1

Electrochemical Synthesis of Peroxyacetic Acid using 1

Conductive Diamond Electrodes 2

Salvador Cotillas, Ana Sánchez-Carretero, Pablo Cañizares, Cristina Sáez and Manuel 3

Andrés Rodrigo*. 4

Department of Chemical Engineering. Facultad de Ciencias Químicas. Universidad de 5

Castilla-La Mancha. Campus Universitario s/n. 13071 Ciudad Real. Spain. 6

7

8

Abstract 9

In this work, the synthesis of peroxyacetic acid and peroxoacetate salts by electrolysis 10

with conductive-diamond anodes is described, using three different raw materials: 11

ethanol, acetaldehyde and sodium acetate. Results show that peroxyacetic acid is 12

produced at significant concentrations during the electrolyses of the three raw materials, 13

although sodium acetate achieves the highest efficiency and, at the same time, the 14

smallest carbon mineralization. Acetaldehyde behaves as a good raw material during a 15

first stage but afterwards it catalyses the decomposition of peroxoacetate to the acetate 16

anion. Moderate current densities and slightly alkaline pH seems to promote the 17

synthesis of peroxyacetic acid and to restrain raw matter mineralization. 18

19

Keywords: Electrosynthesis, peroxyacetic acid, conductive diamond 20

*To whom all correspondence should be addressed. 21

Tel. +34 902204100 ext 3411 22

Fax. +34 926 295256. 23

e-mail: manuel.rodrigo@uclm.es 24

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2

1. Introduction 31

32

Peroxyacetic acid (PAA), also known as peracetic acid, is an organic peroxide in which 33

the carboxylic group of acetic acid (-COOH) is transformed into a peroxocarboxylic 34

group (- COOOH). It is a strong oxidant (E = 1.962 V vs SHE) with a reduction 35

potential larger than those of well- known oxidants, such as chlorine or chlorine 36

dioxide1. Depending on operating conditions, the PAA can present bleaching and 37

delignification properties2. For this reason, the PAA is used as bleaching agent and in 38

the industrial synthesis of epoxides2, 3. It is a very effective oxidant in water treatment4, 39

5. It is also used as a fowl sanitizer, and it is known to be a good disinfectant whose 40

action is based on the hydroxyl radical. PAA is a more potent antimicrobial agent than 41

hydrogen peroxide, being rapidly active at low concentrations against a wide spectrum 42

of microorganisms6-8. Thus, it has been found that hydrogen peroxide required much 43

larger doses than PAA for the same level of disinfection9. 44

45

PAA is commercially available in the form of a quaternary equilibrium mixture 46

containing acetic acid, hydrogen peroxide, PAA, and water. It can be produced from 47

acetic acid and also from acetaldehyde. The first process (eq 1) consists of the oxidation 48

of acetic acid by means of hydrogen peroxide10-12, catalysed by sulphuric acid. It 49

requires long reaction times. 50

51

CH3COOH + H2O2 → CH3COOOH + H2O (1) 52

53

The second process uses acetaldehyde as raw matter. The oxidation of acetaldehyde 54

with air or oxygen produces the initiation of the reaction by means of an acetyl radical 55

3

which forms the peroxide radical with oxygen. The reaction ends with PAA formation13 56

according to eq. 2. 57

58

CH3CHO + O2 → CH3COOOH (2) 59

60

However, the peroxyacetic acid can experience a homolysis of the peroxide group and 61

become to acetic acid. In addition, it is supposed that peroxyacetic acid reacts with 62

acetaldehyde giving α-hydroxiethylperacetate. Later, for a cyclical mechanism of 63

transition, it dissociates itself in two molecules of acetic acid (eq. 3). Therefore, PAA 64

can be the main product if the oxidation is realized in soft conditions, preferably without 65

catalyst and in a solvent such as ethyl acetate. 66

67

68

69

In recent years, electrochemical oxidation with conductive-diamond anodes has become 70

one of the most promising technologies in the treatment of industrial wastes polluted 71

with organics14-24 and in the electrosynthesis of oxidants25-33. Compared with other 72

electrode materials, conductive-diamond has shown higher chemical and 73

electrochemical stability as well as a higher current efficiency. In addition, the high 74

overpotential for water electrolysis is one of the most important properties of 75

conductive-diamond in the processing of aqueous solutions; its electrochemical window 76

is sufficiently large to produce hydroxyl radicals with high efficiency34, and this species 77

seems to be directly involved in the oxidation mechanisms that occur on diamond 78

surfaces. As a result, conductive-diamond electro-oxidation of waste is presently 79

CH3CHO + H-O-O-CCH3

O

2 CH3COOH (3)CH3CHO + H-O-O-CCH3

C

C

H3C

HO O O

C

OH

CH3 2 CH3COOH (3)

4

considered as an advanced oxidation technology. The advantageous properties described 80

above have led to great improvements (in both efficiency and electrode stability) in the 81

use of conductive diamond in the electrosynthesis of oxidants. A number of recent 82

studies have been published in which the generation of peroxodisulphates35, 83

peroxodiphosphate31, percarbonates36, ferrates32, 33 and perchlorates29 by electrochemical 84

techniques are described. Significant improvements are reported as compared to more 85

commonly used synthesis methods. 86

87

With this background in mind, the goal of the work described here was to investigate 88

the feasibility of generating peroxoacetic acid and its salts by electrolyses with 89

conductive-diamond electrodes. In an effort to achieve this aim, bench-scale 90

electrolysis assays of different raw material solutions on conductive diamond anodes 91

were carried out in order to characterize the mechanism of the process and to clarify the 92

role of the most significant process parameters (pH and current density). 93

94

2. Experimental. 95

96

2.1. Analytical procedures. Acetate standard solutions were prepared by dissolving the 97

appropriate amount of CH3COONa in water. Peroxyacetic acid was determined by 98

titration with Na2S2O3. The titration is based on the next procedure37: 4 ml of a 25% 99

(v/v) H2SO4 solution were added to a l0 ml PAA sample. An excess of solid KI was 100

added and the iodide was oxidized by PAA to brownish iodine, then it was titrated with 101

0.01 M Na2S2O3 until only a pale brown color remained (eqs. 4 and 5). One drop of 1% 102

(w/v) starch solution was added and the titration was continued until complete 103

decolorization occurred. 104

5

2I- + CH3COOO- + 2H+ → CH3COO- + I2 + H2O (4) 105

I2 + 2Na2S2O3 → 2NaI + Na2S4O6 (5) 106

107

To dismiss the other oxidants and hydrogen peroxide presence, it was carried out 108

different analytical techniques such as gas chromatography and permanganate addition. 109

Gas chromatographic analyses were carried out in a column SUPELCOWAX 10 (30 m 110

x 0.25 mm) (macroporous particles with 0.25 µm diameter). Volume injection was set 111

to 10 μL. To oxidize hydrogen peroxide, 0.02 M KMnO4 solution was added until the 112

color of the solution turned pale rose. Oxidant stability rules out the hydroxyl radicals, 113

ozone and other unstable oxidants presence. Therefore the oxidant electrogenerated 114

comes from the partial oxidation of raw material forming a peroxo group. 115

116

2.2. Electrochemical cell. The electrosynthesis was carried out in a double-117

compartment electrochemical flow cell. A cationic exchange membrane (STEREOM L-118

105) was used to separate the compartments. Diamond-based material was used as 119

anode and stainless steel (AISI 304) as cathode. Both electrodes were circular (100 mm 120

diameter) with a geometric area of 78 cm2 each and an electrode gap of 15 mm. Boron-121

doped diamond (BDD) films were provided by Adamant (Switzerland) and synthesised 122

by the hot filament chemical vapour deposition technique (HF CVD) on single-crystal 123

p-type Si <100> wafers (0.1 cm, Siltronix).The anolyte and the catholyte were stored 124

in dark glass tanks and circulated through the electrolytic cell by means of a centrifugal 125

pump. A heat exchanger was used to maintain the temperature at the desired set point. 126

The pH was monitored by means of the WTW-InoLab pHmeter. 127

128

6

2.3. Experimental Procedures. Bench scale electrolyses under galvanostatic conditions 129

were carried out to determine the influence of the main parameters in the process. The 130

anolyte and the catholyte consisted of 1 M solutions of ethanol (C2H6O), aceltadehyde 131

(C2H4O) or sodium acetate (CH3COONa). The range of current densities employed was 132

300 to 1000 A m-2. The range of pH studied was 1 to 13. 133

134

3. Results and discussion. 135

136

Figure 1 shows the influence of the raw matter with the applied electric charge, on the 137

production of PAA into the anodic chamber of a double compartment electrochemical 138

cell equipped with conductive-diamond anodes. This Figure also shows the 139

mineralization of carbon obtained during the same electrolyses. The experiments were 140

carried out with three different organic raw materials (ethanol, acetaldehyde and sodium 141

acetate in 1M aqueous solutions) at a current density of 300 A m-2, regulating the 142

temperature at 25oC during the process. As it can be observed, PAA can be obtained 143

from the three species tested with a significant production rate (C2H6O: 0.061 mmol/Ah; 144

C2H4O: 0.203 mmol/Ah; CH3COONa: 0.033 mmol/Ah). However, acetate behaves as 145

the best raw material, because it allows obtaining the best faradaic efficiencies in the 146

production of PAA and, at the same time, it obtains the lower mineralization 147

percentage. Initially, this can be easily interpreted in terms of the hydroxylation of the 148

carboxylic group by means of hydroxyl radicals produced on the surface of the diamond 149

surface (eq 6-9). 150

151

H2O (OH)· + H+ + e- (6) 152

CH3-COOH + OH· (CH3-COO) · + H2O (7) 153

7

(CH3-COO)· + OH· CH3-COOOH (8) 154

155

In this point, it is worth to mention that this process has been previously reported and 156

extensively explained for the production of inorganic peroxosalts such as 157

peroxosulphates and peroxophosphates, obtained from the electrolyses with diamond of 158

sulphates or phosphates solutions25- 35. In those cases, processes are directly related to 159

the production of hydroxyl radicals (or, at least, significantly contributed), which 160

produces the formation of radicals of the anions that in later stages yield the peroxoacid 161

or peroxosalt (depending on the operation pH) as shown in eqs. 9-10 for 162

peroxodisulphate, eqs. 11-12 for peroxodiphosphate and eqs. 11 and 13 for 163

monoperoxophosphoric acid. 164

165

HSO4– + OH· SO4

– · + H2O (9) 166

SO4– · + SO4

– S2O82– (10) 167

HPO43- + OH· (PO4

2-) · + H2O (11) 168

(PO42-) · + (PO4

2-) · P2O84- (12) 169

(H2PO4)· + OH· H3PO5 (13) 170

171

The greater mineralization obtained in the case of the acetaldehyde, and especially in 172

the case of the ethanol, indicates the small selectivity of the conductive-diamond 173

electrolyses towards the direct transformation of the hydroxyl and the aldehyde groups 174

into the peroxocarboxylic one, by the direct attack of oxygenated groups in the organic 175

molecules, and prevent against their use as raw materials. 176

177

8

At this point, it is interesting to observe the changes of the main intermediates found 178

during electrolyses of ethanol and acetaldehyde (Figure 2). As it is shown, during 179

ethanol electrolysis both acetaldehyde and acetic acid are produced, although the 180

concentrations of acetic acid measured were very small. In addition, two other 181

intermediates were also monitored during the electrolyses but their concentrations were 182

negligible and they were not identified (they do not correspond to any C1 or C2 183

alcohols, acids or aldehydes). 184

185

The changes observed for the electrolyses of acetaldehyde are of a great interest, 186

because initially this raw matter shows to be the most efficient in the electrochemical 187

production of the organic peroxoacid, but the trend in the production of PAA meets a 188

maximum and then, it decreases to finally meet a constant value. A possible explanation 189

for such behaviour is the decomposition of PAA catalyzed by acetaldehyde (eq 14), 190

because the plateau is obtained just in the moment in which acetaldehyde is completely 191

depleted from solution. 192

193

194 (14)

195

At this respect, during the electrolyses of acetaldehyde, significant amounts of acetate 196

and smaller concentrations of the two other intermediates were found. This supports the 197

less efficient production of PAA at long reaction times. 198

199

Concerning the other raw matter studied, no intermediates were found by HPLC during 200

the electrolyses of acetate solutions, indicating that mineralization and PAA formation 201

CH3CHO + H-O-O-CCH3

O

2 CH3COOH

9

are the lone processes occurring in the anodic chamber of the electrochemical cell, and 202

that acetate is the best choice as raw matter for PAA production. 203

204

Figure 3 shows the effect of the pH (range studied from 1 to 13) during the electrolyses 205

of solutions containing 1 M CH3COONa. Initially, the pH was expected to have a great 206

influence on the species formed during the electrosynthesis, but surprisingly no 207

intermediates different of PAA were detected during the electrolyses of acetate at any 208

pH range. In addition, it can be observed that the effect is not very important on the 209

PAA production (merely a small increase for both slightly alkaline pH and highly acidic 210

pHs). However it is very significant for mineralization which it is promoted at strongly 211

acidic and alkaline pHs. This advises against the use of extreme pHs in the synthesis of 212

PAA and suggests to use slightly alkaline pHs (range from pH 7 to 10) in order to 213

optimize the yield and simultaneously not promoting carbon mineralization. 214

215

Figure 4 shows the effect of the current density on the sodium acetate electrolysis. In 216

these experiments, the pH is not regulated but simply monitored, and the temperature 217

was maintained in 25ºC. As it can be observed, the initial rate of the oxidants generation 218

does not depend of the current density applied. However, from applied current charges 219

around 10-15 A h dm-3, there is a significant change in the slope (production rate of 220

PAA) for the larger current densities, decreasing significantly the efficiency of the 221

process (although the trend remains linear at any time). At the same time, the 222

mineralization rate is maintained in every case in a very low value and it is not 223

increased by the current density but just maintained (Figure 4b). This can only be 224

explained in terms of the decomposition of PAA to yield oxygen and acetic acid, which 225

seems to be promoted working under harder oxidation conditions. 226

10

4. Conclusions. 227

228

From this work the following conclusions can be drawn: 229

230

Conductive-diamond electrolysis can be successfully used to synthesize PAA 231

from sodium acetate, acetaldehyde and ethanol solutions, although the efficiency 232

and the intermediates are largely affected by the choice of the raw matter. 233

Sodium acetate is the best raw matter because its electrolysis does not promote 234

carbon mineralization and yield merely PAA. Efficiency of the process improves 235

working at current densities close to 300 A m-2 (enough to produce hydroxyl 236

radicals in the electrolytic cell used). Concerning the pH, it does not affect 237

significantly to the efficiency but it can be advised to work under slightly 238

alkaline pHs in order optimize the yield and simultaneously not to promote 239

carbon mineralization. 240

Acetaldehyde seems to behave as a good raw matter for low applied current 241

charges but a side reaction prevents against its use because of the decomposition 242

of the PAA formed. 243

Ethanol electrolysis yields many intermediates and promotes a high 244

mineralization of carbon. 245

246

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11

Acknowledgements 251

252

This work was supported by the JCCM (Junta de Comunidades de Castilla La Mancha, 253

Spain) through the project PEII11-0097-2026. 254

255

References 256

257

(1) Kitis, M. Disinfection of wastewater with peracetic acid: A review. Environ. Int. 258

2004, 30, 47. 259

(2) Yuan, Z.; Ni, Y.; Van Heiningen, A. A kinetic model for peracetic acid brightening 260

of an ozone delignified softwood kraft pulp. J. Wood Chem. Technol. 1998, 18, 83. 261

(3) Murphy, A.; Stack, T.D.P. Discovery and optimization of rapid manganese catalysts 262

for the epoxidation of terminal olefins. J. Mol. Catal. A: Chem. 2006, 251, 78. 263

(4) Koivunen, J.; Heinonen-Tanski, H. Peracetic acid (PAA) disinfection of primary, 264

secondary and tertiary treated municipal wastewaters. Water Res. 2005, 39, 4445. 265

(5) Veschetti, E.; Cutilli, D.; Bonadonna, L.; Briancesco, R.; Martini, C.; Cecchini, G.; 266

Anastasi, P.; Ottaviani, M. Pilot-plant comparative study of peracetic acid and sodium 267

hypochlorite wastewater disinfection. Water Res. 2003, 37, 78. 268

(6) Baldry, M.G.C. The bactericidal, fungicidal and sporicidal properties of hydrogen 269

peroxide and peracetic acid. J. Appl. Bacteriol. 1983, 54, 417. 270

(7) Baldry, M.G.C.; French, M.S. Disinfection of sewage effluent with peracetic acid. 271

Water Sci. Technol. 1989, 21, 203. 272

(8) Fraser, J.A.L.; Godfree, A.F.; Jones, F. Use of peracetic acid in operational sewage 273

sludge disposal to pasture. Water Sci. Technol. 1985, 17, 451. 274

12

(9) Wagner, M.; Brumelis, D.; Gehr, R. Disinfection of wastewater by hydrogen 275

peroxide or peracetic acid: Development of procedures for measurement of residual 276

disinfectant and application to a physicochemically treated municipal effluent. Water 277

Environ. Res. 2002, 74, 33. 278

(10) Alasri, A.; Roques, C.; Michel, G.; Cabassud, C.; Aptel, P. Bactericidal properties 279

of peracetic acid and hydrogen peroxide, alone and in combination, and chlorine and 280

formaldehyde against bacterial water strains Can. J. Microbiol. 1992, 38, 635. 281

(11) Saha, M.S.; Nishiki, Y.; Furuta, T.; Ohsaka, T. Electrolytic synthesis of 282

peroxyacetic acid using in situ generated hydrogen peroxide on gas diffusion electrodes. 283

J. Electrochem. Soc. 2004, 151, 93. 284

(12) Saha, M.S.; Denggerile, A.; Nishiki, Y.; Furuta, T.; Ohsaka, T. Synthesis of 285

peroxyacetic acid using in situ electrogenerated hydrogen peroxide on gas diffusion 286

electrode. Electrochem. Commun. 2003, 5, 445. 287

(13) Zhang, T.; Luo, J.; Chuang, K.; Zhong, L. Peracetic Acid Synthesis by 288

Acetaldehyde Liquid Phase Oxidation in Trickle Bed Reactor. Chin. J. Chem. Eng. 289

2007, 15, 320. 290

(14) Fryda, M.; Herrmann, D.; Schäfer, L.; Klages, C.P.; Perret, A.; Haenni, W.; 291

Comninellis, C.; Gandini, D. Properties of Diamond Electrodes for Wastewater 292

Treatment. New Diamond Front. Carbon Technol. 1999, 9, 229. 293

(15) Cañizares, P.; Díaz, M.; Domínguez, J.A.; Lobato, J.; Rodrigo, M.A. 294

Electrochemical treatment of diluted cyanide aqueous wastes. J. Chem. Technol. 295

Biotechnol. 2005, 80, 565. 296

(16) Rodrigo, M.A.; Michaud, P.A.; Duo, I.; Panizza, M.; Cerisola, G.; Comninellis, 297

Ch. Oxidation of 4-Chlorophenol at Boron-Doped Diamond Electrode for Wastewater 298

Treatment. J. Electrochem. Soc. 2001, 148, 60. 299

(17) Cañizares, P.; García-Gómez, J.; Sáez, C.; Rodrigo, M.A. Electrochemical 300

oxidation of several chlorophenols on diamond electrodes - Part I. Reaction 301

mechanism. J. Appl. Electrochem. 2003, 33, 917. 302

(18) Cañizares, P.; García-Gómez, J.; Sáez, C.; Rodrigo, M.A. Electrochemical 303

oxidation of several chlorophenols on diamond electrodes: Part II. Influence of waste 304

characteristics and operating conditions. J. Appl. Electrochem. 2004, 34, 87. 305

13

(19) Cañizares, P.; Sáez, C.; Lobato, J.; Rodrigo, M.A. Electrochemical Treatment of 4-306

Nitrophenol-Containing Aqueous Wastes Using Boron-Doped Diamond Anodes. Ind. 307

Eng. Chem. Res. 2004, 43, 1944. 308

(20) Cañizares, P.; Sáez, C.; Lobato, J.; Rodrigo, M.A. Electrochemical treatment of 309

2,4-dinitrophenol aqueous wastes using boron-doped diamond anodes. Electrochim. 310

Acta 2004, 49, 4641. 311

(21) Cañizares, P.; Sáez, C.; Lobato, J.; Rodrigo, M.A. Electrochemical oxidation of 312

polyhydroxybenzenes on boron-doped diamond anodes. Ind. Eng. Chem. Res. 2004, 313

43, 6629. 314

(22) Iniesta, J.; Michaud, P.A.; Panizza, M.; Cesirola, G.; Aldaz, A.; Comnimellis, Ch. 315

Electrochemical oxidation of phenol at boron-doped diamond electrode. Electrochim. 316

Acta 2001, 46, 3573. 317

(23) Iniesta, J.; Michaud, P.A.; Panizza,M.; Comnimellis, Ch. Electrochemical 318

oxidation of 3-methylpyridine at a boron-doped diamond electrode: Application to 319

electroorganic synthesis and wastewater treatment. Electrochem. Commun. 2001, 3, 320

346. 321

(24) Cañizares, P.; Díaz, M.; Domínguez, J.A.; García-Gómez, J.; Rodrigo, M.A. 322

Electrochemical oxidation of aqueous phenol wastes on synthetic diamond thin-film 323

electrodes. Ind. Eng. Chem. Res. 2002, 41, 4187. 324

(25) Sánchez-Carretero, A.; Rodrigo, M.A.; Cañizares, P.; Sáez, C. Electrochemical 325

synthesis of ferrate in presence of ultrasound using boron doped diamond anodes. 326

Electrochem. Commun. 2010, 12, 644. 327

(26) Cañizares, P.; Sáez, C.; Sánchez-Carretero, A.; Rodrigo, M.A. Influence of the 328

characteristics of p-Si BDD anodes on the efficiency of peroxodiphosphate 329

electrosynthesis process. Electrochem. Commun. 2008, 10, 602. 330

(27) Sáez, C.; Cañizares, P.; Sánchez-Carretero, A.; Rodrigo, M.A. Electrochemical 331

synthesis of perbromate using conductive-diamond anodes. J. Appl. Electrochem. 2010, 332

40, 1715. 333

(28) Cañizares, P.; Sáez, C.; Sánchez-Carretero, A.; Rodrigo, M.A. Synthesis of novel 334

oxidants by electrochemical technology. J. Appl. Electrochem. 2009, 39, 2143. 335

(29) Sánchez-Carretero, A.; Sáez, C.; Cañizares, P.; Rodrigo, M.A. Electrochemical 336

production of perchlorates using conductive diamond electrolyses. Chem. Eng. J. 2011, 337

166, 710. 338

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(30) Weiss, E.; Sáez, C.; Groenen-Serrano, K.; Cañizares, P.; Savall, A.; Rodrigo, M.A. 339

Electrochemical synthesis of peroxomonophosphate using boron-doped diamond 340

anodes. J. Appl. Electrochem. 2008, 38, 93. 341

(31) Cañizares, P.; Larrondo, F.; Lobato, J.; Rodrigo, M.A.; Sáez, C. Electrochemical 342

synthesis of peroxodiphosphate using boron-doped diamond anodes. J. Electrochem. 343

Soc. 2005, 152, 191. 344

(32) Sáez, C.; Rodrigo, M.A.; Cañizares, P. Electrosynthesis of ferrates with diamond 345

anodes AIChE J. 2008, 54, 1600. 346

(33) Cañizares, P.; Arcís, M.; Sáez, C.; Rodrigo, M.A. Electrochemical synthesis of 347

ferrate using boron doped diamond anodes. Electrochem. Commun. 2007, 9, 2286. 348

(34) Marselli, B.; García-Gómez, J.; Michaud, P.A.; Rodrigo, M.A.; Comninellis, Ch. 349

Electrogeneration of hydroxyl radicals on boron-doped diamond electrodes. J. 350

Electrochem. Soc. 2003, 150, 79. 351

(35) Serrano, K.; Michaud, P.A.; Comninellis, Ch.; Savall, A. Electrochemical 352

preparation of peroxodisulfuric acid using boron doped diamond thin film electrodes. 353

Electrochim. Acta 2002, 48, 431. 354

(36) Saha, M.S.; Furuta, T.; Nishiki, Y. Conversion of carbon dioxide to 355

peroxycarbonate at boron-doped diamond electrode. Electrochem. Commun. 2004, 6, 356

201. 357

(37) Pinkernell, U.; Effkemann, S.; Nitzsche, F.; Karst, U. Rapid high-performance 358

liquid chromatographic method for the determination of peroxyacetic acid. J. 359

Chromatogr. A 1996, 730, 203. 360

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Figure captions 371

372

Fig 1. Variation of the PAA concentration (part a) and carbon mineralization (part b) 373

during the electrolyses with BDD anodes (j 300 Am-2, T 25ºC) of three different raw 374

materials: 1 M C2H6O (▲), 1 M C2H4O (□), 1 M CH3COONa(♦). 375

376

Fig. 2. Main intermediates found during the electrolyses with BDD anodes (j 300 Am-2, 377

T 35ºC) of C2H4O (part a) and C2H6O (part b). acetic acid; acetaldehyde; 378

ethanol; * non identified product 1; + non identified product 2 379

380

Fig. 3. Variation of oxidants concentration (part a) and carbon mineralization (part b) 381

with pH during the electrolysis of CH3COONa solutions at different current charge 382

passed. (1 M CH3COONa, j 300 Am-2, T 25ºC). 383

384

Fig. 4. Variation of oxidants concentration (part a) and total organic carbon (part b) with 385

current density during the electrolysis of CH3COONa solutions. (□) 300 Am-2, (■) 600 386

Am-2, (▲) 1000 Am-2 (1 M CH3COONa, T 25ºC). 387

388

389

390

391

392

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395

16

396

397

398

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Figure 1 400

401

402

403

404

405

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Figure 2 408

409

410

411

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20 25 30

PA

A /

mM

Q/ Ah dm-3

0

20

40

60

0 5 10 15 20 25 30

Car

bo

n m

iner

aliz

ed

/%

Q/ Ah dm-3

a

b

0

100

200

300

400

500

600

700

800

0

1000

2000

3000

4000

5000

6000

0 5 10 15 20 25 30

Chro

mat

ogra

phic

are

a

Q / Ah dm-3

0

100

200

300

400

500

600

700

0

5000

10000

15000

20000

0 5 10 15 20 25 30

Chro

mat

ogra

phic

ar

ea

Q / Ah dm-3

a b

17

412

413

414

415

Figure 3 416

417

418

419

420

421

422

423

424

Figure 4 425

426

427

0

0.2

0.4

0.6

0 2 4 6 8 10 12 14

PA

A /

mM

pH/ units

0

10

20

30

40

50

0 2 4 6 8 10 12 14

min

eral

izat

ion

/ %

pH/ units

5 kA h m-3

25 kA h m-3

50 kA h m-3

5 kA h m-3

25 kA h m-3

50 kA h m-3

a

b

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80 100 120

Oxi

dan

ts / m

M

Q / Ah dm-3

0

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100 120

TO

C /

TO

Co

Q / Ah dm-3

a

b