radical reactions, as in the case of the ozonations of fluorene, nitrobenzene, and 2,6-dinitrotoluene, other reactions not yet included in the mechanism are likely responsible for the increase of the oxidation rate. To confirm this, attention was exclusively paid to the ozonation of nitrobenzene. One of the first intermediates of nitrobenzene is nitrophenol, as identified in a previous work.6,7 This phenol was formed from electrophilic substitution reactions, both from the direct attack of ozone or hydroxyl radicals.41-42 Once nitrophenol (specially o- or p-isomer) was formed, following intermediates of ozonation (through ozone direct reactions) could be deduced from the well-known phenol ozonation mechanism.40,41,43 Thus, it is expected that compounds such as nitrodihydroxybenzenes (nitroresorcinols) and unsaturated carboxylic acids (i.e., nitromuconic acid, etc.) are also formed in a consecutive series of ozonation reactions. Notice that the aromatic ring or carbon double-bond breaking (nitroresorcinol to nitromuconic acid and this one to other lower molecular weight compounds) through 1,3-dipolar cycloaddition reactions40-42 released hydrogen peroxide, a strong initiator of ozone decomposition (reaction 2 in Table 2). It should also be noticed that hydrogen peroxide formation through ozonation of phenol and polynuclear aromatic hydrocarbons is welldocumented.38,41 On the other hand, intermediate compounds such as nitroresorcinol and nitromuconic acid

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Figure 3. Verification of the kinetic model. Evolution of experimental and calculated concentrations of ozone in the gas leaving the reactor with time during ozonation. Symbols (experimental data): dotted curve, without intermediate reactions; solid curve, with intermediate reactions. Conditions: T ) 20 °C, pH 7, and CTPH ) 10-3 M. The inlet ozone partial pressure is 264 Pa, Fg ) 50 L h-1, and CNB0 ) 7.98 × 10-5 M (standard reactor).

Figure 5. Proposed reaction mechanism for the ozonation of nitrobenzene through (a) direct ozone reactions and (b) hydroxyl free radical reactions: (A) electrophilic substitution, (B) dipolar cycloaddition, (1) nitrobenzene, (2) p-nitrophenol, (3) nitroresorcinol, and (4) nitromuconic acid.

Figure 4. Verification of the kinetic model. Evolution of experimental and calculated dimensionless remaining concentrations of phenanthrene with time during (1) ozonation and (2) O3/H2O2 oxidation. Symbols (experimental data): dotted curves, without intermediate reactions. Conditions (standard reactor): T ) 20 °C, pH 7, CTPH ) 10-3 M, and Fg ) 25 L h-1. For ozonation, the inlet ozone partial pressure is 567 Pa and CPH0 ) 4.04 × 10-6 M. For O3/H2O2 oxidation, the inlet ozone partial pressure is 547 Pa, CPH0 ) 1.51 × 10-5 M, and CH2O2T0 ) 10-3 M.

could also be formed from reactions with hydroxyl radicals through a similar series of consecutive steps.44,45 In these cases, hydroperoxide ion radicals were also formed.8 This tentative mechanism of direct and free radical reactions is shown in Figure 5. Accordingly, contribution of these reactions through mole balance equations of the first three intermediates of nitrobenzene ozonation was included in the kinetic model. The

assumed intermediates considered were finally p-nitrophenol (NPH), nitroresorcinol (NR), and muconic acid (MU). These compounds were chosen because of their commercial availability, experimental identification (case of p-nitrophenol6,7), and similarity between phenol and nitrophenol ozonations.40,41,43 A solution of the new set of differential equations first require knowledge of rate constant data of intermediate reactions. Determination of these rate data were accomplished through different methods that are described in detail in previous papers.46-50 Table 7 shows the values obtained. As shown in Figures 1-3, modifications introduced when intermediate reactions were considered significantly improved the kinetic model to predict the concentrations of nitrobenzene and dissolved ozone, although the calculated concentrations of ozone in the gas leaving the reactor still deviated from the experimental ones. The example given in Figure 3, however, represents the worst case found among the simulations made as far as the concentration of ozone in the exit gas was concerned. It should be noticed that this concentration was determined for short reaction periods (2 min) by an iodometric method. This could lead to analytical errors in the concentration values, depending on the ozone partial pressure. In any case, modification of the kinetic model led to calculated concentrations much

Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999 4195 Table 7. Rate Constant Data, Extinction Coefficients, and Quantum Yield for Assumed Intermediates of NB Ozonation compound

pH

z

kd, M-1 s-1

kOHM, M-1 s-1

M, M-1 cm-1

ΦM , mol photon-1

NPH

7

1a

4.5 × 106 a

3.8 × 109 b 2.7 × 109 c,e

1131c

1.05 × 10-2 c,d

3165c 3609c

7.9 × 10-3 c,d

25500c

8.7 × 10-3 c,d

NR MU

9 7 9 7

1c,g 1c,g

14 × 106 f 2.7 × 107 c,h 4.2 × 109 c,h 1.2 × 106 c,h

3.4 × 109 c,e 6.9 × 109 c,e 5.1 × 109 c,e 6.0 × 109 b

a From Beltra ´ n et al., 1992.51 b From Buxton et al., 1988.8 c This work. d From competitive photolysis kinetics.48 e From UV/H2O2 oxidation kinetics.49 f Hoigne´ and Bader, 1983.47 g Following procedure of Sotelo et al., 1990.46 h From competitive ozonation kinetics.50

Figure 6. Verification of the kinetic model. Evolution of experimental and calculated dimensionless remaining concentrations of nitrobenzene with time during (1) ozonation at pH 9, (2) ozonation in the presence of bicarbonate ions, and (3) ozonation in surface water. Symbols (experimental data): 9 (1); b (2); 2 (3). Dotted curves, without intermediate reactions; solid curves, with intermediate reactions. Conditions (standard reactor): (1) T ) 20 °C, pH 9, and CTPH ) 10-3 M. The inlet ozone partial pressure is 1034 Pa, Fg ) 50 L h-1, and CNB0 ) 5.03 × 10-5 M. (2) T ) 20 °C, pH 9, and CTBC ) 0.1 M. The inlet ozone partial pressure is 1216 Pa, Fg ) 50 L h-1, and CNB0 ) 8.82 × 10-5 M. (3) Surface water, River Gevora (Badajoz, Spain); inorganic carbon, 12 mg L-1 (10-3 M total bicarbonate ion), T ) 20 °C and pH 8.5. The inlet ozone partial pressure is 233 Pa, Fg ) 50 L h-1, and CNB0 ) 9.60 × 10-5 M.

closer to the experimental ones, which suggests that proposed intermediate reactions (Figure 5) give a better explanation of the ozonation kinetics. Calculated concentrations of intermediates (not shown) were found to be very low. This supports the fact that these compounds, except nitrophenols, were not identified during the ozonation of nitrobenzene.6 On the other hand, from these concentrations and rate constants of their direct reactions with ozone (see Table 7), the Hatta numbers were always found to be lower than 0.3, which confirms the slow kinetic regime of ozonation. Also, the kinetic model was tested for the ozonation of nitrobenzene at different pH, in the presence of carbonates and in surface water. Calculated results when intermediates were considered were in all cases close to the experimental ones, as shown in Figure 6 as an example. Ozone Plus Hydrogen Peroxide Oxidation. The kinetic model was also checked for combined ozonations

with hydrogen peroxide. For phenanthrene oxidation, calculated results were close to the experimental ones (see also Figure 4) without considering the role of intermediates. In the case of nitrobenzene, oxidation by hydroxyl radicals represents the main way of removal.7 According to this, the presence of hydrogen peroxide should increase the oxidation rate compared to that obtained when ozone alone was applied. However, experimental results of ozonation were similar both in the presence and in the absence of hydrogen peroxide7 at concentrations lower than 10-2 M. This seems to be a contradictory result unless hydrogen peroxide or other species of similar oxidant character (possibly organic peroxides) are also formed during ozonation alone, as proposed in Figure 5. The kinetic model was then used to simulate the ozone-hydrogen peroxide oxidation of nitrobenzene. Figure 1 also presents the experimental and calculated concentrations of nitrobenzene (referred to as the initial concentration) with time corresponding to one ozonation experiment in the presence of hydrogen peroxide. It is observed that the calculated results were much closer to the experimental ones when intermediate reactions of Figure 5 were considered. From the experimental and calculated results follow that the addition of hydrogen peroxide is not necessary because this compound or others of similar roles (organic peroxides) are naturally formed during ozonation, resulting in high oxidation rates of nitrobenzene. Furthermore, the model also predicts that the oxidation rate of nitrobenzene is partially inhibited when hydrogen peroxide is present in concentrations higher than 10-2 M (not shown). This has also been observed in experimental results.7 UV Radiation Involving Systems. UV radiation can be used alone or combined with hydrogen peroxide or ozone to remove aromatic hydrocarbons from water.3,4,7 Aromatic hydrocarbons studied in this work showed in some cases significant quantum yield values at 254 nm (see Table 3) and their UV photolysis has also been studied.3,7 The kinetic model proposed is also appropriate to follow the UV photolysis of aromatic compounds, provided their quantum yields are known. For so doing, the rate of direct photolysis of any hydrocarbon or species, M, has to be considered:33

∑iCi)]

rM ) I0ΦMFM[1 - exp(-2.303L

(15)

where subscript M refers to the compound treated. For the case of ozone in the gas phase, the ozone photolysis rate, rUVO3g, can be defined as follows:3

rUVO3g ) I0ΦO3g

(16)

4196


Figure 7. Verification of the kinetic model. Evolution of experimental and calculated dimensionless remaining concentration of nitrobenzene and phenanthrene with time during UV/H2O2 oxidation. Symbols (experimental data): 9, nitrobenzene, 2, phenanthrene. Solid curves (UV/H2O2 kinetic model with intermediate reactions): (1) nitrobenzene; (2) phenanthrene. Conditions (photochemical reactor): T ) 20 °C, pH 7, I0 ) 3.8 × 10-6 einstein L-1 s-1, and CTPH ) 10-3 M. Nitrobenzene oxidation: Fg (nitrogen) ) 50 L h-1, CNB0 ) 8.35 × 10-5 M, and CH2O2T0 ) 1.1 × 10-3 M. Phenantrene oxidation: Fg (nitrogen) ) 25 L h-1; CPH0 ) 3.87 × 10-6 M, and CH2O2T0 ) 1.0 × 10-3 M.

where ΦO3g is the ozone quantum yield in the gas phase that can be obtained from literature.52 Actinometric and quantum yield data used in this work are presented in Tables 1-3 and 7. Extinction coefficients for ozone and hydrogen peroxide (this one at pH 7) were taken as 3300 and 19 M-1 cm-1, respectively.35,53 The kinetic model was able to simulate the experimental results of the direct photolysis of the aromatic compounds investigated (not shown). Also, as shown in Figure 7, as an example, for the case of nitrobenzene, calculated results of the UV/H2O2 oxidation when intermediate reactions were considered (direct photolysis and hydroxyl radical attack) were also close to the experimental ones. In the case of phenanthrene oxidation, the kinetic model underestimated the experimental concentrations when no intermediates were included (not shown). However, this was expected because, different from ozonation processes, free radical oxidation played an important role during the UV/H2O2 oxidation of phenanthrene (more than 50% oxidation was due to hydroxyl radical attacks4). Thus, to simulate this oxidizing system, the contribution of intermediates should be accounted for in the mechanism. Following the nitrobenzene ozonation mechanism and the fact that 9,10-phenanthrenedione4 was one of the intermediates identified during the UV/ H2O2 oxidation of phenanthrene, it is likely that 9- or 10-phenanthrenol was the first intermediate of oxidation. Because this compound was not available and kept the aromatic rings of phenanthrene, for simulation purposes, it was assumed its extinction coefficient and quantum yield was equal to those of the parent compound, phenanthrene (see Table 3). For the rate constant of its reaction with hydroxyl radical, on the other

Figure 8. Verification of the kinetic model. Evolution of experimental and calculated dimensionless remaining concentration of nitrobenzene and phenanthrene with time during O3/UV oxidation. Symbols (experimental data): 9, nitrobenzene; 2, phenanthrene. Solid curve: O3/UV kinetic model with intermediate reactions for (1) nitrobenzene. Dotted curve: O3/UV kinetic model without intermediate reactions for (2) phenanthrene. Conditions (photochemical reactor): T ) 20 °C, pH 7, and CTPH ) 10-3 M. Nitrobenzene oxidation: Fg ) 50 L h-1, CNB0 ) 1.2 × 10-4 M, and inlet ozone partial pressure is 233 Pa. Phenanthrene oxidation: Fg ) 25 L h-1; CPH0 ) 1.85 × 10-5 M, and inlet ozone partial pressure is 506 Pa.

hand, a value of 5 × 109 M-1 s-1 was also assumed. This represents an average value for this type of reaction.8 Simulation of UV/H2O2 oxidation of phenanthrene with the inclusion of the rate data of the intermediate in the kinetic model improved the calculated concentrations (see also Figure 7). As seen in Figure 7, as far as the UV/H2O2 oxidation system is concerned, both aromatics studied behaved in a similar way. Simulation was significantly improved with the inclusion of intermediate reactions. In the case of combined ozonation with UV radiation, however, the kinetic model was inappropriate as shown in Figure 8 as an example. For these cases, regardless of the presence of intermediate reactions, calculated concentrations of nitrobenzene were always higher than the experimental ones. For this oxidation system, it is likely that the mechanism proposed did not contain other possible reactions that accelerate the oxidation rates. Possible reactions of this type could have been due to the species formed during photolysis of PAHs or NA. Thus, Legrini et al.54 reported that UV radiation of some organic compounds yields superoxide ions radicals. These radicals in the presence of ozone would increase the concentration of hydroxyl radicals and possibly the oxidation rate. Simulation of the UV/O3 oxidation of phenanthrene with no intermediates, on the other hand, led to calculated concentrations lower than the experimental ones for conversions of phenanthrene higher than 30%, as is also shown in Figure 8. Inclusion of the rate data of the assumed intermediate led to poorer results. When calculated data of NB or PH UV/ O3 oxidations is taken into account, it is likely that the

Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999 4197

main reason for the discrepancies observed could have been due to a change in the ozone kinetic regime of absorption. Thus, calculated concentrations of free radicals (hydroxyl and superoxide ion radicals) were found to be higher than 10-10 M. At these concentrations reactions of ozone with these radicals developed in the moderate kinetic regime of absorption (Hatta numbers of reactions 5 and 7 are higher than 0.3, as can be deduced from the data in Table 4). This invalidates the use of the kinetic model in the UV/O3 oxidation. Conclusions The kinetic model proposed in this work uses rate data information obtained experimentally and leads to good predictions of the concentration of main species (hydrocarbon and dissolved ozone) during the advanced oxidation (ozonation alone, ozone-hydrogen peroxide, UV radiation alone, and UV radiation-hydrogen peroxide systems) of nitrobenzene and phenanthrene in water. On the contrary, the kinetic model was unable to reproduce with accuracy the ozone-UV radiation oxidation experimental results. For the aromatic hydrocarbons that react mainly with hydroxyl radicals during ozonation processes, as is the case with nitrobenzene, the kinetic model leads to poor results when intermediate reactions are not accounted for. Results obtained for the simulation of nitrobenzene suggest that the reactions of intermediates are important to improve the kinetic model of aromatic hydrocarbon advanced oxidation. Particularly, the formation of hydrogen peroxide (identified during ozonation reactions), likely from 1,3-ozone cycloaddition reactions of some intermediates, results fundamental to improve the kinetic model. This has been tested in the oxidation of nitrobenzene by considering reactions of some assumed intermediates: p-nitrophenol (identified during oxidation6,7), nitroresorcinol, and muconic acid (the latter two assumed because of the similarity with the phenol ozonation mechanism and commercial availability, case of muconic acid). The kinetic model also allows one to simulate with good results the oxidation of phenanthrene, a compound that reacts exclusively with ozone by a direct method, without the presence of intermediate reactions. Thus, it is evident that the importance of intermediate reactions depends on the contribution of the direct reaction between ozone and the parent aromatic hydrocarbon for the oxidation rate. For compounds such as phenanthrene that reacts exclusively with ozone by direct reaction the kinetic model can be used without mole balance equations of intermediates. For compounds such as nitrobenzene that hardly reacts directly with ozone (hence, free radical oxidation is the primary method of removal) the kinetic model leads to very poor calculated results when compared to the experimental ones if intermediate reactions are not accounted for. The inclusion of mole balance equations of intermediates, as checked in the case of nitrobenzene ozonation, significantly improved the results, yielding calculated concentrations very much closer to the experimental ones. For nonozone advanced oxidation systems, like the UV/H2O2 system, inclusion of intermediates in the kinetic model is necessary to better predict the remaining concentrations of aromatic hydrocarbons, regardless of their nature. In this case, more than 50% of the oxidation rate of NB and PH is due to the action of free radicals.4 The kinetic model, however, is not appropriate to properly reproduce the experimental results of the O3/

UV oxidation. In this case, it is likely that other propagating reactions not accounted for develop. Examples could be the formation of superoxide ion radicals from direct photolysis of aromatics. However, a change of the ozone absorption kinetic regime, which becomes moderate, is likely the main reason for the discrepancies. This change makes unuseful the kinetic model proposed. Further research is still needed to complete kinetic models of the advanced oxidation of complex organic compounds. For so doing, on the one hand, the identification of intermediates and the determination of rate constants of their reactions with ozone and the hydroxyl radical and quantum yields of their direct photolysis are highly recommended. On the other hand, as far as the O3/UV oxidation system is concerned, kinetic equations have to be established corresponding to the moderate or fast kinetic regime of ozone absorption. Acknowledgment Authors thank the CICYT of Spain (Project AMB97/ 339). Nomenclature C ) concentration of any species, M D ) diffusivity of any species in water, m2 s-1 F ) fraction of incident radiation absorbed, defined in eq 11, dimensionless Fg ) gas flow rate, L s-1 He ) Henry’s constant for the ozone-water system, Pa M-1 Ha ) Hatta number defined by eq 8, dimensionless I0 ) intensity of incident radiation, einstein L-1 s-1 k ) rate constant of an irreversible first- or second-order reaction, s-1 or M-1 s-1, respectively kL ) individual liquid-phase mass-transfer coefficient, m s-1 kLa ) volumetric mass-transfer coefficient, s-1 L ) effective path of radiation through the photoreactor, cm N ) absorption rate, M s-1 R ) ideal gas constant, Pa M-1 K-1 r ) chemical reaction rate, M s-1 T ) temperature, K t ) reaction time, s V ) reactor volume z ) stoichiometric coefficient of a direct ozone-organic reaction, dimensionless Greek Letters β ) liquid holdup ) extinction coefficient, M-1 cm-1 Φ ) quantum yield at 254 nm, mol photon-1 µ ) absorbance solution defined in eq 10, cm-1 Subscripts A ) acenaphthene B ) any species reacting with ozone d ) direct ozone-aromatic hydrocarbon or intermediate reaction DNT ) 2,6-dinitrotoluene F ) fluorene HOM ) reaction between hydroxyl radical and aromatic hydrocarbon or intermediate H2O2T ) total hydrogen peroxide i ) any species that absorbs radiation M ) any aromatic hydrocarbon M0 ) any aromatic hydrocarbon at initial time

4198


MU ) muconic acid NB ) nitrobenzene NPH ) nitrophenol NR ) nitroresorcinol O3 ) ozone in water O3g ) ozone in the gas inside the reactor or at the reactor outlet O3gi ) ozone in the gas at the reactor inlet PAH ) polynuclear aromatic hydrocarbon or aromatic hydrocarbon PH ) phenanthrene TBC ) total bicarbonate TPH ) total phosphate UVO3 ) ozone in water in the UV/O3 system UVO3g ) ozone in the gas in the UV/O3 system

Literature Cited (1) Harrison, R. M. Pollution: Causes, Effects and Control. Royal Society of Chemistry: Cambridge, 1990. (2) Beltrań, F. J.; Ovejero, G.; Encinar, J. M.; Rivas, J. Oxidation of Polynuclear Aromatic Hydrocarbons in Water. 1. Ozonation. Ind. Eng. Chem. Res. 1995, 34, 1596. (3) Beltrań, F. J.; Ovejero, G.; Garcıá-Araya, J. F.; Rivas, J. Oxidation of Polynuclear Aromatic Hydrocarbons in Water. 2. UV Radiation and Ozonation in the Presence of UV Radiation. Ind. Eng. Chem. Res. 1995, 34, 1607. (4) Beltrań, F. J.; Ovejero, G.; Rivas, J. Oxidation of Polynuclear Aromatic Hydrocarbons in Water. 3. UV Radiation Combined with Hydrogen Peroxide. Ind. Eng. Chem. Res. 1996, 35, 883. (5) Beltrań, F. J.; Ovejero, G.; Rivas, J. Oxidation of Polynuclear Aromatic Hydrocarbons in Water. 4. Ozone Combined with Hydrogen Peroxide. Ind. Eng. Chem. Res. 1996, 35, 891. (6) Beltrań, F. J.; Encinar, J. M.; Alonso, M. A. Nitroaromatic Hydrocarbon Ozonation in Water. 1. Single Ozonation. Ind. Eng. Chem. Res. 1998, 37, 25. (7) Beltrań, F. J.; Encinar, J. M.; Alonso, M. A. Nitroaromatic Hydrocarbon Ozonation in Water. 2. Combined Ozonation with Hydrogen Peroxide or UV Radiation. Ind. Eng. Chem. Res. 1998, 37, 32. (8) Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A, B. Critical Review of Data Constants for Reactions of Hydrated Electrons, Hydrogen Atoms and Hydroxyl Radicals (.OH/.O-) in Aqueous Solution. J. Phys. Chem. Ref. Data 1988, 17, 513. (9) Glaze, W. H.; Kang, J. H. Advanced Oxidation Processes. Description of a Kinetic Model for the Oxidation of Hazardous Materials in Aqueous Media with Ozone and Hydrogen Peroxide in a Semibatch Reactor. Ind. Eng. Chem. Res. 1989, 28, 1573. (10) Glaze, W. H.; Kang, J. W. Advanced Oxidation Processes. Test of a Kinetic Model for the Oxidation of Organic Compounds with Ozone and Hydrogen Peroxide in a Semibatch Reactor. Ind. Eng. Chem. Res. 1989, 28, 1580. (11) Yurteri, C.; Gurol, M. D. Ozonation of Trace Organic Compounds: Model Predictions versus Experimental Data. Ozone Sci. Eng. 1990, 12, 217. (12) Hayashi, J.; Ikeda, J.; Kusakabe, K.; Morooka, S. Decomposition Rate of Volatile Organochlorines by Ozone and Utilization Efficiency of Ozone with Ultraviolet Radiation in a Bubble Column Contactor. Water Res. 1993, 27, 1091. (13) Laplanche, A.; Bastiment, R.; Boisdon, V. Modelisation de l’oxydation de l’atrazine et de ses sous-produits dans les colonnes d’ozonation a´ bulles. Proceedings 1st Research Symposium on Les sous-produits de traitement et d’epuration des eaux; 29-1, International Ozone Association: Poitiers, France, 1994. (14) Kallas, J.; Hautaniemi, M.; Munter, R.; Trapido, M.; Veressinina, Y. Ozonation and Advanced Oxidation Processes of Polynuclear Aromatic HydrocarbonssMathematical Modeling. Proceedings Regional Conference on Ozone, Ultraviolet Light, Advanced Oxidation Processes in Water Treatment; International Ozone Association: Amsterdam, 1996; p 395. (15) Sunder, M.; Hempel, D. C. Oxidation of Tri- and Perchloroethene in Aqueous Solution with Ozone and Hydrogen Peroxide in a Tube Reactor. Water Res. 1997, 31, 33. (16) Liao, C. H.; Gurol, M. D. Chemical Oxidation by Photolytic Decomposition of Hydrogen Peroxide. Environ. Sci. Technol. 1995, 29, 3007.

(17) Glaze, W. H.; Lay, Y.; Kang, J. W. Advanced Oxidation Processes. A Kinetic Model for the Oxidation of 1,2-Dibromo-3Chloropropane in Water by the Combination of Hydrogen Peroxide and UV Radiation. Ind. Eng. Chem. Res. 1995, 34, 2314. (18) Stefan, M. I.; Hoy, A. R.; Bolton, J. R. Kinetics and Mechanism of the Degradation and Mineralization of Acetone in Dilute Aqueous Solution Sensitized by the UV Photolysis of Hydrogen Peroxide. Environ. Sci. Technol. 1996, 30, 2382. (19) Mak, F. T.; Zele, S. R.; Cooper, W. J.; Kurucz, C. N.; Waite, T. D.; Nickelsen, G. Kinetic Modeling of Carbon Tetrachloride, Chloroform and Methylene Chloride Removal from Aqueous Solution Using the Electron Beam Process. Water Res. 1997, 31, 219. (20) Tang, W. Z.; Tassos, S. Oxidation Kinetics and Mechanisms of Trihalomethanes by Fenton’s Reagent. Water Res. 1997, 31, 1117. (21) Fogler, H. S. Elements of Chemical Reaction Engineering; Prentice Hall: Englewood Cliffs, NJ, 1986. (22) . Staehelin, S.; Hoigne´, J. Decomposition of Ozone in Water: Rate of Initiation by Hydroxyde Ions and Hydrogen Peroxide. Environ. Sci. Technol. 1982, 16, 666. (23) Baxendale, J. H.; Wilson, J. A. Photolysis of Hydrogen Peroxide at High Light Intensities. Trans. Faraday Soc. 1957, 53, 344. (24) Staehelin, S.; Hoigne´, J. Decomposition of Ozone in Water in the Presence of Organic Solutes Acting as Promoters and Inhibitors of Radical Chain Reactions. Environ. Sci. Technol. 1985, 19, 1206. (25) Staehelin, J.; Buhler, R. E.; Hoigne´, J. Ozone Decomposition in Water Studied by Pulse Raiolysis. 2. OH and HO4 as Chain Intermediates. J. Phys. Chem. 1984, 88, 5999. (26) Christensen, H. S.; Sehensted, H.; Corfitzan, H. Reactions of Hydroxyl Radicals with Hydrogen Peroxide at Ambient and Elevated Temperatures. J. Phys. Chem. 1982, 86, 55. (27) Neta, P.; Huie, R. E.; Ross, A. B. Rate Constants for Reactions of Inorganic Radicals in Aqueous Solution. J. Phys. Chem. Ref. Data 1988, 17, 1027. (28) Grabner, G.; Getoff, N.; Schwoerer, F.; Pulseradiolyse von H3PO4, H2PO4-, HPO42- und P2O74- in waesriger loesung. I. Geschwindigkeitskonstanten der reaktionenmit den primaerprodukten der wasser radiolyse. Int. J. Radiat. Phys. Chem. 1973, 5, 393. (29) Weast, R. C. Handbook of Chemistry and Physics, 58th ed.; CRC Press: Cleveland, 1977. (30) Charpentier, J. C. Mass Transfer Rates in Gas-Liquid Absorbers and Reactors. In Advances in Chemical Engineering; Academic Press: New York, 1981; Vol. 11, pp 3-133. (31) Kuczkowski, R. L. Ozone and carbonyl oxides. In 1,3,Dipolar Cycloaddition Chemistry; John Wiley and Sons: New York, 1984; Vol. 2A, pp 197-277, (32) Johnson, P. N.; Davis, R. A. Diffusivity of Ozone in Water J. Chem. Eng. Data 1996, 41, 1485. (33) Leifer, A. The Kinetics of Environmental Aquatic Photochemistry; American Chemical Society: Washington, DC, 1988. (34) Beltrań, F. J. Theoretical Aspects of the Kinetics of Competitive First Order Reactions of Ozone in the O3/H2O2 and O3/UV Oxidation Processes. Ozone Sci. Eng. 1997, 19, 13. (35) Dore´, M. Chimie des oxidants et traitement des eaux; Technique et Documentation-Lavoisier: Paris, 1989. (36) Chen, S.; Hoffman, M. Z.; Parsons, G. H., Jr. Reactivity of the Carbonate Radical Toward Aromatic Compounds in Aqueous Solution. J. Phys. Chem. 1975, 79, 1911. (37) Neta, P.; Huie, R.; Ross, A. B. Rate Constants for Reactions of Inorganic Radicals in Aqueous Solutions. J. Phys. Chem. Ref. Data 1988, 17, 1027. (38) Nakamuro, K.; Ueno, H.; Nakao, M.; Sayato, Y. Formation of Hydrogen Peroxide by Aqueous Ozonation of Humic Acid and Aromatic Hydrocarbons. Chemosphere 1990, 20, 525. (39) Langlais, B., Reckhow, D. A., Brink, D. R., Eds. Ozone in Water Treatment: Application and Engineering; Lewis: Chelsea, MI, 1991. (40) Decoret, C.; Royer, J.; Legube, B.; Dore´, M. Experimental and Theoretical Studies of the Mechanism of the Initial Attack of Ozone on Some Aromatics in Aqueous Medium. Environ. Technol. Lett. 1984, 5, 207. (41) Legube, B. Contribution a´ l’etude de compose´ s aromatiques en solution aqueuse. These d’Etat, Universite´ de Poitiers, France, 1983.

Ind. Eng. Chem. Res., Vol. 38, No. 11, 1999 4199 (42) Bailey, P. S. The Reactions of Ozone with Organic Compounds. Chem. Rev. 1958, 58, 925. (43) Gurol, M. D.; Singer, P. C. Dynamics of the Ozonation of Phenol-II Mathematical Simulation. Water Res. 1983, 17, 1173. (44) Hoigne´, J. Chemistry of Aqueous Ozone and Transformation of Pollutants by Ozonation and Advanced Oxidation Processes. In The Handbook of Environmental Chemistry. Quality and Treatment of Drinking Water II; Hrubec, J., Ed.; SpringerVerlag: Berlin, Heidelberg, 1988; Vol. 5, Part C. (45) Von Sonntag, C.; Schuchmann, H. The Elucidation of Peroxyl Radical Reactions in Aqueous Solution with the Help of Radiation-Chemical Methods. Angew. Chem., Int. Ed. Engl. 1990, 30, 1229. (46) Sotelo, J. L.; Beltrań, F. J.; Gonza´lez, M. Ozonation of Aqueous Solutions of Resorcinol and Pholoroglucinol. 1. Stoichiometric and Absorption Kinetic Regime. Ind. Eng. Chem. Res. 1990, 29, 2358. (47) Hoigne´, J.; Bader, H. Rate Constants of the Reactions of Ozone with Organic and Inorganic Compounds. II. Dissociating Organic Compounds. Water Res. 1983, 17, 185. (48) Beltrań, F. J.; Gonza´lez, M.; Acedo, B.; Jaramillo, J. Contribution of Free Radical Oxidation to Eliminate Volatile Organochlorine Compounds in Water by Ultraviolet Radiation and Hydrogen Peroxide. Chemosphere 1996, 32, 1949.

(49) Beltrań, F. J.; Ovejero, G.; Acedo, B. Oxidation of Atrazine in Water by Hydrogen Peroxide Combined with UV Radiation. Water Res. 1983, 27, 1013. (50) Gurol, M. D.; Nekouinaini, S. Kinetic Behavior of Ozone in Aqueous Solutions of Substituted Phenols. Ind. Eng. Chem. Fundam. 1984, 23, 53. (51) Beltrań, F. J.; Go´mez-Serrano, V.; Durań, A. Degradation Kinetics Of p-Nitrophenol Ozonation in Water. Water Res. 1992, 26, 9. (52) Morooka, S.; Kusakabe, K.; Hayasi, J.; Isomura, K.; Ikemizu, K. Decomposition and Utilization of Ozone in Water Treatment Reactor with Ultraviolet Radiation. Ind. Eng. Chem. Res. 1988, 27, 2372. (53) Glaze, W. H.; Kang, J. W.; Chapin, D. H. The Chemistry of Water Treatment Processes Involving Ozone, Hydrogen Peroxide and Ultraviolet Radiation. Ozone Sci. Eng. 1987, 9, 335. (54) Legrini, O.; Oliveros, E.; Braun, A. M. Photochemical Processes for Water Treatment. Chem. Rev. 1993, 93, 671.

Received for review March 17, 1999 Revised manuscript received July 26, 1999 Accepted August 8, 1999 IE990189R

A Kinetic Model for Advanced Oxidation Processes of Aromatic

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