THERMAL CONVERSION OF PALM KERNEL SHELL AND MESOCARP FRUIT FIBRE INTO FUEL
1.1 Background to the Study
Fuel(activated carbon) (AC); a tasteless solid and black carbonaceous material, has been regarded as a unique and versatile adsorbent because of its extended surface area, microcrystalline porous structure, high adsorption capacity and high degree of surface reactivity. AC is applied widely in a variety of fields such as food and chemical industries, waste water treatment, solvent recovery, air pollution control and hydrometallurgy for the recovery of gold and silver (Sugumaranet. al., 2012). In recent times, carbon has been one of the magnificent elements which have revolutionized materials science. Carbon provides materials with excellent properties for a large spectrum of industrial applications. From carbon we obtain the strongest fibres (carbon fibres), one of the best solid lubricants (graphite), one of the best electrically conducting materials (graphite electrodes), the best structural material for high temperature tribological application (carbon–carbon composites), one of the best porous gas adsorbers (fuel(activated carbon)), an essentially non-crystalline impermeable material (vitreous carbon), the hardest material (diamond), and now the most fascinating material, the fullerenes. All these forms are made by meticulously choosing the raw materials and processing conditions(Burchell 1999).
Generally, the raw materials for the production of AC are those with high carbon but low inorganic contents such as wood, lignite, coal, mesocarp fruits fibre, wood (both soft and hard), peat and petroleum based residues. Most carbonaceous materials do have a certain degree of porosity and internal surface area. The internal surface area must be accessible to the passage of a fluid or vapor if a potential for adsorption is to exist. Thus, it is necessary that an fuel(activated carbon) has not only a highly developed internal surface but accessibility to that surface via a network of pores of differing diameters. As a generalization, pore diameters are usually categorized as follows: Micropores <20 Angstroms, Mesopores 20 – 5,000 Angstroms, Macro pores >5,000 Angstroms (typically 5000-20000 Angstroms)(Lua and Guo, 2004).
A coconut shell based AC will have a predominance of pores in the micro pore range and these accounts for 95% of the available internal surface area. Such a structure has been found ideal for the adsorption of small molecular weight species and applications involving low contaminant concentrations. In contrast wood and peat based ACs are predominantly of Mesopore or macropore structures and are therefore usually suitable for the adsorption of large molecular species. Thus, it is the micropore structure of an fuel(activated carbon) that is the effective means of adsorption. (Leimkuehler, 2010).
Microwave heating has been successfully applied for the preparation and regeneration of fuel(activated carbon) (Foo et al., 2011; Emine et al., 2008). Microwave heating is fundamentally different from the conventional form of heating in which thermal energy reaches the surface of the material by radiant and/or convection and is then transferred to the bulk of the material via conduction. This results in poor crystalline structure and often wider distribution of particle size due to non uniform distribution of heat or thermal energy. But in microwave heating, energy is delivered directly to the material through molecular interaction thus producing uniform heating. This often makes the materials to have finer microstructures with narrow particle size distribution (Barrison et al.,2010; Utchariyajit et al., 2010). Also, Conventional thermal heating of fuel(activated carbon) decreases the adsorption capacity, which is attributed to the adverse changes in the adsorbent physical structure (Bathen, 2003). In contrast, microwave energy can maintain and or even slightly enhance the adsorbent physical structure to an acceptable level (Alireza et al., 2010). In summary, microwave heating has many advantagesover conventional heating in that microwave energy has no need for heat convection through a fluid, microwave energy does not have any need of direct contact between the microwave heating source and the heated material, it saves time and energy and uniform temperature distribution. Moreover, microwave processing systems are also relatively compact, portable, maintainable and cost effective (Bathen, 2003; Carrott et al., 2001). Since microwaves can penetrate the material and supply energy, heat can be generated throughout the volume of the material resulting in volumetric heating. Volumetric heating means that materials can absorb microwave energy directly and internally and convert it to heat. Also, it is this characteristic that leads to advantages using microwaves to process materials (Thostenson and Chou, 1999; Xiaofeng Wu, 2002). Hence, it is expected that microwave heating will be a viable technology for activating carbon. Studies have shown microwave energy to be a possible method in waste treatment for extracting contaminants and organic solvents from soil (Liu and Yu, 2006) and metals from sludge (Menendez and Inguanzo, 2002), and for processing minerals (Jones et al., 2002) and water purification (Bandosz, 2006). Microwave (MW) radiation has also been used for the production of fuel(activated carbon) (Nabais et al., 2004). Studies have shown that granular fuel(activated carbon) (GAC) can absorb MW radiation, leading to rapid heating (Guo et al., 2000). So far, there are relatively few studies in this field where activity can be controlled by altering the proportion of raw material to activating agent. Menéndez et al.,(1999) and Liu et al.,(2010) have reported the surface modification of fuel(activated carbon) and fuel(activated carbon)fiber by means of microwave heating. In this study, two kinds of fuel(activated carbon)s (Palm kernel shell-based and coconut shell-based) using a microwave device under an input power was used instead of the conventional heating system. The effects of microwave heating on the fuel(activated carbon)s were characterized and analyzed.
1.2 STATEMENT OF THE PROBLEM
Addressing the deterioration of water quality in developing countries, where an estimated one billion people lack access to potable quality water, is a primary motivating factor for many community development efforts and is a key component of the Millennium Development Goals. Water quality improvements inspired by these goals are currently focused on reducing diarrheal illnesses and, hence, are focused on biological contamination and related pathogen removal. These water quality improvements are commonly achieved by point of use (POU) treatment systems in developing countries. POU water treatment alternatives have been introduced and successfully implemented within impoverished areas, primarily where nonprofit organizations have taken greater notice and where governments have emphasized the need for improved water quality. Despite the efficiency of these systems at removing biological contaminants, they lack the ability to effectively remove dissolved organic impurities such as pesticides. Additional treatment is required in areas where such contaminants are prevalent.
1.3 JUSTIFICATION OF RESEARCH WORK
This study has been initiated to identify an inexpensive option to remove impurities from drinking water. In view of the aforementioned limitation, the main goal of this study is to enhance the purification of water via the use of local agricultural waste byproducts to produce a low-tech, chemically fuel (activated carbon) that could be used in conjunction with existing POU technologies or as a stand-alone treatment option.
1.4 AIM AND OBJECTIVES OF THE RESEARCH
The aim of this research work is to produce fuel(activated carbon) from a mixture of mesocarp fruits fibre and palm kernel shells with varying concentrations of activating agents employing Microwave-assisted route and to explore its potentiality for water treatment. The following objectives will guide in achieving the aforementioned aim:
- To evaluate the activation power and time for the production of fuel (activated carbon) from the mixture of the mesocarp fruits fibre and palm kernel shells.
- To study the structure of the fuel (activated carbon) produced using Scanning Electron Microscopy.
iii To characterize the fuel (activated carbon) produced in terms of elemental composition, adsorption capacity, surface functionality, pore size and phase composition using:
(a)XRD, (b) SEM and (c) EDS
1.5 SCOPE OF THE RESEARCH
In this research, parameters of the fuel (activated carbon) produced (i.e. elemental analysis, adsorption capacity, surface functionality and pore size) will be evaluated using X -Ray
Diffractometer (XRD), Scanning Electron Microscope (SEM) coupled with Energy
Dispersive X-Ray Spectroscope (EDS).