Microporous structure of chars produced by pyrolysis of preoxidized coals

摘要

In this work, the effect of coal oxidation and pyrolysis conditions, coal rank and particle size on the microporous structure of chars was analyzed. The study was based on two bituminous coals of different rank: a low-volatile bituminous coal (Figaredo) and a medium-volatile bituminous coal (Santa Barbara). Sizes of coal particles between 48 and 855 μm were used. Coals were oxidized in air at several temperatures (150-270℃) over different time periods (6 h-15 days). Chars were obtained from coal pyrolysis at temperatures between 600 and 850℃. The carbonized materials were analyzed by adsorption of CO_2 at 0℃ and N_2 at -196℃. The experimental results showed that both the duration and temperature of coal oxidation determine the development of the microporous structure of the carbonized materials. Coal oxidation temperature was the variable that most significantly affected the microporous development of chars. The coal oxidation process allowed the size of constrictions at the entrance of the micropores to be altered. In this way, the micropores of chars from oxidized coals were more accessible in spite of being narrower (average micropore width around 0.8 nm).