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 m 2. 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.

Preparation 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

and 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 effective 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.

iv. 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.