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169

CHEMICAL ENGINEERING TRANSACTIONS

VOL. 42, 2014

A publication of

The Italian Association

of Chemical Engineering

www.aidic.it/cet
Guest Editors: Petar Sabev Varbanov, Neven Duić

ISBN 978-88-95608-33-4; ISSN 2283-9216 DOI:10.3303/CET1442029

Please cite this article as: Şahin R.Z.Y., Yargıç A.Ş., Özbay N., Önal E., 2014, Removal of phenol from aqueous

solution using sugar beet pulp activated carbon, Chemical Engineering Transactions, 42, 169-174

DOI:10.3303/CET1442029

169

Removal of Phenol from Aqueous Solution Using Sugar

Beet Pulp Activated Carbon

Rahmiye Zerrin Yarbay Şahin*, Adife Şeyda Yargıç, Nurgül Özbay, Eylem Önal

Bilecik Seyh Edebali University, Department of Chemical and Process Engineering, Bilecik, Turkey

zerrin.yarbay@bilecik.edu.tr

In this study, activated carbon was obtained from sugar beet pulp by applying low-temperature

carbonization at 350 °C. Removal of phenol from aqueous solutions was investigated by applying chemical

activation process to activated carbon with HCl and NaOH. For adsorption of phenol removal from

aqueous solutions; effects of pH, adsorbent dosage, phenol concentration, temperature and contact times

were investigated. The highest removal efficiency was achieved as 63 % at pH of 7 for NaOH-treated

activated carbon at 0.1 g adsorbent dosage, 100 mg/L phenol concentration, 1 hour contact time, and

room temperature. Results of the experiments showed that the adsorption kinetics obey pseudo-second

order kinetic model, respectively.

1. Introduction

Phenols are widely used for the commercial production of a wide variety of resins including phenolic

resins, which are used as construction materials for automobiles and appliances, epoxy resins and

adhesives, and polyamide for many applications. Phenols are considered as priority pollutants since they

are harmful to organisms at low concentrations and many of them have been classified as hazardous

pollutants due to their potential harm to human health (Hameed and Rahman, 2008). According to the

World Health Organization regulation, 0.002 mg L
−1

is the permissible limit for phenol concentration and

the wastewater containing phenolic compounds must be treated before their discharge into water streams

to avoid legal problems (Rodrigues et al., 2011).

In the past years, extensive researches have been undertaken to develop alternative and economic

adsorbents produced from a variety of starting materials such as wastes and agricultural residues, wood,

bentonite, and polymers (Dursun et al., 2005). Sugar beet pulp is one of these low-cost sorbents and a by-

product of the sugar refining industry, which exhibits a large capacity to bind metals. This material is cheap

and is essentially used as animal feed. Sugar beet pulp is a natural polysaccharide and is composed of

20 % and more than 40 % of cellulosic (Dronnet et al., 1997);and pectic substances, (Kartel et al., 1999;

Aksu and İşoğlu, 2005.

Sugar beet pulp carbon obtained from different methods to use as an adsorbent was studied for removing

heavy metals in earlier works, such as (Aksu and İşoğlu, 2005) on Copper removal, as well as Cadmium

(Özer and Tümen, 2005), Chromium; Altundoğan, 2005) and phenol (Beker et al., 2010).There are also

some studies of phenol adsorption by sugar beet pulp carbon, but little attention has been paid to the

investigation of pH, adsorbent dosage, phenol concentration, temperature and contact times dependence

of adsorption process and evaluating equilibrium, and kinetic parameters of the system, which are

important in the design of treatment systems (Dursun et al., 2005). This study was carried at low

temperature as 350 °C and also demonstrates that activated carbon can be specifically expressed as

green carbon.

This study presents the adsorption characteristics of sugar beet pulp activated carbon for removing phenol

from aqueous solutions. The binding capacity of activated carbon for phenol was shown as a function of

initial pH, adsorbent dosage, phenol concentration, temperature and contact times in this study.

170

2. Materials and Methods

2.1 Preparation of sugar beet pulp carbons
Sugar beet pulp was collected from Central Region of Anatolia. Sugar beet pulp first washed with distilled

water to remove impurities like dust, then air-dried at room temperature, ground in a ball-mill, sieved and

stored in a dark room. Sugar beet pulp with a mean particle size was carbonized at 350 °C in a furnace.

After being carbonized, samples were first activated with 1 M HCl or NaOH by agitating for 2 hours at room

temperature to obtain two different activated carbons and then all the carbonized samples were washed

several times with hot water to remove residual chemicals until the pH became neutral. The samples were

finally filtered with black label filter paper and classified as ACSP-I, and ACSP-II, represents HCl, and

NaOH treatment, respectively.

2.2 Adsorption studies
Analytical reagent grade phenol (≥ 99 %, Sigma Aldrich), HCl (3 7 %, Merck), and NaOH (99. 8 - 100.5 %,

Sigma Aldrich) were used in the experimental runs. Stock solution of phenol (1000 mg/L) was prepared by

dissolving a weighed amount of phenol in distilled water. The experimental test solutions were prepared by

diluting the respective stock solution of phenol with distilled water and mixing them in the desired

proportion.

Adsorption experiments were carried out in batch processes by agitating 50-500 mg of activated carbon

samples with 50 mL of phenol solution in a thermostated bath with a shaker. The parameters varied in the

experiments from 1 to 9 for pH, from 20 to 100 mg/L with an increase of 20 mg/L for phenol concentration,

0.025 g and from 0.1 g to 0.5 g with an increase of 0.1 g for adsorbent dosage, from 20 to 120 min with an

increase of 20 min for contact time and from 20 to 40 °C with an increase of 10 °C for temperature. The

effect of different treatment agents onto activated carbons was investigated using by HCl and NaOH.

Thus, 0.1 M HCl and 0.1 M NaOH buffer solutions was used in order to adjust solution pH. The pHs of the

solutions were measured regularly using a Thermoscientific Orion 3 Star pH-meter and kept constant by

adding HCl and NaOH solutions during the all batch adsorption experiments. The concentration of phenol

was determined using by a Jasco V-530 UV/visible spectrophotometer at λmax, 270 nm (Beker et al., 2009).

The final phenol concentration was measured from the standard calibration curve. The amount of phenol

adsorbed per unit mass (qe) was calculated using the following equation:

q
e

(Co Cf

C0
(1)

q
t

|(C0 Cf)V|

m
(2)

where qe and qt are the amounts of phenol absorbed at equilibrium and time t; C0 and Cf are the initial and

final phenol concentrations (mg/L) respectively. m is the adsorbent dosage (g) and V is the volume of

solution (L) (Alam et al., 2009).

The phenol removal efficiency ( ) was defined as:

wa (
C0 Ce

C0
) 100 (3)

3. Results and Discussion

3.1 Adsorption studies
The adsorption of phenol was studied within pH range of 1-9 and adsorbent dosage, inital phenol

concentration, contact time and temperature were kept constant at 0.1 g, 100 ppm, 1 hour and room

temperature, respectively. Figure 1 shows the influence of solution pH and according to the results,

maximum removal efficiencies were determined at pH 6 as 58.36 % and 59.42 % for ACSP-I and ACSP-II

respectively. The phenol removal rose with the increase of the pH up to 6, decreased after it. Therefore, at

pH values lower than 6 the surface of activated carbon is charged positively and the activated carbon

surface is charged negatively at pH values higher than 6. Consequently, at pH higher than 6 phenol

molecules are in their dissociated and anionic forms, and the activated carbon surface is negatively

charged.

171

Figure 1: Effect of pH on henol removal onto ACSP I and ACSP II

The anionic form of phenol molecules and the presence of OH
−
groups on the activated carbon surface are

determinant to the characteristics of the adsorption processes (Rodrigues et al., 2011). At basic pH (>7),

phenol adsorption became difficult due to the repulsion of the accumulation for negatively charged hydroxyl ions

around the adsorbent surface.

The effect of the adsorbent dosage on the uptake of phenol was studied using of 50 mL of 100 mg/L

phenol aqueous solutions. A sample of activated carbon was added, which mass ranged from 0.025 to 0.5

g. In all experiments, the temperature was kept at 298 K. Figure 2 shows the results of the study related to

the effect of the adsorbent dosage on the phenol adsorption process. Phenol removal is dependent on the

mass of activated carbon present in the solution and it increased when the adsorbent dosage increased.

This growth can be attributed to the additional number of adsorption sites, which resulted from the

increment on the adsorbent dosage. On the other hand, the total adsorbed amount of phenol (qe)

decreased as the adsorbent dosage increases. This is related to the aggregation or overlapping of

adsorption sites due to overcrowding of adsorbent particles, which resulted in a decrease in total

adsorbent surface available to the phenol. Interaction of particles could also desorb some sorbate

molecules, since these molecules could be bound weakly and reversibly to the surface activated carbons.

Therefore, at high adsorbent dosage, some adsorption sites remained unsaturated during the adsorption

process because they were not accessible (Rodrigues et al., 2011). The adsorbent dosage was

maintained at 0.1 g in all the subsequent experiments, which was considered that 0.5 g and 0.1 g has

similar percentage of removal.

The effect of initial phenol concentration on the adsorption of phenol was determined within constant pH

(6), adsorbent dosage (0.1 g/50 mL), contact time (1 hour) and room temperature. Solutions of phenol

concentration at 20, 40, 60, 80, and 100 mg/L were studied and the results are given in Figure 5. As

shown in Figure 3, the adsorption of phenol by activated carbons increased as the initial phenol

concentration increased. Increasing the initial phenol concentration would increase the mass transfer

driving force and therefore the rate at which phenol molecules pass from the bulk solution to the particle

surface (Banat et al., 2000). This would result in higher phenol adsorption.

Figure 2: Effect of adsorbent dosage on phenol removal onto ACSP-I, and ACSP-II

0 2 4 6 8 10

Phenol Removal
(%) (ACSP-I)

Phenol Removal
(%) (ACSP-II)

qe (ACSP-I)

qe (ACSP-II)

P
h

e
n

o
l
R

e
m

o
v
a

l
(%

)

q
e

(m
g

/g
)

0 0,1 0,2 0,3 0,4 0,5 0,6

P
h

e
n

o
l
R

e
m

o
v
a

l
(%

)

Adsorbent Dosage (g/50 ml)

Phenol Removal
(%) (ACSP-I)

Phenol Removal
(%) (ACSP-II)

qe (ACSP-I)

qe (ACSP-II)

q
e

(m
g

/g
)

172

In the case of lower concentrations, the ratio of phenol to the available sorption sites was low and lower

adsorption yields were obtained. At higher concentrations, the numbers of phenol ions were relatively

higher than available sites for adsorption. The maximum removal was achieved at both 100 mg/L as 45.71

%, and 47.14 % for ACSP-I, and ACSP-II, respectively.

The effects of temperature at 20, 30, and 40 °C and contact time at 20, 40, 60, 80, and 120 minutes were

studied together at optimum pH (6), adsorbent dosage (0.1 g) and phenol concentration (100 mg/L). The

experimental results are represented in Figure 4 and as illustrated, phenol removal decreased according to

increasing contact time and temperature except ACSP-I at 30 °C. ACSP-I and ACSP-II had the highest

removal at 30 °C as 47.6 % and 23 %, respectively.

Figure 3: Effect of initial phenol concentration on phenol removal onto ACSP-I, and ACSP-II

Figure 4: Effect of temperature and contact time on phenol removal onto ACSP I and ACSP II

The adsorption process reached equilibrium after 80 min. After 80 min, the remaining surface sites were

difficult to be occupied because of the repulsion between the solute molecules of the solid. When the

amount of phenol being adsorbed onto the adsorbent was in a state of dynamic equilibrium with the

amount of phenol desorbed from the adsorbent, phenol removal reached a constant value (Ahmad and

Rahman, 2011).

3.2 Kinetic modeling of phenol adsorption

Adsorption mechanism depends on transportation process as well as physical and chemical properties of

adsorbent (Duranoğlu et al., 2012 . The kinetics of adsorption of phenol on activated carbons was studied

using two simplified kinetic models, including pseudo-first-order [Eq(4) and pseudo-second order

equations Eq(5)].

dq
t

dt
k1(qe qt (4)

0 25 50 75 100

q
e

(m
g

/g
)

P
h

e
n

o
l
R

e
m

o
v
a

l
(%

)

Initial Phenol Concentration (mg/L)

Phenol Removal
(%) (ACSP-I)

Phenol Removal
(%) (ACSP-II)

qe (ACSP-I)

qe (ACSP-II)

0 50 100 150

P
h

e
n

o
l
R

e
m

o
v
a

l
(%

)

Time (min)

20 C Phenol Removal
(ACSP-I)

30 C Phenol Removal
(ACSP-I)

40 C Phenol Removal
(ACSP-I)

20 C Phenol Removal
(ACSP-II)

30 C Phenol Removal
(ACSP-II)

40 C Phenol Removal
(ACSP-II)

173

dq
t

dt
k2(qe qt

2
(5)

Here k1 (min) and k2 (g mg-1 min-1) are the rate constants of the pseudo-first-order and second-order

adsorption kinetics, respectively. Integrating Eqs(6) and (7) for the boundary conditions qt = 0 at t = 0 and

qt qt at t t gives (Aroğuz and Gülen, 2008 ,

ln(q
e
q

t
lnq

e
k1t (6)

(q
e
q
t

q
e

k2t (7)

Kinetic parameters calculated from linear plots of both models and correlation coefficient values are given

in Table 1. Correlation coefficients of pseudo-second-order model indicated better correlation coefficients.

According to results, linear plots of pseudo-first-order kinetic model did not fit the data, while pseudo-

second-order plots fitted data very well. Therefore, it can be stated that phenol adsorption onto produced

carbon consist of chemical adsorption due to the fact that pseudo-second-order kinetic model suggests

that adsorption process involved chemisorption mechanism (Duranoğlu et al., 2012 .

4. Conclusions

The removal of phenol from aqueous solution by activated carbons produced from sugar beet pulp and

treated with HCl or NaOH has been investigated under different experimental conditions in batch model.

The amount of adsorption increased with increasing adsorbent dosage and pH until 6. The equilibrium time

of adsorption was found to be 80 min at room temperature. The kinetic of adsorption process was best

described by the pseudo-second-order rate equation. In conclusion, the use of activated carbons from

sugar beet pulp as a green adsorbent could be alternative for the high cost adsorbents due to its low cost

and good efficiency for removal of phenol from aqueous solutions.

Table 1. Comparison of first order and second order adsorption rate constants calculated for different

temperatures

Parameters

Temperature 20 °C 30 °C 40 °C

ACSP-I ACSP-II ACSP-I ACSP-II ACSP-I ACSP-II

Pseudo-first-order

k1 0.048 0.018 0.037 0.011 0.039 0.050

qe 3.033 2.729 2.667 1.621 8.669 14.723

R
2
0.849 0.857 0.959 0.903 0.890 0.850

Pseudo-second-order

k2 0.036 0.011 0.027 0.018 0.001 0.003

qe 8.064 9.523 24.390 11.904 7.936 9.346

R
2
0.999 0.995 1 0.998 0.972 0.972

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