Removal of pesticides from wastewater by ion pair Centrifugal Partition Extraction using betaine-derived ionic liquids as extractants

Removal of pesticides from wastewater by ion pair Centrifugal Partition Extraction using betaine-derived ionic liquids as extractants

Accepted Manuscript Removal of pesticides from wastewater by ion pair centrifugal partition extraction using betaine-derived ionic liquids as extracta...

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Accepted Manuscript Removal of pesticides from wastewater by ion pair centrifugal partition extraction using betaine-derived ionic liquids as extractants Yannick De Gaetano, Jane Hubert, Aminou Mohamadou, Stéphanie Boudesocque, Richard Plantier-Royon, Jean-Hugues Renault, Laurent Dupont PII: DOI: Reference:

S1385-8947(15)01406-0 http://dx.doi.org/10.1016/j.cej.2015.10.012 CEJ 14281

To appear in:

Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

10 July 2015 30 September 2015 4 October 2015

Please cite this article as: Y. De Gaetano, J. Hubert, A. Mohamadou, S. Boudesocque, R. Plantier-Royon, J-H. Renault, L. Dupont, Removal of pesticides from wastewater by ion pair centrifugal partition extraction using betainederived ionic liquids as extractants, Chemical Engineering Journal (2015), doi: http://dx.doi.org/10.1016/j.cej. 2015.10.012

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1

Removal of pesticides from wastewater by ion pair centrifugal partition extraction using

2

betaine-derived ionic liquids as extractants

3

Yannick De Gaetano, Jane Hubert*, Aminou Mohamadou, Stéphanie Boudesocque, Richard

4

Plantier-Royon, Jean-Hugues Renault, Laurent Dupont*.

5

Université de Reims Champagne-Ardenne, Institut de Chimie Moléculaire de Reims (ICMR),

6

CNRS UMR 7312, UFR des Sciences Exactes et Naturelles, Bâtiment 18 Europol’Agro, BP

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1039, F-51687 Reims Cedex 2, France.

8 9

Abstract

10

The extraction of pesticides from aqueous solutions using new ionic liquids (ILs) derived

11

from glycine betaine as extractants was investigated. These ILs incorporate cationic esters of

12

trimethyl(2-alkoxy-2-oxoethyl) ammonium (GBOCn+) associated with inorganic ClO4- or BF4-

13

anions. First, batch extraction experiments were performed by using the liquid-liquid biphasic

14

system IL/ethyl acetate/water (1:1:1; v/v) for four commonly used pesticides: 4-

15

chlorophenoxyacetic acid (4-CPA), 2,4-dichlorophenoxyacetic acid (2,4-D), 2-[(4-methyl-5-

16

oxo-3-propoxy-1,2,4-triazolin-1-yl)carbamidosulfonyl]benzoic acid methyl ester sodium salt

17

(propoxycarbazone) and 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-methoxymethyl

18

nicotinic acid (imazamox). Then, the liquid-liquid extraction unit operation was intensified by

19

transposing the system into a Centrifugal Partition Extraction (CPE) device, using ethyl

20

acetate/n-butanol/water (1:4:5; v/v) as biphasic solvent system and potassium iodide, sodium

21

iodide or sodium perchlorate as potential displacers. The use of a lab-scale CPE column with

22

a capacity of 300 mL allowed the intensification of the extraction procedure. The extraction

23

and back-extraction of individual or mixture of pesticides were studied, with a particular

24

focus on the potential separation of individual pesticides and on the recyclability of the CPE

25

method. In optimal CPE conditions, a quantitative extraction for three of the four pesticides

1

26

was obtained, with recovery percentages of 95.6 %, 98.7 %, 99.0 %, and 100.0% for

27

imazamox, propoxycarbazone, 2,4-D, and 4-CPA, respectively. After the back-extraction

28

step, separated pesticides were recovered in fresh aqueous mobile phase. The recyclability

29

studies showed that the extraction/back-extraction process can be performed at least four

30

times while maintaining a quantitative extraction.

31 32

Keywords: Ionic liquid, pesticide, centrifugal partition extraction, water treatment,

33

decontamination

34

(*) Corresponding author. Address: ICMR (Institut de Chimie Moléculaire de Reims), Université de Reims Champagne-Ardenne, BP 1039,

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51687 Reims Cedex 2, France. Tel.: +33 (0) 3 26 91 33 36; fax: +33 (0) 3 26 91 32 43. E-mail address: [email protected] (L.

36

DUPONT. [email protected] (J. HUBERT).

37 38 39 40

2

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1. Introduction

42

The extensive use of pesticides in modern agriculture has become a major concern due to the

43

potential hazard that these compounds can cause to the environment and their known or

44

supposed toxic effects on human health, such as mutation, cellular degradation, and

45

interruption of hormone functions [1-2].

46

For this reason, the analytical control of pesticide concentrations is mandatory in different

47

water bodies within the EU including drinking waters [3]. Thus the development of efficient

48

purification strategies focused on their elimination remains a critical issue. Industrially, the

49

most common removal techniques of pesticides from water rely on chemical oxidation,

50

filtration on activated charcoal or inverse osmosis. However these processes are still

51

expensive and research efforts are currently made to find other alternatives. To date, the most

52

common laboratory-scale methods to extract pesticides from aqueous media have been based

53

on liquid-liquid extraction [4, 5] and solid-phase extraction (SPE) [6, 7], with typical

54

extraction volumes ranging from around 10 to a maximum of 100 mL. These techniques

55

usually involve the use of chlorinated solvents that exhibit toxicity (such as tetrachloroethane,

56

chlorobenzene, carbon tetrachloride) or n-hexane [8-10]. ILs have been recently considered

57

as interesting ionic species to remove pesticides from water via extraction mechanisms. ILs

58

are non-flammable liquids, exhibiting a negligible vapour pressure and a high thermal

59

stability. Some of them are liquid at room temperature, able to solubilize a wide range of

60

organic and inorganic compounds [11].

61

The utilization of pure ILs for the extraction of pesticides has been already investigated in

62

liquid-liquid extraction [12-14], solid-liquid extraction [15], magnetic solid-phase extraction

63

[16], micro-solid phase extraction [17], dispersive micro-solid phase extraction [18], pipette

64

tip-solid phase extraction [19] and hollow fiber-solid phase microextraction procedures [20].

3

65

However these methods remain time consuming and still display some drawbacks such as low

66

extraction yields, multiple operation steps [21], and high IL consumption. The present work

67

aimed to develop a novel efficient method for the extraction of pesticides that combines the

68

use of ILs as extractants with Centrifugal Partition Extraction (CPE) as liquid-liquid efficient

69

contactor.

70

CPE is a solid support-free liquid-liquid extraction technique involving transfer and

71

distribution of solutes between at least two immiscible liquid phases according to their

72

distribution and mass transfer coefficients.

73

A CPE column (Figure 1) consists in a series series of partition cells connected in cascade by ducts

74

and subjected to a centrifugal acceleration field [22]. One liquid phase is maintained inside

75

the partition cells (the stationary phase) while the other liquid phase (the mobile phase) is

76

pumped through the stationary phase. The separation process is based on the interfacial mass

77

transfer of solutes between the two liquid phases in each cell [23].

78 79

Fig. 1. (a) Centrifugal Partition Extractor FCPE300®, (b) CPE column containing 7 circular

80

partition disks, (c) Scheme of a circular partition disk

81

4

82

The design of CPE partition cells inside the column allows the loading of sample solutions

83

continuously with flow rates ranging from 10 to 100 mL/min at the laboratory-scale, which is

84

of particular interest for the extraction of micropollutants such as pesticides present at low

85

concentrations in aqueous media.

86

Considering the ionic nature of ILs (cation/anion association), it can be expected that the ion-

87

pair displacement mode in CPE [24] would provide interesting results to extract pesticides

88

from water and possibly to separate pesticides from each other at the end of the process. The

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ion pair displacement mode in CPE consists in diluting an anionic or cationic species (here

90

ILs) in the organic stationary phase. By this way ionisable analytes (such as most pesticides)

91

contained in the inlet aqueous solution are captured by the IL inside the CPE column. Then

92

during the back-extraction step, a displacer agent that presents a high affinity for the

93

extractant (i.e. the IL) is introduced into the aqueous mobile phase to force the analytes to

94

competitively progress along the column. As a result the analytes (here the pesticides) initially

95

introduced into the CPE column as a mixture of compounds in a liquid phase are not only

96

extracted from their initial media over the extraction step, but also displaced out of the

97

column during the back-extraction and possibly recovered in a fresh aqueous solution as

98

individual compounds. This method has been successfully applied for the separation and

99

purification of ionizable natural products [25].

100

To date only a few ILs have been synthesized and tested for the extraction of organic

101

compounds. The most common families of ILs employed for this purpose were the 1,3-

102

dialkylimidazolium salts with hexafluorophosphate or bis(trifluoromethylsulfonyl)imide

103

anion, but these ILs exhibited some toxicity [26].

104 105

2. Materials and methods

106

5

107

In the present work, we report the study of the extraction of some pesticides by six news ILs

108

obtained from esterified glycine betaine (Scheme 1) using Centrifugal Partition Extraction.

109

The effects of the nature of both cation and anion forms of the ILs, as well as CPE parameters

110

(e.g.volume of treated solutions, flow rate, nature of the displacer) on the pesticide extraction

111

percentage have been investigated. Results related to the back-extraction of pesticides are also

112

presented.

113

114 115

Scheme 1. Ionic liquids based on Glycine Betaine esters.

116 117

The CPE extraction method was developed by using four systemic herbicides commonly used

118

worldwide for the control of broadleaf weeds. Two members of the phenoxy family of

119

herbicides: the 4-chlorophenoxyacetic acid (4-CPA) and the 2,4-dichlorophenoxyacetic acid

120

(2,4-D), as well as propoxycarbazone and imazamox were selected as models (Scheme 2).

121 122

6

123 124

Scheme 2. Chemical structures of the four pesticides studied.

125 126

2.1. Reagents and solvents

127

All chemicals were of analytical grade. Ethyl acetate (EtOAc) and n-butanol (n-BuOH) were

128

purchased from Carlo Erba Reactifs SDS (Val de Reuil, France). 4-chlorophenoxyacetic acid

129

(4-CPA), 2,4-dichlorophenoxyacetic acid (2,4-D), propoxycarbazone salt and imazamox were

130

purchased from Sigma Aldrich (Saint Quentin, France). Sodium perchlorate and sodium

131

iodide were obtained from Acros (Illkirch, France) and potassium iodide from Alfa Aesar

132

(Schiltigheim, France). All aqueous solutions were prepared in distilled water and stored safe

133

from the light at 4°C.

134 135

2.2. Apparatus: Fast Centrifugal Partition Extractor FCPE300®

136

Extraction experiments were developed on a lab-scale Centrifugal Partition Extractor

137

(FCPE300®, Rousselet Robatel Kromaton, Annonay, France) containing a rotor of 7 circular

138

partition disks engraved with a total of 231 twin partition cells. The stationary phase was

139

maintained inside the CPE column by a centrifugal force field generated by rotation around a

140

single central axis. The total column capacity is 303.5 mL [37]. The rotation speed can be

141

adjusted from 200 to 2000 rpm, producing a relative centrifugal acceleration in the partition

7

142

cell up to 437 g. The mobile phase was pumped through the stationary phase either in the

143

ascending or in the descending mode with low residual pulsation through a KNAUER

144

Preparative Pump 1800® V7115 (Berlin, Germany). Fractions were collected by a Pharmacia

145

Superfrac collector (Uppsala, Sweden). All experiments were conducted at room temperature

146

(20 ± 2 °C). The flow rate was fixed at 10 mL/min and the rotation speed at 1000 rpm for all

147

experiments.

148 149

2.3. HPLC analyses

150

All CPE fractions were analyzed by HPLC on an Ultimate® 3000 HPLC system (Dionex)

151

equipped with a Dionex Ultimate pump (model 3000), a WPS-3000 (SL) autosampler, and a

152

diode array detector DAD-3000(RS). The chromatographic column (Myrsine, 250 × 4.6 mm,

153

5 µm particule size) was maintained at 21 °C. The mobile phases, 0.5% acetic acid in water

154

(solvent A) and acetonitrile (solvent B), were pumped isocratically at 1.5 mL/min with a ratio

155

60/40 (v/v). The injection volume was 20 µL. Data acquisition was controlled by the

156

Chromeleon Software and the chromatograms were recorded for 15 min.

157

UV detection was performed at λ = 254 nm for imazamox (λmax = 250 nm) and

158

propoxycarbazone (λmax = 253 nm) and λ = 280 nm for 4-CPA (λmax = 279 nm) and (λmax =

159

283 nm). Calibration curves were established by serial dilution of two independent stock

160

solutions of each pure pesticide (1 g/L) and by plotting the peak area recorded from HPLC

161

chromatograms as a function of pesticide concentration. The correlation coefficient (R2)

162

calculated from the calibration curves of standard solutions were higher than 0.9996 for all

163

compounds. The four pesticides were identified over CPE experiments by comparison with

164

the HPLC retention time of their corresponding standard molecules. The retention times of

165

imazamox, 4-CPA, 2,4-D and propoxycarbazone were 3.0, 6.8, 9.1 and 13.2 min,

166

respectively. 8

167 168

2.4. Batch tests

169

2.4.1. Optimization of extraction conditions

170

Extraction conditions were optimized in batch tests by using the couple GBOC14-ClO4 and 4-

171

CPA as an IL/analyte test system. Experiments were performed using different molar ratios (

172

nIL n4−CPA

) ranging from 10 to 25 (corresponding to 8, 12, 16 and 20 mg of GBOC14-ClO4). An

173

aqueous solution containing 4-CPA at a concentration of 10-3 mol.L-1 (2 mL) was mixed with

174

an equal volume of IL diluted in ethyl acetate (2 mL). The mixture was stirred for 1 hour at

175

room temperature.

176

analyzed by HPLC. The efficiency of the extraction process was evaluated by determining the

177

extraction percentage (%E) using the following equation:

The liquid phases were then separated and the aqueous phase was

%E =

178

(Cin − C fin ) Cin

x100

179

where Cin and Cfin (mol. L-1) represent the concentrations of the pesticide in the initial and in

180

the final aqueous solutions.

181 182

2.4.2. Choice of the base for the extraction

183

The first goal was to find the best pH conditions to ensure the ionization state of pesticides

184

(COO-, N-) while maintaining their chemical integrity. HPLC analyses of the four pesticides

185

revealed two different peaks for propoxycarbazone at pH > 9, suggesting that this compound

186

is stable only up to this value. The other pesticides were also stable up to pH 9. Therefore the

187

pH was fixed at 9 in all extraction experiments. The pKa values for 4-CPA, 2,4-D and

188

propoxycarbazone are respectively 3.6, 2.7 and 2.1. Imazamox has three protonation sites

189

corresponding to pKa values of 2.3, 3.3 and 10.8 [27]. The first two pKas correspond

190

respectively to the deprotonation of pyridinium and carboxylic groups, whereas the third pKa 9

191

is ascribed to the neutralization of the protonated amidic nitrogen. Consequently, at pH 9,

192

Imazamox, 4-CPA, 2,4-D are present as their carboxylate salt and propoxycarbazone as its

193

anionic form (-N-). These observations are summarized in Table 1.

194

Several alkaline agents including ammoniac buffer (NH4OH), potassium hydroxide (KOH)

195

and sodium hydroxide (NaOH) were tested to adjust the pH of the aqueous solutions. For

196

experiments with NaOH and KOH, 18.6 mg of 4-CPA (corresponding to 0.1 mmol) were

197

firstly diluted in approximatively 100 mL of distilled water and then the pH was adjusted to 9

198

by adding few drops of concentrated solution of the base (1 mol.L-1), in order to obtain a

199

solution of 4-CPA at a concentration of 10-3 mol.L-1. For extraction experiments with

200

ammoniac buffer, 18.6 mg of 4-CPA corresponding to 0.1 mmol were directly diluted in

201

100 mL of ammoniac buffer at a concentration of 0.1 mol.L-1.

202 203

2.4.3. Extractant selection

204

GBOC12-ClO4, GBOC14-ClO4, GBOC16-ClO4, GBOC12-BF4, GBOC14-BF4 and GBOC16-BF4

205

were investigated as ILs for the extraction of 4-CPA. Experiments were performed at pH 9

206

using a molar ratio (

207

temperature.

nIL n4−CPA

) equal to 25. All experiments were carried out at room

208 209

2.4.4. Extraction of individual pesticides with GBOC14-ClO4

210

The fresh pesticides solutions ([C] = 5.10-4 mol.L-1) were independently prepared by

211

dissolving 9.3 mg of 4-CPA; 11.0 mg of 2,4-D; 15.2 mg of imazamox or 21.0 mg of

212

propoxycarbazone in 100 mL of distilled water. Then, 2 mL of each solution containing

213

individual pesticide at a concentration of 5.10-4 mol.L-1 (pH = 9) were mixed with 2 mL of

214

ethyl acetate containing GBOC14-ClO4 at concentrations ranging from 0 to 25 equivalents of

215

pesticide (from 0 to 10.4 mg) for 4-CPA and 2,4-D and from 0 to 50 equivalents of pesticides 10

216

(0 to 20.7 mg) for imazamox and propoxycarbazone. The solutions were stirred for 1 h. The

217

liquid phases were then separated and the aqueous phases were all analyzed by HPLC to

218

determine the extraction percentage of individual pesticides. Extraction experiments were

219

repeated 5 times for each experimental condition.

220 221

2.5. Centrifugal Partition Extraction (CPE)

222

2.5.1. Optimization of the extraction and back-extraction steps with individual pesticides

223

Extraction and back-extraction of individual pesticides were investigated at the preparative

224

scale by using CPE. The extraction step consists in the capture of ionic species (among which

225

pesticides) by the ionic liquid inside the column through the formation of ion pairs, while the

226

other non-ionic compounds are eluted out of the column. In a second step, the back-extraction

227

consists in introducing in the mobile phase a displacer agent (here iodides) which exhibits a

228

higher affinity for the ionic liquid than the captured analytes. By this way a competitive

229

process takes place and the target ionic compounds are eluted selectively in the order of their

230

affinity for the ionic liquid.

231

A biphasic solvent system (2 L) was prepared by mixing EtOAc/n-BuOH/water in the

232

proportions 4:1:5 (v/v/v). The column was filled at 200 rpm with the organic phase used as

233

the stationary phase containing the IL extractant GBOC14-ClO4 at a molar ratio

234

25. Individual pesticides were dissolved in the aqueous phase of the solvent system at a

235

concentration of 62.5 mg/L. The pH was adjusted to 9 by adding KOH (1 mol.L-1) and the

236

aqueous phase containing the pesticide was pumped through the stationary phase at

237

10 mL/min.

238

After pumping slightly more than one column volume (320 mL), aqueous solutions of

239

potassium iodide (KI) or sodium iodide (NaI) were tested for the back-extraction step. In this

nIL n pesticides

of

11

240

process, the pesticide previously extracted, were stripped off the stationary phase, following

241

this equation:

242 243 244

where R-COO- corresponds to the pesticide under his anionic form.

245 246

Fractions of 20 mL were collected over the whole experiments and analyzed by HPLC. The

247

back-extraction step was also studied using different molar ratios:

248 249

ndisplacer nIL

= 5 and

ndisplacer nIL

ndisplacer nIL

= 1,

ndisplacer nIL

= 2,

= 10. Finally, NaI and KI were investigated as displacers in order to

assess the influence of the cation on the back-extraction efficiency.

250 251

2.5.2. Extraction and back-extraction process description with mixtures of pesticides

252

Extraction and back-extraction of an equimolar mixture of the two phenoxyacetic acids 4-

253

CPA and 2,4-D were firstly investigated at a concentration of 2.8 x 10-4 mol.L-1 (21 mg of 4-

254

CPA and 25 mg of 2,4-D; 1.13 x 10-4 mol) were dissolved in 400 mL of distilled water. The

255

preparation of both the mobile and stationary phases is described above. The back-extraction

256

was carried out using a ratio

257

For the preparation of the mixture of the pesticides at a concentration of 2.0 x 10-4 mol.L-1,

258

14.9 mg of 4-CPA, 17.7 mg of 2,4-D, 24.4 mg of imazamox and 33.7 mg of

259

propoxycarbazone (8.0 x 10-5 mol) were dissolved in 400 mL of distilled water.

nKI = 10. nIL

260 261

2.5.3. Back-extraction with sodium perchlorate as displacer 12

262

This extraction was performed on the same pesticide mixture as described in § 2.5.2. Sodium

263

perchlorate was used as displacer. The back-extraction process was performed using a ratio

264

nNaClO4 n4−CPA

= 10.

265 266

2.5.4. Recyclability of the process

267

In order to investigate the recyclability of the whole CPE procedure, 18.6 mg of 4-CPA (10-4

268

mol) were dissolved in 400 mL of distilled water to obtain a solution at a concentration of 2.5

269

x 10-4 mol.L-1. The preparation of the mobile and stationary phases are described in § 2.5.1.

270

The back-extraction process was performed using sodium perchlorate as displacer and a ratio

271

nNaClO4 n4−CPA

= 10. After one cycle of extraction/back-extraction, 18.6 mg of 4-CPA were dissolved

272

in 400 mL of the fresh aqueous phase of the CPE biphasic solvent system and loaded again

273

into the column to perform a second extraction/back-extraction cycle. In total, four

274

consecutive cycles were performed.

275 276

2.5.5. Resolution (Rs) and selectivity factor (α)

277

Resolution (Rs) and selectivity factor (α) were calculated for two consecutive peaks. The Rs

278

is calculated using this following equation:

279

Rs = 2

(t r ( B) − t r ( A)) wb + wa

280

where tr(A) and tr(B) represent the retention time for solutes A and B, with B the more

281

retained solute; wa and wb represent the curve width of solute A and solute B respectively.

282

Selectivity factor is given by this following equation:

283

α=

k ' ( B) k ' ( A)

13

284

where k’(A) and k’(B) represent the capacity factor. These capacity factors are deduced by

285

these two equations:

k ' ( A) =

286 287

(t r ( A) − t 0 ) t0

k ' ( B) =

(t r ( B) − t0 ) t0

with t0 the time for the dead volume.

288 289

3. Results

290

All GBOCn-X ILs were obtained from the esterification reaction of betaine with n-alkyl

291

alcohols using methanesulfonate acid as catalyser, follow by anionic metathesis from the

292

methanesulfonate derivative using sodium perchlorate or sodium tetrafluoroborate [28].

293 294

3.1. Optimization of the extraction conditions in batch tests with 4-CPA as pesticide model

295

The first goal was to evaluate the influence of the pH of the aqueous solution and the nature

296

of the base used to adjust the pH on the pesticide extraction percentage. percentage. For these

297

experiments, 4-CPA and GBOC14-ClO4 were selected as models. Indeed, alkaline conditions

298

are necessary to obtain pesticides in their anionic form and therefore facilitate the formation

299

of ion pairs with ILs. Due to the poor stability of pesticides, especially propoxycarbazone

300

which hydrolyses above pH 9, the pH was limited to this value (Table 1).

301 302

Table 1

303

Chemical structure, molar mass (g.mol-1), stability under alkaline conditions and pKa values

304

of each pesticide. Chemical Structures of

Molar Mass Name

Stability

pKa values

stable

3.56

(g.mol-1)

Pesticides 4-chlorophenoxyacetic acid

186.59 (4-CPA)

14

2,4-dichlorophenoxyacetic acid 221.04

stable

2.73

(2,4-D) 2-[(4-Methyl-5-oxo-3-propoxy1,2,4-triazolin-1Stable at 420.37

yl)carbamidosulfonyl]benzoic

2.10 pH < 9

acid methyl ester sodium salt

(propoxycarbazone) 2-(4 (4-Isopropyl-4-methyl-5-oxo-

2.3(Npyridinium) 2-imidazolin-2-yl)-5305.33

stable

3.3 (COO-)

methoxymethyl nicotinic acid

10.8 (Namide) (imazamox)

305

nIL

306

For the same experimental conditions with a ratio (

307

Table 2 demonstrate that the extraction of 4-CPA using NH4OH buffer or NaOH was less

308

effective (%E = 27.0 - 63.0%) than with KOH (%E (%E = 69.0%). The extraction of 4-CPA under

309

its potassium salt form with GBOC14-ClO4 IL is thus more efficient than under sodium or

310

ammonium salt forms.

n4−CPA

) = 10, the results presented in

311 312

Table 2

313

Extraction percentage (%E) of 4-CPA with three different bases (NH3, NaOH and KOH) and

314

two different ratios

n IL n 4−CPA

.

315

Ratio

Extraction percentage

nIL n4−CPA

10

NH3

NaOH

KOH

27.0

63.0

69.00 15

316

25

47.3

89.5

99.1

317 318

nIL

319

This tendency was confirmed by the results obtained with a ratio (

320

base lead to a nearly quantitative extraction of 4-CPA (99.1%) was observed. However, the

321

extraction percentage was below 90% when using NaOH and 50% with NH4OH buffer. The

322

best extraction conditions were thus fixed at pH 9 with KOH and using 25 equivalents of ILs.

323

To determine the most efficient IL, these conditions were applied for a range of glycine

324

betaine-derived ILs differing from each other by their anionic moiety (ClO4- or BF4-) and

325

alkyl chain length (n=12, 14, 16). The results are summarized in Table 3.

n4−CPA

) = 25 using KOH as

326 327

Table 3.

328

Extraction percentage (%E) of 4-CPA, Experimental conditions: [4-CPA] = 10-3 mol.L-1, pH

329

9 (KOH), ratio (

nIL n4−CPA

) = 25.

ILs

GBOC12-ClO4

GBOC14-ClO4

GBOC16-ClO4

GBOC12-BF4

GBOC14-BF4

GBOC16-BF4

(% E)

92.1

99.1

96.7

59.6

65.5

71.4

330 331

Extraction yields obtained with ILs containing a tetrafluoroborate anion were comprised

332

between 59.6% and 71.4%, while all the extraction yields obtained with ILs containing a

333

perchlorate anion were higher than 90%. This effect is somewhat due to the ability of

334

perchlorate anions to precipitate in the presence of potassium as shown below.

335 336

Indeed, over the course of extraction, an anionic exchange occurs and the insoluble potassium

337

perchlorate salt is formed in the organic phase, thus enhancing the formation of GBOCn+ 416

338

CPA- and leading to a better extraction yield as compared to ILs with other anions. We also

339

observed that extraction yields were improved with ILs containing a longer alkyl chain as

340

observed in previous works [29]. For instance the extraction yields obtained with the

341

tetrafluoroborate series were 59.6. 65.5 and 71.4% for n = 12, 14, and 16, respectively. For

342

the perchlorate series, extraction yields were 92.1, 99.1, and 96.7% for n = 12, 14, and 16,

343

respectively. The lower extraction percentage obtained with GBOC16-ClO4 could be explained

344

by its lower solubility in EtOAc, which limits its efficiency as an extractant. GBOC14-ClO4

345

was therefore selected to perform all others extraction experiments.

346 347

3.2. Influence of IL concentration on the extraction profile of pesticides from aqueous

348

solutions

349

The results depicted in Figure 2 represent the extraction trends for the four pesticides using

350

GBOC14-ClO4 as the extractant.

Extraction percentage

100 80 60 40

4-CPA 2,4D Propoxycarbazone Imazamox

20 0 0

351

10

20

30

40

50

IL equivalents

352

Fig. 2. Extraction behaviors for 4-CPA, 2,4-D, propoxycarbazone and imazamox with

353

GBOC14-ClO4 IL (with a confidence interval +/- 0.3%).

354

17

355

Without IL, only 7.8% and 2.1% of the two chlorophenoxyacetic acids 4-CPA and 2,4-D were

356

transferred into the organic phase. For the two other pesticides, imazamox and

357

propoxycarbazone which are more soluble in water (4 g/L and 2.9 g/L, respectively), only 0.8

358

and 0.2 % of the pesticides were transferred into the organic phase.

359

With 25 equivalents of GBOC14-ClO4, the extraction percentages were 99.1 and 95.1% for 4-

360

CPA and 2,4-D, respectively. For imazamox and propoxycarbazone, the extraction

361

percentages were only 53.5 and 76.0 %, respectively. These lower values could be explained

362

by the higher hydrophilicity of these molecules as compared to 4-CPA and 2,4-D. With 50

363

equivalents of GBOC14-ClO4 ([C] = 2.5 x 10-2 mol.L-1), the extraction yields increased up to

364

61.0% for imazamox and up to 81.3% for propoxycarbazone. The extraction percentage

365

remained lower than those obtained for the two phenoxy herbicides. However, we expected

366

that the transposition of extraction experiments from batch test conditions to CPE by

367

exploiting the length (231 interconnecting partition cells) of the CPE column should provide

368

higher extraction percentages.

369

Each extraction experiment was replicated five times and the extraction percentage variations

370

were less than 1.5% between experiments, indicating a very good reproducibility (Figure 2).

371 372

3.3. Pesticide extraction by Centrifugal Partition Extraction (CPE)

373

Nowadays, ILs are mainly used in micro-extraction for the treatment of very low volumes of

374

aqueous solutions, typically from 2 to 10 mL, with a low amount of pure IL. Micro-extraction

375

is a very efficient process to obtain high enrichment factors (80-500) and extraction yields

376

higher than 90 % [30]. But to our knowledge, no literature deals with the use of ILs for the

377

treatment of large volumes of aqueous solution contaminated with pesticides. The main goal

378

of this work was to develop a preparative-scale process for the extraction process of pesticides

379

by combining ILs as extractants and CPE. Our objective was to extract quantitatively the

18

380

pesticides from aqueous solutions and to investigate the selectivity of the process (i.e. the

381

separation of the different pesticides) and its recyclability.

382 383

3.3.1. CPE: Extraction and back-extraction results on individual pesticides

384

Extraction and back-extraction steps were firstly performed by CPE with each individual

385

pesticide. Experiments were performed at a flow rate of 10 mL/min by using a molar ratio

386

nIL/npesticides = 25 with a pesticide concentration of 62.5 mg/L in the aqueous mobile phase.

387

After pumping slightly more than one column volume (320 mL), no pesticide was detected for

388

4-CPA, 2,4-D and propoxycarbazone in the fractions collected during the extraction step

389

indicating that these compounds were quantitatively extracted from the aqueous mobile phase.

390

However under the same experimental conditions, the extraction of imazamox was less

391

effective with an extraction percentage of 58.0 %. In order to improve the extraction

392

percentage of imazamox, another experiment using twice more extractant GBOC14-ClO4 was

393

carried out, but the extraction percentage remained limited to 63.0 %.

394

For the back-extraction step, KI was first used as a displacer with

395

ranging from 1 to 10. The recovery of 4-CPA during this back-extraction step increased from

396

86 % to 100 % when the molar ratio

397

that a minimum of 10 equivalents of KI are required to obtain a complete back-extraction of

398

4-CPA. Under the exact same conditions, high recovery percentages were obtained for the

399

other pesticides as indicated in table 4. The use of NaI as a displacer instead of KI was also

400

investigated. The results showed that the nature of the cation on the displacer agent did not

401

significantly influence the back-extraction performance, except for 2,4-D for which the back-

402

extraction was slightly improved.

nKI nGBOC14 −ClO4

nKI nGBOC14 −ClO4

molar ratios

increased from 1 to 10. These results showed

403 19

404

Table 4

405

Extraction percentage (%E), Recovery percentage (%R) of different pesticides; Experimental

406

conditions: mobile phase 1 (extraction process): mass of each pesticide = 25 mg, pH = 9

407

(KOH), ratio (

408

NaI (10 equivalents)

n IL n pesticide

) = 25; mobile phase 2 (back-extraction process): aqueous phase KI or

409 410 4-CPA

2,4-D

Propoxycarbazone

Imazamox

%E

quantitative

quantitative

quantitative

58.0

%R

100.0

99.0

98.7

95.6

411 412 413

3.3.2. CPE: Extraction and Back-extraction results on mixture of pesticides

414

Support-free liquid-liquid separation techniques such as CPC (including CPE type devices) or

415

couter-current chromatography (CCC) are well-known for their large sample loading capacity

416

and scaling-up ability, but are also very attractive in terms of selectivity [31,32], especially

417

when the displacement mode (ion-exchange, pH-zone refining) is performed. Here the

418

selective recovery of pesticides was investigated.

419

Firstly, extraction and back-extraction were carried out for a binary mixture of the two

420

phenoxy-herbicides 4-CPA and 2,4-D. During the extraction step, 320 mL of the aqueous

421

mobile phase pumped at a flow rate of 10 mL/min and a rotation speed of 1000 rpm. The two

422

pesticides were quantitatively retained in the organic stationary phase. The extraction/back-

423

extraction profile of these pesticides when using NaI as a displacer (

424

Figure 3. This profile can be divided in three distinct zones: zone 1 covered the range between

425

160 mL and 240 mL (fraction 8-12, recovered mass = 17.0 mg, 9.1 x 10-5 mol), 4-CPA was

nNaI = 10) is shown in nIL

20

426

obtained as a pure compound; zone 2 covered the range between 260 mL and 320 mL

427

(fraction 13-16, m (CPA) = 4.1 mg, 2.1 x 10-5 mol and m (2,4-D) = 5.7 mg, 2.6 x 10-5 mol) in

428

which both compounds were obtained as a mixture, and zone 3 ranged above 320 mL

429

(fraction 17-30, recovery mass = 18.8 mg, 8.5 x 10-5 mol) only 2,4-D was recovered. These

430

results indicate a quite good pesticide separation. Pure fractions of 4-CPA represent 81% of

431

the total injected mass of 4-CPA, and 76% for 2,4-D. The total recovery percentage was

432

quantitative for 4-CPA and 2,4-D, respectively (Figure 3). For this experiment, the selectivity

433

factor (α) calculated was equal to 2.2 with a Rs of 0.86. Zone 1

quantity of pesticides (mol %)

35

Zone 2

Zone 3

30

4-CPA 2,4-D

25 20 15 10 5 0 0

434

100

200 300 400 Volume of displacer (mL)

500

600

435 436

Fig. 3. Back-extraction of the equimolar mixture of 4-CPA and 2,4-D with NaI as displacer,

437

Experimental conditions: ratio nNaI/nIL = 10, flow rate= 10 mL/min, rotation speed 1000 rpm,

438

descending mode

439 440

The second experiment was the extraction and back-extraction of an equimolar mixture of the

441

four herbicides (8.0 x 10-5 mol). During the extraction step (

442

aqueous mobile phase pumped at a flow rate of 10 mL/min and a rotation speed of 1000 rpm),

nIL n pesticides

= 25, 320 mL of the

21

443

4-CPA, 2,4-D and propoxycarbazone were quantitatively retained in the organic stationary

444

phase. Only imazamox was partially extracted (%E = 68.7%). The back-extraction profile

445

obtained with NaI as a displacer (

446

between 80 mL and 120 mL (fraction 4-6, recovered mass = 17.0 mg, 5.6 x 10-5 mol), pure

447

fractions of imazamox were isolated. In zone 2, between 140 mL and 180 mL, a mixture of 4-

448

CPA, imazamox and propoxycarbazone was collected. Zone 3 (200–280mL) corresponds to a

449

mixture of 4-CPA and propoxycarbazone. In zone 4, between 300 and 380 mL, 4-CPA was

450

recovered as a pure compound. Finally zone 5, (400 mL- 600 mL) 2,4-D was isolated as a

451

pure compound. The total recovery percentages were 95.5% for 4-CPA, 98.7% for 2,4-D,

452

96.5% for imazamox and 96.0% for propoxycarbazone. (Figure 4)

nNaI = 10) can be divided in five distinct zones. In zone 1, nIL

453 Zone 5

Zone 4

Zone 3

Zone 2

Zone 1

454 455

Fig. 4. Back-extraction of the equimolar mixture of the four pesticides with NaI as displacer.

456 457

The selectivity factors α and Rs considering two consecutive peaks, between imazamox –

458

propoxycarbazone (peak 1 – peak 2), propoxycarbazone – 4-CPA (peak 2 – peak 3) and 4-

459

CPA – 2,4-D (peak 3 – peak 4) are summarized in Table 5.

22

460

Table 5

461

Selectivity factor α and Resolution Rs calculated for the mixture of the four pesticides.

462

Selectivity factor (α) Resolution (Rs)

peak 1 – peak 2

peak 2 – peak 3

peak 3 – peak 4

220 0.7

1.18 0.14

3.31 1.4

463 464

During this back-extraction step, imazamox and 2,4-D were well separated with a selectivity

465

factor superior to 2.2, but the back-extraction profiles of 4-CPA and propoxycarbazone were

466

rather similar and their separation was less effective.

467 468

3.4. Back-extraction with sodium perchlorate as displacer

469

The regeneration, recyclability and reuse of ILs without significant loss remains a critical

470

issue to make the process economically viable and reduce the potential environmental burden.

471

The recyclability of the method was thus studied.

472

Back-extraction with NaClO4 as a displacer (

473

to regenerate the IL GBOC14-ClO4 directly in the organic stationary phase, and to investigate

474

the possibility to recycle the system (Figure 5).

nNaClO4 nIL

= 10) was performed, the main goal being

23

475 476

Fig. 5. Extraction/Back-extraction cycle of 4-CPA ([C] = 2.5 x 10-4 mol.L-1) with GBOC14-

477

ClO4 IL as extractant and NaClO4 as displacer.

478 479

For this study, the extraction of an equimolar mixture of 4-CPA and 2,4-D, was investigated

480

at a concentration of 2.5 x 10-4 mol.L-1. During the extraction (

481

pesticides were quantitatively retained in the organic stationary phase. It was observed that

482

the back-extraction step was more efficient using NaClO4 as a displacer than with NaI.

483

Indeed, the back-extraction of 4-CPA was completed in only four fractions (80 mL) instead of

484

eight (160 mL) with NaI. In the same manner, the back-extraction of 2,4-D was realized in

485

180 mL instead of 320 mL. But in this latter case, the separation was less marked. The

486

selectivity factor was equal to 1.4 with a Rs value of 0.4. In the other hand, a selectivity factor

487

of 2.2 with a Rs of 0.9 were obtained for the back-extraction with NaI.

488

Only one fraction of pure 4-CPA was isolated (fraction 8). 2,4-D was isolated in fractions 12-

489

16. The total recovery percentage was 100% and 91% for 4-CPA and 2,4-D, respectively

490

(Figure 6).

nIL n pesticides

= 25), the two

491

24

492 493

Fig. 6. Back-extraction of the equimolar mixture of 4-CPA and 2,4-D ([C] = 2.8 x 10-4 mol.L-

494

1

) with NaClO4 as displacer.

495 496

3.5. Process recyclability

497

With regard to the efficiency of NaClO4 as a displacer, the recyclability of the process was

498

studied for four cycles with alternative extraction (0 - 350 mL, 700 - 1050 mL, 1400 - 1750

499

mL and 2100 - 2450 mL) and back-extraction (350 - 700 mL, 1050 – 1400 mL, 17500 – 2100

500

mL and 2450 – 2700 ml) steps. The quantitative extraction of 4-CPA for the two first cycles

501

proves that the regeneration of GBOC14-ClO4 was effective (Figure 7).

502

The high extraction percentages (98.3% and 97.1% for the third and the fourth cycle) showed

503

that IL maintained its extraction capacity over multiple extraction/back extraction cycles.

25

Back-extraction

504 505

(a)

506 507

(b)

508

Fig. 7. (a) Profile curve for four cycles of Extraction/Back-extraction of 4-CPA with NaClO4

509

as displacer. (b) Percentage of 4-CPA recovered during extraction and back-extraction

510

process of 4-CPA with NaClO4 as displacer

511 512

4. Conclusion

513

The main focus of this work was to demonstrate the efficiency of Centrifugal Partition

514

Extraction to remove pesticides from water samples and optimize this extraction process. 26

515

The extraction potential of six new ILs derived from glycine betaine was investigated in batch

516

tests and then transposed to CPE. Batch tests have shown that GBOC14-ClO4 is the most

517

efficient IL for the extraction of the four model pesticides (4-CPA, 2,4-D, propoxycarbazone

518

and imazamox), and the transposition to a larger scale was successfully achieved by CPE.

519

Good extraction yields were obtained by CPE with a quantitative extraction for three of the

520

four pesticides and high recovery rate over the back-extraction step (up to 96%). Selective

521

back-extractions were also obtained for the separation of the two phenoxy herbicides. The

522

recyclability of the process has also demonstrated that the extractant can be regenerated and

523

the extraction/back-extraction cycle can be repeated at least four times. However, it seems

524

worthwhile to extend this work by replacing the perchlorate anion by other anions such as

525

amino-acid which are renewable and convenient, allowing the extension of this method to

526

larger effluent volumes.

527 528

Acknowledgements

529

We are grateful to Dr. Yamina Belabassi (UMR 7312, University of Reims Champagne-

530

Ardenne) for linguistic improvement of this manuscript. We thank the Conseil Régional de la

531

Marne for financial support.

532 533

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534 535

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32

Highlights

662 663 664



Pesticides are extracted from aqueous media using new bio-sourced ionic liquids

665



Extraction conditions were optimized in batch tests and transposed to Centrifugal

666 667

Partition Extraction •

668

Four model pesticides were successfully extracted by CPE in the ion-pair displacement mode

669



Pesticide mixtures were well separated and enriched over the back-extraction step

670



The recyclability of the process was demonstrated

671 672

34