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Abstract:
Coal char has lots of functions such as combustion, gasification, adsorbent, activated carbon production and carbon materials. Most of coal chars are generated from raw coal pyrolysis at high temperature, and later cool down to room temperature before further utilizations. The additional cooling process between the two stages have great influence on char structure, performance and reactivity. Herein, we prepared in-situ char and ex-situ char with different cooling rates from ten typical Chinese coals, including anthracite, bituminous and lignite. SEM morphology, powder X-ray diffraction, elemental H/C ratio, specific surface area and active surface area of the cooling chars were characterized. Results show that carbon structure tends to be graphitized while cooling. In-situ char has the lowest carbon graphitization and thus the highest carbon defects, which provides more active surface area and carbon active sites. Char reactivity decreases in the order of raw coal > in-situ char > rapid cooling char (103–104 K/s) > medium cooling char (10–100 K/s) > slow cooling char (0.1 K/s), where char reactivity is more sensitive to cooling rate in low rank char than high rank char. The decline of reactivity during cooling is probably due to the loss of carbon active sites
