chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310

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Chemical Engineering Research and Design

journa l h om epage: www.elsev ier .com/ locate /cherd

Fixed bed adsorption of Methylene Blue byultrasonic surface modified chitin supported onsand

G.L. Dottoa,∗, J.M. Nascimento dos Santosa, R. Rosaa, L.A.A. Pintob,F.A. Pavanc, E.C. Limad

a Environmental Processes Laboratory, Chemical Engineering Department, Federal University of Santa Maria, UFSM,Roraima Avenue, 1000, 97105-900 Santa Maria, RS, Brazilb Unit Operation Laboratory, School of Chemistry and Food, Federal University of Rio Grande—FURG, Km 08 ItalyAvenue, 96203-900 Rio Grande, RS, Brazilc Institute of Chemistry, Federal University of Pampa, UNIPAMPA, Bagé, RS, Brazild Institute of Chemistry, Federal University of Rio Grande do Sul, UFRGS, Porto Alegre, RS, Brazil.

a r t i c l e i n f o

Article history:

Received 6 April 2015

Received in revised form 28 May

2015

Accepted 1 June 2015

Available online 8 June 2015

Keywords:

Breakthrough curves

Dynamic models

Flow rate

Scale-up

a b s t r a c t

In this research, fixed bed adsorption of Methylene Blue (MB) by ultrasonic surface modi-

fied chitin supported on sand (USM-chitin/sand) was investigated, aiming future scale-up

purposes. USM-chitin was prepared, characterized and supported on sand for the fixed bed

assays. Breakthrough curves were obtained at different flow rates and initial MB concen-

trations. These parameters were optimized by response surface methodology (RSM). Some

dynamic models were fitted to the experimental data and the bed regeneration was stud-

ied. The optimal conditions for the fixed bed adsorption of MB on USM-chitin/sand were

flow rate of 10 mL min−1 and initial MB concentration of 50.0 mg L−1. Under these con-

ditions, the breakthrough time was 370 min, the maximum capacity of the column was

51.8 mg g−1 and the removal percentage was 51.5%. The dynamic models were suitable to

represent the experimental data. The regeneration was possible for five times, maintaining

the same bed performance. These results indicated that the fixed bed adsorption of MB on

USM-chitin/sand is technically viable and suitable for a future scale-up.

© 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

The most common used adsorbent for dyes removal is

1. Introduction

The dye containing effluents from different industries suchas, textile, pulp, paper, leather and paint are very difficultto treat, since the dyes are stable and recalcitrant molecules(Koprivanac and Kusic, 2008). If they are incorrectly treated,these effluents can cause serious environmental impacts inthe receiving water bodies (Gupta and Suhas, 2009). Thusseveral technologies, such as, ion exchange, photo-oxidation,

flocculation, precipitation, microbiological decomposition,

∗ Corresponding author. Tel.: +55 55 3220 8448.E-mail addresses: guilherme dotto@yahoo.com.br (G.L. Dotto), juhm

(R. Rosa), dqmpinto@furg.br (L.A.A. Pinto), flavio.pavan@unipampa.eduhttp://dx.doi.org/10.1016/j.cherd.2015.06.0030263-8762/© 2015 The Institution of Chemical Engineers. Published by

ozonation, adsorption, chemical oxidation and membraneseparation are currently applied for dye removal from aqueousmedia (Gupta and Suhas, 2009; Srinivasan and Viraraghavan,2010; Saratale et al., 2011; Verma et al., 2012). Among these,adsorption is an efficient way, due its low capital investment,abundant raw material source, simplicity in design and oper-ation and non-toxicity (Moussavi and Khosravi, 2011; Dottoet al., 2014; Tovar-Gómez et al., 2015).

nsantos@hotmail.com (J.M.N.d. Santos), rejirr@hotmail.com.br (F.A. Pavan), profederlima@gmail.com (E.C. Lima).

activated carbon, but it is expensive. Thus several low-cost

Elsevier B.V. All rights reserved.

chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310 303

Nomenclature

C0 initial MB concentration (mg L−1)Ct MB concentration at the outlet of the column

(mg L−1)h bed depth of fixed-bed (cm)K adsorption constant rate (mL mg−1 min−1)kTh constant rate of Thomas model

(mL mg−1 min−1)kYN constant rate of Yoon–Nelson model (min−1)m amount of adsorbent in column (g)N0 adsorption capacity (mg L−1)qeq maximum capacity of the column (mg g−1)Q flow rate (mL min−1)R MB removal percentage (%)R2 coefficient of determination (dimensionless)t time (min)tb breakthrough time (min)te exhaustion time (min)ttotal total operation time (min)u linear flow rate (cm min−1)Veff volume of the effluent (mL)Y response variable of Eq. (8) (min or mg g−1 or %)Z bed length (cm)Zm length of mass transfer zone (cm)

Greek symbols˛ regression coefficient of Eq. (8)

regression coefficient of Eq. (8)� regression coefficient of Eq. (8)ı regression coefficient of Eq. (8)ε regression coefficient of Eq. (8)� regression coefficient of Eq. (8)�max maximum absorption wavelength of MB.� time required for 50% adsorbate breakthrough

from Yoon–Nelson model (min)

ac2bbacbc2imfosa

osenaAsh

reagents utilized were of analytical grade and deionized waterwas used to prepare all solutions.

dsorbents have been tested in order to substitute activatedarbon (Gupta and Suhas, 2009; Srinivasan and Viraraghavan,010). These materials include agricultural wastes, algaeiomass, bacterial biomass, chitosan/chitin and fungaliomass (Dotto et al., 2015a). Particularly, chitin can be useds adsorbent since is the second most abundant polysac-haride worldwide and, it can be obtained from wastes, isiodegradable, renewable and presents a compact structureontaining hydroxyl and N-acetyl groups (Dotto et al., 2012,013, 2015a, 2015b). In our recent work (Dotto et al., 2015b),t was proved that ultrasonic surface modified chitin is

ore efficient than chitin for the removal of Methylene Bluerom aqueous solutions. However, the study was performednly in batch system. In this way, the fixed bed adsorptiontudy is essential for future scale-up purposes and industrialpplications (Shafeeyan et al., 2014; Vieira et al., 2014).

In the field of dyes adsorption onto chitin/chitosan, it is rec-gnized that the majority of the studies are conducted only intatic batch experiments (Crini and Badot, 2008; Wan Ngaht al., 2011; Dotto and Pinto, 2011; Dotto et al., 2012). This sce-ario shows the necessity of fixed bed column studies, whichre more relevant to real operating systems (Yin et al., 2009;uta and Hameed, 2014). However, the application of ultra-

onic surface modified chitin for dye adsorption in fixed bed isindered, since the particle characteristics (density, shape and

size) can introduce limitations to the system, such as hydrody-namic pressure drop, obstruction of the column and formationof preferential ways (Dotto et al., 2015b). An alternative to solvethese problems is the use of support materials, such as, glassbeads (Vieira et al., 2014), sand (Wan et al., 2010) or bentonite(Futalan et al., 2011). Based on the best of our knowledge, thereare no studies regarding the use of ultrasonic surface modifiedchitin for fixed bed adsorption.

This work aimed to study the fixed bed adsorption ofMethylene Blue (MB) by ultrasonic surface modified chitinsupported on sand (USM-chitin/sand), aiming future scale-up purposes. The adsorbent was prepared and characterized.Response surface methodology (RSM) was used to optimizethe fixed bed adsorption as a function of flow rate and initialMB concentration. The considered responses were break-through time, maximum capacity of the column and removalpercentage. In the optimal conditions, bed depth service time(BDST), Thomas and Yoon–Nelson models were fitted to theexperimental data. The bed regeneration was also investi-gated.

2. Materials and methods

2.1. Materials and reagents

Sand (density of 2150 kg m−3, sphericity of 0.75 and particlesize ranging from 1.71 to 2.36 mm) was obtained from a localindustry (Santa Maria—RS—Brazil). The sand samples werewashed with distilled water and oven dried at 60 ◦C before theexperiments.

Methylene Blue dye (MB) (purity of 99.0%, color index 52015,molecular weight of 319.8 g mol−1, �max = 664 nm, pKa = 5.6)was purchased from Plury chemical Ltda., Brazil. For the fixedbed assays, MB solutions with pH of 10.0 were prepared usingNaOH (Dotto et al., 2015b). The optimized three-dimensionalstructural formula of MB was obtained from MarvinSketchsoftware, version 14.9.22.0, and is presented in Fig. 1. The other

Fig. 1 – Optimized three-dimensional structural formulae ofMethylene Blue (MB).

304 chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310

2.2. Preparation and characterization of ultrasonicsurface modified chitin

The ultrasonic surface modified chitin (USM-chitin) was pre-pared according to our previous works (Dotto and Pinto, 2011;Dotto et al., 2015b). First, chitin was obtained from shrimpwastes (Penaeus brasiliensis) by demineralization, deproteiniza-tion, deodorization and drying steps (Dotto and Pinto, 2011).The samples were ground (Wiley Mill Standard, model 03, USA)and sieved until the discrete particle size ranging from 105to 125 �m. Afterwards, the chitin samples were mixed withdeionized water and, the water/chitin mixture was treated byan ultrasonic processor (UP400S, Hielscher, Germany) of 400 Wequiped with a titanium sonotrode during 1 h at 24 kHz (thetreatment was performed a cycle of 1.00 and amplitude of60%) (Dotto et al., 2015b). Finally, chitin slurry was separatedby filtration, oven dried (40 ◦C, 24 h) and stored for further use.

The textural characteristics of chitin and USM-chitin werevisualized by scanning electron microscopy (SEM) with mag-nification of 100× and accelerating voltage of 15 kV (Jeol,JSM-6610LV, Japan) (Goldstein et al., 1992). The specific sur-face area was determined by a volumetric adsorption analyzer(Quantachrome Instruments, New Win 2, USA) using theBrunauer, Emmet, Teller (BET) method (Brunauer et al., 1938).The functional groups and the deacetylation degree of theadsorbent were identified by Fourier transform infrared spec-troscopy (FT-IR) (Prestige, 21210045, Japan) (Sabnis and Block,1997; Silverstein et al., 2007). The crystallinity index was deter-mined by X-ray powder diffractometry (XRD) (Rigaku, Miniflex300, Japan) (Al-Sagheer et al., 2009).

2.3. Fixed bed experiments

The fixed bed experiments were performed in a laboratorysystem, as presented in Fig. 2. The breakthrough curves wereconstructed at different flow rates (10, 15 and 20 mL min−1)and initial MB concentrations (50, 100 and 150 mg L−1).The acrylic cylindrical column (internal diameter of 2.5 cmand height of 25.0 cm) was filled with 5.00 g of USM-chitinand 180.0 g of sand (USM-chitin and sand were manuallymixed to guarantee the homogeneity) (these conditions wereselected by several preliminary tests. In these tests the USM-chitin/sand ratio was studied and, it was concluded that 5.00 gof USM-chitin and 180.0 g of sand was a more adequate ratio).The MB solutions were then pumped upward through the col-umn by a peristaltic pump (Master Flex, 07553-75, Canada). Atthe column top, samples were collected at regular time inter-

vals until the bed saturation and, the MB concentration wasdetermined by spectrophotometry at 664 nm (Quimis, Q108

Fig. 2 – Experimental setup for the fixed bed adsorptiontests.

DRM, Brazil). The bed saturation was considered when theoutlet MB concentration was the same that the initial MBconcentration. The assays were carried out in replicate (n = 3),and blanks were performed using sand without USM-chitin(any significant adsorption occurred when sand without USM-chitin was used).

2.4. Column data analysis

The column data analysis was performed in order to obtainthe breakthrough time (tb), exhaustion time (te), length ofmass transfer zone (Zm), effluent volume (Veff), maximumcapacity of the column (qeq) and removal percentage (R),for each experimental breakthrough curve (Geankoplis, 1998;Shafeeyan et al., 2014; Vieira et al., 2014). The breakthroughtime (tb, min) was considered when the outlet MB concen-tration attained 5% of the initial MB concentration and, theexhaustion time (te, min) was considered when the outlet MBconcentration attained 95% of the initial MB concentration(Suzuki, 1990). The Zm (cm) reflects the shortest possible adsor-bent bed length needed to obtain the breakthrough time tb

at t = 0. The metric length of this zone was calculated by thefollowing equation (Suzuki, 1990):

Zm = Z

(1 − tb

te

)(1)

where Z is the bed length (25 cm).The volume of the effluent, Veff (mL), is given by the follow-

ing equation (Martín-Lara et al., 2012):

Veff = Qttotal (2)

where Q is the flow rate (mL min−1) and ttotal is the total oper-ation time (min).

The maximum capacity of the column (qeq, mg g−1) is givenby the following equation (Sugashini and Begum, 2013):

qeq =(QC0/1000)

∫ ttotal0

(1 − (Ct/C0)) dt

m(3)

where C0 is the initial MB concentration (mg L−1) and m is theamount of USM-chitin in the bed (5.00 g). The integral in Eq.(3) is the area above the breakthrough curve from Ct/C0 = 0 toCt/C0 = 1. This area was estimated by Microcal origin 6.0 soft-ware, using analysis/calculus/integrate tool.

The MB removal percentage (R) was calculated by the fol-lowing equation (Sugashini and Begum, 2013):

R =∫ ttotal

0(1 − (Ct/C0)) dt

ttotal100 (4)

2.5. Statistical optimization

The fixed bed adsorption of MB by USM-chitin supportedon sand was optimized using response surface methodol-ogy (RSM) (Myers and Montgomery, 2002). The effects of flowrate (10, 15 and 20 mL min−1) and initial MB concentration(50, 100 and 150 mg L−1) were investigated and, the consid-ered responses were breakthrough time (tb) (min), maximumcapacity of the column (qeq) (mg g−1) and removal percentage(R) (%). These levels and factors were based on preliminary

tests and literature. The responses (tb, qeq and R) were repre-sented as a function of independent variables according to a

chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310 305

qnspgrb

2

Tv(1d

wifitt(crm

rTma

2

Tic(tai(cS

3

3c

U((Ft(

rates (10, 15 and 20 mL min ) and initial MB concentrations(50, 100 and 150 mg L−1) and, are presented in Fig. 4. The results

Table 1 – FT-IR bands and assignments of USM-chitin.

Bands (cm−1) Assignments

3350 O H and N H stretchings3000 CH2 stretching2800 CH3 stretching1652 C O secondary amide stretch1551 N H bend and C N stretch of amide I

uadratic polynomial model. The statistical significance of theonlinear regression was determined by Student’s test. Theecond order model was evaluated by Fischer’s test and theroportion of variance explained by the model obtained wasiven by the coefficient of determination, R2. Experimentaluns were performed at random and the results were analyzedy Statistic version 9.1 (StatSoft Inc., USA) software.

.6. Application of dynamic models

hree common dynamic models, called of bed depth ser-ice time (BDST) (Eq. (5)) (Hutchins, 1973), Thomas (Eq. (6))Thomas, 1944) and Yoon–Nelson (Eq. (7)) (Yoon and Nelson,984) were fitted to the experimental data in the optimal con-itions.

C0

Ct= 1 + exp

(KN0h

u− KC0t

)(5)

C0

Ct= 1 + exp

(kThqeqm

Q− kThC0t

)(6)

C0

Ct= 1 + exp (kYN� − kYNt) (7)

here K is the adsorption constant rate (mL mg−1 min−1), N0

s the adsorption capacity (mg L−1), h is the bed depth ofxed-bed (cm), u is the linear flow rate (cm min−1), kTh ishe constant rate of Thomas model (mL mg−1 min−1), qeq ishe equilibrium adsorption capacity from the Thomas modelmg g−1), m is the amount of adsorbent in column (g), kYN is theonstant rate of Yoon–Nelson model (min−1) and � is the timeequired for 50% adsorbate breakthrough from Yoon–Nelson

odel (min).The dynamic parameters were determined by nonlinear

egression using the software Statistic 9.1 (StatSoft Inc., USA).he objective function was Quasi–Newton. The fit quality waseasured according to the coefficient of determination (R2)

nd sum of square errors (SSE) (El-Khaiary and Malash, 2011).

.7. Elution tests

he elution tests were performed ten times in order to ver-fy the bed regeneration and reuse for several consecutiveycles. After the adsorption, USM-chitin/sand loaded with MBobtained in the optimal adsorption conditions according Sec-ion 3.3) was removed from the bed, oven dried at 60 ◦C for 24 hnd, placed in the bed again. The elution tests were performedn a laboratory system (Fig. 2) using HCl solution 0.3 mol L−1

Dotto et al., 2015b) at flow rate of 20 mL min−1. The MB con-entration at the column top was determined according toection 2.3.

. Results and discussion

.1. Characteristics of ultrasonic surface modifiedhitin

SM-chitin was characterized by SEM, specific surface areaBET), FT-IR, deacetylation degree and crystallinity indexXRD). The SEM images of chitin and USM-chitin are shown inig. 3. A rigid ad smooth surface, without visible pores or cavi-

ies can be observed for chitin (Fig. 3(a)). However, USM-chitinFig. 3(b)) presented a rough surface with protuberances and

Fig. 3 – SEM images of (a) chitin and (b) USM-chitin.

some cavities. The specific surface areas of chitin and USM-chitin were, respectively, 2.5 and 50.8 m2 g−1. The FT-IR bandsand its respective assignments for USM-chitin are presented inTable 1 (the same bands were found for chitin). For both, chitinand USM-chitin the deacetylation degree was 45 ± 1%. Thecrystallinity index was 85% for chitin and 63% for USM-chitin.These results are in accordance with our previous works (Dottoet al., 2015b) and confirm that USM-chitin has more adequatecharacteristics for adsorption purposes than raw chitin.

3.2. Interpretation of the breakthrough curves

The breakthrough curves were constructed at different flow−1

1018 C O asymmetric stretch in phase ring745 NH out of plane bending

306 chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310

Table 2 – Experimental conditions and results for the adsorption of MB on USM-chitin supported sand.

Exp. Flow rate, Q (mL min−1) C0 (mg L−1) tb (min)* te (min)* Zm (cm)* Veff (mL)* qeq (mg g−1)* R (%)*

1 10 (−1) 50 (−1) 370 922 15.0 9920 51.8 51.52 10 (−1) 100 (0) 123 215 10.7 2800 29.8 54.03 10 (−1) 150 (+1) 93 200 13.4 2600 37.6 47.94 15 (0) 50 (−1) 171 400 14.3 6600 38.1 58.75 15 (0) 100 (0) 81 195 14.6 3150 35.6 57.66 15 (0) 150 (+1) 60 155 15.3 3300 38.1 39.57 20 (+1) 50 (−1) 122 250 12.9 7500 38.7 51.38 20 (+1) 100 (0) 50 135 15.7 3100 31.0 50.39 20 (+1) 150 (+1) 45 105 14.3 2600 33.8 44.6

∗ Mean values for two experiments (the maximum error for all values was 6.4%).

regarding breakthrough time (tb), exhaustion time (te), lengthof mass transfer zone (Zm), effluent volume (Veff), maximumcapacity of the column (qeq) and removal percentage (R) areshown in Table 2.

It was found in Fig. 4 and Table 2 that the column per-formance was, in general, improved at lowest initial MBconcentration and flow rate. Three specific facts can be seenin Fig. 4 and Table 2: (1) the C0 and Q decrease provided longerbreakthrough and exhaustion times; (2) the higher values forqeq and Veff were found using 50 mg L−1 and 10 mL min−1;(3) In spite of the good bed performance at 50 mg L−1 and10 mL min−1, the higher R value was not found in this condi-tion. The first fact is because at lower concentration gradientsa slower mass transfer occurred, increasing the residencetime in the bed and, allowing the interaction between USM-chitin and MB. Furthermore, at lowest flow rates, the residencetime of the solute in the bed is sufficient to guarantee theMB diffussion in the USM-chitin structure. When the flowrate is increased, the residence time became insufficient toattain a suitable adsorption capacity. The second fact occurredbecause, at lower initial MB concentration and flow rate,extended breakthrough curves were obtained (Fig. 4), indicat-ing that a higher effluent volume could be treated (Table 2). Asconsequence, the area above the curve was higher, improv-ing the bed performance. The third fact occurred because thehigh length of mass transfer zone found for the experiment1 (Table 2), which provided a high MB concentration at thebed outlet for a long time (Fig. 4). Similar trends regarding theeffects of flow rate and initial concentration were found by Tanet al. (2008) in the MB adsorption onto palm shell activatedcarbon and, Ahmad and Hameed (2010) in the adsorption ofreactive dye onto activated carbon from bamboo.

3.3. Determination of the optimal adsorptionconditions

Aiming to obtain the optimal fixed bed adsorption conditions,

the responses, breakthrough time (tb), maximum capacityof the column (qeq) and removal percentage (R) (%) were

Table 3 – Regression coefficients and statistical parameters of thtime (tb), maximum capacity of the column (qeq) and removal p

Response Regression coefficients

� �

tb (min) 124.22 −122.00 −30.83 −155.83

qeq (mg g−1) 32.49 −2.57 −0.29 −3.11

R (%) 55.35 −1.26 −2.14 −4.85

∗ Significance level of 95% (p < 0.05); the degree of freedom for regression a

optimized as a function of flow rate (Q) and initial MB con-centration, using the response surface methodology. Theexperimental conditions (real and coded) and results areshown in Table 2.

To verify the significance of Q and C0 on the responses,Pareto charts were constructed (Fig. 5). As presented inFig. 5(a)–(c), all linear, quadratic and interaction effects weresignificant on the responses tb, qeq and R (p < 0.05). The sta-tistical polynomial quadratic model, which represents thedependence of tb, qeq and R in relation to Q (coded value) andC0 (coded value) is given by the following equation:

Y = � + ˛Q + ˇQ2 + �C0 + ıC20 + εQC0 (8)

being, Y the considered response (tb, qeq or R), �, ˛,ˇ, �, ı and ε, the regression coefficients, which are presented,for each response, in Table 3.

For an adequate representation of the experimental data,the statistical model (Eq. (8)) should be predictive and sig-nificant (Myers and Montgomery, 2002). The prediction andsignificance of the statistical model were evaluated by analysisof variance and Fischer’s F test. The coefficients of determina-tion were higher than 0.81 and were considered suitable (seeTable 3). Then the models were significant. It was found inTable 3 that the calculated F values (FCALC) were higher thanthe standard F value showing that the models were predictive.In addition, the reliability of the models was evaluated com-paring the experimental versus predicted values (Fig. 6). Themodel reliability can be confirmed on the basis in Fig. 6. Once isstatistically suitable, the model (Eq. (8)) was used to generateresponse surfaces, which represents tb, qeq and R as a func-tion of flow rate and initial MB concentration. These responsesurfaces are shown in Fig. 7.

Based on the response surfaces and Eq. (8), the optimalconditions for the fixed bed adsorption of MB on USM-chitinsupported on sand were determined. These conditions were:flow rate of 10 mL min−1 and initial MB concentration of

50.0 mg L−1. Under these conditions, the breakthrough timewas 370 min, the maximum capacity of the column was

e quadratic models which represent the breakthroughercentage (R).

Statistical parameters

ı ε R2 Fcalc Ftab*

−59.08 102.50 0.9502 45.76 3.11

7.33 2.27 0.8121 6.19−5.10 −0.88 0.8327 6.68

nd residues were, respectively, 5 and 12 for all responses.

chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310 307

0 20 0 40 0 60 0 80 0 100 0

0.0

0.2

0.4

0.6

0.8

1.0

50 mg L-1

100 mg L-1

150 mg L-1

(a) 10 mL min-1

CtC/

0

Time (min)

0 10 0 20 0 30 0 40 0

0.0

0.2

0.4

0.6

0.8

1.0

50 mg L-1

100 mg L-1

150 mg L-1

(b) 15 mL min-1

CtC/

0

Time (min)

0 50 10 0 15 0 20 0 25 0 30 0 35 0

0.0

0.2

0.4

0.6

0.8

1.0

50 mg L-1

100 mg L-1

150 mg L-1

(c) 20 mL min-1

CtC/

0

Time (min)

Fig. 4 – Breakthrough curves for the adsorption of MB byUSM-chitin supported on sand: (a) Q = 10 mL min−1, (b)Q = 15 mL min−1 and (c) Q = 20 mL min−1 (�C0 = 50 mg L−1; �C0 = 100 mg L−1; � C0 = 150 mg L−1).

5mwta

Fig. 5 – Pareto charts for the responses: (a) breakthroughtime, (b) maximum capacity of the column and (c) removal

Comparing our results with the literature, it can be affirmed

1.8 mg g−1 and the removal percentage was 51.5%. Also, theass transfer zone was 15.0 cm and the effluent volumeas 9920 mL. The effluent volume treated until the break-

hrough time was 3700 mL. Auta and Hameed (2014) studied

dsorption of Methylene Blue by chitosan–clay composite

percentage.

in a fixed-bed column (internal diameter of 1.2 cm, heightof 2.5 cm, C0 = 50 mg L−1 and Q = 5 mL min−1). They found tb

lower than 50 min and qeq of 40.8 mg g−1. Han et al. (2009)studied adsorption of Methylene Blue by phoenix tree leafpowder in a fixed-bed column (internal diameter of 1.2 cm,height of 15.0 cm, C0 = 50 mg L−1 and Q = 8 mL min−1). Theyfound tb about 150 min, qeq of 145 mg g−1 and R of 50.6%. Gonget al. (2015) studied adsorption of methylene blue by graphiteoxide coated sand in a fixed-bed column (internal diameter of2.0 cm, height of 15.0 cm, C0 = 50 mg L−1 and Q = 2 mL min−1).They found tb lower than 200 min and qeq of 0.40 mg g−1.

that the fixed bed adsorption of MB on USM-chitin/sand is

308 chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310

0 50 100 150 200 250 300 350 400 450

Obser ved Values

0

50

100

150

200

250

300

350

400

PredictedV

alues

(a) Breakthro ugh tim e

25 30 35 40 45 50 55

Observed Values

26

28

30

32

34

36

38

40

42

44

46

48

50

PredictedV

alues

(b) Maximum ca pacity of the column

36 38 40 42 44 46 48 50 52 54 56 58 60 62

Observed Values

38

40

42

44

46

48

50

52

54

56

58

PredictedV

alues

(c) Removal perce ntage

Fig. 6 – Observed versus predicted values for (a)breakthrough time, (b) maximum capacity of the column

C 0(mg L

-1 )50

15010

20

15

100

Flow Rate (mL min -1)

tb (min)

350

150

200

250

300

100

50

(a)

(b)

qeq (mg g-1)

50

30

35

45

40

C 0(m

g L-1 )

Flow Rate (mL min -1)

100

150

15

10

20

50

20

55

Flow Rate (mL min -1) C 0(m

g L-1 )

(c)

150

100

50

R (%)

40

45

50

60

15

10

Fig. 7 – Response surfaces for (a) breakthrough time, (b)maximum capacity of the column and (c) removalpercentage as a function of the independent variables.

and (c) removal percentage.

technically viable and suitable for future scale-up purposes,since a promising column performance was obtained.

3.4. Dynamic models

In order to find a simple model to represent the fixed bedadsorption of MB on USM-chitin/sand (in the optimal con-ditions), the dynamic models called bed depth service time(BDST) (Eq. (5)), Thomas (Eq. (6)) and Yoon–Nelson (Eq. (7)) werefitted with the experimental data. The results are shown inFig. 8 and Table 4.

Based on the high values of R2 (R2 > 0.97) and low values ofsum of square errors (SSE < 0.14) (Table 4) it can be affirmedthat all dynamic models were suitable to represent the exper-imental breakthrough curve (in the optimal condition). The

good fit can be visualized in Fig. 8. Since the models are math-ematically equal (Yin et al., 2009), R2 and SSE were also equal.

The experimental qeq value (qeq(exp)) was underestimated inonly11.4% by the Thomas model (qeq) (Table 4). The valueof � from the Yoon–Nelson model is in agreement with theexperimental value (�(exp)), with percentage deviation of 1.3%.These facts can be visualized in Fig. 8. BDST, Thomas andYoon–Nelson models were suitable for other fixed bed adsorp-

tion systems (Yin et al., 2009; Sugashini and Begum, 2013;Vieira et al., 2014).

chemical engineering research and design 1 0 0 ( 2 0 1 5 ) 302–310 309

Fig. 8 – Experimental and predicted breakthrough curve (inthe optimal condition).

Table 4 – Dynamic parameters for the MB adsorptionaccording BDST, Thomas and Yoon–Nelson models.

BDST modelK (mL mg−1 min−1) 0.54N0 (mg L−1) 1870R2 0.9781SSE 0.1361

Thomas modelkTh (mL mg−1 min−1) 0.54qeq (mg g−1) 45.9qeq (exp) (mg g−1) 51.8R2 0.9781SSE 0.1361

Yoon–Nelson modelkYN (min−1) 0.027� (min) 458�(exp) (min) 452R2 0.9781SSE 0.1361

3

TatSs

.5. Column regeneration

he column regeneration is a key factor regarding industrialpplications and costs of the adsorption process. In this work,en adsorption–elution cycles were performed according to

ection 2.7. The elution curve after the fourth cycle is pre-ented in Fig. 9. It was found that, after the fourth cycle, all

0 20 40 60 80 10 0 12 0 14 0 16 0 18 00

100

200

300

400

500

600

700

800

Ct(m

gL

-1)

Time (min)

Fig. 9 – Column elution curve.

dye was removed from the bed until 150 min. The bed perfor-mance in terms of tb, te, Zm, Veff, qeq and R was maintained forfive adsorption–elution cycles. After, the bed performance wasstrongly impaired. These results confirm the technical viabil-ity of the fixed bed adsorption of MB onto USM-chitin/sand.

4. Conclusion

The technical viability of the fixed bed adsorption of Methy-lene Blue (MB) by ultrasonic surface modified chitin supportedon sand (USM-chitin/sand) was evaluated, aiming futurescale-up purposes. The optimal bed performance was attainedwith flow rate of 10 mL min−1 and initial MB concentrationof 50 mg L−1. The breakthrough time was 370 min, the maxi-mum capacity of the column was 51.8 mg g−1 and the removalpercentage was 51.5%. The effluent volume was 9920 mLand effluent volume treated until the breakthrough timewas 3700 mL. In the optimal conditions, BDST, Thomas andYoon–Nelson models were suitable to predict the bed parame-ters, such as, � and qeq. The bed performance was maintainedafter five adsorption–elution cycles. In general lines, it wasdemonstrated the technical viability of the fixed bed adsorp-tion of MB on USM-chitin/sand, which is important for futurescale-up and industrial applications.

Acknowledgements

The authors would like to thank CAPES (Coordination forthe Improvement of Higher Education Personnel) and CNPq(National Council for Scientific and Technological Develop-ment) for the financial support. We also thank to Chemaxonfor furnishing an Academic Research license for the softwareMarvinSketch Version 14.9.22.0, (http://www.chemaxon.com),2014, that was used for obtaining the physical propertiesof the dye. Furthermore, the authors would like to thankCEME-SUL/FURG (Electron Microscopy Center of South / Fed-eral University of Rio Grande/RS/Brazil) due to the scanningelectron microscopy images.

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