Celoslovenská študentská vedecká konferencia Aplikované prírodné vedy 2017
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DEGRADATION OF MONOCHLOROACETIC ACID BY ALUMINIUM MODIFIED FENTON PROCESS ALBERT LLORT SALA1, LUKÁŠ HRDLIýKA2, JOSEF PROUSEK2 1
Departament d’Enginyeria Química, Universitat Politècnica de Catalunya, Escola D’Enginyeria de Barcelona Est d’Enginyeria Eduard Maristany 10-14, 08930 Barcelona, España (
[email protected]) 2 Department of Environmental Engineering, Faculty of Chemical and Food Technology, Slovak Technical University in Bratislava, Radlinského 9, SK-812 37 Bratislava, Slovak Republic Abstract: This study investigates the degradation of monochloroacetic acid (MCA) by aluminium modified Fenton Process. Fenton reaction and its modifications using zero-valent aluminium (ZVAl) and Al3+ ions have been performed. Influencing factors such as different amounts of hydrogen peroxide, ZVAl and aluminium ions have been studied. The results obtained from seven different sets of experiments are presented. In each system MCA degradation has been achieved and classical Fenton reaction has been improved. From obtained results is clear, that aluminium modified Fenton reaction is promising method for degradation of chlorinated pollutants in high concentration. Key words: aluminium ions, Fenton reaction, monochloroacetic acid, zero-valent aluminium
1. Introduction Monochloroacetic acid (MCA) is used as a reagent for the synthesis of other products such as plastics, carboxymethylcellulose (CMC) or crop protection chemicals. MCA has a low pressure of vapour and high water solubility. From this reason MCA can be expected in wastewater streams and subsequently in water ecosystem. The Predicted Natural Environmental Concentration in water for MCA is about 0.58 Pg.Lí1 (IHCP, 2005). MCA is classified as priority pollutant in environment because of its phytotoxic and carcinogenic effect. At the present many natural and anthropogenic sources of halogenated compounds are known. One of them are degradation processes of chlorinated compounds such as 1,1,1-trichloroethane and trichloroethene in atmosphere (BALLSCHMITER, 2003). Due to industrialization, the generation of wastewater is continuously growing up. This is an environmental problem that must be taken into account. Advanced oxidation processes (AOPs) seem to be a promising solution to treat those wastewater streams. These processes are able to oxidize organic compounds into CO2 and water by hydroxyl radical (HO•). HO• is very reactive radical particle with high redox potential (E° = 2.73 V), which is much higher than other oxidizing species like ozone (E° = 1.52 V) or hydrogen peroxide (E° = 1.31 V) (NEYENS et al., 2003). According to HO• radical generation methods AOPs can be classified as chemical, electro-chemical, sono-chemical and photochemical. This study was focused on chemical method to generate HO• radical. One chemical reaction to produce hydroxyl radical is Fenton reaction (FR). It is based on the decomposition of hydrogen peroxide (H2O2)by ferrous ions (Fe2+) to produce HO• radicals, hydroxide anions (HOí) and ferric ions (Fe3+) under acidic conditions (1). Moreover, with addition of higher amount of H2O2 is possible to regenerate the Fe2+ ions (2). In FR only the small amount of Fe2+ions is needed and the fact that H2O2 readily decomposes to harmless substances are the main advantages of Fenton’s process (PROUSEK, 1996). As the main issue is the HO• generation, zero-valent metals have been used in the last years. Although zero-valent iron (ZVI) has been the most tested, recently some experiments with ZVAl have been performed (BOKARE and CHOI, 2009). The main reason is low reduction potential of aluminium (Al3+/Al = í1.67 V), meanwhile iron is í0.44 V (Fe2+/Fe).
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ZVAl in the presence of H2O2 is able to produce reactive HO• radicals and aluminium ions and hydroxide ions (reaction No. 3). Fe2+ + H2O2 ĺ Fe3+ + HOí + HO• Fe3+ + H2O2 ĺ Fe2+ + H+ + HOO• Al0 + 3 H2O2 ĺ Al3+ + 3 HOí + 3 HO•
(1) (2) (3)
The purpose of this study is to investigate removal of high concentration of MCA, with aluminum modified FR. Influencing factors into FR such as amount of H2O2 or addition of aluminium ions or ZVAl were investigated.
2. Material a methods Monochloroacetic acid (ClCH2COOH, purity > 99 %) was purchased from LACHEMA (Czech Republic). Sulfuric acid (H2SO4, purity 96 %) and sodium hydroxide (NaOH, purity > 98 %) were purchased from MikroCHEM (Slovakia). As a source of ZVAl (Al0) aluminium foil (99.5 % purity) was used and before reaction was activated by NaOH (conc. 5 %), and rinsed three times with deionized water. The chemicals for the chloride ions determination were: potassium dichromate (K2Cr2O7, purity > 99.8 %) purchased from LACHEMA (Czech Republic), silver nitrate (AgNO3, purity > 99.5 %) was purchased from LPChem (Slovakia). Seven different sets of experiments have been performed. The procedure used in all experiments was: pH of MCA solution (5.10í3 M) was adjusted by H2SO4 solution (conc. 5 %) to pH 3r0.1. Into four different 250 mL Erlenmeyer 100 mL of MCA solution and 0.1 g of FeSO4.7H2O (M = 278.0 g·mol–1) was added. Depending on the set of experiments, an amount of Al2(SO4)3.18H2O (M = 666.0 g·mol–1) or ZVAl previously activated with NaOH (5 %) and subsequently washed by deionized water were added. Afterwards, 0.1, 0.2, 0.4, 0.8 mL of H2O2 (conc. 5 %) were added depending on reaction condition. Flasks were covered with aluminium foil due to the photosensibility of the reaction. In 30, 60, 120, and 180 min 10 mL of sample was taken. Samples were neutralized by NaOH (conc. 5 %), filtrated and diluted in 100 mL flasks. At last, all the samples were titrated using AgNO3 (5.10-3 M) and K2Cr2O7 (5 %) as indicator according HORÁKOVÁ (2003). The UV spectrum of each final sample (after 180 min) was measured in the spectrophotometer Hach-Lange DR5000 between190 and 400 nm.
3. Results and discussion 3.1. Classic Fenton reaction FR is an important method for degradation of toxic organic compounds in water environment (PROUSEK, 1995). However, as is shown in Fig. 1, classical Fenton reaction has in our mild conditioned experiments only 2 % efficiency (addition of 0.1 mL of H2O2). With higher amount of added H2O2 the efficiencies increased. In experiment with the highest amount of added H2O2 (0.8 mL) degradation efficiency achieved 36 %. FR reaction produce HO• radicals, which immediately react with MCA and starts its oxidative degradation (reactions No. 4 and 5). Known products of MCA oxidative degradation are formic and oxalic acid (HRDLIýKA, 2014). HO• + ClCH2COOH ĺ H2O + ClC•HCOOH ClC•HCOOH + O2 ĺ Products of oxidative degradation
(4) (5)
It is important to note that although results after 180 min are presented in Fig. 1, most of experiments had their efficiency stabilized after one hour of reaction, because of Fenton’s catalysts (Fe2+ and H2O2) was consumed.
Celosloveenská študentsská vedecká konferencia k Applikované prírrodné vedy 20017
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3.2. Moodified Fentton Reactioon with ZV VAl With thhe additionn of ZVA Al the bestt results are a achieveed. Small amount of ZVAl has no significant s effect on the efficieency (2 % equal thaan classical Fenton reaction) r when 0..1 mL of H2O2 was addded. Howeever, when the amounnt of ZVAl was 0.2 an nd 0.4 g the efficciency was increased significantly s y. It reacheed 17.8 % and a 15.8%. In this casse ZVAl can reduuce Fe3+ ions effectiveely (reactionn No. 6), which w can reeact with reesidual H2O2 by FR again (rreaction No.. 1). 3 3 3 Fe3+ + Al0ĺ 3 Fe2+ + Al3+
(6)
In the other o hand, the efficienncy grew too 59.4 % an nd 63.4 % (with the addition of 0.2/0.4 0 g of ZVA Al) when 0.8 mL of H2O2 weree added. Th hat means 1.62 and 1.73 timess higher, respectiively, than the t efficienncy in classiical Fenton n reaction. When W 0.2 annd 0.4 mL of H2O2 were addded, 0.2 g of ZVAl haad the best results. Thee efficiencyy grows to 222.7 % and 41.6 %. That is 1.64 and 1.332 times higgher than inn classical Fenton F reacttion (Fig. 1)). ClassicFento on Fe2+/Al3+(5 5:1)
ZVA Al0.05g Fe2 2+/Al3+(1:1)
ZVAl0..2g Fe2+/A Al3+(1:5)
ZVAl0.4g
70 Efficiency[%] (180min)
60 50 40 30 20 10 0 0.1
0 0.2
0.4
0.8
%[mL] H2O2 5%
i classical and aluminnium modiffied Fenton reaction Fig. 1: Efficiency of MCA deegradation in mounts of reeagents afteer 3 hours. with iniitial pHi = 3.0r0.1 and different am 3.3. Moodified Fentton Reactioon with Alu uminium io ons Regardiing experim ments withh aluminiuum ions, only o those with stoicchiometric amount with ferrrous ions (0.2 g) show wed better results r than classical Fenton F reacttion. The effficiency was 13.6 %, 27.3 %, % 39.0 %, 41.8 %, resspectively, which w is 6.88, 1.96, 1.233, 1.14 timees higher wer amountt of aluminiium ions than in classical Feenton reactions for eachh amount of H2O2. Low inhibited FR in all a studied cases. Higgher than stoichiometrric amount improve FR F only in the case c of the lowest l amoount of H2O2. There is a presumpption, that aluminium ions may play a role r as a shhuttle of eleectron betweeen Fe2+ an nd H2O2 (reeactions No. 7 and 8). Al2+ ion is know wn only undder extremee conditionn or it’s proposed p inn different types of complex c compouunds (EXLE EY, 2012; KISS, K 2013). F 3+ + [Al2+] Fe2+ + Al3+ĺ Fe 2+ [Al ] + H2O2ĺA Al3+ + [H2O2]•í
(7) (8)
4. Conclusio ons w additioon of alumiinium ions or zeroResults indicate thhat the classsical Fentonn reaction with Al obtained d higher valent aluminium has been improved. All the experiments with ZVA r with aluminiu um ions, efficienncy than Fennton reactioons. Regardding modifieed Fenton reactions
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only samples with stoichiometric amount of aluminium have shown improvement for all H2O2 amounts. There is also a non-linear dependence between the amount of H2O2 and the obtained efficiency. That non-linear dependence makes difficult to predict the optimal operation point. Although it seems reasonable to maximize the efficiency obtained per mL of H2O2. Other aspects such as the current legislation or economical budget should be considered. Acknowledgment: Thank to Department of Environmental Engineering of Slovak Technical University in Bratislava for giving chance doing this work.
References BALLSCHMITER, K.: Pattern and sources of naturally produced organohalogens in the marine environment: biogenic formation of organohalogens. Chemosphere, 52, 2003, p. 313-324. BOKARE, A.D., CHOI, W.: Zero-valent aluminum for oxidative degradation of aqueous organic pollutants. Environ. Sci. Technol., 43, 2009, p. 7130-7135. EXLEY, CH.: The coordination chemistry of aluminium in neurodegenerative disease. Coord. Chem. Rev., 256, 2012, p. 2142-2146. IHCP: MCA Summary risk assessment report. Institute for Health and Consumer Protection, European Chemicals Bureau, Bilthoven, Netherlands, 2005. KISS, T.: From coordination chemistry to biological chemistry of aluminium. J. Inorg. Biochem., 128, 2013, p. 156-163. HORÁKOVÁ, M.: Analytika vody. 2nd ed, VŠCHT Praha, Czech Republic, 2003, 335 p. HRDLIýKA, L.: Chemické reakcie. [e-book] FChPT, STU in Bratislava, 2014, 333 p. NEYENS, E., BAENYS, J.: A review of classic Fenton’s peroxidation as an advanced oxidation technique. J. Hazard. Mater., 98, 2002, p. 33-50. PROUSEK, J.: Fenton reaction after a century. Chem. Listy, 89, 1995, p. 11-21. PROUSEK, J.: Advanced oxidation processes for water treatment. Chemical processes. Chem. Listy, 90, 1996, p. 229-237.
