Effect of pyrolysis conditions on the improvement of the physicochemical structure of activated carbon obtained from Jixi bituminous coal

AbstractDifferent pyrolysis conditions have been confirmed as a useful way to improve the physicochemical structure of Jixi bituminous char to obtain fully developed porosity after a low burn‐off during activation. In this paper, a series of coal‐char samples were prepared at different pyrolysis temperatures, rates, and residence times. The effect of the pyrolysis temperature on the physicochemical structure in coal char is important because it can control the breakage and recombination of different types of chemical bonds. The impact of the pyrolysis rate gradually increases with increasing temperature, indicating that its influence is closely related to the pyrolysis temperature. However, an extension of the residence time at different pyrolysis temperatures and rates can only help the evolution of the chemical structure. It was determined that the typical char (KJX800‐40) produced by rapid pyrolysis at 800°C over a long residence time (40 min) is the most suitable for subsequent activation due to its disordered carbon structure, abundant initial pores, and active sites. The initial pores that developed in the KJX800‐40 char facilitate the diffusion of activated gas to avoid serious carbon losses on the surface of the particles; alternatively, more active sites help the etching of the carbon structure to promote the rapid and continuous development of the micropores, following nonhierarchical development. On the basis of these results, a pyrolysis condition with a high SBET (859.14 m2/g)/burn‐off ratio (25.2%) of 34.09 m2/(g•%) was identified.