Preparation of activated carbon from asphalt and heavy oil fly ash and coal fly ash by pyrolysis

Activated carbons were prepared by the pyrolysis of a mixture of fly ash and road paving asphalt dissolved in kerosene at 650 °C in N₂ atmosphere. Asphalt provides a porous carbonaceous structure and also acts as a binder to hold the fly ash particles together. The fly ash acts as a support for this carbon structure. The preparation variables studied were the pretreatment of asphalt-fly ash composite in air or N₂; and the asphalt ratio (amount of asphalt in grams added to 100 g of fly ash) of the raw mixture. The pretreatment of asphalt-fly ash composite at 250 °C in air resulted in a higher effective asphalt carbon yield than no pretreatment or pretreatment in N₂. The effective asphalt carbon yield increased with asphalt ratio up to 20 and then decreased at higher ratios. For heavy oil fly ash, the optimum asphalt ratio was 50-60 for maximum carbon yield. The specific surface areas of the asphalt and fly ash carbons were in the range of 500-800 m²/(g-asphalt derived carbon), depending on the asphalt derived carbon content of the sample. The asphalt ratio in the raw materials also affected the macropore structure of the product carbon: the macropore diameter of the sample increased with asphalt ratio.