Activated carbon is a carbon that being treated physically to increase it adsorption properties. It consists of a carbonaceous, highly porous adsorptive medium with a complex structure and have a large surface area per unit volume due to the pores form on the carbon surface. This properties give the significance value of the adsorption process by the activated carbon and widely used in industry in variety form of applications.The networks of pores in activated carbons area unit channels created inside a rigid skeleton of disordered layers of carbon atoms, linked together by chemical bonds, stacked unevenly, creating a highly porous structure of nooks, crannies, cracks and crevices between the carbon layers.
Activated carbons are usually manufactured from coconut shell, peat, hard and soft wood, lignite coal, bituminous coal, olive pits and various carbonaceous specialty materials. The high carbon content in the natural compound are the primary raw material used for activated carbon.The carbon-based material is reborn to carbon through physical modification and thermal decomposition in a very chamber, under a controlled atmosphere and temperature.The intrinsic pore network within the lattice structure of activated carbons permits the removal of impurities from aerosolized and liquid media through a mechanism cited as surface assimilation.
Key properties of Activated Carbon
A carbon product are often characterised by its activity and physical properties.
Activity properties include pore size distribution that defines the available pore volume in the activated carbon. Pore size distribution properties area unit key indicators of a carbon’s potential performance for removing contaminants (adsorbates) from water. Each form of carbon has its own distinctive distribution of pore sizes. They’re cited as micropores (small), mesopores (medium) and macropores (large). Carbons for adsorb many varieties of gas molecules area unit microporous. The best carbons for decolorization have a better distribution of mesopores,
Pore size region
Micropores r 25nm
Physical properties consist of surface area, product density, mesh size, abrasion resistance, and ash content. Carbon properties include:
Surface Area – Generally, higher the internal surface area, gives effectiveness process of the carbon adsorption.The expanse of carbon is spectacular, 500 to 1500 m2/g or even more; a spoonful of activated carbon easily equates the surface area of a soccer field. It is within the activation method that this immense expanse is formed. The most common method is steam activation; at around 1000°C steam molecules by selection burn holes into the turn material, thus creating a multitude of pores inside the carbonaceous matrix.In chemical activation, phosphoric acid is used to build up such a porous system at a lower temperature.
Total Pore Volume – Refers to all pore spaces inside a particle of activated carbon.It is expressed in milliliters per gram (ml/g), volume in relation to weight.In general, the upper the pore volume, the higher the effectiveness.However, if the sizes of the molecules to be adsorbable don’t seem to be a decent match to the pore size, some of the pore volume will not be utilized.Total pore volume (T.P.V.) differs by material supply and sort of activation technique.
Pore Radius – The mean (average) pore radius, often measured in angstroms, differs by activated carbon type.
2) LITERATURE REVIEW ; DISCUSSION
a) Detail review on the material in term of theoretical aspect inclusive knowledge on material engineering technology
Activated carbon is a carbonaceous material with a large internal surface area and have highly developed porous substances resulting from the processing of the raw material under high temperature reactions. (Hay Carb Activated Carbon Solution, 2018) The activated carbon composed of 87% to 97% carbon but also contain other element depending on the processing method used and raw material it is derived from. The porous structure allow the activated carbon to adsorb material from liquid and gas phase. The procedure for processing. The process in producing activated carbon are divided into two carbonization and oxidation.
Carbonization process consist of conversion of raw material to carbon by minimizing the volatile matter and increase the carbon content of the mateial at 400 – 800o C. (what is activated carbon, t.t) This process enhance the strenght of the material and initiate the initial porous structure for activation process. It is important to make sure that the carbonization temperature are at optimum temperature cause if it is too high the reactivity of the carbon increase but the formation of pore throughout the carbon will decrease. The temperature for production depend on the usage of the activated carbon. Oxidation process is referred as process in producing micropores 25 nm, serving as access pores. Activated carbons with open pore structures and good desorption characteristics are used in the recovery of solvents with mid- to high boiling points, whereas activated carbon types with higher micro pore concentrations are used for highly volatile substances. In liquid phase adsorption processes, macro pores serving as access pores also have a substantial impact on adsorption kinetics. The effectiveness at which activated carbon can remove contaminants from a stream is not based on the quantity of carbon, but, the activated carbon adsorption capacity. The greater the capacity, the more contaminants the activated carbon will be able to adsorb in volume
Figure 1 shows the differential pore radius distribution for bituminous coal based steam activated carbon
Figure 2 shows the differential pore radius distribution for coconut shell based steam activated carbon
Activated carbons may differ widely with respect to quality, adsorptive properties and physio-chemical properties depending upon the raw materials and activation methods employed. These differences are reflected in the characteristic data (quality features) of the various grades of activated carbon. For instance, molasses number that measured the decolorizing capacity of activated carbon. A high molasses number indicates a high adsorption of big molecules (range 95–600 nm). Caramel dp (decolorizing performance) is similar to molasses number.
A impregnated activated carbon can removed a number of pollutant that pollutants are either partially or totally resistant to separation through adsorption such as chlorine, ammonia, amines, sulphur dioxide, mercury, hydrogen sulphide and few through chemisorptive effect. In chemisorption, the substances to be removed are either chemically bonded by the impregnating agent on the activated carbon or converted by these agents into a form that adsorbs on activated carbon. Impregnating agents include metal salts, iodine, sulphur as well as acids and bases.
Important physical properties are the number and size distribution of the pores, bulk density, dry impact hardness, wet abrasion resistance, and particle-size distribution. Thus, Table 1 below shows the properties mostly manufactures used to characterize their activated carbon usage product. A high-activity coconut-shell carbon that activated thermally using steam which is usually employed in gas-phase application and in processes for the recovery of gold from cyanide leach liquors shows those quality features.
Table 1 shows the physical properties and chemical-adsorption characteristic of coconut shell based steam activated carbon
c) Advantage and disadvantage of activated carbon
Advantages of activated carbon
Activated carbon is widely being used in some industries such as separation and purification industry. The advantages of activated carbon are, it can remove the contaminants in water, improving taste and odour of the water, can exist in various form, can be reused for many times and lastly being able to adsorb a wide range of materials in the water.
Generally, activated carbon is known as a natural filter media where filters that are based on activated carbon are been used in majority of water filter systems as a complementary filter or a standalone filter. The activated carbon can be used as a filter because of its porous surface area and also highly adsorbent nature. Due to this characteristics of activated carbon, these filters will be good in removing the contaminants in the water and also it also can help in improving the taste and odor of water.
Moreover, the activated carbon can exist in various forms. Each different forms of activated carbon will offer different material properties thus make it ideally suited for specific applications. Depending on the applications of activated carbon, it may be used in powdered, granular, extruded or in a liquid form. Commonly, in water treatment systems, the granular or powdered activated carbon from bituminous coal are being used.
Furthermore, activated carbon can be reused many times and it will save cost when regenerated. Regeneration of activated carbon is where the ‘spent’ carbon is processed to be recycle, the adsorbed components can be desorbed while the spent carbon will be regenerated thus allowing the activated carbon to be used repeatedly. However, not all of the activated carbon that can be regenerated.
According to the United State Environmental Protection Agency (EPA), activated carbon can adsorb a wide range of materials in the water. Some of the classes of organic or inorganic components that can be adsorb by the activated carbon that has been listed by the EPA are aromatic solvents, chlorinated aromatics, polynuclear aromatics, fuels, pesticides, aliphatic and aromatic acids, phenolics, soluble organic dyes and manymore. One gram of activated carbon consists of 54000 square feet of surface area. This surface area is a place where the contaminants in the water whether organic or inorganic components will be trapped and be adsorbed onto the carbon.