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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

Copyright Š 2012, Asian Business Consortium | AJASE

ISSN 2305-915X

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

ISSN 2305-915X

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

ISSN 2305-915X

Evaluation of the Correlation between Selected Quality Indices of Activated Carbon: A Review Benjamin Edem Meteku Post Graduate Researcher, Chemical Engineering Department, Kwame Nkrumah University of Science and Technology, Kumasi, GHANA

ABSTRACT The choice of activated carbon for use depends on the quality, which is measured by selected indices. The correlation between BET surface area, iodine number, ash content and bulk density, major quality indices for characterisation were investigated in this study. The iodine number and surface area were strongly correlated (R2= 0.9684 and 0.9577). The bulk density and ash content were highly correlated with surface area with coefficient of determination (R2) values of 0.9040 and 0.9788 respectively for samples from same raw material under similar treatment. The ash content could also be used as an approximate estimate of iodine number and bulk density with R2 values of 0.5966 and 0.6236 respectively. Key Words: activated carbon, adsorption, activity, correlation, coefficient of determination.

1 INTRODUCTION

A

ctivated carbon, an amorphous, porous form of carbon with high surface area is the most widely used industrial adsorbent [1], [2]. It is used in the manufacture of protective gas mask for the entrapment of toxic gases in the plant and also in the manufacture respiratory devices for personal protection during chemical warfare [3]. In medicine; activated charcoal (carbon) is frequently used treating and managing severe, acute poisoning [4]. In hydrometallurgy, it is used in precious metal (such as Au and Ag) recovery processes and also for the removal of organic pollutants in drinking water and industrial wastewater processing [5],[6]. Activated carbon is also used in the removal of compounds that adversely affect taste, colour and odour in food processing industries and also in the removal of dye in effluent streams in the textile industry [7][8]. The versatility of activated carbon for use in the fore stated processes is due to its large surface area, a property that enables it to be used effectively for adsorption. Depending on the intended use of activated carbon, various quality parameters including surface area, activity, bulk density and ash content are tested for in a sample. The surface area, the total area of the surface of a powder or a solid including both external and accessible internal surface (from voids, cracks, open porosity and fissures) is an important parameter used in the determination of the quality of activated carbon. Generally, the higher the measured surface area value of an activated carbon sample, the

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

ISSN 2305-915X

better the carbon for adsorption operations. It is usually determined by the BET (Brunauer, Emmett and Teller) method [9]. Activity, the measure of the adsorptive capacity of an adsorbent (activated carbon) usually determined by a standard test is a major quality test carried on activated carbon. Various forms of activity test are carried out depending on the end user application: Iodine number (standard for liquid phase application such as water treatment), Molasses number or Caramel decolourising performance (colour adsorption processes such as in sugar industry), carbon tetrachloride value (vapour phase application) fresh carbon activity (gold mine operations) [10],[11],[12] Bulk density, the mass per unit volume of a material (activated carbon) including voids in the material is another parameter used sometimes to estimate the quality of carbon. A Low bulk density value may imply a relatively high surface area, a good indicator of high adsorption capacity. [9],[13]. The ash content of activated carbon is the inorganic residue that remains when the carbonaceous portion is burned off. It is used as an estimate of the adsorptive property of carbon. The inorganic residues (mainly silica and oxides of metals) are non porous and hence high ash content invariably results in low adsorptive capacity of the carbon [9]. Although considerable amount of research has been carried out on the production activated carbon from various raw materials for adsorption, little has been done on finding a concrete relationship (not speculative) between the quality indices used in characterising carbon. In this paper, a conscious effort is made in finding the correlation (if any) between selected quality indices (surface area, bulk density, iodine number and ash content) used in characterising activated carbon.

2 TOOLS AND METHODS The correlation between the selected quality indices were determined by finding the Pearson correlation coefficient (R) values between the chosen parameters in the works of other authors on the subject matter using Microsoft excel spreadsheet. The meaningfulness or strength of the correlation coefficient is ascertained from the coefficient of determination (R2). The formula for the correlation coefficient (R) is:

R

1 ( x  x)( y  y)  n 1 sx s y

Where n is number of pairs of data,

x

and

y

are the means for x and y respectively, s x

and s y represent the standard deviations for the x-values and y-values.

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

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3 RESULTS AND DISCUSSION 1400 y = 0.625x + 223.8 R² = 0.957

Iodine Number (mg/g)

1200 1000 800 600 400 200 0 0

500

1000

1500

2000

BET Surface Area (m2/g) Fig 1: Correlation between Iodine Number and Surface Area for Activated Carbon Prepared from Bituminous Coal, Carbonised at 800°C and Activated under same conditions with different chemicals. (Source: Adapted from Cuhadaroglu and Uygun, 2008.) [14]

600 y = 0.94x - 120.3 R² = 0.968

Iodine Number (mg/g)

550 500 450 400 350 300 250 200 400

450

500

550

600

650

700

750

800

BET Surface Area (m2/g) Fig .2: Correlation between Iodine Number and Surface Area for Activated carbon from Jute Stick Char under same conditions but different Activation temperatures. (Source: Adapted from Asadullah et al., 2007) [15]

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

ISSN 2305-915X

510 Bulk Density (kg/m3)

500 490

480 470 y = -0.069x + 555.9 R² = 0.477

460 450 440 800

900

1000

1100

1200

1300

1400

1500

BET Surface Area (m2/g)

Fig. 3: Correlation between Bulk Density and Surface Area for different samples of Activated carbon used in industrial processes in Iran. (Source: Adapted from Soleimani and Kaghazchi, 2008) [5]

0.9

Bulk Density (g/cm3)

0.8 0.7 0.6 y = -0.001x + 1.621 R² = 0.904

0.5

0.4 0.3 600

700

800

900

1000

1100

BET Surface Area (m2/g) Fig. 4: Correlation between Bulk Density and Surface Area of Activated carbon from different raw materials by both physical and chemical activation (Source: Adapted from Yusufu et al., 2012) [16]

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BET Surface Area (m2/g)

Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

2000 1800 1600 1400 1200 1000 800 600 400 200 0

ISSN 2305-915X

y = -178.8x + 1718. R² = 0.978 0

2

4

6

8

10

Ash Content (%)

Fig.5: Correlation between Surface Area and Ash Content of Activated carbon from Olive Mill Waste Chemically activated with KOH (Source: Adapted from Moreno-Castilla et al., 2001) [17]

1600

BET Surface Area (m2/g)

1400 1200 1000

y = -48.06x + 1305. R² = 0.747

800 600 400 200 0 0

2

4

6

8

10

Ash Content (%) Fig. 6: Correlation between Surface Area and Ash Content of Different samples of Activated carbon used in industrial processes in Iran (Source: Adapted from Soleimani and Kaghazchi, 2008) [5]

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

ISSN 2305-915X

Bulk Density (g/cm3)

0.6 y = 0.002x + 0.474 R² = 0.517

0.55 0.5 0.45 0.4 0.35 0.3 0

5

10

15

20

25

30

35

40

Ash Content (%)

Fig. 7: Correlation between Bulk Density and Ash Content of Activated carbon from Palm Oil Shell Physically activated at 750°C( optimum conditions for different sizes) (Source: Adapted from Vitidsant et al., 1999) [18]

0.9

Bulk Density (g/cm3)

0.85 y = 0.002x + 0.566 R² = 0.623

0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.45 0.4 0

20

40

60

80

100

Ash Content (%) Fig. 8: Correlation between Bulk Density and Ash Content of Activated carbon from different raw materials by both physical and chemical activation (Source: Adapted from Yusufu et al., 2012) [16]

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

ISSN 2305-915X

270 Iodine Number (mg/g)

265 260 255 250 245 240

y = -3.142x + 286.5 R² = 0.572

235 230 6

8

10

12

14

16

18

Ash Content (%) Fig. 9: Correlation between Iodine Number and Ash Content of Activated Carbon from Fluted Pumpkin Seed Shell by Chemical activation (Source: Adapted from Verla et al., 2012) [19]

700 Iodine Number (mg/g)

600 500 400 y = -6.496x + 574.0 R² = 0.596

300 200

100 0 0

10

20

30

40

50

Ash Content (%) Fig. 10: Correlation between Iodine Number and Ash Content of Activated Carbon from Palm Oil Shell Physically activated at 750°C( optimum conditions for different sizes) (Source: Adapted from Vitidsant et al., 1999) [18] The Iodine number values and the BET surface area were highly correlated (Fig.1 and Fig.2). About 96% - 97% of the variation in iodine number can be explained by variations in the surface area. This is probably the reason why in liquid phase applications, the iodine number remains the basic quality test for adsorptive capacity of carbon, a measure of the

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

ISSN 2305-915X

available surface area for adsorption processes. A similar trend of high correlation between iodine number and surface area was observed elsewhere [18]. Generally, an expected inverse relation exists between density and surface area [13]. This assertion is confirmed by the nature of the high coefficient of determination (R2 = 0.9040) in Fig. 4. Although a relatively weak correlation (R =0.6908) exist between density and surface area as shown in Fig. 3, about 48% of the variation in density may be accounted for by variations in the surface area. Bulk density may there only be used for approximate estimation surface area (adsorption capacity for that matter). The ash content is known to interfere with pore structure development and hence adversely affect adsorption. High ash content may therefore correspond to low surface area [20]. As shown in Fig. 5 and Fig. 6, there is a strong correlation between surface area and ash content. For activated carbon from the same raw material and prepared in similar manner (olive mill waste activated with KOH), about 97% of the variations in the surface area are explained by the variations in ash content (Fig.5). A similar trend is observed in the same work when H3PO4 was used as activating agent [17]. However, for activated carbon samples from different precursors, variations in surface area may only be explained by about 75% variations ash. The Disparity could be a reflection of degree of variation in the chemical composition of each raw material which reflects in the inorganic residues after combustion, the ash content. A positive correlation exists between the density of activated carbon and the ash content (Fig. 7 and Fig. 8). Variations in density may be explained by variations in ash content by 50-60%. The observed trend in ash and density is expected as both parameters impact negatively on surface area as seen in the foregoing analysis. Generally, the inorganic residues that make up the ash (such as SiO 2, Na2O) are non adsorptive and therefore high ash content in an activated carbon sample may correspond to low iodine number. Although there is a general negative correlation between the iodine number and ash content (Fig. 9 and 10), the ash content is not as strongly correlated to the iodine number (R2 = 0.60). The ash content could perhaps only be used as a rough estimate of the iodine number and any other measure of activity.

4 CONCLUSION The studies conducted on some selected quality indices of activated carbon ( BET Surface area, Iodine number, ash content and bulk density) from randomly selected scholarly articles on the subject matter gave an indication of a very strong correlation between Iodine number and Surface area( R2 = 0.9684 and 0.9577). Disparities in the correlation between density and surface area as well as ash content and surface area, show that ash and density may only be useful for approximate estimation of surface area or when the carbon samples are from the same raw material and produced in like manner. Though moderate, a correlation exist between bulk density and ash content (R2 = 0.517 and 0.6236). The ash content may also be used as an approximate forecast of Iodine number (R 2 ď‚ť 0.60).

REFERENCES [1] [2] [3]

Daintith, J. (2004), Oxford Dictionary of Chemistry, Fifth Edition, Oxford University Press,U.K., page 121 Seader ,J.D. and Henley E.J.(2007),Separation Process Principles, Second Edition, John Wiley and Sons ,NJ , U.S.A, pages 551-554 Activated Carbon Manufacture, Structure and Properties (2006), Cameron Carbon Incorporated, Accessed on 20th October, 2013 from http://www.cameroncarbon.com/documents/carbon_structure.pdf

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

[4] [5] [6] [7]

[8]

[9] [10] [11]

[12] [13] [14]

[15]

[16]

[17]

[18]

[19]

[20]

ISSN 2305-915X

Cooney, D.O.,(1995), Activated Charcoal in Medical Applications, Marcel Dekker, New York Soleimani, M. and Kaghazchi, T. (2008), Activated Hard Shell of Apricot Stones: A promising Adsorbent in Gold Recovery, Chinese Journal of Chemical Engineering, 16 (1), 112-118 Adinata, D., Daud, W.M.A., Aroua, M.K. (2007), Preparation of Activated Carbon from Palm shell by Chemical Activation, Bioresource Technology, 98 , 145- 149 Qureshi, K., Bhatti, I., Kazi, R., Ansari, A.K., (2008), Physical and Chemical Analysis of Activated Carbon Prepared from Sugarcane Bagasse and Use for Sugar Decolourisation, International Journal of Chemical and Biological Engineering, 1(3), 144-148 Bello, O.S., Ahmad, M.A., Siang, T.T., (2011), Utilisation of the Cocoa Pod Husk for the Removal of Remazol Black B Reactive Dye from Aqueous Solutions: Kinetic, Equilibrium and Thermodynamic Studies, Trends in Applied Sciences Research, 6 (8): 794-812 ASTM Committee E02 on Terminology (2005), ASTM Dictionary of Engineering Science and Technology, 10th Edition, Mayfield PA. Frank Desilva, (2000) Activated Carbon Filtration, Accessed on 11 th November, 2013 from http://www.resintech.com/pdf/activatedcarbonfiltration.pdf Faulkner, D.W., Urbanic, J.E., Ruckel, R.W. (1987), Activated Carbon for Precious metal Recovery, Academic Paper Presented at the 110th Annual Meeting of the Society of Mining Engineers and the Metallurgical Society, Denver, CO. February 23-27, 1987 Adsorptive Characteristics, Indo German Carbon Limited (IGCL), Accessed on 11 th November, 2013 from http://www.igcl.com/php/activated_carbon.php Saleh, N.J., Ismaeel, M.I., Ibrahim, R.I., Zablouk, M.A., Amer, A. (2008), Preparation of Activated Carbon from Iraqi Reed, Engineering & Technology Journal, Vol. 26, No. 3. Cuhadaroglu, D. and Uygun, O.A. (2008), Production and Characterisation of Activated Carbon from Bituminous Coal by Chemical Activation, African Journal of Biotechnology, 7 (20), 3703- 3710 Asadullah, M., Rahman, M.A., Motin, M.A. and Sultan, M.B. (2007), Adsorption Studies on Activated Carbon Derived from Steam Activation of Jute stick Char, Journal of Surface Science Technology, 23, (2), 73-80. Yusufu M.I., Arihu C.C. and Igbabul B.D. (2012), Selection and Characterisation of Activated Carbon from Selected Local Raw Materials, African Journal of Pure and Applied Chemistry, 6(9), 123-139 Moreno-Castilla, C., Carrasco-Marin, F., Lopez-Ramon, V.M., Alvarez-Merino, M.A., (2001), Chemical and Physical Activation of Olive - Mill Waste Water to Produce Activated Carbon, Carbon 39 (2001) 1415-1420. Vitidsant, T., Suravattanasakul, T., Damronglerd, S.,(1999), Production of Activated Carbon from Palm Oil Shell by Pyrolysis and Steam Activation in a Fixed Bed Reactor, ScienceAsia 25 (1999): 211-222 Verla, A. W, Horsfall (Jnr), M., Verla, E.N., Spiff, A.I., Ekpete, O.A.,(2012), Preparation and Characterisation of Activated Carbon from Fluted Pumpkin Seed Shell, Asian Journal of Natural and Applied Sciences, Vol. 1 No.3 Devi, V.B., Jahagirdar, A.A., Ahmed, M.N.Z., (2012), Adsorption of Chromium on Activated Carbon Prepared from Coconut Shell, International Journal of Engineering Research and Applications, Vol. 2, Issue 5.

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Asian Journal of Applied Science and Engineering, Volume 3, No 1 (2014)

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