Abstract
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CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF STUDY
Activated carbon, also widely known as activated charcoal or activated coal is a
form of carbon which has been processed to make it extremely porous and thus to
have a very large surface area available for adsorption or chemical reactions
(Mattson et al., 1971). The word active is sometimes used in place of activated. It
is characterized by high degree of micro porosity. A gram of activated carbon can
have a surface area in excess of 500 m2. Sufficient activation for useful
applications may come solely from the high surface area, though further chemical
treatment generally enhances the adsorbing properties of the material. Activated
carbon is most commonly derived from charcoal.
Waste biomass is getting increasing attention all over the world for activated
carbon development as it is renewable, widely available, cheap and
environmentally friendly resource. The common method of development is
thermochemical (Kumar et al., 2005). The main concern is the removal of
chemical component by adsorption from the liquid or gas phase (Bansal et al.,
1988). Today, activated carbon has been produced from various biomass such as
corncob, rice husk, cherry stones, coconut shells, palm shells, to mention but a few.
2Preparation of activated carbon with ultra-high specific surface area from biomass
such as lignin, corncob, cornstalk, dates, etc., has attracted much attention. Among
these carbon sources, corncob is a good precursor for preparing carbon with ultra
high specific surface area (Li, 2007). The carbons prepared from corncob have
been used in wastewater treatment such as removal of organic pollutants (Sun et
al., 2006).
However, a comprehensive study of activating corncob with different activation
strategies to prepare carbon with ultra-high specific surface area and pore volumes,
and their subsequent performance in water purification as the impurity adsorption
has not to our knowledge been reported. Therefore, in this study we report the
synthesis of ultra-high surface area carbon materials using two preparation
strategies namely, chemical activation procedure using a chemical activator such as
ammonium sulphate ((NH4)2SO4) and microwave-synthesized activation
procedure. We also report the adsorption capacity of those carbons for water
purification.
To prepare activated carbon, conventional heating method is usually adopted, in
which the heat is produced by electrical furnace. However, in some cases, the
thermal process may take several hours, even up to a week to reach the desired
level of activation (Yuen et al., 2009). Another problem related to the furnace is
that the surface heating does not ensure a uniform temperature for different shapes
3and sizes of samples. This generates a thermal gradient from the hot surface to the
kernel of the sample particle, blocks the effective diffusions of gaseous products to
its surroundings and finally results in activated carbon quality decrease (Peng et
al., 2008). Furthermore, there is a considerable risk of overheating or even thermal
runaway (exothermic process) of portion of sample, leading to the complete
combustion of the carbon (Williams et al., 2008).
Recently, microwave has been widely used in preparation and regeneration of
activated carbon. The main difference between microwave devices and
conventional heating systems is heating pattern. In microwave device, the energy is
directly supplied to the carbon bed. The conversion of microwave energy is not by
conduction or convection as in conventional heating, but by dipole rotation and
ionic conduction inside the particles (Jones, 2002). Therefore, the treatment time
can be significantly reduced through microwave heating.1.2 STATEMENT OF PROBLEM
In recent years, increasing awareness of environmental impact of organic and
inorganic compounds has prompted the purification of waste water prior to
discharge into natural waters. A number of conventional treatment technologies
have been considered for treatment of waste water contaminated with organic
substance. Among them, the adsorption process has been found to be the most
4effective method while activated carbon is regarded as the most effective material
for controlling this organic load. Common active carbons available are usually
developed by thermochemical means using activating agents and heating ovens,
thus producing activated carbons which take a longer time with limited pore
structures. With the advent of microwave technology, a better and efficient
activated carbon can be produced within a short period and a cheaper cost.
1.3 OBJECTIVE OF THE RESEARCH
The aim of this research project is to determine and compare the performance of
chemically and microwave synthesized activated carbon from corn cob.
1.4 SIGNIFICANCE OF THE RESEARCH
When this research project is successfully completed, it will provide the following
benefits:
i. Corn cobs are abundant in Nigeria.
ii. Encourage the establishment of industries that will use Agricultural
waste materials to produce activated carbon.
iii. It will create job opportunities, thereby reducing unemployment in the
country.
5iv. It will attract foreign exchange for Nigeria as activated carbon has
very wide industrial applications.
1.5 SCOPE OF RESEARCH
This research work focuses on the following:
i. Preparation of activated carbon from corn cob by thermal and microwave
means
ii. Comparative study of the adsorption capacities of chemically and
microwave synthesized activated carbon.