Electrochemical Oxidation of Aqueous Phenol Wastes on Synthetic

Ind. Eng. Chem. Res. 2002, 41, 4187-4194

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Electrochemical Oxidation of Aqueous Phenol Wastes on Synthetic Diamond Thin-Film Electrodes P. Can ˜ izares,† M. Dıáz,‡ J. A. Domıńguez,‡ J. Garcıá-Go´ mez,† and M. A. Rodrigo*,† Departamento de Ingenierıá Quı´mica, Universidad de Castilla La Mancha, Campus Universitario s/n, 13004 Ciudad Real, Spain, and Departamento de Ingenierıá Quı´mica, Instituto Superior Polite´ cnico “Jose´ Antonio Echevarrıá”, Ciudad de la Habana, Cuba

The electrochemical oxidation of phenol in basic media using a diamond thin-film electrode has been studied. Within the parameter ranges used (temperature: 15-60 °C, initial total carbon concentration: 360-1450 mg of C dm-3; current density: 15-60 mA cm-2), almost complete mineralization of the organic waste is obtained. The mineralization rate increases with current density and temperature. Current efficiency depends mainly on mass transfer limitations: in the absence of mass transfer limitations, instantaneous current efficiencies of 1 are obtained. The main intermediates formed are maleic, fumaric, and oxalic acids. A simple model based on mass transfer and kinetic considerations, which involves four species (phenol, maleic/fumaric acid, oxalic acid, and carbon dioxide), can be used to explain the experimental behavior of the system, regardless of the conditions applied. Introduction Many industrial processes generate wastes containing small concentrations of refractory organic compounds. In appropriate circumstances, the organic compounds contained in these wastes can be economically recovered, but usually the best method to treat these wastes is their destruction by oxidation techniques. Among existing processes, photochemical degradation, chemical oxidation, wet oxidation, and electrochemical oxidation are of particular interest. The use of direct1-9 and mediated9-16 electrochemical oxidation for the destruction of the organics contained in wastewaters has been tried on both bench and pilot plant scales. Indeed, there are several commercial processes currently in use. The main problem associated with the electrochemical treatment is its high operating cost. In recent years, more research has been undertaken with the aim of gaining a better insight into this process and, consequently, to develop a less expensive application. It has been determined that the electrochemical treatment of organic wastewaters depends on a wide variety of factors, including anode material, waste characteristics, and oxidation conditions. The testing of numerous different anodes has been described in the literature. Analysis of reaction intermediates and the measurement of current efficiencies have shown that traditional anode materials (Pt, Ti/ IrO2, Ti/RuO2) favor electrochemical conversion (carboxylic acids are the final oxidation products) but with low current efficiency.17-19 This situation is in contrast to that found for Ti/SnO2 and diamond thin-film anodes, which not only give high current efficiencies but also favor electrochemical combustion.20-26 The anode mater-

ial also influences the electrochemical oxidation of organic compounds in the presence of mediators such as NaCl, because it has been observed that these mediators catalyze the oxidation of organic matter only in conjunction with certain anode materials.10 Besides the anode material, operating conditions play an important role in the electrochemical oxidation of organic wastewaters.27-31 Two parameters are considered to affect the process: current density and temperature. High temperatures increase the oxidation reaction rate and the current efficiency, as well as reducing the extent of polymerization. High current densities increase most reaction rates, but they also favor the formation of polymers. The third factor to consider is the waste characteristics, which govern the efficiency of electrochemical process.31-40 The organic compounds contained in the wastewater can have different degrees of oxidizability, and for specific compounds, the electrochemical process can lead to the formation of polymers. Moreover, the pH of the wastes has a great influence on the current efficiency and, for aromatic compounds, on the reaction intermediates. Aqueous phenol solutions are frequently used as reference wastes in the study of the electrochemical treatment of wastewaters. These solutions are representative of the wastes generated in various industrial areas (e.g., agrochemical, pulp and paper, pharmaceutical, and dyestuff industries). The goal of the work described here was to study the electrochemical oxidation of aqueous phenol wastes in basic media using diamond thin-film electrodes and to determine the influence of the initial concentration of phenol, temperature, and current density on the efficiency of the process. Experimental Details

* To whom correspondence should be addressed. E-mail: [email protected]. † Universidad de Castilla La Mancha. ‡ Instituto Superior Politećnico “Jose´ Antonio Echevarrıá”.

Analytical Procedure. Carbon concentrations were monitored using a Shimadzu TOC-5050 analyzer. Chemical oxygen demand (COD) was determined using a

10.1021/ie0105526 CCC: $22.00 © 2002 American Chemical Society Published on Web 07/19/2002

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Ind. Eng. Chem. Res., Vol. 41, No. 17, 2002

Figure 1. Lay out of the pilot plant. Detail of the electrochemical cell section.

HACH DR200 analyzer (method 8000). Organic compounds were identified and quantified by liquid chromatography (HPLC). The separation and analysis of carboxylic acids was performed on a Supelcogel H column, with a mobile phase of 0.15% phosphoric acid solution at a flow rate of 0.15 cm3/min. The UV detector was set at 210 nm. Aromatics were monitored using a Nucleosil C18 column, with a mobile phase of 40% methanol/60% water at a flow rate of 0.50 cm3/min. In this case, the UV detector was set to 270 nm. Determination of the Instantaneous Current Efficiency (ICE). The COD method was used for the determination of the current efficiency for the oxidation of phenol.5 In this method, the COD was measured during electrolysis and the instantaneous current efficiency was calculated using the relation

ICE )

[CODt+∆t - CODt]FV 8I∆t

(1)

where CODt and CODt+∆t are the chemical oxygen demand (in g of O2 dm-3) at times t and t+∆t (in seconds), respectively, I is the current intensity (A), F is the Faraday constant (96 487 C eq-1), V is the volume of the electrolyte (dm3), and 8 is a dimensional factor for unit consistence ((32 g of O2 × mol-1 of O2)/(4 mol of e- × mol-1 of O2)). Electrochemical Cell. The oxidation of phenol was carried out in a single compartment electrochemical flow cell (Figure 1). Diamond-based materials were used as the anode and stainless steel (AISI 304) as the cathode. Both electrodes were circular (100 mm diameter) with a geometric area of 78 cm2 each and with an electrode gap of 9 mm. The electrolyte was stored in a 500 mL glass tank and circulated through the electrolytic cell by a centrifugal pump. A heat exchanger was used to maintain the temperature at the desired set point. Preparation of the Diamond Electrode. Borondoped diamond films were provided by CSEM (Switzerland). These electrodes were produced by the hot filament chemical vapor deposition technique (HF CVD)

Table 1. Experimental Conditions Studied in This Work exptl run

C0 (mg of C dm-3)

i (mA cm-2)

T (°C)

voltage (V)

1 2 3 4 5 6 7

836 1432 351 699 1155 787 1105

30 30 30 15 60 30 30

25 25 25 25 25 15 60

7.3 6.9 7.3 6.0 8.5 9.9 8.0

on single-crystal p-type Si 〈100〉 wafers (0.1 Ω cm, Siltronix). The temperature range of the filament was 2440-2560 °C and that of the substrate was maintained at 830 °C. The reactive gas used was methane in an excess of dihydrogen (1% CH4 in H2). The dopant gas was trimethylboron with a concentration of 3 ppm. The gas mixture was supplied to the reaction chamber at a flow rate of 5 dm3 min-1, giving a growth rate of 0.24 µm h-1 for the diamond layer. The diamond film thickness obtained was about 1 µm. This HF CVD process produces a columnar, random texture, polycrystalline film. Previous to its use in galvanostatic electrolyses essays, the electrode is polarized during 30 min with an 1 M H2SO4 solution at 50 mA cm-2 to remove any kind of impurity from its surface. Experimental Procedures. Galvanostatic electrolyses were carried out to determine the influence of the main parameters in the process. The average composition of the wastewater used in the experiments was 750 mg of C dm-3 (phenol), 5000 mg of Na2SO4 dm-3, and NaOH in suitable amounts to give a pH of 12. The pH was kept constant at 12.0 ( 0.1 during electrolysis by the continuous introduction of sulfuric acid (or sodium hydroxide) to the electrolyte reservoir. The range of current densities studied was 15-60 mA cm-2 and the range of temperatures 15-60 °C. To establish the influence of the initial organic compound concentrations (C0), several experiments were perfomed in which the phenol reference concentrations were modified in the range 360-1450 mg of C dm-3 (phenol). Table 1 presents the conditions applied in each experimental

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Figure 3. Evolution of the instantaneous current efficiency (ICE) with the specific electrical charge passed: (9) run 1; (2) run 2; ([) run 3; (b) run 4; (]) run 5; (O) run 6; (4) run 7 (see experimental conditions in Table 1).

Figure 2. Evolution of TOC with the specific electrical charge passed: (9) run 1; (2) run 2; ([) run 3; (b) run 4; (]) run 5; (O) run 6; (4) run 7 (see experimental conditions in Table 1).

run. The cell potential was constant during each electrolysis, indicating that neither appreciable deterioration of the electrode nor passivation phenomena took place. The resulting potential of each experiment is also shown in Table 1. The electrolyte flow rate through the cell was 1250 cm3 min-1. Results and Discussion General Behavior of the Process. Figure 2 shows the evolution of the total organic carbon concentration (TOC) in the electrolyte with the specific electrical charge passed (A h dm-3); the data relate only to some of the experiments performed. It can be observed that TOC decreases to the point where these compounds are almost completely removed, regardless of the conditions used. It can also be seen that the rate of TOC removal decreases with increasing current density and with decreasing initial phenol concentration, indicating a decrease in the current efficiency. Likewise, higher temperature leads to an increase in the mineralization process rate, although its effect is less significant (not visible) than those of current density and initial phenol concentration. Figure 3 shows the evolution of the ICE in the electrolyte with the specific electrical charge passed. These data were obtained at different initial concentrations of phenol, current densities, and temperatures. It can be seen that, for low current densities or high initial phenol concentrations, the initial values of ICE are close to 1. This value of ICE is maintained with the specific electrical charge passed, before decreasing with time to finally reach a value not far from zero. In contrast, it can be seen that the current efficiency does not change significantly with temperature. These observations can

Figure 4. Evolution of ICE with COD at a constant current density (30 mA cm-2): (9) run 1; (2) run 2; ([) run 3; (O) run 6; (4) run 7 (see experimental conditions in Table 1).

be explained by taking into account mass transfer considerations. The conditions in which the process is kinetic or diffusion-controlled are fixed mainly by the ratio current density/organic matter concentration. High values of this ratio lead to diffusion-controlled processes, while low values may correspond to kinetically controlled processes.26 Figure 4 shows the ICE versus COD plot for four of the experiments performed. In these experiments, the effect of temperature and initial phenol concentration was studied and the current density was maintained constant. Two different zones can be distinguished as a function of COD value. For high COD values, the ICE is maintained at a constant value of 1, indicating a kinetically controlled process. Conversely, for lower values of COD, a decrease in ICE is observed, which may suggest the occurrence of a diffusion-controlled process. Figure 5 shows the ICE evolution with COD for three different current densities. It can be seen that the COD value at which the process becomes diffusioncontrolled depends on current density: for higher current densities the process becomes diffusion-controlled at higher COD. It can be concluded that diamond electrodes can oxidize phenol and its intermediates with a current efficiency close to 100% and that the decrease in current efficiency is due to diffusional limitations. For this reason, this anode material can reduce the specific energy requirement of electrochemical oxidation of organics in aqueous wastes to 20-70 kW h kg-1 of

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Figure 5. Evolution of ICE with COD at different current densities: (9) run 1; (b) run 4; (]) run 5 (see experimental conditions in Table 1). Table 2. Main Aromatic and Carboxylic Acid Intermediatesa

organic intemediates

specific electrical charge passed for the maximum concentration peak (A h dm-3)

maximum detected concentration (mg of C dm-3)

hydroquinone benzoquinone fumaric acid maleic acid oxalic acid

4 4 6 6 10

11.2 × 10-3 14.5 × 10-3 1.5 12.4 44.6

a Run #1: temperature, 25 °C; C0, 836 mg of carbon dm-3; current density, 30 mA cm-2.

phenol removed (depending on the cell design and on the operating conditions applied). Analysis of the electrolyte during the electrolysis process (Table 2) revealed that the main intermediates present in the system are carboxylic acids, namely, maleic acid (C4 acids) and oxalic acid (C2 acids). Aromatic compounds (e.g., hydroquinone and benzoquinone) and other carboxylic acids (such as fumaric acid) were also detected in low concentrations. Model of the Process. A simple model of the process previously described was developed in order to aid interpretation of the results. The model considers mass transfer and reaction processes and incorporates four species: phenol (mmol of C dm-3) (S1), fumaric/maleic acid (mmol of C dm-3) (S2), oxalic acid (mmol of C dm-3) (S3), and carbon dioxide (mmol of C dm-3) (S4). An exhaustive mathematical description of the process, which allows for the calculation of the concentration profile of every compound, would lead to a very complex system involving several partial differential equations, because the concentration of every compound considered in the model depends on time and on the distance to the electrode surface. The typical theoretical profile of concentration is shown in Figure 6a. A zone close to the anode surface can be seen where the value of component concentration changes markedly with the distance from the electrode. Another zone, which covers the remaining volume, can also be seen where the concentration of every compound is uniform. In this system, components react mainly at the anode surface (direct electrochemical oxidations) or inside a zone very close to the anode surface (reactions mediated by very strong oxidants). In the remaining volume of the reaction system, some mediated electrochemical reactions can develop, albeit to a lesser extent.

Figure 6. Sketch of the model for process characterization (Si, organic compound i; M/M• redox couple of an inorganic reagent; × average concentration of each organic compound in the two zones).

Given the complexity of this system, a number of assumptions were made in order to simplify the model. The first assumption was to divide the reactor into two zones (Figure 6b): a small volume (Vr) close to anode surface (reaction zone), where electrochemical and some strong mediated oxidation processes develop, and the remaining reactor volume (Vb), where some mediated oxidation reactions can develop (bulk zone). In both zones, the concentration of every compound is considered to be constant with position and is only timedependent. Thus, in the bulk zone, this concentration is the same as the uniform concentration measured experimentally. In the reaction zone, on the other hand, the concentration has a value somewhere between the concentration at the anode surface (which cannot be measured) and the concentration in the bulk zone (uniform concentration). Mass Transport Processes. Four mass transport processes must be considered between the reaction and the bulk zone: (1) diffusion of phenol (S1) into the reaction zone; (2) diffusion of C4 carboxylic acids (S2) into the bulk solution; (3) diffusion of C2 carboxylic acids (S3) into the bulk solution; and (4) diffusion of carbon dioxide (S4) into the bulk solution. These processes can be modeled by mass balances. The local rate of exchange between the reaction and the bulk zones is assumed to be proportional to the concentration difference in the two phases and can be represented by expression 2

J ) kA([Si]* - [Si])

(2)

where [Si]* is the concentration (mol m-3) of component i in the reaction zone, [Si] is the concentration (mol m-3) of this component in the bulk solution, k (m s-1) is the mass transfer coefficient, and A is the specific interfacial area (m2) between the reaction and the bulk zones.


equation,41 which gives a value of 1.02 × 10-9 m2 s-1. The diffussion layer thickness can be estimated (eq 4) from the k and D values as 3.60 × 10-5 m. Taking into account the electrode surface value, the volume of the reaction zone is taken to be 0.28 cm3. Expression 5 is proposed for modeling the kinetics of the oxidation of each compound (ri) in the reaction zone.

ri ) kOH•(ICE)θi

Figure 7. Experimental determination of limit conditions from a representation of ICE versus concentration of oxidizable compounds.

Parameter k can be determined experimentally from limit current conditions using expression 3.

in which kOH•, the hydroxyl generation rate, is multiplied by ICE to give the amount of OH• that oxidizes organics and by θi to determine the quantity of OH• that attacks organic Si (i ) 1-3). Parameters from eq 5 can be evaluated from the operating conditions. Thus, kOH• can be calculated from the current intensity value using expression 6, assuming that each electron gives one hydroxyl radical.15,21

kOH• ) I/F

3

[Si]lim ∑ i)1

Ilim ) zFkA

(3)

where I is the current intensity (A), z is the average number of exchanged electrons, F is the Faraday constant (C mol-1), and ∑i)13[Si]lim is the concentration of oxidizable compounds (i.e., all modeled compounds apart from carbon dioxide) (mol m-3) for which limit conditions are verified. The value of k is supposed to be constant (not depending on the composition), because the organics concentrations in the wastewater are low. A value for k of 2.83 × 10-5 m s-1 was obtained after the application of eq 3 to the data shown in Figure 7. Reaction Zone. According to the nature of the reaction intermediates and to the literature,26 the strong oxidation performed in the reaction zone upon using a diamond thin-film electrode can be produced by physisorbed hydroxyl radicals. These radicals are initially produced on the electrode surface by the electrochemical oxidation of water, and they then react with phenol in a three step process: (step 1) aromatic ring (S1) opening to form carboxylic acids C4 (S2) and C2 (S3); (step 2) oxidation of carboxylic acid C4 (S2) to C2 (S3); and (step 3) oxidation of carboxylic acid C2 (S3) to carbon dioxide (S4). Depending on mass transfer limitations, hydroxyl radicals can give side reactions such as oxygen evolution or the formation of electrogenerated reagents. Small amounts of these oxidizing agents can react within the reaction zone and, thus, cannot be detected later by analysis. The model considers these reactions as direct reactions. The reaction zone is assumed to be equivalent to the diffusion layer, because the direct, and most of the indirect, oxidation processes occur in this zone. The thickness of the diffusion layer can be expressed in terms of the mass transfer (k) and diffusion (D) coefficients by expression 4.

δ ) D/k

(4)

As the concentration of organics is low, the diffusion coefficient can be estimated using the Wilke and Chang

(5)

(6)

ICE can be calculated from eq 7 because, as can be seen in Figures 4 and 5, this parameter is proportional to the concentration of organics up to unity, before becoming constant at 1.

ICE ) 1 if I < Ilim ICE )

3

1 3

[Si]lim ∑ i)1

[Si] ∑ i)1

if I > Ilim

(7)

Figure 7 shows experimental versus modeled ICE values for some of the experiments performed. It is clear that this model reproduces the results in a satisfactory manner. Factor θi is calculated using expression (8) and can be interpreted as the fraction of compound Si in the reaction zone, modified by a certain factor fi, that quantifies the oxidizability of compound Si with respect to phenol (by definition f1 ) 1).

θi )

fi[Si]* 3

(8)

fj[Si]* ∑ j)1 Factors f2 and f3 are assumed to depend only on temperature and they have to be adjusted by mathematical fitting. Bulk Zone. In the bulk zone only mediated oxidation reactions, such as hydrogen peroxide- or persulfuric acid-mediated oxidations, can occur. In the work described here, reactions in this zone were not considered because oxidant compounds were not detected. System Resolution. By using the mass transport and kinetics expressions proposed and taking into account the stoichiometric coefficients which relate the organic compounds with the hydroxyl radicals needed to oxidize them, the mass balances around the experi-

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Figure 8. Results obtained [simulation (line) versus experimental (points) data] for four experimental runs ([) (a) phenol; (9) (b) C4 carboxylic acids; (2) (c) C2 carboxylic acids; (b) (d) carbon dioxide.

mental system used in this work are expressed in eqs 9-16.

Vr Vr

Vr

d[S1] Vb ) k([S1]* - [S1]) dt

(9)

Vb

d[S2] ) k([S2]* - [S2]) dt

(10)

Vb

d[S3] ) k([S3]* - [S3]) dt

(11)

Vb

d[S4] ) k([S4]* - [S4]) dt

(12)

d[S1]* kOH• ) -k([S1]* - [S1]) (ICE)θ1 (13) dt 14

kOH• d[S2]* ) -k([S2]* - [S2]) + (ICE)θ1 dt 14 kOH• (ICE)θ2 (14) 8 kOH• d[S3]* ) -k([S3]* - [S3]) + (ICE)θ1 + dt 14 kOH• kOH• (ICE)θ2 (ICE)θ3 (15) 4 2 Vr

d[S4]* ) -k([S4]* - [S4]) + kOH•(ICE)θ3 (16) dt

To determine the influence of the different conditions on the adjustable parameters, the concentrations of the different organic species were calculated, for every experiment, using total carbon (TC), total organic carbon (TOC), and HPLC data. The differential equation system was solved using the first-order Euler discretization method. Model parameters (f2 and f3) were calculated by a nonlinear least squares regression method. The results obtained (simulation versus experimental data)

Figure 9. Influence of temperature on the oxidizability of C4 (f2) and C2 (f3) carboxylic acids respect to phenol. Table 3. Values of the Coefficient of Variation Obtained for the Simulation of Each Experiment experimental conditions i (mA

cm-2)

30 30 30 15 60 30 30

T (°C)

C0 (mg of C dm-3)

CV (%)

25 25 25 25 25 15 60

836 1432 351 699 1155 787 1105

1.36 8.32 3.68 5.15 2.14 13.2 5.44

for four experimental runs are shown in Figure 8. As can be seen, good agreement is obtained in all cases. These agreements are parametrized in Table 3 as a coefficient of variation. It can be seen that the values of this parameter are always below 14% (average value approximately 6%). The evolution of parameters f2 and f3 with temperature is shown in Figure 9. It is apparent that the oxidizability of the compounds represented by the model increases in the order S3 (C2 carboxylic acids) < S1 (phenol) < S2 (C4 carboxylic acids). Moreover, the oxidizability of phenol increases in a linear manner over both carboxylic acids with temperature. These results are in agreement with other previously published in the


literature29,40,42 and indicate that the oxidation of oxalic acid is the limiting step in the electrochemical treatment of phenol aqueous wastes. Conclusions The following conclusions can be drawn from the work described here. (1) Electrochemical oxidation using diamond thin-film electrodes can be successfully used for treating aqueous phenol wastes. An almost total mineralization of the waste is obtained, regardless of the current intensity, initial phenol concentration (within the range studied), and temperature. (2) An increase in the initial concentration and temperature lead to an increase in the initial mineralization rate. (3) Instantaneous current efficiencies of 1 are obtained when organic mass transfer limitations are not involved. (4) A simple model containing four species (phenol, carboxylic acids C4 and C2, and carbon dioxide) and several reaction and mass transport processes can be used to explain the experimental behavior of the system. The model has only two adjustable parameters and reproduces the experimental behavior with coefficients of variation below 15%. (5) Some of the parameters used in this model (total oxidation rate, mass transport coefficient) can be calculated from experimental conditions or data. The remaining parameters (oxidizability of carboxylic acids with respect to phenol) can be obtained by mathematical fitting. Acknowledgment This work was supported by the MCT (Ministerio de Ciencia y Tecnologıá, Spain) and by the EU (European Union) through the Project REN2001-0560. Literature Cited (1) Mieluch, J.; Sadkowski, A.; Wild, J.; Zoltowski, P. Electrochemical Oxidation of Phenol Compound in Aqueous Solution. Prezm. Chem. 1975, 54, 513. (2) Papouchado, L.; Sandford, R. W.; Petrie, G.; Adams, R. N. Anodic Oxidation Pathways of Phenolic Compounds. J. Electroanal. Chem. 1975, 65, 275. (3) Smith de Sucre, V.; Watkinson, A. P. Anodic Oxidation of Phenol for Wastewater Treatment. Can. J. Chem. Eng. 1981, 59, 52. (4) Sharifian, H.; Kirk, D. W. Electrochemical Oxidation of Phenol. J. Electrochem. Soc. 1986, 133, 921. (5) Comninellis, Ch.; Pulgarin, C. Anodic Oxidation of Phenol for Wastewater Treatment. J. Appl. Electrochem. 1991, 21, 703. (6) Comninellis, Ch. Electrochemical Treatment of Wastewater Containing Phenol. Trans. IchemE 1992, 70 (B), 219. (7) Boudenne, J.-L.; Cerclier, O.; Galeá, J.; Van der Vlist, E. Electrochemical Oxidation of Aqueous Phenol at a Carbon Black Slurry Electrode. Appl. Catal. 1996, 143, 185. (8) Boudenne, J. L.; Cerlier, O.; Bianco, P. Voltammetric Studies of the Behaviour of Carbon Black During Phenol Oxidation on Ti/Pt Electrodes. J. Electrochem. Soc. 1998, 148, 2763. (9) Cossu, R.; Polcaro, A. M.; Lavagnolo, M. C.; Mascia, M.; Palmas, S.; Renoldi, F. Electrochemical Treatment of Landfill Leachate: Oxidation at Ti/PbO2 and Ti/SnO2 Anodes. Environ. Sci. Technol. 1998, 32, 3570. (10) Comninellis, Ch.; Nerini, A. Anodic Oxidation of Phenol in the Presence of NaCl for Waste Water Treatment. J. Appl. Electrochem. 1995, 25, 23. (11) Farmer, J. C.; Wang, F. T.; Hawley-Fedder, R. A.; Lewis, P. R.; Summers, L. J.; Foiles, L. Electrochemical Treatment of Mixed and Hazardous Wastes: Oxidation of Ethylene Glycol and Benzene by Silver(II). J. Electrochem. Soc. 1992, 139, 654.

(12) Leffrang, U.; Ebert, K.; Flory, K.; Galla, U.; Schmieder, H. Organic Waste Destruction by Indirect Electrooxidation. Sep. Sci. Technol. 1995, 30, 1883. (13) Alvarez-Gallegos, A.; Pletcher, D. The Removal of Low Level Organics Via Hydrogen Peroxide formed in a Reticulated Vitreous Carbon Cathode Cell. Part 1. The Electrosynthesis of Hydrogen Peroxide. Electrochim. Acta 1998, 44, 853. (14) Alvarez-Gallegos, A.; Pletcher, D. The Removal of Low Level Organics Via Hydrogen Peroxide formed in a Reticulated Vitreous Carbon Cathode Cell. Part 2. The Removal of Phenols and Related Compounds from Aqueous Effluents. Electrochim. Acta 1999, 44, 2483. (15) Brillas, E.; Bastida, R. M.; Llosa, E.; Casado, J. Electrochemical Destruction of Aniline and 4-Chloroaniline for Wastewater Treatment using a Carbon-PTFE O2-fed Cathode. J. Electrochem. Soc. 1995, 142, 1733. (16) Brillas, E.; Sauleda, R.; Casado, J. Degradation of 4-Chlorophenol by Anodic Oxidation, Electro-Fenton, Photoelectro-Fenton, and Peroxi-coagulation Processes. J. Electrochem. Soc. 1998, 145, 759. (17) Vercesi, G. P.; Rolewicz, J.; Comninellis, Ch. Characterization of DSA type Oxygen Evolving Electrodes. Choice of Base Metal. Thermochim. Acta 1991, 176, 31. (18) Gattrell, M.; Kirk, D. W. A Study of the Oxidation of Phenol at Platinum and Preoxidized Platinum Surfaces. J. Electrochem. Soc. 1993, 6, 1534. (19) Iotov, P. I., Kalcheva S. V. Mechanistic Approach to the Oxidation of Phenol at a Platinum/Gold Electrode in an Acid Medium. J. Electroanal. Chem. 1998, 442, 19. (20) Comninellis, Ch. Electrocatalysis in the Electrochemical Conversion/Combustion of Organic Pollutants for Waste Water Treatment. Electrochim. Acta 1994, 39 (11-12), 1857. (21) Foti, G.; Gandini, D.; Comninellis, C.; Perret, A.; Haenni, W. Oxidation of Organics by Intermediates of Water Discharge on IrO2 and Synthetic Diamond Anodes. Electrochem. Solid-State Lett. 1999, 2, 228. (22) Comninellis, Ch.; Pulgarin, C. Electrochemical Oxidation of Phenol for Wastewater Treatment using SnO2 Anodes. J. Appl. Electrochem. 1993, 23, 108. (23) Tahar, N. B.; Savall, A. Mechanistic Aspects of Phenol Electrochemical Degradation by Oxidation on a Ta/PbO2 Anode. J. Electrochem. Soc. 1998, 145, 3427. (24) Tahar, N. B.; Savall, A. A Comparison of Different Lead Dioxide Coated Electrodes for the Electrochemical Destruction of Phenol. J. New. Mater. Electrochem. Syst. 1999, 2, 19. (25) Polcaro, A. M.; Palmas, S.; Renoldi, F.; Mascia, M. On the Performance of Si/SnO2 and Ti PbO2 Anodes in Electrochemical Degradation of 2-Chlorophenol for Wastewater Treatment. J. Appl. Electrochem. 1999, 29, 147. (26) Rodrigo, M. A.; Michaud, P. A.; Duo, I.; Panizza, M.; Cerisola, G.; Comninellis, Ch. Oxidation of 4-Chlorophenol at Boron-Doped Diamond electrodes for Wastewater Treatment. J. Electrochem. Soc. 2001, 148 (5), D60. (27) Gattrell, M.; Kirk, D. W. The Electrochemical Oxidation of Aqueous Phenol at a Glassy Carbon Electrode. Can. J. Chem. Eng. 1990, 68, 997. (28) Ko¨tz, R.; Stucki, S.; Carcer, B. Electrochemical Waste Water Treatment using High Overvoltage Anodes. Part I: Physical and electrochemical properties of SnO2 anodes. J. Appl. Electrochem. 1991, 21, 14. (29) Stucki, S.; Ko¨tz, R.; Carcer, B.; Suter, W. Electrochemical Waste Water Treatment using High Overvoltage Anodes. Part II: Anode Performance and Applications. J. Appl. Electrochem. 1991, 21, 99. (30) Can˜izares, P.; Domıńguez, J. A.; Rodrigo M. A.; Villasenõr, J.; Rodrı´guez, J. Effect of the Current Intensity in the Electrochemical Oxidation of Aqueous Phenol Wastes at an Activated Carbon and Steel Anode. Ind. Eng. Chem. Res. 1999, 38, 3779. (31) Awad, Y. M.; Abuzaid, N. A. The Influence of Residence Time on the Anodic Oxidation of Phenol. Sep. Purif. Technol. 2000, 18, 227. (32) Savall, A. Electrochemical Treatment of Industrial Organic Effluents. Chimia 1995, 49, 23. (33) Pulgarin, C.; Adler, N.; Peringer, P.; Comninellis, Ch. Electrochemical Detoxification of a 1,4-Benzoquinone Solution in Wastewater Treatment. Water Res. 1994, 28, 887.

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(34) Feng, J.; Houk, L. L.; Johnson, D. C.; Lowery, S. N.; Carey, J. J. Electrocatalysis of Anodic Oxygen Transfer Reactions: the Electrochemical Incineration of Benzoquinone. J. Electrochem. Soc. 1995, 142 (11), 3626. (35) Boudenne, J.-L.; Cerclier, O. Performance of Carbon BlackSlurry Electrodes for 4-Chlorophenol Oxidation. Water Res. 1999, 33, 494. (36) Bunce, N. J.; Merica, S. G.; Lipkowski, J. Prospects for the use of Electrochemical Methods for the Destruction of Aromatic Organochlorine Wastes. Chemosphere 1997, 35 (11), 2719. (37) Polcaro, A. M.; Palmas, S. Electrochemical Oxidation of Chlorophenols. Ind. Eng. Chem. Res. 1997, 36, 1791. (38) Rodgers, J. D.; Jedral, W.; Bunce, N. J. Electrochemical Oxidation of Chlorinated Phenols. Environ. Sci. Technol. 1999, 33, 1453.

(39) Azzam, M. O.; Al-Tarazi, M.; Tahboub, Y. Anodic Destruction of 4-Chlorophenol Solution. J. Hazard. Mater. 2000, B75, 99. (40) Gandini, D.; Mahe´, E.; Michaud, P. A.; Haenni, W.; Perret, A.; Comninellis, Ch. Oxidation of Carboxylic Acid at Boron-doped Diamond Electrodes J. Appl. Electrochem. 2000, 30 (12), 1345. (41) Wilke, C. R.; Chang, P. AIChE J. 1955, 1, 264-270. (42) Bock, C.; MacDougall, B. The Anodic Oxidation of pBenzoquinone and Maleic Acid. J. Electrochem. Soc. 1999, 146 (8), 2925-2932.

Received for review June 27, 2001 Revised manuscript received December 11, 2001 Accepted March 31, 2002 IE0105526

Electrochemical Oxidation of Aqueous Phenol Wastes on Synthetic

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