INFLUENCE OF COAL OXIDATION ON THE STRUCTURE OF CHAR

The effect of coal preoxidation and pyrolysis conditions on the structure of char from low-volatile coal was studied. Coal particles (0.125-0.425 mm) were oxidized at 100, 150 and 200-degrees-C for up to 7 days. Pyrolysis was conducted at heating rates of 10, 60 and 150 K min-1, temperatures of 600-850-degrees-C and soaking times of 0 and 1 h. The char structure was characterized by mercury porosimetry, adsorption of CO2 (0-degrees-C) and N2 (- 196-degrees-C), and optical microscopy. Preoxidation reduced the fluidity of the coal and led to an increase in char microporosity and a decrease in anisotropic content. At long oxidation times the char micropore entrances were widened. Coal preoxidation makes it possible to obtain chars with a high microporosity which are good precursors for activated carbon preparation.