Directional preparation of coal-based activated carbon：principles, approaches and applications

China is rich in abundant coal resources and has become the largest coal-based activated carbon producer in the world. A concise history of origin and development of coal-based activated carbon industry in China, as well as a brief introduction to the preparation method, technology and application of coal-based activated carbon were conducted in this paper. Then the concept, principles, approaches and applications of directional preparation of activated carbon (DPAC) were presented in detail. Besides, several important issues faced by the activated carbon industry in the near future were figured out and some urgent topics to be investigated were proposed. The results show that activated carbon has developed pore structure with unique ability in selective adsorption of trace components in gas and liquid phase, and has been widely used in national defense, medicine, food and chemical industry, and in recent years, it has found great application prospects in energy and environment fields. Steam activation is the dominating method for the production of coal-based activated carbon. At present, crushed coal-based activated carbon, extruded activated carbon and especially the briquetted activated carbon are the primary products of coal-based activated carbon industry. The briquetted activated carbon production technology has become the priority process for the newly-built or expanded activated carbon plant, because it is characterized as large production capacity, high and stable product quality, especially suitable for pore adjustment by coal blending and additives. It is well known that pore texture, surface chemistry, shape and forms, mechanical strength and fluid characteristics are the influencing factors when activated carbon are utilized. DPAC, i.e. activated carbon with suitable composition, pore texture and kinds of specifications is turned out strictly in accordance with the requirements of application. When all factors relating to DPAC, including specifications of activated carbon and their interactions, influencing factors, adjusting methods and complexity were all taken into account, a strategy for development of DPAC could be made out, in which the regulation of pore texture is both the obstacle and the core. Pore texture regulation is to adjust the proportion of pores with different sizes in the total pore volume of activated carbon according to the application requirements on the premise of ensuring the full development of pores in activated carbon. When the measures such as selecting feedstock coal, coal blending, additives and process parameters optimization were adopted alone or simultaneously, the carbonization process of coal can be controlled to some extent and proceeds in the direction of producing isotropic, non-graphitizable char with high reactivity and developed preliminary pores, which will lay a foundation for the adjusting steam-carbon matrix reaction rate and porosity development in the activation process, consequently results in the pore texture regulation. Thus, low ash and high specific surface area activated carbon, magnetic activated carbon and activated carbon for electrode with double electric layer capacitance and Faraday capacitance, can be directionally prepared with the application of principles of DPAC. In the case that a single kind of activated carbon is impossible to meet a set of requirements demanded by an application, carbon blending may be an efficient alternative. With the aim to further improvement of preparation technology of coal based activated carbon, focuses should be paid on the precise and quantitative control of the pore texture of activated carbon on industrial scale, the preparation of mesoporous activated carbon and carbon blending. Meanwhile, study of the activated carbon application, exploitation of inner alkali and alkaline earth metals in western coal in controlling over the pore texture of activated carbon, as well as establishment of cleaner manufacturing process of activated carbon are the important issues in development of coal based activated carbon industry in our country.