COMPARATIVE ANALYSIS OF COAL AND COCONUT ACTIVATED CARBON

Thesis Overview

INTRODUCTION1.1 HISTORY OF ACTIVATED Activated carbon was first know to treat mater over 2000 years ago. It was first produced commercially at the beginning of the 20th century and was only available in powder form. Initially activated carbon was mainly treatment to remove taste and then from 1930 for mater treatment to remove taste and odor. Granular activated carbon was developed as a consequence of WWI for gas masks and has been used subsequently for mater treatment, solvent recovery and air purification. The unique structure of activated carbon produces a very large surface area.11b of granular activated carbon typically provides a surface area of 125 acres {1kg = 1000000 sq}. Activated carbon be produced from a variety of carbonaceous raw material, the primary ones being coal, coconut shills, mood and lignite. The intrinsic properties of the activated carbon are dependent on the raw martial source. The activated carbon surface is non-polar which results in an affinity for non- polar adsorbates such as organics.Adsorption is a surface phenomenon in which an adsorbate is held onto the surface of the activated carbon by van der waals forces and saturated is represented by an equilibrium point. These forces are physical in nature, which means that the process is reversible (using heal, pressme etc) Activated carbon also capable of chemisorptions, whereby a chemical reaction occurs a the carbon interface, changing the state of the adsorbate {dechlorination is an example of a chemisorptions process}1.2 FORMS OF ACTIVATED CARBONThere are three main forms of activated carbon and these include:A. GRANULAR ACTIVATED CARBON: this is irregular in shape with respect to its particles. The particles sizes ranges from 0.2 to 5mm. It is used in both liquid and gas phase applications.B. POWDER ACTIVATED CARBON: This is a pulverized carbon with a size predominantly less than 0.18mm. these are mainly used in liquid phased applications and for flue gas treatment.C. PELLETIZED ACTIVATED CARBON: it is extruded and cylindrical shaped with diameters from 0.8 to 3mm. These are mainly used for gas phase application because of their low pressure drop, high mechanical strength and low dust content.1.3 KINDS OF ACTIVATED CARBON There are end kinds of activated carbon1. LOW DENSITY ACTIVATED CARBON: this is used for ligind phase adsorption2. HIGH DENSITY ACTIVATED CARBON: This is used for gas phase adsorption1.4 ACTIVATED CARBON PROPERTIES The following are the properties possessed by activated carbons irrespective of the base material from which they are made.1. 10 DINE NUMBER/VALUE: This is the fundamental property used to characterize activated carbon performance. It measures the activity level, higher number indicates higher degree of activation.2. METHYLENE BLUE: This is a measure of mesopore structure of activated carbon. It is between 20-500A.3. CARAMEL DP {MOLASSES VALUE}: This is the measure of macro pore structure, it is less than 500A. it is important for decolorizing performance of activated carbon. 4. SURFACE AREA: This is use to measure the adsorption capacity. Pore size distribution or pore volume is also important to determine ultimate performance.5. APPARENT DENSITY: Activated carbon with higher density possesses greater volume activity and this normally indicates better quality activated carbon.6. PARTICLE SIZE: Smaller particle size provides quicker rate of adsorption which reduces the amount of contact time required. Smaller particle size brings about greater pressure drop.7. HARDNESS/ABRASION NUMBER: It is a measure of activated carbons resistance to attrition, and important indicator of activated carbon to maintain its physic integrity and with stand frictional forces imposed by mashing etc.8. DECHLORINATION HALF-VALUE LENGTH: This is a test to measure the dechlorination efficiency of activated carbon. The depth of activated carbon to reduce influent chlorine level from 5pm to 2.5ppm lower half-value length indicates superior performance.9. ASH CONTENT: This reduces overall activity of activated carbon and efficiency of reactivation. Metals {Fe203} can leach out of activated carbon resulting in discoloration. Acid/water soluble ash content is more significant then total ash content.1.5 ADSORPTION PARAMETERS OF ACTIVATED CARBON The adsorption parameters of activated carbon show the trend and degree of adsorption of activated carbon and they are:1. CAPACITY VERSUS KINETIC RATE: capacity parameters determine loading characteristics of activated carbon. Maximum adsorption capacity of activated carbon is only achieved at equilibrium. Kinetic parameters only determine the rate of adsorption and have reliable effect on adsorption capacity.2. SURFACE AREA: adsorption capacity is proportional to surface area and it is determined by degree of activation.3. PORE SIZE: correct fore size distribution is necessary to facilitate the adsorption process by providing adsorption site and the appropriate channels to transport adsorbate.4. PARTICLE SIZE: smaller particle size provide quicker rate of adsorption. Note that total surface area is determined by degree of activation and pore structure and not particle size.5. TEMPERATURE: lower temperature increases adsorption capacity except in the case of viscous liquids.6. CONCENTRATION OF ADSORBATE: adsorption capacity is proportional to concentration of adsorbate.7. PH: adsorption capacity increases under PH conditions, which decreases the solubility of the adsorbate.8. CONTACT TIME: sufficient content time is required to reach adsorption equilibrium and to maximize adsorption efficiency1.6 APPLICATIONS OF ACTIVATED CARBON Activated carbon is mainly used as an agent for refining, decolorizing, purifying or filtering substances in varied industries.It is used in air deodorants and separation of permanent and rare gases from air sulphur removal from synthesis gases, removal of foreign odor from in carbon dioxide from dry ice or carbonated beverages, gelatin in cold storage and refrigerators. It is also used in deodorizing vegetasusores, purification of various organic liquids, water purification and recovery of gold and silver from ones.1.7 DEFINITION OF TERMS ADSORBENT: This is a natural or synthetic material of microcrystalline structure in loose internal surface is accessible for selective combination of solid and solute.ADSORPTION: It is the process by which liquid or gaseous molecules are concentrated on a solid surface, in this case activated carbon . It is a surface phenomenon.SELECTIVITY: It is the ability of activated carbon [adsorbent] to adsorb certain component more strongly than other Adsorbent.ADSORBENT: this is the solute liquid or gaseous molecules that is concentrated on the solid of the solid adsorbent.