Active carbon is an amorphous form of carbon, which is specially treated to produce a very large surface area, ranging from 300 to 2000 m2/g. This commodity is assuming increasing importance in the control of air pollution, in purifying and controlling the general chemic environment, in certain biomedical applications and for the removal of organic matter from water and waste water.
This study was undertaken to explore certain indigenous cellulosic and mineral based raw materials like inferior woods, a variety of agrowastes, low rank coals and certain cellulosic precursors, as potential raw
materials for the preparation of powdered, granular and fibrous activated carbons. Another aim of this study was to characterize these products, in liquid and gas phase, by Standard Methods, as well as for certain specific industrial requirements.
Among indigenous woods, seven inferior woods were explored and Babul (Acacia arabica), was found to be the most suitable, for preparing powdered as well as granular activated carbons. Suitable method of activation and working conditions in respect of particle size, appropriate Activating agent, its impregnation ratio, activation temperature and time were established for preparing powdered and granular products from this particular raw material. It is notable, that during the course of these studies, '1 complete new method for standardization of putty, used in granulization, was also established and got patented.
As regards agroresidues, a variety of indigenous ones were investigated, but rice husk was found to be the most appropriate one, in view of its abundant availability. A complete new methodology was developed and got patented for the deashing of rice husk. Moreover, detailed studies were carried out for preparing powdered and granular activated carbons from high as well as low ash rice husk by the method of chemical activation and working conditions were established, by designing and performing a series of experiments 1JLnder different set of variables.
Local deposits of low rank coals of Lakhra and Sharigh, in the province of Sindh and Baluchistan respectively, were appropriately being used for the preparation of powdered activated carbon, by the m0thod of chemical activation Detailed methodology as well as various working parameters were established, and it was inferred that coaI of Lakhra origin, although lignitic in nature, but found to be comparatively more suitable for this spl1cific purpose.
Different indigenous cellulosic precursors were also studied in respect of their suitability as possible raw material for the preparation of fibrous / filament activated carbon. It was thereafter established, that a product of desired strength and appropriate adsorptive capacity may be prepared from bleached cotton cloth.
Local technology for 'the preparation of granular activate carbon, by the method of physical activation, was develope,1. In this respect, a pilot scale fluidized bed reactor was indigenously designed, fabricated and installed. Two locally available Taw materials viz. Babul (Acacia arabica) and coconut shells were being explored as possible raw materials, for this purpose. Suitable working conditions were established, as regards particle size of the raw material activation temperature, operating pressure of the fluidizing medium, activation time etc, for preparing a product of desired strength and adsorptive properties inn suitable yield. Babul (Acacia arabica) was not found to be a suitable raw material for physical activation process by fluidization, due to its less inherent strength as compared to coconut shells.
All products of powdered, granular and fibre / filament type, were initially characterized in liquid as well as gas phase, by adsorption against adsorbates of certain molecular dimensions. Products of suitable strength and physical and chemical characteristics, in respect of their micro, meso and macroporous surface area, hardness etc, and initially selected from standard evaluation, were then subjected to their detailed characterization.
Detailed characterization of these selected products was carried out, in respect of their elemental analysis (C,H,N',O,S), surface area determination by BET method (low temperature nitrogen adsorption) ,ascertaining of functional groups present on the surface of these products by FTIR spectroscopy and selective neutralization techniques and adsorption of certain trace metals and lower aliphatic & unsaturated organic acids. Physical adsorption of gases and vapours by these active carbons was also determined by calculation of different parameters like characteristic energy, microspore volume, pore width and external surface area, by adsorption of benzene at 293 K, under reduced pressure, using Dubinin Radushkevich (D-R) equation.
An outcome of this study, if; the establishment of suitability of different indigenous preCU1:'sors like Babul (Acacia arabica), low ash rice husk, Lakhra coal and bleached cotton cloth, as prospective raw materials, for the preparation of powdered, granular and fibrous activated carbons. Moreover, detailed methodology I techniques for the preparation and characterization of these products were also evolved.