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Yogyakarta-Indonesia, 4-5 th

December 2007

Chemical Engineering Department , Gadjah Mada University

14TH REGIONAL SYMPOSIUM ON CHEMICAL ENGINEERING 2007

ISBN 978-979-16978-0-4

ABSTRACT

This paper presents the findings of N2 adsorption isotherm and BET surface area of polyethyleneimine

(PEI) impregnated palm shell activated carbon (AC) as compared to its virgin form. PEI is a

well-recognized organic-based polymer with high metal complexation capability. Three types of low

molecular weight PEI distinguished by molecular number and weight, namely, Mn of 423, Mn of 600 andMw of 1,200 were used for impregnation. The impregnation process was conducted using straightforward

batch adsorption procedure with deionized water as background solution. Generally, the volume of N2

adsorbed was reduced with increased quantity of PEI impregnated on the AC. It was surmised that the type

of PEI used play a essential role in the adsorbability of PEI as the maximum amount of adsorbed PEI on AC

vary considerably for the different types (in terms of molecular weight/number) of PEI used.

Keywords: palm shell activated carbon, polyethyleneimine, N2 adsorption isotherm, BET surface area

I. INTRODUCTION

Adsorption using activated carbon (AC) is often used in the tertiary wastewater treatment stage for polishing

incoming influent before final discharge into the environment. Usage of AC for treatment of organic pollutants has

been proved to be effective due to the hydrophobicity of its surface which facilitates physical adsorption via van

der Waals forces. Hydrophobicity, however, relatively inhibits similar applications for metal ions in wastewater

albeit the presence of some acidic surface functional groups on its surface may aid slightly in metal chemisorption

via electrostatic interactions between the metal ions and surface of activated carbon rendering in mechanisms such

as cation exchange (primary) and complexation (secondary). As such, recent research has focused on modification

of activated carbon to enhance metal affinity and/or increase the activated carbon’s affinity towards a certain metal

species. One method to enhance metal affinity is to impregnate AC with a chelating polymer as proven in a

previous study [1]. It was shown in that study that the PEI-impregnated activated carbon (29.82 wt% PEI/AC –

surface saturated) significantly increased the maximum batch single adsorption capacity for Cd2+

by as much as

96% as compared to virgin activated carbon. However, this impregnation resulted in significantly reduced free

surface area by approximately 97% due to clogging of pores by PEI molecules. As such, it is deemed that the next

step is to optimize the impregnation process so that the metal adsorption capacity of AC can be increased to a

maximum at the lowest reduction of surface area. The objective of this study was to investigate the effects of

amount of PEI impregnation (for three different PEI types based on their molecular numbers, Mn) on the surface

characteristics of the AC.

N2 Adsorption Isotherm and BET Surface Area of

Polyethyleneimine-Impregnated Activated Carbon: Comparison with

Virgin Activated Carbon

Chun Yang Yin,a,b Mohamed Khiereddine Aroua,b Wan Mohd Ashri Wan Daudb aFaculty of Chemical Engineering, Universiti Teknologi MARA, Shah Alam, 40450, Selangor, Malaysia.

b Department of Chemical Engineering, Faculty of Engineering, University of Malaya, 50603, Kuala Lumpur,

Malaysia

Email: [email protected]

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December 2007



ISBN 978-979-16978-0-4

II. MATERIALS AND METHODS

The activated carbon used in the study was oil palm shell-based which was produced by physical activation

process with steam as the activating agent. It was supplied by Bravo Green Sdn Bhd (Malaysia). The activated

carbon was sieved to sizes range from 710 to 850 µm, washed with deionized water (>18 MΩ cm) to remove fines

and dirt, oven dried at 105°C for a day and stored in plastic containers. PEI impregnation was carried via batch

adsorption process conducted in an earlier study8. Three types of low molecular weight PEI distinguished by their

molecular numbers, Mn: 423 (catalog no: 468533), 600 (catalog no: 408719) and 1,200 (catalog no: 482595)

obtained from Sigma-Aldrich were used for impregnation. A molecular number is the average value of molecular

weights of individual polymers (which exist in different lengths and sizes) for a type of polymer. PEI

concentrations in the impregnation process were analysed by measuring their absorbances at 222 nm (Mn 423),

210nm (Mn 600) and 214 nm (Mn 1,200) respectively via Cary IE Varians UV-Vis Spectrophotometer. The

equilibrium PEI adsorption capacity was calculated using:

M

V C C q e

e

)( 0 −= (1)

where qe (mg g-1

) is the equilibrium adsorption capacity, C 0 and C e are the initial and equilibrium concentration (mg

l-1

) of PEI in solution, V (l) is the volume and M (g) is the weight of AC. The BET surface area and other physical

characteristics of the samples were determined from N2 adsorption isotherm at 77 K using the N2 adsorption

isotherm using ThermoQuest Sorptomatic 1990 Series analyzer. Prior to analysis, the samples were degassed at

120°C for at least 24 hours.

III. RESULTS AND DISCUSSION

Table 1 shows the effect of PEI impregnation on textural characteristics of AC samples. It was determined that

the impregnation percentages for PEI surface saturation for 423-, 600- and 1200-PEI are 29.82, 8.26 and 3.92 wt%

PEI/AC respectively. It is surmised that the type of PEI used play a vital role in the adsorbability of PEI as the PEI

surface saturation percentages on AC vary considerably for the different types (in terms of molecular number) of

PEI used. This observation is expected as it is possible that PEI molecules with higher molecular number is larger

and therefore diffusion into the micropores of AC is rendered more difficult. The increase of percentage PEI

impregnation reduces the BET surface area for a particular type of PEI implying that higher quantity of PEI in bulk

solution promotes higher adsorption on the surface of the AC resulting in decrease of free surface area.

Table 1. Effect of PEI Impregnation on Textural Characteristics of AC Samples

Type of PEI Percentage impregnation

(wt% PEI/AC)

BET surface area (m2 /g) Monolayer volume (cm3 /g)

Virgin 592 135.91

4.76 509 116.87

8.41 250 57.44

16.68 83 19.17

423-PEI

29.82 40 9.29

3.10 469 107.74

4.51 432 99.42

7.69 381 87.58

600-PEI

8.26 386 88.64

1.40 563 129.37

2.08 510 117.31

3.54 497 114.27

1200-PEI

3.92 495 113.93

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The molecular sizes (in terms of diameter) of the 423-, 600- and 1200-PEI are estimated to be 0.82 nm, 1.03 nm

and 1.32 nm respectively using “radius of inertia” equation shown by Schurer et al.[2]. These values are useful in

determining the accessibility of the three different types of PEI into the micropores of AC. Figure 1 shows the

nitrogen adsorption-desorption isotherms of the virgin and PEI-impregnated AC at 77 K. The virgin AC isotherm

has a well-defined plateau and is classified as Type 1 in accordance with the IUPAC classification with

predominant microporous characteristic as evident by high volume of nitrogen adsorbed within the relative

pressures range of 0 – 0.2. Generally, the volume of N2 adsorbed is reduced with increased quantity of PEIimpregnated on the AC. While the virgin AC is almost devoid of mesopores as indicated by its isotherm, PEI

impregnation appears to create additional mesopores, albeit at a marginal quantity. The isotherms also show a trend

analogous to reduction of BET surface area for different types of PEI used. The significant reduction of volume

adsorbed from virgin AC to 29.82 wt% 423-PEI/AC clearly indicates bulk filling of 423-PEI molecules into

micropores of AC which subsequently inhibits penetration of N 2 molecules into the inner pores. While

impregnation of 600- and 1200-PEI also provides a similar trend, nevertheless, these molecules are deemed too

large to infiltrate the micropores, which at this point, the diameter of the micropores can be estimated to be

predominantly less than 1 nm. This phenomenon is especially prominent for 1200-PEI/AC in which filling of

micropores with 1200-PEI molecules is marginal.

0

50

100

150

200

250

0 0.2 0.4 0.6 0.8 1

Relative pressure, P/Po

V o l u m e a d s o r b e d , c m

3 / g

Virgin4.76 wt% PEI/AC8.41 wt% PEI/AC16.68 wt% PEI/AC29.82 wt% PEI/AC

(a) 423-PEI

0

50

100

150

200

250

0 0.2 0.4 0.6 0.8 1


V o l u m e a d s o r b e d ( c m

3 / g )

Virgin

3.1 wt% PEI/AC

4.51 wt%PEI/AC

7.69 wt% PEI/AC8.26 wt% PEI/AC

(b) 600-PEI

0

50

100

150

200

250

0 0.2 0.4 0.6 0.8 1


V o l u m e a d s o r b e d

( c m

3 / g )

Virgin1.4 wt% PEI/AC2.08 wt% PEI/AC3.54 wt% PEI/AC3.92 wt% PEI/AC

(c) 1200-PEI

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ISBN 978-979-16978-0-4

Fig. 1. Nitrogen adsorption-desorption isotherms of AC samples at 77 K

IV. CONCLUSION

Only impregnation of 423-PEI was successful in the study. It is surmised that reduction and constriction of pore

size of macropores due to adsorbed 600- and 1200-PEI molecules on their walls results in creation of additionalmesopores.

ACKNOWLEDGMENT

The authors gratefully acknowledge the Ministry of Science, Technology and Innovation, Malaysia for the IRPA

research grant and Bravo Green Sdn Bhd, Kuching, Malaysia for generous provision of palm shell activated carbon

for research purposes.

REFERENCES

[1] C. Y. Yin, M. K. Aroua and W. M. A. W. Daud. (In press). Impregnation of palm shell activated carbon with

polyethyleneimine and its effects on Cd2+ adsorption. Colloids Surf. A.

[2] J. W. Schurer, P. H. J. Hoedemaeker and I. Molenaar. (1977). Polyethyleneimine as tracer particle for (Immuno)

electron microscopy. J. Histochem. Cytochem. 25. pp. 384-387.

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