Adsorption of Reactive Dyes by Palm Kernel Shell...

ISSN: 0973-4945; CODEN ECJHAO

E-Journal of Chemistry

http://www.e-journals.net 2009, 6(4), 949-954

Adsorption of Reactive Dyes by Palm Kernel

Shell Activated Carbon: Application of Film

Surface and Film Pore Diffusion Models

M. M. NOUROUZI, T.G. CHUAH* and THOMAS S.Y.CHOONG

Department of Chemical and Environmental Engineering,

Faculty of Engineering, Universiti Putra,

Malaysia, 43300 UPM Serdang, Selangor, Malaysia.

[email protected]

Received 1 October 2008; Revised 17 February 2009; Accepted 15 March 2009

Abstract: The rate of adsorption of two reactive dyes, Reactive Black 5 and

Reactive Red E onto palm kernel shell-based activated carbon was studied. The

experiment was carried out to investigate three models: film diffusion model, film-

surface and film-pore diffusion models. The results showed that the external

coefficients of mass transfer decreased with increasing of initial adsorbate

concentration. In addition, it was found that the adsorption process was better

described by using the two resistance models, i.e. film-surface diffusion.

Keywords: Adsorption, Reactive dye, Palm kernel shell, Film-surface-pore diffusion.

Introduction

Industries, such as textile, ceramic, paper, printing and plastic, use dye as their raw material,

thus generating a large amount of colored wastewater. Adsorption methods are promising in

decolorizing textile effluents, but this application is limited by the high cost of adsorbents.

The activated carbon derived from agricultural wastes is important due to the fact that it is

inexpensive, adequate to remove organic and inorganic contaminants from wastewater and

locally available1. Malaysia is a major producer of palm oil. In 2002 alone, the amount of

palm kernel shell generated in Malaysia was approximately 4.3 million tons which can cause

serious disposal problem2. Considering the volume of this waste, several studies were

initiated to utilize Palm Kernel Shell as the crude material for activated carbon and it is

reported that a good quality product can be obtained, such as its granular structure,

insolubility in water, chemical stability and high mechanical strength2,3

.

It is important to be able to predict the rate at which pollutant is removed from aqueous

solutions in order to design appropriate sorption treatment plants. Therefore, the kinetics that

describes the dye uptake rate needs to be determined. The adsorption mechanism can be

described by three essential steps4:

950 T.G. CHUAH et al.

1. External mass transfer from bulk solution to adsorbent surface across the boundary

layer surrounding the adsorbent surface particle.

2. Intraparticle diffusion within the internal structure of particle. Internal diffusion is

diffusion of molecule inside the pores and surface diffusion is diffusion of the

molecules on surface phase.

3. Adsorption at an interior site.

Generally, the total rate of the kinetic process is controlled by the rate of the slowest

process. The transport of the adsorbate from the bulk of fluid phase to the external surface of

adsorbent forms an important step in the uptake process.

Single resistance models involve only a liquid film resistance, pore diffusion resistance

or surface diffusion resistance5. In most cases, single resistance models are not adequate to

explain the adsorption process for porous adsorbents. Therefore, two resistance mass

transfer models which incorporate both external and intraparticle diffusion effects is

applied6. Two resistance models can be divided into:

1. Film-pore diffusion model.

2. Film-surface diffusion model.

A model which incorporated film, pore diffusion and concentration dependent surface

diffusion was introduced7 and later on a three-resistance model based on external mass

transfer, pore and concentration dependent surface diffusion for removal of methylene blue

by PKS based-AC was presented8. They expressed that the film-pore-concentration-

dependent surface diffusion (FPCDSD) model was able to fit the experimental data using a

single set of mass transfer parameters for a wide range of initial dye concentrations.

However, a two resistance model may be easier for implementation.

Experimental

PKS-based activated carbon supplied from KD Technology Sdn. Bhd was used without any

chemical or physical treatment. Two reactive dyes were used for this investigation, namely,

Reactive Black 5 (RB 5) and Reactive Red E (RR E) supplied from Texchem-Pack Bhd. The

chemical structure of these dyes is given in Table 1. According to data obtained from pH

meter, for single solution pH of the solution of RB 5 and RRE was 6.5 and 6.4, respectively.

For binary solution, treating both dyes RB 5 and RR E in one solution, pH was 6.4. To

prepare the stock solution, 1.000 g (+0.0005) of each dye was dissolved in 1 L distilled

water. In order to maintain homogenous condition, the solution was shaken for 5 hours using

orbital incubator shaker (Sepilau Saintifik, Malaysia) at 28oC. Then the solution was kept in

dark place for avoiding any off-color due to sunlight. The stock solution would then be

diluted into desired concentration.

Batch kinetic study

Batch kinetic studies were performed to investigate the dynamic behavior of PKS - based

activated carbon for removal of reactive dyes. The experiments were accomplished in

shaking conical flasks with 1000 mL dye solution at a constant temperature of 28 °C (+ 2 °C),

using an incubator. The pH of the solutions was without any modification. Sample of 1 mL

was carefully withdrawn at every 3 minutes for the first 30 minutes and at every 5 minutes

for the next 30 minutes of adsorption process. For the next 60 minutes, sampling was done

every 10 minutes and eventually every 60 minutes for the next 20 hours and every 6 hours

until equilibrium point. The same procedure was applied for kinetic study for binary mixture

at concentration of 20 mg/L (for each dye) and activated carbon mass of 2 g/L.

Adsorption of Reactive Dyes by Palm Kernel Shell Activated Carbon 951

Table 1. Properties of RB 5 and RR E9.

C.I. Reactive Black 5 C.I. Reactive Red E

Type Reactive dye Reactive dye

Chemical structure

Molecular length, nm 3.61 2.32

Molecular width, nm 0.25 0.72

Max wave length of

adsorption (λmax,) nm

596

540

Theoretical model

External mass transfer

The mass transfer rate at the external surface layer of the adsorbent particle10

is:

Nt = kf SA (cb-cs) (1)

Where Nt is adsorption rate at time t, kf is the interphase mass transfer coefficient, SA is

surface area, cb and cs are adsorbate concentration in the bulk of fluid and that at the fluid-

particle interface, respectively.

The differential mass balance is given by:

dt

qMd

dt

VdcN b

t =−=

(2)

pp

Aa

MS

ρ

3=

(3)

where q is average adsorbed-phased concentration, M is mass of adsorbent, V is volume of

solution, ap is particle radius and ρp is pellet density. The concentration of adsorbate, q , with

respect to time is related to the mass transfer coefficient kf by:

)(3

sb

pp

fcc

a

k

dt

qd−=

ρ

(4)

Equation 4 can be solved with appropriate initial condition:

0,0 <== tqandcc sbob

(5)

Intraparticle mass transfer

Film-surface diffusion

Fick’s second law of diffusion suggested that the adsorbate molecule is transferred through the

adsorbent particles by creeping from one adsorption site to another on the solid surface. The

surface diffusivity Ds of adsorbed molecules is assumed here to be concentration independent.

The mass transport in the spherical particle is described by following equation.

0,0,11 2

2≥≤≤

∂

∂

∂

∂=

∂

∂tar

r

qr

rrt

q

Dp

S

(6)

Equation 6 was solved with appropriate initial and boundary conditions:


0,0,0 <≤≤= tarq p (7)

0,0 ==∂

∂r

r

q

(8)

The second-boundary condition for external mass transfer is10

:

0),(33

≥−=∂

∂= tcc

a

k

r

q

a

Dparb

pp

f

p

s

ρ

(9)

The external mass transfer coefficient, kf, is estimated from the single-resistance model.

To calculate the value of the solid phase diffusivity, Ds, equation 6 was solved numerically,

considering the value of kf obtained from single-resistance model.

Film-pore diffusion

Pore diffusion equations are described as follow:

p

p

pp arr

cr

rr

D

t

q

t

c≤≤

∂

∂

∂

∂=

∂

∂+

∂

∂0),( 2

2ρε (10)

00,0,0 <≤≤== tarqc p (11)

0,0,0 ≥==∂

∂tr

r

c (12)

0,),()( ≥=∂

∂=− tar

r

cDcck ppbf

(13)

where Dp is pore diffusivity.

Both the two resistance models were solved by using finite-difference method, as

approximating the spatial derivation by central difference expression.

Results and Discussion

To evaluate the external mass diffusion, the values of external mass transfer coefficient kf were

calculated for different initial concentrations. Table 2 presents the values of kf for adsorption of

RR5 and RR E onto PKS based-AC. It can be noted that these values, ranging between 3.7×10-3

to 3.7×10-4

cm/s, decrease with an increase in initial dye concentration. The value of kf in a single

resistance mass transport model is normally expected to be constant, variation of external mass

coefficient shows that intraparticle diffusion is playing a significant role in the mass transport

process6. It is expressed that the values of kf decreased with increasing of initial adsorbate

concentration11

. The same results were shown for adsorption of dye onto bagasse pith12

. It can be

noted from the Table 2 that it agrees with finding of this work. It is possible that increasing the

concentration of dyes, considering the large molecule of dye, causes the reduction of mobility of

transferring adsorbates into the boundary layer4.

Table 2. External mass transfer coefficient kf for adsorption of RB 5 and RR E onto PKS-

based AC (single system).

Isotherm model Interphase Mass Transfer Coefficient, cm/s

100, mg/L 20, mg/L

RB 5 / PKS Pellet 5.5×10-4

3.7×10-3

RR E / PKS Pellet 3.7×10-4

7.4×10-4

By changing the values of kf and Ds it is possible to obtain the best fit to the

experimental curves for batch adsorption. Table 3 presents the values of Ds for adsorption

of RB 5 and RR E with dye concentration 20 mg/L onto PKS-based AC with dosage 2 g/L.

Time, h

Time, h

Cb/C

bo

C

b/C

bo

Adsorption of Reactive Dyes by Palm Kernel Shell Activated Carbon 953

Some values of the surface diffusivity, reported in other literature are listed in Table 3, as well.

It can be seen that the values of Ds ranges between 1.5×10-9

to 1.5×10-10

cm2/s. From Table 3, it

can be noted that the values of Ds for RB 5 and RR E are different from values of other

literatures. The difference shows specificity of adsorption. In other word interaction between

adsorbate and adsorbent is characteristic for each system and it is not common for all systems13

.

Table 3. Values of Ds, reported in the literature on adsorption of different dyes using

different adsorbents and this work.

Material Dye Surface Diffusivity, cm2/s Reference

Filtrasorb-400 AC Cibacron reactive red 1.5×10-10

14

Filtrasorb-400 AC Tectilon Red 2B 1.5×10-9

15

PKS-AC RB 5 1×10-6

This work.

PKS-AC RR E 9×10-7

This work.

Figures 1(a) and 1(b) show the comparisons of results of both adsorptions of RB 5 and

RR E onto PKS-based activated carbon with predictions based on the film-surface diffusion

and film-pore diffusion models. It is obvious from these figures that prediction based on the

film-surface diffusion model fits better with experiment data than the film-pore diffusion

model, and it agrees with both dyes. The values of SSE for film-surface diffusion are

significantly less than values of SSE for film-pore diffusion, as shown in Table 5. As a

result, it indicated that the adsorption process was governed by the resistance models, i.e.

film-surface diffusion mechanism. The values of Dp are as listed in Table 4.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40 60 80 100 120 140

Cb

/Cb

o

20 mg/L S.D

20 mg/L Exp data

20 mg/L P.D

Figure 1(a). Comparison between prediction of film-surface diffusion (S.D) and film-pore

diffusion (P.D) models with experiments data from adsorption of RB 5 onto PKS-based activated

carbon at dye concentration of 20 mg/L and dosage of adsorbent 2 g/L (single system).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 50 100 150 200 250

Cb

/Cb

o

20 mg/L S.D

20 mg/L Exp data

20 mg/L P.D

Figure 1(b). Comparison between prediction of film-surface diffusion (S.D) and film-pore

diffusion (P.D) models with experiments data from adsorption of RR E onto PKS-based activated

carbon at dye concentration of 20 mg/L and dosage of adsorbent 2 g/L (single system).


Table 4. Values of Dp for adsorption of RB 5 and RR E onto PKS based-AC.

Kinetic Model pD , cm

2/s

RB 5/PKS 2.4×10-7

RR E/PKS 4.7×10-8

Table 5. Comparison of SSE of film-surface diffusion and film-pore diffusion models for

adsorption of RB 5and RR E onto PKS based-AC.

Kinetic model SSE

Film-surface diffusion Film-pore diffusion

RB 5/PKS 13.9 153.6

RR E/PKS 4.5 101.6

Conclusion

The rate of the kinetic process for both dyes was better described by two resistance models.

Based on SSE, the film-surface diffusion model was able to fit experimental better than the

film-pore diffusion model for both RB 5 and RR E on palm kernel based activated carbon.

Acknowledgement

The authors are grateful to KD Technology Sdn. Bhd. for supplying granular PKS.

References

1. Mohan D and Pittman Jr C U Journal of Hazardous Materials., 2007, 142, 1-53.

2. Ma A N, Palm Oil Engineering Bulletin, 2002, 24-26.

3. Chuah T G, Jumasiah A, Gimbon J, Choong T S Y and Azni I, Desalination, 2005,

186, 57-64.

4. McKay G, Bino M J and Altememi A, Water Res., 1986, 20, 435-442.

5. Al-Qoudah Z, Water Res., 2000, 34, 4295-4303.

6. Choy K K H, Ko D C K, Cheung C W C, Porter J F and McKay G, J Colloid

Interface Sci., 2004, 271, 284-295.

7. Choy K K H, Porter J F and McKay G, Adsorption, 2001, 7, 305-317.

8. Choong T S Y, Wong T N, Chuah T G and Idris A, J Colloid Interface Sci., 2006,

301, 436-440.

9. Kim S I, Yamamoto T, Endo A, Ohmori T and Nakaiwa M, Microporous and

Mesoporous Materials, 2006, 96, 191-196.

10. Tien C, Adsorption calculation and modeling; Butterworth-Heinemann, 1994, 99-119.

11. Tsai W T, Chang CY, Ing C H and Chang C F, J Colloid Interface Sci., 2004, 275, 72-78.

12. Mckay G, El Geundi M and Nassar M M, Water Res., 1988, 22, 1527-1533.

13. Meshko V, Markovska L, Mincheva M and Rodrigues A E, Water Res., 2001, 14,

3357-3366.

14. Yang X Y and Al-Duri, Chemical Engineering Journal, 2001, 83, 15-23.

15. Walker G M and Weatherley L R, Water Res., 1999, 33, 1895-1899.

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