Microstructural variations of lignite,subbituminous and bituminous coals and their high temperature chars

Microstructure of a North Dakota lignite, a Washington subbituminous and a New Mexico bituminous coal and their chars produced by devolatilization in nitrogen at 1000 to 1300°C was investigated in this work using the CO₂ adsorption method conducted at 25°C. For each coal and char, specific surface area, micropore volume, micropore surface area, mean equivalent radius of micropores and characteristic energy of adsorption, as well as micropore volume distribution, were determined, and their variations with devolatilization temperature studied and interpreted. It was found that, overall, specific surface areas, micropore volumes and micropore surface areas of chars decreased monotonically as devolatilization temperature was raised from 1000 to 1300°C, although most of these values were much larger than that of their parent coals. The micropore volume distributions of the three coals and their high temperature chars were interpreted and found to provide an interesting insight into the micro structural variations of these coals and chars.