Microsoft Word - 82Lambri.doc CCHHEEMMIICCAALL EENNGGIINNEEEERRIINNGG TTRRAANNSSAACCTTIIOONNSS VOL. 38, 2014 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Enrico Bardone, Marco Bravi, Taj Keshavarz Copyright © 2014, AIDIC Servizi S.r.l., ISBN 978-88-95608-29-7; ISSN 2283-9216 Discoloration of Azo Dye Solutions by Adsorption on Activated Carbon Prepared from the Cryogenic Grinding of Used Tires I. Ould Brahima, M. Belmedani*a, A. Belgacema, H. Hadounb, Z. Sadaouib aLaboratory of transfer phenomena, bLaboratory of Reaction Engineering, Faculty of Mechanical and Processes Engineering, University of Sciences and Technology Houari Boumediene, BP n°32 El Alia, bab ezzouar 16111 Algiers, Algeria mbelmedani@usthb.dz This present work reports a study about the adsorption of cationic dye (Methylene blue) by activated carbon prepared from the cryogenic grinding of used tires. Characterization of the obtained activated carbon by chemical analysis, FTIR and SEM, was studied and resumed that the activated carbon was mesoporous. The effect of various experimental parameters such as contact time, solution pH, adsorbent dose and dye concentration, on the dye adsorption uptake on the activated carbon has been investigated using batch adsorption experiments. According to the experiments results, it was shown, that equilibrium was achieved in less than 114 min. The effect of pH investigated for values ranging from 2 to 11, showed maximum adsorption for pH 11. The equilibrium adsorption isotherms models of Langmuir, Freundlich and Dubinin-Radushkevich, were tested for the quantitative description of the dye adsorption. The Langmuir isotherm provided the best fit for dye adsorption onto the prepared activated carbon and the maximum adsorption capacity was found to be 30.21 mg.g-1. The results show that the produced activated carbon from used tire is an alternative low-cost adsorbent for removing dyes from solutions. 1. Introduction Dyes are recalcitrant molecules, which are difficult to degrade biologically. With the increasing use of a wide variety of dyes, pollution by dyes wastewater is becoming increasingly alarming. Most of the dyes decompose to give out hazardous products, such as carbon monoxide (CO), carbon dioxide (CO2) and hydrogen chlorides and can reduce light penetration photosynthesis (Gupta et al., 2011). Moreover dyes itself are toxic to some organism. Methylene blue (MB) is a cationic dye having various applications in chemistry, biology, medical science and dyeing industries. Its long term exposure can cause vomiting, nausea, anemia and hypertension (Pathania et al., 2013). Color removal, in particular, has recently become a major scientific interest. The typical dyestuff treatment include physical and chemical methods, such as coagulation/flocculation, adsorption, ozonation, sodium hypochlorite treatment, photochemical decolourization, membrane separation process, electrochemical and aerobic and anaerobic microbial degradation, these methods are not very successfully due to suffering from many restrictions (Sulak et al., 2007). Among all of these methods, adsorption has been preferred due to its cheapness and the high- quality of the treated effluents especially for well-designed sorption processes (Qadeer, 2007). However, despite its inherent advantages, adsorption using activated carbon remains an expensive process. This fact has incited a growing interest into the production of low-cost alternatives to activated carbons (Zuorro et al., 2013). Taking into account the problems related to the worn tires in Algeria (air and visual Pollution) we propose in our article to develop the worn tires into activated carbon which will be used thereafter for the adsorption of the dyes (Trouzine et al., 2011). The aim of the present work was to investigate the potential feasibility of activated carbon prepared from used tyres with cryogenic grinding for the adsorption of Methylene Blue. The effect of various parameters such as contact time, initial pH, adsorbent dose and initial concentration of dye was investigated. The experimental adsorption data were modeled using the conventional isotherm equations including Langmuir, Freundlich, and Dubinin-Radushkevich isotherms. DOI: 10.3303/CET1438021 Please cite this article as: Ould Brahim I., Belmedani M., Belgacem A., Hadoun H., Sadaoui Z., 2014, Discoloration of azo dye solutions by adsorption on activated carbon prepared from the cryogenic grinding of used tires, Chemical Engineering Transactions, 38, 121-126 DOI: 10.3303/CET1438021 121 2. Materials and methods 2.1 Preparation of activated carbon For the production of the activated carbon, we use fractions of tires powder sized between 0.063 cm and 0.2 cm obtained from cryogenic grinding. The impregnation with phosphoric acid (20 %) was performed for about one hour. Then the mixture was placed in an oven at 110 °C for 2 h. 5 grams of dried and impregnated powder is placed in a stainless steel tubular reactor and then introduced in a muffle furnace for activation. After that we proceeded to the carbonisation at inert atmosphere of nitrogen at 110 °C for 24 h and stored on hermetic bottle for subsequent use. 2.2 Adsorbate Methylene blue was chosen as the adsorbate, due to its extensive use in the textile industry. It contains one –N N– (azo), it’s physico-chemical properties are presented in Table 1. Table 1: Physico-chemical properties of dye Methylene Blue Molecular formula C16H18N3SCl IUPAC name 3.7-bis(Dimethylamino)-phenothiazin-5-ium chloride Molar weight (g.mol-1) 319.85 λmax(nm) 663 2.3 Adsorption experiments Batch adsorption experiments were performed at ambient temperature using 50 mL glass bottles containing a given mass of activated carbon and 10 mL of the dye solution. The initial concentration of the dye was varied from 10 to 100 mg.L-1, depending on the experimental conditions. The glass bottles were agitated in orbital shaker (Wise Shake) for three hours and then centrifugated at 7000 rpm for 30 min. The sample was collected and diluted before analysis using UV-visible spectrophotometer (Model Specot 200 plus) at 663 nm. The equilibrium adsorption capacity and the yield of adsorption were calculated respectively by Eq. (1) and (2): qe = (C0 - Ce) V/m (1) Re (%) = [(Co-Ce)/ Co ]*100 (2) where, m is the mass of adsorbent (g), V is the volume of the solution (L), Co is the initial concentration of dye (mg.L-1) and qe is the dye quantity adsorbed at equilibrium (mg of dye/g of adsorbent). 2.4 Calculation of adsorption isotherms parameters The tests concerning the study of the adsorption equilibrium were carried out for dye concentrations of 10 mg.L-1 to 100 mg.L-1. During adsorption, a rapid equilibrium is established between the quantity of dye adsorbed on the adsorbent (qe) and dye remaining in solution (Ce). The isotherms data were characterized by the Langmuir (3) and Freundlich (4) equations: qe = qmax bCe / (1+bCe) (3) qe = KF Cen (4) where (b, qmax) and (KF, n) are empirical constants of Langmuir and Freundlich isotherms, respectively, that will be calculated from the linear forms of the equations (3) and (4) : 1/qe = (1/qmaxb).1/Ce + 1/qmax (5) ln qe = ln KF +n ln Ce (6) Dubinin-Radushkevih (D-R) model is more general than the Langmuir isotherm, because it does not assume a homogeneous surface or constant sorption potential. The D-R equation is: qe = qmax exp([-B[RT) Ln(1+1/Ce)]2)] (7) 122 where B is a constant related to the adsorption energy, R (8.314 J.mol-1.K-1) is the gas constant, and T (K) is the absolute temperature. The constant B (mol2 .kJ-2) gives the mean free energy E (kJ.mol-1) of sorption per molecule of the sorbate when it is transferred to the surface of the solid from infinity in the solution and can be computed using the relationship: E = 1/(2.B)0.5 (8) This parameter gives information about chemical or physical adsorption. The magnitude of E between 8 and 16 kJ.mol-1 indicates that the biosorption process follows chemical ion-exchange, while for the values of E< 8 kJ.mol-1, the biosorption process is of a physical nature. The linear form of this model is expressed by : Lnqe = lnqmax – B.ε2 (9) Where ε = RT Ln(1+1/Ce) (10) 3. Results and discussions 3.1 Characterisation of activated carbon SEM micrograph of activated carbon obtained from cryogenic grinding of used tires, clearly indicate the surface texture and porosity of the rubber tire adsorbent. Carbon being the prominent component indicates the carbonaceous nature which in turn imparts porosity observed in the SEM results. SEM micrograph was processed and segmented and illustrated in Figure 1. The Infrared Spectroscopy spectra of the activated carbon which is illustrated in Figure 2, indicates the presence of a prominent band at region of 3590-3650 cm-1, 2850-3000 cm-1, 1670-1640 cm-1, 1640- 1550cm-1, 1070-1150 cm-1, 720-725 cm-1 and 675-725 cm-1 which can be inferred to the presence of functions normally detected on this type of products such as hydroxyl acids, carboxyl acids, the aromatic rings or bands corresponding to C-H bonds. All results of the characterisation were presented in our previously paper (Belgacem et al., 2013). 3.2 Effect of operating parameters 3.2.1 Effect of contact time Figure 3 indicates that the sorption increased with increasing contact time initially and became almost constant after 114 min of contact. From the plots, it is evident that for the investigated initial concentrations of MB, maximum adsorption rate of 93 % is achieved almost in 114 min of contact. A further increase in 4000, 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400 40,0 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 Wave number (cm-1) % T 3437,5 1624,56 1381,75 1039,15 571,33 2924,36 2857,14 1320,27 1102,0 9 777,6 517,48 475,52 Figure 1: SEM micrograph of activated carbon obtained after processing and segmentation Figure 2: Transmittance FTIR spectra of activated carbon 123 the contact time has a negligible effect on the rate of MB adsorption. The rate of dye removal is higher in the beginning due to a larger surface area of the sawdust being available for dye adsorption. Same results were reported by Pathania et al. (2013) 3.2.2 Effect of solution pH The pH factor is very important in the adsorption process especially for dye adsorption. The pH of a medium will control the magnitude of electrostatic charges which are imparted by the ionized dye molecules. The effect of pH on the MB removal by activated carbon resulting from the cryogenic grinding of the tire was investigated over the pH range from 2 to 11. The results were presented in Figure 4. It has been revealed that the MB removal was increased from 86 to 93 % as pH varies from 2 to 11. At high pH solution, the positive charge at the solution interface decreases and the adsorbent surface appears negatively charged (Özcan et al., 2007). It resulted in higher force of attraction between cationic MB and negatively charged adsorbent surface ultimately leading to higher MB adsorption (Gupta and Pathania, 2014). 3.2.3 Effect of activated carbon dosage Study of the effect of adsorbent dosage gives an idea of the effectiveness of an adsorbent and the ability of dye to be adsorbed with a minimum dosage. The results of the effect of adsorbent dose on the removal of Methylene Blue by the activated carbon are shown on Figure 5. They indicate that dye removal efficiency increased with the adsorbent dosage. This is due to the availability of more binding sites as the dose of biosorbent increases (Okeola et al.., 2012). However the removal will grow up to certain limit and then remains constant, the limit in each case is still related to the effect of adsorbate on adsorption. This will be attributed to metal concentration shortage in solution (Fourest and Roux, 1992). 3.2.4 Effect of initial dye concentration The percentage removal of dye is highly dependent on the initial amount of dye concentration. The effect of the initial of dye concentration factor depends on the immediate relation between the concentration of the dye and the available binding sites on an adsorbent surface. Figure 5 shows the progress of the MB removal with different initial MB concentrations. It is clear that the Yield of MB adsorption increased from 62 % to 96 % as the Methylene blue concentration was increased from 5 mg.L-1 to 40 mg.L-1. The increase in initial dye concentration will cause an increase in the loading capacity of the adsorbent and this may be due to the high driving force for mass transfer at a high initial dye concentration (Bulut and AydIn, 2006). Though, further increase in dye concentration, don’t affect the adsorption yield. This will be attributed to the saturation of adsorption sites on the adsorbent surface (Eren and Acar, 2006). Figure 3: Kinetic of MB sorption on activated carbon (initial MB concentration: 5 mg.L-1, pH: 6, AC concentration: 1 g L-1, T: 25°C) Figure 4: Effect of initial pH on sorption of MB by Activated carbon (initial MB concentration: 5 mg.L-1, Activated carbon concentration:1g.L-1,T: 25°C) 124 3.2.5 Adsorption isotherms The adsorption capacity of the obtained activated carbon for MB can be determined by measuring equilibrium isotherms. Adsorption isotherm plays a crucial role in the predictive modelling procedures for the analysis and design of an adsorption system. Thus, the correlation of the equilibrium data by either theoretical or empirical equations is essential to practical operation (Poots et al., 1976). Adsorption isotherms were analysed according to the linear form of Langmuir, Freundlich and Dubinin- Radushkevich isotherms, Table 2 displays the results of the calculated isotherm constants. Table 2. Isotherm constants for Methylene Blue adsorption onto activated carbon The experimental results are well represented by the Langmuir model, with higher value of correlation coefficient. The maximum adsorption capacity estimated by means of the Langmuir model was 30.21 mg.g-1, namely higher than the maximum adsorption capacities reported for some other adsorbents in the available literature and collected in Table 3. Table 3. Maximum capacity of MB adsorption on some adsorbents Langmuir Freundlich Dubinin-Radushkevich qmax (mg.g-1) b (L.mg-1) R2 KF n R2 qmax (mg.g-1) B (mol2.J-2) E (kJ.mol-1) R2 30.21 0.19 0.94 5.466 1.92 0.605 23.178 4.,3.10-7 1.07 0.69 qmax (mg.g-1) References AC prepared from waste tyre rubber 49.0 (San Miguel et al., 2002) AC prepared from Delonix Regia pods (flame-tree-pods) Cross linked poly(4-vinylpyridine /crotonic acid) 25.1 19.96 (Ho et al., 2009) (Coşkun, 2011) AC prepared from Wheat shell 16.56 (Ghaedi et al., 2013) AC prepared from cryogenic grinding of uses tires 30.21 Present study Figure 5: Effect of AC dosage on MB sorption on activated carbon (initial MB concentration: 5 mg L-1, pH: 6, T: 25°C) Figure 6: Effect of initial MB concentration on MB sorption on activated carbon (AC dosage: 1 g.L-1, pH: 6, T: 25°C) 125 4. Conclusions Liquid phase adsorption process was employed in this study and adsorption isotherms were used to investigate adsorption capacity and ability of the activated carbon prepared from the cryogenic grinding of used tire to remove Methylene Blue from aqueous solutions. Effects of the experimental conditions on the performance of the adsorbent were investigated. According to the experiments results, it was shown, that equilibrium was achieved in less than 114 min. The effect of pH investigated for values ranging from 2 to 11, showed maximum adsorption of MB on the activated carbon for pH 11. The equilibrium adsorption isotherms models of Langmuir, Freundlich and Dubinin-Radushkevich, were tested for the quantitative description of the dye adsorption. The Langmuir isotherm provided the best fit for dye adsorption onto the prepared activated carbon and the maximum adsorption capacity was found to be 30.21 mg.g-1. 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