Modeling char surface area during coal pyrolysis: Validation of relationship between pore structure and polymer network

The relationship between pore structure and polymer network during coal pyrolysis was studied by analyzing the evolution of microcrystal, pore structure, and functional groups of char prepared from Naomaohu subbituminous coal by a drop-tube furnace reactor at 600–1000°C. The char specific surface area changes little with aliphatic bridge cleaving at temperatures lower than 700°C; starts to increase at 800°C with the beginning of side chain cleaving; then reaches the maximum with the methyl and methylene content together at 900°C; finally decreases with the further cleaving of aliphatic structures at higher temperatures. Moreover, the lattice stacking height is minimum at 900°C, indicating aliphatic structure can reduce the lattice order degree. These phenomena support the assumption in the CPD-PS model that the side chain cleaving generates open pores and meanwhile reduces the adsorption sites in them, making the char specific surface area first increase and then decrease.