Physical and Chemical Analysis of Activated Carbon Prepared from Sugarcane Bagasse and Use for Sugar Decolorisation

Abstract

Activated carbon is used in sugar industries for the removal of colorants from sugar liquor and for treatment of drinking water and industrial wastewater. Coal is a commercially used activated carbon, which is a limited non renewable resource. There are different renewable resources such as sugarcane Bagasse, Almond nutshells, Rice husk, Rice straw, Coconut shells, which could be used as alternatives. In the present work bagasse, the byproduct of sugar industries, was treated and converted into adsorbent. Sugarcane bagasse was mixed with molasses, the binder, and compressed into moulding press to make homogenized pellets at 5000 psi. The sample was then pyrolyzed at 700 ºC in an inert atmosphere and subsequently activated at different temperatures from
700 ºC to 900 ºC. The Physical (bulk density, yield, burn off, hardness) and chemical properties (pH, conductivity, ash) of the activated samples were analyzed using standard methods. These samples were also analyzed at Matiari sugar mill to evaluate the effectiveness for percent color removal from a Melt sugar liquor
solution. Relative efficiency of Decolorization was compared with the commercial activated carbon (Cane Cal from Calgon Carbon). It was found that the sample, steam activated at 900 ºC, showed the satisfactory Physical and chemical Properties. The decolorizing property was much better than the commercial carbon making it a good decolorizer in the sugar refinery industry.

Full text

Abstract—Activated carbon is used in sugar industries for the
removal of colorants from sugar liquor and for treatment of drinking
water and industrial wastewater. Coal is a commercially used
activated carbon, which is a limited non renewable resource. There
are different renewable resources such as sugarcane Bagasse,
Almond nutshells, Rice husk, Rice straw, Coconut shells, which
could be used as alternatives. In the present work bagasse, the
byproduct of sugar industries, was treated and converted into
adsorbent. Sugarcane bagasse was mixed with molasses, the binder,
and compressed into moulding press to make homogenized pellets at
5000 psi. The sample was then pyrolyzed at 700 ºC in an inert
atmosphere and subsequently activated at different temperatures from
700 ºC to 900 ºC. The Physical (bulk density, yield, burn off,
hardness) and chemical properties (pH, conductivity, ash) of the
activated samples were analyzed using standard methods. These
samples were also analyzed at Matiari sugar mill to evaluate the
effectiveness for percent color removal from a Melt sugar liquor
solution. Relative efficiency of Decolorization was compared with
the commercial activated carbon (Cane Cal from Calgon Carbon). It
was found that the sample, steam activated at 900 ºC, showed the
satisfactory Physical and chemical Properties. The decolorizing
property was much better than the commercial carbon making it a
good decolorizer in the sugar refinery industry.
Keywords—Activated carbon, Decolorization, Sugarcane
Bagasse, Sugar refining.
I. INTRODUCTION
RANULAR activated carbon are versatile adsorbents with
wide range of applications. They are most effective
adsorbents in treating drinking water and industrial
wastewater.
Khadija Qureshi is Assistant Professor in the department of Chemical
Engineering, Mehran University of Engineering & Technology, Jamshoro,
Sindh Pakistan.(corresponding author phone: 92-22-2771262; fax: 92-22-
2771262; e-mail: khadijamuet@yahoo.com).
Inamullah Bhatti is Assistant Professor in the department of Chemical
Engineering, Mehran University of Engineering & Technology, Jamshoro,
Sindh Pakistan (e-mail: bhatti_inam@yahoo.com).
Dr. A. K. Ansari is professor and Head of the department of Chemical
Engineering, Mehran University of Engineering & Technology, Jamshoro,
Sindh Pakistan (e-mail: quakpk@yahoo.com).
Dr. R. A. Kazi is professor in the Institute of Petroleum and Gas
Engineering and Now he is working as R&D manager BP Pakistan
(qazi_ra@bp.co.pk)
The food industry is also a major consumer of activated
carbon, where it is used to remove compounds that adversely
effect color, taste and odor. In the mineral industry activated
carbon are used to recover gold from leached liquors.
Medicinal uses and pharmaceutical industry is also another
wide area for the utilization of activated carbon. In gas
cleaning applications activated carbon are extensively used in
air filters at industrial level as well as in general air
conditioning application.
Commercially activated carbon is produced from
bituminous or lignite coal. The long-term availability of coal,
environmental impacts and potentially increasing cost has
encouraged researchers to find other alternatives, which may
be cast effective and equally potential. Activated carbon can
be manufactured from any material that has reasonable
elemental carbon content. Any lignocellulosic material can be
converted to an activated carbon.
The literature mentions many precursors for activated
carbon such as bagasse [1] scrap tires and saw dust [2],
almond, pecan, English walnut ,black walnut and macadamia
nut [3] pistachio [4] hazelnut shells [5] rice husk [6] rice bran
[7] etc.
Sugar cane bagasse is a byproduct of sugarcane industries
obtained after the extraction of juice for production of sugar.
About 54 million dry tones of bagasse are produced annually
throughout the world [8]. In Pakistan 16.6 million tones is
produced annually [9]. It is presently used as fuel for boilers
or supplied as raw material for the manufacturing of pulp,
paper and building boards.
Sugarcane bagasse in its natural state is a poor adsorbent of
organic compound such as sugar colorants and metal ion [10].
Bagasse must be modified physically and chemically to
enhance its adsorptive properties towards organic molecules
or metal ions, routinely found in water and wastewater. This is
effectively accomplished by converting bagasse to an
activated carbon. Bagasse is reported as a suitable resource for
preparation of activated carbon.
The present study is focused on production of Granular
Activated Carbon (GAC) from sugarcane bagasse by
activating at different temperatures, using molasses as a
binder. Since the commercial application of activated carbon
is effected by their physical and chemical properties. This
study includes a comparison of the physical and chemical
properties of carbons to those of the commercial carbon
“Calgon Filtrasorb 400”.
Physical and Chemical Analysis of Activated
Carbon Prepared from Sugarcane Bagasse and
Use for Sugar Decolorisation
Khadija Qureshi*, Inamullah Bhatti*, Rafique Kazi **, Abdul Khalique Ansari**
G
International Journal of Chemical and Biomolecular Engineering 1:3 2008
145

II. MATERIAL AND METHODS
A. Production of Granular Activated Carbon (GAC)
Sugarcane bagasse milled in the hammer mill “CONDUX
D 6451” to reduce the size and sieved using the 5-10 mesh
sieve (US standard sieve) approximately equal to 4 mm to
1.68 mm. The sample of bagasse retained on mesh no 10 was
selected for this study. The binder, Sugarcane molas, was
heated to 80 °C and 50 gms were mixed with 100 gm of
sieved bagasse with the “Midget stirrer Model Mz 800H”. The
sample was stirred until the homogeneous product was
obtained. Pellets of 1 inch diameter were made on the
“Simplimet II Mounting Press 20-1320” by applying 5000 psi
pressure. The pellets were stored in decicator for 2-3 days. A
cylindrical shaped reactor of 7.5 inch length and 2.5 inch
diameter was designed for the activation with the inlet and
outlet for nitrogen and steam. The reactor was placed inside
the Table Top Furnace “Model Soft Temp 2FC Tanaka
Scientific instrument CO LTD TOKYO furnace”. A coil
connected with the “Mini flow pump type 304” was arranged
inside of the furnace to produce steam. To provide the
nitrogenous atmosphere for pyrolysis “BOC” Nitrogen gas
cylinders of 99.99% purity was used. For the removal of
noncarbon elements the pellets for 1 hour were held in an inert
atmosphere to pyrolise at 700 °C. The pyrolised sample was
cooled overnight in the furnace in inert atmosphere. The
sample was sieved on 12-40 mesh approximately of size
1.14mm-380µm. The sample of size 380µm was activated at
different temperatures 700 °C to 900 °C for 45 min in N2
atmosphere. The sample was cooled overnight in inert
atmosphere. The granules were washed with 0.1 M HCI to
remove the ash materials and drained with distilled water until
pH 6-8 of slurry was achieved. The sample was dried
overnight in oven at 50 °C for further use.
B. Carbon Analysis
The physical (bulk density, hardness, carbon yield and burn
off) chemical (pH, conductivity and ash) decolorizing
efficiency (% color and relative efficiency) were analyzed.
[11].
TABLE I
BAGGAS ACTIVATED AT DIFFERENT TEMPERATURES
SR. NO NAME
OF
SAMPL
E
BINDE
R
FLOW
OF N2
GAS
ML/MIN
STEAM
FLOW
ML/MIN
PYROL
YSIS
TEMP °
C
ACTIV
ATION
TEMP °
C
1 BM21 MOLAS
S
0.1 2.5 700 700
2 BM25 MOLAS
S
0.1 2.5 700 750
3 BM26 MOLAS
S
0.1 2.5 700 760
5 BM31 MOLAS
S
0.1 2.5 700 780
6 BM34 MOLAS
S
0.1 2.5 700 800
7 BM8 MOLAS
S
0.1 2.5 700 850
8 BM50 MOLAS
S
0.1 2.5 700 900
There is an important relationship among them and for their
application and efficiency in sugar decolorisation. Calgon
Carbon (CCAL) is an excellent decolorizer of organic liquids
such as raw sugar liquors [12].The commercial carbon was
used as a reference in order to judge the characteristics of our
carbon for use for sugar decolorization in a sugar refinery.
III. RESULTS AND DISCUSSION
A. Physical Analysis of Product
Carbons with an adequate density also help to improve the
filtration rate by forming an even cake on the filter surface.
When two carbons differing in bulk density are used at the
same weight per liter, the carbons having higher bulk density
will be able to filter more liquor volume before the available
cake space is filled. Generally a carbon with a bulk density of
about 0.5 g/ml is adequate for sugar decolorization. Bone
chars currently used for sugar decolorization have a bulk
density of about 0.6g/ml. [13].
The GAC prepared from bagasse (bagasse is mixed with
cane molasses as a binder) by steam activation process is
reported in Fig. 1. The density of these experimental carbons
was in the range of 0.25-0.28 gm/ml.
Fig. 1 density of steam activated carbon
0.235
0.24
0.245
0.25
0.255
0.26
0.265
0.27
0.275
0.28
0.285
BM21
BM25
BM26
BM31
BM34
BM8
BM50
REF
samples
density gm/ml
Bulk density can be increased by increasing the ratios of
binders. Bagasse are low density materials and binders are
used so that bagasse may remain intact as granules after
pyrolysis and activation.The reported bulk density of bagasse
0.3gm/ml which increased to 0.35gm/ml when the ratio of the
byproduct and binder increased from (1:0.5) to (1:1).[14]
The American water work Association has set a lower limit
on bulk density at 0.25gm/ml for GACs to be of practical
use.[15]
Carbon yield is the amount of original precursor remaining
after Pyrolisis and activation treatment. The carbon yield is
change, when different activation conditions are used.The
carbon yield of ssteam activated bagasse was 15 to 23% as
shown in Fig. 2. Burn off is the weight loss of pyrolyzed char
and this is obtained during the activation process. The burn off
values of the GACs increases when byproduct binder ratio is
increased.
International Journal of Chemical and Biomolecular Engineering 1:3 2008
146

Fig. 2 yield of steam activated carbon
0
5
10
15
20
25
30
BM21
BM25
BM26
BM31
BM34
BM8
BM50
pre work
samples
yield
Low burn off are usually undesirable as they lead to low
surface area which in turn may lead to a low adsorption
capacity for target molecules.
The burn off the bagasse based products is reported in Fig.
3 the highest burn off achieved was 45.12%.
Fig. 3 burn off of steam activated carbon
0
5
10
15
20
25
30
35
40
45
50
BM21
BM25
BM26
BM31
BM34
BM8
BM50
ref
samples
burn off %
A carbon should possess sufficient mechanical strength to
withstand the abrasion resulting from continued use. In the
course of carbon usage particle may breakdown and dust
formation occur due to the continous mechanical friction
between carbon particle and sugar liquor. Therefore carbons
designed for sugar decolorization should have enough
abrasion resistance to minimize attrition.
Bagasse based carbon hardness ranges from 40.26% to
42.4% as shown in Fig .4 this seeems to be reasonable and
showed no breakage during different application ( for Cr
removal and sugar decolorisation). Hardness of commercial
carbon was in range of 70-90%. Physical activation produces
the hardest GAC while chemical activation yielded softer
carbon.
Fig. 4 Hardness of steam activated carbon
0
10
20
30
40
50
60
BM21
BM25
BM26
BM31
BM34
BM8
BM50
REF
samples
hardness %
B. Chemical analysis of product
A carbon pH of 6-8 is acceptable for most application such as
sugar decolorization, water treatment, etc.
All the steam activated carbon had pH in the range 6 to 8 as
reported in Fig. 5 except BM21 which had a pH of 9.01. BM 8
showed a pH 5.53 making it an acid sample more extensive
washing might reduce the pH.BM 34 has a pH of 8.8 which
very much relates to the commercial carbon (CCAL) pH 8.70.
Fig. 5 pH of steam activated carbon
0
2
4
6
8
10
12
BM21
BM25
BM26
BM31
BM34
BM8
BM50
REF
samples
pH
The acid or basic nature of an activated carbon depends on
its preparation and inorganic matter and chemically active
oxygen groups on its surface as well as the kind of treatment
to which the activated carbon was submitted. Activated
carbon pH may influence color by changing the pH of the
sugar solution. Such a change affects the pH sensitive fraction
of solution colorants causing unreliable color measurements
[16]. Moreover acid carbons for example may be a better
decolorizer [17] but a sugar refiner would seldom employ a
highly acidic carbon because the acid would cause inversion
of sucrose to noncrystallizable sugars with subsequent lower
International Journal of Chemical and Biomolecular Engineering 1:3 2008
147

yield [18]. Sugar decolorization a distinctly acidic activated
carbon may cause inversion of sucrose and distinctly alkaline
carbon may cause color development through alkaline
degradation of organic impurities [19]. Hence a carbon pH of
6-8 is acceptable for most application.
The water soluble minerals were studied by electrical
conductivity. The conductivity test is important because it
shows the presence of leach able ash which is considered
impurity and undesirable in activated carbon.
All the bagasse based carbons except BM34 (which showed
the highest conductivity 102.5µS) exhibited good conductivity
in the range of 51.85 µS to 70.75µS as shown in Fig. 6
Commercial carbon CCAL used for the purpose of sugar
decolorisation has low leachable waste having conductivity of
7.25µS .
Fig. 6 Conductivity of steam activated carbon
0
50
100
150
200
250
300
350
400
BM21
BM25
BM26
BM31
BM34
BM8
BM50
REF
samples
conductivity
In comparison to the commercial carbons most of the
experimental carbons exhibiting high conductivity values
indicated that an acid or water wash was not enough to reduce
leach able ash to levels observed in commercial carbon. The
results of electrical conductivity indicated that even though
the tested samples were acid or water washed substantial
amounts of water soluble minerals remained in the carbons.
Such high leach able mineral content are unacceptable when
carbons are to be used for commercial sugar decolorization.
This is because ash especially leach able ash in activated
carbon is not desirable and is considered an impurity.
Ash content is the indicator of the quality of an activated
carbon. It is the residue that remains when carbonaceous
portion is burned off. The ash consists mainly of minerals
such as silica, aluminum, iron, magnesium, and calcium. Ash
in activated carbon is not desirable and is considered an
impurity. Ash leached into sugar liquor during the process of
decolorization is known to cause uneven distribution of heat
in the boiler during sugar crystallization. Ash may also
interfere with carbon adsorption through competitive
adsorption and catalysis of adverse reactions. For instance the
ash content may affect the pH of the carbon since the pH of
most commercial carbons is produced by their inorganic
components. Usually materials with the lowest ash content
produce the most active products.
All the samples of bagasse had ash content in the range 9.26
to 11.24 except BM34 (ash content 20.26%)as shown in Fig. 7
this was due to the low conductivity values. The CCAL had a
high ash content 920%. Marshall has reported the ash content
of bagasse based products as 42.74%.[20].
Fig. 7 Ash of steam activated carbon
0
5
10
15
20
25
30
35
40
45
BM21
BM25
BM26
BM31
BM34
BM8
BM50
REF
samples
ash%
C. Uses of GAC for Sugar Decolarisation
The GACs produced from different precursors were assessed
by use in sugar refinery.
1) Sugar decolorisation
The amount of colorants that can be removed from a
solution by activated carbon depends on factors such as
contact time, carbon dosage, temperature, concentration or
viscosity of the solution and the intrinsic features of the
carbon itself. A study was conducted to evaluate the effect of
the type of activated carbon on the percent color removed
from a melt sugar liquor of 60 brix at Matairi sugar mill.
The commercial carbon CCOAL had a capacity to remove
18% color. BM 50 had the best decolourising power, which
effectively removed 29.79% color as reported in Fig. 8.
Fig. 8 % Color removal of steam activated carbon
0
5
10
15
20
25
30
35
BM21
BM25
BM26
BM31
BM34
BM8
BM50
ref
samples
% color removal
The carbon prepared from sugarcane bagasse using corn
syrup as binder was the best sugar decolorizer 17% [20].
While when molasses was used as binder only 7% removal
was achieved [20]. Carbons prepared from rice husk with coal
tar as binder removed 12% color [20].
International Journal of Chemical and Biomolecular Engineering 1:3 2008
148

2) Percent relative efficiencies
The percent relative efficiencies were based on the percent
sugar color removed by Calgon Cane Cal which had the
highest value. The percentage relative efficiency of the
bagasse based products was greater than the previous work.
BM 50 had the highest percentage relative efficiency of 165 as
reported in Fig. 9.
Fig. 9 % relative efficiency of steam activated
carbon
0
50
100
150
200
BM21
BM25
BM26
BM31
BM34
BM8
BM50
REF
samples
% relative efficiency
IV. CONCLUSION
All the bagasse based products exhibited satisfactory
Physical Properties (bulk density, yield, burn off and
hardness).
The pH of most the samples were in the acceptable range
except two samples. BM34 exhibited the highest conductivity
and ash content, while other samples showed conductivity less
than 70.75 μS and low ash content as well.
BM 50 had the capacity of removing 29.79 % of color. The
sugar decolorization efficiency of two samples was higher
than that of Calgon CPG LF.
Steam activated sample of bagasse at 900 ºC showed the
best potential for producing activated carbon with both
satisfactory Physical and chemical Properties making it a good
cndidate for sugar decolorizer.
REFERENCES
[1] M Ahmedna, WE Marshall, RM Rao, Surface Properties of granular
activated carbons from agricultural byproducts and their effects on raw
sugar decolorization”, Bioresource technology , 71(2000) 103-112.
[2] Nadhem K Hamadi , Xiao Dong Chen, Mohaqmmed M Farid , Max GH
Lu, “Adsorption kinetics for the removal of chromium (VI) from
aqueous solution by adsorbents derived from used tyres and saw dust”
chemical engineering journal 84 (2001) 95-105.
[3] Christopher A Toles, Wayne E Marshall , Mitchell M John, “Phosphoric
acid activation of nutshells for metals and organic remediation process
optimization” J Chem technol Biotechnol, 1998 72, 255-263.
[4] L H Wartelle , WE Marshall , “ Nutshell as granular activated carbon
physical chemical and adsorptive properties,” Journal of chemical
technology and biotechnology (2001) 76 451-455.
[5] M Kobya “Adsorption kinetics and equlibrium studies of Cr(VI) by
hazelnut shell activated carbon, Adsorption science and technology , vol
22 no1 2004.
[6] Nevin Yalem , Vadettin Sevine, “Studies of the surface area and porosity
of actrivated carbon prepared from rice husk”, Carbon vol 38 (2000)
pp1943-1945.
[7] Mubeena Akhtar , M I Bhanger , Shahid Iqbal , S Moosa Hasany, “
Efficiency of rice bran for the removal of selected organics from water
kinetics and thermodynamics investigation”, Journal of Agricultural and
food chemistry, 2005, 53, 8655-8662.
[8] Umesh K Garg , Dhirag sud, “ Optimization of Process Parameter for
removal of Cr(V) from aqueous solution using modified sugarcane
bagasse”,Electronic Journal of Environmental Agriculture and food
chemistry, ISSN 1579-4377.
[9] Fedral Bureau of Statistics Dvision of Pakistan june 2006.
[10] Marshall and Champagne ,J Environ Sci Health, 1995 A30(2) 241-261.
[11] M Ahmedna MM Johns, S J Clarke, WE Marshall, RM RAO, “Potential
of agricultural by products based activated carbon for use in raw sugar
decoloristion” J Sci Food A gri 1997, 75, 117-124.
[12] Calgon Granular carbon Technical Bulletin no 23-142a Calgon carbon
corp, Pittsburgh PA 1987.
[13] Carpenter F.G (1985) Cane sugar refining , Cane sugar handbook,
eleventh edition chen J.C.P (ED) John Wiley and sons New York.
[14] B Pendyal, MM Johns, Marshall, M A hmedna, R.M Rao, “ The effect of
binders and agricultural byproducts on Physical and chemical Properties
of garnular activated carbons,” Bioresource Technology , 68 (1999),
247-25.
[15] American Water Works Association, AWWA Standards for granular
activated carbons American Water Works Association , ANSI/AWWA
B604-90 Denver Co 1991.
[16] Ahmedna M, S.J Clarke, RM Rao, WE Marshall, M.M Johns, “ Use of
filtration and buffers in raw sugar color measurement , J, Sci Food,
Agric, 75, 109-116.
[17] Paton NHP and Smith (1983),” Colorants adsorption in refinery”, Int
sugar J. 85 (1013) 139.
[18] Mantell, CL (1946) Industrial carbon its elemental adsorptive and
manufactured forms second edition, D Van Nostrand Company Inc New
York.
[19] Bernardin, Jr., F.E. (1985). Experimental design and testing of
adsorption and adsorbates. Ch. 1 In Adsorption Technology: A Step-by-
step Approach to Process Evaluation and Application. Chemical
Industries 19. F.L. Sleijko (ed). p. 37-90. Marcel Dekker, Inc. N.Y.
[20] Ahmedna M. ; Marshall W. E. ; Rao R. M. "Production of granular
activated carbons from select agricultural by-products and evaluation of
their physical, chemical and adsorption properties",Bioresource
technology, 2000, vol. 71, no2, pp. 113-123 (27 ref.)
Dr. Khadija Quresi is the first young lady of Pakistan to be awarded the
doctors degree in chemical engineering by Mehran University of Engineering
& Technology, Jamshoro in 2008.
She joined chemical Engineering Department of Mehran University as
lecturer in 1996 after her graduation and now she is working as assistant
professor in the same department. This paper is produced from her PhD work.
International Journal of Chemical and Biomolecular Engineering 1:3 2008
149