preparation of spherical activated carbon and their ... 2009 preparation of spherical activated...

Journal of the Korean Ceramic Society

Vol. 46, No. 6, pp. 568~573, 2009.

− 568 −

ReviewDOI:10.4191/KCERS.2009.46.6.568

†Corresponding author : Won-Chun Oh

E-mail : [email protected]

Tel : +82-41-660-1337 Fax : +82-41-688-3352

Preparation of Spherical Activated Carbon and TheirPhysicochemical Properties

Won-Chun Oh*†, Jong-Gyu Kim***, Hyuk Kim***, Ming-Liang Chen*, Feng-Jun Zhang*,

**, Kan Zhang

*, and Ze-Da Meng*

*Department of Advanced Materials & Science Engineering, Hanseo University, Chungnam 356-706, Korea**Anhui Key Laboratory of Advanced Building Materials, Anhui University of Architecture, Anhui Hefei, 230022, China

***Hanil Green Tech Co. Ltd., Chungnam 323-824, Korea

(Received August 9, 2009; Revised August 22, 2009; Accepted August 25, 2009)

ABSTRACT

In this study, we used coal based activated carbons as starting material and phenolic resin (PR) as a bonding agent to prepare

spherical shaped activated carbons. The textural properties of SAC were characterized by BET surface area, XRD, SEM, iodine

adsorption, strength intensity and pressure drop. According to the results, the spherical activated carbon prepared with activated

carbon and PR at a ratio of 60:40 was found to have the best formation of spherical shape, which was found in sample SAC40.

After activation, SAC40 has high BET surface area, iodine adsorption capability and strength value, and lowest pressure drop.

Key words : Spherical activated carbon, BET surface area, Iodine adsorption

1. Introduction

n recent years, carbon materials have found many

new applications such as catalyst supports, battery

electrodes, double layer capacitors, elements in gas storage,

components in biomedical engineering, and adsorbents for

bulky molecules.1–6) Carbon materials of such applications

usually possess high mesoporosity (2~50 nm), thereby

allowing efficient adsorption of molecules and ions that are

too large to enter micropores. It has been reported that the

pore size and pore size distributions of activated carbons

have a strong effect on the adsorption of organic com-

pounds.7) Mesopores are generally required for activated

carbons applied in liquid-phase adsorption due to the larger

size of liquid molecules. These mesopores not only contrib-

ute significantly to adsorption via the mechanism of capil-

lary condensation, but also alleviate pore obstruction and

maintain a fast kinetic adsorption rate as the main trans-

port arteries for the adsorbate.7-9) As a result, the presence

of mesopores in the activated carbon can significantly

enhance adsorption capacities, especially for large adsor-

bates.7,10-13)

Activated carbons have been applied in several fields,

including water treatment, chromatography and natural

gas storage.14) Some of these applications do not require rig-

orous control of their physical–chemical properties, regard-

ing purity, particle shapes, mechanical, esistance, homo-

geneity and specific surface area. On the other hand, these

properties are required when activated carbon is used as

catalytic support or as catalyst. Therefore, extensive

research has been carried out in recent years aiming at the

production of activated carbon from routes that allow the

control of these properties.

The adsorption capacity of activated carbon depends on

various factors such as the surface area, pore volume, pore-

size distribution and surface chemistry.15–18) Activated car-

bon fibers (ACFs) and granular activated carbons (GACs)

are two kinds of the most widely used activated carbon

materials. However, spherical activated carbons (SACs)

have received considerable recent attention for their various

potential advantages over ACFs and GACs such as

extremely low resistance to liquid diffusion, higher adsorp-

tion efficiency, better mechanical properties, and more

resistance to abrasion.19) Pitch,20) oil agglomerated bitumi-

nous coals,21) phenolic resin,19) ion exchange resin,22, 23) sty-

rene-divinylbenzene copolymers,24) and acrylonitrile-diviny-

lbenzene copolymer25) have been used to prepare SACs by

physical activation or catalytic activation.

The aim of the present work was to prepare activated car-

bons of spherical shape from coal based activated carbon.

The preparation conditions affecting the yield and textural

properties were investigated. The textural properties of

SACs were characterized by BET surface area, XRD, SEM,

iodine adsorption, strength intensity and pressure drop.

2. Experimental

2.1. Materials

The main material was coal based activated carbon with

I

569 Journal of the Korean Ceramic Society - Won-Chun Oh et al. Vol. 46, No. 6

size of 100~400 mesh, which was provided by Hanil Green

Tech (Korean). Phenolic rosin (PR) was used as a bonding

agent, and was purchased from KangNam Chemical Co.,

Ltd (Korean). Alcohol (95%) was used as a dispersing agent,

and was purchased from SamChun Pure Chemical Co., Ltd

(Korean). For preparing and forming the spherical activated

carbons, shaped mould, shaker sieve and shaker were also

used, which we made by ourselves. The appearances of

these machines are shown in Fig. 1.

2.2. Preparation of spherical activated carbon (SACs)

The method of SACs production includes three stages, i.e.,

formation, carbonization and activation.

2.2.1. Formation of SACs

First, activated carbons and PR were mixed with 20~30%

alcohol. The mixture was then put into the shaped mould to

form agglomerates. To make spheres of these agglomerates,

a shaker and a sieve with size of 30~50 mesh was used with

a shaking rate of 50 round/min and sirocco at 80~90oC.

After shaking for 10~15 min, the agglomerates formed

spheres and dried in the activated carbon powder at

100~200oC.

2.2.2. Carbonization and activation

In the first part of this experimental work, the agglomer-

ates were formed in spherical shapes. These spherical

agglomerates were heat-treated in activated carbon powder

at 350~500oC for 1 h with a heating rate of 6oC/min to form

SACs. Then, the sample of heat-treated SACs was heated in

an inert atmosphere with N2 at a flowing rate of 150 mL/

min at 700oC for 2 h. Then, the carbonized agglomerate was

heated with CO2 at a flowing rate of 150 mL/min at about

950oC for 2 h with a heating rate of 10oC/min.

For comparison, we prepared four kinds of samples with

different amounts of activated carbons and PR. The manu-

facturing procedure of the SACs and the preparation condi-

tions with the sample codes are shown in Fig. 1 and Table 1,

respectively.

2.3. Characterization

The surface morphology and structure of the SACs was

examined in an SEM (JSM-5200, JEOL, Japan). XRD was

used for crystal phase identification of the SACs. XRD pat-

terns were obtained at room temperature with a Shimata

XD-D1 (Japan) using CuKα radiation. The BET surface

area of the SACs was measured using a Quantachrome

surface area analyzer (Monosorb, USA).

2.4. Iodine number determination

The iodine number was determined based on ASTM D

4607-8626) by using the sodium thiosulfate volumetric

method. The SACs were passed through a 325 mesh screen.

Standard iodine solution was added to SACs (0.5 g) and

after equilibration time of 30 s, the residual iodine concen-

tration was determined by titration with standard sodium

thiosulfate with starch as an indicator. The iodine number

was defined as the quantity of iodine adsorbed (in mg/g of

carbon) at a residual iodine concentration.

2.5. Strength measurement

Strength measurement was determined based on JIS R

721227) by using one-point bending (Instron 4201) with sup-

port distance of 30 mm/min and cross head speed of 0.5 mm/

min. The diameter size of sample was about 5 mm, and the

strength density was calculated by the following equation:

Where is strength density (kg/m2), P is breaking load

(kg), L is support distance (cm), B is width of sample (cm)

and D is thickness of sample (cm).

2.6. Pressure drop measurement

Pressure drop of sample was measured by a circulating

pipe with an inside diameter of 27 mm and a length of 12 m.

The samples in the tank were introduced into the pipe by a

pump (2NE-20A) with the capacity of 3.5 m3/h. The pressure

drop was determined by changing the velocity in the range

of 0.25~1.7 m/sec in the pipe. The Hazen-Williams equation

for calculating the pressure drop due to frication for a given

pipe diameter and flow rate is as follows.28)

△P = 6.174×Q1.85×105/(C1.85

×d4.87)

σF

3PL

2BD2

--------------=

σF

Fig. 1. Manufacturing procedure of spherical activated car-bons.

Table 1. Preparation Method and Nomenclature

Preparation method (wt%) Nomenclature

Powdered Activated Carbons (65) +Phenol Resin (35)

SAC35


SAC37


SAC40


SAC43

November 2009 Preparation of Spherical Activated Carbon and Their Physicochemical Properties 570

Where, P = frictional pressure drop, kg/cm2

Q = flow rate, L/min

D = pipe inside diameter, mm

C = Hanzen-Williams C factor, dimensionaless (120)

3. Results and discussion

3.1. Textural characterization of SACs

Fig. 2 shows the photographs of the prepared SACs. From

Fig. 2, we can see that after activation, a crack is formed by

the change of the amount of PR in SACs. It is due to the PR

beginning to pyrolyze slowly at 350oC and then form pores

after carbonization and activation at high temperature. The

crack is decreased by the increasing of amount of PR. The

crack is well formed in SAC35, which had the lowest amount

of PR, and the strength of this sample is relatively low. It can

be considered that the PR is too low to agglomerate with the

activated carbon. The sample SAC37 has a few cracks. How-

ever, the cracks of SAC43, which had the greatest amount of

PR, were also very well formed. It can be considered that the

amount of PR was much greater, and so the pores are also

much better formed after carbonization and activation at

high temperature, because the sample easily cracked. As a

consequence, the sample SAC40 has the best formation of

spherical shapes with diameters of 4~5 mm.

The SEM image of the SACs is shown in Fig. 3. It is indi-

cated that after mixing with PR, and after carbonization

and activation at high temperature, the structure of the

activated carbon is not changed and is instead homogenous.

Fig. 4 shows the XRD pattern of the SACs. After carboniza-

tion and activation at high temperature, the strong (002)

diffractions of the hexagonal carbon at 2θ of about 25.88c

together with the weak (100) diffractions at 2θ of about 44.8o

indicate the carbon structure of the prepared SACs.

Fig. 5 shows the changes of BET surface area of the SACs

before and after activation. It is clearly seen that this

surface area is decreased with an increasing amount of PR

before activation, and that the same is true after activation.

It can be considered that the PR was introduced into the

pores of the activated carbon, and thus decreased the BET

surface area. Moreover, comparing with the surface area

before activation, the BET surface area of SACs is much

more improved after activation, about 2~3 times improved.

Comparing samples SAC35 and SAC37 with samples

SAC40 and SAC43, the BET surface area decreased by

almost 50% before activation. It can be considered that the

PR was little by little clogged in the pores in the activated

carbon when the amount of PR increased. After activation,

the BET surface area decreased slowly because the PR was

pyrolyzed and the pores were re-formed, thus relatively

increasing the BET surface area of the SACs.

3.2. Iodine adsorption capability of SACs

In generally, the iodine adsorption capability of the granu-

Fig. 2. Preparation of spherical activated carbons; (a) SAC35,(b) SAC37, (c) SAC40, and (d) SAC43.

Fig. 3. SEM image of spherical activated carbons: (a) frac-ture (×5,000) and (b) sphere surface (×1,500).

Fig. 4. XRD pattern of spherical activated carbons.


lar activated carbons and powder activated carbons is about

900~1200 mg/g.29) However, the iodine adsorption capability

is markedly decreased when carbons are treated with metal

or formed in different shapes.30,31) Fig. 6 shows the changes

of iodine adsorption capability of SACs before and after acti-

vation. Comparing with the iodine adsorption capability of

the SACs before activation, the samples after activation

have much more iodine adsorption capability, about 720~

780 mg/g. Because PR was pyrolyzed and the pores were re-

formed, high iodine adsorption capability resulted. The

iodine adsorption capability of the SACs decreased with an

increasing amount of PR.

3.3. Strength and pressure drop of SACs

Fig. 7 shows the strength values of SACs after activation.

From the results, it is clearly seen that the strength values

of the SACs are increased with an increasing amount of PR.

This indicates that the bonding agent has a significant

influence on the strength of the SACs, and that if the spher-

ical shapes formed well, the strength value is also high. As

shown in Fig. 2, SAC40 has the best formation of spherical

shapes, and can be considered to have the highest strength

value of all the samples. The results shown Fig. 7 directly

support this point.

Fig. 8 shows the pressure drop of the SACs after activa-

tion. We can clearly see that the pressure drop of the SACs

is decreased with an increasing amount of PR. However, in

the case of SAC43, the pressure drop improves again. This

can indicate that the formation is an important factor for

the pressure drop. As shown in Fig. 2, SAC40 has the best

formation of spherical shapes, and can be considered to

have the lowest pressure drop. The results of Fig. 8 directly

support this point.

4. Conclusions

In this work, we have successfully prepared spherical acti-

Fig. 5. BET surface area of spherical activated carbons beforeand after activation.

Fig. 6. Iodine adsorption capacity of spherical activated car-bons before and after activation.

Fig. 7. Strength intensity of spherical activated carbons afteractivation.

Fig. 8. Pressure drop of spherical activated carbons after acti-vation.

November 2009 Preparation of Spherical Activated Carbon and Their Physicochemical Properties 572

vated carbon from coal based activated carbon with phenolic

resin as a bonding agent. Among the prepared SACs, the

sample SAC40 has the best formation of spherical shapes.

From the SEM image, the structure of the SACs is found to

be homogenous after mixing with PR and after carboniza-

tion and activation at high temperature. From the XRD pat-

tern of the SACs, the strong (002) diffractions of the

hexagonal carbon at 2θ of about 25.88o together with the

weak (100) diffractions at 2θ of about 44.8o indicate the car-

bon structure. The BET surface area of the SACs decreased

with an increasing amount of PR before activation, the

same as was found after activation. Comparing with the

surface area before activation, the BET surface area of the

SACs is much improved after activation, by about 2~3 times.

Comparing with the iodine adsorption capability of the

SACs before activation, the samples after activation have

much more iodine adsorption capability, which was about

720~780 mg/g. The strength and pressure drop values of the

SACs increased with an increasing amount of PR. In conclu-

sion, the spherical activated carbon prepared with activated

carbon and PR at a ratio of 60 :40 has the best formation of

spherical shapes, which was found in sample SAC40. After

activation, SAC40 has the highest BET surface area, iodine

adsorption capability and strength value, and the lowest

pressure drop.

Acknowledgment

본 연구는 2008년도 중소기업청 주관 산학공동기술 개발지

원사업에 의거하여 이루어졌으며, 이에 감사드립니다.

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