CATALYTIC WET HYDROGEN PEROXIDE OXIDATION OF REACTIVE PROCION MARINE H-EXL DYE SOLUTIONS

5 INTERNATIONAL SCIENTIFIC CONFERENCE 24 25 November 25, GABROVO CATALYTIC WET HYDROGEN PEROXIDE OXIDATION OF REACTIVE PROCION MARINE H-EXL DYE SOLUTIONS Carmen Zaharia, Mariana Neamţu, Ayfer Yediler 1, Mioara Surpăţeanu and Matei Macoveanu Department of Environmental Engineering and Management, Faculty of Chemical Engineering Gh.Asachi Technical University, D.Mangeron Blvd., no.71a, 75 - Iasi, Romania 1 GSF-National Research Centre, Institute for Ecological Chemistry, Neuherberg-Münich, Germany Abstract The decomposition of reactive Procion Marine H-EXL azo dye solutions using a catalytic wet hydrogen peroxide oxidation (CWHPO) was studied. The catalyst currently named Fe-exchanged Y zeolite (FeY 5 ) was prepared by ion-exchange, using a commercially ultra stable Y-zeolite. All experiments were performed on a laboratory scale set-up at ph range of 3-7, catalyst amount of.5-1.25 g/l and respectively, hydrogen peroxide concentration of 1-2 mmol/l. The effects of different variables as ph, catalyst and hydrogen peroxide concentrations on wet hydrogen peroxide dye oxidation have been assessed. The dye decomposition rates were expressed through dye or color and COD removal (treatment degrees). The results indicate that after only 1 minutes at t=5 C, 2 mmol/l H 2 O 2 and 1g/L FeY 5, the color removal was 94.91 % at ph=3 and 34.93 % at ph=5. The operational conditions corresponding to a ph=5, temperature of 5 C, 2 mmol/l H 2 O 2 and 1g/L FeY 5 but minutes of wet oxidation lead to more than 97.84 % dye removal which corresponds to 64.23 % COD removal (treatment degree). A preliminary study of catalytic wet hydrogen peroxide oxidation of a synthetic textile wastewater containing the Procion Marine H-EXL dye was also performed. The catalyst allows almost total dye elimination and a significant COD removal without significant leaching of Fe ions. With this type of catalyst, it is possible to extend the range of ph values for which Fenton-type oxidation can not occur and no iron hydroxide sludge is forming. Keywords: catalytic wet hydrogen peroxide oxidation, Fe-exchanged ultra stable Y zeolite (FeY 5 ), Procion Marine H-EXL dye. INTRODUCTION Some textile wastewaters are strongly coloured and are found to be toxic and carcinogenic to the aquatic environments. Azo dyes constitute one of the most important classes of commercial dyes. These dyes comprise about one half of all dyes used today and currently presented into the textile wastewaters [1]. Among many methods of wastewater treatment, a promising approach is the advanced oxidation process (AOP). This method implies generation and subsequent reaction of hydroxyl radicals, which are the most powerful oxidizing species after fluorine [2]. The Fenton processes have been used as a powerful source of hydroxyl radicals from H 2 O 2 in the presence of transition metal cations. So, these systems offer an effective source of hydroxyl radicals but also two major disadvantages that limit the industrial application of this technology: (i) the tight range of ph in which the reaction proceeds and (ii) the need for recovering of precipitated catalyst after the dye treatment. The resulted sludge may contain organic substances as well as heavy metals and has to be further treated, increasing thus the overall costs. A solution of this problem could be the use of heterogeneous solid Fenton catalysts, such as zeolites [2-7]. Some catalysts based on zeolites with ferrous iron in composition together with hydrogen peroxide can be efficiently used into the dye decomposition process. The oxidation mechanism is based on reaction between iron (II) and hydrogen peroxide with OH generation. The hydroxyl radicals have a very high oxidation potential (2. V). The mechanism is similar with the action of Feroxide process [8]. The decomposition compounds after the catalytic wet hydrogen peroxide dye oxidation were intermediate compounds as amines, organic acids and inorganic compounds as oxalates, carbonates, nitrates, sulphates etc. [9]. The target of this paper is assessing the catalytic performances of the Fe-exchanged ultra Международна научна конференция УНИТЕХ 5 Габрово II-383

stable Y zeolite, named FeY 5, on the wet hydrogen peroxide oxidation of reactive Procion Marine H-EXL dye solutions or a synthetic textile wastewater containing this type of azo dye. EXPERIMENTAL 1. Materials and reagents The Reactive Procion Marine H-EXL dye was obtained from BASF Company (Germany) as commercial available azo dye. The hydrogen peroxide solution (3 %) of analytical degree and all the organic components (p.a.) were provided from Merck Company, Germany. Aqueous solutions containing mg/l azo dye were prepared with ultra pure water (conductivity of.56 µs/cm) from Milli Q Millipore Waters purification unit. A synthetic textile wastewater was prepared by dilution of a synthetic dye-bath (1:). The synthetic dye-bath was prepared using Procion Marine H-EXL (2 %), Slipper (1 g/l), Mollan (as ion acceptor,,5 g/l), Na 2 CO 3 (18 g/l), NaOH (1,32 g/l), acetic acid (.5 g/l), NaCl (63 g/l) and Na 2 S 2 O 3 (as antiperoxide, 2 g/l). The catalyst was prepared based on the commercially available Y zeolite, produced by Zeolyst International, S.U.A. The characteristics of this solid product are given in Table 1 and represented in Fig. 1. This zeolite was ionically exchanged three times with an excess of Fe(NO 3 ) 3 1M for 6 h at ºC. After that the sample was washing with distilled water and dried at ºC for 12 h. Table 1. Characteristics of Y zeolite (for FeY 5 preparation) Zeolite SiO 2 /Al 2 O 3 Molar Ratio Na 2 O Weight, % Unit cell size, Å Surface area, m 2 /g Y 5.2 24.35 6 2. Analytical determinations UV/visible absorption spectra of Reactive Procion H-EXL dye solutions were recorded using a Varian Cary 1 spectrophotometer. The visible light absorbance corresponding to the characteristic wavelength of this azo dye (5 nm) was recorded to follow the decolouring progress during catalytic wet hydrogen peroxide oxidation. The absorbance of the synthetic aqueous samples (e.g. textile wastewater) at 2 nm and 254 nm are accepted as qualitative indicators of the aromatic content (e.g. aminochlorotriazine) and respectively, double bonds in the components. Also, the absorbance of synthetic aqueous dye samples at 435 nm, 525 nm and 62 nm are accepted as colour index by the Romanian standard for water and wastewater internationally approved [1]. COD determination (chemical oxygen demand) was done with commercially available test kits of the company Machery & Nagel, Düren, for dyestuff solutions with no significant chloride content (for more chloride content would be used the company reagent for chloride inhibition). 3. Experimental procedure Catalytic wet hydrogen peroxide dye oxidation was carried out into a glass reactor of 25 ml equipped with a magnetic stirrer, a reflux condenser and a ph electrode. The reactor is thermostatically stabilized using RCD 6 LAUDA equipment. Thus, the temperature was constantly kept for the whole period of experiment. The solid catalyst was introduced into ml dye solution under continuous stirring. After the stabilization of the temperature at the selected value and the adjustment of ph, the dye solution was initially analyzed to confirm the absence of adsorption on catalyst. Then, an adequate volume of H 2 O 2 solution (3 %) was added to achieve the selected H 2 O 2 /dye ratio. Samples from the aqueous dye solution were withdrawn within regular intervals. In these samples, the catalytic wet hydrogen peroxide oxidation process was blocked by increasing the ph to 9-1 using NaOH 1 M and adding of solid MnO 2. Thus, it is allowing the samples to sit overnight. Each aqueous samples was analyzed for dye (or colour index) and COD content. II-384 Fig. 1. Schematic representation of the Y zeolite Международна научна конференция УНИТЕХ 5 Габрово RESULTS AND DISCUSSION There were performed kinetic experiments of catalytic wet hydrogen peroxide oxidation on Procion Marine H-EXL dye solutions using Fe-

exchangeable Y zeolite (FeY 5 ) as catalyst. The influence of ph, initial concentrations of catalyst and H 2 O 2 was investigated. To choose the most indicated operational conditions, kinetic experiments on a synthetic textile wastewater containing Procion Marine H- EXL dye were performed in order to evaluate the treatment efficiency. 1. The ph influence on dye CWHPO process The studied phs to determine the highest treatment degree using CWHPO with FeY 5 were chosen between 3 and 7 by adding H 2 SO 4 or NaOH 1 M into the initial studied dye solution. The initial operational conditions were chosen as: t=5 C, 1 g/l FeY 5, 2 mmol/l H 2 O 2 and continuous stirring. The effect of ph on the dye treatment degree is shown into the next two figures (Fig. 2 and Fig. 3). Dye removal, % 2 5 15 Time, min ph=3 ph=5 ph=7 Fig. 2. The ph effect on dye removal efficiency (dye treatment degree). Initial operational conditions: t=5 C, 1 g/l FeY 5 and 2 mmol/l H 2 O 2. Treatment degree, % 2 ph=3 ph=5 ph=7 Dye removal COD removal Fig. 3. The ph effect on dye and COD removals after minutes of catalytic wet hydrogen peroxide dye oxidation It seems that the maximum treatment degree of 95 % was achieved after 2 minutes from the beginning of the catalytic wet peroxide oxidation when the ph of dye solution was of 3. Into the experiments performed with homogeneous Fe species as catalyst, it was demonstrated that the rate of the wet peroxide oxidation depends strongly of ph value. Contrarily, the heterogeneous catalyst remains active even at neutral ph, having different behavior comparison with the homogeneous ferrous catalyst. This activity could be related to the particular environment of Fe cations inside the pore structure of the zeolite, where strong electrostatic fields are presented. The distribution of iron species in this structure, as a function of ph is not completely elucidated, but it is believed that is different from that appears into solution. It seems that the interaction of Fe 3+ with the negative charged zeolite framework can prevent or slow down the precipitation of iron hydroxides, even at quasi-neutral ph values [11]. An appropriate distribution of the negative charge over the zeolite framework appears to be the key factor that controls the activity of iron species as a function of ph. It is clear that at ph of 7, some active iron species are presented and able to establish an effective redox system with H 2 O 2 [9], [11]. The leaching of Fe cations from zeolites into the solution can occur during the process and thus is generating a secondary pollution. In order to avoid it, the quantity of Fe cations after the catalytic wet hydrogen peroxide oxidation must be minimized. It is known that the leaching of Fe cations out of zeolites and amorphous silica depends strongly on the ph. The decolouring efficiency increases when the ph decreases and the leaching of Fe (III) cations enhances at low ph value [4], [12-15]. The results indicate that it is possible to operate up to an initial ph value close to 5., using Fe-exchanged Y zeolite (FeY 5 ) as catalyst, which represents an improvement of the wet hydrogen peroxide oxidation (WHPO process). Consequently, a thorough investigation of the process at ph of 5. was performed. 2. The catalyst influence on dye CWHPO process The dye removal efficiencies vs. time are presented in Fig.4 for an initial controlled ph value of 5 into the following initial operational conditions: t=5 C, 2 mmol/l H 2 O 2 and continuous stirring. After minutes of catalytic wet hydrogen peroxide dye oxidation using a dose of.5 g/l FeY 5 applied on the Procion Marine H-EXL solution, the dye removal was higher than 47 %, but after minutes of 91.69%. 89.3 % of COD was removed in the same operational conditions but after a wet hydrogen peroxide oxidation time of minutes. Международна научна конференция УНИТЕХ 5 Габрово II-385

Further increasing of catalyst amount leads to increase of dye and COD removal efficiencies, but the limitative value of 1. g/l was considering good enough for the treatment degree (avoiding presence of iron ions and precipates into the aqueous system). Barrault [12] and Neamţu [9] found out that by increasing the catalyst amount, an increase of iron concentration in solution was appearing and always detected. The results for dye and COD removals degrees after minutes of catalytic wet hydrogen peroxide oxidation are presented in Fig.5. Dye removal, % 2.5 g/l 1 g/l 5 15 Time, min dye solutions with different H 2 O 2 amounts were investigated in the same operational conditions: t=5 C, ph=5, 1 g/l FeY 5 and continuous stirring. The results were synthetically presented in Fig.6 and respectively, Fig.7. As expected, the increase of hydrogen peroxide concentration accelerates the Procion Marine H-EXL decolouring process into the first 2 minutes of experimental operational conditions. This fact could be explained by the positively oxidative effect generated by the additionally produced OH radicals. Introducing of 35 mmol/l H 2 O 2, no highly improvements on dye decomposition degree can be observed, in comparison with the experimental data performed with lower H 2 O 2 amounts (2 mmol/l). Whereas, the COD removal efficiency increases slightly by increasing the hydrogen peroxide amount. After an operational time of 3 minutes for the studied catalytic wet dye oxidation with a dose of 2 mmol/l H 2 O 2, a dye removal of 92.19 % was achieved. Fig. 4. The influence of FeY 5 catalyst on dye removal efficiency (treatment degree) vs. time. Initial operational conditions: t=5 C, ph=5 and 2 mmol/l H 2 O 2. Dye removal, % 2 1 mmol/l 2 mmol/l 35 mmol/l Treatment degree, % 2.5 g/l 1 g/l Dye removal COD removal 2 1 Time, min Fig. 6. The influence of hydrogen peroxide concentration on the dye removal (dye treatment degree). Initial operational conditions: t=5 C, ph=5 and 1 g/l FeY 5. Fig. 5. The dye and COD removals after minutes of catalytic wet hydrogen peroxide dye oxidation An observation is necessary to be mentioned that the concentration of FeY 5 catalyst must be situated between.5 1. g/l, which corresponds to 9-18 mg Fe 3+ /L. To avoid the iron leaching, the concentration of 1 g/l of catalyst could be selected but no more. Treatment degree, % 2 2 mmol/l 35 mmol/l 5 mmol/l Dye removal COD removal 3. The influence of hydrogen peroxide concentration on dye CWHPO process The kinetic studies of catalytic wet hydrogen peroxide oxidation on Procion Marine H-EXL Fig. 7. The influence of hydrogen peroxide concentration on dye and COD removals after minutes of catalytic wet hydrogen peroxide dye oxidation II-386 Международна научна конференция УНИТЕХ 5 Габрово

It must be mentioned that after minutes, the COD removal degree was 75.91 %. Increasing the H 2 O 2 concentration leads to no significantly effect on dye decomposition. For a concentration of 35 mmol/l H 2 O 2 more than 89 % of COD removal degree was possible. 4. An experimental study of CWHPO process applied on a synthetic textile wastewater containing Reactive Procion Marine H-EXL azo dye From the practical point of view, a synthetic dye-bath was prepared. It is important to assess the treatment performance of studied oxidative process in the presence of several dye assisting chemicals. The high amounts of dissolved salts and auxiliary ingredients could inhibit the efficient decolouring and mineralization of the dye-house wastewater. The effect of these ingredients on catalytic wet hydrogen peroxide oxidation of Procion Marine H-EXL dye was studied. The exhausted dye-bath investigated in this study was simulated according to typical reactive dyeing formulae. The chemical composition of such dye-bath mixture is listed in Table 2. Table 2. Ingredients of the simulated dye-bath Ingredient Comment Concentration Procion Marine H-EXL Reactive azo dye 2 % Slipper anti-creasing agent 1 g/l Mollan 129 Na 2 CO 3 NaOH Ion-acceptor, Polyacrylate copolymer.5 g/l 18 g/l 1.32 g/l NaCl 63 g/l CH 3 COOH.5 g/l Na 2 S 2 O 3 antiperoxide 2 g/l The dye and, consequently, color removal degrees of the synthetic textile wastewater (diluted 1:) using a catalytic wet hydrogen peroxide oxidation were determined. The operational treatment was performed at t=5 C, ph=5, 1 g/l FeY 5, 5 mmol/l H 2 O 2 and continuous stirring (Table 3). The colour removal efficiency was studied by decreasing of absorbance at three wavelengths in accordance with the Romanian internationally approved standard (435 nm, 525 nm and 62 nm) (Table 3). Table 3. The colour removal (treatment degree) of synthetic textile wastewaters using the catalytic wet hydrogen peroxide oxidation (TCV 62 = 298 m -1 ; TCV 525 = 1 m -1 ; TCV 435 = 9 m -1 ) Time, Color removal, % min 435 nm 525 nm 62 nm... 1 62.75 47.22 62.75 2 83.22 66.11 83.22 3 92.28 78.33 92.28 98.66 92.78 98.66 9 66.46 96.67 99.46 99.73 98.33 99.73 Colour removal, % 2 435 nm 525 nm 62 nm 5 15 Time. min Fig. 8. Colour removals vs. time for CWHPO process on a synthetic wastewater containing Procion Marine H-EXL dye. Initial operational conditions: t=5 C, ph=5, 1 g/l FeY 5 and 5 mmol/l H 2 O 2. It seems that after minutes of catalytic wet hydrogen peroxide oxidation, the colour removal applied for the synthetic textile wastewater was almost completely. The corresponding COD removal was higher than 89.3%. The experimental data performed for dye treatment (5 nm) indicated that after only 3 minutes the dye removal (treatment degree) was higher than 92 %. Using a dilution of synthetic dye-bath of 1:15 and applying the CWHPO process in the same operational conditions, the results were not good (only 3.33 % dye removal after minutes of catalytic wet hydrogen peroxide dye oxidation). Международна научна конференция УНИТЕХ 5 Габрово II-387

CONCLUSION The presented studies of catalytic wet hydrogen peroxide oxidation (CWHPO) on aqueous Procion Marine H-EXL solutions using the ultra stable Y zeolite, FeY 5, lead to following conclusions: 1. The most important factors with high influence on the catalytic wet hydrogen peroxide oxidation were found to be: ph, catalyst and hydrogen peroxide concentrations. 2. The experimental results indicate that it is possible to operate up to an initial ph value close to 5., using Fe-exchanged Y zeolite (FeY 5 ) as catalyst. This fact represents an improvement of the WHPO process. To avoid the iron leaching, the concentration of 1 g/l of catalyst must be maintained as maximum admissible concentration. 3. The best results on dye or colour and COD removals were obtained when the experiments are performed at ph=5, t = 5 C, 1 g/l FeY 5 and 2 mmol/l H 2 O 2 ; 4. The catalytic wet hydrogen peroxide oxidation of a synthetic textile wastewater containing Procion Marine H-EXL dye assures high colour removal up than 99 % and COD removal (> 89 %) after an operational time of only 3 minutes; 5. Catalytic wet hydrogen peroxide oxidation of Procion Marine H-EXL solutions or dye-bath effluents containing this dye using the FeY 5 exchanged zeolite can be considered a suitable pre-treatment procedure for complete decolouring of effluents from textile dyeing and finishing processes, once the optimum operational conditions were established. ACKNOWLEDGEMENTS This work was financially supported through research grant of Bilateral Cooperation between German Ministry of Science, Education and Technology (BMBF) and Romanian Ministry of Education and Research (RMER) (WTY Project ROM 99/8 and Project C-17172/1999). REFERENCE [1] Herrera F., Lopez A., Mascolo G., Alber S., Kiwi J., (21), Appl. Catal. B: Environmental, 29, 147-162. [2] Larachi F., Levesque S., Sayari A., (1998), J. Chem. Biotechnol., 73, 127-13. [3] Fajerwerg K., Debellefontaine H., (1996), Appl. Catal. B: Environment, 1, 229-235. [4]Fajerwerg K., Foussard J.N., Perrard A., Debellefonai-ne H., (1997), Wat.Sci.Tech., 35(4), 13-11. [5] Valange S., Gabelica Z., Abdellanoui M., Clacens J.M., Barrault J., (1999), Microporous and Mesoporous Mater., 3, 177-185. [6] Centi G., Perathoner S., Torre T., Verduna M.G., (2), Catal. Today, 55, 61-69. [7] Centi G., Perathoner S., Romeo G., (21), Studies in Surface Science and Catal., 13, 635-647. [8] Dolejs P., Kaouskova N., Paillard H., Prados M., Legube B., (1994), Chemical Water and Wastewater Treatment. III, Springer-Verlag Eds., Berlin, Heidelberg, pp.117-129. [9] Neamţu M., Zaharia C., Catrinescu C., Yediler A., Macoveanu M., Kettrup A., (24), Applied Catalysis B: Environmental, 48, 287-294. [1] Romanian standard no. SR ISO 789-1, (1998), Colour determination in waters and wastewaters. [11] Catrinescu C., Neamţu M., Yediler A., Macoveanu M., Kettrup A., (22), Env.Eng.Manag.J.,1(2), 177-186. [12] Barrault J., Abdellaoui M., Bouchoule C., Majeste A., Tatibouet J.M.,. Louloudi A., Papayannakos N. and Gangas N.H., (2), Appl.Catal. B: Environment, 27, 225-23. [13] Barrault J., Bouchoule C., Echachoui K., Frini- Srasra N., Trablesi M. and Bergaya F., (1998), Appl. Catal. B: Environmental, 15, 269-274. [14] Frini N., Crespin M., Trabelsi M., Messad D., Van Damme H., Bergaya F., (1997), Applied Clay Science, 12, 281-292. [15] Keiichi T., Kanjana P., Teruaki H., (2), Wat.Res., 34 (1), 327-333. II-388 Международна научна конференция УНИТЕХ 5 Габрово