POTENTIOMETRIC MONITORING OF ANIONIC SURFACTANTS DECOMPOSITION USING PHOTO-OXIDATIVE UV/H2O2 PROCESES Potenciometrijsko praćenje ragradnje anionskih tenzida foto-oksidativnim UV/H2O2 procesom Polycarboxylates are used in household cleaning products, and a variety of technical applications as dispersing agents for avoiding incrustation and soil redeposition. They are generally used in neutralised form (pH 1, 6-8) as their sodium salts [1]. Major polycarboxylates used in detergent products are homopolymers 1of acrylic acid and copolymers of acrylic/maleic acid. Mean molecular weight of the homopolymers and copolymers of acrylic/maleic acid ranges from approximately 1000 to 78000 (most commonly in liquid detergents 4500), and 12000 to 100000 (most commonly in powder detergents 70000), respectively.
Z. Lovinčić Kraljević , D. Madunić-Čačić *
1SAPONIA, Chemical, Pharmaceutical and Foodstuff Industry, M.Gupca 2, HR-31000 Osijek, Croatia
Keywords: Surfactant-sensitive electrode, PVC membrane, cationic surfactant, anionic surfactant, potentiometric titration
Corresponding autor:
[email protected]
The history of advanced oxidation processes (AOP) began with Fenton chemistry (1894). Until then AOP´s have become of great interest. In last few decades the importance of hydroxyl radical (HO·) reactions wastewaters treatment has been recognised and viewed as potentially convenient and economical way to generate oxidizing species for treating chemical wastes [1]. This study reported about the decomposition of sodium and sodium dodecylether sulphate (NaLES) and sodium dodecylbenezene sulphonate (NaDBS) using photooxidative UV/H2O2 process. The decomposition was monitored by potentiometric titration using PVC based self-made electrode for end-point detection [2]. Advantage of this method is in determination of surfactants formed in partial digestion [3,4] of anionic surfactants using cost effective analytical technique (Figure 1). Even the difference of two C-atoms between the titratable anionic surfactants exhibited two inflexion points. The first one related to the anionic surfactant which formed a heavily soluble ion-pair (greater number of C-atoms) [2]. Using potentiometric titration as a method for determination of anionic surfactants in wastewater treated by UV/H2O2, AS can be titrated differentially when the difference between the C-chains is at least 2 (investigated on modal mixtures). Titration results on the samples treated by photo-oxidative UV/H2O2 process confirmed degradation of NaDBS and NaSLES to molecules of lower Mw (C8, C9, C10).
EXPERIMENTAL
RESULTS AND DISCUSSION
REAGENTS AND MATERIALS Analytical grade: 1,3-didecyl-2-methylimidazolium chloride (DMIC) was used as a titrant. Sodium dodecylsulfate sodium 1-octanesulfonate monohydrate, sodium 1-nonanesulfonate, 1 sodium 1decanesulfonate and sodium 1-undecanesulfonate
On Fig. 2 and 3 are shown titration curves of model mixtures made of NaDBS and NaLES with alkyl sulfonate homologous 1-octanesufonate and 1-nonanesulfonate. On Fig. 4 are presented titrations performed for the sake of monitoring of the NaLES decomposition using photo-oxidative UV/H2O2 process. Results from this investigation are compared with the results obtained for the NaDBS decomposition using photooxidative UV/H2O2 process [5] are presented in Table 1. Using potentiometric titration as a method for determination of anionic surfactants in wastewater treated by UV/H2O2, AS can be titrated differentially when the difference between the C-chains is at least 2 (investigated on modal mixtures). Titration results on the samples treated by photo-oxidative UV/H2O2 process confirmed degradation of NaDBS to molecules of lower Mw (C8, C9, C10).
400
300 40
200 dE/dV
DMIC (c=2 mmol/L) was used as a titrant. NaDDS (c=2 mmol/L) was used for titrant standardisation, and standard addition in potentiometric titrations, when necessary. Homologous of the alkylsulfonate were used for model solutions.
60
E/mV
All above mentioned reagents were purchased from commercial supplier SigmaAldrich.
NaLES:Alkyl (C8) sulfonate(4:8 µmol) NaLES:Alkyl (C8) sulfonate(8:4 µmol) NaLES:Alkyl (C9) sulfonate(4:8 µmol) NaLES:Alkyl (C9) sulfonate(8:4 µmol)
500
100 300
30 SDBS+Decanesulfonate SDBS+Nonanesulfonate SDBA+Octanesulfonate
20
200
Technical grade: NaLES (EMPICOL® ESB 70, Basel, Switzerland) and Sodium dodecylbenzenesulfonate (NaDBS; Marlon A 350, Sasol, Germany) were used for model solutions for decomposition using photooxidative UV/H2O2 processes.
0 20 dE/dV
E/mV
100
-100
0 10
APPARATUS AND MEASUREMENTS -100
-200
0 0
where E0 is the constant potential term, S is the sensor slope, and a(AS-) is the activity of surfactant anion. The sensor showed Nernstian response to NaDBS and NaDDS [2] . PROCEDURE Performing titration with a highly-sensitive surfactant selective potentiometric sensor for anionic surfactants and a fully-automated titration system, under strictly controlled conditions (drift control, electrode response-time) is possible to obtain slightly distorted inflection corresponding to anionic surfactant titrations analysed in model mixtures.
6
15
20
25
30
35
Fig. 3 Titration curves and their first derivatives of the NaLES mixtures with 1-octane sulfonate and 1-nonane sulfonate. DMIC (c=2 mmol/L) was used as a titrant and a DMI–TPB sensor as the end-point detector. Curves of the titration of NaLES and 1-nonane sulfonate are rised for 300 mV vertically, for clarity.
40
V/mL
Fig. 2 Titration curves and their first derivatives of the mixtures of NaDBS and sodium alkanesulfonate homologous 60
200
60
200
150
50
150
50
150
50
150
50
100
40
100
40
100
40
100
40
50
30
50
30
50
30
50
30
0
20
0
20
0
20
0
20
-50
10
-50
10
-50
10
-50
10
-100
0
-100
0
-100
0
-100
-10
-150
Start; c(NaLES)=50 ppm NaLES residual + Std. Addition Std.Addition
-150 0
2
4
V/mL
6
-10
8
NaLES 100 ppm + H2O2/UV
10
Start; c(NaLES)=100 ppm NaLES residual + Std. Addition Std.Addition
-150 0
2
4
V/mL
6
-10
8
NaLES 200 ppm + H2O2/UV
10
Start; c(NaLES=200 ppm) NaLES residual + Std. Addition Std.Addition
-150 0
2
4
6 V/mL
8
60
NaLES 500 ppm + + H2O2/UV
E/mV
200
E/mV
60
NaLES 50 ppm + H2O2/UV
10
0
Start; c(NaLES=500 ppm) NaLES residual + Std. Addition Std.Addition 0
2
4
V/mL
6
8
-10 10
Fig. 4 Titration curves and their first derivatives of photo-assisted decomposition of NaLES in concentration range 50-500 mg/L. 100
Start Analyte
NaLES H2O2
After reaction
NaDBS
Decomposed
After reaction
Decomposed
c (mg/L)
c (mmol/L)
c (mg/L)
%
c (mg/L)
%
50 100 200 500
0,4 0,8 1,6 4,0
3,8 25,1 75,6 223,4
92,4 74,9 62,2 55,3
17,4 37,6 151,3 431,0
65,2 42,4 24,4 13,8
80
Decomposed (%)
Table 1 Photo-assisted decomposition of NaLES and NaDBS in concentration range 50-500 mg/L.
NaDBS NaLES Power (NaDBS)
y = 214,39x-0,224 R² = 0,9634 60
40
y = 955,96x-0,684 R² = 0,9975 20
0 0
100
200
300
400
500
600
Start concentration of the AS (mg/L)
Fig. 5 Photo-assisted decomposition of NaLES and NaDBS in concentration range 50-500 mg/L.
ACKNOWLEDGEMENT This study is based on the work financed by SAPONIA Chemical, Pharmaceutical and Foodstuff Industry, Osijek, Croatia.
Literature [1] [2] [3] [4] [5]
8
dE/dV
E = E0 + S log a(AS-)
10
dE/dV
Sensor characteristics The electromotive force of the membrane sensor assembly dipped in the solution of anionic surfactant (AS) is given by the Nernst equation:
200
5
dE/dV
Sensor preparation Electroactive material for membrane preparation was prepared by mixing NaTPB and DMIC solution. A formed white precipitate (DMI-TPB) was extracted with dichloromethane and purified by recristallisation. Isolated complex was used as electroactive material for membrane preparation composed of o-nitrophenyloctylether (o-NPOE) as plasticizer (66%), high molecular weight poly (vinyl chloride) (PVC; 33%) and DMI-TPB complex as electroactive material (1,0 %). Membrane was mounted in a Philips electrode body IS-561 (Glasblaeserei Moeller, Zurich, Switzerland). Sodium chloride (c=2 mol/L) was employed as the internal filling solution.
Fig. 1 Laboratory equipment used for potentiometric monitoring of anionic surfactants decomposition using photooxidative UV/H2O2 processes.
0 0
dE/dV
DMI-TPB senor [2] was used for end-point determination in potentiometric titrations A silver/silver(I) chloride reference electrode (Metrohm, Switzerland) with reference electrolyte sodium chloride solution (c=2 mol/L), was used as one reference.
-200
E/mV
POTENTIOMETRIC DETERMINATION The all-purpose titrator 906 Titrando Metrohm 806 Exchange unit Magnetic stirrer 727 Ti Stand (Metrohm, Switzerland) Tiamo software was used for the titrator control All from Metrohm, Switzerland
4 V/mL
E/mV
H2O2/UV - DECOMPOSITION EXPERIMENTS: Gass batch reactor, V = 750 ml Pen-Ray mercury lamp, UVP Magnetic stirrer
2
J. J. Pignatello, E. Oliveros, A. MacKay, Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry, Crit. Rev. Environ. Sci. Tech. 36 (2006) 1-84. D. Madunić-Čačić, M. Sak-Bosnar, R. Matešić-Puač, Z. Grabarić, Determination of Anionic Surfactants in Real Systems Using 1,3-Didecyl-2-Methyl-Imidazolium-Tetraphenylborate as Sensing Material, Sensor Lett. 6 (2008) 339-346. D. Juretić, H. Kusić, N. Koprivanac, A. Lončarić Božić, Photooxidation of benzene-structured compounds: influence of substituent type on degradation kinetic and sum water parameters, Water Res. 46 (2012) 3074-3084. D. Juretic, H. Kusic, D. D. Dionysiou, B. Rasulev, I. Peternel, A. Loncaric Bozic, Prediction of key structural features responsible for aromaticity of single-benzene ring pollutants and their photooxidative intermediates, Chem. Engineering Journal 276 (2015) 261–273 D. Madunić-Čačić, Z. Lovinčić Kraljević, A Lončarić Božić, Potentiometric determination of sodium dodecylbenzene decomposition by advanced oxydation process, 24. HSKIKI, Zagreb, April 2015
