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Fe-pillared clay as a Fenton-type heterogeneous catalyst for cinnamic acid degradation
ARTICLE IN PRESS
Journal of Environmental Management 80 (2006) 342–346 www.elsevier.com/locate/jenvman
Fe-pillared clay as a Fenton-type heterogeneous catalyst for cinnamic acid degradation Djamel Tabeta, Mohamed Saidib, Mohamed Houaria, Pierre Pichatc, Hussein Khalafa, a
Department of Chemical Engineering, University of Blida; P.O. Box 270-09000, Blida, Algeria b Centre Universitaire, Medea, Algeria c Laboratoire ‘‘Photocatalyse, Catalyse et Environnement’’, CNRS UMR ‘‘IFoS’’, Ecole Centrale de Lyon, 69134 Ecully Cedex, France Received 25 August 2004; received in revised form 3 October 2005; accepted 5 October 2005 Available online 20 March 2006
Abstract Fe-pillared montmorillonite has been used as a Fenton-type heterogeneous catalyst for the removal of cinnamic acid in water. The influences of the cinnamic acid, catalyst and H2O2 concentrations and pH on the removal rate of cinnamic acid have been studied. The results show that the efficiency of Fe-pillared montmorillonite is higher than that of the Fe ions in the homogeneous phase, and less sensitive to pH. r 2006 Elsevier Ltd. All rights reserved. Keywords: Cinnamic acid; Fenton reaction; Montmorillonite; Pillared clays; Olive mills waste
1. Introduction The production of olive oil in the Mediterranean countries accounts for approximately 95% of the world production. It generates around 30 million m3 of wastewater a year (Chamkha et al., 2001). According to some reports, the COD and BOD values of these wastewaters are 200–400 times higher than those of typical municipal sewage. Therefore, the overall contamination by olive oil wastewaters in the Mediterranean countries is equivalent to that produced by at least 60 millions inhabitants. The very high content of organic matter comprises phenols, polyphenols, pectin, colloids, lipids, and simple aromatic compounds (tyrosol; syringic, vanillic, veratric, caffeic, p-coumaric and cinnamic acids, etc.) resulting from olive cell wall degradation during oil extraction (Chamkha et al., 2001; Al-Mallah et al., 2000; Centi et al., 2001; Cossu et al., 1993). Lipids are considered toxic for certain strains of bacteria, whilst phenols and other aromatic compounds are considered as biorecalcitrant and can be a source of chlorinated phenols when chlorination is used for water Corresponding author. Tel./fax: +54 21325433631.
E-mail address: [email protected] (H. Khalaf). 0301-4797/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2005.10.003
disinfection. This high phenolic and aromatic content in olive oil mill effluents is also of great concern in anaerobic treatment because they can have an inhibition effect on bacteria, even though this effect is weaker than that of lipids (Beccari et al., 2002). The conventional biological or physico-chemical treatments are slow or non-destructive, and consequently are considered as inadequate for eliminating these classes of contaminants (Benitez et al., 1997; Velioglu et al., 1992). Attempts to develop an appropriate technology based on partial oxidation of phenolic and aromatic compounds using ozone as an oxidant or by applying wet air oxidation have been reported. However, these methods are either expensive or require a high reaction temperature (Centi et al., 2001). As an alternative, it has been proposed to use H2O2 and Fe ions (Fenton’s reagent). Highly oxidative OH radicals are generated from H2O2 in the presence of ferrous and ferric ions as shown below: Fe2þ þH2 O2 þHþ ! Fe3þ þ OH þ H2 O: Because the OH radical is a non-selective oxidizing species, the Fe2+/H2O2 and Fe3+/H2O2 reagents could
ARTICLE IN PRESS D. Tabet et al. / Journal of Environmental Management 80 (2006) 342–346
degrade nearly all organic compounds. But the Fe ions can be complexed by various chemicals, which may lead to the need for adding an excess of Fe salts, thus increasing its concentration in the active sludge (Boari and Mancini, 1990). To get rid of these drawbacks, it has been proposed, in earlier works, to use goethite (Zinder et al., 1986), as well as Fe or Cu ions immobilized on alumina (Al-Hayek and Dore´, 1990). As was reported by these authors, the rate of oxidation was related to the amount of ferrous ions leached from the solids. In more recent works (Fajerwerg and Debellefontaine, 1996; Centi et al., 2000) it has been proposed to use Fe ions-containing zeolites for the oxidation of phenol and carboxylic acids. Other authors (Barrault et al., 1998; Barrault et al., 2000; Chirchi and Ghorbel, 2002) have proposed the use of Cu/Al-pillared or Fe/Al-pillared clays as heterogeneous catalysts for phenol and nitrophenols oxidation. According to these studies, the redox reactions involve Fe or Cu ions immobilized in the cavities of zeolites or in the interlayer spaces of clays and not ions leached from the solids. Because of the relatively small pore size of zeolites, access of large molecules is prevented; accordingly, some organic compounds are not oxidized. On the other hand, the use of impregnation or exchange methods for fixing Fe or Cu cations in zeolites or clays limits the amount of these cations to a few wt% and, consequently, does not allow one to achieve high activities. Recently, Mantzavinos (2003) compared the homogenous and heterogeneous removal of cinnamic acid derivatives in water using ferrous and Cu ions supported on g-Al2O3 as heterogeneous catalysts. He concluded that the homogeneous catalysts are more effective than heterogeneous oxidation catalysts but the heterogeneous catalysts are preferable to homogeneous catalysts as they can be easily removed from the oxidized effleunt prior to any subsequent treatment or disposal. Furthermore, he concluded that the reactivity of cinnamic acid derivatives depends on the number, type and position of the functional groups attached to the aromatic ring and generally increases, as expected, with an increasing number of hydroxyl groups (i.e. caffeic acid4coumaric acid4cinnamic acid), while the presence of the methoxy group decreases the reactivity. Pillared clays are a relatively new class of catalysts and adsorbents with a bi-dimensional open structure. They result from intercalation of inorganic polycations into the interlayer space of clays to form rigid cross-linked materials of uniform microporosity. The purpose of this paper is to present the results of an investigation regarding the removal of cinnamic (cis-3-phenylpropenoic) acid using a Fe-pillared montmorillonite. Cinnamic acid was chosen because along with its substituted derivatives, such as ferulic and p-coumaric acids, it is considered to be a model of lignin derivatives. Furthermore, these various aromatic acids are typically found in wastewaters of agricultural origin. The influences of pH and molar ratios of Fe, H2O2 to cinnamic acid on the removal rate of cinnamic acid have been studied.
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2. Experimental 2.1. Catalyst preparation Bentonite issued from the deposit of Maghnia in western Algeria was used as a starting material. It is composed essentially of montmorillonite with minor impurities (quartz, feldspar, calcite, etc.). It has a cation exchange capacity of 90 meq 100 g1 of bentonite. Its chemical composition (wt%) is: SiO2 69.4; Al2O3 14.7; Fe2O3 1.2; MgO 1.1; CaO 0.3; Na2O 0.5; K2O 0.8; TiO2 0.2. Its mass loss by ignition at 1173 K is 11%. It was purified by a method described previously (Khalaf et al., 1997) which we sum up briefly here. The raw bentonite is dispersed in 1 mol L1 NaCl solution in order to obtain homoionized Na-montmorillonite, then it is separated from the solution and washed several times with distilled water. For separating the fraction of size o2 mm, a suspension of 2 wt% is placed in gradual cylinders for allowing particles 42 mm to settle down. The suspension at the depth of 10 cm containing only the particles of size o2 mm is collected with an Andreasen pipette. This operation is repeated several times until the suspension becomes almost transparent at the depth of 10 cm. The particles of a size smaller than 2 mm thus collected are recovered by centrifugation, washed with distilled water, and finally dialyzed to eliminate chloride ions in excess. This fraction was used in the pillaring process. The pillaring solution was prepared by slowly adding a 0.4 mol L1 NaOH solution to a 0.2 mol L1 Fe (NO3)3 solution under constant stirring, up to an OH/Fe molar ratio equal to 2. The resulting solution was aged for 8 days, and subsequently mixed with a 1 wt% bentonite aqueous suspension in such proportions as to achieve a ratio of 4 mmol of Fe/g of bentonite. The mixture was allowed to react at room temperature for 8 h. The solid was then separated by centrifugation, washed several times with distilled water, and finally calcined at 773 K for 1 h. 2.2. Catalytic degradation procedure The oxidation of cinnamic acid with the Fenton reagent was carried out in homogeneous and heterogeneous phase using a 500 mL batch reactor, made of borosilicate glass, into which 100 mL of an aqueous solution containing 120 mg L1 of cinnamic acid was poured. To determine the decrease of cinnamic acid concentration due to adsorption, the catalyst alone was added under vigorous stirring and the concentration was determined after one hour under continuous stirring. The pH was adjusted with 6 mol L1 solutions of either HCl or NaOH. All experiments were carried out at 353 K, the optimum temperature according to preliminary tests. The same optimum temperature has been reported (Fajerwerg and Debellefontaine, 1996; Centi et al., 2000) for the wet H2O2 oxidation of phenol and carboxylic acids.
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2.3. Analytical procedure The removal of cinnamic acid was monitored spectrophotometrically by the decrease in the absorption band of cinnamic acid at l ¼ 304 nm. Absorption by H2O2 is negligible at this wavelength. At given time intervals, 3 mL of the solution or suspension was withdrawn, hot filtered by a 0.45 mm-filter, and then analyzed by recording the absorption spectrum between 200 and 1000 nm. The concentration of cinnamic acid was determined by use of a calibration curve. 3. Results and discussion The XRD patterns of purified parent clay and Fepillared clay are shown in Fig. 1. Upon Fe-pillaring the basal spacing increases from 1.4 nm for purified bentonite up to 2.5 nm and the surface area from 81 up to 265 m2 g1. Consequently, the Fe was accessible to relatively large molecules. 3.1. Control experiments When H2O2 was added alone to the cinnamic acid solution, almost no change in the cinnamic acid concentration, C, was observed. A decrease in C of less than 2% on adding Fe-pillared clay without H2O2 was attributed to adsorption. On the other hand, the potential leaching of Fe ions from the solid was checked by three means. First, the catalytic activity was tested under the same conditions, after separation, immediately after use, of the solid catalyst by hot filtration for avoiding the readsorption of Fe cations that might have been leached. It was found that the variation in C was negligible after 2 h. Second, the used solution was analyzed by atomic absorption spectroscopy for determining the Fe content. Third, it was found that the Fe content in the solid before and after a catalytic test remained equal to 20 wt%. Furthermore, catalysts
0
5
10
Fig. 1. XRD patterns of: bentonite.
15 2 théta J
20
25
30
¼ purified bentonite; + ¼ Fe-pillared
calcined at 573 K for 3 h after use in cinnamic acid removal had almost the same catalytic activity as the freshly prepared catalysts.
3.2. Effect of pH Three pH were chosen: 2.9, 4 and 5. Our investigation was limited to this pH domain because beyond these values the efficiency was low as was shown by preliminary tests. Fig. 2 shows that a lower pH led to a higher removal. For example, in the case of the homogenous medium, the residual concentration of cinnamic acid was 36 ppm after 180 min at pH 5, whereas it fell down to 12 ppm when the pH was 2.9. In the case of the heterogeneous catalyst, C was 13 ppm at pH 5 and 5 at pH 2.9, also after 180 min. From Figs. 2 and 3 it can be seen that the heterogeneous Fenton reagent was more efficient in reducing C, particularly at pH 5. It might be the result of the affinity of the organic species for the clay surface. Furthermore, the heterogeneous catalyst activity was slightly less sensitive than that of the homogenous catalyst to pH variations in the 2.9–5 range after 3 h, while during the first 2 h the sensitivity in the two cases was similar. Further research is needed to better understand the origins of the influence of pH on the cinnamic acid removal rate. Note that the influence was reported to be negligible in the pH range 2.75–5.5, in the case of heterogeneous oxidation of carboxylic acids (Centi et al., 2000), while Barrault et al. (2000) found that the homogeneous phenol conversion passed through a maximum in the pH range 2.5–3.5 under nitrogen, whereas under air (in the presence of oxygen) the maximum was shifted towards a higher value in the pH range 3.5–4. In our study, a higher elimination rate of cinnamic acid was obtained at pH ¼ 2.9. Hence, this pH was used in the experiments dealing with the effects of the concentrations of Fe and H2O2.
Fig. 2. Influence of pH on the disappearance of cinnamic acid as a function of time at various pH at Fe/cinnamic acid molar ratio ¼ 10 and H2O2/cinnamic acid molar ratio ¼ 83. Solid symbols refer to homogenous catalysis and open symbols to heterogeneous catalysts: E, B: pH ¼ 5; ’, &: pH ¼ 4 and m, W: pH ¼ 2.9.
ARTICLE IN PRESS D. Tabet et al. / Journal of Environmental Management 80 (2006) 342–346
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1
0.8
C/C0
0.6
0.4
0.2
0
2.9
4.0 pH
5.0
Fig. 3. Abatement of cinnamic acid concentration at the indicated pH, at Fe/cinnamic acid molar ratio ¼ 10 and H2O2/cinammic acid molar ratio ¼ 83; homogeneous medium after 30 min; heterogeneous medium after 30 min; ¼ homogeneous medium after 180 min; ¼ heterogeneous medium after 180 min.
Fig. 4. The effect of Fe/cinnamic acid molar ratio on cinnamic acid removal as a function of time at pH ¼ 2.9 and H2O2/cinnamic acid molar ratio ¼ 83. Solid symbols refer to homogenous catalysis and open symbols to heterogeneous catalysts. E, B ¼ Fe/cinnamic acid molar ratio ¼ 0.2; ’, & ¼ Fe/cinnamic acid molar ratio ¼ 0.5; m, W ¼ Fe/cinnamic acid molar ratio ¼ 2; K,J ¼ Fe/cinnamic acid molar ratio ¼ 10.
3.3. Effect of the Fe/cinnamic acid molar ratio Fig. 4 shows that the maximum removal (90%) of cinnamic acid after 1 h was obtained for the Fe/cinnamic acid molar ratio ¼ 2 in heterogeneous medium. Beyond this ratio the degradation rate did not increase. In the homogenous medium, it was observed that the elimination of cinnamic acid was increased by increasing the Fe/ cinnamic acid ratio up to a value of 10, beyond which it became constant. At all ratios of Fe/cinnamic acid the removal of cinnamic acid was lower in the homogeneous medium than in the heterogeneous medium. For example, after 1 h, the residual concentrations of cinnamic acid in the homogeneous medium were 53, 43, 36 and 22 ppm at the ratios of 0.2, 0.5, 2 and 10, respectively, while in the case of the heterogeneous medium after the same time, they were 28, 18, 12 and 12 ppm, respectively, i.e. always lower. Note that the decrease in C was satisfactory for a ratio of 0.5 for the pillared clay. The lower efficiency of Fe ions in the homogenous medium might be explained by an easier complexation by organic intermediate degradation products, such as carboxylic acids, which can in turn diminish the removal rate of cinnamic acid.
Fig. 5. Influence of H2O2/cinnamic acid molar ratio on cinnamic acid removal as a function of time at pH ¼ 2.9 and Fe/cinnamic acid molar ratio ¼ 10. Solid symbols refer to homogenous catalysis and open symbols to heterogeneous catalysts H2 O2 /cinnamic acid molar ratio: E, B ¼ 14; ’, & ¼ 28; m, W ¼ 40; K, J ¼ 83.
acid residual concentrations in the homogeneous medium were 42, 29, 26 and 18 ppm at H2O2/cinnamic acid ratios of 14, 28, 40 and 83, respectively, whereas in the heterogeneous medium they were 36, 24, 19 and 13 ppm. Note, also, that relatively high ratios in the range studied have a markedly favorable effect. 4. Conclusion
3.4. Effect of the H2O2/cinnamic acid molar ratio On the basis of the results indicated above, we operated at pH 2.9 and with a Fe/cinnamic acid molar ratio ¼ 10 for studying the influence of the H2O2/cinnamic acid molar ratio. Fig. 5 shows that the maximum degradation rate of cinnamic acid in both homogeneous and heterogeneous phases was obtained for the H2O2/cinnamic acid molar ratio ¼ 83. Using higher ratios led to lower removal rates (results not shown). Again a greater efficiency of the solid catalyst was observed. For example, after 1 h, the cinnamic
This comparative study of the oxidative efficiency of Fepillared clays with homogeneous-type Fenton reagent for cinnamic acid removal shows that the heterogeneous process presents several advantages with respect to the homogeneous one:
It avoids the release of ferric cations in the discharged water. It leads to higher removal rates of cinnamic acid by a factor of 1.5–2.5, depending on the operating conditions.
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In addition, it is slightly less sensitive to pH variations, but to a lesser extent than what we had expected at the beginning of this study according to previous reports relative to phenol and carboxylic acids (Fajerwerg and Debellefontaine, 1996; Centi et al., 2000).
Acknowledgments Financial support from the ‘‘Comite´ Mixte d’Evaluation et de Prospective de coope´ration interuniversitaire francoalge´riennne’’ (C.M.E.P.) within the framework of Project 02 MDU 556 is gratefully acknowledged. References Al-Hayek, N., Dore´, M., 1990. Oxidation of phenols in water by hydrogen peroxide on alumine supported iron. Water Research 24 (8), 973–982. Al-Mallah, K., Azzam, O.J., Abu Lail, N.I., 2000. Olive mills effluent (OME) wastewater post-treatment using activated clay. Separation and Purification Technology 20, 225–234. Barrault, J., Bouchoule, C., Echachoui, K., Frini-Srasra, N., Trabelsi, M., Bergaya, F., 1998. Catalytic wet peroxide oxidation (CWPO) of phenol over mixed (Al–Cu) pillared clay. Applied Catalysis B 15, 269–274. Barrault, J., Abdelloui, M., Bouchoule, C., Majeste´, A., Tatiboue¨t, J.M., Louloudi, A., Papayannakos, N., Gangas, N.H., 2000. Catalytic wet oxidation over mixed (Al–Fe ) pillared clays. Applied Catalysis 27, 225–230. Beccari, M., Carucci, G., Lanz, A.M., Majone, M., Petrangeli Papini, M., 2002. Removal of molecular weight fractions of COD and phenolic compounds in an integrated treatment of olive oil mill effluents. Biodegradation 13, 401–410. Benitez, F.J., Beltran, J., Heredia, J., Torregrosa, J., 1997. Treatments of wastewater from olive oil mills by UV radiation and combined
ozone—UV radiation. Toxicological and Environmental Chemistry 61, 173–185. Boari, G., Mancini, I.M., 1990. Combined treatment of urban and olive mill effluents in Apulia, Italy. Water Science and Technology 22, 235–240. Centi, G., Perathoner, S., Torre, T., Verduna, M.G., 2000. Catalytic wet oxidation with H2O2 of carboxylic acids on homogeneous and heterogeneous Fenton type catalysts. Catalysis Today 55, 61–69. Centi, G., Cimino, G., Grasso, G., Perathoner, S., Romeo, G., Toscano, V.G., 2001. Catalytic wet H2O2 oxidation of olive oil mills wastewater: development of a Fe/ZSM-5 catalyst system, CPS, Chemeng/0011003. www.Chemweb.com. Chamkha, M., Patel, B.K.C., Garcia, J.L., Labat, M., 2001. Isolation of clostridium biofermentants from oil mill wastewater converting cinnamic acid to 3-phenylpropionic acid and emendation of species. Anaerobe 7, 189–197. Chirchi, L., Ghorbel, A., 2002. Use of various Fe-modified montmorillonite samples for 4-nitrophenol degradation by H2O2. Applied Clay Science 21, 271–276. Cossu, R., Blakey, N., Cannas, P., 1993. Influence of codisposal of municipal solid waste and olive vegetation water on anaerobic digestion of sanitary landfill. Water Science and Technology 27, 261–271. Fajerwerg, K., Debellefontaine, H., 1996. Wet oxidation of phenol by hydrogen peroxide using heterogeneous catalysis Fe-ZSM-5: a promising catalyst. Applied Catalysis B 10, L229–L235. Khalaf, H., Bouras, O., Perrichon, V., 1997. Synthesis and characterization of Al-Pillared and cationic surfactant modified algerian bentonite. Microporous Materials 8, 141–150. Mantzavinos, D., 2003. Removal of Cinnamic acid derivatives from aqueous effluents by Fenton and Fenton-like processes as an alternative to direct biological treatment. Water, Air, and Soil pollution: Focus 3, 211–221. Velioglu, S.G., Curi, K., Camlilar, S.R., 1992. A sludge treatability of olive oil-bearing wastewater. Water Research 26, 1415–1420. Zinder, B., Furrer, G., Stumm, W., 1986. The coordination chemistry of weathering II. Dissociation of Fe (III) oxides. Geochimica et Cosmochimica Acta 50, 1861–1869.
Journal of Environmental Management 80 (2006) 342–346 www.elsevier.com/locate/jenvman
Fe-pillared clay as a Fenton-type heterogeneous catalyst for cinnamic acid degradation Djamel Tabeta, Mohamed Saidib, Mohamed Houaria, Pierre Pichatc, Hussein Khalafa, a
Department of Chemical Engineering, University of Blida; P.O. Box 270-09000, Blida, Algeria b Centre Universitaire, Medea, Algeria c Laboratoire ‘‘Photocatalyse, Catalyse et Environnement’’, CNRS UMR ‘‘IFoS’’, Ecole Centrale de Lyon, 69134 Ecully Cedex, France Received 25 August 2004; received in revised form 3 October 2005; accepted 5 October 2005 Available online 20 March 2006
Abstract Fe-pillared montmorillonite has been used as a Fenton-type heterogeneous catalyst for the removal of cinnamic acid in water. The influences of the cinnamic acid, catalyst and H2O2 concentrations and pH on the removal rate of cinnamic acid have been studied. The results show that the efficiency of Fe-pillared montmorillonite is higher than that of the Fe ions in the homogeneous phase, and less sensitive to pH. r 2006 Elsevier Ltd. All rights reserved. Keywords: Cinnamic acid; Fenton reaction; Montmorillonite; Pillared clays; Olive mills waste
1. Introduction The production of olive oil in the Mediterranean countries accounts for approximately 95% of the world production. It generates around 30 million m3 of wastewater a year (Chamkha et al., 2001). According to some reports, the COD and BOD values of these wastewaters are 200–400 times higher than those of typical municipal sewage. Therefore, the overall contamination by olive oil wastewaters in the Mediterranean countries is equivalent to that produced by at least 60 millions inhabitants. The very high content of organic matter comprises phenols, polyphenols, pectin, colloids, lipids, and simple aromatic compounds (tyrosol; syringic, vanillic, veratric, caffeic, p-coumaric and cinnamic acids, etc.) resulting from olive cell wall degradation during oil extraction (Chamkha et al., 2001; Al-Mallah et al., 2000; Centi et al., 2001; Cossu et al., 1993). Lipids are considered toxic for certain strains of bacteria, whilst phenols and other aromatic compounds are considered as biorecalcitrant and can be a source of chlorinated phenols when chlorination is used for water Corresponding author. Tel./fax: +54 21325433631.
E-mail address: [email protected] (H. Khalaf). 0301-4797/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvman.2005.10.003
disinfection. This high phenolic and aromatic content in olive oil mill effluents is also of great concern in anaerobic treatment because they can have an inhibition effect on bacteria, even though this effect is weaker than that of lipids (Beccari et al., 2002). The conventional biological or physico-chemical treatments are slow or non-destructive, and consequently are considered as inadequate for eliminating these classes of contaminants (Benitez et al., 1997; Velioglu et al., 1992). Attempts to develop an appropriate technology based on partial oxidation of phenolic and aromatic compounds using ozone as an oxidant or by applying wet air oxidation have been reported. However, these methods are either expensive or require a high reaction temperature (Centi et al., 2001). As an alternative, it has been proposed to use H2O2 and Fe ions (Fenton’s reagent). Highly oxidative OH radicals are generated from H2O2 in the presence of ferrous and ferric ions as shown below: Fe2þ þH2 O2 þHþ ! Fe3þ þ OH þ H2 O: Because the OH radical is a non-selective oxidizing species, the Fe2+/H2O2 and Fe3+/H2O2 reagents could
ARTICLE IN PRESS D. Tabet et al. / Journal of Environmental Management 80 (2006) 342–346
degrade nearly all organic compounds. But the Fe ions can be complexed by various chemicals, which may lead to the need for adding an excess of Fe salts, thus increasing its concentration in the active sludge (Boari and Mancini, 1990). To get rid of these drawbacks, it has been proposed, in earlier works, to use goethite (Zinder et al., 1986), as well as Fe or Cu ions immobilized on alumina (Al-Hayek and Dore´, 1990). As was reported by these authors, the rate of oxidation was related to the amount of ferrous ions leached from the solids. In more recent works (Fajerwerg and Debellefontaine, 1996; Centi et al., 2000) it has been proposed to use Fe ions-containing zeolites for the oxidation of phenol and carboxylic acids. Other authors (Barrault et al., 1998; Barrault et al., 2000; Chirchi and Ghorbel, 2002) have proposed the use of Cu/Al-pillared or Fe/Al-pillared clays as heterogeneous catalysts for phenol and nitrophenols oxidation. According to these studies, the redox reactions involve Fe or Cu ions immobilized in the cavities of zeolites or in the interlayer spaces of clays and not ions leached from the solids. Because of the relatively small pore size of zeolites, access of large molecules is prevented; accordingly, some organic compounds are not oxidized. On the other hand, the use of impregnation or exchange methods for fixing Fe or Cu cations in zeolites or clays limits the amount of these cations to a few wt% and, consequently, does not allow one to achieve high activities. Recently, Mantzavinos (2003) compared the homogenous and heterogeneous removal of cinnamic acid derivatives in water using ferrous and Cu ions supported on g-Al2O3 as heterogeneous catalysts. He concluded that the homogeneous catalysts are more effective than heterogeneous oxidation catalysts but the heterogeneous catalysts are preferable to homogeneous catalysts as they can be easily removed from the oxidized effleunt prior to any subsequent treatment or disposal. Furthermore, he concluded that the reactivity of cinnamic acid derivatives depends on the number, type and position of the functional groups attached to the aromatic ring and generally increases, as expected, with an increasing number of hydroxyl groups (i.e. caffeic acid4coumaric acid4cinnamic acid), while the presence of the methoxy group decreases the reactivity. Pillared clays are a relatively new class of catalysts and adsorbents with a bi-dimensional open structure. They result from intercalation of inorganic polycations into the interlayer space of clays to form rigid cross-linked materials of uniform microporosity. The purpose of this paper is to present the results of an investigation regarding the removal of cinnamic (cis-3-phenylpropenoic) acid using a Fe-pillared montmorillonite. Cinnamic acid was chosen because along with its substituted derivatives, such as ferulic and p-coumaric acids, it is considered to be a model of lignin derivatives. Furthermore, these various aromatic acids are typically found in wastewaters of agricultural origin. The influences of pH and molar ratios of Fe, H2O2 to cinnamic acid on the removal rate of cinnamic acid have been studied.
343
2. Experimental 2.1. Catalyst preparation Bentonite issued from the deposit of Maghnia in western Algeria was used as a starting material. It is composed essentially of montmorillonite with minor impurities (quartz, feldspar, calcite, etc.). It has a cation exchange capacity of 90 meq 100 g1 of bentonite. Its chemical composition (wt%) is: SiO2 69.4; Al2O3 14.7; Fe2O3 1.2; MgO 1.1; CaO 0.3; Na2O 0.5; K2O 0.8; TiO2 0.2. Its mass loss by ignition at 1173 K is 11%. It was purified by a method described previously (Khalaf et al., 1997) which we sum up briefly here. The raw bentonite is dispersed in 1 mol L1 NaCl solution in order to obtain homoionized Na-montmorillonite, then it is separated from the solution and washed several times with distilled water. For separating the fraction of size o2 mm, a suspension of 2 wt% is placed in gradual cylinders for allowing particles 42 mm to settle down. The suspension at the depth of 10 cm containing only the particles of size o2 mm is collected with an Andreasen pipette. This operation is repeated several times until the suspension becomes almost transparent at the depth of 10 cm. The particles of a size smaller than 2 mm thus collected are recovered by centrifugation, washed with distilled water, and finally dialyzed to eliminate chloride ions in excess. This fraction was used in the pillaring process. The pillaring solution was prepared by slowly adding a 0.4 mol L1 NaOH solution to a 0.2 mol L1 Fe (NO3)3 solution under constant stirring, up to an OH/Fe molar ratio equal to 2. The resulting solution was aged for 8 days, and subsequently mixed with a 1 wt% bentonite aqueous suspension in such proportions as to achieve a ratio of 4 mmol of Fe/g of bentonite. The mixture was allowed to react at room temperature for 8 h. The solid was then separated by centrifugation, washed several times with distilled water, and finally calcined at 773 K for 1 h. 2.2. Catalytic degradation procedure The oxidation of cinnamic acid with the Fenton reagent was carried out in homogeneous and heterogeneous phase using a 500 mL batch reactor, made of borosilicate glass, into which 100 mL of an aqueous solution containing 120 mg L1 of cinnamic acid was poured. To determine the decrease of cinnamic acid concentration due to adsorption, the catalyst alone was added under vigorous stirring and the concentration was determined after one hour under continuous stirring. The pH was adjusted with 6 mol L1 solutions of either HCl or NaOH. All experiments were carried out at 353 K, the optimum temperature according to preliminary tests. The same optimum temperature has been reported (Fajerwerg and Debellefontaine, 1996; Centi et al., 2000) for the wet H2O2 oxidation of phenol and carboxylic acids.
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2.3. Analytical procedure The removal of cinnamic acid was monitored spectrophotometrically by the decrease in the absorption band of cinnamic acid at l ¼ 304 nm. Absorption by H2O2 is negligible at this wavelength. At given time intervals, 3 mL of the solution or suspension was withdrawn, hot filtered by a 0.45 mm-filter, and then analyzed by recording the absorption spectrum between 200 and 1000 nm. The concentration of cinnamic acid was determined by use of a calibration curve. 3. Results and discussion The XRD patterns of purified parent clay and Fepillared clay are shown in Fig. 1. Upon Fe-pillaring the basal spacing increases from 1.4 nm for purified bentonite up to 2.5 nm and the surface area from 81 up to 265 m2 g1. Consequently, the Fe was accessible to relatively large molecules. 3.1. Control experiments When H2O2 was added alone to the cinnamic acid solution, almost no change in the cinnamic acid concentration, C, was observed. A decrease in C of less than 2% on adding Fe-pillared clay without H2O2 was attributed to adsorption. On the other hand, the potential leaching of Fe ions from the solid was checked by three means. First, the catalytic activity was tested under the same conditions, after separation, immediately after use, of the solid catalyst by hot filtration for avoiding the readsorption of Fe cations that might have been leached. It was found that the variation in C was negligible after 2 h. Second, the used solution was analyzed by atomic absorption spectroscopy for determining the Fe content. Third, it was found that the Fe content in the solid before and after a catalytic test remained equal to 20 wt%. Furthermore, catalysts
0
5
10
Fig. 1. XRD patterns of: bentonite.
15 2 théta J
20
25
30
¼ purified bentonite; + ¼ Fe-pillared
calcined at 573 K for 3 h after use in cinnamic acid removal had almost the same catalytic activity as the freshly prepared catalysts.
3.2. Effect of pH Three pH were chosen: 2.9, 4 and 5. Our investigation was limited to this pH domain because beyond these values the efficiency was low as was shown by preliminary tests. Fig. 2 shows that a lower pH led to a higher removal. For example, in the case of the homogenous medium, the residual concentration of cinnamic acid was 36 ppm after 180 min at pH 5, whereas it fell down to 12 ppm when the pH was 2.9. In the case of the heterogeneous catalyst, C was 13 ppm at pH 5 and 5 at pH 2.9, also after 180 min. From Figs. 2 and 3 it can be seen that the heterogeneous Fenton reagent was more efficient in reducing C, particularly at pH 5. It might be the result of the affinity of the organic species for the clay surface. Furthermore, the heterogeneous catalyst activity was slightly less sensitive than that of the homogenous catalyst to pH variations in the 2.9–5 range after 3 h, while during the first 2 h the sensitivity in the two cases was similar. Further research is needed to better understand the origins of the influence of pH on the cinnamic acid removal rate. Note that the influence was reported to be negligible in the pH range 2.75–5.5, in the case of heterogeneous oxidation of carboxylic acids (Centi et al., 2000), while Barrault et al. (2000) found that the homogeneous phenol conversion passed through a maximum in the pH range 2.5–3.5 under nitrogen, whereas under air (in the presence of oxygen) the maximum was shifted towards a higher value in the pH range 3.5–4. In our study, a higher elimination rate of cinnamic acid was obtained at pH ¼ 2.9. Hence, this pH was used in the experiments dealing with the effects of the concentrations of Fe and H2O2.
Fig. 2. Influence of pH on the disappearance of cinnamic acid as a function of time at various pH at Fe/cinnamic acid molar ratio ¼ 10 and H2O2/cinnamic acid molar ratio ¼ 83. Solid symbols refer to homogenous catalysis and open symbols to heterogeneous catalysts: E, B: pH ¼ 5; ’, &: pH ¼ 4 and m, W: pH ¼ 2.9.
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1
0.8
C/C0
0.6
0.4
0.2
0
2.9
4.0 pH
5.0
Fig. 3. Abatement of cinnamic acid concentration at the indicated pH, at Fe/cinnamic acid molar ratio ¼ 10 and H2O2/cinammic acid molar ratio ¼ 83; homogeneous medium after 30 min; heterogeneous medium after 30 min; ¼ homogeneous medium after 180 min; ¼ heterogeneous medium after 180 min.
Fig. 4. The effect of Fe/cinnamic acid molar ratio on cinnamic acid removal as a function of time at pH ¼ 2.9 and H2O2/cinnamic acid molar ratio ¼ 83. Solid symbols refer to homogenous catalysis and open symbols to heterogeneous catalysts. E, B ¼ Fe/cinnamic acid molar ratio ¼ 0.2; ’, & ¼ Fe/cinnamic acid molar ratio ¼ 0.5; m, W ¼ Fe/cinnamic acid molar ratio ¼ 2; K,J ¼ Fe/cinnamic acid molar ratio ¼ 10.
3.3. Effect of the Fe/cinnamic acid molar ratio Fig. 4 shows that the maximum removal (90%) of cinnamic acid after 1 h was obtained for the Fe/cinnamic acid molar ratio ¼ 2 in heterogeneous medium. Beyond this ratio the degradation rate did not increase. In the homogenous medium, it was observed that the elimination of cinnamic acid was increased by increasing the Fe/ cinnamic acid ratio up to a value of 10, beyond which it became constant. At all ratios of Fe/cinnamic acid the removal of cinnamic acid was lower in the homogeneous medium than in the heterogeneous medium. For example, after 1 h, the residual concentrations of cinnamic acid in the homogeneous medium were 53, 43, 36 and 22 ppm at the ratios of 0.2, 0.5, 2 and 10, respectively, while in the case of the heterogeneous medium after the same time, they were 28, 18, 12 and 12 ppm, respectively, i.e. always lower. Note that the decrease in C was satisfactory for a ratio of 0.5 for the pillared clay. The lower efficiency of Fe ions in the homogenous medium might be explained by an easier complexation by organic intermediate degradation products, such as carboxylic acids, which can in turn diminish the removal rate of cinnamic acid.
Fig. 5. Influence of H2O2/cinnamic acid molar ratio on cinnamic acid removal as a function of time at pH ¼ 2.9 and Fe/cinnamic acid molar ratio ¼ 10. Solid symbols refer to homogenous catalysis and open symbols to heterogeneous catalysts H2 O2 /cinnamic acid molar ratio: E, B ¼ 14; ’, & ¼ 28; m, W ¼ 40; K, J ¼ 83.
acid residual concentrations in the homogeneous medium were 42, 29, 26 and 18 ppm at H2O2/cinnamic acid ratios of 14, 28, 40 and 83, respectively, whereas in the heterogeneous medium they were 36, 24, 19 and 13 ppm. Note, also, that relatively high ratios in the range studied have a markedly favorable effect. 4. Conclusion
3.4. Effect of the H2O2/cinnamic acid molar ratio On the basis of the results indicated above, we operated at pH 2.9 and with a Fe/cinnamic acid molar ratio ¼ 10 for studying the influence of the H2O2/cinnamic acid molar ratio. Fig. 5 shows that the maximum degradation rate of cinnamic acid in both homogeneous and heterogeneous phases was obtained for the H2O2/cinnamic acid molar ratio ¼ 83. Using higher ratios led to lower removal rates (results not shown). Again a greater efficiency of the solid catalyst was observed. For example, after 1 h, the cinnamic
This comparative study of the oxidative efficiency of Fepillared clays with homogeneous-type Fenton reagent for cinnamic acid removal shows that the heterogeneous process presents several advantages with respect to the homogeneous one:
It avoids the release of ferric cations in the discharged water. It leads to higher removal rates of cinnamic acid by a factor of 1.5–2.5, depending on the operating conditions.
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In addition, it is slightly less sensitive to pH variations, but to a lesser extent than what we had expected at the beginning of this study according to previous reports relative to phenol and carboxylic acids (Fajerwerg and Debellefontaine, 1996; Centi et al., 2000).
Acknowledgments Financial support from the ‘‘Comite´ Mixte d’Evaluation et de Prospective de coope´ration interuniversitaire francoalge´riennne’’ (C.M.E.P.) within the framework of Project 02 MDU 556 is gratefully acknowledged. References Al-Hayek, N., Dore´, M., 1990. Oxidation of phenols in water by hydrogen peroxide on alumine supported iron. Water Research 24 (8), 973–982. Al-Mallah, K., Azzam, O.J., Abu Lail, N.I., 2000. Olive mills effluent (OME) wastewater post-treatment using activated clay. Separation and Purification Technology 20, 225–234. Barrault, J., Bouchoule, C., Echachoui, K., Frini-Srasra, N., Trabelsi, M., Bergaya, F., 1998. Catalytic wet peroxide oxidation (CWPO) of phenol over mixed (Al–Cu) pillared clay. Applied Catalysis B 15, 269–274. Barrault, J., Abdelloui, M., Bouchoule, C., Majeste´, A., Tatiboue¨t, J.M., Louloudi, A., Papayannakos, N., Gangas, N.H., 2000. Catalytic wet oxidation over mixed (Al–Fe ) pillared clays. Applied Catalysis 27, 225–230. Beccari, M., Carucci, G., Lanz, A.M., Majone, M., Petrangeli Papini, M., 2002. Removal of molecular weight fractions of COD and phenolic compounds in an integrated treatment of olive oil mill effluents. Biodegradation 13, 401–410. Benitez, F.J., Beltran, J., Heredia, J., Torregrosa, J., 1997. Treatments of wastewater from olive oil mills by UV radiation and combined
ozone—UV radiation. Toxicological and Environmental Chemistry 61, 173–185. Boari, G., Mancini, I.M., 1990. Combined treatment of urban and olive mill effluents in Apulia, Italy. Water Science and Technology 22, 235–240. Centi, G., Perathoner, S., Torre, T., Verduna, M.G., 2000. Catalytic wet oxidation with H2O2 of carboxylic acids on homogeneous and heterogeneous Fenton type catalysts. Catalysis Today 55, 61–69. Centi, G., Cimino, G., Grasso, G., Perathoner, S., Romeo, G., Toscano, V.G., 2001. Catalytic wet H2O2 oxidation of olive oil mills wastewater: development of a Fe/ZSM-5 catalyst system, CPS, Chemeng/0011003. www.Chemweb.com. Chamkha, M., Patel, B.K.C., Garcia, J.L., Labat, M., 2001. Isolation of clostridium biofermentants from oil mill wastewater converting cinnamic acid to 3-phenylpropionic acid and emendation of species. Anaerobe 7, 189–197. Chirchi, L., Ghorbel, A., 2002. Use of various Fe-modified montmorillonite samples for 4-nitrophenol degradation by H2O2. Applied Clay Science 21, 271–276. Cossu, R., Blakey, N., Cannas, P., 1993. Influence of codisposal of municipal solid waste and olive vegetation water on anaerobic digestion of sanitary landfill. Water Science and Technology 27, 261–271. Fajerwerg, K., Debellefontaine, H., 1996. Wet oxidation of phenol by hydrogen peroxide using heterogeneous catalysis Fe-ZSM-5: a promising catalyst. Applied Catalysis B 10, L229–L235. Khalaf, H., Bouras, O., Perrichon, V., 1997. Synthesis and characterization of Al-Pillared and cationic surfactant modified algerian bentonite. Microporous Materials 8, 141–150. Mantzavinos, D., 2003. Removal of Cinnamic acid derivatives from aqueous effluents by Fenton and Fenton-like processes as an alternative to direct biological treatment. Water, Air, and Soil pollution: Focus 3, 211–221. Velioglu, S.G., Curi, K., Camlilar, S.R., 1992. A sludge treatability of olive oil-bearing wastewater. Water Research 26, 1415–1420. Zinder, B., Furrer, G., Stumm, W., 1986. The coordination chemistry of weathering II. Dissociation of Fe (III) oxides. Geochimica et Cosmochimica Acta 50, 1861–1869.