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Activated Carbon

Activated carbon (AC), also called activated charcoal or activated coal is a form of carbon that has been processed to make it extremely porous by treatment with oxygen to open up millions of tiny pores between the carbon atoms.  AC is a unique and effective agent for purification of gases, removal of odour, tastes and colorants from liquids and for isolation and recovery of trace materials and metals from solutions. It has a very large surface area available for adsorption or chemical reactions. In adsorption, organic molecules contained in a liquid or gas are attracted and bound to the surface of the pores of the activated carbon as the liquid or gas is passed through. Mainly three types of pores i.e. macro pores, meso pores and micro pores are responsible for the adsorption of molecules in the solution which pass through AC. While the pore structure limits the size of molecules which can be adsorbed and the surface area developed limits the amount of material which can be absorbed, assuming suitable molecular size. The adsorption of molecules, therefore, takes place through the pores and by the chemical reaction on contact with the surface area of AC. The use of carbon extends so far back into history that its origin is impossible to document. Charcoal was used for drinking water filtration by ancient Hindus in India, and carbonized wood was used as a medical adsorbent and purifying agent by the Egyptians as early as 1500 B.C. Similar uses throughout history have been reported by a variety of historians. Powdered activated carbon was first produced commercially in Europe in the early 19th century, using wood as a raw material. The first documented use of activated carbon in a large scale water treatment application was in 19th-century England, where it was used to remove undesirable odours and tastes from drinking water. During the last three to four decades, treatment with AC has become an important unit process for separation and purifications in food and non-food processing industries.

 

Applications: Activated Carbon has wider applications in Industry, mainly on account of filtration of liquids and it remains a choice media for water filtration in domestic water connections and municipalities. It has large scale use in the Beverage, Pharmaceutical, Sugar, Vegetable Oil, Chemicals and Textiles Industry. Activated Carbon is mainly produced in powder, granules and pellets forms due to its varied applications. An abstract of grade wise application of Activated Carbon is given below:

Manufacturing process:

Activated Carbon can be produced from any carbonaceous material having high carbon content, which on activation attains porous structure and consequently a large surface area. Usually organic based materials such as wood chips, saw dust, coconut and walnut shells, rice husk, corn cobs, seeds and agriculture waste and lignite, anthracite and bituminous coal are used as basic raw materials. This kind of feed stock has high carbon content ranging from 35% to 70%. Most of the raw material to manufacture AC is therefore local and is available in abundance at nominal cost. The manufacturing process of AC involves the following stages:

a)    The preparation of raw material involves sorting of dirt and crushing of material to suitable size. The crushed material is dried to remove the moisture. b)    Carbonization of raw material takes place when it is heated in the absence of air in the fixed bed reactor, which results into its decomposition, the resulting product is also called charcoal. Carbonization can also be done in the presence of chemicals such as zinc chloride, magnesium chloride, calcium chloride and phosphoric acid. c)    Activation of carbonaceous material takes place under steam activation or chemical activation methods. The commonly used, steam activation method involves, reacting charcoal with steam at a temperature of 800-1000°C under controlled atmosphere in a fluidized bed reactor to facilitate uniform heat distribution and improved gas solid contact. The process takes place in rotary kiln or steel furnace. Under steam activation, initial gasification of the carbonized material with steam occurs. As this reaction is endothermic, temperature is maintained by partial burning of the CO and H2. d)    The activation process produces carbonaceous substances with many small pores and thus a very large surface area. The final product is then crushed to yield a granular or pulverized product.

The steam activation method which is mostly used all over the world for the manufacture of activated carbon is depicted in Figure 1.

 

The World Scenario: During the year 2007, World’s total exports were valued at $ 907 million. World’s present annual demand of around 0.600 MMT is growing at 5 – 6 % per annum. Due to stringent environment regulations, an increasing awareness to treat waste water for re-use along with its wider applications, Activated Carbon would continue to be in high demand in the developed and developing world.

 

Activated Carbon Market in Pakistan: The demand of many industrial inputs has never been as high as has recently been witnessed. Amongst the industrial sectors, food and beverages, pharmaceuticals, sugar, vegetable oil, paper and board, textiles and chemicals are the fast growing sectors. Increasing sensitivity to use better quality water in the industrial processes and treatment to the waste water is growing due to environmental regulations and quality concerns.

 

Recommendation: Pakistan does not have a single manufacturer of Activated Carbon, despite a regular demand. Manufacturing Activated Carbon from the abundantly available local raw material, including agricultural and wood waste, walnut and peanut shell, lignite and bituminous coal and cheaper labor, makes perfect business sense to manufacture activated carbon locally. Increasing awareness leading to more applications in the purification of water and solutions in the various industrial sectors and drinking water supply, therefore, could lead to substantial consumption. In Pakistan, the present demand of 1,300 MT is therefore, anticipated to go double in the next 4-5 years. A healthy return on investment, through high value addition to various types of agricultural and wood waste, therefore, makes the investment a perfect business proposition.  

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