A_comparative_study_of_chemical_and_microwave_synthesized_activated_carbon from corn cob

Thesis Overview

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